JP2011209759A - Method of manufacturing five-tone photomask and method of transferring pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a five-tone photomask, wherein five tones can be obtained by etching three times.SOLUTION: The method of obtaining five tones by etching three times includes steps of: preparing a photomask blank having a first translucent film having etching selectivity and a light-shielding film in this order on a transparent substrate; forming a first resist pattern on the light-shielding film; etching the light-shielding film by using the first resist pattern as a mask to carry out first patterning; removing the first resist pattern and forming a second resist pattern; etching the first translucent film by using the second resist pattern as a mask to carry out second patterning; removing the second resist pattern and forming a second translucent film having etching selectivity with respect to the first translucent film, over the whole substrate surface; forming a third resist pattern on the second translucent film; and etching the second translucent film by using the third resist pattern as a mask to carry out third patterning.

Description

  The present invention relates to a five-tone photomask manufacturing method, a five-tone photomask, and a pattern transfer method using the photomask, which are suitably used for manufacturing a liquid crystal display (LCD). Is.

  Currently, in the field of LCDs, thin film transistor liquid crystal displays (hereinafter referred to as TFT-LCDs) are easy to make thinner and have lower power consumption than CRTs (cathode ray tubes). Commercialization is progressing rapidly. A TFT-LCD includes a TFT substrate having a structure in which TFTs are arranged in pixels arranged in a matrix, and a color filter in which red, green, and blue pixel patterns are arranged corresponding to each pixel. It has a schematic structure superimposed under the intervention of. In TFT-LCD, the number of manufacturing processes is large, and the TFT substrate alone is manufactured using 5 to 6 photomasks. Under such circumstances, a method of manufacturing a TFT substrate using four photomasks has been proposed.

  In this method, the number of masks to be used is reduced by using a photomask called a gray tone mask having a semi-transparent portion (gray tone portion) in addition to the light shielding portion and the translucent portion. Here, the semi-transparent portion means that when a pattern is transferred to a transfer object using a mask, the amount of exposure light transmitted therethrough is reduced by a predetermined amount, and the photoresist film on the transfer object after development is developed. The part that controls the amount of remaining film.

  As the gray tone mask used here, one having a structure in which the semi-transparent portion is formed with a fine pattern below the resolution limit of an LCD exposure machine using the gray tone mask is known. A structure having a semi-transparent portion as a semi-transparent semi-transparent film is also known. Regardless of the structure, it is possible to expose the semi-translucent portion with a predetermined amount of light exposure, and transfer two transfer patterns having different resist residual film values onto the transfer target. Therefore, the number of masks can be reduced by performing a process for two conventional photomasks using one gray tone mask.

  The gray tone mask is a three-tone photomask having a light-shielding portion, a light-transmitting portion, and a semi-light-transmitting portion, and changing the exposure light transmittance in three stages. Therefore, if one more multi-tone photomask is used, the number of masks can be further reduced.

  Conventionally, a multi-tone photomask whose light transmittance changes in three or more stages and obtained by repeating resist pattern formation and etching of a film such as a metal compound a desired number of times is disclosed in Patent Document 1 below. ing. In addition to the light-shielding portion and the light-transmitting portion, a 4-tone photomask having a first semi-transparent portion and a second semi-transparent portion having different light transmittances can be manufactured by a lithography process with a small number of times of drawing. A photomask manufacturing method is disclosed in Patent Document 2 below.

JP 9-146259 A JP 2007-249198 A

  However, in the method of manufacturing a multi-tone photomask disclosed in Patent Document 1, the number of times of etching a film of a metal compound or the like is equal to the number of times of drawing for forming a resist pattern for the etching mask. Therefore, the number of times of drawing increases in order to obtain a desired multi-gradation. For example, in order to manufacture a multi-tone photomask in which the exposure light transmittance is changed in five steps or more, drawing must be performed at least four times, and if the number of drawing increases, the alignment is highly accurate. However, it is difficult to carry out the process, which affects the accuracy of the mask pattern to be formed. In recent years, it has been required to form a finer pattern also in the manufacture of a TFT substrate, and the pattern accuracy on a photomask is very important. Increasing the number of photolithography processes also increases the probability of inconveniences such as defects, and there is concern about simply increasing the gradation.

  In addition, according to the method for manufacturing a four-tone photomask disclosed in Patent Document 2, a four-tone photomask can be manufactured by reducing the number of times of drawing to two by a photolithography process. Further, when manufacturing a multi-tone photomask, for example, a 5-tone photomask, it is of course impossible to apply the manufacturing method limited to the 4-tone photomask as it is.

  The present invention has been made in view of the above-described conventional circumstances, and provides a five-tone photomask manufacturing method capable of manufacturing a five-tone photomask with a small number of semi-transparent films and a small number of writings. This is the first purpose. A second object of the present invention is to provide a five-tone photomask in which a fine pattern is formed with high accuracy. It is a third object of the present invention to provide a pattern transfer method using the five-tone photomask.

In order to solve the above problems, the present invention has the following configuration.
(Configuration 1) On the transparent substrate, there is a light shielding portion, a light transmitting portion, and a mask pattern composed of a first semi-transmissive portion, a second semi-transmissive portion, and a third semi-transmissive portion having different exposure light transmittances. A method for manufacturing a five-tone photomask, comprising: preparing a photomask blank having a first semi-transparent film and a light-shielding film having etching selectivity with respect to an etchant in this order on a transparent substrate; A step of drawing and developing a resist film formed on the blank light shielding film to form a first resist pattern; a step of etching the light shielding film using the first resist pattern as a mask and performing a first patterning; , After removing the first resist pattern, drawing and developing a resist film formed on the patterned surface including the light shielding film to form a second resist pattern; Etching the first semi-transparent film using the second resist pattern as a mask and performing second patterning; and removing the second resist pattern and then patterning the light-shielding film and the first semi-transparent film Forming a second semi-transparent film having etching selectivity with respect to an etchant with the first semi-transparent film on the entire surface of the substrate including the translucent film; and a resist film formed on the second semi-transparent film Drawing and developing to form a third resist pattern, and etching the second semi-transparent film using the third resist pattern as a mask to perform a third patterning. A method for manufacturing a five-tone photomask.

(Configuration 2) On a transparent substrate, a light shielding portion, a light transmitting portion, and a mask pattern made up of a first semi-transmissive portion, a second semi-transmissive portion, and a third semi-transmissive portion having different exposure light transmittances are provided. A method for manufacturing a five-tone photomask, comprising: preparing a photomask blank having a light shielding film on a transparent substrate; and drawing and developing a resist film formed on the light shielding film of the photomask blank. Forming a resist pattern, etching the light shielding film using the first resist pattern as a mask, performing a first patterning, removing the first resist pattern, and then patterning the light shielding film A step of forming a first semi-transparent film on the entire surface of the substrate, a step of drawing and developing a resist film formed on the first semi-transparent film to form a second resist pattern, and the second resist Etching the first semi-transparent film using a strike pattern as a mask to perform second patterning, and removing the second resist pattern, and then patterning the light-shielding film and the first semi-transparent film Forming a second semi-transparent film having etching selectivity with respect to an etchant with the first semi-transparent film, and drawing and developing a resist film formed on the second translucent film And forming a third resist pattern, and etching the second semi-transparent film using the third resist pattern as a mask to perform a third patterning. Mask manufacturing method.

(Structure 3) The first semi-transparent part, the second semi-transparent part, and the third semi-transparent part are the first semi-transparent film, the second semi-transparent film, and the first semi-transparent film. 3. The method for manufacturing a five-tone photomask according to Configuration 1 or 2, wherein the method is formed by any one of a transparent film and a laminated film of the second semi-transparent film.
(Structure 4) The light shielding film and the second semi-transparent film are both made of a material containing chromium as a main component, and the first semi-transparent film is made of a material containing molybdenum silicide as a main component. A manufacturing method of a five-tone photomask according to any one of configurations 1 to 3.

(Configuration 5) On the transparent substrate, there is a light shielding portion, a light transmitting portion, and a mask pattern including a first semi-transmissive portion, a second semi-transmissive portion, and a third semi-transmissive portion having different exposure light transmittances. The light-shielding portion is formed of at least a light-shielding film formed on the transparent substrate, and the light-transmitting portion is formed of the exposed transparent substrate, and the first semi-transmissive portion and the second semi-transmissive portion are formed. The light part and the third semi-transparent part are formed on the transparent substrate, the first semi-transparent film and the second semi-transparent film having different exposure light transmittances, and the first semi-transparent film, A five-tone photomask, wherein the exposure light transmittance is changed in five stages by being formed by any one of the laminated films of the second semi-transparent films.
(Structure 6) The light shielding film and the second semi-transparent film are both made of a material containing chromium as a main component, and the first semi-transparent film is made of a material containing molybdenum silicide as a main component. 5. The five-tone photomask according to Configuration 5.

(Configuration 7) An exposure step of irradiating a transfer target with exposure light using the photomask according to any one of Configurations 1 to 4 or the photomask according to Configuration 5 or 6, A pattern transfer method, wherein a transfer pattern having 5 gradations is formed on a transfer object.

According to the five-tone photomask manufacturing method of the present invention, in addition to the light-shielding film, a combination of a first semi-transmissive film and a second semi-transmissive film having different exposure light transmittances is used, and a photolithography method is used. Thus, the number of drawing can be reduced to 3 times, and a photomask having five gradations with different exposure light transmittances in five stages can be manufactured.
Further, as described above, since the number of times of drawing can be reduced to three, it is possible to obtain a five-tone photomask in which a fine pattern is formed with high accuracy.
Further, according to the pattern transfer method using the five-tone photomask according to the present invention, highly accurate multi-tone pattern transfer can be performed, and as a result, for example, in the manufacture of a TFT substrate, the number of masks is increased. Can be significantly reduced.

It is sectional drawing for demonstrating 1st Embodiment of the 5 gradation photomask which concerns on this invention, and the pattern transfer method using the said 5 gradation photomask. It is sectional drawing which shows the manufacturing process of the 5-tone photomask which concerns on the said 1st Embodiment in order of a process. It is sectional drawing for demonstrating 2nd Embodiment of the 5 gradation photomask which concerns on this invention, and the pattern transfer method using the said 5 gradation photomask. It is sectional drawing which shows the manufacturing process of the 5-tone photomask which concerns on the said 2nd Embodiment in order of a process. The pattern of the semi-translucent part B sandwiched between the light-shielding parts A (FIG. 1A) and the light intensity distribution of the transmitted light of the semi-transparent part B (FIG. 2B) are shown. ) Shows a case where the width of the semi-translucent region is 4 μm, and FIG. It is a figure which shows the relationship between the transmittance | permeability of exposure light in the semi-transmission part of the width | variety corresponding to the channel width and this channel width.

The best mode for carrying out the present invention will be described below with reference to the drawings.
[First Embodiment]
FIG. 1 is a cross-sectional view for explaining a first embodiment of a five-tone photomask according to the present invention and a pattern transfer method using the five-tone photomask.
A five-tone photomask 10 shown in FIG. 1 is used as, for example, a multi-tone graytone mask for manufacturing a thin film transistor (TFT), a color filter, a plasma display panel (PDP), or the like of a liquid crystal display device (LCD). Thus, resist patterns 23 having different thicknesses are formed stepwise or continuously on the transfer target 20 shown in FIG. In FIG. 1, reference numerals 22 </ b> A, 22 </ b> B, 22 </ b> C, and 22 </ b> D denote films stacked on the substrate 21 in the transfer target 20.

  Specifically, the photomask 10 of the present embodiment includes a light shielding portion 11 that shields exposure light (transmittance is approximately 0%) when the photomask 10 is used, and a surface of a transparent substrate 14 such as a glass substrate. Is exposed and transmits the exposure light, and the exposure light transmittance of the light transmitting portion 12 is 100%, the transmittance is about 10 to 80%, preferably about 20 to 70%. In this range, the first semi-transparent part 13A, the second semi-transparent part 13B, and the third semi-transparent part 13C having different exposure light transmittances in three stages are configured. The semi-translucent portion is configured by forming a semi-translucent film that is semi-transparent on the transparent substrate 14, and in the present embodiment, the first semi-transparent portion 13A of the semi-transparent portion is transmissive to the exposure light wavelength. The first semi-transparent film 16 and the second semi-transparent film 17 having different rates are formed, and the second semi-transparent portion 13B is formed by the first semi-transparent film 16 and the third semi-transparent film. The translucent part 13 </ b> C is formed by the second semi-transparent film 17. In addition, the light shielding unit 11 includes the first semi-transparent film 16, the light shielding film 15 formed by stacking the light shielding layer 15 a and the antireflection layer 15 b, and the second semi-transparent film 17 in this order on the transparent substrate 14. It is provided and formed. Therefore, the photomask 10 is a five-gradation photomask having different exposure light transmittances in five stages. In addition, the pattern shape of the light-shielding part 11, the translucent part 12, and the semi-transparent parts 13A-13C shown in FIG. 1 is an example to the last.

  When the pattern transfer to the transfer target 20 is performed using the five-tone photomask 10 as described above, the exposure light is not substantially transmitted through the light shielding unit 11 and the exposure light is transmitted through the light transmitting unit 12. And the exposure light is reduced in the first to third semi-transparent portions 13A to 13C according to the respective light transmittances. Therefore, the resist film (here, positive photoresist film) applied on the transfer target 20 has the largest thickness in the portion corresponding to the light-shielding portion 11 when developed after pattern transfer. In addition, the portions corresponding to the first to third semi-transparent portions 13A to 13C are all thinner than the portion corresponding to the light-shielding portion 11, but for example, the exposure light of the first semi-transparent film 16 When the transmittance is set to be lower than the exposure light transmittance of the second semi-transparent film 17, the film thickness gradually decreases in the portion corresponding to the semi-transparent portion. Further, there is no film in the portion corresponding to the light transmitting portion 12. As a result, resist patterns 23 having different film thicknesses in five stages (one of which has no film) are formed. For example, the transmittance of the first to third semi-transparent parts can be about 20%, 40%, and 60%, respectively, when the translucent part is 100%. In the case of using a negative photoresist, it is necessary to design in consideration of the reverse of the resist film thickness.

  Then, first etching is performed on, for example, the films 22 </ b> A to 22 </ b> D in the transferred body 20 in a portion where the film of the resist pattern 23 shown in FIG. Subsequently, the thinnest part (the part corresponding to the third semi-transparent part 13C) of the film of the resist pattern 23 is removed by ashing or the like, and, for example, the films 22B to 22D in the transferred body 20 are removed. A second etching is performed. Subsequently, the next thinnest part of the resist pattern 23 (the part corresponding to the second semi-translucent portion 13B) is removed by ashing or the like, and this part is formed on, for example, the films 22C and 22D in the transferred body 20. A third etching is performed. Subsequently, the next thinnest portion of the resist pattern 23 (the portion corresponding to the first semi-translucent portion 13A) is removed by ashing or the like, and this portion is transferred to, for example, the film 22D in the transferred body 20. 4 Etching is performed. In this way, the process for four conventional photomasks in the manufacture of a TFT substrate, for example, is carried out using a single five-tone photomask 10, and the number of masks is greatly reduced compared to the prior art. It becomes possible to do.

Next, a method for manufacturing the above-described five-tone photomask will be described. FIG. 2 is a cross-sectional view showing the manufacturing steps of the five-tone photomask 10 of the first embodiment in the order of steps.
As shown in FIG. 2A, the photomask blank used is a light-shielding film comprising a first semi-transparent film 16, a light-shielding layer 15a and an antireflection layer 15b on a transparent substrate 14 such as a glass substrate. 15 are formed in order. However, the first semi-transparent film 16 and the light shielding film 15 are selected from a combination of materials having etching selectivity with respect to the etchant used in the etching process. Therefore, as the light shielding layer 15a, for example, chromium or a compound thereof (for example, CrN, CrO, CrC, etc.) is preferably cited. Further, as the first semi-transparent film 16, for example, metal silicide, particularly molybdenum silicide compound (MoSix, MoSi nitride, oxide, oxynitride, carbide, etc.) and the like are preferably mentioned. The first semi-transparent film 16 preferably has a transmission amount of about 10 to 80%, preferably about 20 to 70% with respect to the transmission amount of the exposure light of the transparent substrate 14 (translucent portion).

  The first semi-transparent film 16 and the second semi-transparent film 17 which will be described later have different exposure light transmittances. The second semi-transparent film 17 is set in consideration of the balance between the film material and the film thickness.

  First, a resist is applied on the photomask blank to form a resist film, and a first drawing is performed. In this embodiment, for example, laser light is used. A positive photoresist is used as the resist. Then, by drawing a predetermined device pattern on the resist film and performing development after the drawing, for example, a first resist pattern 30 is formed in a region corresponding to the light shielding portion 11 of the manufactured photomask (FIG. 2 ( b)).

  Next, by using the first resist pattern 30 as an etching mask, the light shielding film 15 formed by stacking the light shielding layer 15a and the antireflection layer 15b is etched to form a light shielding film pattern (see FIG. 2C). When the light shielding film 15 mainly composed of chromium is used, the etching means can be either dry etching or wet etching. For example, in the case of a large-sized photomask used for manufacturing a large liquid crystal display panel, wet etching is used. Is preferred. In the wet etching, for example, cerium diammonium nitrate is used as an etchant. Since the light shielding film 15 and the first semi-transparent film 16 therebelow are formed of a material having etching selectivity with respect to the etchant, the first semi-transparent film 16 is etched when the light shielding film 15 is etched. It is hard to be done.

  After the remaining first resist pattern 30 is removed (see FIG. 2D), the same resist film as described above is formed again on the entire surface, and a second drawing is performed. That is, a predetermined pattern is drawn on the resist film, and development is performed after the drawing. For example, the light shielding part 11 and the first semi-transparent part 13A and the second semi-transparent part 13B of the manufactured photomask A second resist pattern 31 is formed in the corresponding region (see FIG. 2E).

  Next, using the second resist pattern 31 as an etching mask, the exposed third semi-transparent portion 13C and the first semi-transparent film 16 on the translucent portion 12 region are etched (see FIG. 2F). When the first semi-transparent film 16 containing Mo compound as a main component is used, either dry etching or wet etching can be used as an etching means. In wet etching, for example, ammonium hydrogen fluoride is mainly used as an etching solution. Use ingredients.

  After the remaining second resist pattern 31 is removed (see FIG. 2G), the second semi-transmissive film 17 is formed on the entire surface of the substrate including the patterned light-shielding film 15 and the first semi-transmissive film 16. (See FIG. 2 (h)). However, the second semi-transparent film 17 is made of a material having etching selectivity with respect to the etchant with the first semi-transparent film 16. Therefore, when using, for example, the aforementioned Mo compound for the first semi-transparent film 16, the second semi-transparent film 17 is preferably a chromium compound, for example. The chromium compounds include chromium oxide (CrOx), chromium nitride (CrNx), chromium carbide (CrCx), chromium oxynitride (CrOxN), chromium fluoride (CrFx), and those containing carbon and hydrogen. The second semi-transparent film 17 also has a transmission amount of about 10 to 80%, preferably about 20 to 70% with respect to the transmission amount of the exposure light of the transparent substrate 24 (translucent portion). However, it is set by selecting the film material and film thickness of the second semi-transparent film 17 so that the exposure light transmittance is different from that of the first semi-transparent film 16 at the same time.

  Next, the same resist film as described above is formed again on the entire surface of the first semi-transparent film 17, and a third drawing is performed. That is, a predetermined pattern is drawn on the resist film, and development is performed after the drawing. For example, the light shielding portion 11 of the manufactured photomask, the first semi-transmissive portion 13A, and the third semi-transmissive portion 13C. A third resist pattern 32 is formed in a region corresponding to (see FIG. 2I).

  Next, using the third resist pattern 32 as an etching mask, the exposed second semi-transparent portion 13B and the second semi-transparent film 17 on the translucent portion 12 region are simultaneously etched (see FIG. 2J). When the second semi-transparent film 17 containing a chromium compound as a main component is used, the etching means can be either dry etching or wet etching. In wet etching, for example, cerium nitrate ammonium nitrate is used as an etching solution. Use. Note that the second semi-transparent film 17 and the first semi-transparent film 16 are formed of a material having etching selectivity with respect to the etchant, and thus, for example, in the region of the second semi-transparent portion 13B, At the time of etching the semi-transparent film 17, the first semi-transparent film 16 therebelow is hardly etched. If the etching selectivity is not sufficient, an etching stopper film can be interposed, but the above method is more advantageous in order to make the photolithography process more efficient and reduce the probability of defect occurrence.

  Then, the remaining third resist pattern 32 is removed. Thus, on the transparent substrate 14, the light-shielding portion 11 formed by stacking the first semi-transmissive film 16, the light-shielding film 15 including the light-shielding layer 15 a and the antireflection layer 15 b, and the second semi-transmissive film 17, the transparent substrate 14 is exposed, the first semi-transparent part 13A formed by stacking the first semi-transparent film 16 and the second semi-transparent film 17, and the second semi-transparent film 16 is formed. A photomask 10 having five gradations with different exposure light transmittances in five stages is formed, in which a mask pattern having a semi-transparent portion 13B and a third semi-transparent portion 13C made of the second semi-transparent film 17 is formed. (See FIG. 2 (k)).

As described above, according to the present embodiment, in addition to the light-shielding film, a combination of the first semi-transmissive film and the second semi-transmissive film having different exposure light transmittances is used, and the number of times of drawing is performed by photolithography. Can be reduced to three times, and a five-gradation photomask with different exposure light transmittances in five stages can be manufactured with a small number of films and a small number of writings.
Further, as described above, since the number of times of drawing can be reduced to three, it is possible to obtain a five-tone photomask in which a fine pattern is formed with high accuracy.

  In addition, when pattern transfer using the five-tone photomask according to the present invention as shown in FIG. 1 is performed, a highly accurate multi-tone transfer pattern can be formed on the transfer target. As a result, for example, the number of masks can be greatly reduced in the manufacture of TFT substrates.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a cross-sectional view for explaining a second embodiment of a five-tone photomask according to the present invention and a pattern transfer method using the five-tone photomask, and FIG. It is sectional drawing which shows the manufacturing process of the 5-tone photomask 10 of 2nd Embodiment in process order. In addition, the same code | symbol is attached | subjected to the location equivalent to FIG.1 and FIG.2 which shows the above-mentioned 1st Embodiment.

  The photomask 10 of this embodiment shown in FIG. 3 specifically blocks exposure light (transmittance is approximately 0%) when the photomask 10 is used, as in the first embodiment. The light-shielding part 11, the light-transmitting part 12 through which the surface of the transparent substrate 14 such as a glass substrate is exposed to transmit the exposure light, and the light-transmitting part 12 exposure light transmittance of 100%, the transmittance is 10 to 80 %, Preferably within the range of about 20 to 70%, and within this range, the first semi-translucent portion 13A, the second semi-transparent portion 13B, and the third semi-transmission portion having different exposure light transmittances in three stages. The light transmitting portion 13C is included. The first semi-transparent portion 13A is formed of a laminated film of a first semi-transparent film 16 and a second semi-transparent film 17 having different transmittances with respect to the exposure light wavelength, and the second semi-transparent portion 13B. Is formed by the first semi-transparent film 16, and the third semi-transparent portion 13 C is formed by the second semi-transparent film 17. In the present embodiment, the light-shielding portion 11 is formed on the transparent substrate 14 with the light-shielding film 15 including the light-shielding layer 15 a and the antireflection layer 15 b, the first semi-transparent film 16, and the second semi-transparent film. The point from which the translucent film | membrane 17 is provided and formed in order differs from 1st Embodiment. Therefore, the photomask 10 is a five-gradation photomask having different exposure light transmittances in five stages.

  When pattern transfer to the transfer target 20 is performed using the five-tone photomask 10 according to the present embodiment, the light shielding portion 11 does not substantially transmit the exposure light, and the light transmitting portion 12 The exposure light is transmitted, and the exposure light is reduced according to the respective light transmittances in the first to third semi-transparent portions 13A to 13C. Therefore, the resist film (here, positive photoresist film) applied on the transfer target 20 has the largest thickness in the portion corresponding to the light shielding portion 11 when the development is performed after pattern transfer. Although the portions corresponding to the first to third semi-transparent portions 13A to 13C are all thinner than the portion corresponding to the light-shielding portion 11, the exposure light transmittance of the first semi-transparent film 16 is, for example, When the exposure light transmittance of the second semi-transparent film 17 is set lower than that of the second semi-transparent film 17, the film thickness gradually decreases in the portion corresponding to the semi-transparent portion and also corresponds to the translucent portion 12. A resist pattern 23 having no film and having different film thicknesses in five stages (one of which has no film) is formed.

  Then, as described above, for example, in the manufacture of a TFT substrate, for example, by etching the films 22A to 22D in the transfer target 20 using the resist patterns 23 having different film thicknesses in five stages as shown in FIG. Thus, the process for four photomasks is carried out, and the number of masks can be greatly reduced as compared with the prior art.

Next, a manufacturing method of the five-tone photomask according to the present embodiment will be described with reference to FIG.
As shown in FIG. 4A, the photomask blank to be used has a light shielding film 15 formed of a laminate of a light shielding layer 15a and an antireflection layer 15b on a transparent substrate 14 such as a glass substrate. As the light shielding layer 15a, for example, chromium or a compound thereof (for example, CrN, CrO, CrC, and the like) is preferably exemplified. .
The transmittance of the light shielding part 11 in the photomask to be manufactured is set mainly by selecting the film material and film thickness of the light shielding layer 15a and the antireflection layer 15b.

  First, a resist is applied on the photomask blank to form a resist film, and a first drawing is performed. In the present embodiment, for example, laser light is used for drawing. A positive photoresist is used as the resist. Then, a predetermined device pattern is drawn on the resist film, and development is performed after the drawing, thereby forming a first resist pattern 30 in a region corresponding to the light shielding portion 11 of the manufactured photomask, for example (FIG. 4 ( b)).

  Next, by using the first resist pattern 30 as an etching mask, the light shielding film 15 formed by laminating the light shielding layer 15a and the antireflection layer 15b is etched to form a light shielding film pattern (see FIG. 4C). When the light shielding film 15 mainly composed of chromium is used, the etching means can be either dry etching or wet etching. For example, in wet etching suitable for manufacturing a large size photomask, Cerium diammonium nitrate is used.

After removing the remaining first resist pattern 30, the first semi-transparent film 16 is formed on the entire surface of the substrate including the patterned light shielding film 15 (see FIG. 4D).
Preferred examples of the first semi-transparent film 16 include Mo compounds (MoSix, MoSi nitride, oxide, oxynitride, carbide, etc.). In the present embodiment, the first semi-transparent film 16 is not particularly required to have etching selectivity with respect to the light shielding film 15, and therefore, for example, chromium or a chromium-based compound can be used as in the case of the light shielding film. The chromium-based compounds include chromium oxide (CrOx), chromium nitride (CrNx), chromium carbide (CrCx), chromium oxynitride (CrOxN), chromium fluoride (CrFx), and those containing carbon and hydrogen. The first semi-transparent film 16 preferably has a transmission amount of about 10 to 80%, preferably about 20 to 70% with respect to the transmission amount of the exposure light of the transparent substrate 14 (translucent portion).

  In addition, the first semi-transparent film 16 is required to have etching selectivity at the same time as the second semi-transparent film 17 to be described later, and at the same time, the exposure light transmittance of the two is different. The film material and film thickness of the first semi-transparent film 16 are set in consideration of the balance between the film material and film thickness of the second semi-transparent film 17 described later.

  Next, the same resist film as described above is formed again on the entire surface, and a second drawing is performed. That is, a predetermined pattern is drawn on the resist film, and development is performed after the drawing. For example, the light shielding part 11 and the first semi-transparent part 13A and the second semi-transparent part 13B of the manufactured photomask A second resist pattern 31 is formed in the corresponding region (see FIG. 4E).

  Next, using the second resist pattern 31 as an etching mask, the exposed third semi-transparent portion 13C and the first semi-transparent film 16 on the translucent portion 12 region are etched (see FIG. 4F). When the first semi-transparent film 16 containing Mo compound as a main component is used, either dry etching or wet etching can be used as an etching means. In wet etching, for example, ammonium hydrogen fluoride is mainly used as an etching solution. Use ingredients. In addition, when the first semi-transparent film 16 containing a chromium-based compound as a main component is used, either dry etching or wet etching is possible. In wet etching, for example, cerium nitrate ammonium nitrate is used as an etchant. .

  After removing the remaining second resist pattern 31 (see FIG. 4G), the second semi-transmissive film 17 is formed on the entire surface of the substrate including the patterned light-shielding film 15 and the first semi-transmissive film 16. (See FIG. 4 (h)). However, the second semi-transparent film 17 is made of a material having etching selectivity with respect to the etchant with the first semi-transparent film 16. Therefore, for example, when the Mo compound described above is used for the first semi-transparent film 16, the second semi-transparent film 17 is preferably a chromium compound, for example. On the other hand, when a chromium-based compound is used for the first semi-transparent film 16, for example, a Mo compound is preferably used as the second semi-transparent film 17, for example. The second semi-transparent film 17 also has a transmission amount of about 10 to 80%, preferably about 20 to 70% with respect to the transmission amount of the exposure light of the transparent substrate 24 (translucent portion). However, it is set by selecting the film material and film thickness of the second semi-transparent film 17 so that the exposure light transmittance is different from that of the first semi-transparent film 16 at the same time.

  Next, the same resist film as described above is formed again on the entire surface of the first semi-transparent film 17, and a third drawing is performed. That is, a predetermined pattern is drawn on the resist film, and development is performed after the drawing. For example, the light shielding portion 11 of the manufactured photomask, the first semi-transmissive portion 13A, and the third semi-transmissive portion 13C. A third resist pattern 32 is formed in a region corresponding to (see FIG. 4I).

  Next, using the third resist pattern 32 as an etching mask, the exposed second semi-transparent portion 13B and the second semi-transparent film 17 on the translucent portion 12 region are etched (see FIG. 4J). As an etching means for the second semi-transparent film 17, either dry etching or wet etching can be used. Note that the second semi-transparent film 17 and the first semi-transparent film 16 are formed of a material having etching selectivity with respect to the etchant, and thus, for example, in the region of the second semi-transparent portion 13B, At the time of etching the semi-transparent film 17, the first semi-transparent film 16 therebelow is hardly etched.

  Then, the remaining third resist pattern 32 is removed. In this way, on the transparent substrate 14, the light-shielding part 11 formed by the lamination of the light-shielding film 15 including the light-shielding layer 15 a and the antireflection layer 15 b, the first semi-transparent film 16 and the second semi-transparent film 17, and the transparent substrate 14. Is exposed, the first semi-transparent portion 13A formed by stacking the first semi-transparent film 16 and the second semi-transparent film 17, and the second semi-transparent film 16. A photomask 10 having five gradations with different exposure light transmittances in five stages is formed, in which a mask pattern having a light transmissive part 13B and a third semi-light transmissive part 13C made of the second semi-light transmissive film 17 is formed ( (Refer FIG.4 (k)).

Also in the present embodiment described above, in addition to the light-shielding film, a combination of the first semi-transmissive film and the second semi-transmissive film having different exposure light transmittances is used, and the number of times of drawing is 3 by photolithography. Thus, a five-tone photomask having different exposure light transmittances in five stages can be manufactured with a small number of films and a small number of writings.
Further, as described above, since the number of times of drawing can be reduced to three, it is possible to obtain a five-tone photomask in which a fine pattern is formed with high accuracy.

  In addition, when pattern transfer using the five-tone photomask according to the present embodiment as shown in FIG. 3 is performed, a highly accurate multi-tone transfer pattern can be formed on the transfer target. . As a result, for example, the number of masks can be greatly reduced in the manufacture of TFT substrates.

In addition to the above, the five-tone photomask according to the present invention has the following advantages.
In general, a multi-tone photomask to which the present invention belongs (a photomask having three or more tones having a semi-transparent portion in addition to a light-shielding portion and a light-transmitting portion) has a desired remaining film value on a transfer target. In order to obtain a resist pattern, the exposure light transmittance of the semi-translucent portion is selected and determined. The transmittance is defined using the transmittance of the semi-transmissive film when the transmittance of the light transmitting portion (that is, the portion where the transparent substrate is exposed) is 100%. This is not a problem when specifying the transmittance of a pattern of a wide area above a certain level, but strictly speaking, for a pattern with a size of a certain degree or less, exposure that contributes to actual pattern transfer. The amount of light is not accurately reflected. Since this is due to diffraction of exposure light, this tendency becomes more prominent as the exposure light wavelength becomes longer as the pattern becomes smaller. However, the present situation is that the change in transmittance with respect to light sources having different pattern dimensions and spectral characteristics is not accurately taken into consideration.

  Specifically, when a pattern shape including a very narrow width and a pattern shape of a relatively wide region are present in the semi-transparent portion, the semi-transparent portion has a resist film on the transfer target, Where a constant residual film value should always be given, a resist pattern with a different residual film value is formed due to the pattern shape, and if the residual film value varies beyond the desired tolerance, There is a problem that it becomes an unstable factor in device manufacturing.

  For example, a multi-tone photomask for a thin film transistor is often used in which a region corresponding to a channel portion is a semi-translucent portion and a region corresponding to a source and a drain adjacent to each other is formed by a light shielding portion. The This photomask is normally exposed using exposure light in the wavelength band of i-line to g-line, but as the size (width) of the channel portion becomes smaller, the boundary with the adjacent light-shielding portion is the actual exposure. The exposure light transmittance of the channel portion is lower than the transmittance of the semi-transmissive film. FIG. 5 shows a pattern of the semi-transparent portion B sandwiched between the light-shielding portions A (FIG. 1 (1)) and the light intensity distribution of the transmitted light of the semi-transparent portion B (FIG. 2). FIG. 6A shows the case where the width of the semi-translucent region is 4 μm as an example, and FIG. That is, as shown in FIGS. 5A and 5B, the light intensity distribution of the transmitted light of the semi-transparent part B sandwiched between the light-shielding parts A is as follows. The whole is lowered and the peak is lowered. In other words, the transmittance that actually contributes to the exposure is relatively low for the pattern having the narrow width region, while the transmittance that contributes to the actual exposure is the pattern that has the relatively wide line width. Relatively high. For example, as shown in FIG. 6, when the channel width is 5 μm or less, the transmissivity of light contributing to actual exposure in the semi-transparent portion having a width corresponding to the channel width is significantly reduced.

Therefore, the transmissivity of the semi-transparent part having a certain size is distinguished from the transmissivity inherent to the film, and the actual amount of exposure light transmission is determined as the effective transmissivity in the ratio of the transmissivity of the translucent part. It is necessary to grasp.
On the other hand, the transmittance specific to the film is determined by the composition and film thickness of the film in a sufficiently wide region where the film is formed on the transparent substrate. A sufficiently wide region refers to a region where the effective transmittance does not substantially change due to a change in the size of the region. In FIG. 6, the transmittance of the region is represented by the peak value of the light intensity distribution of the transmitted light of the semi-translucent portion B. The transmittance of this portion has a correlation with the resist residual film value on the transfer target when the multi-tone mask is used for exposure.

Therefore, by changing the film-transmitting film in that portion according to the pattern shape of the semi-transparent portion, the remaining film value of the resist film in the semi-transparent portion can be made almost the same regardless of the pattern shape.
For example, according to the method of the present invention, a multi-gradation photomask having five gradations can be obtained. That is, in addition to the light transmitting portion and the light shielding portion, a semi-light transmitting portion having three different film transmittances can be obtained. With these three types of semi-transparent portions, resist patterns having different resist residual film values may be formed on the transfer target. However, on the other hand, the three types of semi-transparent portions have different pattern dimensions on the transfer target (thus, if semi-transparent portions having the same film transmittance are used, the resist residual film value formed However, a resist pattern having a certain resist residual film value may be formed. In other words, a semi-transparent portion having three types of film transmittances as the film configuration and having substantially the same effective transmittance may be formed. In this case, the photomask of the present invention is used as a three-tone photomask.

Of course, of the three types of semi-transparent portions, two types may be used for patterns with different shapes having the same effective transmittance, and the remaining one type may be used for patterns having different effective transmittances. In this case, the photomask of the present invention is used as a four-tone photomask.
The present invention has a great advantage in mass production in that a multi-tone photomask that provides such an excellent effect can be manufactured by a process that is efficient and has a low probability of occurrence of defects.

  In both the first embodiment and the second embodiment described above, the exposure light transmittance of the first semi-transmissive film 16 is higher than the exposure light transmittance of the second semi-transmissive film 17. However, the exposure light transmittance of the first semi-transparent film 16 is opposite to that of the second semi-transparent film 16 because the exposure light transmittance of the two is different. The exposure light transmittance of the optical film 17 may be set higher.

10 5 gradation photomask 11 light-shielding part 12 light-transmitting part 13A first semi-light-transmitting part 13B second semi-light-transmitting part 13C third semi-light-transmitting part 14 transparent substrate 15 light-shielding film 16 first semi-light-transmitting film 17 second Semi-transparent films 30 to 32 First to third resist patterns 20 Transfer object 23 Resist pattern

Claims (6)

A mask pattern comprising a light-shielding portion, a light-transmitting portion where the transparent substrate is exposed, and a first semi-transmissive portion, a second semi-transmissive portion, and a third semi-transmissive portion having different exposure light transmittances on the transparent substrate. A method of manufacturing a five-tone photomask having
Preparing a photomask blank having, in this order, a first semi-transparent film and a light-shielding film having etching selectivity with respect to an etchant on a transparent substrate;
Drawing and developing a resist film formed on the light shielding film of the photomask blank, and forming a first resist pattern in a region corresponding to the light shielding part;
Performing the first patterning by wet-etching the light shielding film using the first resist pattern as a mask;
After removing the first resist pattern, a resist film formed on the patterned surface including the light shielding film is drawn and developed, and the light shielding portion, the first semi-transparent portion, and the second semi-transparent portion are drawn. Forming a second resist pattern in a region corresponding to the portion;
Performing the second patterning by wet-etching the first semi-transparent film using the second resist pattern as a mask;
After removing the second resist pattern, a second semi-transparent film having etching selectivity with respect to the etchant with the first semi-transparent film is formed on the entire surface of the substrate including the patterned light-shielding film and the first semi-transparent film. Forming a photo film;
A resist film formed on the second semi-transparent film is drawn and developed to form a third resist pattern in regions corresponding to the light-shielding portion, the first semi-transparent portion, and the third semi-transparent portion. And a process of
Performing a third patterning by wet-etching the second semi-transparent film using the third resist pattern as a mask;
A method for manufacturing a five-tone photomask, characterized in that five gradations are obtained with three etchings.   2. The film forming process according to claim 1, wherein the film forming process includes only three film forming processes including the light shielding film, the first semi-transmissive film, and the second semi-transmissive film. A method for manufacturing a five-tone photomask.   The method for manufacturing a five-tone photomask according to claim 1, wherein the light shielding film is formed by stacking a light shielding layer and an antireflection layer.   The first semi-transparent part, the second semi-transparent part, and the third semi-transparent part are the first semi-transparent film, the second semi-transparent film, and the first semi-transparent film. 4. The method of manufacturing a five-tone photomask according to claim 1, wherein each of the second semi-transparent films is formed of any one of the laminated films.   2. The light shielding film and the second semi-transparent film are both made of a material containing chromium as a main component, and the first semi-transparent film is made of a material containing molybdenum silicide as a main component. 5. A method for producing a five-tone photomask according to any one of items 1 to 4. 6. An exposure process for irradiating an object to be transferred with exposure light using the photomask produced by the manufacturing method according to claim 1 to form a five-tone transfer pattern on the object to be transferred. A pattern transfer method characterized by the above.

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