JP2007187744A - Method for forming pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a pattern by which the difference in etching shapes caused by the pattern density can be eliminated, and which is excellent in rapid response to the variation of the etching shift amount or the like and is at low cost. <P>SOLUTION: In etching of a film 2 to be etched, which is used for forming a circuit pattern having different pattern densities, the thickness of a resist film capable of imparting a desired etching shift amount is determined depending on respective pattern densities so as to form the film 2 to be etched, which may have a desired dimension regardless of the pattern density after etching, and etching is performed by using the resist film 4 as a mask, in which the film thicknesses is varied in accordance with the pattern density. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  INDUSTRIAL APPLICABILITY The present invention can suppress variation in etching shape due to pattern density in lithography, patterning, and etching steps performed when manufacturing a semiconductor device or a circuit board of the semiconductor device. The present invention relates to a pattern forming method.

  Currently, as the miniaturization of semiconductor devices progresses, the layout of circuit patterns is complicated due to the memory and logic being integrated into one chip. In dry etching using plasma used to form fine patterns, even if the resist mask has a uniform shape, it is often known that the line width and hole diameter after etching change due to the density of the pattern. It has been.

  FIG. 5 is a cutaway side view of a main part showing a wafer at a process point for explaining an etching process in the case of forming a gate. In the figure, 11 is a substrate, 12 is a lower layer film, and 13 is a covered film. An etching film, 14A shows a resist film with a sparse pattern, 14B shows a resist film with a dense pattern, and FIG. (A) shows a state after resist films 14A and 14B are formed through a resist process of lithography technology. FIG. 4B shows the state after the etching of the etching target film 13 is completed and the etching target film 13A having a sparse pattern and the etching target film 13 (B) having a dense pattern are formed.

  In general, a dense pattern corresponds to a memory circuit such as a static random access memory (SRAM), and a sparse pattern corresponds to a logic circuit. As is clear from FIG. 5A, the width of the sparse pattern resist film 14A is equal to the width of the dense pattern resist film 14B, but the sparse pattern in the film to be etched 13 after the etching is completed. The width a of the film to be etched 13A and the width b of the film to be etched 13B having a dense pattern are a ≠ b (here, a> b).

  In plasma dry etching, depending on conditions such as plasma gas type, pressure, and resist material, the sparse pattern may be thin and the dense pattern may be thick.

  In general, the etching amount in the lateral direction in etching is called an etching shift amount, and this factor is that the etching shift amount changes due to pattern density.

  Factors affecting the etching shift amount include charging of reaction products and resist masks accompanying etching. That is, the reaction product is deposited on the side wall of the pattern, and the reaction product film acts as a protective film against etching. Further, the angle of ions incident on the wafer is changed by charging the resist mask. Changes in these phenomena due to pattern density affect the shift amount.

  Conventionally, in order to make the shape after etching equal regardless of pattern density, etching conditions such as plasma generation mechanism and gas species optimization have been improved, and an etching method has been developed in which the shape after etching is not affected by pattern density. (For example, see Patent Document 1 and Patent Document 2).

  In addition, a lithography technique has also been developed in which the resist mask size is changed in accordance with the pattern density in anticipation that the etching shift amount varies depending on the pattern density (see, for example, Patent Document 3).

  Furthermore, a technique has been proposed in which a reaction product generated from a mask material is changed during etching by using a mask having different components depending on pattern density, and a different sidewall protective film is formed depending on pattern density. (For example, see Patent Document 4).

  However, when optimizing the etching conditions so as to eliminate the influence of the pattern density difference, the change in the etching conditions also affects the etching rate and the selectivity to the mask. This is an extremely difficult task. Furthermore, since the etching conditions must be specified for each material to be etched, work for optimizing the etching conditions is required every time the material to be etched changes.

  Further, as described above, the amount of etching shift gradually changes depending on the state of the etching apparatus, as mentioned above, due to the accumulation of reactive organisms on the inner wall of the vacuum chamber and the consumption due to etching of the components in the chamber. It is done. For this reason, even if the etching conditions are optimized so as to correct the influence of the pattern density difference, the possibility that the conditions can be used permanently is small, and the etching conditions should be optimized as needed in response to the shift amount variation. It is difficult for the reason described above.

  Furthermore, when the shape after etching is made uniform by changing the resist mask depending on the pattern density, it is necessary to prepare the reticle used for lithography according to the pattern density, and the variation in shift amount, etc. Therefore, when the etching shift amount due to pattern density changes, changing the reticle accordingly leads to a significant increase in manufacturing cost.

Furthermore, even when the mask material is changed according to the pattern density, it is difficult to extract the optimum mask material for each material to be etched and the etching conditions, and the amount of etching shift varies depending on the state of the etching apparatus. Correspondingly, it is almost impossible to select a mask material.
JP-A-3-129821 JP 7-94469 A JP 2004-302263 A JP 2002-261267 A

  In the present invention, it is possible to eliminate a difference in etching shape due to pattern density, and to provide a low-cost pattern forming method that is excellent in quick response to variation in etching shift amount and the like. .

  In the pattern forming method according to the present invention, in etching of a film to be etched that requires formation of circuit patterns having different pattern densities, the film to be etched having a desired dimension is formed after etching regardless of the pattern density. Basically, the resist film thickness at which a desired etching shift amount is obtained is determined in accordance with each pattern density, and etching is performed using a resist film having a film thickness changed in accordance with the pattern density as a mask.

  By adopting the above means, it is possible to realize a pattern after etching of the film to be etched having a desired dimension without depending on the pattern density.

  In the method of changing the resist film thickness corresponding to the pattern density according to the present invention, it is not necessary to change the etching conditions by changing the resist film thickness, and there is almost no influence on the plasma state. It is not necessary to change the difference, and the density difference can be eliminated.

  Further, it is possible to cope with a film made of different materials to be etched by obtaining a correlation between the resist film thickness and the etching shift amount in advance, and the influence of pattern density can be quickly eliminated.

  In addition, since the work required to implement the present invention is only to change the resist film thickness corresponding to the pattern density, the fluctuation is also affected by the shift amount variation such as the change over time of the etching apparatus. The influence of the pattern density can be corrected immediately.

  Moreover, the setting of the resist film thickness in accordance with the change in the etching shift amount in the past will further increase the effect of the present invention. By monitoring the past etching results and reflecting the results in the resist film thickness setting as needed, the effect of improving the processing accuracy in etching can be obtained, and therefore the pattern can be obtained without significantly increasing the manufacturing cost. Regardless of the density, the line width and hole diameter after etching can be processed into desired dimensions, which can contribute to improvement in yield.

  In the present invention, by utilizing the influence of the resist film thickness on the etching shift amount, the resist is deposited on the film to be etched with a different film thickness according to the pattern density, and is subjected to etching through patterning by lithography. It is characterized by doing. Further, the etching shift amount in the sparse pattern and the dense pattern after etching is measured, and the resist film thickness with respect to the pattern sparse / dense is optimized based on the measured value.

  In order to deposit resists having different film thicknesses depending on the pattern density, patterning and etching are performed using a mask corresponding to the pattern density. When the etching shape is precisely controlled for each pattern density, the resist film thickness is changed to two or more by adding these steps. Although the mask used for this depends on the layout of the circuit, it is not necessary to have a definition comparable to the mask for gate and wiring processing in the manufacture of semiconductor devices, and the burden due to the addition of this processing is not great.

  As a method of changing the resist film thickness in accordance with the pattern density, it is possible to etch the resist or the resist underlayer film only at a desired location by using an energy beam such as an electron beam and an ion beam. .

  The correlation between the resist film thickness and the etching shift amount differs depending on the etching apparatus and plasma conditions. In order to control the etching shift amount that changes depending on the pattern density by changing the resist film thickness, the etching shift amount when the resist film thickness is changed is prepared in advance, and the pattern density is calculated based on the correlation. The resist film thickness is set accordingly.

  Furthermore, in setting the resist film thickness, by optimizing the resist film thickness according to the pattern density based on the etching shift amount obtained in the past etching, the etching shift amount due to the aging of the etching apparatus can be reduced. It is possible to respond immediately to situations such as fluctuations.

  1A and 1B are explanatory views of Embodiment 1 in the present invention, where FIG. 1A shows a process flow, and FIG. 1B shows a cut side surface of a main part of a wafer at a process point. In both (A) and (B), the process proceeds according to the arrow. Also, here, as a circuit corresponding to the pattern density, the sparse pattern is a logic circuit, and the density pattern is a memory circuit such as an SRAM. Therefore, the circuit is a mixed LSI device as a whole.

  FIG. 1 shows a case where the etching shape of the sparse pattern and the dense pattern is set to a desired dimension by depositing resists with two kinds of film thickness according to the pattern sparse and dense.

  When considering the pattern density and further improving the dimensional accuracy after etching, it is possible to increase the resist film thickness to two or more types according to the pattern density.

  As shown in the cross-sectional shape after etching in FIG. 1, a series of processes related to gate etching with a large etched area is illustrated, but for etching and etching of an interlayer insulating film with a small etched area, etc. However, it is almost the same except that the etching area is different.

(1)
By applying the CVD method, a film to be etched 2 made of polycrystalline Si is formed on the substrate 1. Next, a hard mask film 3 made of SiO ₂ or Si ₃ N _{4 is formed} .

(2)
Only the hard mask film 3 corresponding to the dense pattern region is etched to make a difference in the resist film thickness depending on the pattern density. In this case, in order to realize a desired resist film thickness, the etching depth of the hard mask film 3 is adjusted by controlling the etching time. On the contrary, depending on the etching characteristics due to the plasma generation mechanism or the like, it may be necessary to etch only the sparse pattern. Further, local etching using an energy beam such as an ion beam may be used as a means that can be substituted for a process from patterning to etching corresponding to pattern density.

(3)
After providing a step in the hard mask film 3 according to the pattern density, a resist film 4 is deposited.
At this time, processing by reflow or CMP (chemical mechanical polishing) is performed in order to flatten the resist surface so that a desired resist film thickness is obtained with a sparse pattern and a dense pattern. If the resist has a low viscosity, the planarization operation can be simplified or further omitted.

(4)
As described above, the influence of the pattern density can be eliminated by patterning the resist film 4 having a changed thickness by normal lithography and etching the film 2 to be etched using the resist film 4 as a mask. .

  2A and 2B are explanatory views of Embodiment 2 in the present invention, where FIG. 2A shows a process flow, and FIG. 2B shows a cut side of a main part of a wafer at a process point. The part indicated by the same symbol as that of the existing symbol represents the same or effective part. In both (A) and (B), the process proceeds according to the arrow. Also, here, as a circuit corresponding to the pattern density, the sparse pattern is a logic circuit, and the density pattern is a memory circuit such as an SRAM. Therefore, the entire pattern is a mixed LSI device.

  The second embodiment is an example using a so-called double resist film in which a resist film is used in a stacked manner without using the hard mask film 3 shown in the first embodiment as an etching mask. In this case, a lower resist film 4A and an upper resist film 4B are formed on the etching target film 2, and the upper resist film 4B is left only for a pattern that needs to be thickened. The resist film thickness is changed between a certain logic circuit and a memory circuit such as SRAM having a dense pattern. In this case, as described in the first embodiment, the upper resist film 4B is patterned by performing exposure and development processes using a mask corresponding to the density, or using local etching by an energy beam. In Example 2, as in Example 1, the pattern density is not limited. When further improvement in processing accuracy is required, the resist film thickness may be increased to two or more types. Depending on the etching characteristics, it is possible to reverse the steps of the resist film thickness in the dense pattern.

  3A and 3B are explanatory diagrams of Embodiment 3 in the present invention, where FIG. 3A shows a process flow, and FIG. 3B shows a cut side of a main part of a wafer at a process point. The part indicated by the same symbol as that of the existing symbol represents the same or effective part. In both (A) and (B), the process proceeds according to the arrow. Also, here, as a circuit corresponding to the pattern density, the sparse pattern is a logic circuit, and the density pattern is a memory circuit such as an SRAM. Therefore, the entire pattern is a mixed LSI device.

  In Example 3, a desired resist film thickness corresponding to the pattern density is formed by forming a single thick resist film 15 and half-etching only the portion corresponding to the sparse pattern. Is realized.

  In order to perform patterning corresponding to pattern density as in the first embodiment, etching after masking or local etching using an energy beam is used. In addition, it is possible to improve the processing accuracy by increasing the resist film thickness to two or more types, and depending on the etching characteristics, the steps of the resist film thickness in the dense pattern may be reversed.

  FIG. 4 is an explanatory diagram showing an overall process from film formation of a resist film to length measurement after etching, and a process flow for optimizing the resist film thickness from the length measurement result.

  As is apparent from the figure, the etching shift amount is obtained by length measurement performed after etching of the film to be etched. In addition, the correlation between the resist film thickness and the etching shift amount is prepared in advance for each etching apparatus, etching conditions, and resist material. Based on the measured values of the etching shift amounts of the sparse pattern and the dense pattern, a shift amount correction value for obtaining a desired processing dimension is obtained. With respect to the correlation between the resist film thickness and the etching shift amount, the shift film thickness correction value is introduced to obtain the resist film thickness corresponding to the pattern density. By applying the resist film thickness obtained in this way to the next process, it is possible to suppress fluctuations in the etching shift amount due to a change in the state of the etching apparatus. As a result, it will be understood that the method of the present invention can immediately cope with process variations that appear in pattern sparseness.

  In the method disclosed by the present invention, a technique for correcting the etching shift amount by changing the resist film thickness is provided, and not only the correction corresponding to the pattern density but also the resist film thickness is made constant with respect to the film to be etched. Thus, the etching shift amount of the entire pattern can be corrected uniformly, and this is because the control of the dimension of the entire etching surface is important by suppressing the dimensional variation after etching caused by the pattern density. It is effective when it is done.

  Since the present invention can be implemented in many forms including the above-described embodiment, it will be exemplified below as an additional note.

(Appendix 1)
In etching a film to be etched that requires the formation of circuit patterns having different pattern densities,
Regardless of the pattern density, in order to form a film to be etched having a desired dimension after etching, the resist film thickness for obtaining a desired etching shift amount is determined according to each pattern density,
Etching is performed using a resist film whose thickness is changed in accordance with the pattern density as a mask.

(Appendix 2)
In order to form the resist film with the film thickness determined in (Appendix 1), the resist film is deposited on a hard mask having a step according to the pattern density, and the resist film surface is flattened as desired. A pattern forming method as set forth in (Appendix 1), wherein a resist film having a thickness of 1 is formed.

(Appendix 3)
In order to form a resist film with the film thickness determined in (Appendix 1), a desired resist film thickness is realized by using a plurality of stacked resist films and removing the upper resist film according to the pattern density. (Attachment 1) The pattern formation method of description.

(Appendix 4)
In order to form the resist film with the film thickness determined in (Appendix 1), a desired resist film thickness is realized by half-etching the single layer resist film according to the pattern density using the single layer resist film. The pattern forming method as described in (Appendix 1).

(Appendix 5)
When realizing a step for changing the film thickness of the resist film corresponding to the pattern density, the step is formed by patterning with a mask manufactured corresponding to the pattern density and etching subsequent to the patterning (Appendix 1). ) The pattern forming method described.

(Appendix 6)
The pattern formation according to (Appendix 1), characterized in that, when realizing the step for changing the film thickness of the resist film corresponding to the pattern density, it is formed by locally etching using an energy beam. Method.

(Appendix 7)
It is characterized in that the resist film is adjusted to have a film thickness necessary for obtaining a desired processing dimension in the next etching based on the actually measured value of the etching shift amount related to the pattern density (Appendix 1). The pattern formation method as described.

(Appendix 8)
In order to correct the etching shift amount based on the resist film thickness, a desired resist film thickness is calculated based on the correlation between the resist film thickness obtained in advance and the shift amount. Method.

It is explanatory drawing showing the process flow (A) of Example 1 in this invention, and the principal part cutting | disconnection side surface (B) of the wafer in a process important point, respectively. It is explanatory drawing showing the principal part cutting side surface (B) of the process flow (A) of Example 2 in this invention, and the wafer in the process important point, respectively. It is explanatory drawing showing the principal part cutting side surface (B) of the process flow (A) of Example 3 in this invention, and the wafer in the process important point, respectively. It is explanatory drawing which shows the processing flow which optimizes the resist film thickness in this invention. It is a principal part cutting side view showing the wafer in the process important point for demonstrating the conventional etching process in the case of forming a gate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Film to be etched 3 Hard mask film 4 Resist film 4A Lower resist film 4B Upper resist film 15 Single layer thick resist film

Claims (5)

In etching a film to be etched that requires the formation of circuit patterns having different pattern densities,
Regardless of the pattern density, in order to form a film to be etched having a desired dimension after etching, the resist film thickness for obtaining a desired etching shift amount is determined according to each pattern density,
Etching is performed using a resist film whose thickness is changed in accordance with the pattern density as a mask. In order to form the resist film with the film thickness determined by the method according to claim 1, the resist film is deposited on a hard mask provided with a step according to the pattern density, and the resist film surface is planarized as necessary. 2. The pattern forming method according to claim 1, wherein a resist film having a desired thickness is formed. In order to form a resist film with a film thickness determined by the method according to claim 1, a desired resist film thickness is realized by using a plurality of stacked resist films and removing the upper resist film according to the pattern density The pattern forming method according to claim 1, wherein: In order to form a resist film with a film thickness determined by the method according to claim 1, a desired resist film thickness is obtained by half-etching the single-layer resist film according to a pattern density using a single-layer resist film. The pattern forming method according to claim 1, which is realized. 2. The pattern forming method according to claim 1, wherein a desired resist film thickness is calculated based on a correlation between a resist film thickness obtained in advance and a shift amount in order to correct the etching shift amount based on the resist film thickness. .

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