JPH10308380A - Recessed part formation method by etching processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a recessed part formation method by an etching processing capable of suitably obtaining a forward mesa shape. SOLUTION: In a high-speed corrosion layer formation process, a silicon dioxide film 50 for which an etching speed is higher than the side etching speed of the [011] direction of a wafer 46 is formed on a surface 48. Then, in a resist formation process, photoresist 52 is formed in a prescribed pattern on the silicon dioxide film 50. Thereafter, in an etching process, the etching processing is performed from the side of the surface 48. Thus, since the advance speed of the etching of the silicon dioxide film 50 is higher than the advance speed of the side etching of the wafer 46 in the [011] direction which is an opposite mesa direction, the silicon dioxide film 50 is removed and moved back prior to the side face of a recessed part 40 to be formed at the wafer 46.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an etching method for forming a recess on the surface of a predetermined object such as a compound semiconductor.

[0002]

2. Description of the Related Art For example, in manufacturing a semiconductor device such as a light emitting diode or a semiconductor laser, a current confinement structure for forming a point light source and a mesa structure (trapezoidal shape) for increasing a light emission output are formed. , Epitaxial
An etching process for removing a part of a wafer (hereinafter, simply referred to as a wafer) and processing the surface into a predetermined shape is performed. There are various methods for the etching treatment performed for such a purpose, and a wet etching method using an etching solution is advantageous in terms of mass productivity and manufacturing cost. Hereinafter, the term “etching” in the present application means wet etching.

[0003]

The process of forming a recess by the above-mentioned wet etching is described in, for example, FIG.
It is performed according to the steps shown in (a) to (c). That is, first, a resist (photoresist) 12 is formed in a predetermined pattern on the surface of the wafer 10 as shown in FIG. In general, the wafer 10 is formed by sequentially epitaxially growing and stacking a plurality of types of compound semiconductors so as to obtain a predetermined function of a semiconductor element. However, in the drawing, boundaries between compound semiconductors are omitted. I have. Next, the wafer 10 is etched from the surface 14 side with an etchant (etchant) determined for each type of compound semiconductor constituting the surface layer portion. As a result, as shown in FIG.
A part of the four-side part where the resist 12 is not provided is exclusively corroded and removed, and a recess 16 is formed. After the recess 16 having a predetermined shape is formed in this manner, the resist 12 is removed using a resist stripper as shown in FIG. Note that, for example, the wafer 10
When the surface layer is made of a GaAs-based compound semiconductor, a citric acid-hydrogen peroxide-based etchant or the like is preferably used as an etchant for etching the wafer 10.

In the etching process shown in FIG. 1 (b), when the side surface 18 of the recess 16 is exposed with the progress of corrosion in the direction perpendicular to the surface 14, the side surface 18 is removed. A phenomenon referred to as side etching or undercut in which corrosion progresses in the lateral direction of retreat occurs. Therefore, the wafer 10 is partially corroded even at the position covered with the resist 12,
As shown in FIG. 1B, the opening area of the recess 16 formed by the etching process is larger than the opening area of the resist 12.

However, compound semiconductors generally have anisotropy in which the etching rate varies depending on the crystal direction. Therefore, in the direction where the etching rate in the lateral direction is higher than the etching rate in the vertical direction (forward mesa direction), the surface 14
Since the side etching becomes larger on the side, the cross-sectional shape perpendicular to the lateral direction is formed in a forward mesa (trapezoidal) shape as shown in FIG. 2A, while the etching rate in the lateral direction is In the direction lower than the etching rate (inverted mesa direction), the side etching becomes larger toward the inner side, so that the cross-sectional shape perpendicular to the lateral direction becomes an inverted mesa (inverted trapezoidal) shape as shown in FIG. 2 (b). There is a problem of formation. For example, in a GaAs-based compound semiconductor in which the crystal surface 14 is a (100) plane, the direction shown in (1) below is the forward mesa direction which is the lateral direction in FIG.
The [011] direction is the reverse mesa direction which is the horizontal direction in FIG. When such an inverted mesa shape is formed, as shown in FIG. 1 (d), when the passivation film 20 is provided on the surface 14 of the wafer 10 for the purpose of suppressing its oxidation, etc. When the passivation film 20 is interrupted and it is difficult to cover the entire surface 14 including the surface of the recess 16, when a current confinement structure is formed immediately below the recess 16, current concentrates near the bottom surface of the recess 16 and deteriorates. This causes inconveniences such as easy operation. In FIG. 2, the dashed line is an example of the boundary between the elements that are individually divided in a later process. In this case, an element having a convex portion is produced as a result, but as shown in FIG. In the case of manufacturing a device having a place 16, the wafer 10 is divided at an intermediate position between them. That is, FIG. 1 shows the etching process for one element formed on the wafer 10. Therefore, the above-mentioned “recess forming process” includes not only an etching process for manufacturing an element or the like having a recess as shown in FIG. 1 but also a convex portion as a result as shown in FIG. It can also be referred to as an etching process for forming a recess in a wafer or the like before being separated into individual elements or the like in order to manufacture a device or the like that has been manufactured.

[Outside 1]

When a polycrystalline material such as alumina having an isotropic etching rate is etched, an inverted mesa shape due to a low lateral etching rate is not formed. However, in such an isotropic material, the etching rate in the vertical direction and the etching rate in the horizontal direction are the same, so that FIG.
As shown in (b), the side surface of the recess 22 formed by corrosion is formed in a continuous arc shape from the bottom surface, and the upper end of the side surface is perpendicular to the surface 24. Therefore, for example, if a film is further formed on the surface 24, a void may be generated at a boundary portion between the recess 22 and the surface 24. Therefore, it is desirable that a normal mesa shape is formed even in such an etching process.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method of forming a concave portion by an etching process capable of suitably obtaining a normal mesa shape.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the gist of the present invention is a method of forming a recess in a surface by etching a predetermined object to be processed from the surface. (A) with respect to an etching rate by a predetermined etching solution, a high-speed corrosion layer having a side etching rate higher than that in a predetermined direction among side etching rates that progress in a lateral direction along the surface of the object to be processed. (B) a resist forming step of forming a resist that is not substantially corroded by the predetermined etching solution in a predetermined pattern on the high speed corrosion layer; An etching step of performing an etching process from the front side with the etching solution.

[0009]

In this way, when forming a recess on the surface of the object to be processed, the etching rate of the predetermined etching solution along the surface of the object to be processed in the high-speed corrosion layer forming step is reduced. A resist which is not substantially corroded by a predetermined etching solution in a resist forming step, in which a high-speed corrosion layer having a side etching rate higher than that in a predetermined direction among side etching rates progressing in a lateral direction is formed on the surface. Is formed in a predetermined pattern on the high-speed corrosion layer, and then, in an etching step, is etched from the surface side by the predetermined etching solution. Therefore, in the above-described predetermined lateral direction, the speed of the side etching of the high-speed corroded layer in the etching step is higher than the speed of the side etching of the object to be processed. Prior to the sides, the fast corrosion layer is removed and retracted. Therefore, in the portion where the high-speed corrosion layer has been removed, the surface of the object to be processed is exposed to the etching solution, so that the corrosion proceeds in a direction perpendicular to the surface, so that the side etching is substantially performed. The speed is increased toward the surface. Thereby, when forming the recess by the etching process, the formation of the inverted mesa shape due to the low etching rate in the lateral direction is suppressed, and the inclination angle of the side surface of the recess is moderately controlled. A recess with a regular mesa shape is obtained.

[0010]

In another embodiment of the present invention, the high-rate corrosion layer preferably has a side etching rate higher than a minimum value among side etching rates of the object to be processed with respect to an etching rate by the predetermined etching solution. Have With this configuration, since the side etching rate of the high-speed corrosion layer is higher than that of the object to be processed in at least a part of the lateral direction, the high-speed corrosion layer is retreated before the side surface of the recess in that direction. The surface of the object is exposed, and the formation of the inverted mesa shape is suppressed based on the fact that the side etching rate is substantially increased toward the surface.

Preferably, the high-speed corrosion layer has a side etching rate higher than a vertical etching rate that progresses in a direction perpendicular to the surface of the workpiece with respect to an etching rate by the predetermined etching solution. Things. With this configuration, in the direction in which the inverted mesa shape can be formed due to the side etching rate of the object to be processed being lower than the vertical etching rate, the high-speed corroded layer is removed by the side etching and the side face of the recess is formed. As the surface of the object is exposed and the side etching rate is substantially increased toward the surface side, the formation of the inverted mesa shape is suppressed. Therefore, a recess having a forward mesa shape in all directions can be suitably obtained.

When the side etching rate of the object to be processed is higher than the vertical etching rate in all directions, a forward mesa shape can be obtained in all directions without providing a high-speed corroding layer. By providing the high-speed corrosion layer, the side etching rate is increased toward the surface side, so that the effect of reducing the inclination angle of the slope forming the recess is obtained. That is, there is an advantage that a recess having a slope with a desired inclination angle can be obtained when the recess is formed by the etching process. Incidentally, in the case of forming a recess in a compound semiconductor, in order to increase continuity of a passivation film, etc.,
It is desirable that the inclination angle of the slope forming the recess be made as gentle as possible.

Preferably, the object to be processed is made of a single crystal in which an etching rate of the predetermined etching solution is different depending on a crystal direction. The direction is lower than the etching rate in the vertical direction. In this way, even when the object to be processed is made of anisotropic single crystal, the etching rate of the high-speed corrosion layer is higher than that of the side etching rate in the direction lower than the vertical etching rate. Be killed. Therefore, in the direction where the side etching speed is low, the high-speed corrosion layer is retreated before the side surface of the recess. As a result, the side etching speed in the direction substantially increases toward the surface, and a recess having a forward mesa shape is formed.

Preferably, the object to be processed is a GaAs-based compound semiconductor, and the rapid corrosion layer is made of silicon dioxide (Si).
O ₂ ). In this way, the GaAs-based compound semiconductor generally has anisotropy having a forward mesa direction and a reverse mesa direction. A mesa shape is formed. In this case, the rapid corrosion layer is made of hydrofluoric acid (H
F) is composed of silicon dioxide which is easily corroded by, for example, hydrofluoric acid hardly corrodes the GaAs-based compound semiconductor. It is possible to easily make the etching rate of the high-speed corrosion layer sufficiently higher than the side etching rate of the object to be processed.

Preferably, the step of forming a high-speed corrosion layer includes forming the high-speed corrosion layer on the entire surface of the object to be processed. Using another etching solution that corrodes the high-speed corrosion layer but does not substantially corrode the object, the high-speed corrosion is performed by removing the high-speed corrosion layer according to the pattern of the resist and exposing the surface of the object. It further includes a layer patterning step. With this configuration, since the high-speed corrosion layer is also formed in a predetermined pattern prior to the etching step, the workpiece is immediately corroded by the etchant in the etching step.
Etching control becomes easier.

[0016]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following description, the dimensional ratios and the like of each part are not necessarily drawn accurately.

FIG. 3 (a) shows a main part of a point light source light emitting diode (hereinafter, referred to as LED) 30 having a small light emitting diameter manufactured by using the recess forming method according to one embodiment of the present invention. FIG. 3B is a plan view schematically showing the LED 30. The LED 30 is, for example, an n-GaAs compound semiconductor or an n-
Well-known liquid phase growth (Liquid Phase Epitaxy) and metal-organic chemical vapor deposition (Metal-Organic Chemical Vapor Deposition) on substrates made of AlGaAs compound semiconductors, etc.
A semiconductor element portion 32 composed of an epitaxial wafer formed by sequentially growing a cladding layer and an active layer of a GaAs compound semiconductor, an AlGaAs compound semiconductor, and the like by a crystal method, and an upper surface 3 of the semiconductor element portion 32
4 and a lower electrode fixed to a lower surface (not shown), and a passivation film 38 provided to cover the upper electrode 36 and a part of the upper surface 34 of the semiconductor element portion 32. .

The semiconductor element portion 32 includes, for example, a p-type region 32a including an active layer functioning as a light emitting layer, and an n-type region 32 formed as a current blocking layer formed thereon.
b, and an n-type region 32c formed thereover. The n-type region 32c constituting the uppermost portion of each of these regions has a thickness of, for example, about 3 (μm), and
Although it is composed of an n-GaAs compound semiconductor, a part thereof is removed in a substantially inverted truncated cone shape over the entire thickness direction. For this reason, on the upper surface 34 of the semiconductor element portion 32,
A regular mesa-shaped recess 40 having a diameter of about 160 (μm) at the opening and about 150 (μm) at the bottom and having a slope facing the opening side (ie, the upper surface 34 side) is formed. The passivation film 38 is provided according to the shape of the upper surface 34 including the recess 40. Further, the semiconductor element portion 32 has an impurity such as zinc (Zn) which is a p-type dopant, for example, having a depth smaller than the thickness of the n-type region 32c and larger than the thickness of the n-type region 32b from the upper surface 34 side. Is provided at a high concentration, and a part of the n-type region 32b and the n-type region 32c is
It has been flipped to a mold. Thereby, the semiconductor element portion 3
2 has a current constriction structure in which a current is passed only through a path passing through the inversion region indicated by the diagonal line, so that light is emitted only from the recess 40 which is a partial region of the upper surface 34. The emission diameter is very small. That is, the recess 40 functions as a light emitting window of the LED 30.

The passivation film 38 is made of, for example, silicon nitride (Si ₃ N ₄ ) and has a thickness of 0.1 μm by a chemical vapor deposition (CVD) method, a sputtering method, or the like.
m). Further, the upper electrode 3
Reference numeral 6 denotes an ohmic electrode which has a thickness of, for example, about 0.5 (μm) and is formed by laminating an Au—Zn alloy and Au in this order from the semiconductor element portion 32 side except the inside of the recess 40. In the figure, reference numeral 44 denotes an electrode lead for supplying electricity to the upper electrode 36, which is fixed to the upper electrode 36 by wire bonding or the like within a rectangular area where the passivation film 38 is not partially provided.

By the way, the LED configured as described above
30 is manufactured according to a manufacturing process including a wafer process, for example. Hereinafter, the LED 3 will be described with reference to FIGS. 4A to 4F which schematically show the processing state of the wafer at each stage of the process.
0 will be described. First, the semiconductor element portion 32 is formed on a substrate by using a crystal growth technique such as MOCVD.
Are sequentially grown by crystal growth to form a wafer 46 having a GaAs compound semiconductor layer on its surface.
(See FIG. 4A). At this time, the surface 48 of the wafer 46 is, for example, a (100) plane. In a normal wafer process, a plurality of LEDs 30 are formed in a wafer 46 grown on one substrate, but only a portion corresponding to one LED 30 is shown in FIG. Then, in a high-speed corrosion layer forming step shown in FIG. 4 (a), a solution in which, for example, silicon dioxide (SiO ₂ ) is dissolved in an organic solvent is applied to the surface 48 of the wafer 46 by SOG (spin).
A silicon dioxide film 50 having a thickness of about 50 (nm) is formed by coating using an on-glass method or the like and baking at a high temperature (baking), or by using a thin film process such as a sputtering method. . In this embodiment, the wafer 46
Corresponds to the object to be processed, and the silicon dioxide film 50 corresponds to the high-speed corrosion layer.

In a resist forming step shown in FIG. 4B, a photoresist (resist) 52 is formed on the surface of the silicon dioxide film 50 in a predetermined pattern. The photoresist 52 is provided with an opening 54 having a diameter of about 150 (μm) and a smaller diameter than the opening at a position corresponding to the recess 40. After the silicon dioxide film 50 and the photoresist 52 are provided on the wafer 46 in this manner, in the high-speed corrosion film patterning step shown in FIG. 4C, for example, buffered hydrofluoric acid (a mixed solution of hydrofluoric acid and ammonia) or Hydrofluoric acid is used as an etchant (hereinafter referred to as etchant A)
And an etching process is performed. Since the etching solution A hardly corrodes the photoresist 52 and the compound semiconductor such as GaAs and AlGaAs, and corrodes silicon dioxide, the silicon dioxide film 50 is selectively removed according to the opening pattern of the photoresist 52. A part of the wafer 46 is exposed. Then, in the etching step shown in FIG. 4D, after the wafer 46 is washed with pure water or the like,
The wafer 46 is subjected to an etching process using an etching solution (hereinafter, referred to as an etching solution B) in which buffered hydrofluoric acid is mixed with a citric acid-hydrogen peroxide-based etchant. As a result, a part of the GaAs compound semiconductor layer constituting the surface layer of the wafer 46 is removed while the silicon dioxide film 50 is retracted from the opening 54, and the recess 40 of the semiconductor element section 32 is formed. At this time, the recess 40 is
Is formed into a larger opening diameter than the photoresist 52 by side etching. The etching solution B also hardly corrodes the photoresist 52. For example, the etching solution B is buffered against citric acid (dissolved in 50% water) 77% and hydrogen peroxide 20%. Those containing about 3% hydrofluoric acid are preferably used.

After the above-described etching process is performed for a predetermined time to form the recess 40 at a predetermined depth, the wafer 46 is taken out of the etching solution B and washed with pure water or the like to stop the etching process. Thereafter, as shown in FIG. 4E, a photoresist 52 and a silicon dioxide film 50 are formed.
Is removed. The photoresist 52 is formed using a commonly used resist stripping solution, and the silicon dioxide film 50 is formed as shown in FIG.
The removal is performed by using the etching solution A as in the case shown in FIG. Then, the diffusion portion 42 is formed by diffusing impurities such as zinc from the surface 48 by heat diffusion or the like such as a sealed tube diffusion method, and further, after the upper electrode 36 and the lower electrode are provided, FIG. As shown in (1), a series of wafer processes is completed by forming the passivation film 38 on the surface 48 by the CVD method, the sputtering method, or the like.
At this time, since the recess 40 is formed in a forward mesa shape in all directions along the surface 48 as shown in FIGS. 3A and 3B, the entire surface of the passivation film 38 is not interrupted. Continuously formed on the wafer 4
6 is covered to protect it from oxidation and contamination. Note that, in the drawing, the diffusion portion 42, the upper electrode 36, and the like are omitted. Thereafter, the LED 30 is further cut by dicing into blocks corresponding to individual elements, die-bonded to a TO18 flat stem or the like (not shown), and the electrode lead 44 is fixed and used in a sealed state.

Here, FIG. 5 is a view for explaining the principle that all directions are formed in a forward mesa shape in the above etching step. In the drawing, a, f, and -k indicated by broken lines represent the positions of the end surfaces of the silicon dioxide film 50 at the start of the etching process t0 and at times t1 to t10 obtained by dividing the etching process time into ten equal parts. Is at time t0
, F at time t5, i at time t8, and j at time t9.
And k corresponds to time t10. On the other hand, a1, a2, to a10 similarly shown by broken lines (however, a part extending in the horizontal direction in the drawing of a10 is not displayed because it overlaps with a dashed-dotted line indicating the bottom surface of the recess 40) is time t0. From time t1, t2, to t10 starting from the end face position a at
The range of the wafer 46 that is removed by corrosion (etching) every time is shown. The figure shows Ga having a low etching rate by the etchant B in a direction perpendicular to the surface 48.
The [011] direction of the As compound semiconductor (generally the direction opposite to the mesa direction) coincides with the left-right direction. Therefore, as is clear from the broken line in the figure, the amount removed by side etching increases from the surface 48 toward the inside,
The removal range starting from the end face a has an inverted mesa shape.

However, the silicon dioxide film 50 has a higher etching rate with respect to the etching solution B regardless of the crystal direction of the wafer 46 (that is, the wafer 4).
6 has a higher etching rate than either the reverse mesa direction or the direction perpendicular to the surface 48). In other words, since the etching solution B used is one in which the etching rate of the silicon dioxide film 50 is higher than that of the wafer 46, the end surface thereof is formed after the side surface of the concave portion 40 which is sequentially retracted and expanded. It is retracted by side etching prior to retreat. Therefore, at time t5, since the end face of silicon dioxide film 50 is retracted to position f, wafer 46 is not moved after time t5.
Is corroded starting from the end face position f. Broken line f
Reference numerals 6, f7, to f10 denote removal ranges every time starting from the end face position f. That is, the portion between the end face position a and the end face position f of the wafer 46 is at time t
The side surfaces of the recess 40 formed between 0 and t5 are laterally etched and removed by side etching, and vertically from a portion of the surface 48 newly exposed by the retreat of the silicon dioxide film 50. Is also corroded and removed. Similarly, at time t8, the end face is retracted to position i, and thereafter, the ranges indicated by i9 and i10 are removed at time t9 and t10, and at time t9, the end face is retracted to position j. Therefore, thereafter, the range indicated by j10 is removed by time t10.

For this reason, the removal range of the wafer 46 as a whole, ie, the contour line of the recess 40, is the range of the removal range starting from the end face position of the silicon dioxide film 50 at each time changed in the range of a to k. Although it is formed as an envelope (shown by a dashed line), the etching time to be corroded from the newly formed end face becomes shorter at the right side position in the drawing that is retracted from the end face of the opening 54. Therefore, the amount of removal provided by the envelope in the direction perpendicular to the surface 48 becomes smaller as the distance from the opening 54 decreases, and the side etching speed is substantially reduced.
Since the height is increased toward the eighth side, a forward mesa shape in which the slope is directed to the surface side is formed even in the so-called reverse mesa direction of the compound semiconductor, as shown by the dashed line in the figure. In addition,
Also in the normal mesa direction (the crystal direction shown in the above 1) perpendicular to the direction shown in the figure, the vertical corrosion at the lower position of the photoresist 52 is promoted due to the retreat of the end face of the silicon dioxide film 50. Is done. Therefore, the forward mesa shape is maintained in this direction, but the inclination of the slope of the recess 40 becomes gentle.

As described above, according to the present embodiment,
When forming the recess 40 in the surface 48 of the wafer 46, a high speed corrosion layer forming step shown in FIG.
A silicon dioxide film 50 having an etching rate by the etching solution B higher than the side etching rate in the [011] direction of the wafer 46 is formed on the front surface 48, and then FIG.
In the resist forming step shown in (b), a photoresist 52 which is not substantially corroded by the etchant B is formed on the silicon dioxide film 50 in a predetermined pattern, and thereafter, in the etching step shown in FIG. Is etched from the surface 48 side by the etching solution B. Therefore, in the [011] direction, which is the reverse mesa direction, the progress speed of the side etching of the silicon dioxide film 50 in the etching step is higher than the progress speed of the side etching of the wafer 46, so that the recess formed in the wafer 46 is formed. Silicon dioxide film 50 prior to the side of 40
Is removed and retracted. Therefore, in the portion where the silicon dioxide film 50 is removed, since the surface 48 of the wafer 46 is exposed to the etching solution, the surface 48 is exposed.
Corrosion also proceeds in a direction perpendicular to the surface, so that the side etching speed is substantially increased toward the surface 48 side.
Accordingly, when the recess 40 is formed by the etching process, the formation of the inverted mesa shape due to the low etching rate in the lateral direction is suppressed, so that the recess 40 having a proper mesa shape is obtained. .

That is, as in the present embodiment, even when the wafer 46 made of a single crystal having an etching rate different from that of the etching solution B depending on the crystal direction is etched, the etching rate in the reverse mesa direction is lower than that in the vertical direction. A silicon dioxide film 50 having an etching rate higher than the etching rate is provided between the wafer 46 and the photoresist 52, and the silicon dioxide film 50 is retracted prior to the side surface of the recess 40 in a direction in which the side etching rate is lower. Therefore, the corrosion progresses in the vertical direction in the portion where the wafer 46 is newly exposed, so that the side etching speed in that direction is substantially increased toward the surface 48, and the concave portion having the regular mesa shape is formed. A place 40 is formed.

The inclination angle of the inclined surface of the recess 40 depends on the ratio between the etching rate in the direction (depth direction) perpendicular to the surface 48 of the wafer 46 and the etching rate of the silicon dioxide film 50. The inclination angle can be easily controlled to a desired value by changing the etching rate of the silicon film 50 by changing the concentration of hydrofluoric acid in the etching solution B, the quality of the silicon dioxide film 50, and the like. That is, in the present embodiment, the concentration of hydrofluoric acid in the etching solution B is about 3 (%), but the concentration can be changed as appropriate.

Incidentally, as shown in FIG. 1, in the conventional manufacturing method in which the recess 16 is provided by etching without providing the silicon dioxide film 50, the adhesion between the photoresist 12 and the wafer 10 is reduced. It has been empirically known that the worse the worse, the lower the inclination angle of the side surface (inclined surface) 18 of the recess 16 is, and sometimes a preferable forward mesa shape is obtained even in the reverse mesa direction as shown in the figure. . The reason why this phenomenon occurs is that the etchant penetrates into the interface between the photoresist 12 and the wafer 10 due to poor adhesion and causes vertical corrosion from the surface 14 immediately below the photoresist 12. Can be That is,
By positively reducing the adhesion of the photoresist 12, the formation of the inverted mesa shape can be suppressed. However, it is extremely difficult to control the adhesion to an appropriate state in order to obtain a desired inclination angle, and if the adhesion is reduced, there is a possibility that the portion where the shape should be maintained may be corroded. Is not a practical method.
On the other hand, according to the present embodiment, as described above, by appropriately changing the hydrofluoric acid concentration in the etching solution B and the film quality of the silicon dioxide film 50, not only the formation of the inverted mesa shape can be suppressed, but also There is an advantage that the inclination angle can be easily controlled.

In this embodiment, the high-speed corrosion layer forming step shown in FIG. 4A is to form the silicon dioxide film 50 over the entire surface 48 of the wafer 46.
Prior to the etching step shown in FIG. 4D, the photoresist 52 is etched using a etching solution A which corrodes the silicon dioxide film 50 but does not substantially corrode the wafer 46.
A high-speed corrosion film patterning step shown in FIG. 4C for removing the silicon dioxide film 50 and exposing the surface 48 of the wafer 46 according to the pattern shown in FIG. Therefore, since the silicon dioxide film 50 is also formed in a predetermined pattern prior to the etching step, the wafer 46 is immediately corroded by the etching solution B in the etching step, so that the etching control is further facilitated.

FIG. 6A is a diagram for explaining another embodiment of the present invention. In the figure, the processing object 56 in which the recess 22 is formed by the etching process is made of alumina (Al ₂ O ₃ ).
It consists of. The object 56 is formed on a substrate (not shown) by a thin film process such as sputtering.
(μm). This object 56
When the concave portion 22 is provided in the substrate, first, after the film to be processed is formed as described above, a low-density layer 58 made of alumina is further formed thereon. This low-density layer 58
For example, it has a film thickness of about 0.5 (μm) and is made of substantially the same material as the object to be processed 56. Then, a high bias is further formed by sputtering. Therefore, the etching rate of the low-density layer 58 by hydrofluoric acid is increased to about 1.6 times that of the object 56 to be processed. In the drawing, broken lines indicate the contours of the object 56 and the low-density layer 58 before the etching process, and solid lines indicate those after the etching process. Also in this embodiment, by using hydrofluoric acid as an etchant, the low-density layer 58 having a high etching rate is retracted prior to the side surface of the recess during the etching process, and the processing target covered with the photoresist 52 is removed. The surface 24 of the body 56 is sequentially exposed. Therefore, as in the above-described embodiment, the side etching rate of the portion is substantially increased toward the surface 24 side, so that the concave portion 22 having the inclined surface suitably facing the surface 24 side is formed as shown in the drawing. Is done. In this embodiment, since the high-speed corrosion layer is formed only by slightly changing the film forming conditions, there is an advantage that the process is not particularly complicated.

While the embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be embodied in still another embodiment.

For example, in the embodiment, the present invention is directed to a method of forming the recess 40 in the n-type region 32c made of a GaAs-based compound semiconductor in order to form a light emitting window of the point light source type LED 30, or a method of forming a light-emitting window made of alumina. Although the case where the present invention is applied to the method of forming the recess 22 in the processing body 56 has been described, the present invention provides a processing object made of various materials such as other compound semiconductor single crystals or the like having a recess having a normal mesa shape. The same applies if it is formed. Further, when forming a forward mesa shape for obtaining a high output in a light emitting diode, that is, when manufacturing a device or the like having a convex portion as a result, when forming a concave portion on a dividing line between elements of a wafer. The same effect can be obtained by applying the present invention.

In the embodiment, the recesses 40, 22
As the etchant for forming the silicon oxide, a mixture of citric acid-hydrogen peroxide-based etchant mixed with buffered hydrofluoric acid, hydrofluoric acid, or the like was used. 46, object 56 etc.)
Type and fast corrosion layer (silicon dioxide film 50, low density layer 58
Depending on the type, etc., the fast corrosion layer is retreated at a speed higher than the retreat speed of the recess side surface, and does not substantially corrode the photoresist 52 (ie, the corrosion of the photoresist 52 during the etching process). By surface 4
8 and 24 are not newly exposed). Note that hydrofluoric acid may be used instead of buffered hydrofluoric acid, and buffered hydrofluoric acid may be used instead of hydrofluoric acid.

In the embodiment, the silicon dioxide film 50 and the low-density layer 58 made of alumina are used as the high-speed corrosion layer. However, these materials can be used depending on the material of the object to be processed. It is appropriately changed according to the type of the liquid and the like. That is, a film made of silicon nitride or the like may be provided instead of the silicon dioxide film 50, and if the etching rate is higher than that of the object 56, the surface 24 of the object 56 made of alumina may be provided. May be used. In the case where a recess is provided in the AlGaAs compound semiconductor layer, for example, GaAs having a lower etching rate with a tartaric acid-hydrogen peroxide-based etchant is used.
An oxide film or the like can be used as the high-speed corrosion layer.

Further, in the embodiment, the silicon dioxide film 50 is removed after the recess 40 is formed by the etching process. However, in the case where the object to be processed is made of a material which does not cause a problem in function, It is not always necessary to remove it.

In the embodiment shown in FIGS. 3 to 5, the side etching rate is lower than the etching rate in the entire crystal direction (ie, the direction perpendicular to the surface 48 and the entire lateral direction) of the wafer 46 to be processed. The silicon dioxide film 50 having a high corrosion rate is provided as a high-speed corrosion layer. However, if the silicon dioxide film 50 has a side etching rate higher than at least the side etching rate in the reverse mesa direction ([011] direction in GaAs), The effect of suppressing the formation of the inverted mesa shape can be obtained. Further, in the direction in which the inverted mesa shape is largest,
In the case where the effect can be obtained only by reducing the downward inclination of the side surface of 0 in the forward mesa direction, it is sufficient if at least a high-speed corrosion layer having a side etching speed higher than the minimum value among the side etching speeds is provided. It is.

Although not specifically exemplified, the present invention can be variously modified without departing from the spirit thereof.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (d) are diagrams illustrating a conventional etching method and its disadvantages.

FIG. 2 is a view for explaining the inclination direction of the side surface of the concave portion according to the crystal direction in the conventional etching method, and FIG.
Indicates the case of the forward mesa direction, and (b) indicates the case of the reverse mesa direction.

FIG. 3A is a diagram showing a configuration of a main part of a light-emitting diode to which a recess forming method according to one embodiment of the present invention is applied;
(b) is a plan view in (a).

FIGS. 4A to 4F are views for explaining a wafer process in a manufacturing process of the light emitting diode of FIG. 3;

FIG. 5 is a diagram for explaining the progress of corrosion in the etching process in the wafer process of FIG. 4;

FIG. 6 (a) is a diagram illustrating a recess forming method according to another embodiment of the present invention, and FIG. 6 (b) is a diagram illustrating a conventional recess forming method.

[Explanation of symbols]

 40: recess 46: wafer (workpiece) 48: surface 50: silicon dioxide film (high-speed corrosion layer) 52: photoresist

Claims (3)

[Claims] 1. A method of etching a predetermined object from a surface to form a recess in the surface, the method comprising: etching a predetermined object with a predetermined etchant; A high-speed corrosion layer forming step of forming a high-speed corrosion layer having a side etching rate higher than that of a predetermined direction on the surface in a side etching speed progressing in a direction, substantially not corroded by the predetermined etching solution A method for forming a recess, comprising: a resist forming step of forming a resist on the high-speed corrosion layer in a predetermined pattern; and an etching step of etching from the front side with the predetermined etching solution. 2. The concave portion according to claim 1, wherein the high-speed corrosion layer has a side etching rate higher than a minimum value among side etching rates of the object to be processed with respect to an etching rate by the predetermined etching solution. Place formation method. 3. The high-speed corroding layer has a side etching rate higher than a vertical etching rate progressing in a direction perpendicular to the surface of the object to be processed, with respect to an etching rate by the predetermined etching solution. Item 7. The method for forming a recess according to Item 1.