JP5254266B2 - Method for producing pattern on semiconductor surface - Google Patents

Description

  The present invention relates to a method for producing a desired pattern on a semiconductor surface.

  In the research and development of high-performance and high-function devices, it is important to integrate complex device structures. For that purpose, device manufacturing process technology such as processing technology (etching, etc.), crystal regrowth technology, etc. is necessary. Especially when a plurality of structures are integrated, a plurality of etching processes are usually required. Multiple mask formations and etchings have led to waste in terms of time and cost, which has been a problem. In consideration of such a problem, it has been substantially difficult to form fine and complicated structures having different depths by etching.

  A conventional etching process will be described with reference to FIG. In the case where etching of different depths is performed on the sample 1110 such as InP crystal, first, a portion that is not etched in the first etching is covered with a first mask 1120 (such as a dielectric) (FIG. 1A). After that, etching is performed (FIG. 1B). Next, after removing the first mask 1120 (FIG. 1C), a portion that is not etched in the second etching is covered with the second mask 1140 (FIG. 1D). Then, etching is performed (FIG. 1E), and the second mask 1140 is removed (FIG. 1F). Thus, in order to integrate a plurality of structures, in this case, grooves having different depths, the mask formation process and the etching process must be repeated.

  In order to solve the above-mentioned problem, a method has been invented that enables the formation of grooves having different depths by a single etching by using a mask having a different opening area corresponding to the etching depth. Patent Document 1). In the case of dry etching using a plasma state gas for etching a semiconductor, as shown in FIGS. 2A to 2C, the etching proceeds by the reaction between the semiconductor 411 and the etching species (etching gas) 412 on the semiconductor surface. To do. Therefore, when the surface of the semiconductor is covered with a material that does not react with the etching species 512 (for example, a dielectric such as silicon oxide or silicon nitride) using the mask 513 during dry etching, the etching species 512 on the mask diffuses. Thus, the semiconductor surface not covered with the mask is reached (FIG. 3B). As a result, the density of the etching species 512 increases on the semiconductor surface near the mask, and the increase in the etching species 512 increases the etching rate of the semiconductor. As described above, the etching species flying on the mask diffuses on the semiconductor surface and promotes the etching of the semiconductor, so that the etching of the semiconductor increases as the mask area increases. Therefore, according to this method, a simple groove structure with a varying depth can be easily produced according to the mask design.

  However, problems still remain when using this method to make diffraction gratings of varying depth. In order to manufacture a diffraction grating whose depth changes on the semiconductor surface, first, a first mask 81 having a diffraction grating pattern is formed. Then, in order to change the depth of the diffraction grating, a second mask 82 for controlling the amount of etching species diffused into the opening of the diffraction grating pattern is formed on the first mask 81. As can be seen from the above description with reference to FIGS. 2 and 3, the depth varies by changing the area ratio between the opening and the mask of the second mask 82 in the vicinity of each opening of the diffraction grating pattern. Etching becomes possible. The problem is that not only the etching species 84 flying on the second mask 82 but also the etching species 83 flying on the first mask 81 affects the etching, so that the etching shape of the diffraction grating can be controlled. It is a difficult point.

  In order to solve this problem, the depth of the second mask 82 provided on the first mask 81 is made thicker than that of the first mask 81 having the above-described diffraction grating pattern. A method has been invented that enables the production of a changing diffraction grating by a single etching (see Patent Document 2). FIG. 5 is a diagram for explaining the influence of the film thickness of the mask on the etching. When a thin mask is used (FIG. 5A), the etching species can be diffused from the semiconductor surface over the mask edge onto the mask, so that the etching species density on the semiconductor surface does not increase. Therefore, the etching rate of the semiconductor does not increase. On the other hand, when a thick mask is used (FIG. 5B), the etching seeds are confined on the semiconductor surface because the mask edge becomes a barrier and cannot be crossed, and the etching seed density on the semiconductor surface is reduced. Will increase. As a result, the etching rate of the semiconductor increases. Therefore, if the thickness of the second mask 82 described above is made thicker than that of the first mask 81 having the diffraction grating pattern, the contribution of the etching species diffusing from the second mask 82 having a thick mask thickness is large. The contribution of the etching species from the first mask 81 having a thin mask thickness can be reduced. For example, in a wide mask width region, a large amount of etching species that do not react on the second mask 82 diffuse into the opening of the diffraction grating pattern, resulting in a high concentration of etching species at the opening and an increase in the etching rate. To do. On the other hand, in a region with a narrow mask width, the amount of etching species that does not react on the second mask 82 and diffuses into the opening is smaller than that in a region with a large mask width, and the etching rate is slow. Thus, the etching depth is deep in the region where the second mask 82 has a large mask width, and shallow in the region where the mask width is narrow.

JP 2004-247710 A JP 2006-032573 A

  However, the etching species on the second mask 82 do not all diffuse into the opening of the diffraction grating pattern of the first mask 81. There are also etching species that do not reach the opening and do not contribute to the etching and desorb from the mask. Since there exist etching species that do not contribute to etching in this way, the etching amount and the opening region to be etched are limited. Therefore, the size of the diffraction grating formed by etching is limited. Therefore, in order to increase the amount of etching and the opening area to be etched and increase the degree of freedom in designing the diffraction grating, a large amount of etching species can be efficiently transferred from the second mask 82 to the opening of the diffraction grating pattern. It was necessary to diffuse. This problem has been described with respect to the diffraction grating pattern. However, the problem is not limited to the case where the pattern is a diffraction grating, but is similarly a problem in the production of a desired pattern whose depth changes.

  The present invention has been made in view of such problems, and an object of the present invention is to control the amount of etching species diffused into a first mask having a desired pattern and an opening of the desired pattern. In the method for producing a desired pattern whose depth changes on the semiconductor surface using the second mask for the purpose, the number of etching species contributing to etching is increased.

  In order to achieve such an object, a first aspect of the present invention is a method for producing a desired pattern of varying depth on a semiconductor surface, wherein the desired pattern is applied to the semiconductor surface. Forming a first mask having a second mask for controlling an amount of etching species diffused into a plurality of openings of the desired pattern, and forming the first and second masks. And supplying an etching species to the semiconductor surface to etch the semiconductor surface, wherein the second mask has an opening whose side wall is inclined and whose width is narrowed toward the semiconductor surface. And the ratio of the area of the opening of the second mask and the area of the mask of the second mask in the vicinity of each opening of the desired pattern is the plurality of the patterns of the desired pattern. Aperture Characterized in that it changes along the arrangement direction.

  According to a second aspect of the present invention, in the first aspect, the etching is dry etching using a plasma state gas.

  According to a third aspect of the present invention, in the second aspect, the gas used for the dry etching is a hydrocarbon gas and a hydrogen gas.

  According to a fourth aspect of the present invention, in the third aspect, the etching step includes the step of etching the hydrocarbon-based gas and the hydrogen gas, the hydrocarbon-based gas obtained from the hydrocarbon-based gas and the hydrogen gas, and Supplying a hydrogen plasma under a first plasma condition that produces a first polymer on the semiconductor surface, etching the semiconductor surface without producing the first polymer, and supplying a plasma containing oxygen And removing the first polymer, and supplying the hydrocarbon-based gas and the hydrogen gas under a second plasma condition different from the first plasma condition to etch the semiconductor surface. It is characterized by including.

  According to a fifth aspect of the present invention, in the fourth aspect, the second plasma condition is that a hydrocarbon plasma and a hydrogen plasma obtained from the hydrocarbon-based gas and the hydrogen gas are polymerized on the semiconductor surface. It is the condition that does not generate.

  According to a sixth aspect of the present invention, in the fourth aspect, the second plasma condition is a condition in which a region in which a polymer is generated on the semiconductor surface is narrower than the first plasma condition. The etching under the second plasma condition is characterized by etching the semiconductor surface where no polymer is generated under the second plasma condition.

  According to a seventh aspect of the present invention, in any one of the first to sixth aspects, the desired pattern is a diffraction grating pattern.

  According to the present invention, the second mask for controlling the amount of the etching species diffused into the opening of the desired pattern of the first mask has the side wall inclined and the width toward the semiconductor surface. And the ratio of the area of the opening of the second mask and the area of the mask of the second mask in the vicinity of each opening of the desired pattern is the desired pattern. By forming the plurality of openings so as to change along the arrangement direction of the plurality of openings, it is possible to increase the number of etching species that contribute to etching in a method for producing a desired pattern whose depth changes on the semiconductor surface. it can.

It is a figure for demonstrating the conventional etching process. It is a figure for demonstrating the dry etching using the gas of a plasma state. It is a figure for demonstrating the dry etching using the gas of a plasma state. It is a figure for demonstrating the preparation methods of the diffraction grating from which the conventional depth changes. It is a figure for demonstrating the influence which the film thickness of a mask has on etching. FIG. 10 is a diagram for describing a method for forming a mask formed by the manufacturing method of the present invention. It is a figure which shows density | concentration distribution in case an etching seed | species diffuses from the mask end to the surface of a semiconductor substrate. It is a figure which shows the relationship between the spreading | diffusion of an etching seed | species, and the shape of the conventional mask. It is a figure which shows the relationship between the spreading | diffusion of an etching seed | species, and the shape of the conventional mask. It is a figure which shows the relationship between the spreading | diffusion of an etching seed | species, and the shape of the mask of this invention. It is a figure which shows the ratio of the etching seed | species C1 supplied to the opening part of width W1 with respect to the total amount Co of the etching seed | species diffused from a mask end. It is a figure which shows W1 dependence of the density | concentration C2 of the etching seed | species which is supplied to the opening part of width W1, and reaches the semiconductor surface. It is a figure which shows the mask opening part width W2 dependence of the etching seed | species density | concentration which contributes to an etching. It is a figure for demonstrating 1st Embodiment of the preparation methods of this invention. It is sectional drawing which followed the 15-15 line of FIG.14 (b). It is a figure for demonstrating 1st Embodiment in the cross section along line 16-16 of FIG.14 (b). It is a figure which shows the structure of a DBR semiconductor laser provided with the diffraction grating produced with the production method of 1st Embodiment. (A) is a figure which shows the coupling coefficient which a diffraction grating has, (b) is a figure which shows the reflection spectrum at the time of using the diffraction grating which has the said coupling coefficient (white circle). The reflection spectrum when the coupling coefficient is constant at 80 cm ⁻¹ is also shown for comparison (black circle). Is a diagram illustrating a SiN _x / SiO ₂ mask is formed on the sample surface in the second embodiment. It is a figure for demonstrating the dry etching in the case of using hydrocarbon gas for gas. It is a figure for demonstrating the dry etching in the case of using hydrocarbon gas for gas. It is a figure for demonstrating the manufacturing method of the diffraction grating in 2nd Embodiment. It is a figure for demonstrating the manufacturing method of the diffraction grating in 2nd Embodiment. It is a figure for demonstrating the manufacturing method of the diffraction grating in 2nd Embodiment. It is a figure for demonstrating the manufacturing method of the diffraction grating in 2nd Embodiment. It is a figure for demonstrating the manufacturing method of the diffraction grating in 2nd Embodiment. It is sectional drawing of the waveguide from which layer thickness changes in the same surface produced in Example 1 of 3rd Embodiment. It is a figure for demonstrating the preparation methods of the waveguide of FIG. It is a figure for demonstrating the preparation methods of the waveguide of FIG. It is a figure for demonstrating the preparation methods of the waveguide of FIG. It is a figure for demonstrating the preparation methods of the waveguide of FIG. It is a figure for demonstrating the preparation methods of the waveguide of FIG. FIG. 28 is a diagram showing a waveguide whose layer thickness varies in multiple stages from FIG. 27 as a modification of Example 1 of the third embodiment. It is a figure which shows the waveguide from which layer thickness changes gradually as a modification of Example 1 of 3rd Embodiment. It is a figure which shows the structure of the semiconductor laser element using the waveguide structure where layer thickness changes concerning Example 2 of 3rd Embodiment for the spot size conversion part.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, the mask formed by the manufacturing method of the present invention will be described, and then the first to third embodiments will be described. The description will be made with reference to specific substance names and numerical values, but it should be noted that the present invention is not intended to be limited thereto.

(Mask formed by the manufacturing method of the present invention)
FIG. 6F shows a structure of a mask formed by the manufacturing method of the present invention. On the first mask 1311 having a diffraction grating pattern (corresponding to “desired pattern”), a second mask 1321 for controlling the amount of etching species diffused into the opening of the diffraction grating pattern is provided. In the second mask 1321, the sidewall of the opening is inclined, and the opening width W1 on the upper surface is larger than the opening width W2 on the lower surface. In other words, the width of the opening narrows toward the surface of the semiconductor substrate 1310. Using the first mask 1311 and the second mask 1321, a diffraction grating pattern whose depth changes is formed on the surface of the semiconductor substrate 1310.

This mask can be formed as follows. First, a silicon oxide (SiO ₂ ) film having a thickness of 30 nm is formed on the surface of the InP substrate 1310 having an InP cladding layer (corresponding to “semiconductor surface”). After applying a resist on the SiO ₂ film, a resist pattern for a diffraction grating production mask is produced by an electron beam exposure method. By processing the SiO ₂ film by reactive ion etching (RIE) using a fluorocarbon-based gas (CF ₄ , C ₂ F _6, etc.) using the resist pattern as a mask, the resist pattern is converted into an SiO ₂ film. Transcript to. By removing the resist pattern, an SiO ₂ mask 1311 having a diffraction grating pattern is formed on the InP substrate 1310 (FIGS. 6A and 6B).

Next, a 1 μm thick silicon nitride (SiN _x ) film 1321 is formed on the surface of the InP substrate 1310 having the SiO ₂ mask 1311 (FIG. 6C).

After applying a resist on the SiN _x film 1321, a resist pattern 1331 for the second mask is produced (FIG. 6D). This resist pattern 1331 can be formed not only by electron beam exposure but also by resist exposure by ordinary photolithography.

By processing the SiN _x film 1321 by first RIE using sulfur hexafluoride based gas (SF ₆ or the like) the resist pattern 1331 as a mask, the resist pattern is transferred to 1331 in the SiN _x film 1321 (FIG. 6 (e )). Here, if the gas pressure at the time of RIE is set to a pressure (for example, 20 Pa) higher than a normal pressure (for example, 2 Pa), the ionicity in the etching characteristics decreases. At this time, etching proceeds not only in the depth direction but also in the lateral direction, and the side etching amount increases. Therefore, when the etching proceeds in the depth direction, the upper portion of the mask is exposed to the etching gas atmosphere for a long time, so that the side etching amount is increased as compared with the lower portion of the mask. As a result, the opening width of the upper surface of the mask is wider than that of the lower surface of the mask. At this time, since the SiO ₂ mask 1311 is resistant to sulfur fluoride gas (SF ₈ or the like), it remains without being etched.

Finally, by removing the resist pattern 1311 using oxygen plasma irradiation, an SiO ₂ mask 1311 having a thickness of 30 nm on the InP substrate 1310 and an opening width of the upper portion of the mask that is thicker than the SiO ₂ mask 1311. Thus, a SiN _x mask 1321 having a thickness of 1 μm wider than that of the lower portion of the mask can be obtained (FIG. 6F). The SiN _x mask 1321 has an inclined side wall, and is hereinafter also referred to as an “inclined mask”.

  The effect of the mask thus obtained on etching will be described. First, FIG. 7 shows a concentration distribution when the etching species diffuses from the mask end of the mask as shown in FIG. 5 to the surface of the semiconductor substrate. The vertical axis represents density Cx = C (x) / Cs normalized by the density Cs at the mask edge, and the horizontal axis represents distance x from the mask edge. This distribution was calculated using the following diffusion equation, assuming that the diffusion distance Ld in the diffusion from the mask of the etching species to the opening is 5 μm.

Cx = C (x) / Cs = erfc (x / Ld)
The relationship between the etching species diffusing with such a distribution and the mask shape is shown in FIGS. FIG. 11 shows the ratio (C1 / Co) of the etching species C1 supplied to the opening having the width W1 with respect to the total amount Co of etching species diffusing from the mask edge (or the opening on the upper surface when the mask has an inclined structure). Show. Co is a value obtained by integrating the normalized density Cx from the distance 0 to infinity, and is a standardized total amount. C1 is a value obtained by integrating the normalized density Cx from the distance 0 to the opening width W1, and is a normalized density. Further, FIG. 12 shows the W1 dependence of the concentration C2 of the etching species that is supplied to the opening having the width W1 (the opening on the upper surface in the case of the inclined structure) and reaches the semiconductor surface, and the side wall of the mask is perpendicular to the bottom surface. This is shown in the case of a vertical structure and an inclined structure that is inclined. C2 is C1 / W2 and is a standardized concentration. An alternate long and short dash line indicates a case where the mask has a vertical structure, and a solid line indicates a case where the mask has an inclined structure. When the mask has an inclined structure, the width W2 of the lower part in contact with the surface of the semiconductor substrate is 1 μm. In this case, since the opening width W1 of the upper portion is wider than the opening width W2 of the lower portion, the opening width of 1 μm or less is not plotted.

  FIG. 8 shows a case where the mask has a vertical shape as in the prior art and the opening width W1 is 1 μm. Only a portion (colored portion in FIG. 8A) of the entire etching species diffusing from the mask edge is supplied to the opening of the mask and contributes to the etching. As shown in FIG. 11, the ratio of the etching species supplied to the opening with respect to the etching species diffusing from the mask edge is 0.32.

  FIG. 9 shows a case where the opening width W1 is increased to 5 μm in order to increase the ratio of the etching species supplied to the opening. Many portions (colored portions in FIG. 9A) of the entire etching species diffusing from the mask edge are supplied to the openings of the mask and contribute to the etching. As shown in FIG. 11, the ratio of the etching species supplied to the opening with respect to the etching species diffusing from the mask edge increases to 0.91. However, since the surface of the semiconductor substrate in the opening also increases, the etching species concentration C2 on the surface of the semiconductor substrate decreases when the width of the opening is increased from 2 μm to 5 μm, as shown by a dashed line in FIG. This indicates that the etching species supplied from the mask edge have little effect on the etching.

  FIG. 10 shows a mask used in the manufacturing method of the present invention. The structure of the mask is an inclined type, and the opening width W1 of the upper surface of the mask is 5 μm, and the opening width W2 of the lower portion near the semiconductor substrate surface is 1 μm. Many portions (colored portions in FIG. 10A) of the entire etching species diffusing from the mask edge are supplied to the openings and contribute to etching. As shown in FIG. 11, the ratio of the etching species supplied to the opening with respect to the etching species diffusing from the mask edge increases to 0.91. Further, assuming that the etching species supplied to the opening in the upper part of the mask are all supplied to the surface of the semiconductor substrate without detaching, the opening width W1 in the upper part is set to 2 μm to 5 μm as shown by the solid line in FIG. Increasing the etching species increases the etching species concentration C2 on the surface of the semiconductor substrate. When the opening width W1 of the upper portion is 5 μm, the concentration is about five times higher than that of the vertical structure. As described above, in this mask, the etching species can be efficiently diffused into the opening and supplied to the surface of the semiconductor substrate, so that the etching can be controlled efficiently.

  Here, a few points that can be read from FIGS. 11 and 12 are pointed out. As can be seen from FIG. 11, the ratio of the etching species supplied to the opening of the mask with respect to the etching species diffusing from the mask edge when the opening width W1 of the upper portion is 2 μm or more increases to 0.50 or more, The opening width W1 of the portion increases to 0.91 or more at 5 μm or more. Further, as can be seen from FIG. 12, when the opening width W1 on the upper surface exceeds 1 μm, that is, exceeds the value of the opening width W2 on the lower surface, the inclined structure mask is more semiconductor than the vertical structure mask. The etching seed concentration C2 supplied to the substrate surface is increased. When the width of the opening W1 on the upper surface is 2 μm or more, it increases to 0.3 or more, which is half or more of the maximum value (0.56), and when it is 5 μm or more, it increases to 0.5 or more. When it becomes 8 μm or more, it is saturated to the maximum value (0.56).

  FIG. 13 shows the dependency of the etching seed concentration that contributes to etching on the mask opening width W2. The vertical axis represents C2 at each W2 when the opening width W1 on the upper surface is 10 μm. When W2 changes from 1 μm to 10 μm, the etching species changes from about 0.2 to about 0.1 in the vertical structure, whereas in the inclined structure, 0.6 changes due to the change in the opening width W2. It varies from about 0.1 to 0.1. Thus, it can be seen that when the inclined structure of the present invention is used, an etching species having a concentration about three times higher than that of the vertical structure is involved in the etching. If the etching species contributing to the etching are large, the etching proceeds and the etching depth becomes deep, and if the etching species contributing to the etching is small, the etching proceeds less and the etching depth becomes shallow. When used, the etching depth can be varied over a wide range compared to the vertical structure.

(First embodiment)
A first embodiment of the manufacturing method of the present invention will be described. In the present embodiment, a diffraction grating pattern is considered as a desired pattern of the first mask, and a case where reactive ion beam etching (RIBE) is used as a dry etching method used for etching a semiconductor surface will be described. To do.

FIGS. 14A and 14B show a SiO ₂ mask 1410 and a SiN _x mask 1411 (hereinafter also referred to as “SiN _x / SiO ₂ mask”) manufactured by the method described with reference to FIG. . The mask thickness of the SiO ₂ mask 1410 having the diffraction grating pattern is 20 nm, the diffraction grating length 1412 is 500 μm, the width 1413 is 2 μm, and the pitch (period) 1414 is 240 nm (SiO ₂ part: 120 nm, opening (window part): 120 nm). The mask thickness of the SiN _x mask 1411 is 1 μm. The inclined mask 1411 has a flat portion 1411A and an inclined portion 1411B. Both the widths 1415A and 1415B are narrow at both ends of the element and wide at the center of the element. The mask width 1415A of the flat portion 1411A is 5 μm at both ends and 20 μm at the element center. The mask width 1415B of the inclined portion 1411B is 5 μm at both ends and 10 μm at the element center. The width W2 of the opening of the inclined portion 1411B is the same as the width 1413 of the diffraction grating pattern and is 2 μm. Hereinafter, the opening of the SiN _x mask 1411, refers to the opening width W2 of the inclined portion 1411B, the mask portion of the SiN _x mask 1411, the width of the inclined portion 1411B mask portion width 1415A of the flat portion 1411A 1415B The part which put together the mask part. FIG. 15 is a cross-sectional view taken along line 15-15 in FIG.

FIGS. 16A to 16C are diagrams for explaining a fabrication process of a diffraction grating pattern with a varying depth using a SiN _x / SiO ₂ mask. For simplicity, the SiN _x mask 1411 is omitted, and only the SiO ₂ mask 1410 is shown. When RIBE is performed using chlorine as an etching gas (etching species), a gas flow rate of 4 sccm, a gas pressure of 10 Torr, a microwave discharge power of 300 W, an ion extraction voltage of 500 V, and a substrate temperature of 200 ° C., FIG. ) Structure is obtained. Finally, the SiN _x / SiO ₂ mask is removed by RIE using SF ₆ to form a diffraction grating deep at the center and shallow at both ends.

In this etching, the contribution of ionized or radicalized chlorine atoms (chlorine plasma) as an etching species from the SiN _x mask 1411 having a large mask thickness is large, and the contribution of chlorine plasma from the SiO ₂ mask 1410 having a thin mask thickness is small. . Accordingly, a large amount of chlorine plasma that does not react on the mask diffuses into the opening at the center of the diffraction grating having a wide mask width, so that the chlorine plasma at the opening becomes high in concentration and the etching rate increases. On the other hand, at both ends of the diffraction grating having a narrow mask width, chlorine plasma that does not react on the mask and diffuses into the opening is less than that in the wide mask width region, and the etching rate is slow. Here, since the product at the time of etching diffuses along the arrangement direction of the plurality of openings included in the diffraction grating pattern, the etching rate is not suppressed by the retention of the product. Therefore, in the diffraction grating, the etching depth is deep at the center and shallow at both ends. Since the width W2 of the opening of the SiN _x mask is constant in the present embodiment, the ratio of the area of the opening of the SiN _x mask and the area of the mask of the SiN _x mask in the vicinity of each opening of the diffraction grating pattern is It can be said that the depth of the diffraction grating to be formed is changed by changing along the arrangement direction of the plurality of openings of the diffraction grating pattern. As the area ratio of the mask portion to the opening portion increases, the etching rate increases.

The mask used in the manufacturing method of this embodiment has an inclined structure, and as described with reference to FIG. 13, more etching species are involved in the etching than the vertical structure, and the vertical type is used. Compared to the structure, the etching depth can be changed in a wide range. As can be seen from FIG. 13, in this embodiment, since the width W2 of the opening of the SiN _x mask is set to 2 μm in the inclined structure, the etching depth can be changed about twice as much as that in the vertical structure.

In this embodiment, chlorine or methane is used as an etching gas in dry etching for processing a semiconductor such as a diffraction grating. However, other gases such as other hydrocarbon gases such as ethane and gases such as bromine are used. May be used. In addition, as a dilution gas when a mixed gas is used as an etching gas, not only hydrogen gas but also nitrogen or argon may be used, and the dilution gas may not be used. Further, although RiBE and RIE methods are used for the dry etching method, processing can also be performed using ion beam assist etching or the like. In addition to dry etching using a plasma state gas, it is also possible to perform processing by gas etching using a non-plasma state gas or wet etching using an acid solution. In addition to the electron beam exposure method, an interference exposure method can be used for producing the resist pattern. Although silicon oxide (SiO ₂ ) is used as a mask formed on the semiconductor surface during etching, a dielectric such as silicon nitride or titanium oxide, or a metal such as gold or titanium can also be used.

EXAMPLE FIG. 17 shows the structure of a DBR semiconductor laser provided with a diffraction grating manufactured by the manufacturing method of the first embodiment. After removing the SiN _x / SiO ₂ mask on the sample surface having the diffraction grating of different depth produced by the production method of the first embodiment, the sample is laminated on the diffraction grating by metal organic vapor phase epitaxy (MOVPE). As a result, the DBR semiconductor laser structure using the diffraction grating whose depth changes as shown in FIG. 17 is manufactured.

  On an n-type InP substrate 150, an n-type InP buffer layer 151, a diffraction grating 152, an InGaAsP (composition wavelength: 1.1 μm) guide layer 153, and eight InGaAsP strained quantum well (strain amount: 1.0%) layers And an active layer 154 (light emission wavelength: 1.55 μm, active layer length: 400 μm) consisting of a multi-quantum well layer as a barrier layer and a five-layer InGaAsP (composition wavelength: 1.3 μm), DBR diffraction grating region InGaAsP (composition wavelength: 1 .4 μm) guide layer 155 (diffraction grating length is 400 μm before and after active layer 154), InGaAsP (composition wavelength: 1.3 μm) guide layer 156, p-type InP cladding layer 157, p-type InGaAs (composition wavelength: 1.85 μm) ) A contact layer 158 is sequentially formed. An n-type ohmic electrode 1591 is formed on the n-type InP substrate 150, and a p-type ohmic electrode 1592 is formed on the p-type InGaAs (composition wavelength: 1.85 μm) contact layer 158. The oscillation wavelength of the element is 1.55 μm. The length of the element is 1500 μm. The pitch (period) of the diffraction grating 152 is 240 nm (convex portion: 120 nm, concave portion: 120 nm), and the depth is 5 nm which is shallow at both ends of the element, and 30 nm which is deep at the center of the element.

FIG. 18A shows the coupling coefficient of this diffraction grating. 5nm in depth element end portions of the diffraction grating, by varying such that the 30nm at the center, the coupling coefficient kappa 5 cm ^-1 at element end portions, changes 80 cm ^-1 at the central portion. FIG. 18B shows a reflection spectrum when this diffraction grating is used (white circle). For comparison, a reflection spectrum when the coupling coefficient is constant at 80 cm ⁻¹ is shown (black circle). It can be seen that the side mode of the reflection spectrum is suppressed by changing the depth of the diffraction grating, that is, the coupling coefficient. This suggests that the side mode in the oscillation spectrum when the DBR laser using this diffraction grating is operated is suppressed.

In this embodiment, the depth of the diffraction grating is set to 5-30 nm, but the depth is not limited to this. At this time, the depth of the diffraction grating does not need to be symmetrical in the element length direction. The coupling coefficient that changes in accordance with this depth is also set to 5-80 cm ⁻¹ , but is not limited to this value.

  In this embodiment, a compound semiconductor InP crystal is used as the element semiconductor crystal. However, a compound semiconductor crystal such as GaAs or SiGe or a mixed crystal such as InGaAsP, AlGaInAs, InGaN, GaInNAs, or AlGaSb can be used. is there.

  Further, although 1.55 μm is used as the wavelength of the laser beam to which the apparatus according to the present invention is applicable, the wavelength is changed from 1.0 μm to 1.7 μm by changing the structure such as the composition of the InGaAsP crystal and the pitch (period) of the diffraction grating. Can be used for long wavelength bands up to 1, and by using other materials (InGaAlN, AlGaInP, AlGaSb, etc.) for the active layer, it is also compatible with short wavelength bands of less than 1.0 μm and long wavelength bands of 1.7 μm or more. it can. The multi-quantum well structure in the active layer includes an 8 layer, 5 nm thick InGaAsP strained quantum well layer (strain amount: 1.0%), a 5 layer, 10 nm thick InGaAsP barrier layer (composition wavelength: 1.1 μm). However, the structural factors such as the amount of strain, the number of layers, the layer thickness, and the crystal composition may be changed.

(Second Embodiment)
A second embodiment of the manufacturing method of the present invention will be described. In the present embodiment, a polymer generated in dry etching using a hydrocarbon gas is used. In the SiN _x / SiO ₂ mask used for etching, the widths 1915A and 1915B of the SiN _x mask 1911 are constant, but the width 1913 of the SiO ₂ mask 1910 changes. This is different from the case where the widths 1415A and 1415B of the SiN _x mask 1411 are changed and the width 1413 of the SiO ₂ mask 1410 is constant in the first embodiment.

FIG. 19 shows a SiO ₂ mask 1910 and a SiN _x mask 1911 (hereinafter also referred to as “SiN _x / SiO ₂ mask”) formed on the sample surface in this embodiment. The mask thickness of the SiO ₂ mask 1910 having the diffraction grating pattern is 20 nm, the diffraction grating length 1912 is 500 μm, and the width 1913 changes along the arrangement direction of the plurality of openings of the diffraction grating pattern. It is wide at both ends of the element (width is 3 μm) and narrow at the center of the element (width is 1.5 μm). The pitch (period) 1914 is 240 nm (SiO ₂ part: 120 nm, opening (window): 120 nm). On the other hand, the mask thickness of the SiN _x mask 1911 is 1.0 μm. The mask width 1915A of the flat portion 1911A is constant at 20 μm, and the mask width 1915B of the inclined portion 1911B is constant at 10 μm. Like the first embodiment, the opening of the SiN _x mask 1911, refers to the opening width W2 of the inclined portion 1911B, the mask portion of the SiN _x mask 1911, mask portion width 1915A of the flat portion 1911A And a portion obtained by combining the mask portion having the width 1915B of the inclined portion 1911B.

In dry etching using a plasma state gas for semiconductor etching, when a hydrocarbon-based gas such as methane or ethane is used as this gas, the gas is decomposed into hydrocarbon groups and hydrogen in the plasma state, and is ionized or chemically separated. Is activated (radicalized). Hereinafter, the ionized or radicalized hydrocarbon group is referred to as “hydrocarbon plasma”, and the ionized or radicalized hydrogen atom is referred to as “hydrogen plasma”. When the hydrocarbon plasma and the hydrogen plasma come into contact with the semiconductor surface, a process of etching the semiconductor and a process of forming and depositing a polymer on the semiconductor surface without etching the semiconductor occur. In general, when there is sufficient hydrogen plasma, the etching process is the main process, and when hydrogen plasma is insufficient, the process of polymer deposition is the main process. On the surface of the dielectric (such as SiO ₂ ) mask, hydrocarbon plasma and hydrogen plasma do not react with the dielectric, and thus deposit as a polymer. In order to increase the hydrogen plasma, hydrogen gas may be supplied together with the hydrocarbon-based gas.

A case where the above-described dry etching is performed on a sample having a SiN _x / SiO ₂ mask will be described with reference to FIGS. In the region without the SiN _x / SiO ₂ mask, hydrogen plasma is uniformly distributed on the sample surface with respect to methane in the plasma state (FIG. 20A). When the concentration of the uniformly distributed hydrogen plasma is low, the hydrogen plasma is insufficient for etching, so that a polymer is generated on the sample surface to cover the sample surface and the etching does not proceed (FIG. 20B). On the other hand, in a region having a SiN _x / SiO ₂ mask, first, hydrogen plasma is uniformly distributed on the sample surface both on the SiN _x / SiO ₂ mask and in the opening (FIG. 21A). )). Since the mask material (such as SiO ₂ ) is not etched on the SiN _x / SiO ₂ mask, the methane plasma does not contribute to the etching and a polymer is generated. The hydrogen plasma on the mask diffuses into the opening without reacting with the methane plasma. As a result, the concentration of hydrogen plasma at the opening increases (FIG. 21B). Therefore, the etching proceeds because the hydrogen plasma concentration at the opening reaches a concentration sufficient to cause etching (FIG. 21C). Thus, the polymer is generated in the region with the mask and the etching does not proceed, and the etching proceeds in the region (opening) without the mask.

22 to 26 are diagrams for explaining a method of manufacturing a diffraction grating in the present embodiment. A SiO ₂ mask 2010 having a variable width and a SiN _x mask 2011 having a constant width are formed on the semiconductor surface (FIG. 22). Here, the widths of the plurality of openings 2001, 2002, 2003, and 2004 included in the diffraction grating pattern of the SiO ₂ mask 2010 are 1.5, 2.0, 2.5, and 3.0 μm, respectively. In a series of etching processes described below, the contribution of methane plasma and hydrogen plasma from the SiN _x mask 2011 having a large mask thickness is large, and the contribution of methane plasma and hydrogen plasma from the SiO ₂ mask 2010 having a thin mask thickness is small.

  When RIE using a mixed gas of methane and hydrogen is performed at a methane flow rate of 40 sccm, a hydrogen flow rate of 2 sccm, a gas pressure of 10 Pa, and a discharge power of 100 W (corresponding to the “first plasma condition”), the width is 1.5 μm or less. In the opening 2001, since the hydrogen plasma is sufficiently supplied from above the mask, etching proceeds without polymer deposition. On the other hand, in the openings 2002, 2003, and 2004 having a width larger than 1.5 μm, the supply of hydrogen plasma from the mask is insufficient, so that the polymer 2201 is deposited and the etching does not proceed (FIG. 23).

  Subsequently, when the oxygen plasma is irradiated at an oxygen flow rate of 10 sccm, a gas pressure of 10 Pa, and a discharge power of 400 W for 1 minute, the deposited polymer is removed (FIG. 24). Here, in addition to oxygen plasma, oxygen-containing plasma may be used. For example, a mixed gas of oxygen and an inert gas such as nitrogen or argon, a mixed gas of oxygen and hydrogen, or the like may be used.

  Next, when RIE is performed under the conditions of increasing the hydrogen flow rate (methane flow rate 40 sccm, hydrogen flow rate 5 sccm, gas pressure 10 Pa, discharge power 100 W) (corresponding to “second plasma condition”), the width is 2 μm or less. In the openings 2001 and 2002, since the supply of hydrogen plasma increases, etching proceeds without polymer deposition. On the other hand, in the openings 2003 and 2004 having a width larger than 2 μm, since the supply of hydrogen plasma from the mask is still insufficient, the polymer 2041 is deposited and the etching does not proceed (FIG. 25). Accordingly, in the opening 2001 having a width of 1.5 μm or less, the second RIE etching further proceeds after the first RIE etching, so that the depth is wider than 1.5 μm and 2 μm or less. It becomes deeper than the depth of the opening 2002.

  Subsequently, after removing the polymer by irradiation with oxygen plasma, RIE and oxygen plasma irradiation are repeated alternately. At this time, by increasing the hydrogen flow rate each time RIE is performed, diffraction gratings having different depths can be formed (FIG. 26). At this time, the hydrogen flow rate can be increased to 100 sccm.

  Then, after removing the mask and processing the mesa structure, the element structure shown in FIG. 17 and the like can be manufactured by stacking on this diffraction grating by metal organic vapor phase epitaxy (MOVPE).

  The mask used in the manufacturing method of this embodiment has an inclined structure, and as described with reference to FIG. 13, more etching species are involved in the etching than the vertical structure, and the vertical type is used. Compared to the structure, the etching depth can be changed in a wide range. Looking at FIG. 13 with attention paid to hydrogen plasma as an etching species, for example, in a vertical structure, the normalized concentration of hydrogen when the width W2 of the opening is 1 μm is about 0.18. In the inclined structure, this value can be obtained when the width W2 is 3 μm. This indicates that etching that could not be realized unless the width W2 is 1 μm or less in the vertical structure can be realized even when the width W2 is 3 μm, and the degree of freedom in designing the diffraction grating is increasing.

  In the present embodiment, hydrogen plasma that has not contributed to the reaction flows on both ends of the opening of the diffraction grating. Etching proceeds with the reaction of methane by this amount of hydrogen plasma. Therefore, even in the opening where the polymer is deposited, the etching proceeds only at a part of both ends. Thus, there may be a problem that the depth is not uniform over the entire opening. However, since a mesa structure is adopted in an actual device, both ends of the opening are cut off when the mesa is formed, and this does not cause a problem in actual device fabrication.

  In this embodiment, the amount of hydrogen that contributes to etching in the opening during RIE is changed by the hydrogen flow rate. However, the change in the hydrogen diffusion distance from the mask due to the gas pressure (0.01 Pa-50 Pa) or the discharge power ( 50-500 W) can also be changed by changing the amount of ionized hydrogen, and the same effect can be obtained.

  In the present embodiment, the second plasma condition is referred to as a region where the polymer is generated on the semiconductor surface is narrower than the first plasma condition. However, as the second plasma condition, the polymer is completely generated. Conditions that are not used may be used. Even in this case, since the region etched only under the first plasma condition is different from the region etched under the second condition, a desired pattern with a varying depth can be produced.

(Third embodiment)
In the above description, the configuration in which the second mask for controlling the amount of the etching species diffused into the opening of the desired pattern is provided on the first mask having the desired pattern has been described. Depending on the desired pattern, the first mask is not necessarily required, and the pattern can be formed using only the second mask. Hereinafter, such an embodiment will be described.

Example 1
As Example 1, a method of manufacturing a waveguide whose layer thickness varies within the same plane will be described. In this embodiment, a polymer generated in dry etching using a hydrocarbon-based gas is used.

  FIG. 27 is a cross-sectional view of a waveguide whose layer thickness varies in the same plane manufactured in this example. On the n-type InP 2700, an InGaAsP waveguide layer 2701 and an InP cladding layer 2702 having a composition wavelength of 1.2 μm are formed.

28 to 32 are views for explaining a method of manufacturing a waveguide in this example. For the sake of simplicity, the SiN _x mask 2815 is not shown in the cross-sectional view (b) of FIGS. On the surface of the InGaAsP waveguide layer 2701 on the n-type InP 2700, a SiN _x mask 2815 in which the width 2910A of the opening 2800 changes is formed (FIG. 28). The film thickness of the SiN _x mask 2815 is 1.0 μm. The flat portion 2815A has a constant width 2820A of 20 μm, and the inclined portion 2815B has a constant width 2820B of 10 μm. The waveguide length 2810B is 500 μm. The etching process when dry etching is performed on a sample with a mask using a hydrocarbon-based gas such as methane or ethane is the same as in the second embodiment.

For this sample, when RIE using a mixed gas of methane and hydrogen is first performed at a methane flow rate of 40 sccm, a hydrogen flow rate of 2 sccm, a gas pressure of 10 Pa, and a discharge power of 100 W, the opening 2800A having a width of 1.5 μm or less is obtained. Since the hydrogen is sufficiently supplied from above the SiN _x mask 2815, the etching proceeds without polymer deposition. On the other hand, in the openings 2800B and 2800C having a width larger than 1.5 μm, the supply of hydrogen from the SiN _x mask 2815 is insufficient, so that the polymer 2901 is deposited and the etching does not proceed (FIG. 29). A portion of the opening 2800 that is not covered with the polymer 2901 is a region where etching proceeds. In the openings 2800B and 2800C, the polymer 2901 is deposited in almost all regions, but the etching proceeds only at the boundary with the SiN _x mask 2815.

  Subsequently, when the oxygen plasma is irradiated at an oxygen flow rate of 10 sccm, a gas pressure of 10 Pa, and a discharge power of 400 W for 1 minute, the deposited polymer is removed (FIG. 30).

Next, when RIE is performed under the conditions in which the hydrogen flow rate is increased (methane flow rate 40 sccm, hydrogen flow rate 5 sccm, gas pressure 10 Pa, discharge power 100 W), in the openings 2800A and 2800B having a width of 2 μm or less, Since the supply increases, the etching proceeds without polymer deposition. On the other hand, in the opening 2800C having a width larger than 2 μm, the supply of hydrogen from the SiN _x mask 2815 is still insufficient, so that the polymer 2902 is deposited and the etching does not proceed (FIG. 31). Therefore, in the opening 2800A having a width of 1.5 μm or less, the etching by the second RIE further proceeds after the etching by the first RIE. Therefore, the depth of the opening 2800B having the width from 1.5 μm to 2 μm is increased. Become deeper than the depth.

Subsequently, after removing the polymer by irradiation with oxygen plasma, RIE and oxygen plasma irradiation are repeated alternately. At this time, by increasing the hydrogen flow rate every time RIE is performed, waveguides having different depths can be formed (FIG. 32). At this time, the hydrogen flow rate can be increased to 100 sccm. Thereafter, after removing the mask, an InP clad layer 2702 is laminated by metal organic vapor phase epitaxy (MOVPE), thereby producing the element structure shown in FIG.

  Here, the effect of the present embodiment will be described with reference to FIG. The opening width W1 of the flat portion 2915A is 10 μm. When the opening width W2 of the inclined portion 2915B changes from 1 μm to 10 μm, hydrogen changes from about 0.2 to about 0.1 in the vertical structure, whereas in the inclined structure of this embodiment, the opening It changes from about 0.6 to 0.1 by changing the width W2. As described above, when the tilted structure of this embodiment is used, hydrogen having a concentration about three times higher than that of the vertical structure is involved in etching. This indicates that the etching depth can be changed in a wide range when the inclined structure of this embodiment is used as compared with the vertical structure. For example, in a vertical structure, the normalized concentration of hydrogen when the opening width W2 is 1 μm is about 0.18. With this value, in the inclined structure, the opening width W2 can be 3 μm. This indicates that the etching that can be realized only in the vertical structure when the opening width W2 is 1 μm or less can be realized up to the opening width W2 of 3 μm.

  In the present embodiment, the etching using three opening widths and the depth changing in three stages has been described. However, the waveguide layer whose layer thickness is changed in more stages using a mask having a larger number of opening widths. Can be produced. An example is shown in FIG. 33, and the cross-sectional view 33 (b) shows the structure after the cladding layer is formed. In addition, a waveguide layer whose layer thickness gradually changes can be manufactured using a mask whose opening width gradually changes. An example is shown in FIG. 34, and the cross-sectional view 34b shows the structure after the formation of the cladding layer.

  In the examples, a polymer generated in dry etching using a hydrocarbon-based gas is used. However, a waveguide can be manufactured using dry etching using chlorine gas as in the first embodiment. .

Example 2
FIG. 35 shows the structure of a semiconductor laser device using a waveguide structure with a varying layer thickness for the spot size conversion unit. This laser element is characterized by having a spot size converter in the outgoing light portion. The spot size conversion unit is a device that widens the diameter of the emitted light beam in order to improve the efficiency (coupling efficiency) of the light emitted from the element to enter the optical fiber. In this spot size conversion section, the light distribution is oozed out into the cladding layer by gradually reducing the thickness of the waveguide layer to increase the spot size. 1800 is an n-type InP substrate, 1801 is an n-type InP buffer layer, 1802 is an active layer, 1803 is an InGaAsP (composition wavelength: 1.2 μm) guide layer for spot size conversion, and 1804 is an InGaAsP (composition wavelength: 1.1 μm) guide 1805 is a p-type InP buried layer, 1806 is an n-type InP buried layer, 1807 is a p-type InP cladding layer, 1808 is a p-type InGaAs (composition wavelength: 1.65 μm) contact layer, 1809 is an SiO ₂ layer, 1810 is An n-type ohmic electrode 1811 is a p-type ohmic electrode. The active layer 1802 includes an InGaAsP (composition wavelength: 1.1 μm) guide layer, six InGaAsP strained quantum well (strain amount: 0.8%) layers, and five InGaAsP (composition wavelength: 1.1 μm) barrier layers. It consists of an active layer composed of a multiple quantum well layer (emission wavelength: 1.3 μm) and an InGaAsP (composition wavelength: 1.1 μm) guide layer.

A method for manufacturing the spot size conversion portion in this laser structure will be described. A SiN _x mask similar to that in Example 1 is formed on the surface of the spot size converting InGaAsP (composition wavelength: 1.2 μm) guide layer 1803 adjacent to the active layer. This mask has a shape in which the mask width on the boundary side with the active layer is wide and the mask width on the emission end side is narrow. At the same time, the entire surface of the active layer is covered with a mask. When dry etching shown in Example 1 is performed on this sample, the etching depth is shallow on the boundary side of the active layer and deep on the emission end side. Next, after laminating the InP clad layer, a spot size conversion portion is formed by forming a mesa forming stripe mask and processing it into a mesa structure. With regard to this structure, the structure of the semiconductor laser device of this example is fabricated by forming electrodes after the growth of the pn structure buried layer and the growth of the cladding layer and the contact layer.

  As described above, by using this embodiment, a waveguide layer (spot size converting portion) whose layer thickness can be easily changed can be manufactured. The fabricated device exhibits good characteristics such that the optical loss in the waveguide layer (spot size conversion portion) is reduced, the threshold current at room temperature is 6.7 mA, and the efficiency is 0.42 W / A.

1310 Semiconductor substrate 1311 SiO ₂ mask (corresponding to “first mask”)
1321 SiN _x mask (corresponding to “second mask”)
1331 Resist pattern for _second mask 1410 SiO ₂ mask (corresponding to “first mask”)
1411 SiN _x mask (corresponding to “second mask”)
1411A Flat portion 1411B Inclined portion 1412 Length of diffraction grating pattern 1413 Width of diffraction grating pattern 1414 Pitch of diffraction grating pattern 1415A Width of flat portion 1415B Width of inclined portion 1910 SiO ₂ mask (corresponding to “first mask”)
1911 SiN _x mask (corresponding to "second mask")
1911A Flat portion 1911B Inclined portion 1912 Diffraction grating pattern length 1913 Diffraction grating pattern width 1914 Diffraction grating pattern pitch 1915A Flat portion width 1915B Inclination portion width 2001, 2002, 2003, 2004 Diffraction grating pattern opening 2010 SiO ₂ masks (corresponding to “first mask”)
2011 SiN _x mask (corresponding to “second mask”)
2700 n-type InP
2701 InGaAsP waveguide layer 2702 InP cladding layer 2800, 2800A, 2800B, 2800C opening 2810A width of opening 2800 2810B waveguide length 2815 SiN _x mask 2815A flat portion 2815B inclined portion 2820A width of flat portion 2815A 2820B width of inclined portion 2815B 2901, 2902 Polymer W1 Width of opening on upper surface of second mask W2 Width of opening on lower surface of second mask

Claims (5)

A method for producing a desired pattern of varying depth on a semiconductor surface,
Forming a SiO ₂ mask having the desired pattern and a SiN _X mask for controlling the amount of etching species diffused into a plurality of openings of the desired pattern on the semiconductor surface;
Supplying an etching species to the semiconductor surface on which the SiO ₂ and SiN _X masks are formed, and etching the semiconductor surface;
The etching is dry etching using chlorine gas in a plasma state or a mixed gas of hydrocarbon gas and hydrogen gas as the etching species,
The SiN _X mask has an opening whose side wall is inclined and whose width is narrowed toward the semiconductor surface;
The SiN _X mask is thicker than the SiO ₂ mask,
The ratio of the area of the opening of the SiN _X mask in the vicinity of each opening of the desired pattern and the area of the mask of the SiN _X mask is along the arrangement direction of the plurality of openings of the desired pattern. A method characterized by changing. The etching step includes
The gas mixture obtained from the hydrogen gas and the hydrocarbon gas, such that the hydrocarbon plasma and hydrogen plasma is obtained from hydrocarbon gas and said hydrogen gas to produce a first polymer on the semiconductor surface Supplying a hydrocarbon-based gas flow rate, a hydrogen flow rate, a gas pressure, and discharge power under a first plasma generation condition, and etching the semiconductor surface on which the first polymer is not generated;
Providing a plasma containing oxygen to remove the first polymer;
And supplying the hydrocarbon-based gas and the hydrogen gas according to a second plasma generation condition having a hydrogen flow rate different from that of the first plasma generation condition, and etching the semiconductor surface. Item 2. The method according to Item 1 . The second plasma generation conditions, according to claim 2, wherein the hydrocarbon plasma and hydrogen plasma obtained from said hydrocarbon gas and said hydrogen gas is a condition that does not produce polymer on the semiconductor surface the method of. The second plasma generation condition is a condition in which a region where a polymer is generated on the semiconductor surface is narrower than the first plasma generation condition,
The etching by the second plasma generation conditions, the method according to claim 2, wherein the etching the polymer by a second plasma generating conditions are not generated the semiconductor surface. The desired pattern, the method according to any one of claims 1 to 4, characterized in that the diffraction grating pattern.

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