JP2005285879A - Semiconductor film-forming substrate manufacturing method, semiconductor substrate using the manufacturing method, and semiconductor light-emitting device - Google Patents

Abstract

In a method for manufacturing a semiconductor film forming substrate, an uneven portion is formed in order to form a good semiconductor film on the substrate. However, it is difficult to process the uneven portion with high accuracy.
A step of forming a photoresist pattern having a reverse mesa cross section on a main surface of a substrate, a step of forming a metal thin film on the main surface of the substrate by a sputtering method using the photoresist pattern as a mask, and a lift-off method Removing the photoresist pattern and forming the metal thin film as a pattern on a main surface of the substrate; forming a recess in the substrate by a dry etching method using the metal thin film pattern as a mask; and A substrate for semiconductor film formation is manufactured by a process of removing the pattern with an acidic solution to form a substrate having an uneven shape.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor film forming substrate, a semiconductor substrate using the manufacturing method, and a semiconductor light emitting device.

  In recent years, various studies and developments for growing a semiconductor film on a substrate such as sapphire, silicon carbide, and spinel have been studied.

  When a semiconductor film is grown on a substrate made of various materials as described above, a difference in lattice constant between the substrate and the semiconductor film or a difference in thermal expansion makes it impossible to perform good growth of the semiconductor film. Even if it could be implemented, there was a problem that its crystallinity was extremely low.

  In order to solve such a problem, an uneven portion is provided on the main surface of the substrate on which the semiconductor film is formed, thereby performing lateral crystal growth, and having high crystallinity with good crystallinity with reduced dislocation density of the film. Obtaining a semiconductor film is actively carried out.

  Here, as a method for forming the concavo-convex portion on the substrate on which the semiconductor film is formed as described above, for example, a method of making a concavo-convex portion by scratching the substrate surface with a diamond cutter or the like (scribing), or a dicing saw A method (dicing) is used in which a kerf is processed by using this to make it an uneven portion (see Patent Document 1).

Further, after a uniform layer made of Ni or the like is formed on the substrate by using a film forming means such as a vapor deposition method, a striped etching mask is manufactured by performing photolithography on the layer. Next, the substrate main surface is partially etched away by plasma etching through this etching mask to produce a substrate having irregularities (see Patent Document 2).
JP 2000-174335 A JP 2002-93726 A

  However, the method of Patent Document 1 has a problem that processing strain enters the crystal growth surface. If the crystal growth surface is distorted as described above, dislocations are generated from the distorted portion even if the crystal is grown, and the dislocation cannot be reduced. Further, if scribing is performed on the surface of the substrate one by one, it is a method with very poor productivity.

  In addition, since the method of Patent Document 2 uses a photolithography technique, the processing accuracy of the concavo-convex grooves on the substrate is improved as compared with the conventional method, but the edge portion of the mask formed of a metal thin film formed on the substrate. The accuracy and adhesion are not stable, the masking effect is not fully exhibited, the edge part cannot withstand the plasma etching process at the time of groove processing, it is processed together with the substrate, and part of the uneven groove There was a problem that the processing accuracy, particularly the processing accuracy of the convex portion, was significantly lowered.

  In view of the above problems, the present invention provides a method for producing a substrate for forming a semiconductor film, comprising a step of forming a photoresist pattern having a reverse mesa cross section on the main surface of the substrate, and a main substrate by sputtering using the photoresist pattern as a mask. A step of forming a metal thin film on the surface, a step of removing the photoresist pattern by a lift-off method to form the metal thin film on the main surface of the substrate as a pattern, and a dry etching method using the pattern of the metal thin film as a mask. The method includes a step of forming a recess in the substrate and a step of forming a substrate having an uneven shape by removing the pattern of the metal thin film with an acidic solution.

  Further, the angle formed between the side of the inverted mesa shape of the cross section of the photoresist pattern and the main surface of the substrate is 45 ° or more and less than 90 °.

  Furthermore, the edge part of the metal thin film pattern cross section is a curved surface having a radius of curvature of 0.5 to 10 μm.

  The metal thin film pattern may have a cross-sectional thickness of 0.3 to 10 μm.

  In addition, the semiconductor substrate is characterized by using the manufacturing method described above.

  In addition, the semiconductor light-emitting element is characterized by having an element structure in which a semiconductor crystal layer including a light-emitting layer is stacked on a semiconductor substrate manufactured using the above-described manufacturing method.

  According to the configuration of the present invention, a mask made of a metal thin film is formed along a photoresist film having a cross-sectionally inverted mesa shape, and a mask with high linearity and accuracy can be formed. Therefore, dry etching is performed using the metal thin film as a mask. It is possible to prevent damage to the edge portion of the convex portion of the substrate when performing.

  Further, by using a metal thin film as a mask, it is possible to perform processing at a higher speed, and it is possible to perform deeper groove processing on the substrate surface.

  In addition, since the metal thin film is formed by sputtering, the adhesion between the metal thin film and the substrate can be improved, so that the mask can be prevented from being peeled off during dry etching. Furthermore, since the number of steps is shorter than that of the conventional mask forming process and a large number of sheets can be processed, the mass productivity is excellent.

  Further, since a flat metal thin film can be formed on the substrate surface, the process can be performed with a high yield.

  A semiconductor crystal layer with a low dislocation can be obtained by laminating a semiconductor crystal layer on a concavo-convex substrate with higher accuracy than the conventional one obtained by the above-mentioned process. A strong semiconductor light emitting device can be produced.

  Hereinafter, the best mode for carrying out the present invention will be described.

The present invention includes a step of forming a photoresist pattern having a reverse mesa shape on the main surface of the substrate;
Forming a metal thin film on the substrate main surface by a sputtering method using the photoresist pattern as a mask; removing the photoresist pattern by a lift-off method to form the metal thin film on the substrate main surface as a pattern; Forming a recess in the substrate by a dry etching method using the metal thin film pattern as a mask, and forming a substrate having an uneven shape by removing the metal thin film pattern with an acidic solution. It is a feature.

  As the material of the substrate, ceramics such as sapphire, silicon carbide, and spinel are generally used, and sapphire has been used frequently recently. The selection of these substrates depends on the thermal expansion coefficient and crystal form of the semiconductor film formed on the substrate. As the substrate shape, a flat plate shape is mainstream, but if it is sapphire, there is a limit to the size that can be manufactured by the manufacturing method, and a substrate having a size of 2 to 3 inches is used.

  Here, as the photoresist pattern formed on the main surface of the substrate, it is preferable that the cross section thereof is a photoresist pattern 2 having a reverse mesa shape as shown in FIG. The reason why the reverse mesa shape is good as described above is that the edge portion of the metal thin film is brought into close contact with the substrate surface with higher accuracy in the subsequent metal thin film formation step using the sputtering method (FIG. 1B). Because.

  As described above, as a method of making the photoresist pattern 2 into an inverted mesa shape, for example, when an image reversal type resist is used, after applying the resist to the substrate 1, pre-baking (heating treatment) is performed and ultraviolet light or the like is used. It is obtained by exposing using a photomask, image reversal baking, and then exposing the entire surface without a photomask to remove uncured portions of the resist.

  Further, the thickness of the photoresist pattern 2 may be any thickness, but in consideration of exposure, it is preferably within a range of 100 μm or less.

  The photoresist can be either water-soluble or solvent-based, and forms a photoresist pattern with a reverse mesa shape in cross section, either a positive resist where the exposed part is not developed or a negative resist where the exposed part remains. Is possible.

  Then, after forming the photoresist pattern as described above, 3a formed on the photoresist film and 3b formed on the substrate as shown in FIG. 1B by sputtering using this as a mask. Then, a metal thin film 3 made of 3c formed on the side surface of the photoresist cross section is formed on the substrate 1.

  Here, as the material of the metal thin film 3, it is preferable to use chromium, nickel, aluminum, titanium, platinum or the like.

  Here, the sputtering method is used to form the metal thin film 3 for the following reason. That is, as shown in FIG. 2 (a), in the conventional vacuum deposition method, the gas molecules of the dissolved metal thin film material are good for the plane perpendicular to the substrate as shown by the arrow A in the figure. 3a and 3b of the metal thin film 3 can be formed because of adhering to the metal, but the metal thin film component is not deposited on the side surface of the inverted mesa-shaped cross section represented by 3c. In addition, the edge portion of the metal thin film on the substrate represented by 3b is thin. As a result, when the photoresist film 2 is removed in the subsequent process and dry etching is performed using the metal thin film 3 as a mask, the edge portion of the metal thin film 3b for forming the convex portion on the substrate is more than the other portion. The thickness is thin and the substrate is processed together with the substrate by dry etching, and the processing accuracy of the edge portion of the substrate convex portion after processing becomes extremely bad.

  In comparison with this, the sputtering method, as shown in FIG. 2B, the metal thin film material particles repelled by the ions generated by the sputtering phenomenon are not in the direction perpendicular to the substrate as indicated by the arrow B. In order to move and adhere in the direction, the metal thin film 3 can be satisfactorily formed also in FIG. Thereafter, if the photoresist film is removed, a metal thin film 3 having a shape as shown in FIG. 1C is formed on the substrate. With such a shape, the metal thin film 3 is also formed in the subsequent plasma etching step. It is possible to form a good concavo-convex portion without the thickness variation and the like, without the edge portion of the convex portion formed on the substrate being dry-etched together with the metal thin film 3.

  Further, when the metal thin film 3c is to be satisfactorily formed by sputtering as described above, the angle between the side surface of the cross section of the photoresist pattern 2 in FIG. 1A and the main surface of the substrate, that is, the reverse taper angle θ. Is preferably in the range of 45 ° to 90 °. This is because it is difficult to form the metal thin film 3c even by a sputtering method at an angle lower than 45 °. If it is larger than 90 °, the metal thin film 3c formed on the other side accurately processes the substrate during dry etching. This is an obstacle to the above, and causes the processing accuracy of the uneven portion to deteriorate.

  Furthermore, as shown in an enlarged view of FIG. 3, the edge portion of the metal thin film 3 is a curved surface having a radius of curvature R of 0.5 to 10 μm at the boundary between the metal thin films 3b and 3c. If the R surface is smaller than 0.5 μm, the accuracy of the convex portion of the substrate is impaired during substrate processing by dry etching, and if it is 10 μm or more, the adhesion with the metal thin film 3 is impaired. In order to make the edge portion of the metal thin film 3 curved as described above, the metal thin film 3c of FIG. 1B is formed by forming the metal thin film 3 by the sputtering method using the reverse mesa-shaped photoresist pattern. There must be.

  Further, the pattern cross-sectional thickness of the metal thin film 3 is more preferably 0.3 to 10 μm. If it is thinner than 0.3 μm, it is processed together with the substrate during the subsequent plasma etching and cannot serve as a mask. If it is 10 μm or more, the photoresist film 3 is removed when the photoresist film is removed. This is because the strength of the bonding portion between the metal thin film 3a and the metal thin film 3c formed on the substrate increases, and the metal thin film 3 on the substrate is removed together with the unnecessary metal thin film when the photoresist film is removed.

  Next, after the metal thin film 3 is formed, as shown in FIG. 1D, an uneven portion is formed on the main surface of the substrate by dry etching using this as a mask. As the dry etching method, it is more preferable to use the plasma etching method as described above. This plasma etching method is performed by an RIE (reactive ion etching) apparatus. The groove 4 can be formed on the substrate 1 by processing by irradiating plasma in the direction of the arrow in FIG.

  Here, any commercially available apparatus can be used as the RIE apparatus, but a great amount of output is required depending on the material of the substrate. In this case, the metal thin film 3 formed on the substrate for forming the uneven portion may be processed at the same time, and it is necessary to sufficiently study the processing conditions.

  And after finishing the uneven | corrugated process to the substrate surface by the said RIE apparatus, the metal thin film 3 on a substrate surface is removed, and it is set as the board | substrate which has an uneven | corrugated | grooved part on the surface as shown in FIG.1 (e). For the removal of the metal thin film 3, an acidic solution may be used. As the acidic solution, nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid, phosphoric acid or the like can be specified, but depending on the material of the metal thin film 3 to be used, the removal solution Must be selected.

  By using the above-described manufacturing method, an uneven portion is formed on the semiconductor film forming substrate. The substrate on which the concavo-convex portion is formed is then preferably used as a substrate for a light emitting element by growing a crystal made of GaN or the like on the substrate to form a semiconductor film. Since the semiconductor film forming substrate having the concavo-convex portion formed by the method of the present invention has good processing accuracy of the concavo-convex portion and can have a good crystal growth surface during the crystal growth, a higher-density semiconductor film Can be formed on the substrate surface. As a method for performing the crystal growth, HVPE, MOCVD, MBE method or the like is used. In particular, when forming a thick film, it is preferable to use the HVPE method, and when forming a thin film, the MOCVD method or the MBE method is used.

  In addition, as a more preferable range of the width | variety of the uneven | corrugated | grooved part of the said board | substrate for semiconductor film-forming, the depth, and a pitch, an uneven | corrugated | grooved part width is 0.5-10 micrometers, a depth 0.5-3 micrometers, and a pitch 1-20 micrometers. If the width of the concavo-convex portion is smaller than 0.5 μm, formation of the concavo-convex is difficult, and if it is larger than 10 μm, good crystal growth cannot be performed. Further, even when the depth and pitch are out of the above ranges, good crystal growth cannot be performed.

  Furthermore, the substrate on which the semiconductor film is formed as described above can be suitably used as a substrate for a semiconductor light emitting element such as an LED, and various layers and electrodes such as p-type and n-type required for light emission are formed. Then, it can be applied to a liquid crystal projector, a light emitting diode, or the like as a chip.

  Examples of the present invention will be specifically described below.

  A substrate having a C-plane main surface of single crystal sapphire is prepared, and a photoresist film is applied on the main surface. At this time, HMDS treatment may be performed in order to improve the adhesion between sapphire and the photoresist.

  Next, exposure is performed using a mask having an opening having a desired pattern shape, and then the resist is immersed in a developing solution to develop a cross-section having a reverse mesa shape, with a photoresist film thickness of 2 μm and an uneven portion width of A photoresist pattern of 2 μm and a reverse taper angle of 80 ° is formed. In addition, in order for the said photoresist pattern to have a cross-section with a reverse mesa shape and the reverse taper angle to be 80 degrees, it is necessary to preset the exposure conditions at the time of the said exposure. Specifically, the irradiation conditions may be set by calculating the attenuation depth in the thickness direction of the photoresist film using ultraviolet light used for exposure.

  Next, a sapphire substrate is set in the sputtering apparatus, and here, for example, 1 μm of Ni is deposited.

  Here, when the substrate is cleaned by performing reverse sputtering for 1 minute before forming the Ni film, the adhesion of the Ni film can be improved. The reverse sputtering time is preferably 30 seconds to 2 minutes.

  In addition, in order to prevent deformation of the resist, film formation by sputtering is performed without heating the substrate. The substrate temperature is preferably 0 ° C. to 150 ° C. And a metal thin film can be deposited even to the side part of a photoresist film cross section by forming a metal thin film on a sapphire substrate main surface by sputtering method. At this time, the thickness of the metal thin film is preferably smaller than the thickness of the photoresist film in consideration of the later removal of the photoresist film and the removal of the metal thin film formed on the photoresist film.

  Next, the sapphire substrate on which the formation of the metal thin film has been completed is taken out of the sputtering apparatus, immersed in acetone, and ultrasonic waves are applied to remove the photoresist pattern and unnecessary metal thin film deposited around the metal, thereby removing the metal. A thin film pattern is formed. The obtained metal thin film pattern had a curved surface R of the edge portion of 5 μm, and a desired cross-sectional shape was obtained.

  Then, using this metal thin film pattern as a mask, the sapphire substrate was set in an RIE apparatus, and the surface of the sapphire substrate was processed by 0.5 μm to form a recess having a depth of 0.5 μm on the substrate surface.

  Thereafter, the metal thin film pattern is removed with an acidic solution made of nitric acid, hydrochloric acid, or the like, and cleaning is performed.

From the above, a single crystal sapphire substrate having a concavo-convex width of 2 μm and a depth of 0.5 μm could be produced.

  The single crystal sapphire substrate manufactured according to Example 1 was set in a semiconductor film forming apparatus.

  Next, the substrate is heated to 1150 ° C. in a hydrogen atmosphere and subjected to hydrogen annealing, and then the temperature of the substrate is decreased to 500 ° C. Using MOVPE, trimethylaluminum (TMA) and ammonia (NH 3) are used. A low temperature GaN buffer layer was deposited. Furthermore, the temperature was raised to 1100 ° C. to grow a GaN layer. This GaN layer was a high quality GaN film with few threading dislocations.

(A)-(e) is the schematic which shows the formation method of the uneven | corrugated | grooved part of the substrate surface of this invention. It is the schematic which shows the manufacturing method at the time of forming a metal thin film on the substrate surface, (a) is a cross-sectional schematic when a metal thin film is formed by a vacuum evaporation method and (b) is a sputtering method. It is an expanded schematic diagram which shows the edge part of the metal thin film of the board | substrate surface formed with the manufacturing method of this invention.

Explanation of symbols

1: Substrate 2: Photoresist pattern 3: Metal thin film 3a: Metal thin film 3b on the photoresist pattern: Metal thin film 3c on the substrate: Metal thin film formed on the side of the cross section of the reverse mesa-shaped photoresist pattern

Claims (6)

Forming a photoresist pattern having a reverse mesa cross-section on the main surface of the substrate;
Forming a metal thin film on the substrate main surface by a sputtering method using the photoresist pattern as a mask;
Removing the photoresist pattern by a lift-off method and forming the metal thin film as a pattern on the substrate main surface;
Forming a recess in the substrate by a dry etching method using the metal thin film pattern as a mask;
And a step of forming a substrate having an uneven shape by removing the pattern of the metal thin film with an acidic solution. 2. The method for manufacturing a semiconductor film forming substrate according to claim 1, wherein an angle formed between the side of the inverted mesa shape of the cross section of the photoresist pattern and the main surface of the substrate is 45 ° or more and less than 90 °. 3. The method for manufacturing a semiconductor film-forming substrate according to claim 1, wherein an edge portion of the cross-section of the metal thin film pattern is a curved surface having a radius of curvature of 0.5 to 10 μm. 4. The method for manufacturing a semiconductor film-forming substrate according to claim 1, wherein the metal thin film pattern has a cross-sectional thickness of 0.3 to 10 [mu] m. A semiconductor film forming substrate manufactured using the manufacturing method according to claim 1. 6. A semiconductor light emitting device comprising: a semiconductor substrate manufactured using the manufacturing method according to claim 5; and a semiconductor crystal layer including a light emitting layer laminated on the substrate.

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