JP2010056129A - Substrate used for crystal growth of nitride-based compound semiconductor, and method for crystal growth of nitride-based compound semiconductor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate used for crystal growth of a nitride-based compound semiconductor, which can make the crystal quality of the target nitride-based compound semiconductor uniform in a surface of a substrate by reducing generation of a distribution of growth temperature in the surface of the substrate; and to provide a method for crystal growth of the nitride-based compound semiconductor. <P>SOLUTION: The substrate used for crystal growth of the nitride-based compound semiconductor is characterized by having an infrared absorption layer 2, e.g. a carbon film on a surface of a substrate 1 for crystal formation, e.g. an Si(111) substrate on the opposite side to a side where crystal growth is made. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a substrate used for crystal growth of a nitride compound semiconductor and a crystal growth method for a nitride compound semiconductor.

  Nitride-based compound semiconductors (GaN, AlN, InN, BN, and mixed crystals thereof) are as high as about 1000 ° C. in order to obtain good crystal quality in the MOCVD method generally used as a crystal growth method. It is necessary to perform crystal growth in a temperature atmosphere. The heating at this time is performed by placing a substrate used for crystal growth on a carbon susceptor or the like as a supporting member, heating the carbon susceptor by a resistance heater, induction heating, or the like, and transferring heat from there to the substrate. In this method, the temperature distribution in the crystal growth substrate becomes non-uniform for the following reasons.

  First, the heating atmosphere is overwhelmingly often made reducible or inert by creating a gas flow in the reaction furnace with hydrogen, nitrogen, or the like. At this time, the balance of thermal energy differs between the substrate surface and the back surface. Heating from the susceptor and heat conduction to the substrate surface occur on the back surface side, and heat conduction from the back surface and heat conduction to the ambient gas occurs on the surface side. Therefore, a temperature gradient occurs in which the surface temperature is lower than the back surface. Substrates (sapphire, SiC, Si, GaN, etc.) often used as crystal substrates for nitride-based compound semiconductors have a positive coefficient of thermal expansion with respect to temperature, so the back side expands more than the front side. Then, the substrate warps in a concave shape. At this time, the outer peripheral portion of the substrate is lifted from the susceptor compared to the central portion.

  Second, when crystal growth of the nitride compound semiconductor is started on the heated crystal growth substrate, not only the temperature gradient but also the lattice constant and the thermal expansion coefficient of the substrate and the nitride compound semiconductor. Depending on the difference, new stress begins to be applied to the substrate. In the GaN growth on the Si substrate, the substrate warps in a convex shape as the crystal growth of the GaN layer proceeds. At this time, the central portion of the substrate is lifted from the susceptor compared to the outer peripheral portion.

  Compared to when the backside of the substrate and the susceptor are in close contact, the floating part does not conduct heat directly from the susceptor, either from the close contact, or the gas present in the gap with the radiation from the susceptor. Will be heated by heat conduction through the substrate, and the temperature will be lower than that of the close contact portion (for example, FIG. 2 of Non-Patent Document 1 below summarizes the relationship between the warpage of the substrate and the temperature difference). Is). In particular, it appears remarkably in the growth temperature range of nitride-based compound semiconductors.

  At this time, if the substrate side can efficiently absorb the radiation, that is, the infrared rays from the susceptor, it is possible to minimize the temperature drop of the floating portion. In particular, the Si substrate does not transmit the infrared rays without absorbing the infrared rays. Reflected and the effect of warpage is increased.

  Not only nitride compound semiconductors but generally semiconductor crystal growth temperature and crystal quality (dislocation density, background carrier concentration, existence of non-radiative recombination centers, etc.) are known to be closely related. Improving the uniformity of the heat distribution in the substrate is important for forming a semiconductor layer having a uniform crystal quality on the substrate.

With respect to the problem of warping of the substrate, as described in Patent Document 1 below, by inserting a layer that relieves strain between the silicon substrate and the target nitride-based semiconductor, the crystal on the substrate is warped by warping. Techniques have been devised to prevent cracks in the grown nitride compound semiconductor. However, this focused on the warpage when the crystal growth was completed and cooled to room temperature, and the substrate during crystal growth was kept flat and the heat distribution was not uniform. .
Japanese Patent No. 3352712 “Growth of blue GaN LED structures on 150-mm Si (111)”, A. Dadgar et al., J. Crystal Growth Vol. 297 (2006), pp. 279-282.

  The present invention has been made in view of the above problems, and the problem to be solved by the present invention is that the substrate is warped when the nitride compound semiconductor is formed, so that the growth temperature is increased in the plane of the substrate. Provided are a substrate used for crystal growth of a nitride compound semiconductor and a method for crystal growth of a nitride compound semiconductor that can alleviate the distribution and make the crystal quality of the desired nitride compound semiconductor in-plane uniform. It is to be.

In the present invention, in order to solve the above problem, as described in claim 1,
A nitride compound semiconductor crystal growth characterized in that it has an infrared absorption layer on a surface opposite to the crystal growth side of the crystal forming substrate, which is used for crystal growth of the nitride compound semiconductor. The board | substrate used for is comprised.

In the present invention, as described in claim 2,
The substrate used for crystal growth of the nitride-based compound semiconductor according to claim 1, wherein the substrate is placed on a pedestal with a surface on the side where crystal growth occurs of the substrate as an upper surface, and is heated by heat transfer from the pedestal. When the crystal growth of the nitride compound semiconductor occurs on the upper surface, the temperature of the upper surface is higher than that in the case where the infrared absorption layer is not provided. Configure the substrate to be used.

In the present invention, as described in claim 3,
3. The substrate used for crystal growth of a nitride-based compound semiconductor according to claim 1 or 2, wherein the infrared absorption layer is a carbon film.

In the present invention, as described in claim 4,
4. The substrate used for crystal growth of a nitride-based compound semiconductor according to claim 3, wherein the carbon film has a thickness of 100 nm to 5 μm. To do.

In the present invention, as described in claim 5,
5. The substrate used for crystal growth of a nitride-based compound semiconductor according to claim 1, wherein the crystal forming substrate is a silicon substrate, and a plane orientation thereof is (111) or an equivalent plane orientation. A substrate used for crystal growth of a nitride-based compound semiconductor is characterized.

In the present invention, as described in claim 6,
A method for crystal growth of a nitride-based compound semiconductor, wherein the substrate used for crystal growth of the nitride-based compound semiconductor according to any one of claims 1 to 5 is used with a surface of the substrate where crystal growth occurs as an upper surface. The nitride-based compound semiconductor crystal growth method is characterized in that the nitride-based compound semiconductor is crystal-grown on the upper surface by being placed on a pedestal and heated by heat transfer from the pedestal.

  A layer capable of efficiently absorbing infrared rays is formed in advance on the back side of the substrate for crystal growth, and by using the substrate, the distribution of the growth temperature in the plane of the substrate is mitigated, and the desired nitride compound semiconductor It is possible to provide a substrate used for crystal growth of a nitride-based compound semiconductor and a method for crystal growth of the nitride-based compound semiconductor, in which the crystal quality can be made uniform in-plane.

  FIG. 1 shows a basic structure of a substrate used for crystal growth of a nitride compound semiconductor according to the present invention. The substrate 1 for crystal formation usually uses a surface on which crystal growth is actually carried out (upper surface in FIG. 1) as mirror-finished as possible at the atomic level, and the rear surface is mirror-finished or as-cut etched depending on the purpose. .

  In the present invention, in addition to the above processing, an infrared absorption layer 2 that efficiently absorbs infrared rays is formed in advance on the back side of the substrate. The infrared absorbing layer 2 in close contact with the back surface of the crystal forming substrate 1 absorbs infrared rays emitted from a pedestal (susceptor) on which the substrate is placed, and the crystal forming substrate 1 is heated by heat conduction, thereby temporarily Even when warped due to strain during crystal growth, the temperature difference between the part that is in contact with the susceptor and heated directly from the susceptor by heat conduction and the part that has been lifted from the susceptor due to warping becomes small. This is schematically shown in FIG.

  Since the infrared absorbing layer 2 efficiently absorbs infrared rays, the temperature inside the substrate is improved as described above, and the temperature of the upper surface of the substrate where crystal growth of the nitride compound semiconductor occurs is not caused by the infrared absorbing layer 2. Higher than the case. In parallel with this, the temperature uniformity within the substrate improves as the temperature rise increases.

  When application to high-frequency electronic devices is taken into consideration, the infrared absorption layer 2 may be a factor that degrades device characteristics as a parasitic capacitance component, and electrodes are formed on the back side including optical devices. In the case where it is important to form the electrode, the infrared absorption layer 2 may make it difficult to form an electrode. Therefore, the infrared absorption layer 2 after crystal growth is removed by polishing or washing as necessary. Therefore, it is desirable that the infrared absorption layer 2 be easily removed.

  Furthermore, considering that the nitride-based compound semiconductor generally undergoes crystal growth at a high temperature, the material of the infrared absorption layer 2 is preferably a heat-resistant material that hardly causes thermal diffusion or alteration even at a high temperature.

  Considering the above, as a material for the infrared absorption layer 2, carbon is a suitable material because of its large infrared absorption coefficient. Carbon can be attached to the rear surface of the crystal forming substrate 1 by vacuum deposition or spin coating, and, if necessary, ashing in an oxygen atmosphere or cleaning with carbon tetrachloride or the like. Can be removed. In particular, when a Si substrate is used, hydrofluoric acid-based chemicals are often used for surface treatment, but it is also convenient that carbon is not attacked by hydrofluoric acid.

  In the above method, since the amount of infrared absorption varies depending on the film thickness, it is desirable to deposit a carbon film of at least 100 nm or more. Further, it is desirable that the thickness of the carbon film is 5 μm or less so that the carbon film can be easily removed.

  The present invention can be applied to all substrates used for crystal growth of nitride-based compound semiconductors, but is particularly effective when the crystal forming substrate 1 is a silicon substrate transparent to infrared rays.

[Example of embodiment]
As an embodiment of the present invention, a Si (111) substrate is used as the crystal forming substrate 1 as shown in FIG. 3, but the present invention is not limited to this and can be applied.

  The Si (111) substrate, which is the crystal forming substrate 1, is washed with the RCA method or a hydrofluoric acid solution to obtain a clean surface.

  Next, 200 nm or more of carbon (carbon) is deposited on the back side of the Si (111) substrate by ECR sputtering to form the infrared absorption layer 2 that is a carbon film. Thereafter, the surface is cleaned again with a hydrofluoric acid solution to recover the clean surface on the front side of the Si (111) substrate. The processed substrate is loaded into the MOCVD apparatus, and the temperature is raised in a hydrogen atmosphere to perform thermal cleaning.

  After the cleaning, a target nitride compound semiconductor layer is formed. That is, the above substrate is placed on a pedestal (susceptor) with the surface on which crystal growth occurs as the upper surface, and heated by heat transfer from the pedestal to grow a nitride-based compound semiconductor on the upper surface.

  For the growth of the nitride-based compound semiconductor layer, a metal organic vapor phase epitaxy (MOVPE) method, which is excellent in supplying nitrogen atoms as a group V raw material, is preferable. ) Method or a crystal growth method such as halogenated vapor phase epitaxy (HVPE) method may be used.

  As an example, when a 2 μm target GaN layer is to be deposited on a 3 inch Si (111) substrate, if the deposition is attempted without applying the present invention, the temperature at the center of the substrate increases as the growth of the GaN layer proceeds. It will be 30 ° C lower than the temperature in the surrounding area. On the other hand, when a GaN layer having the same thickness is grown by applying the present invention, the temperature difference is reduced to less than 10 ° C.

  After the completion of crystal growth, cleaning with carbon tetrachloride or ashing is performed on the back surface of the substrate to remove carbon deposited as the infrared absorption layer 2.

It is a figure which shows the basic composition of the board | substrate used for the crystal growth of the nitride type compound semiconductor based on this invention. It is a schematic diagram which shows the case where the board | substrate used for the crystal growth of the nitride type compound semiconductor based on this invention and the board | substrate warped by distortion when actually performing crystal growth. It is a figure which shows the structure when vapor-depositing carbon as an infrared rays absorption layer on the back surface of a crystal forming substrate, and carrying out the crystal growth of the target nitride type compound semiconductor.

Explanation of symbols

  1: Crystal-forming substrate, 2: Infrared absorbing layer.

Claims (6)

  A nitride compound semiconductor crystal growth characterized in that it has an infrared absorption layer on a surface opposite to the crystal growth side of the crystal forming substrate, which is used for crystal growth of the nitride compound semiconductor. Substrate used for The substrate used for crystal growth of the nitride-based compound semiconductor according to claim 1,
When the substrate is placed on the pedestal with the surface on the side where crystal growth of the substrate occurs as an upper surface, heated by heat transfer from the pedestal, and crystal growth of the nitride compound semiconductor occurs on the upper surface, A substrate used for crystal growth of a nitride-based compound semiconductor, characterized in that the temperature of the upper surface is higher than that without the infrared absorption layer. The substrate used for crystal growth of the nitride-based compound semiconductor according to claim 1 or 2,
A substrate used for crystal growth of a nitride-based compound semiconductor, wherein the infrared absorption layer is a carbon film. The substrate used for crystal growth of the nitride-based compound semiconductor according to claim 3,
A substrate used for crystal growth of a nitride-based compound semiconductor, wherein the carbon film has a thickness of 100 nm to 5 μm. The substrate used for crystal growth of the nitride-based compound semiconductor according to any one of claims 1 to 4,
A substrate used for crystal growth of a nitride-based compound semiconductor, wherein the crystal-forming substrate is a silicon substrate and the plane orientation is (111) or an equivalent plane orientation.   A method for crystal growth of a nitride-based compound semiconductor, wherein the substrate used for crystal growth of the nitride-based compound semiconductor according to any one of claims 1 to 5 is used with a surface of the substrate where crystal growth occurs as an upper surface. A crystal growth method for a nitride compound semiconductor, comprising: placing on a pedestal, heating by heat transfer from the pedestal, and growing a nitride compound semiconductor on the upper surface.

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