JP2007324549A - Dislocation detecting method for semiconductor crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and safely detect dislocation of GaN in a method of easily detecting a defect owing to dislocation of group III nitride semiconductor crystal for which Ga is essential. <P>SOLUTION: Crystal of GaN is etched for one hour with a TMAH (tetramethyl ammonium hydroxide) of 25% in concentration warmed at 85°C. Then an etch pitch is formed on a crystal surface of GaN. The etch pit is formed at a dislocation part, so the dislocation can be detected through the etch pit. Further, the dislocation density can be measured by counting etch pits through an optical microscope etc., and then the quality of the crystal can be evaluated. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for easily detecting defects due to dislocations in a group III nitride semiconductor crystal in which Ga is essential.

  In recent years, Group III nitride semiconductors have been actively researched and developed. This material is very useful and promising as a material for light-emitting devices such as LEDs and LDs, and as a material for high-frequency devices, and its importance is expected to increase in the future.

  These electronic devices are composed of Group III nitride semiconductor crystals, and the dislocation density of the crystals greatly affects the performance of the electronic devices. In particular, since a crystal of a group III nitride semiconductor has a dislocation density larger than that of other semiconductor crystals, it is very important to evaluate the quality of the crystal by measuring the dislocation density.

  As a method for measuring the dislocation density of a group III nitride semiconductor crystal, a method is known in which the dislocation density is measured by counting the number of etch pits formed in the dislocation portion by etching.

  Patent Document 1 describes a method of measuring dislocation density by etch pits formed by using a mixed solution of sulfuric acid and phosphoric acid or a molten solution of a mixture of sulfuric acid compound and phosphoric acid compound as an etching agent. Has been. It is described that the mixed solution of sulfuric acid and phosphoric acid is used at 180 ° C. to 280 ° C., and the melt of the mixture of sulfuric acid compound and phosphoric acid compound is used at 200 ° C. to 400 ° C.

  Similarly to Non-Patent Document 1, there is a method of detecting dislocations by etch pits generated by mixing sulfuric acid and phosphoric acid in a ratio of 1: 3 and etching GaN with a solution heated to 250 ° C. Are listed.

A method using a KOH melt as an etching agent is also known. For example, Patent Document 2 discloses a method in which dislocation is detected by etching pits formed by etching using a KOH melt at 300 ° C. to 360 ° C. Further, TMAH (tetramethylammonium hydroxide aqueous solution is known to etch silicon as described in Patent Documents 3 and 4. However, gallium nitride, gallium and nitrogen are removed by the TMAH solution. It is not known that the essential group III nitride semiconductor can be etched.
Patent No. 366374 JP 2001-39799 A JP-A-2005-175223 Patent No. 3027030 Solid-State Electronics 46 (2002) 555-558

  However, any of the above-mentioned etching agents is dangerous because the operating temperature is high. In particular, sulfuric acid heated to a high temperature is very dangerous, and the sulfur oxide gas generated by heating is toxic to the human body. In addition, it is difficult to control the concentration because the evaporation of water is intense at high temperatures. Therefore, when using these etching agents, sufficient care is required for handling for safety. Furthermore, the KOH melt also has a problem in that it takes time to remove KOH adhering to the group III nitride semiconductor crystal after etching.

  Therefore, the present invention provides a method for detecting dislocations in a group III nitride semiconductor crystal in a safe and simple manner by using an etching agent different from the conventional one.

In the present invention, a group III nitride semiconductor crystal containing Ga as an essential component is etched with a TMAH (tetramethylammonium hydroxide: (CH ₃ ) ₄ NOH) solution, and dislocations are detected by etch pits formed in the crystal. This is a dislocation detection method characterized by the above.

  The temperature of the TMAH solution is desirably 50 ° C to 100 ° C, and more desirably 80 ° C to 100 ° C. Below 50 ° C., the etching rate is slow, and etch pits are not formed so much, which is not desirable. In particular, also in the case of a TMAH aqueous solution, the temperature is desirably 50 ° C to 100 ° C as described above, and more desirably 80 ° C to 100 ° C. On the other hand, when the temperature is 100 ° C. or higher, bubbles are generated in the solution and adhere to the crystal, which is undesirable. It is also undesirable in that the concentration changes due to evaporation of moisture or solvent.

The TMAH solution is most preferably an aqueous TMAH solution.
The concentration of the TMAH aqueous solution is desirably 5% to 50%, and more desirably 6% to 25%. If it is 5% or less, the etching rate is slow, which is not desirable. If it is 50% or more, it may be supersaturated and may cause precipitation, which is not desirable.

  The etching rate depends on the concentration and temperature of the TMAH solution, and the diameter of the etch pit depends on the etching rate and the etching time. Therefore, the size of the etch pit can be adjusted by changing the concentration, temperature, and etching time of the TMAH solution as necessary. For example, when measuring the dislocation density, it is easier to count the number of etch pits by using an optical microscope than by using an SEM or AFM. It should be large enough to be observed.

  In the present invention, the TMAH solution used for etching, in particular, the TMAH aqueous solution is not harmful to the human body and is used at a low temperature of 50 ° C to 100 ° C. Therefore, handling is easy and it is relatively safe. Further, since TMAH is non-volatile, when the TMAH aqueous solution is used, it is easy to adjust the concentration of the aqueous solution. Furthermore, since alkali metal ions are not included like KOH, the sample after etching can be easily cleaned. As described above, by using a TMAH solution, in particular, a TMAH aqueous solution, as an etching agent, dislocations in the group III nitride semiconductor crystal can be detected more easily than before. Further, by counting the etch pits detected by the method according to the present invention with an optical microscope or the like, the dislocation density can be measured, and the quality of the crystal can be evaluated.

  Hereinafter, specific examples of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples.

  A sample was prepared by laminating a low-temperature buffer layer 2 of AlN on a sapphire C-plane substrate 1, a low-temperature buffer layer 3 of GaN thereon, and a GaN layer 4 thereon (see FIG. 1). The surface 5 of the GaN layer 4 is a C plane. The thickness of each layer is 50 nm for the buffer layer 2, 0.3 μm for the buffer layer 3, and 3 μm for the GaN layer 4. This sample was etched for 1 hour with a 25% strength aqueous TMAH solution heated to 85 ° C. As a result, it was confirmed that many etch pits were formed. FIG. 2 is an optical micrograph of an etch pit formed on the surface 5 of the GaN layer 4. Several etch pits with almost the same diameter can be confirmed. FIG. 3 is a SEM photograph in which an etch pit is photographed by tilting the sample by 45 degrees. The diameter of the etch pit is about 8 μm. A pyramid is visible at the edge of the etch pit. In FIG. 2, it is this pyramid portion where the periphery of the etch pit is white.

From this, it is considered that the etch pits and pyramids are formed as follows.
The TMAH aqueous solution cannot etch the surface 5 of the GaN layer 4 that is the C plane. However, even in the C plane, the dislocation portion 6 can be etched. As the etching proceeds, the TMAH aqueous solution reaches the buffer layer 3. Since the buffer layer has many defects due to dislocations and the like, and the etching rate is high, the buffer layers 2 and 3 are etched faster than the surface other than the C surface of the GaN layer 4 (see FIG. 4). Thereafter, etching proceeds from bottom to top along the R plane of the GaN crystal, the etch pit diameter increases, and a pyramid having the R plane as a side surface is generated due to anisotropic etching (see FIG. 5). The side surface of the hexagonal pyramid in the micrograph in FIG. 3 is the R surface of GaN.

  Although GaN was used in Example 1, dislocations can be similarly detected by etch pits even when a group III nitride semiconductor such as AlGaN, InGaN, or InGaAlN is used. The Al composition ratio of these group III nitride semiconductors can be 30% or less. Since AlN can be etched with an acid, it is not particularly advantageous to use a TMAH solution.

  As described above, the present invention is useful for measuring the dislocation density in a group III nitride semiconductor having Ga and N as essential elements. In particular, it is effective for measuring the dislocation density on the C plane.

  The present invention can be used for quality evaluation of a group III nitride semiconductor crystal containing Ga.

A typical sectional view of a sample. An optical micrograph showing etch pits generated by etching. SEM photo of the etch pit taken from a 45 degree angle. The schematic diagram of the formation process of an etch pit. The schematic diagram of the formation process of an etch pit.

Explanation of symbols

1: Sapphire substrate 2: Buffer layer 3: Buffer layer 4: GaN layer 5: GaN layer surface 6: Dislocation portion

Claims (4)

In a method for detecting dislocations in a group III nitride semiconductor crystal containing Ga as an essential component,
Etching the group III nitride semiconductor crystal with a TMAH (tetramethylammonium hydroxide) solution,
A dislocation detection method comprising detecting dislocations by etch pits formed in the group III nitride semiconductor crystal.   The dislocation detection method according to claim 1, wherein the temperature of the TMAH solution is 50 ° C. to 100 ° C.   The dislocation detection method according to claim 1 or 2, wherein the concentration of the TMAH solution is 5% to 50%. The dislocation detection method according to any one of claims 1 to 3, wherein the TMAH solution is a TMAH aqueous solution.