JP2004247629A - Evaluation method of phosphide single crystal wafer and epitaxial phosphide single crystal wafer using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method of a phosphide single crystal wafer which can predict warp of a wafer after an epitaxial process by preliminary evaluation of a wafer for phosphide single crystal measurement, and a phosphide single crystal wafer which is suitable for epitaxy obtained using it. <P>SOLUTION: In the evaluation method of a phosphide single crystal wafer, the wafer is subjected to etching treatment and then subjected to heat treatment at a temperature of 800 to 1,000°C, and then warp of the wafer is measured after it is cooled down to a room temperature. The phosphide single crystal wafer is 250 to 350 μm thick and is subjected to one side mirror surface polishing wherein etching treatment is carried out in a rear, both-sided mirror surface polishing or both-sided etching treatment. In the epitaxial phosphide single crystal wafer, warp measured by the evaluation method is at most 30 μm. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for evaluating a phosphide single crystal wafer and a phosphide single crystal wafer for epitaxial growth using the same, and more particularly, a pre-evaluation of a phosphide single crystal measurement wafer, whereby a wafer after undergoing an epitaxial process is evaluated. The present invention relates to a method for evaluating a phosphide single crystal wafer capable of predicting warpage, and a phosphide single crystal wafer suitable for epitaxial use obtained by using the method.
[0002]
[Prior art]
A method for evaluating the warpage of a phosphide single crystal wafer is based on a method for evaluating a single crystal wafer for epitaxial growth of a compound semiconductor such as gallium phosphide (GaP), indium phosphide (InP), or gallium arsenide (GaAs) used as a substrate in an epitaxial process. It relates to the method of evaluating residual strain, which is one of the important quality indicators.
[0003]
A phosphide single crystal wafer such as gallium phosphide or indium phosphide is used in an epitaxial process as a substrate of an optical compound semiconductor device such as a light emitting element, a laser element, and a light receiving element. In recent years, as the demand has increased, the required quality as a substrate has been increasing in order to efficiently obtain a high-quality epitaxial film in an epitaxial process. For example, gallium phosphide single crystal wafers (hereinafter sometimes abbreviated as GaP wafers) are widely used as substrates for growing epitaxial films for light emitting devices. In this epitaxial process, a light emitting layer is formed on a substrate by a liquid phase epitaxial growth method or a vapor phase epitaxial growth method. For example, in the liquid phase epitaxial growth method, a dopant is added to a saturated solution of GaP polycrystal dissolved in metal Ga at around 1000 ° C. in a hydrogen stream, and a GaP single crystal is deposited on the substrate by controlling the temperature.
[0004]
Here, in order to obtain a good-quality epitaxial film for a light-emitting element, it is desirable that the GaP wafer is a good-quality single-crystal substrate with few crystal defects and residual strain. That is, when a GaP wafer obtained from a GaP single crystal ingot grown by the liquid sealing Czochralski (hereinafter abbreviated as LEC) method is used as a substrate and crystal growth is performed by an epitaxial growth method, crystal defects of the GaP wafer are reduced. It is said that it propagates to the epitaxial growth layer and degrades the device characteristics, and if there is residual strain in the GaP wafer, dislocations are generated due to heating in the epitaxial process, which multiply, thereby increasing the warpage of the substrate. Because it is. Therefore, it is important to prevent the occurrence of residual distortion and to eliminate it.
[0005]
The residual strain of a GaP wafer is generally formed during the manufacturing process. Generally, a manufacturing process of a GaP wafer is performed according to the following procedure.
(1) Raw Material Preparation In the LEC method, a raw material GaP polycrystal and an n-type impurity selected from S, Te or Si are placed in a quartz crucible arranged at the center of a high-pressure vessel of a vertical single crystal growing furnace. And a liquid sealant is placed thereon. The liquid sealing agent is for forming a liquid sealing layer on the GaP melt at the time of melting the raw material to prevent the volatile decomposition of phosphorus, and usually, B ₂ O ₃ is used.
[0006]
(2) Crystal Growth Next, the inside of the high-pressure vessel is set to a high pressure under an atmosphere of an inert gas such as nitrogen or argon, and the graphite heater of the growth furnace is energized to raise the temperature to the melting point of GaP or more. After the GaP raw material is melted, the seed crystal attached to the upper shaft is lowered and immersed in the GaP melt located immediately below the liquid sealing layer. After that, while rotating the quartz crucible, the temperature of the melt interface is lowered to a predetermined temperature, and then the seed crystal is rotated and raised to solidify the melt at the interface, thereby growing a GaP single crystal.
[0007]
(3) The processed and grown single crystal ingot is cylindrically ground to adjust its outer shape, and then cut into wafers having a thickness of 250 to 400 μm using an inner peripheral blade cutter or a wire saw.
[0008]
(4) Evaluation GaP wafers are inspected for electrical characteristics, processing accuracy, warpage, crystal defects, and appearance, and those that pass are single crystal wafers for epitaxial substrates. Among the inspection items, the warpage of the GaP wafer is related to the residual strain.
[0009]
In the crystal growth in the above manufacturing process, the temperature gradient near the interface between the solidified single crystal and the melt is as steep as about 100 ° C./cm. Therefore, a thermal stress is generated in the solidified single crystal, and a strain that causes elastic deformation generally remains even after cooling to room temperature. The elastic deformation caused by the residual strain is the warpage of the GaP wafer. Further, it is said that the heating in the epitaxial process generates dislocations due to residual strain, which multiplies, thereby increasing the warpage of the substrate. However, when an epitaxial process is performed using a GaP wafer having a desired warp value as a substrate, the warp generated on the substrate has no correlation with the warp of the original GaP wafer. Therefore, there is a problem that the measured value of the warp of the GaP wafer cannot predict the warpage of the substrate after the epitaxial process.
[0010]
On the other hand, as a technique for evaluating the residual strain of a GaP wafer, an optically isotropic semiconductor wafer is inserted between orthogonal polarizing plates, and a method of evaluating birefringence caused by residual strain and processing strain in the wafer (for example, Patent Document 1) can be used.
The sample for measurement of the GaP wafer used in the above method includes etching with a solution such as aqua regia that can dissolve GaP, or mirror polishing by mechanical chemical polishing in order to remove the processing strain layer introduced at the time of cutting the ingot from the wafer. Polishing is performed. Therefore, if the GaP wafer does not have the residual strain introduced during crystal growth, the orthogonal polarizing plate does not transmit light, but if the GaP wafer has the residual strain, a polarized image is observed. Here, if the area of the polarization image on the GaP wafer is large, the region distorted by residual strain is wide, and if it is small, it means that the region distorted is narrow. it can. The qualitative evaluation of the residual strain of the wafer can be used when optimizing the conditions for growing a single crystal in order to reduce the residual strain. Furthermore, in the evaluation of GaAs wafers and InP wafers, there is a commercially available apparatus that quantitatively measures the relative intensity of strain by applying the above principle.
[0011]
However, the method using the orthogonal polarization technique can evaluate the residual strain at the time of growing a single crystal. However, when the wafer is actually heated in the epitaxial process, the residual strain of the wafer is changed to the shape of the wafer. We can't foresee what changes will be made. For example, among the GaP wafers obtained in the above manufacturing process, a polarization image due to orthogonally polarized light is detected, and even when a wafer having a very low warpage, for example, a wafer having a value of 30 μm is used, even after the epitaxial process, the wafer is 200 μm or more. The range of the change in the warpage varies greatly, for example, some warp. That is, the change in the warp of the substrate in the epitaxial process cannot be evaluated by measuring the warp of the GaP wafer or the polarization image of the orthogonally polarized light. For this reason, many defects due to warpage occur in the epitaxial process, increasing the load of the epitaxial process, which is a major obstacle to the production efficiency.
From the above situation, the wafer which becomes defective due to the increase in the warpage in the epitaxial process is detected by the preliminary evaluation at the wafer stage, and by excluding the wafer, the defect rate in the epitaxial process can be reduced. An evaluation method and a phosphide single crystal wafer suitable for epitaxial obtained by using the evaluation method are required.
[0012]
[Patent Document 1]
Japanese Patent No. 2645252 (pages 1 to 3)
[0013]
[Problems to be solved by the invention]
An object of the present invention is to evaluate a phosphide single crystal wafer capable of predicting a warp of a wafer after an epitaxial process by preliminarily evaluating a phosphide single crystal measurement wafer in view of the above-described problems of the related art. It is an object of the present invention to provide a phosphide single crystal wafer suitable for epitaxial growth obtained by using the method.
[0014]
[Means for Solving the Problems]
The present inventors have conducted intensive studies on a method for evaluating the warpage of a phosphide single crystal wafer to achieve the above object, and as a result, selected an appropriate phosphide single crystal measurement wafer from a single crystal ingot. When the wafer was heat-treated under specific conditions and the warpage was measured, it was found that the warpage of the wafer after undergoing the epitaxial process could be accurately predicted, and the present invention was completed.
[0015]
That is, according to the first invention of the present invention, there is provided a method for evaluating in advance a phosphide single crystal wafer which becomes defective due to an increase in warpage in an epitaxial step. After selecting at least one phosphide single crystal measurement wafer, the wafer is etched, then heat treated at a temperature of 800 to 1000 ° C., and then cooled to room temperature, and then the warpage of the wafer is measured. A method for evaluating a phosphide single crystal wafer is provided.
[0016]
According to a second aspect of the present invention, there is provided the method for evaluating a phosphide single crystal wafer according to the first aspect, wherein the heat treatment is performed in air or an inert gas. .
[0017]
According to a third aspect of the present invention, there is provided the method for evaluating a phosphide single crystal wafer according to the first aspect, wherein the heat treatment is performed for 30 minutes or more.
[0018]
According to a fourth aspect of the present invention, in the first aspect, the method for evaluating a phosphide single crystal wafer is characterized in that the thickness of the phosphide single crystal measurement wafer is 250 to 350 μm. Is provided.
[0019]
According to a fifth aspect of the present invention, in the first aspect, the phosphide single crystal measurement wafer is selected from a plurality of sections divided in a growth direction of the single crystal ingot. A method for evaluating a phosphide single crystal wafer is provided.
[0020]
According to a sixth aspect of the present invention, there is provided the method for evaluating a phosphide single crystal wafer according to any one of the first to fifth aspects, wherein the phosphide is gallium phosphide.
[0021]
Further, according to the seventh invention of the present invention, there is provided a phosphide single crystal wafer having a thickness of 250 to 350 μm subjected to single-sided mirror polishing, double-sided mirror polishing, or double-sided etching, the back surface of which is etched. And a phosphide single crystal wafer for epitaxial use, wherein the warpage measured by any one of the first to sixth evaluation methods is 30 μm or less.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for evaluating a phosphide single crystal wafer of the present invention and a phosphide single crystal wafer for epitaxial use using the same will be described in detail.
1. Evaluation Method The method for evaluating the warpage of a phosphide single crystal wafer according to the present invention comprises the steps of: heat treating a phosphorus compound single crystal measurement wafer; and warping the wafer in the epitaxial process of the phosphorus compound single crystal wafer from the warpage of the wafer before and after the heat treatment. To try to foresee.
[0023]
(1) Phosphide single crystal wafer The phosphide single crystal wafer to be evaluated in the present invention is not particularly limited. For example, gallium phosphide (GaP) and indium phosphide (InP) grown by various methods are used. )), A wafer obtained by cutting from a phosphide single crystal ingot, etching and polishing is used.
As a method for growing this single crystal ingot, for example, the LEC method is used. The size of the single crystal ingot is not particularly limited. For example, a single crystal ingot having a diameter of 50 mm or more and a length of a straight body (a part whose diameter is stably obtained to a design value) of 50 mm or more is used. In particular, those having a diameter of 70 to 80 mm and a length of a straight body of 50 to 100 mm are usually used.
[0024]
The single crystal ingot is subjected to cylindrical grinding to adjust its outer shape, and then cut into a plurality of sections with the straight body portion in the growth direction. The measurement wafer is taken out from each section. For example, as shown in FIG. 1, the straight body of the ingot is cut into a plurality of sections in the growth direction, and a measurement wafer is collected from each section. The division in the growth direction of the straight body portion of the ingot is for selecting the sections to be sent to the epitaxial process, and the number of the sections is not particularly limited. For example, one section is set for every 20 wafers. Is determined, taking into account the allowable range of warpage, the stability of crystal growth, and the like. Cutting of the ingot and collection of the wafer for measurement are performed using an inner peripheral blade cutting machine or a wire saw.
[0025]
The thickness of the measurement wafer collected from each section is not particularly limited, and is preferably 250 to 400 μm, and particularly preferably 250 to 350 μm.
If the thickness is out of the range, the target evaluation cannot be performed.
[0026]
(2) The etching process measurement wafer must be subjected to an etching process and a polishing process prior to the heat treatment in order to dissolve and remove a processing strain layer formed by cutting on the wafer surface and accurately evaluate a change in warpage after the heat treatment. Is preferred. The etching process and the polishing process are not particularly limited, and for example, at least one method selected from a single-sided mirror polishing method, a double-sided mirror polishing method, or a double-sided etching method in which the back surface is subjected to an etching process is used. Is preferred.
The etchant used at this time is not particularly limited. For example, a solution capable of chemically dissolving phosphide is used. Among them, an aqueous solution containing H ₂ SO ₄ and H ₂ O ₂ is particularly preferable. Good for environmental measures.
[0027]
(3) Heat treatment The heat treatment temperature in the evaluation method of the present invention is 800 to 1000 ° C, preferably 840 to 900 ° C. When the heat treatment temperature is lower than 800 ° C., the generation and propagation of dislocations in the phosphide single crystal wafer are less likely to occur, and when it exceeds 1000 ° C., the phosphide becomes unstable due to thermal decomposition. It is important that the temperature of the phosphide single crystal wafer is gradually increased to the heat treatment temperature so as not to introduce new thermal stress.
[0028]
The heat treatment time in the evaluation method of the present invention is not particularly limited, but is preferably 30 minutes or more, and more preferably 30 to 50 minutes. If the heat treatment time is less than 30 minutes, dislocation generation and growth of the phosphide single crystal wafer do not sufficiently occur in the epitaxial process.
The atmosphere for the heat treatment in the evaluation method of the present invention is not particularly limited. For example, air or an inert gas stream such as nitrogen or argon is preferable.
This is because the wafer may be deteriorated in a reducing atmosphere.
[0029]
The heat treatment method is not particularly limited, but is preferably a method in which a processing gas is circulated through a quartz tube provided in a heating furnace maintained at a predetermined temperature, a measurement wafer is set therein, and processing is performed for a predetermined time. . For example, as shown in FIG. 2, a measurement wafer 1 cut out of an ingot, etched and polished is placed in a heating furnace 3, heated to a predetermined temperature, and passed a predetermined gas 4. The heat treatment can be performed by charging the quartz tube 2.
[0030]
(4) Measurement of Warp In the evaluation method of the present invention, after the heat treatment, the wafer for measurement is cooled to room temperature, and the warpage of the wafer for measurement is measured with a stylus type surface roughness meter. From this measured value, warpage of the wafer in the epitaxial process can be predicted.
[0031]
2. Phosphide single crystal wafer for epitaxial use The phosphide single crystal wafer for epitaxial use according to the present invention is a single-sided mirror-polished backside-etched, double-sided mirror-polished or double-sided etched phosphorous having a thickness of 250 to 350 μm. A phosphide single crystal wafer having a warpage of 30 μm or less as measured by the method for evaluating a phosphide single crystal wafer of the present invention.
In the present invention, in a single-sided mirror-polished, double-sided mirror-polished, or double-sided etched phosphide single crystal wafer having a back side subjected to an etching treatment, the thickness is measured by the evaluation method of the present invention. Those having a warpage of 30 μm or less are regarded as acceptable products. If the warp exceeds 30 μm, the occurrence of defects due to the warp in the processing in the epitaxial process increases. Wafers included in the same category as the passed measurement wafers are selected and used as epitaxial phosphide single crystal wafers.
[0032]
According to the evaluation method of the present invention, the warpage of the wafer after undergoing the epitaxial process can be predicted very accurately, and the phosphide single crystal wafer obtained by using the same reduces the defect rate in the epitaxial process. be able to.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.
(Example 1)
Using a GaP single crystal ingot having a diameter of 76 mm and a length of 70 mm in the straight body grown by the LEC method, as shown in FIG. The wafer was divided into five sections (v) and a GaP measurement wafer having a thickness of 350 μm was collected from each section. This wafer was treated at 65 ° C. for 5 minutes using an etchant (a mixture of H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 3: 1: 1 by volume) to form a processing strain layer due to cutting. After removal, single-sided mirror polishing was performed by mechanical chemical polishing to obtain a measurement wafer. Here, the warpage of the measurement wafer was measured with a stylus type surface roughness meter.
[0034]
Next, the measurement wafer was placed in a quartz tube maintained at a temperature of 850 ° C. and into which an argon gas was introduced over 15 minutes, and then left still for 30 minutes to perform a heat treatment. Thereafter, the measurement wafer was taken out of the quartz tube over 15 minutes and cooled to room temperature. Here, the warpage of the measurement wafer after the heat treatment was measured by a stylus type surface roughness meter. FIG. 3 shows the results of the warpage of the measurement wafer before and after the heat treatment.
From FIG. 3, the warp after the heat treatment of the measurement wafer (the upper two sections (i) to (ii) of the straight body portion of the single crystal ingot) in which the warp before the heat treatment was about 10 μm increased to 85 μm, and The warp after the heat treatment of the measurement wafers of the three sections (the three lower sections (iii) to (v) of the straight body portion of the single crystal ingot) was 30 μm or less, and was smaller after the heat treatment.
GaP wafers having a warpage of 30 μm or less after the above heat treatment were used as epitaxial GaP single crystal wafers, and epitaxial growth was performed. When implemented by this manufacturing method, the failure rate due to the increase in the warp in the 466 lots of ingots introduced into the epitaxial process is 0.003%, and the failure rate due to the increase in the warp in 33,420 input GaP wafers is 0.0004%. And was very low.
[0035]
(Comparative Example 1)
All categories (i) to (v) of a wafer obtained by performing the same cutting, etching, and polishing as in Example 1 using a GaP single crystal ingot manufactured in the same manner as in Example 1. Was used as a substrate in the epitaxial process. When implemented by this manufacturing method, in the epitaxial process, the rate of occurrence of defects due to the increase in the warp in the 42 lots of ingots introduced into the epitaxial step is 55.1%, and the defect rate due to the increase in the warp in the 3,012 input GaP wafers is It was very high at 7.2%.
[0036]
【The invention's effect】
As described above, the method for evaluating a phosphide single crystal wafer of the present invention is an evaluation method capable of predicting the warpage of a wafer after undergoing an epitaxial process by a preliminary evaluation, and is obtained by using the method. The phosphide single crystal wafer has a low defect rate in the epitaxial process and is suitable, and its industrial value is extremely large.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of collecting a measurement wafer according to the present invention.
FIG. 2 is a diagram showing an example of a method of heat treatment of a measurement wafer according to the present invention.
FIG. 3 is a diagram illustrating warpage of a GaP wafer before and after heat treatment in an example.
[Explanation of symbols]
1 Wafer for measurement 2 Quartz tube 3 Heating furnace 4 Gas

Claims (7)

A method for evaluating in advance a phosphide single crystal wafer that becomes defective due to an increase in warpage in an epitaxial process,
After selecting at least one phosphide single crystal measurement wafer from the section to be evaluated in the single crystal ingot, the wafer is etched, then heat-treated at a temperature of 800 to 1000 ° C., and then cooled to room temperature. Measuring the warpage of the wafer, and then evaluating the phosphide single crystal wafer. The method for evaluating a phosphide single crystal wafer according to claim 1, wherein the heat treatment is performed in air or an inert gas. The method for evaluating a phosphide single crystal wafer according to claim 1, wherein the heat treatment is performed for 30 minutes or more. 2. The method for evaluating a phosphide single crystal wafer according to claim 1, wherein the thickness of the phosphide single crystal measurement wafer is 250 to 350 μm. 3. 2. The method for evaluating a phosphide single crystal wafer according to claim 1, wherein the phosphide single crystal measurement wafer is selected from a plurality of sections divided in a growth direction of the single crystal ingot. The method for evaluating a phosphide single crystal wafer according to any one of claims 1 to 5, wherein the phosphide is gallium phosphide. A single-sided mirror-polished single-sided wafer with a thickness of 250 to 350 μm subjected to a single-sided mirror polishing, a double-sided mirror polishing, or a double-sided etching that has been subjected to etching on the back surface,
A phosphide single crystal wafer for epitaxial use, characterized in that the warpage measured by the method for evaluating a phosphide single crystal wafer according to claim 1 is 30 μm or less.

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