JP2018107220A - Inspection method for semiconductor substrate, quality discrimination method for semiconductor substrate, and semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of an inspection and a quality discrimination relating to crystallinity or current collapse by acquiring information that is derived from each of laminated crystal layers in PL measurement.SOLUTION: The present invention relates to an inspection method for a semiconductor substrate in which a second crystal layer 114 is lattice-matched or pseudo-lattice-matched to a first crystal layer 112 and bandwidth energy of the second crystal layer 114 is higher than that of the first crystal layer 112. The inspection method for the semiconductor substrate includes: radiating a first excitation light of a first wavelength from the side of the second crystal layer 114; measuring photo luminescence caused by the first excitation light as a first observation light; calculating a ratio I/Iof a peak strength Iof band end emission BE included in the first observation light and a peak strength Iof emission YL that appears at a longer wavelength side than a peak wavelength λof BE; and inspecting the ratio I/I. A ratio α/αof a light absorption coefficient αof the first crystal layer 112 in the first wavelength and a light absorption coefficient αof the second crystal layer 114 in the first wavelength ranges from 0.5 to 1.0.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor substrate inspection method, a semiconductor substrate quality determination method, and a semiconductor substrate.

  For example, Non-Patent Document 1 discloses a technique for suppressing current collapse in a HEMT (High Electron Mobility Transistor) using GaN epitaxially grown on a Si substrate as an active layer. In this document, to apply GaN-HEMT to power electronics, it is necessary to eradicate current collapse. For this purpose, optimization of the field plate structure to alleviate electric field concentration, and in the epitaxial layer There is a description that it is necessary to reduce defects or interface states. In addition, this document refers to the relationship between PL measurement (Photo Luminescence) and the on-resistance increase rate, which is one of the evaluation indicators of current collapse, with respect to the reduction of defects in the epitaxial layer. There is a description that the ratio (YL / BE) of the yellow luminescence intensity (YL) to the band edge emission intensity (BE) matches the on-resistance increase rate in the distribution within the wafer. That is, it is disclosed that the ON resistance increase rate (current collapse) is improved by keeping YL / BE low.

Wataru Saito, “Suppression of Collapse of GaN-HEMT on Si Substrate”, Science and Technology Exchange Foundation, 8th Nitride Semiconductor Application Study Group, June 24, 2010, http: //www.astf.or .jp / cluster / event / semicon / 20100624 / Mr_saito.pdf

  According to Non-Patent Document 1, if the PL measurement is performed and the ratio (YL / BE) of the yellow luminescence intensity (YL) to the band edge emission intensity (BE) is calculated, the on-resistance increase rate can be estimated, and the current collapse can be estimated. Can be evaluated.

  However, in the PL measurement in Non-Patent Document 1, He—Cd laser light having a wavelength of 325 nm is used as excitation light. Although light having a wavelength of 325 nm is absorbed by the GaN crystal, it is hardly absorbed by the AlGaN crystal having an aluminum composition of 0.15 or less, and as a result, a GaN / GaN having an AlGaN layer formed on the GaN layer. In the PL measurement for the AlGaN laminated crystal layer, there is a problem that the measurement result does not include information from the AlGaN layer and is limited to information from the GaN layer.

  The object of the present invention is to obtain photoluminescence information derived from each layer of the stacked crystal layer in the PL measurement for the stacked crystal layer including the AlGaN layer, and to inspect the crystallinity or current collapse of the semiconductor substrate and the accuracy of the quality determination. It is to provide a technology that enhances.

In order to solve the above problems, in a first aspect of the present invention, a base substrate, a first crystal layer, and a second crystal layer are provided, and the base substrate, the first crystal layer, and the second crystal layer include The base substrate, the first crystal layer, and the second crystal layer are positioned in this order, and the second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched to the first crystal layer. A method for inspecting a semiconductor substrate, wherein a bandwidth energy E _g2 of a crystal constituting the second crystal layer is larger than a bandwidth energy E _g1 of a crystal constituting the first crystal layer, wherein the second crystal layer Irradiating the first excitation light of the first wavelength from the side of the first and measuring the photoluminescence by the first excitation light as the first observation light, and the peak intensity I of the band edge emission BE included in the first observation light and _BE1, said van Calculating a ratio _I YL1 _{/ I BE1} between the peak intensity _{I YL1} emitting YL appearing from the peak wavelength lambda _BE edge emitting BE to the long wavelength side, the steps of the test values of the ratio _I YL1 _{/ I BE1} has the light absorption coefficient alpha ₁ in the first wavelength of the first crystal layer, the ratio alpha _{2 /} alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer, 0 Provided is a method for inspecting a semiconductor substrate in the range of .5 to 1.0.

In a second aspect of the present invention, a base substrate, a first crystal layer, and a second crystal layer are included, and the base substrate, the first crystal layer, and the second crystal layer are the base substrate, the first crystal layer, and the first crystal layer. The second crystal layer is positioned in the order of the crystal layer and the second crystal layer, and the second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched with the first crystal layer to constitute the second crystal layer A method for inspecting a semiconductor substrate, wherein a bandwidth energy E _g2 of a crystal to be produced is greater than a bandwidth energy E _g1 of a crystal constituting the first crystal layer, wherein the first wavelength of the first wavelength is from the second crystal layer side. A step of irradiating one excitation light and measuring photoluminescence by the first excitation light as a first observation light, and a second excitation light having a second wavelength longer than the first wavelength from the second crystal layer side Is irradiated with the second excitation light. Measuring a O preparative luminescence as a second observation light, and the peak intensity I _BE1 of the band edge emission BE contained in the first observation light emerges from the peak wavelength lambda _BE of the band edge emission BE to the long wavelength side The step of calculating the ratio I _YL1 / I _BE1 with the peak intensity I _YL1 of the emitted light YL, the peak intensity I _BE2 of the band edge emitted BE included in the second observation light, and the peak wavelength λ _{BE of the} band edge emitted _BE Calculating a ratio I _YL2 / I _BE2 with a peak intensity I _YL2 of the emitted light YL appearing on a longer wavelength side, and at least one selected from the ratio I _YL1 / I _BE1 and the ratio I _YL2 / I _BE2 has the steps of the calculated value from the value or the one or more values and test values, the, the light absorption coefficient alpha ₁ in the first wavelength of the first crystalline layer, the second The ratio alpha _{2 /} alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the crystal layer is, the light absorption coefficient beta ₁ in the second wavelength of the first crystalline layer, said second crystalline layer second Provided is a method for inspecting a semiconductor substrate having a ratio β ₂ / β ₁ greater than a light absorption coefficient β ₂ at a wavelength.

The first crystal layer may be an Al _x Ga _1-x N (0 ≦ x <1) layer, more specifically a GaN layer, and the second crystal layer may be Al _y Ga _1-y N. More specifically, an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer may be mentioned as the (0 <y ≦ 1, x <y) layer. The first wavelength may be in a range of 180 to 300 nm.

According to a third aspect of the present invention, there is provided a method for determining a quality of a semiconductor substrate using the inspection method according to the first aspect, wherein the semiconductor substrate is inspected using the inspection method, and the ratio I _YL1 A method for determining the quality of a semiconductor substrate, comprising: determining that the semiconductor substrate to be inspected is a defective product when / I _BE1 exceeds a predetermined value. Here, as the first crystal layer, a GaN layer can be exemplified, and as the second crystal layer, an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer can be exemplified, and the first wavelength. The range of 180 to 300 nm can be exemplified as the range of 0.1, and 0.1 can be exemplified as the predetermined value.

According to a fourth aspect of the present invention, there is provided a semiconductor substrate quality determination method using the above-described inspection method of the second embodiment, the step of inspecting the semiconductor substrate using the inspection method, and the ratio I _YL1 / I _BE1 and a ratio of one or more selected from the ratios I _YL2 / I _BE2 and a step of determining the semiconductor substrate to be inspected as a defective product when the ratio exceeds a predetermined value. A determination method is provided. Here, as the first crystal layer, a GaN layer can be exemplified, and as the second crystal layer, an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer can be exemplified, and the first wavelength. As the range, a range of 180 to 300 nm can be exemplified, and as the range of the second wavelength, a range exceeding 300 nm can be exemplified, and a predetermined value can be exemplified as 0.1.

In a fifth aspect of the present invention, a base substrate, a first crystal layer, and a second crystal layer are provided, and the base substrate, the first crystal layer, and the second crystal layer are the base substrate, the first crystal layer, and the first crystal layer. The second crystal layer is positioned in the order of the crystal layer and the second crystal layer, and the second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched with the first crystal layer to constitute the second crystal layer The bandwidth energy E _g2 of the crystal to be produced is larger than the bandwidth energy E _g1 of the crystal constituting the first crystal layer, and the first wavelength of the first crystal layer (however, the first wavelength is in the range of 180 to 300 nm). the light absorption coefficient alpha ₁ at a.), the ratio alpha ₂ / alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer is in the range of 0.5 to 1.0, A semiconductor substrate, wherein the second crystal layer is formed on the semiconductor substrate. Irradiating the first excitation light of the first wavelength from the side, to measure the photoluminescence by the first excitation light as the observation light, and the peak intensity I _BE1 of the band edge emission BE contained in the first observation light , when calculating the ratio _I YL1 _{/ I BE1} between the peak intensity _{I YL1} emitting YL appearing from the peak wavelength lambda _bE of the band edge emission bE to the long wavelength side, the ratio _I YL1 _{/ I BE1} 0.1 A semiconductor substrate is provided.

1 is a cross-sectional view of a semiconductor substrate 100. FIG. It is the figure which showed an example of PL emission spectrum of the semiconductor substrate 100 when the 1st crystal layer 112 is made into a GaN layer and the 2nd crystal layer 114 is made into an AlGaN layer. It is the graph which showed the detection depth at the time of carrying out PL measurement of the AlGaN layer using two types of light sources with which wavelengths differ as excitation light as a function of Al composition. It is the figure which showed typically the generation | occurrence | production position of the observation light (photoluminescence) in PL measurement. It is a SIMS measurement result about Experimental Examples 1-3, and shows the depth profile of a carbon atom. It is the graph which plotted the carbon concentration of the 2nd crystal layer 114 obtained by SIMS measurement, and the relationship of YL / BE. It is the graph which plotted the hole mobility about Experimental Examples 1-3 and Comparative Examples 1 and 2 with respect to YL / BE. 2 is a diagram showing a YL / BE ratio and a PL emission spectrum of Example 1. FIG. It is a figure which shows YL / BE ratio of Example 2, and PL emission spectrum. It is a figure which shows YL / BE ratio of Comparative Example 1, and PL emission spectrum.

  FIG. 1 is a cross-sectional view of a semiconductor substrate 100 used in the inspection method of the present embodiment. The semiconductor substrate 100 includes a base substrate 102, a reaction suppression layer 104, a buffer layer 106, and a device formation layer 108. The buffer layer 106 includes a two-layer stack 106c including a first layer 106a and a second layer 106b. The device formation layer 108 includes a first crystal layer 112 and a second crystal layer 114. The base substrate 102, the first crystal layer 112, and the second crystal layer 114 are located in the order of the base substrate 102, the first crystal layer 112, and the second crystal layer 114.

  The base substrate 102 is a support substrate that supports the reaction suppression layer 104, the buffer layer 106, and the device formation layer 108. The base substrate 102 is preferably a silicon substrate. By using a silicon substrate as the base substrate 102, the material price can be reduced and a semiconductor manufacturing apparatus used in a conventional silicon process can be used. Thereby, cost competitiveness can be improved. Furthermore, by using a silicon substrate as the base substrate 102, a large substrate having a diameter of 150 mm or more can be used inexpensively and industrially.

When the base substrate 102 is a silicon substrate, the reaction suppression layer 104 suppresses the reaction between silicon atoms contained in the silicon substrate and group III atoms contained in the buffer layer 106 and the like. When the nitride crystal layer on the reaction suppression layer 104 is a GaN-based semiconductor layer such as AlGaN or GaN, alloying of Ga atoms and silicon atoms contained in the GaN-based semiconductor layer can be prevented. . As a reaction inhibiting layer _{104, Al z Ga 1-z} N (0.9 ≦ z ≦ 1) can be mentioned, typically mention may be made of AlN layer. The reaction suppression layer 104 can protect the surface of the base substrate 102 and ensure the support of the upper layer. In addition, the reaction suppression layer 104 can form an initial nucleus of a crystal layer formed on the base substrate 102. The thickness of the reaction suppression layer 104 can be greater than or equal to 30 nm and less than or equal to 300 nm.

  The buffer layer 106 is located between the base substrate 102 and the device formation layer 108. The buffer layer 106 has a multilayer stacked structure in which a two-layer stack 106c including a first layer 106a and a second layer 106b is repeatedly stacked. A compressive stress is generated by such a multilayer stacked structure, and as a result, the buffer layer 106 functions as a stress generating layer that reduces the warpage of the entire semiconductor substrate 100. The buffer layer 106 also functions as an insulating layer that electrically insulates between the base substrate 102 and the device formation layer 108.

  The first layer 106a is made of a group III nitride crystal having a lattice constant a1 in the bulk crystal, and the second layer 106b is made of a group III nitride crystal having a lattice constant a2 (a1 <a2) in the bulk crystal. . The number of repetitions of the two-layer stack 106c can be set to 2 to 500, for example. By stacking a large number of the two-layer stack 106c, the compressive stress generated by the buffer layer 106 can be increased. Further, the magnitude of the compressive stress generated by the buffer layer 106 can be easily controlled by the number of stacked layers 106c. Furthermore, by increasing the number of the two-layer stack 106c, the withstand voltage can be further improved by the first layer 106a.

  In this embodiment, the buffer layer 106 having a configuration in which a plurality of two-layer stacks 106c are repeatedly stacked is illustrated, but the two-layer stack 106c may not be stacked repeatedly, and in this case, a single layer The two-layer stack 106 c constitutes the buffer layer 106. The buffer layer 106 may have a three-layer structure including a first crystal layer 106a and a second layer 106b and a third crystal layer having a lattice constant a3 (a2 <a3) in the bulk crystal. Alternatively, a graded crystal layer in which the lattice constant of the bulk crystal increases continuously or stepwise as it moves away from the vicinity of the base substrate 102 may be used. Furthermore, it is good also as a multilayer laminated structure in which the three-layer lamination | stacking or the graded crystal layer was laminated | stacked repeatedly.

Examples of the first layer 106a include Al _q Ga _1-q N (0.9 ≦ q ≦ 1), and examples of the second layer 106b include Al _p Ga _1-p N (0 ≦ p ≦ 0.3). The thickness of the first layer 106a can be 1 nm or more and 20 nm or less, preferably more than 5.0 nm and less than 20 nm. The thickness of the second layer 106b can be 5 nm to 300 nm, preferably 10 nm to 300 nm.

The device formation layer 108 includes a first crystal layer 112 and a second crystal layer 114, and is a crystal layer on which an arbitrary device such as a transistor or an LED (light emitting diode) can be formed. For example, a high electron mobility transistor (HEMT) using a two-dimensional electron gas (2DEG) formed at the heterointerface between the first crystal layer 112 and the second crystal layer 114 as a channel can be formed. The second crystal layer 114 is in contact with the first crystal layer 112 and lattice-matched or pseudo-lattice-matched to the first crystal layer 112, and the bandwidth energy E _g2 of the crystal constituting the second crystal layer 114 is the first crystal layer It is larger than the bandwidth energy E _{g1 of} the crystal constituting the layer 112.

The first crystal layer 112 is, for example, an Al _x Ga _1-x N (0 ≦ x <1) layer, and can be specifically exemplified by a GaN layer. The thickness of the first crystal layer 112 can be selected within a range of 200 to 2000 nm, and can be set to 800 nm, for example.

The second crystal layer 114 is, for example, an Al _y Ga _1-y N (0 <y ≦ 1, x <y) layer, specifically, Al _y Ga _1-y N (0.1 <y ≦ 0. 3) A layer, for example, Al _0.25 Ga _0.75 N can be exemplified. The thickness of the second crystal layer 114 can be selected in the range of 10 to 100 nm, and can be, for example, 25 nm.

The reaction suppression layer 104, the buffer layer 106, and the device formation layer 108 can be formed using a general MOCVD (Metal Organic Chemical Vapor Deposition) method. For example, when the layers formed by the MOCVD method are an AlN layer, an AlGaN layer, and a GaN layer, trimethylaluminum (Al (CH ₃ ) ₃ ) and trimethylgallium (Ga (CH ₃ ) ₃ ) are used as the group III source gas. Ammonia (NH ₃ ) can be used as the nitrogen source gas. The growth temperature can be selected in the range of 1100 to 1260 ° C., and the flow rate ratio V / III ratio of the group V source gas to the group III source gas can be selected in the range of 160 to 5000. The thickness of the layer to be formed can be controlled by, for example, calculating the growth time corresponding to the design thickness from the growth rate obtained in the preliminary experiment and by controlling the growth time.

As an inspection method of the semiconductor substrate 100 described above, two inspection methods will be described. The first inspection method is as follows. First, the first excitation light having the first wavelength is irradiated from the second crystal layer 114 side, and photoluminescence by the first excitation light is measured as the first observation light. Next, the ratio of the peak intensity I _BE1 of the band edge emission BE included in the first observation light to the peak intensity I _YL1 of the emission YL appearing on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE I _YL1 / I _BE1 is calculated and used as an inspection value. Here, the light absorption coefficient alpha ₁ in the first wavelength of the first crystal layer 112, the ratio alpha ₂ / alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer 114, 0.5 to 1 The first wavelength is selected to be in the range of .0.

The second inspection method is as follows. First, the first excitation light having the first wavelength is irradiated from the second crystal layer 114 side, the photoluminescence due to the first excitation light is measured as the first observation light, and from the first wavelength from the second crystal layer 114 side. The second excitation light having the second wavelength having a long wavelength is irradiated, and photoluminescence by the second excitation light is measured as the second observation light. Next, the ratio of the peak intensity I _BE1 of the band edge emission BE included in the first observation light to the peak intensity I _YL1 of the emission YL appearing on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE I _YL1 / I _BE1 is calculated, and the ratio between the peak intensity I _BE2 of the band edge emission BE included in the second observation light and the peak intensity I _YL2 of the emission YL that appears on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE I _YL2 / I _BE2 is calculated, and one or more values selected from the ratio I _YL1 / I _BE1 and the ratio I _YL2 / I _BE2 or a value calculated from the one or more values is used as the inspection value. Here, the light absorption coefficient alpha ₁ in the first wavelength of the first crystal layer 112, the ratio alpha ₂ / alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer 114, the first crystal layer 112 the light absorption coefficient beta ₁ at two wavelengths, selects the first wavelength and the second wavelength to be greater than the ratio beta _{2 /} beta ₁ of the light absorption coefficient beta ₂ at the second wavelength of the second crystal layer 114.

  The above two inspection methods will be described in more detail. FIG. 2 is a diagram showing an example of a PL emission spectrum of the semiconductor substrate 100 in which the first crystal layer 112 is a GaN layer and the second crystal layer 114 is an AlGaN layer. GaN band edge emission (BE) appears at peak A, and yellow luminescence (YL) appears at peak B on the longer wavelength side (low photon energy side) than peak A. The yellow luminescence (YL) of peak B is considered to be caused by crystal defects or impurities, and the value of the yellow luminescence intensity (YL / BE) normalized by the band edge emission intensity is the crystallinity (crystal defect or It can be used as an evaluation index for impurities and the like.

  FIG. 3 is a graph showing the detection depth as a function of the Al composition when the AlGaN layer is subjected to PL measurement using two types of light sources having different wavelengths as excitation light. In the He—Cd laser beam (emission wavelength: 325 nm) used in the prior art (Non-patent Document 1), the detection depth suddenly increases from the vicinity where the Al composition exceeds 0.15. This indicates that the AlGaN layer having an Al composition of more than 0.15 has little absorption of He—Cd laser light and does not perform sufficient excitation, so that PL measurement is difficult. On the other hand, when the fourth harmonic light of YAG laser (emission wavelength 266 nm) is used, the detection depth is constant at about 200 nm even when the Al composition exceeds 0.15, which is difficult to measure with He-Cd laser light. This shows that PL measurement of a simple AlGaN layer (Al composition is 0.15 or more) can be performed by using a YAG laser quadruple wave light.

  FIG. 4 is a diagram schematically showing the generation position of observation light (photoluminescence) in PL measurement. When He—Cd laser light is used as excitation light on the left side in the figure, YAG laser 4 is shown on the right side in the figure. A case where double wave light is used as excitation light is shown. When the He—Cd laser light is used as the excitation light, the He—Cd laser excitation light E1 is almost transparent to the second crystal layer 114, and thus passes through the second crystal layer 114 without absorption, and the first crystal layer 112. To be absorbed. Therefore, the observation light O1 by the He—Cd laser excitation light E1 is mainly generated in the first crystal layer 112. On the other hand, when YAG laser quadruple wave light is used as excitation light, YAG laser quadruple wave excitation light E2 is absorbed by second crystal layer 114 and second crystal layer 114, and is observed by YAG laser quadruple wave excitation light E2. The light O 2 is generated in both the second crystal layer 114 and the first crystal layer 112.

PL measurement is performed using excitation light (first excitation light) absorbed by the second crystal layer 114 such as YAG laser quadruple wave light, and the peak intensity I of the yellow luminescence light YL with respect to the peak intensity I _BE1 of the band edge emission BE. the ratio _I YL1 _{/ I BE1} of _YL1 calculates, by the inspection value this can be carried crystallinity evaluation of the device formation layer 108 including the AlGaN layer. As a result, the accuracy of the inspection / determination for the current collapse of the semiconductor substrate 100 can be increased. In this case, _{when one} of the light absorption coefficient alpha for the first crystal layer 112 at the wavelength (first wavelength) of the YAG laser fourth harmonic _light, the light absorption coefficient for the second crystal layer 114 at the same wavelength is alpha _2, alpha ₂ / Α ₁ is in the range of 0.5 to 1.0. This is because the absorption coefficient α ₁ of the first crystal layer 112 (GaN layer) at the excitation light wavelength (first wavelength) and the first crystal layer 112 when the YAG laser quadruple wave light is excitation light (first excitation light). absorption coefficient alpha ₂ of (AlGaN layer) is clearly substantially equal 3, seems to be towards the alpha ₁ is slightly large value. Therefore, α ₂ / α ₁ is a value close to 1, and is in the range of 0.5 to 1.0, preferably in the range of 0.7 to 0.95, and more preferably in the range of 0.8 to 0.9. It is considered appropriate.

In addition to the PL measurement using the first excitation light that is also absorbed by the second crystal layer 114, the PL measurement is also performed using the second excitation light having a wavelength longer than that of the first excitation light such as He-Cd laser light. The ratio I _YL1 / I _BE1 by the first excitation light and the ratio I _YL2 / I _BE2 by the second excitation light are calculated in the same manner as the first excitation light, and the ratio I _YL1 / I _BE1 and the ratio I _{YL2 are calculated.} One or more values selected from / I _BE2 or a value calculated from the one or more values can be used as the inspection value. Thereby, the crystallinity evaluation of the device forming layer 108 including the AlGaN layer can be performed, and the accuracy of inspection / determination for the current collapse of the semiconductor substrate 100 can be improved. In this case, alpha ₂ / alpha ₁ and similarly, can the ratio beta ₂ / beta ₁ is defined between the light absorption coefficient beta ₂ of the light absorption coefficient beta ₁ of the first crystal layer 112 in the second wavelength the second crystal layer 114 , Α ₂ / α ₁ can be greater than β ₂ / β ₁ . Assuming that the second wavelength is the wavelength of the He—Cd laser beam, the light absorption coefficient β ₂ for the second crystal layer 114 is very small as compared with the light absorption coefficient β ₁ for the first crystal layer 112, as is apparent from FIG. ₂ / α ₁ is considered to be larger than β ₂ / β ₁ . The value of alpha ₂ / alpha ₁ is larger than beta ₂ / beta _1, preferably alpha ₂ / alpha ₁ is beta ₂ / beta ₁ of 2 times or more, more preferably to more than three times.

  The first wavelength can be in the range of 180 to 300 nm, and the second wavelength can be in the wavelength range exceeding 300 nm.

(Example)
A Si wafer having a (111) plane as a main surface was used as the base substrate 102, and the reaction suppression layer 104, the buffer layer 106, and the device formation layer 108 were formed. As the reaction suppression layer 104, an AlN layer having a designed thickness of 150 to 160 nm was formed. As the buffer layer 106, an AlN / AlGaN stacked structure (two-layer stack 106c) composed of an AlN layer (first layer 106a) having a design thickness of 5 nm and an AlGaN layer (second layer 106b) having a design thickness of 28 nm is repeatedly stacked. Formed. As the device formation layer 108, a GaN layer (first crystal layer 112) having a design thickness of 800 nm and an AlGaN layer (second crystal layer 114) having a design thickness of 25 nm were formed. The Al composition of the AlGaN layer (second crystal layer 114) was 0.25.

  The MOCVD method is used to form the reaction suppression layer 104, the buffer layer 106, and the device forming layer 108 (AlN layer, AlGaN layer, and GaN layer), trimethylaluminum and trimethylgallium are used as the group III source gas, and ammonia is used as the nitrogen source gas. Was used. The growth temperature was selected in the range of 1100 to 1260 ° C., and the flow rate ratio V / III ratio of the group V source gas to the group III source gas was selected in the range of 160 to 3700. Since the thickness of each layer is controlled by the growth time calculated from the growth rate obtained in the preliminary experiment, the actual thickness and the design thickness of each layer are different.

Experimental Examples 1 to 3 and Comparative Examples 1 and 2 were prepared by changing the V / III ratio during the growth of the Al _0.25 Ga _0.75 N layer as the second crystal layer 114. The V / III ratio in Experimental Example 1 is 3700, the V / III ratio in Experimental Example 2 is 2500, the V / III ratio in Experimental Example 3 is 620, the V / III ratio in Comparative Example 1 is 600, and the V / III ratio in Comparative Example 2 is V / III The III ratio was 588.

For each of Experimental Examples 1 to 3 and Comparative Examples 1 and 2, PL measurement using YAG laser quadruple wave light as excitation light was performed, and peak intensity I _BE1 of band edge emission BE and peak wavelength λ _BE of band edge emission BE were measured. The ratio I _YL1 / I _BE1 (YL / BE) with the peak intensity I _YL1 of the luminescence (yellow luminescence) YL appearing on the longer wavelength side was calculated. In addition, the hole mobility was measured for each of Experimental Examples 1 to 3 and Comparative Examples 1 and 2. Furthermore, SIMS (Secondary Ion Mass Spectrometry) depth measurement over a part of the second crystal layer 114 and the first crystal layer 112 was performed for Experimental Examples 1 to 3. Table 1 shows the measurement results of the YL / BE value and the hole mobility.

  FIG. 5 shows SIMS measurement results for Experimental Examples 1 to 3, and shows the depth profile of carbon atoms. FIG. 6 is a graph plotting the relationship between the carbon concentration of the second crystal layer 114 and YL / BE obtained by SIMS measurement. FIG. 7 is a graph in which the hole mobility for Experimental Examples 1 to 3 and Comparative Examples 1 and 2 is plotted against YL / BE.

  From the results shown in Table 1 and FIGS. 5 to 7, it can be seen that as the V / III ratio decreases, the carbon concentration in the AlGaN layer (second crystal layer 114) increases and the YL / BE ratio increases. It can also be seen that the hole mobility gradually decreases until the YL / BE ratio reaches 0.1, and when it exceeds 0.1, the hole mobility decreases rapidly. That is, the hole mobility changes critically when the YL / BE ratio is 0.1, and the hole mobility rapidly deteriorates when the YL / BE ratio is 0.1 or more.

From the above results, the semiconductor substrate is inspected by using the above inspection method, and the inspection target semiconductor substrate is determined as the ratio I _YL1 / I _BE1 (YL / BE ratio) exceeds a predetermined value (for example, 0.1). It can be determined as a defective product.

Of the two inspection methods described above, the embodiment has described the embodiment of the first inspection method and the defective product determination method. However, the second inspection method may also be used to determine the defective product. Is possible. For example, when a semiconductor substrate is inspected using the second inspection method and one or more ratios selected from the ratio I _YL1 / I _BE1 and the ratio I _YL2 / I _BE2 exceed a predetermined value, the inspection target This semiconductor substrate can be determined as a defective product.

  8 to 10 are diagrams showing YL / BE ratios and PL emission spectra of Example 1, Example 2, and Comparative Example 1, respectively. 8 to 10, the upper portion shows the YL / BE ratio at each measurement position when the measurement position is changed from the substrate center to the outer peripheral direction, that is, the in-plane distribution of the YL / BE ratio. The plots marked with “Δ” are when He—Cd laser light (wavelength 325 nm) is used as excitation light, and the plots with “♦” are those when YAG laser quadruple wave light (wavelength 266 nm) is used as excitation light. In the PL emission spectrum shown in the lower part of each of FIGS. 8 to 10, an emission spectrum by He—Cd laser light (wavelength 325 nm) and an emission spectrum by YAG laser quadruple wave light (wavelength 266 nm) are shown simultaneously.

  In Examples 1 and 2, it can be seen that the YL / BE ratio is low and the in-plane distribution is almost uniform. On the other hand, in Comparative Example 1, the YL / BE ratio when the He—Cd laser beam is used as the excitation light is low and the in-plane distribution is substantially uniform, but the YL / BE ratio when the YAG laser quadruple wave light is used as the excitation light. The BE ratio has a large value and the in-plane distribution is not uniform. In the prior art using He—Cd laser light as excitation light, Comparative Example 1 is determined as a non-defective product, but in this example, YAG laser quadruple wave light is used as excitation light, so Comparative Example 1 is considered as a defective product. It is determined that the accuracy of the inspection determination is high. In the PL emission spectrum in Comparative Example 1 of FIG. 10, the yellow luminescence when the YAG laser quadruple wave light is used as the excitation light is shifted to the high energy side (C portion in the figure). This is presumably because the YAG laser quadruple wave light is absorbed by the AlGaN layer (second crystal layer 114), and yellow luminescence derived from the AlGaN layer is observed.

  As described above, according to the inspection method and quality determination method of the present embodiment, yellow luminescence derived from the AlGaN layer (second crystal layer 114) is observed, and it is possible to perform inspection and quality determination with high accuracy. Become.

Although the invention has been described as a semiconductor substrate inspection method or quality determination method, the invention can also be grasped as a semiconductor substrate. That is, the present invention includes the base substrate 102, the first crystal layer 112, and the second crystal layer 114, and the base substrate 102, the first crystal layer 112, and the second crystal layer 114 are formed of the base substrate 102, the first crystal layer 114, and the first crystal layer. 112 and the second crystal layer 114 are arranged in this order, and the second crystal layer 114 is in contact with the first crystal layer 112 and lattice-matched or pseudo-lattice-matched with the first crystal layer 112 to form the second crystal layer 114. The bandwidth energy E _g2 of the crystal is larger than the bandwidth energy E _g1 of the crystal constituting the first crystal layer 112, and the first wavelength of the first crystal layer 112 (however, the first wavelength is in the range of 180 nm to 300 nm). The ratio α ₂ / α ₁ of the light absorption coefficient α ₁ of the second crystal layer 114 and the light absorption coefficient α ₂ of the second crystal layer 114 at the first wavelength is in the range of 0.5 to 1.0. So The semiconductor substrate is irradiated with the first excitation light having the first wavelength from the second crystal layer 114 side, the photoluminescence due to the first excitation light is measured as the first observation light, and the band edge included in the first observation light is measured. when the peak intensity _{I BE1} emitting bE, and calculating the ratio _I YL1 _{/ I BE1} between the peak intensity _{I YL1} emitting YL appearing from the peak wavelength lambda _bE band edge emission bE to the long wavelength side, the ratio _{I YL1} / It can be grasped as a semiconductor substrate in which I _BE1 is 0.1.

  DESCRIPTION OF SYMBOLS 100 ... Semiconductor substrate, 102 ... Base substrate, 104 ... Reaction suppression layer, 106 ... Buffer layer, 106a ... First layer, 106b ... Second layer, 106c ... Two-layer lamination, 108 ... Device formation layer, 112 ... First crystal Layer, 114 ... second crystal layer.

Claims (10)

A base substrate, a first crystal layer and a second crystal layer;
The base substrate, the first crystal layer, and the second crystal layer are positioned in the order of the base substrate, the first crystal layer, and the second crystal layer,
The second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched to the first crystal layer;
A method for inspecting a semiconductor substrate, wherein a bandwidth energy E _g2 of a crystal constituting the second crystal layer is larger than a bandwidth energy E _g1 of a crystal constituting the first crystal layer,
Irradiating a first excitation light having a first wavelength from the second crystal layer side, and measuring photoluminescence by the first excitation light as a first observation light;
The ratio I _YL1 / I between the peak intensity I _BE1 of the band edge emission BE included in the first observation light and the peak intensity I _YL1 of the emission YL that appears on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE. Calculating _BE1 ;
And using the ratio I _YL1 / I _BE1 as an inspection value,
Wherein the light absorption coefficient alpha ₁ in the first wavelength of the first crystal layer, the ratio alpha _{2 /} alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer is 0.5 to 1. A method for inspecting a semiconductor substrate that is in a range of 0. A base substrate, a first crystal layer and a second crystal layer;
The base substrate, the first crystal layer, and the second crystal layer are positioned in the order of the base substrate, the first crystal layer, and the second crystal layer,
The second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched to the first crystal layer;
A method for inspecting a semiconductor substrate, wherein a bandwidth energy E _g2 of a crystal constituting the second crystal layer is larger than a bandwidth energy E _g1 of a crystal constituting the first crystal layer,
Irradiating a first excitation light having a first wavelength from the second crystal layer side, and measuring photoluminescence by the first excitation light as a first observation light;
Irradiating a second excitation light having a second wavelength longer than the first wavelength from the second crystal layer side, and measuring photoluminescence by the second excitation light as a second observation light;
The ratio I _YL1 / I between the peak intensity I _BE1 of the band edge emission BE included in the first observation light and the peak intensity I _YL1 of the emission YL that appears on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE. Calculating _BE1 ;
The ratio I _YL2 / I between the peak intensity I _BE2 of the band edge emission BE included in the second observation light and the peak intensity I _YL2 of the emission YL that appears on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE. Calculating _BE2 ;
Using one or more values selected from the ratio I _YL1 / I _BE1 and the ratio I _YL2 / I _BE2 or a value calculated from the one or more values as a test value,
The light absorption coefficient alpha ₁ in the first wavelength of the first crystal layer, the ratio alpha _{2 /} alpha ₁ of the light absorption coefficient alpha ₂ in the first wavelength of the second crystal layer, of the first crystalline layer A method for inspecting a semiconductor substrate, wherein the ratio of the light absorption coefficient β ₁ at the second wavelength and the light absorption coefficient β _{2 at} the second wavelength of the second crystal layer is greater than β ₂ / β ₁ . The first crystal layer is an Al _x Ga _1-x N (0 ≦ x <1) layer;
The method for inspecting a semiconductor substrate according to claim 1, wherein the second crystal layer is an Al _y Ga _1-y N (0 <y ≦ 1, x <y) layer. The first crystal layer is a GaN layer;
The semiconductor substrate inspection method according to claim 3, wherein the second crystal layer is an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer. The semiconductor substrate inspection method according to claim 4, wherein the first wavelength is in a range of 180 to 300 nm. A method for determining the quality of a semiconductor substrate using the inspection method according to claim 1,
Inspecting the semiconductor substrate using the inspection method;
When the ratio I _YL1 / I _BE1 exceeds a predetermined value, determining the semiconductor substrate to be inspected as a defective product;
A method for determining the quality of a semiconductor substrate comprising: The first crystal layer is a GaN layer;
The second crystal layer is an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer, and the first wavelength is in a range of 180 to 300 nm,
The semiconductor substrate quality determination method according to claim 6, wherein the predetermined value is 0.1. A method for determining the quality of a semiconductor substrate using the inspection method according to claim 2,
Inspecting the semiconductor substrate using the inspection method;
_{Determining the} semiconductor substrate to be inspected as a defective product when one or more ratios selected from the ratio I _YL1 / I _BE1 and the ratio I _YL2 / I _BE2 exceed a predetermined value;
A method for determining the quality of a semiconductor substrate comprising: The first crystal layer is a GaN layer;
The second crystal layer is an Al _y Ga _1-y N (0.1 <y ≦ 0.3) layer, and the first wavelength is in a range of 180 to 300 nm,
The second wavelength exceeds 300 nm;
The semiconductor substrate quality determination method according to claim 8, wherein the predetermined value is 0.1. A base substrate, a first crystal layer and a second crystal layer;
The base substrate, the first crystal layer, and the second crystal layer are positioned in the order of the base substrate, the first crystal layer, and the second crystal layer,
The second crystal layer is in contact with the first crystal layer and lattice-matched or pseudo-lattice-matched to the first crystal layer;
The bandwidth energy E _g2 of the crystal constituting the second crystal layer is larger than the bandwidth energy E _{g1 of} the crystal constituting the first crystal layer,
Wherein the first wavelength of the first crystal layer (where the first wavelength is in the range of 180 to 300 nm.) And the light absorption coefficient alpha ₁ in the optical absorption coefficient at the first wavelength of the second crystal layer alpha ₂ The ratio α ₂ / α ₁ to the semiconductor substrate is in the range of 0.5 to 1.0,
Irradiating the semiconductor substrate with first excitation light of the first wavelength from the second crystal layer side, and measuring photoluminescence by the first excitation light as first observation light;
The ratio I _YL1 / I between the peak intensity I _BE1 of the band edge emission BE included in the first observation light and the peak intensity I _YL1 of the emission YL that appears on the longer wavelength side than the peak wavelength λ _BE of the band edge emission BE. _{When BE1} is calculated,
A semiconductor substrate in which the ratio I _YL1 / I _BE1 is 0.1.