JP5579206B2 - Defect determination apparatus and method - Google Patents

Description

  The present invention relates to a defect discriminating apparatus and a method for discriminating defects in a semiconductor element using a semiconductor, particularly silicon carbide.

  For example, in manufacturing a semiconductor element using a silicon carbide single crystal substrate, it is extremely important to evaluate the quality of the substrate. This is because the quality of the substrate affects the operation accuracy of a semiconductor element manufactured using the substrate and deteriorates its electrical characteristics. When considering manufacturing a semiconductor element using a substrate whose quality has been evaluated, it is assumed that the quality evaluation is performed non-destructively.

  There are several methods for performing non-destructive evaluation of the quality of a substrate. Among them, a photoluminescence (PL) method is widely used.

  Photoluminescence (PL) is emission specific to a crystal, which is emitted when a crystal is irradiated with light having energy equal to or higher than the band gap of the crystal. In a crystal irradiated with light having energy higher than the band gap of the crystal, electron-hole pairs are excited and recombined after a certain time. There are a plurality of recombination processes, and light emission (PL) reflects these processes.

  Since the recombination process greatly depends on the presence or absence of crystal defects or the like, the quality of the crystal, that is, the quality of the substrate can be evaluated by evaluating PL. Also, it is possible to grasp the three-dimensional distribution of crystal defects in the substrate by performing PL mapping measurement that displays PL at a specific emission wavelength by performing PL measurement over the entire area of the substrate surface (Patent Document). 1).

  In silicon carbide crystals, there are point defects such as carbon vacancies and mixed impurity atoms, linear defects such as threading screw dislocations, threading edge dislocations, dislocations in the basal plane, and stacking faults that are planar defects. There is a kind. The stacking faults, which are planar defects, include defects formed with a characteristic surface form on the surface of the epitaxial layer on a slightly inclined substrate having a so-called off angle, such as carrot defects and triangular defects.

  Many stacking faults, which are planar defects, emit light at a specific wavelength during PL measurement. By performing PL mapping measurement on the entire substrate using the specific wavelength, the two-dimensional distribution of stacking faults can be clarified. Can be caught.

JP 2006-147848 A

  However, the stacking faults include those that do not adversely affect the operation of the semiconductor element (hereinafter referred to as defect A) and those that adversely affect the operation of the semiconductor element (hereinafter referred to as “defect A”) despite the similar emission wavelength in PL measurement. , Defect B). Examples of adverse effects on the operation of the semiconductor element, that is, deterioration of the operation of the semiconductor element include that the electric signal cannot be sent correctly, the switching cycle of the output electric signal is delayed, and a larger current flows than expected. For example, there is a decrease in electrical characteristics, for example, causing a current leak phenomenon (a phenomenon in which a current flows in a state where a current should not flow).

  Since the defect A and the defect B are displayed as similar images in the normal PL mapping measurement over the entire substrate, they cannot be distinguished by the method shown in Patent Document 1. Therefore, in order to determine in advance whether the operation of the semiconductor element to be manufactured is good or bad, a technique for determining these has been required.

  The present invention has been made to solve the above-described problems, and provides a defect determination apparatus and method that can appropriately determine crystal defects and determine in advance whether the operation of a semiconductor element is good or bad. The purpose is to provide.

A defect determination apparatus according to the present invention performs photoluminescence measurement along a step flow growth direction of a triangular defect formed in a triangular shape in plan view on a surface of a silicon carbide semiconductor substrate having an off angle, and emits light of a specific wavelength. A light detection unit that detects a line profile; and a determination unit that determines a type of the triangular defect based on the detected light emission line profile , wherein the determination unit determines a maximum emission intensity from the light emission line profile. And a first half-value point and a second half-value point that are present between the maximum point and the emission intensity is half of the maximum point, and the maximum point is the first half-point and the second half-value based on whether read at a position close to any point, it characterized that you identify the type of the triangular defects.

According to the defect determination method of the present invention, (a) on the surface of a silicon carbide semiconductor substrate having an off angle, a photoluminescence measurement is performed along a step flow growth direction of a triangular defect formed in a triangular shape in plan view. A step of detecting a light emission line profile of a wavelength; and (b) determining a type of the triangular defect based on the detected light emission line profile , wherein the step (b) includes (b-1) the step Reading from a light emission line profile a maximum point of emission intensity and a first half-value point and a second half-value point that are present across the maximum point and at which the emission intensity is half of the maximum point; 2) based on whether the maximum point is read at a position close to either of the first half point and the second half point, and a step of determining the type of the triangular defects Rukoto And features.

  According to the defect discriminating apparatus of the present invention, the type of the triangular defect is discriminated in the discriminating unit based on the light emission line profile, and it is discriminated whether or not the type of the semiconductor element is deteriorated. The quality of the operation can be determined in advance.

  According to the defect determination method of the present invention, it is determined whether or not the type of the semiconductor element is deteriorated by the step of determining the type of the triangular defect based on the light emission line profile, and the operation of the semiconductor element is determined as good or bad. Can be determined in advance.

It is the schematic which shows the structural example of a defect discrimination device. It is a schematic diagram which shows the software structure of a defect discrimination device. It is a flowchart which shows a defect discrimination | determination process. It is a schematic diagram which shows the measurement position of PL line profile. It is the schematic diagram which looked at the triangular defect of the silicon carbide substrate surface from right above. It is a figure which shows typically the cross-sectional structure of the defect A and the defect B. FIG. It is a figure which shows the PL line profile of the defect A and the defect B.

<Embodiment 1>
<Configuration>
Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram of the defect determination apparatus according to the present embodiment. As shown in FIG. 1, the defect discriminating apparatus includes a mirror 12 that changes the path of the excitation light 11 (Hd—Cd laser or the like) emitted from the excitation light source 10, and further changes the path of the excitation light 11. A half mirror 13 that transmits light, an objective lens 14 that condenses the excitation light 11 on the sample 15, a spectroscope 17 that is a diffraction grating that splits the luminescence light 16 that has passed through the half mirror 13, and the luminescence light 16. A photodetector 18 which is a CCD camera or the like for detecting the information of the luminescent light 16 and a computer 19 for storing the information of the luminescent light 16 as a spectrum.

  In particular, when a system that collects the luminescence light 16 from the sample 15 can be formed outside, a photodetector 18 that detects the luminescence light 16 and a computer 19 that stores information of the luminescence light 16 as a spectrum are provided. It only has to be.

  The excitation light 11 travels from the excitation light source 10 toward the mirror 12. Next, the excitation light 11 whose course has been changed by the mirror 12 is further changed by the half mirror 13 and travels toward the objective lens 14.

  Excitation light 11 collected by objective lens 14 is applied to the surface of sample 15 (such as an epitaxial layer of a silicon carbide substrate having an off angle). The sample 15 is disposed on the XY movable stage 20. At this time, the excitation light 11 is focused on the surface of the sample 15 by the objective lens 14.

  The luminescence light 16 emitted from the sample 15 by applying the excitation light 11 is collected by the objective lens 14 and passes through the half mirror 13.

  The luminescence light 16 transmitted through the half mirror 13 is split by the spectroscope 17 and travels toward the photodetector 18.

  Information on the luminescence light 16 obtained in the photodetector 18 is stored as a spectrum (PL spectrum) by the computer 19. In this way, a PL spectrum at one point on the sample 15 is acquired. When measuring a wide range of luminescence light 16 such as the entire substrate, the XY movable stage 20 controlled by the computer 19 can be moved for each point measurement.

  FIG. 2 is a diagram schematically showing a software configuration in the computer 19 of FIG. As shown in FIG. 2, the computer 19 receives the output from the photodetector 18, analyzes the data received by the receiving unit 100, determines the type of crystal defect, and the crystal defect A storage unit 102 that stores a spectrum, a position, and the like, and a control unit 103 that controls a moving operation of the XY movable stage 20 are provided.

<Operation>
Next, the defect determination operation will be described with reference to FIG.

  FIG. 3 is a flowchart showing the process of defect determination operation.

  As shown in FIG. 3, first, in step S <b> 1, the movement of the XY movable stage 20 is controlled by the control unit 103 of the computer 19, and PL mapping measurement is performed on, for example, the entire region of the epitaxial layer surface of the silicon carbide substrate. The PL mapping measurement is performed on the entire surface of the substrate by applying the excitation light 11 to the surface of the sample 15 and changing the position of the XY movable stage 20.

  The luminescence light 16 emitted when the excitation light 11 is applied to the surface of the sample 15 passes through the half mirror 13 and is split by the spectroscope 17. The split luminescence light 16 is detected as spectral data by the photodetector 18 and is stored in the storage unit 102 of the computer 19 together with its position information.

  Next, in step S <b> 2, for example, a triangular defect that emits light near 540 nm is detected by the photodetector 18, and the defect position is stored in the storage unit 102 of the computer 19. In addition, the wavelength of the luminescence light 16 to be detected is not limited to a single wavelength.

  In step S3, the control unit 103 of the computer 19 moves the XY movable stage 20 to the defect position where the triangular defect is detected.

  Next, in step S4, as shown in FIG. 4, the target triangular defect 1 is a defect A (a crystal defect that does not degrade the operation of the semiconductor element) or a defect B (a crystal defect that degrades the operation of the semiconductor element). Is detected by the photodetector 18 on the straight line 40 along the step flow growth direction 4 with respect to the triangular defect 1. The PL measurement is performed, for example, for an emission wavelength near 540 nm. About 10 measurement points from the defect start point 2 to the defect end point 3 are desirable. The step flow growth direction refers to a direction on a substrate where an epitaxial layer such as a slightly inclined substrate undergoes step flow growth. Moreover, what showed the change of the emitted light intensity measured in multiple points along the step flow growth direction is made into PL line profile (light emitting line profile).

  Here, the inventor observed a plurality of triangular defects existing in the epitaxial layer of the 4H type silicon carbide substrate with a transmission electron microscope, and found the difference between the defect A and the defect B.

  It is known that the triangular defect 1 has a triangular surface form on the surface of the epitaxial layer as shown in FIG. 5, and further includes a 3C-type silicon carbide layer (3C layer) inside the epitaxial layer 6 as shown in FIG. ing. This 3C layer has a lower dielectric breakdown electric field (weak to high voltage) than the 4H type layer that should originally constitute the epitaxial layer, and when the voltage is applied in the opposite direction to the flow of current, the 3C layer leaks current. (That is, leakage current is generated due to a decrease in breakdown voltage).

  According to the inventor's investigation, a thin 3C layer 9 having a maximum thickness of about 12 nm exists along the off angle 7 from the point on the silicon carbide substrate 5 to the surface of the epitaxial layer 6 in the defect A. (See FIG. 6 (a)). Here, in the defect A, a surface on which the 3C layer 9 exists is defined as a base surface 8.

  On the other hand, inside the defect B, as shown in FIG. 6B, the entire region on the surface side of the epitaxial layer 6 from the basal plane 8 in the defect B is a 3C layer 90 (3C polytype). It was revealed. Therefore, it can be seen that the defect B is more likely to contribute to a decrease in the breakdown voltage than the defect A, and easily affects the operation of the semiconductor device.

  As described above, those classified as defects A have a thin 3C layer having a thickness of about 12 nm at the maximum, as shown in FIG. Moreover, as for the thing classified into the defect B, as shown in FIG.6 (b), the whole area | region above the base face 8 is 3C polytype.

  Next, a PL line profile (light emission line profile) in the vicinity of a wavelength of 540 nm is acquired by the photodetector 18. When a PL line profile at a light emission wavelength near 540 nm is obtained on a straight line along the step flow growth direction of the target triangular defect, it is classified into the profile shapes as shown in FIGS. 7 (a) and 7 (b). Can do.

  FIGS. 7A and 7B are PL line profiles of triangular defects present in an epitaxial layer 6 having a thickness of 10 μm formed on a 4H-silicon carbide (0001) substrate having a 4 ° off-angle. is there. The vertical axis represents emission intensity (au), and the horizontal axis represents distance (μm) from the reference position. The reference position here is a position further outside the defect starting point 2.

  These PL line profiles are obtained in a state in which, for example, a He—Cd laser (325 nm) is used as an excitation light source, and the excitation light 11 is focused on the surface of the epitaxial layer 6 using the objective lens 14. The penetration length of the He—Cd laser into silicon carbide is about 10 μm, and light emission caused by the 3C layer immediately below the defect start point 2 on the surface of the epitaxial layer 6 is also captured. Since it is attenuated in the process until it reaches, the detected emission intensity decreases.

  That is, the change in the emission intensity of the specific wavelength acquired along the step flow growth direction includes information on the position and amount of the 3C layer in the depth direction of the sample 15. Therefore, the discriminating unit 101 of the computer 19 can discriminate whether it is the defect A or the defect B based on the emission intensity change of the specific wavelength acquired along the step flow growth direction (step S5). A specific discrimination method will be described below.

  A point a shown in FIG. 7 is a maximum point of emission intensity at a wavelength of 540 nm as a specific wavelength, and points b and c are both half-value points at which the emission intensity is half of the maximum value. It is assumed that the half-value point b (first half-value point) is closer to the defect start point 2 and the half-value point c (second half-value point) is closer to the defect end point 3.

  Comparing FIG. 7 (a) and FIG. 7 (b), the maximum point a is closer to the half-value point c side in the defect A than the intermediate point between the half-value point b and the half-value point c. In B, it exists in the half-value point b side rather than the intermediate point of the half-value point b and the half-value point c. The difference in the PL line profile shape occurs for the following reason.

  In the case of the defect A, as shown in FIG. 6A, the thin 3C layer 9 gradually approaches the surface of the epitaxial layer 6 along the 4 ° off-angle in the section from the defect start point 2 to the defect end point 3. It becomes. That is, since the layer emitting light at a wavelength of 540 nm gradually approaches the sample surface as it proceeds in the step flow growth direction, the effect of attenuation due to the depth distance becomes moderate, and the light emission intensity increases. Therefore, the light emission intensity gradually increases between the half-value point b and the maximum point a in FIG.

  On the other hand, in the vicinity of the defect end point 3, the 3C layer 9 that emits light at a wavelength of 540 nm rapidly decreases as it proceeds in the step flow growth direction, and finally disappears. Therefore, the maximum point a in FIG. Between the half-value point c, the emission intensity at 540 nm rapidly decreases.

  In the case of the defect B, as shown in FIG. 6B, the width of the 3C layer 90 in the depth direction suddenly increases from the vicinity of the defect start point 2, and the PL measurement is performed along the step flow growth direction. The emission intensity at 540 nm also increases accordingly. Therefore, between the half-value point b and the maximum point a in FIG. 7B, the rise of the PL line profile becomes steep, and the emission intensity increases rapidly.

  On the other hand, when proceeding in the direction of step flow growth toward the defect end point 3, the 3C layer 90 emitting light at a wavelength of 540 nm gradually decreases, but the basal plane 8 of the 3C layer 90 approaches the sample surface, and thus emits light as a whole. The strength decreases gradually. Accordingly, the emission intensity gradually decreases between the maximum point a and the half-value point c in FIG. 7B.

  The difference in the acquired PL line profile shape is determined by the determination unit 101 as follows, for example.

  The distance between the half-value point b and the maximum point a is d1, and the distance between the maximum point a and the half-value point c is d2. When these ratios d2 / d1 are less than 1, the maximum point a of the emission intensity exists between the half-value point b and the midpoint between the half-value point b and the half-value point c, and d2 / d1 is 1 or more. In this case, the local maximum point a exists between the intermediate point and the half-value point c. That is, when d2 / d1 is less than 1, the maximum point a exists at a position close to the half-value point b, and when d2 / d1 is 1 or more, the maximum point a exists at a position close to the half-value point c. Will do.

  Therefore, the defect A and the defect B can be discriminated by obtaining the value of d2 / d1. In the defect A shown in FIG. 7, d2 / d1 = 0.45, which is less than 1, and in the defect B, d2 / d1 = 2.53, which is 1 or more.

  As described above, the PL line profile along the step flow growth direction is acquired for the target triangular defect, and the change in emission intensity at 540 nm, that is, the position where the emission intensity is at the maximum point and the emission intensity is at the maximum point. The defect A and the defect B can be discriminated from the relationship with the position of the half-value point that is half. However, the method for determining the defect A and the defect B is not limited to the method. The determined crystal defect position on the substrate is stored in the storage unit 102 of the computer 19.

  Next, in step S <b> 6, the computer 19 determines whether any other triangular defect is detected by the photodetector 18. If there is another triangular defect, the control unit 103 moves the XY movable stage 20 to the next target defect position, similarly measures the PL line profile, and the discrimination unit 101 similarly determines the crystal defect. To do.

  When the discrimination process for all the triangular defects is completed, the crystal defect discrimination process ends. Since the position of the crystal defect is stored in the storage unit 102 of the computer 19, only the semiconductor element manufactured at the position where the defect B is detected can be quickly excluded.

  By performing the above processing, it is possible to eliminate defective elements in advance without measuring the electrical characteristics of each semiconductor element.

<Modification>
In FIG. 1, the light detector 18 is provided separately from the computer 19, but a case in which the light detector 18 includes a computer is also possible.

  Further, FIG. 3 shows the case where the crystal defect determination process for the entire substrate is performed, but the defect determination process may be performed for a part of the substrate.

  In the above embodiment, the crystal defects of the 3C polytype that emits light at 540 nm are shown as an example, but the present invention can be similarly applied to 2H, 6H, or other polytypes. Further, the substrate is not limited to the 4H type (4H polytype).

  As a method for detecting a target crystal defect from the entire substrate before acquiring the PL line profile, for example, PL mapping measurement as in Patent Document 1 may be used.

<Effect>
According to the embodiment of the present invention, in the defect determination apparatus, PL along the step flow growth direction 4 of the triangular defect 1 formed in a triangular shape in plan view on the surface of the silicon carbide substrate 5 having an off angle. A photodetector 18 that performs measurement and detects a PL line profile (light emission line profile) of a specific wavelength, and a determination unit 101 that determines the type of the triangular defect 1 based on the detected PL line profile.

  According to such a defect discriminating apparatus, the type of the triangular defect is discriminated by the discriminating unit 101 based on the light emission line profile, and it is discriminated whether or not the type is a type (defect B) that degrades the operation of the semiconductor element. The quality of the operation of the semiconductor element can be determined in advance.

  Further, by storing the position coordinates of crystal defects on the surface of silicon carbide substrate 5 in storage unit 102, it is possible to eliminate a semiconductor element manufactured at the corresponding position as a defective product. By processing in this way, defective elements can be excluded without conducting an energization test or the like, and the time for quality evaluation of semiconductor elements can be shortened.

  Further, according to the embodiment of the present invention, in the defect determination apparatus, the determination unit 101 exists from the PL line profile (light emission line profile) with the maximum point a of the emission intensity and the maximum point a interposed therebetween. The half-value point b as the first half-value point and the half-value point c as the second half-value point at which the light emission intensity is half of the maximum point a are read, and the maximum point a is close to either the half-value point b or the half-value point c. The type of triangular defect 1 is determined based on whether it is read.

  According to such a defect determination device, when the half-value point b is the defect start point 2 side and the half-value point c is the defect end point 3 side, the distance d1 between the maximum point a and the half-value point b, the maximum point a, For example, when d2 / d1, which is the ratio to the distance d2 from the half-value point c, is less than 1, it can be determined as a defect A, and when it is 1 or more, it can be determined as a defect B. Therefore, it is possible to accurately determine the defect A that degrades the operation of the semiconductor element and the defect B that does not degrade the operation of the semiconductor element, and determine in advance whether the operation of the semiconductor element is good or bad.

  Further, according to the embodiment of the present invention, in the defect determination apparatus, the determination unit 101 is a type in which the triangular defect 1 is a type that reduces the electrical characteristics of a semiconductor element manufactured using the silicon carbide substrate 5. It is determined whether or not.

  According to such a defect discriminating apparatus, it is possible to discriminate a crystal defect (defect B) that deteriorates the electrical characteristics of the semiconductor element, which cannot be discriminated from the surface form or normal PL mapping measurement, and the crystal defect The portion of the silicon carbide substrate 5 where is located can be removed, and a semiconductor element that operates properly can be efficiently manufactured.

  Further, according to the embodiment of the present invention, in the defect determination device, the photodetector 18 detects a single wavelength PL line profile (light emission line profile) of the triangular defect 1.

  According to such a defect discriminating apparatus, it is possible to obtain a PL line profile including information in the depth direction of a crystal defect without performing PL measurement using a plurality of excitation lights 11, and the crystal quality evaluation time Can be shortened.

  It should be noted that the present invention can be modified or omitted in any constituent elements in the present embodiment within the scope of the invention.

  DESCRIPTION OF SYMBOLS 1 Triangular defect, 2 Defect start point, 3 Defect end point, 4 Step flow growth direction, 5 Silicon carbide substrate, 6 Epitaxial layer, 7 Off angle, 8 Base surface, 9,90 3C layer, 10 Excitation light source, 11 Excitation light, 12 Mirror, 13 Half mirror, 14 Objective lens, 15 Sample, 16 Luminescence light, 17 Spectrometer, 18 Photo detector, 19 Computer, 20 XY movable stage, 40 Straight line, 100 Reception unit, 101 Discriminating unit, 102 Storage unit, 103 Control unit.

Claims (8)

A photodetection unit that performs photoluminescence measurement along a step flow growth direction of a triangular defect formed in a triangular shape in plan view on the surface of a silicon carbide semiconductor substrate having an off angle, and detects a light emission line profile of a specific wavelength When,
A determination unit that determines the type of the triangular defect based on the detected light emission line profile ;
The discriminating unit reads from the light emission line profile a maximum point of light emission intensity and a first half-value point and a second half-value point that exist between the maximum point and at which the light emission intensity is half of the maximum point. ,
Based on whether the maximum point is read at a position close to either of the first half point and the second half point, it characterized that you identify the type of the triangular defects,
Defect determination device. The determining unit determines whether or not the triangular defect is a type that decreases electrical characteristics of a semiconductor element manufactured using the silicon carbide semiconductor substrate .
The defect determination apparatus according to claim 1. The light detection unit detects the emission line profile of a single wavelength of the triangular defect ,
The defect determination apparatus according to claim 1 or 2. The light detection unit detects the emission line profile of the triangular defect having a wavelength of 540 nm ,
Defect discriminating device according to any one of claims 1 3. (A) A step of performing photoluminescence measurement along a step flow growth direction of a triangular defect formed in a triangular shape in plan view on the surface of a silicon carbide semiconductor substrate having an off angle, and detecting a light emission line profile of a specific wavelength When,
(B) determining the type of the triangular defect based on the detected light emitting line profile,
The step (b)
(B-1) From the light emission line profile, the local maximum point of the light emission intensity and the first half-value point and the second half-value point that are present across the maximum point and at which the light emission intensity is half of the maximum point are read. Process,
(B-2) determining a type of the triangular defect based on whether the local maximum point is read at a position closer to the first half-value point or the second half-value point. ,
Defect determination method . The step (b) is a step of discriminating whether or not the triangular defect is a type that deteriorates electrical characteristics of a semiconductor element manufactured using the silicon carbide semiconductor substrate.
The defect determination method according to claim 5 . The step (a) is a step of detecting the emission line profile of a single wavelength of the triangular defect.
The defect discrimination method according to claim 5 or 6. The step (a) is a step of detecting the emission line profile with a wavelength of 540 nm of the triangular defect.
The defect determination method according to any one of claims 5 to 7 .

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