CN114509457A - Method for detecting internal stress of bulk silicon carbide single crystal - Google Patents

Method for detecting internal stress of bulk silicon carbide single crystal Download PDF

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CN114509457A
CN114509457A CN202210179190.2A CN202210179190A CN114509457A CN 114509457 A CN114509457 A CN 114509457A CN 202210179190 A CN202210179190 A CN 202210179190A CN 114509457 A CN114509457 A CN 114509457A
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谢雪健
胡小波
陈秀芳
彭燕
徐现刚
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Shandong University
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Abstract

The invention relates to a method for detecting internal stress of bulk silicon carbide single crystal, which comprises the following steps: carrying out directional operation on the surface of a bulk SiC single crystal sample to be detected to obtain a crystal face on the surface of the SiC sample; performing neutron diffraction test on the obtained crystal face on the surface of the SiC sample to obtain a test result; and comparing the diffraction peak in the test result with the diffraction peak of the corresponding crystal face in the unstressed crystal to obtain strain values in different directions of the SiC crystal, obtaining a strain tensor in a sample coordinate system through coordinate conversion, and finally calculating the stress size and distribution in the bulk SiC crystal. The penetration ability of neutrons in the SiC single crystal adopted by the method is strong and can reach centimeter magnitude, and the stress distribution in different directions in the SiC single crystal can be obtained by performing neutron diffraction on the SiC crystal.

Description

Method for detecting internal stress of bulk silicon carbide single crystal
Technical Field
The invention relates to the technical field of semiconductor single crystal detection, in particular to a method for detecting internal stress of bulk silicon carbide single crystal.
Background
SiC semiconductor materials are third generation semiconductor materials developed after the elemental semiconductors Si, Ge and the compound semiconductors GaAs, InP and the like. SiC is used as a member of wide bandgap semiconductor materials, has the characteristics of high critical breakdown field strength, good thermal stability, high saturated drift velocity of current carriers, high thermal conductivity and the like, and is a key material for preparing high-temperature, high-frequency and high-power electronic devices. At present, SiC plays an important role in the fields of optoelectronic devices, microelectronic devices, power electronic devices, and the like, with its excellent semiconductor properties.
Physical vapor transport is considered to be the most mature method in producing large-diameter SiC single crystals. When the SiC single crystal is grown by adopting a physical vapor transport method, SiC seed crystal is placed at the top of the crucible, and SiC powder is placed at the bottom of the crucible. A temperature gradient exists in the axial direction inside the crucible, and the axial temperature gradient transports silicon and carbon gas phase components to the seed crystal, so that the growth of the crystal in the axial direction (namely, the growth and the thickness of the crystal) are realized. The temperature around the crucible is higher than that in the center of the crucible, and a radial gradient exists in the radial direction, and the radial gradient realizes the growth (namely expanding growth) of the crystal in the radial direction, so that the diameter of the obtained crystal is equivalent to that of the seed crystal. After the crystal growth is finished, the heating power is required to be gradually reduced, so that the temperature of the crystal is reduced from the growth temperature to the room temperature. The radial temperature gradient existing in the crystal growth process and the cooling process carried out after the crystal growth are finished can generate thermal stress in the crystal. In addition, the grown SiC crystal may rub against the diamond wheel during subsequent machining processes such as surface grinding and rounding, and thus may be subjected to mechanical stress. When the thermal stress and the mechanical stress inside the crystal exceed the critical threshold of the SiC single crystal, the SiC single crystal can crack, which is characterized in that: after the crystal growth is finished, the crystal is cracked or the crystal is cracked in the subsequent processing processes of plane grinding, round rolling and the like. Therefore, the stress in the SiC crystal is tested, and the method has important significance for optimizing the crystal growth process and guiding the crystal processing.
The stress detection methods commonly used at present include: synchrotron radiation topography, X-ray diffraction methods, stress polarimeters, Raman spectroscopy, and the like. The synchrotron radiation method requires a specific radiation light source, and also requires the procedures of exposure, film washing in a darkroom and the like for a sample, which is complicated. The X-ray diffraction method can be used only for analyzing the stress at the surface or interface of a material due to a shallow X-ray penetration depth (e.g., a penetration depth of only 70 μm in a SiC single crystal), and cannot detect the distribution of bulk stress inside the crystal. The stress polarization Raman spectrum can test the stress of the film, taking a SiC film material as an example, the magnitude of the stress can be calculated quantitatively by detecting the peak position movement of the TO mode, but the sensitivity of the method is limited, the variation of the TO mode is difficult TO observe for bulk SiC crystals, and the method cannot give the magnitude of the stress in different directions, so the method cannot realize the measurement of the internal stress of the bulk SiC crystals.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides the method for detecting the internal stress of the bulk silicon carbide single crystal, the method can be used for quantitatively calculating the stress size and distribution in the SiC single crystal, and theoretical guidance is provided for optimizing the growth process and the processing process of the SiC single crystal.
In order to achieve the purpose, the invention provides the following scheme:
a bulk silicon carbide single crystal internal stress detection method includes:
carrying out directional operation on the surface of a bulk SiC single crystal sample to be detected to obtain a crystal face on the surface of the SiC sample;
performing neutron diffraction test on the obtained crystal face on the surface of the SiC sample to obtain a test result;
and comparing the diffraction peak in the test result with the diffraction peak of the corresponding crystal face in the unstressed crystal with the same crystal form to obtain strain values of the SiC crystal in different directions, obtaining a strain tensor in a sample coordinate system through coordinate conversion, and finally calculating the stress size and distribution in the bulk SiC single crystal.
Preferably, in the process of orienting the surface of the bulk SiC single crystal sample, an X-ray diffraction orienter is selected for orienting, wherein the diameter of the bulk SiC single crystal is in the range of 2 inches to 8 inches, and the thickness of the single crystal is not less than 5 mm.
Preferably, the neutron diffraction mode in the neutron diffraction test is a normal wavelength neutron diffraction mode or a time-of-flight neutron diffraction mode.
Preferably, the neutron diffraction test is performed while performing a single-crystal SiCPoint-by-point or point-by-point testing is carried out, the number of linearly independent crystal faces for neutron diffraction testing is not less than six, the requirement of linear independence is met among different crystal faces, and the crystal face Bragg angle theta for neutron diffraction is carried outBTheta is more than or equal to 20 degreesB≤145°。
Preferably, the diffraction intensity in the neutron diffraction test is adjusted using a slit or an integration time; the width of the entrance slit and the width of the exit slit are 0.5-10 mm, the integration time is 0.001-5 s, the shapes of the entrance slit and the exit slit are determined according to the diffraction volume, and the neutron diffraction test is performed in a test coordinate system Y1-Y2-Y3.
Preferably, in combination with a bragg diffraction formula, the diffraction peak in the test result is compared with the diffraction peak of the corresponding crystal face in the unstressed crystal, and the strain tensor in the direction of the diffraction crystal face in the test coordinate system is calculated
Figure BDA0003521712140000041
And calculating the strain tensor in the sample coordinate system according to the coordinate transformation principle in the crystal physical
Figure BDA0003521712140000042
Preferably, the strain tensor in the direction of the diffraction lattice plane in the test coordinate system
Figure BDA0003521712140000043
The calculation method of (a) is as follows (1):
Figure BDA0003521712140000044
wherein d is0The interplanar spacing when the diffraction plane is unstrained,
Figure BDA0003521712140000045
delta theta is the difference of neutron diffraction peak potential between the unstressed SiC sample and the SiC sample to be detected, theta is the interplanar distance after strain occursBThe neutron diffraction peak position of the unstressed SiC sample is shown.
Preferably, the strain tensor is converted according to the transformation principle of a second-order tensor in crystal physics in a new coordinate system and an old coordinate system
Figure BDA0003521712140000046
Expressed in the sample coordinate system X1-X2-X3 as:
Figure BDA0003521712140000047
wherein, a3k，a3lRespectively is the cosine of the included angle between the coordinate axis Y3 and each coordinate axis X1-X2-X3,
Figure BDA0003521712140000048
for each strain component under the sample coordinate system X1-X2-X3.
Preferably by a second order strain tensor εklAnd fourth order elastic stiffness coefficient tensor CijklCalculating the stress tensor σ in the bulk SiC single crystalij；
Wherein the second order strain tensor ε in the sample coordinate systemklThe calculating step comprises:
the strain tensor in the sample coordinate system obtained by calculation is used
Figure BDA0003521712140000049
(k, l is 1,2, 3) obtaining a strain tensor epsilon in a stress coordinate system by a coordinate transformation principlekl(k, l ═ 1,2, 3), the transform expression is:
Figure BDA0003521712140000051
wherein, bijAnd the direction cosine of the included angle between each axis of the stress coordinate system M1-M2-M3 and the sample coordinate system X1-X2-X3, wherein i, j is 1,2 and 3.
Preferably, the stress tensor in the bulk SiC single crystal is calculated according to hooke's law:
Figure BDA0003521712140000052
according to the stipulation in crystal physics, the expression method of simplifying the subscript is adopted for both stress tensor and strain tensor, wherein the stress tensor is as follows: sigma11＝σ1，σ22＝σ2，σ33＝σ3，σ23＝σ32＝σ4，σ13＝σ31＝σ5，σ12＝σ21＝σ6(ii) a Elastic stiffness constant: cijThe elastic stiffness coefficients of the SiC single crystal in different directions are obtained; the strain tensor is: epsilon11＝ε1，ε22＝ε2，ε33＝ε3，
Figure BDA0003521712140000053
The invention has the beneficial effects that:
(1) the neutron source adopted by the method provided by the invention skillfully utilizes the characteristics that the penetration capability of neutrons in the SiC single crystal is strong and can reach the centimeter magnitude, and carries out neutron diffraction on 6 linearly independent diffraction crystal faces of the SiC single crystal, so that the stress distribution in different directions in the SiC single crystal can be obtained; by adjusting the depth of the neutron source in the crystal, the stress distribution conditions of different depths of the crystal can be obtained, so that the evolution conditions of internal stress of the SiC single crystal at different growth stages can be obtained, and the optimization of the nucleation and growth processes of the single crystal can be guided.
(2) The method for representing the SiC bulk single crystal stress by neutron diffraction has high precision, and the strain precision can reach 8 multiplied by 10-5Compared with the traditional stress meter for quantitatively testing the wafer stress through imaging, the method provided by the invention can accurately and quantitatively give specific values of strain and stress in the crystal, and the obtained stress value is more accurate.
(3) The neutron diffraction method of the invention belongs to nondestructive detection, and does not damage or pollute the SiC single crystal sample; and neutron diffraction represents the SiC bulk single crystal stress method, the principle is simple, and the method is easy to popularize and use.
(4) The neutron diffraction method can obtain the three-dimensional stress mapping result in the crystal and the stress distribution result by testing the SiC single crystal point by point, and is particularly suitable for researching the growth stress distribution uniformity of the crystal with the diameter of 6 inches or more and guiding the growth process of the large-diameter SiC single crystal.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.
Fig. 1 is a schematic diagram of neutron diffraction of a SiC single crystal in embodiment 1 of the present invention, in which 1 is a neutron source, 2 is a perfect crystal monochromator, 3 is an entrance slit, 4 is a neutron diffraction volume, 5 is a sample stage, 6 is a SiC single crystal to be tested, 7 is an exit slit, and 8 is a detector;
FIG. 2 is a schematic diagram of the transformation of a sample coordinate system, a test coordinate system and a crystallographic coordinate system in an embodiment of the present invention;
FIG. 3 is a schematic diagram of a sample coordinate system X1-X2-X3 and a test coordinate system Y1-Y2-Y3 in an embodiment of the present invention,
Figure BDA0003521712140000071
is X1 and
Figure BDA0003521712140000072
the included angle psi between the axes is the included angle between X3 and Y3;
FIG. 4 is a schematic diagram of a crystallographic coordinate system Z1-Z2-Z3 and a stress-chemical coordinate system M1-M2-M3 in accordance with an embodiment of the present invention;
FIG. 5 is a schematic diagram showing the results of neutron diffraction tests on different crystal planes of a 4H-SiC single crystal grown in a 2-inch flat temperature field in an embodiment of the present invention;
FIG. 6 is a flowchart of a method for measuring internal stress of a bulk silicon carbide single crystal according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.
Description of terms:
strain: when a material cannot be displaced by an external force, its geometry and dimensions change, and this deformation becomes a strain.
Stress: when the material deforms, reaction forces with equal magnitude and opposite directions are generated inside the material to resist the external force, the reaction force on the unit area is defined as stress, and the dimension is Pa.
Neutron diffraction: which refers to bragg diffraction that occurs when neutrons with a de broglie wavelength of about 0.1nm pass through crystalline materials.
Sample coordinate system: in this embodiment, the coordinate system refers to X1-X2-X3. Assume that the surface of the sample is (h)0k0l0) X1 and X2 are located on the sample surface (h)0k0l0) Inner, X3 axis is the sample surface (h)0k0l0) Normal line.
Test coordinate system: in this embodiment, the coordinate system is Y1-Y2-Y3. Assuming that the diffraction crystal plane is (hkl), the axis Y2 is located on the sample surface (h)0k0l0) In the formula, the Y3 axis is the normal of the diffraction crystal plane (hkl), and the projection of the Y1 axis on the sample surface is
Figure BDA0003521712140000081
A shaft therein
Figure BDA0003521712140000082
Is X1 and
Figure BDA0003521712140000083
the included angle psi is the included angle between X3 and Y3, as shown in fig. 3.
Crystallographic coordinate system: in this example, the Z1-Z2-Z3 coordinate system, Z1// crystallographic a axis, and Z3// crystallographic c axis are shown.
Stress coordinate system: in this embodiment, the coordinate system M1-M2-M3 is obtained by reciprocal space transformation of crystallographic coordinates, M1, M2, and M3 are expressed by reciprocal basis vectors of the crystallographic coordinate system, and M1, M2, and M3 are orthogonal in pairs.
Examples 1,
Referring to fig. 6, the present invention provides a method for detecting internal stress of a bulk silicon carbide single crystal, comprising:
(1) and orienting the SiC bulk single crystal to be detected by using an orientation apparatus to obtain a crystal face on the surface of the SiC sample.
(2) A SiC single crystal having a small size and a small stress is selected, and the stress in the SiC single crystal is considered to be 0 approximately. Setting the slit width and the diffraction integral time in the optical path system, rotating the sample table according to the surface of the crystal, adjusting parameters such as diffraction angle, azimuth angle and the like, and carrying out neutron diffraction test on different crystal faces of the SiC single crystal, wherein the test result is used as a stress-free SiC single crystal neutron diffraction standard value.
(3) And (3) performing neutron diffraction tests on different crystal faces of the SiC bulk single crystal to be detected in the step (1), wherein the tested crystal face is the same as the crystal face in the step (2).
(4) According to the test results in the steps (2) and (3), combining a Bragg diffraction formula, calculating the strain tensor of the diffraction crystal face in the test coordinate system in the finding direction
Figure BDA0003521712140000091
And calculating the strain tensor in the sample coordinate system according to the coordinate transformation principle in the crystal physical
Figure BDA0003521712140000092
(5) According to Hooke's law, through a second order strain tensor εklAnd fourth order elastic stiffness coefficientTensor CijklCalculating the stress tensor sigma in the SiC bulk single crystalij。
And (3) orienting the surface of the SiC sample in the step (1) by using an X-ray diffraction orientation instrument, and referring to the attached figure 1. When the SiC sample is a 4H-SiC or 6H-SiC single crystal, the crystal plane of the SiC surface is a (0001) c plane, a (1000) a plane, or a (1-100) m plane.
In the further optimization scheme, the diameter of the SiC block single crystal to be detected in the step (1) is 2-8 inches, the thickness of the single crystal is not less than 5mm, and the crystal can be grown primary crystal, annealed crystal and crystal in the subsequent processing process.
In a further optimization scheme, in the step (2), the small-size and low-stress SiC single crystal is a SiC crystal with a size not larger than 2 inches grown in a flat temperature field, and more preferably, the small-size and low-stress SiC single crystal in the step (2) is a 2-inch SiC crystal with internal stress removed through multiple annealing. In this embodiment, the unstressed SiC single crystal may be replaced with SiC single crystal powder. Before testing, the stress-free crystal needs to be annealed for more than 50h in a flat temperature field at the growth temperature or lower to completely eliminate internal stress.
The neutron diffraction mode is a normal-wavelength neutron diffraction mode or a time-of-flight neutron diffraction mode; the neutron diffraction mode is a normal-wavelength neutron diffraction mode, and the neutron wavelength is 0.12-0.28 nm.
The number of the linear independent crystal faces for neutron diffraction is not less than 6. Crystal face Bragg angle theta for neutron diffractionBThe requirements are as follows: theta is more than or equal to 20 degreesBIs less than or equal to 145 degrees. Further optimization scheme, 2 thetaBThe angle is approximately equal to 90 degrees, the purpose is to ensure that the volumes of different crystal planes are the same diffraction volume when diffraction occurs, and more accurate information is obtained. When the neutron diffraction test is performed, a single-point or point-by-point test can be performed on the SiC single crystal. When point-by-point testing is carried out, the distance between adjacent points is 2-10mm, and finally, a stress mapping graph of the whole SiC crystal can be obtained.
The diffraction intensity can be adjusted using slits or integration time. The optimization scheme is further optimized, the width of the entrance slit and the width of the exit slit are 0.5-10 mm, and the integration time is 0.001-5 s. The shapes of the entrance slit and the exit slit are determined according to the diffraction volume. In the present embodiment, the shape of the slit is circular, rectangular, or square.
In the steps (2) to (3), the neutron diffraction test is carried out in a test coordinate system, and the fourth-order elastic stiffness coefficient tensor C in the step (5)ijklExpressed in a crystallographic coordinate system, stress tensor σijExpressed in a stress coordinate system. FIG. 2 is a schematic diagram showing the transformation of a sample coordinate system, a test coordinate system and a crystallographic coordinate system, FIG. 3 is a schematic diagram showing the transformation of a sample coordinate system X1-X2-X3 and a test coordinate system Y1-Y2-Y3,
Figure BDA0003521712140000101
is X1 and
Figure BDA0003521712140000102
the included angle between the axes psi is the included angle between X3 and Y3, and FIG. 4 is a schematic diagram of a crystallographic coordinate system Z1-Z2-Z3 and a stress system M1-M2-M3.
The calculation of the strain tensor in the step (4) is as follows: the strain in the (hkl) plane along the Y3 axis under the test coordinate system Y1-Y2-Y3 can be expressed as:
Figure BDA0003521712140000111
wherein, Delta theta is the difference of neutron diffraction peak potentials of the unstressed SiC sample and the SiC sample to be detected, and thetaBThe neutron diffraction peak position of the unstressed SiC sample is shown.
According to the transformation principle of the second order tensor in the crystal physics in the new and old coordinate systems,
Figure BDA0003521712140000112
in the sample coordinate system X1-X2-X3 can be expressed as:
Figure BDA0003521712140000113
wherein, a3k，a3lRespectively, coordinate axes Y3 and X1-X2-X3The cosine of the included angle is,
Figure BDA0003521712140000114
for each strain component under the sample coordinate system X1-X2-X3.
Matrix a of cosine of included angle between each coordinate axis of Y1-Y2-Y3 and X1-X2-X3ij(i, j ═ 1,2, 3) is:
Figure BDA0003521712140000115
combining the formulas (1) to (3) to obtain:
Figure BDA0003521712140000116
substituting the test results of 6 different diffraction crystal faces obtained in the steps (2) and (3) into the formula (4) to obtain 6 strain equation sets of the crystal at the test position, and calculating each strain component in the sample coordinate system X1-X2-X3
Figure BDA0003521712140000117
The strain tensor calculation step in step (5) is as follows:
expressing the crystallographic coordinate basis vector in an orthogonal coordinate system:
Figure BDA0003521712140000121
the above basis vectors are expressed in reciprocal space as:
Figure BDA0003521712140000122
in the stress coordinate system M1-M2-M3 of FIG. 4, the director can be written as:
Figure BDA0003521712140000123
the strain tensor in the sample coordinate system obtained by the calculation in the step (4) is used for calculating
Figure BDA0003521712140000124
Obtaining the strain tensor epsilon in the stress coordinate system by the coordinate transformation principleklThe transformation expression is:
Figure BDA0003521712140000125
wherein, bijAnd (i, j is 1,2 and 3) is the direction cosine of an included angle between the stress coordinate system M1-M2-M3 and each axis of the sample coordinate system X1-X2-X3.
The stress tensor in the SiC bulk single crystal was calculated according to hooke's law:
Figure BDA0003521712140000126
in the above formula, according to the provisions in crystal physics, the expression method of simplified subscripts is adopted for both stress tensor and strain tensor. Stress tensor: sigma11＝σ1，σ22＝σ2，σ33＝σ3，σ23＝σ32＝σ4，σ13＝σ31＝σ5，σ12＝σ21＝σ6(ii) a Elastic stiffness constant: cijThe elastic stiffness coefficients of the SiC single crystal in different directions are obtained; a strain tensor: epsilon11＝ε1，ε22＝ε2，ε33＝ε3，
Figure BDA0003521712140000131
The stress detection method is also suitable for single crystal materials such as sapphire, monocrystalline silicon and the like, and is particularly suitable for crystal materials of a hexagonal system.
The above-mentioned methods are not limited in detail and are in accordance with the state of the art.
Examples 2,
As described in embodiment 1, a method for detecting the stress of a SiC bulk single crystal includes the following specific operation steps:
(1) a4-inch 4H-SiC bulk single crystal was selected and examined by an X-ray orientation machine, and the surface of the 4H-SiC bulk single crystal was a (0001) c-plane.
(2) A4H-SiC bulk single crystal grown in a 2-inch flat temperature field is taken as an unstressed 4H-SiC single crystal, the surface of a sample is a c surface, and the de Broglie wavelength corresponding to neutrons is 0.154 nm. Referring to fig. 5; the entrance slit and the exit slit are both round hole slits with the diameter of 0.5mm and the integration time of 5 s. Neutron diffraction tests of (205), (108), (206), (109), (204) and (118) crystal planes are respectively carried out on the unstressed SiC single crystal, and the corresponding 2 thetaB87.925 °, 85.358 °, 95.334 °, 96.812 °, 81.843 °, 104.726 ° respectively, and the test results are shown in fig. 5.
(3) And (3) performing neutron diffraction tests on different crystal faces of the 4-inch 4H-SiC in the step (1), wherein the tested crystal faces are the same as those in the step (2).
(4) And (4) calculating strain tensors under different coordinate systems according to the difference of the diffraction peak positions of the corresponding crystal faces in the steps (2) and (3).
(5) And (5) obtaining a stress tensor (unit: MPa) according to the Hooke's law and the strain tensor in the step (4), wherein the result is as follows:
Figure BDA0003521712140000141
that is, the stress distribution at the test points is:
Figure BDA0003521712140000142
examples 3,
The method for detecting the stress of the SiC bulk single crystal is different from that described in example 2 in that:
in the step (1), 6-inch 4H-SiC bulk single crystals are selected and detected by an X-ray orientation instrument, and the surface of the 4H-SiC bulk single crystals is a (0001) c surface.
In the step (2), a 6H-SiC bulk single crystal grown in a 2-inch flat temperature field is taken as an unstressed 6H-SiC single crystal, the wavelength corresponding to neutrons is 0.1587nm, the entrance slits and the exit slits are square slits with the size of 5mm multiplied by 5mm, and the integration time is 0.001 s. Neutron diffraction tests of (205), (108), (206), (109), (204) and (107) crystal planes are respectively carried out on the unstressed SiC single crystal, and the corresponding 2 thetaB91.202 °, 88.488 °, 99.081 °, 100.666 °, 84.781 °, 77.704 ° respectively.
In the step (3), neutron diffraction tests of different crystal faces are carried out on the 6-inch 4H-SiC in the step (1), and the tested crystal faces are the same as those in the step (2).
And (5) calculating to obtain a stress tensor (unit: MPa) as follows:
Figure BDA0003521712140000151
that is, the stress distribution at the test points is:
Figure BDA0003521712140000152
examples 4,
The difference from the method for detecting the stress of the SiC bulk single crystal described in example 2 is that:
in the step (1), 8-inch 6H-SiC bulk single crystals are selected and detected by an X-ray orientation instrument, and the surface of the 6H-SiC bulk single crystals is a (100) a surface.
In the step (2), the wavelength corresponding to the neutron is 0.28nm, the entrance slit and the exit slit are both rectangular slits, the size is 0.6mm multiplied by 3mm, and the integration time is 1 s. Performing neutron diffraction tests on the (102), (103), (104), (105), (106) and (2-10) crystal planes of the unstressed SiC single crystal respectively to obtain corresponding 2 thetaB67.840 °, 73.085 °, 80.201 °, 89.139 °, 100.011 ° and 131.406 °.
In the step (3), a neutron diffraction test is carried out on the 8-inch 6H-SiC bulk single crystal, and the test crystal face is the same as the crystal face in the step (2).
And (5) calculating to obtain a stress tensor (unit: MPa) as follows:
Figure BDA0003521712140000161
that is, the stress distribution at the test points is:
Figure BDA0003521712140000162
from the description of examples 2-4, it can be seen that the magnitude and distribution of stress in bulk SiC single crystals can be characterized using the method of the present invention.
The invention can test the internal stress condition of the bulk SiC single crystal by adopting a neutron diffraction method. Preferred crystal forms of SiC include, but are not limited to, hexagonal crystal systems such as 2H-SiC, 4H-SiC, and 6H-SiC, and the same applies to hexagonal crystal systems. Compared with the traditional method, the method has the beneficial effects that:
(1) the neutron source adopted by the method provided by the invention skillfully utilizes the characteristics that the penetration capability of neutrons in the SiC single crystal is strong and can reach the centimeter magnitude, and carries out neutron diffraction on 6 linearly independent diffraction crystal faces of the SiC single crystal, so that the stress distribution in different directions in the SiC single crystal can be obtained. By adjusting the depth of the neutron source in the crystal, the stress distribution conditions of different depths of the crystal can be obtained, so that the evolution conditions of internal stress of the SiC single crystal at different growth stages can be obtained, and the optimization of the nucleation and growth processes of the single crystal can be guided.
(2) The method for representing the SiC bulk single crystal stress by neutron diffraction has high precision, and the strain precision can reach 8 multiplied by 10-5Compared with the traditional stress meter for quantitatively testing the wafer stress through imaging, the method provided by the invention can accurately and quantitatively give specific values of strain and stress in the crystal, and the obtained stress value is more accurate.
(3) The neutron diffraction method of the invention belongs to nondestructive detection, and does not damage or pollute the SiC single crystal sample; and neutron diffraction represents the SiC bulk single crystal stress method, the principle is simple, and the method is easy to popularize and use.
(4) The neutron diffraction method can obtain the three-dimensional stress mapping result in the crystal and the stress distribution result by testing the SiC single crystal point by point, is particularly suitable for researching the growth stress distribution uniformity of the crystal with the diameter of 6 inches or more, and is used for guiding the growth process of the large-diameter SiC single crystal.
The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.

Claims (10)

1. A method for detecting internal stress of a bulk silicon carbide single crystal, comprising:
carrying out directional operation on the surface of a bulk SiC single crystal sample to be detected to obtain a crystal face on the surface of the SiC sample;
performing neutron diffraction test on the obtained crystal face on the surface of the SiC sample to obtain a test result;
and comparing the diffraction peak in the test result with the diffraction peak of the corresponding crystal face in the unstressed crystal with the same crystal form to obtain strain values of the SiC crystal in different directions, obtaining a strain tensor in a sample coordinate system through coordinate conversion, and finally calculating the stress size and distribution in the bulk SiC single crystal.
2. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 1, wherein an X-ray diffraction orientation machine is selected for orientation during orientation of the surface of the bulk SiC single crystal sample, wherein the bulk SiC single crystal has a diameter in the range of 2 inches to 8 inches and a single crystal thickness of not less than 5 mm.
3. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 1, wherein the neutron diffraction mode in the neutron diffraction test is a normal wavelength neutron diffraction mode or a time-of-flight neutron diffraction mode.
4. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 3, wherein the neutron diffraction test is performed on a SiC single crystal in a single-point or point-by-point test, wherein the number of linearly independent crystal planes subjected to the neutron diffraction test is not less than six, the number of different crystal planes satisfies the requirement of linear independence, and the Bragg angle θ of the crystal plane subjected to the neutron diffraction is the same as that of the crystal planeBTheta is more than or equal to 20 degreesB≤145°。
5. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 4, wherein the diffraction intensity in the neutron diffraction test is adjusted using a slit or an integration time; the width of the entrance slit and the width of the exit slit are 0.5-10 mm, the integration time is 0.001-5 s, the shapes of the entrance slit and the exit slit are determined according to the diffraction volume, and the neutron diffraction test is performed in a test coordinate system Y1-Y2-Y3.
6. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 5, wherein a Bragg diffraction formula is combined to compare a diffraction peak in the test result with a diffraction peak of a corresponding crystal face in an unstressed crystal, and a strain tensor in the direction of the diffraction crystal face in the test coordinate system is calculated
Figure FDA0003521712130000021
And calculating the strain tensor in the sample coordinate system according to the coordinate transformation principle in the crystal physical
Figure FDA0003521712130000022
7. The method of detecting internal stress of a bulk silicon carbide single crystal as claimed in claim 6, wherein the method comprises measuring internal stress of the bulk silicon carbide single crystalTensor strain in direction of diffraction crystal plane in experimental coordinate system
Figure FDA0003521712130000023
The calculation method of (a) is as follows (1):
Figure FDA0003521712130000024
wherein d is0The interplanar spacing when the diffraction plane is unstrained,
Figure FDA0003521712130000025
delta theta is the difference of neutron diffraction peak potential between the unstressed SiC sample and the SiC sample to be detected, theta is the interplanar distance after strain occursBThe neutron diffraction peak position of the unstressed SiC sample is shown.
8. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 7, wherein the strain tensor is a second-order tensor in crystal physics according to a principle of transformation of the tensor in a new coordinate system and an old coordinate system
Figure FDA0003521712130000026
Expressed in the sample coordinate system X1-X2-X3 as:
Figure FDA0003521712130000027
wherein, a3k，a3lRespectively is the cosine of the included angle between the coordinate axis Y3 and each coordinate axis X1-X2-X3,
Figure FDA0003521712130000031
for each strain component under the sample coordinate system X1-X2-X3.
9. The method of detecting internal stress of a bulk silicon carbide single crystal as claimed in claim 7, wherein the second-order strain tensor ε is passedklAnd fourth order elastic stiffness coefficient tensor CijklCalculating the stress tensor σ in the bulk SiC single crystalij；
Wherein a second order strain tensor ε in the sample coordinate systemklThe calculating step comprises:
the strain tensor in the sample coordinate system obtained by calculation is used
Figure FDA0003521712130000032
Obtaining the strain tensor epsilon in the stress coordinate system by the coordinate transformation principlekl(k, l ═ 1,2, 3), the transform expression is:
Figure FDA0003521712130000033
wherein, bijAnd the direction cosine of the included angle between each axis of the stress coordinate system M1-M2-M3 and the sample coordinate system X1-X2-X3, wherein i, j is 1,2 and 3.
10. The method for detecting internal stress of a bulk silicon carbide single crystal according to claim 1, wherein a stress tensor in the bulk SiC single crystal is calculated according to hooke's law:
Figure FDA0003521712130000034
according to the stipulation in crystal physics, the expression method of simplifying the subscript is adopted for both stress tensor and strain tensor, wherein the stress tensor is as follows: sigma11＝σ1，σ22＝σ2，σ33＝σ3，σ23＝σ32＝σ4，σ13＝σ31＝σ5，σ12＝σ21＝σ6(ii) a Elastic stiffness constant: cijThe elastic stiffness coefficients of the SiC single crystal in different directions are obtained; the strain tensor is: epsilon11＝ε1，ε22＝ε2，ε33＝ε3，
Figure FDA0003521712130000041
CN202210179190.2A 2022-02-25 2022-02-25 Method for detecting internal stress of bulk silicon carbide single crystal Pending CN114509457A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114858324A (en) * 2022-07-07 2022-08-05 浙江大学杭州国际科创中心 Method and system for detecting residual stress of silicon carbide crystal
CN116657249A (en) * 2023-05-31 2023-08-29 上海天岳半导体材料有限公司 Silicon carbide wafer with uniformly distributed stress and nondestructive and accurate wafer directional stress measuring method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114858324A (en) * 2022-07-07 2022-08-05 浙江大学杭州国际科创中心 Method and system for detecting residual stress of silicon carbide crystal
CN114858324B (en) * 2022-07-07 2022-09-30 浙江大学杭州国际科创中心 Method and system for detecting residual stress of silicon carbide crystal
CN116657249A (en) * 2023-05-31 2023-08-29 上海天岳半导体材料有限公司 Silicon carbide wafer with uniformly distributed stress and nondestructive and accurate wafer directional stress measuring method

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