JP2013124196A - Method for inspecting adhesion state of seed crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for inspecting the adhesion state of a seed crystal, which has high precision.SOLUTION: An object to be inspected IS having a seed crystal 11, an adhesive layer 30 to which the seed crystal 11 adheres, and a support part 41 to which the seed crystal 11 adheres by the adhesive layer 30 is prepared. The surface to be inspected SS of the object to be inspected IS is irradiated with an ultrasonic wave UL so that the wave transmits through either of the seed crystal 11 and the support part 41, and reaches the adhesive layer 30. Distribution of the attenuation constant of the reflected wave RF of the ultrasonic wave on the surface to be inspected SS is calculated.

Description

  The present invention relates to a method for inspecting the adhesion state of a seed crystal.

  According to Japanese Patent Application Laid-Open No. 2008-110913, there is disclosed a method aimed at suppressing macro defects generated due to poor adhesion when a seed crystal and a seed crystal support are bonded in the growth of a single crystal. Has been. According to this method, first, the seed crystal and the seed crystal support are brought into contact with each other through the adhesive, and in this state, the adhesive is dried and cured by the first heat treatment. The adhesive is carbonized by the second heat treatment. Then, the quality of the fixed state is determined based on the brightness of the reflected light obtained by observing the carbonized layer of the adhesive through the seed crystal.

JP 2008-110913 A

  The most serious defect of the adhesive layer adhering the seed crystal is the presence of voids. Therefore, in the inspection of the adhesion state of the seed crystal, it is required to detect the void with high accuracy. However, when the adhesion state of the seed crystal is determined based on the brightness of the reflected light as in the technique of the above publication, the brightness of the reflected light is greatly influenced by factors other than the void, so that the accuracy of detecting the void is sufficient. It was not expensive. Therefore, the adhesion state of the seed crystal could not be inspected with high accuracy.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a highly accurate inspection method for the adhesion state of a seed crystal.

  The inspection method for the adhesion state of the seed crystal of the present invention is a method for inspecting the adhesion state of the seed crystal, and includes the following steps. An object to be inspected having a seed crystal, an adhesive layer to which the seed crystal is bonded, and a support portion to which the seed crystal is bonded by the adhesive layer is prepared. Ultrasonic waves are applied to the surface to be inspected so as to pass through either the seed crystal or the support and reach the adhesive layer. The distribution of the attenuation constant of the reflected wave of the ultrasonic wave on the surface to be inspected is calculated.

  According to this inspection method, it is possible to accurately grasp the presence of a void by detecting that the attenuation constant of the reflected wave of the ultrasonic wave decreases due to the void in the adhesive layer. Therefore, the adhesion state of the seed crystal can be inspected with high accuracy.

  Preferably, in the inspection method described above, the ratio of the portion of the surface to be inspected whose attenuation constant is within a predetermined threshold range is calculated. Thereby, a test result can be quantified.

  Preferably the seed crystal is made of silicon carbide. Since the seed crystal made of silicon carbide is particularly susceptible to voids in the adhesive layer, the inspection method of the present invention is particularly suitable.

  Preferably, the adhesive layer includes a layer made using a C-based or SiC-based adhesive. When these adhesives are used, voids are particularly likely to occur. Therefore, inspection with high accuracy is possible by the inspection method of the present invention that can accurately grasp voids.

  Preferably, the ultrasonic frequency is 10 MHz or more and 100 MHz or less. If the frequency is too low, the rate at which the ultrasonic waves that have entered from the inspection surface of the inspection object reach the opposite surface increases, and the inspection accuracy decreases due to the influence of the reflected wave from the opposite surface. Therefore, the frequency is preferably 10 MHz or more. If the frequency is too high, the intensity of the reflected wave from the adhesive layer becomes excessively small due to excessive attenuation of the ultrasonic wave in the inspection object. For this reason, inspection accuracy falls. Therefore, the frequency is preferably 100 MHz or less.

  As described above, according to the present invention, the adhesion state of the seed crystal can be accurately inspected.

It is sectional drawing which shows roughly the 1st process of the inspection method of the adhesion state of the seed crystal in one embodiment of this invention. It is sectional drawing which shows roughly the 2nd process of the test | inspection method of the adhesion state of the seed crystal in one embodiment of this invention. It is sectional drawing which shows schematically the 3rd process of the test | inspection method of the adhesion state of the seed crystal in one embodiment of this invention. It is sectional drawing which shows the state in which the void of the contact bonding layer is not detected in the 4th process of the manufacturing method of the single crystal in one embodiment of this invention. It is a graph which shows the time change of the intensity | strength of the reflected wave detected in the process of FIG. It is sectional drawing which shows the state in which the void of the contact bonding layer is detected in the 4th process of the manufacturing method of the single crystal in one embodiment of this invention. It is a graph which shows the time change of the intensity | strength of the reflected wave detected in the process of FIG. It is a graph which shows an example of the 5th process of the inspection method of the adhesion state of the seed crystal in one embodiment of this invention. It is a top view which shows an example of the 6th process of the test | inspection method of the adhesion state of the seed crystal in one embodiment of this invention. It is sectional drawing which shows roughly 1 process of the manufacturing method of the single crystal using the seed crystal inspected using the inspection method of the adhesion state of the seed crystal in one embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. For crystallographic description, individual planes are indicated by () and aggregate planes are indicated by {}. As for a negative index, “−” (bar) is attached on the number, but in this specification, a negative sign is attached before the number.

(Preparation of inspection object)
First, a method for preparing an inspection object IS (FIG. 3) to be inspected by the inspection method in the present embodiment will be described. The inspected object IS includes a seed crystal 11, an adhesive layer 30 to which the seed crystal 11 is bonded, and a support portion 41 to which the seed crystal 11 is bonded by the adhesive layer 30, as will be described in detail later. is there.

  Referring to FIG. 1, seed crystal 11 is prepared. The seed crystal 11 has a front surface (a lower surface in the drawing) on which a single crystal is to be grown, and a rear surface (a surface to be attached to the support portion 41 (not shown in FIG. 1)). In the figure. Seed crystal 11 is made of silicon carbide (SiC) having a single crystal structure. The thickness of the seed crystal 11 (the vertical dimension in the figure) is, for example, not less than 0.5 mm and not more than 10 mm. The planar shape of the seed crystal 11 preferably includes a circle with a diameter of 100 mm. Further, the off angle (inclination) of the plane orientation of the seed crystal from the {0001} plane, that is, the off angle from the (0001) plane or the (000-1) plane is preferably 15 ° or less, and more preferably 5 ° or less.

  Preferably, processing for increasing the surface roughness of the back surface of the seed crystal 11 is performed. This processing can be performed by polishing the back surface using abrasive grains having a sufficiently large particle diameter. The particle size distribution of the abrasive grains preferably has a component of 16 μm or more. The average particle size of the abrasive is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 30 μm or less, and further preferably 12 to 25 μm.

  More preferably, the abrasive is made from diamond. Preferably, the abrasive grains are used by being dispersed in a slurry. Therefore, the above polishing can be performed using, for example, a diamond slurry.

  Instead of performing the step of increasing the surface roughness of the back surface of the seed crystal 11, a back surface having a sufficiently large surface roughness from the beginning may be formed and used without polishing the back surface. Specifically, the back surface of the seed crystal 11 formed by slicing with a wire saw may be used without polishing. That is, an as-sliced surface that is a surface formed by slicing and not polished thereafter may be used as the back surface. Preferably, the above-mentioned abrasive grains are used in slicing with a wire saw.

  Next, a coating film 21 containing carbon, in other words, a coating film 21 containing carbon atoms is formed on the back surface of the seed crystal 11. Preferably, the surface roughness of the coating film 21 is made smaller than the surface roughness of the back surface of the seed crystal 11 on which the coating film 21 is formed.

  Preferably, this formation is effected by application of a liquid material, more preferably the liquid material does not contain solids such as particulates. Thereby, the thin coating film 21 can be formed easily and uniformly.

  The covering film 21 is an organic film in the present embodiment. This organic film is preferably formed from an organic resin. As the organic resin, for example, various resins such as an acrylic resin, a phenol resin, a urea resin, and an epoxy resin can be used, and a resin that is formed as a photosensitive resin that is crosslinked or decomposed by the action of light can also be used. it can. As this photosensitive resin, a positive type or negative type photoresist used for manufacturing a semiconductor device can be used, and since a coating technique by spin coating is established for these, the coating film 21 is used. Can be easily controlled. The spin coating method is performed as follows, for example.

  First, the seed crystal 11 is adsorbed on the holder. The seed crystal 11 is rotated by rotating the holder at a predetermined rotation speed. After the photoresist is dropped on the rotating seed crystal 11, the photoresist is applied thinly and uniformly by continuing the rotation for a predetermined time. In order to ensure uniformity over the entire surface of the seed crystal 11, for example, the rotation speed is 1000 to 10,000 rotations / minute, the time is 10 to 100 seconds, and the coating thickness is 0.1 μm or more.

  Next, the applied photoresist is dried to be solidified. The drying temperature and time can be appropriately selected depending on the photoresist material and the coating thickness. Preferably, the drying temperature is from 100 ° C. to 400 ° C., and the drying time is from 5 minutes to 60 minutes. For example, when the drying temperature is 120 ° C., the time required for volatilization is, for example, 15 minutes at a thickness of 5 μm, 8 minutes at a thickness of 2 μm, and 3 minutes at a thickness of 1 μm.

  Note that the coating film 21 can be formed by performing the above-described steps of application and drying once, but a thicker coating film 21 may be formed by repeating this process. If the number of repetitions is too large, this step is not preferable in that it takes more time than necessary, and it is usually preferable to limit the number of repetitions to about 2 to 3 times.

  Referring to FIG. 2, support portion 41 having an attachment surface to which seed crystal 11 is attached is prepared. The mounting surface preferably includes a surface made of carbon, and more preferably includes a surface made of graphite. For this purpose, the support part 41 can be made of graphite. Preferably, the mounting surface is polished to improve the flatness of the mounting surface.

Next, the adhesive 22 is applied on at least one of the support portion 41 and the coating film 21. The application amount of the adhesive 22 is preferably 10 mg / cm ² or more and 100 mg / cm ² or less. The thickness of the adhesive is preferably 100 μm or less, more preferably 50 μm or less.

  In the present embodiment, a C (carbon) adhesive is used as the adhesive 22. A C-based adhesive is one whose composition after curing is mainly C. The C-based adhesive may include a resin that becomes non-graphitizable carbon when heated and a solvent. Further, a filler may be further added to the adhesive. Carbohydrates may be added. Further, a surfactant, a stabilizer and the like may be added.

  Examples of the resin that becomes non-graphitizable carbon when heated include novolac resin, phenol resin, and furfuryl alcohol resin. Here, the non-graphitizable carbon is carbon having an irregular structure that suppresses the development of the graphite structure when heated in an inert gas.

  As the solvent, a solvent capable of dissolving and dispersing the above resin and carbohydrate is appropriately selected. The solvent is not limited to a single type of liquid, and may be a mixed liquid of a plurality of types of liquid. For example, a solvent containing alcohol that dissolves carbohydrates and cellosolve acetate that dissolves resin may be used.

  As the filler, graphite fine particles, diamond fine particles, or a mixture of these fine particles can be used. The amount of graphite or diamond fine particles is preferably less than the amount of resin based on the number of moles of carbon atoms. The particle diameter of the fine particles is, for example, 0.1 to 10 μm.

  As the carbohydrate, a saccharide or a derivative thereof can be used. The saccharide may be a monosaccharide such as glucose or a polysaccharide such as cellulose.

  Next, the coating film 21 and the support portion 41 are brought into contact with each other with the adhesive 22 interposed therebetween. Preferably, this contact is performed such that the two are pressed against each other at a temperature of 50 ° C. to 120 ° C. and a pressure of 0.01 Pa to 1 MPa. Further, if the adhesive 22 is prevented from protruding from the region sandwiched between the seed crystal 11 and the support portion 41, the adverse effect of the adhesive 22 will be adversely affected in a single crystal growth process using the seed crystal 11 described later. Can be suppressed. Note that after the contact, the adhesive 22 may be pre-baked. The pre-baking temperature is preferably 150 ° C. or higher.

  Further, referring to FIG. 3, coating film 21 and adhesive 22 (FIG. 2) are heated. By being carbonized by this heating, the coating film 21 becomes a carbon film 31. That is, the carbon film 31 is provided on the seed crystal 11. Further, by this heating, the adhesive 22 is cured between the carbon film 31 and the support portion 41 to form the fixed layer 32. The heating temperature for curing the adhesive 22 is preferably 1000 ° C. or higher, more preferably 2000 ° C. or higher. This heating is preferably performed in an inert gas.

  As described above, the back surface of the seed crystal 11 is fixed to the support portion 41 by the adhesive layer 30 having the carbon film 31 and the fixing layer 32. That is, an inspection object IS including a seed crystal 11, an adhesive layer 30 that adheres the seed crystal 11, and a support portion 41 to which the seed crystal 11 is adhered by the adhesive layer 30 is prepared. Ideally, it is desirable that the adhesive layer 30 has no voids, but in practice, a certain amount of voids VD (FIG. 3) is often formed.

(Modification example of adhesive)
Other types of adhesives may be used instead of the C-based adhesives described above, and for example, SiC-based adhesives may be used. The SiC-based adhesive is one whose main composition after curing is SiC. As the SiC-based adhesive, for example, a fluid containing polycarbosilane or a derivative thereof can be used. For example, xylene can be used as a solvent for the adhesive. The fluid is not limited to a solution, and may be a gel, a sol, or a slurry, for example. Here, the “derivative” of polycarbosilane refers to a polymer having a structure in which at least one of atoms and functional groups of polycarbosilane is substituted. Such substitution can occur, for example, due to impurities that are unintentionally incorporated in the production process of polycarbosilane.

  The atmosphere used for the heat treatment for curing preferably has a low oxygen partial pressure in order to prevent an oxidation reaction, and is, for example, an inert atmosphere or a vacuum atmosphere. The atmospheric pressure is preferably atmospheric pressure or lower. The temperature of the heat treatment is preferably 800 ° C. or higher, for example, about 1000 ° C. When it is desired to sufficiently remove hydrogen contained in the adhesive, the heat treatment temperature is preferably 1300 ° C. or higher. When more sufficient crystallization of the adhesive is desired, the heat treatment temperature is preferably 1600 ° C. or higher. The heat treatment temperature is set to 2000 ° C. or lower, preferably 1800 ° C. or lower in order to suppress sublimation of silicon carbide. The heat treatment time is, for example, about 30 minutes.

(Inspection of inspection object)
Next, a method for inspecting the adhesion state of the seed crystal 11 in the inspection object IS (FIG. 3) prepared as described above will be described.

  Referring to FIG. 4, an ultrasonic microscope having a head HD is prepared. The head HD performs irradiation of the ultrasonic wave UL and detection of the reflected wave RF of the ultrasonic wave UL. Preferably, the frequency of the ultrasonic wave UL is 10 MHz or more and 100 MHz or less. The resolution of the ultrasonic microscope is, for example, about 1 μm.

  Next, it arrange | positions so that the surface of the seed crystal 11 as to-be-inspected surface SS may oppose head HD. Preferably, the space between the surface to be inspected SS and the head HD is filled with liquid. This liquid is, for example, water.

  Next, observation with an ultrasonic microscope is performed. That is, the ultrasonic wave UL is irradiated onto the surface SS to be inspected IS so as to pass through the seed crystal 11 and reach the adhesive layer 30, and the reflected wave RF of the ultrasonic wave UL is detected. The irradiation of the ultrasonic wave UL and the detection of the reflected wave RF are repeated at different positions in the surface of the inspection surface SS. In order to measure different positions in the surface SS to be inspected parallel to the xy-plane, for example, the position of the head HD may be moved in the x direction (the direction of the arrow x in FIG. 4) and the y direction. . Instead of moving the head HD, the inspection object IS may be moved.

  In the above observation, a pulse of the ultrasonic wave UL is first incident on each observation position on the inspection surface SS. When there is no void VD in the adhesive layer 30 at the inspection position, the reflected wave RF is mainly the reflected wave RFa from the surface SS to be inspected. However, as the frequency of the ultrasonic wave UL is lower, the reflected wave RFb from the opposite surface of the surface SS to be inspected is also included.

  When there is no void VD in the path through which the ultrasonic wave UL is transmitted, as shown in FIG. 5, when the pulse of the ultrasonic wave UL from the head HD disappears, the intensity I of the reflected wave RF becomes time as shown in FIG. Decays rapidly as t passes. On the other hand, as shown in FIG. 6, when there is a void VD in the path through which the ultrasonic wave UL passes, after the pulse of the ultrasonic wave UL from the head HD disappears, as shown in FIG. The intensity I of the sound attenuates more slowly. This is because the reflected wave RFm (FIG. 6) from the void VD is not easily attenuated due to multiple scattering in the void VD.

The attenuation constant of the reflected wave RF is obtained for each observation position on the inspection surface SS. Here, the attenuation constant of the reflected wave RF is a parameter representing the attenuation characteristic of the reflected wave RF generated after the disappearance of the pulse of the ultrasonic wave UL. In the present embodiment, a logarithmic attenuation rate δ is used as the attenuation constant. The logarithmic damping rate δ is obtained by taking the natural logarithm of the ratio of adjacent amplitudes of the damped free vibration waveform as shown in FIG. For example, the n-th amplitudes a _n, as shown in FIG. 7, n + 1 th amplitude a _{n + 1,} when a and n + m-th amplitude a _{n + m} are detected, logarithmic decrement δ is
δ = (1 / m) · ln (a _n / a _{n + m} )
Defined by

  As shown in FIG. 8, the distribution of the logarithmic attenuation rate δ of the reflected wave RF of the ultrasonic wave UL on the inspection surface SS is calculated by scanning the observation position of the inspection surface SS. Next, a portion of the surface to be inspected SS in which the logarithmic attenuation rate δ is within the predetermined threshold value TH is recognized as a defective area FL, and a portion in which the logarithmic attenuation rate δ is outside the predetermined threshold value TH is preferable. Recognized as a region PS. Thereby, as shown in FIG. 9, the distribution of the defective area FL and the suitable area PS is created on the surface SS to be inspected. Next, the ratio (defective ratio) of the defective area FL on the inspection surface SS is calculated. That is, the ratio of the portion where the logarithmic attenuation rate δ is within the range of the predetermined threshold TH on the surface to be inspected SS is calculated.

  It is determined that the inspection object IS having a defect ratio equal to or less than a predetermined value satisfies the standard, and the inspection object IS having a defect ratio exceeding a predetermined value is determined not to satisfy the standard. For example, it is determined that a defective rate of less than 20% satisfies the standard.

(Production of single crystal)
The inspection object IS (FIG. 3) determined to satisfy the above-described standard is prepared.

  Referring to FIG. 10, raw material 51 is stored in crucible 42. When a single crystal of silicon carbide is grown, for example, silicon carbide powder is placed in a graphite crucible. Next, the support part 41 is attached so that the seed crystal 11 faces the inside of the crucible 42. As shown in FIG. 10, the support portion 41 may function as a lid for the crucible 42.

  Next, a single crystal 52 is grown on the seed crystal 11. When silicon carbide single crystal 52 is manufactured using silicon carbide seed crystal 11, a sublimation recrystallization method can be used as the formation method. That is, the single crystal 52 can be grown by depositing the sublimate on the seed crystal 11 by sublimating the raw material 51 as indicated by the arrows in the figure. The temperature in this sublimation recrystallization method is, for example, 2100 ° C. or higher and 2500 ° C. or lower. The pressure in the sublimation recrystallization method is preferably 1.3 kPa or more and atmospheric pressure or less, and more preferably 13 kPa or less in order to increase the growth rate.

(Function and effect)
According to the present embodiment, by detecting that the logarithmic attenuation rate δ of the reflected wave RF of the ultrasonic wave UL decreases due to the void VD (FIG. 4) in the adhesive layer 30 (FIG. 8), the void Presence of VD can be accurately grasped. Therefore, the adhesion state of the seed crystal 11 can be inspected with high accuracy.

  Further, the ratio of the portion where the logarithmic attenuation rate δ falls within the predetermined threshold TH in the surface SS to be inspected is calculated (FIG. 9). Thereby, a test result can be quantified.

  Seed crystal 11 is made of silicon carbide. Since the seed crystal 11 made of silicon carbide is particularly susceptible to the void VD in the adhesive layer 30, this inspection method is particularly suitable.

  Preferably, the adhesive layer 30 includes a layer made using a C-based or SiC-based adhesive. When these adhesives are used, void VD is particularly likely to occur. Therefore, it is possible to inspect with high accuracy by this inspection method capable of accurately grasping the void VD.

  Preferably, the frequency of the ultrasonic wave UL is 10 MHz to 100 MHz. If the frequency is too low, the rate at which the ultrasonic wave UL that has entered from the inspection surface SS of the inspection object IS reaches the opposite surface becomes high, and inspection accuracy is caused by the influence of the reflected wave RFb from this opposite surface. Decreases. Therefore, the frequency is preferably 10 MHz or more. If the frequency is too high, the intensity of the reflected wave RFm from the adhesive layer 30 becomes excessively small due to excessive attenuation of the ultrasonic wave in the inspection object IS. For this reason, inspection accuracy falls. Therefore, the frequency is preferably 100 MHz or less.

(Appendix)
In the above embodiment, the ultrasonic wave UL is irradiated to the surface SS to be inspected IS so as to pass through the seed crystal 11 and reach the adhesive layer 30 (FIG. 4). The ultrasonic wave UL may be applied to the surface to be inspected of the inspection object IS so as to pass through the portion 41 and reach the adhesive layer 30.

  Moreover, although what was formed from SiC as the seed crystal 11 was illustrated, what was formed from another material may be used. As this material, for example, GaN, ZnSe, ZnS, CdS, CdTe, AlN, or BN can be used.

  In the above embodiment, the coating film 21 is carbonized when the adhesive 22 is cured (FIG. 2). However, the coating film 21 may be carbonized before the adhesive 22 is formed. Further, the formation of the coating film 21 may be omitted. In this case, since the carbon film 31 (FIG. 3) is not formed, the fixed layer 32 contacts the seed crystal 11 instead of the carbon film 31.

  Further, the substrate may be manufactured using the single crystal 52 (FIG. 10). Such a substrate is obtained, for example, by slicing the single crystal 52.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  11 seed crystal, 21 coating film, 22 adhesive, 30 adhesive layer, 31 carbon film, 32 fixing layer, 41 support part, 42 crucible, 51 raw material, 52 single crystal, FL defective area, HD head, IS test object , PS suitable area, RF reflected wave, SS surface to be inspected, UL ultrasonic wave, VD void.

Claims (5)

A method for inspecting the adhesion state of a seed crystal,
Preparing an inspection object having the seed crystal, an adhesive layer bonding the seed crystal, and a support part to which the seed crystal is bonded by the adhesive layer;
Irradiating ultrasonic waves onto the surface to be inspected of the object to be inspected so as to pass through either the seed crystal or the support and reach the adhesive layer;
And a step of calculating a distribution of attenuation constants of the reflected waves of the ultrasonic waves on the surface to be inspected.   The seed crystal adhesion state inspection method according to claim 1, further comprising a step of calculating a ratio of a portion of the surface to be inspected in which the attenuation constant falls within a predetermined threshold range.   The seed crystal adhesion method according to claim 1 or 2, wherein the seed crystal is made of silicon carbide.   The said adhesion layer is an inspection method of the adhesion state of the seed crystal of any one of Claims 1-3 containing the layer made using C type | system | group or a SiC type | system | group adhesive agent.   The inspection method of the adhesion state of the seed crystal according to any one of claims 1 to 4, wherein a frequency of the ultrasonic wave is 10 MHz or more and 100 MHz or less.

Images