CN116660628A - Method for testing resistivity of cut conductive silicon carbide wafer - Google Patents
Method for testing resistivity of cut conductive silicon carbide wafer Download PDFInfo
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- 238000012360 testing method Methods 0.000 title claims abstract description 71
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 title claims abstract description 57
- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims abstract description 37
- 235000012431 wafers Nutrition 0.000 claims abstract description 185
- 238000004140 cleaning Methods 0.000 claims abstract description 39
- 239000002585 base Substances 0.000 claims abstract description 34
- 238000009826 distribution Methods 0.000 claims abstract description 21
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- 239000003960 organic solvent Substances 0.000 claims abstract description 12
- 239000000523 sample Substances 0.000 claims abstract description 11
- 238000010586 diagram Methods 0.000 claims abstract description 10
- 239000002253 acid Substances 0.000 claims abstract description 9
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 6
- 239000003513 alkali Substances 0.000 claims abstract description 5
- KRHYYFGTRYWZRS-UHFFFAOYSA-N Fluorane Chemical compound F KRHYYFGTRYWZRS-UHFFFAOYSA-N 0.000 claims description 24
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 21
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims description 20
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 claims description 18
- 238000005259 measurement Methods 0.000 claims description 18
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- 238000010998 test method Methods 0.000 claims description 13
- KWYUFKZDYYNOTN-UHFFFAOYSA-M Potassium hydroxide Chemical compound [OH-].[K+] KWYUFKZDYYNOTN-UHFFFAOYSA-M 0.000 claims description 12
- 238000011068 loading method Methods 0.000 claims description 7
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 6
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 6
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R27/00—Arrangements for measuring resistance, reactance, impedance, or electric characteristics derived therefrom
- G01R27/02—Measuring real or complex resistance, reactance, impedance, or other two-pole characteristics derived therefrom, e.g. time constant
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/34—Purifying; Cleaning
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/041—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The application discloses a method for testing resistivity of cut conductive silicon carbide wafers, which belongs to the technical field of silicon carbide wafers and comprises the following steps: a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank in which an organic solvent, acid liquor or alkali liquor and water are placed, cleaning the silicon carbide wafer, performing ultrasonic treatment in the organic solvent, and drying the silicon carbide wafer; b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer, and finally obtaining the average value of thickness data; c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points according to point location distribution, testing the probe twice on each point location during testing, and finally drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value. The resistivity test is advanced before grinding by using the limited type of solution for cleaning, so that the cost is saved; matching specific point location distribution provides accurate basis for judging wafer quality.
Description
Technical Field
The application relates to a method for testing resistivity of a cut conductive silicon carbide wafer, and belongs to the technical field of silicon carbide wafers.
Background
The resistivity of a conductive silicon carbide wafer is an important parameter, both for characterizing the wafer itself and the physical properties of the semiconductor device. For wafers, resistivity characterizes the uniformity of the wafer's growth and doping; for downstream devices, it directly affects the series resistance, capacitance, threshold voltage, hot carrier degradation of the MOS devices, and other related parameters of the devices. Thus, resistivity data for conductive silicon carbide wafers is one of the key parameters that must be tested.
There are many methods for testing resistivity of conductive silicon carbide wafers, such as four-probe, van der waals, and eddy current methods. In industry, eddy current methods are generally preferred because they are a non-destructive inspection. The testing principle of the vortex method is as follows: an alternating current with a certain frequency flows through the conductive coil to form an alternating magnetic field, meanwhile, eddy currents are induced on the wafer, and the magnetic field change generated by the eddy currents can be detected by the sensor, so that the square resistance of the substrate can be calculated. Meanwhile, according to the thickness of the wafer obtained by the test, the resistivity of the wafer can be directly obtained. Since the eddy current density is highest on the surface, the quality of the surface state directly affects the test accuracy. For conductive silicon carbide wafers, typical surface state measurement parameters include physical parameters such as surface contamination, surface roughness, flatness, warpage, and surface defects. These parameters affect the surface eddy current variations and, in general, these defects result in reduced eddy currents and thus larger resistivity data from the test. To solve these problems, the industry typically performs wafer processing on wafers, where the processing flow is: cutting the crystal bar, grinding, mechanical polishing and chemical mechanical polishing. The flatness of the wafer subjected to continuous processing is improved, and surface contamination can be cleaned, so that resistivity testing is facilitated. Typically resistivity testing is after the lapping process.
If resistivity data is obtained after dicing the wafer, the rejected wafer is screened out, which saves a significant portion of the polishing and cleaning throughput. In addition, the resistivity test is performed at the initial stage of wafer processing (after dicing), so that unnecessary scratch introduction is reduced in the finished wafer, and the yield is improved. In summary, testing resistivity immediately after dicing the resulting wafer can save costs and reduce unnecessary wafer damage, so we propose a solution for resistivity testing here.
The current resistivity test of conductive silicon carbide wafers is performed after the polishing process, rather than after dicing to obtain wafers. After dicing, subsequent grinding and cleaning are required to perform resistivity testing. Thus, the wafer with unqualified resistivity can be downloaded to the polishing and the cleaning process after polishing, and the polishing and the cleaning productivity are extruded. And after cutting, the unqualified wafers are subjected to chamfering treatment, so that unnecessary waste is caused, and the production cost is increased. In addition, during resistivity test, the wafer is required to be directly contacted with a metal base of a test instrument, and extra scratches are extremely easy to introduce in the contact process, so that further downloading and processing are not facilitated. Therefore, it is necessary to conduct resistivity testing early in the processing of silicon carbide wafers.
Chinese patent CN111320982 a-a micro-etching roughening treatment agent for wafer surface and its treatment method, discloses that micro-etching roughening treatment is performed on the wafer surface after chemical polishing and polishing by using the micro-etching roughening treatment agent, so that a uniform inverted residual spin structure is formed on the wafer surface, and the metal wiring yield in the subsequent process is improved, wherein a solution such as mixed acid is used, but the solution is finally used for later wiring, the problem of early resistivity of the wafer is not concerned, and the solution is a common silicon wafer, and if the silicon carbide wafer is processed, the surface morphology is affected, and the measurement result is affected.
In the prior art, the main reason that the resistivity test of the wafer is not carried out after cutting is that the surface state of the wafer after cutting is poor, the resistivity result obtained by direct test is larger than the true value, so that the partially qualified wafer is also easily judged to be unqualified, the yield is influenced, but the accuracy of the measurement result is also easily influenced if the wafer is processed.
Disclosure of Invention
In order to solve the above problems, a method for testing resistivity of cut conductive silicon carbide wafers is provided, in which the roughness of the wafers is reduced by cleaning with a defined kind of solution, and the resistivity testing process can be advanced before grinding, thus saving processing cost; meanwhile, specific point location distribution is matched, so that the resistivity data of the whole silicon carbide wafer can be obtained, the resistivity distribution and uniformity of each area of the wafer can be comprehensively evaluated, and a more accurate basis is provided for judging the quality of the wafer.
According to one aspect of the present application, there is provided a method of testing resistivity of a cut conductive silicon carbide wafer, comprising the steps of:
a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank in which an organic solvent, acid liquor or alkali liquor and water are placed, cleaning the silicon carbide wafer, performing ultrasonic treatment in an ultrasonic machine filled with the organic solvent, and drying the silicon carbide wafer;
b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer, and finally obtaining the average value of thickness data;
c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points according to point location distribution, testing the probe twice on each point location during testing, and finally drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value.
Optionally, four acid-base tanks are used in the step a, absolute ethyl alcohol, hydrofluoric acid, hydrochloric acid and ultrapure water are respectively filled in the four acid-base tanks, and a basket for loading the wafer sequentially passes through the four acid-base tanks and finally is subjected to ultrasonic treatment in an ultrasonic machine filled with the absolute ethyl alcohol.
Optionally, hydrofluoric acid with the mass percentage concentration of 2-5% and hydrochloric acid with the mass percentage concentration of 85-88% are used in the step a, and the conductivity of the ultrapure water is below 2 mu S/cm.
Optionally, three acid-base tanks are used in the step a, absolute ethyl alcohol, potassium hydroxide or sodium hydroxide solution and ultrapure water are respectively filled in the step a, and a basket for loading the wafer sequentially passes through the three acid-base tanks and finally is ultrasonically processed in an ultrasonic machine filled with the absolute ethyl alcohol.
Optionally, 45-50% potassium hydroxide or sodium hydroxide solution is used in step a, and the conductivity of the ultrapure water is below 2 mu S/cm.
Optionally, the temperature of the solution in each acid-base tank is 70-80 ℃, and the basket stays in each acid-base tank for at least 5min.
Optionally, the ultrasonic power is 140-160W, the ultrasonic frequency is 10-50kHz, and the ultrasonic time is 3-5min; the drying method is to wipe clean the surface of the wafer with clean non-woven fabrics or blow-dry with a nitrogen gun, and put the wafer into an ultra-clean room to be tested.
Preferably, the ultrasonic power is 150W, the ultrasonic frequency is 30kHz, and the ultrasonic time is 4min.
Optionally, in step c, the surface of the sample wafer operation table for resistivity test is wiped clean with alcohol, the silicon surface is required to face upwards when the wafer is placed, and after the wafer is placed, the average thickness of the wafer is input, wherein the unit is mu m, and the unit is accurate to the next decimal point.
Optionally, in step c, the resistivity is measured by using a 73-point test method, 8 concentric circles with the radius of 8mm, 16mm, 24mm, 32mm, 40mm, 48mm, 56mm and 64mm are formed outwards by taking the center of the wafer as the circle center, and meanwhile, radial lines with the circle center outwards being sequentially separated by 20 degrees intersect with each concentric circle.
Optionally, taking the circle center as a first locus, sequentially selecting an intersection point as a measuring locus on a minimum concentric circle at intervals of one radial line, selecting 9 intersection points as measuring loci on each concentric circle, and measuring loci of adjacent concentric circles are not on the same radial line.
The beneficial effects of the application include, but are not limited to:
1. according to the method for testing the resistivity of the cut conductive silicon carbide wafer, the cleaning solution and the sequence are limited, so that surface contamination is removed, the surface roughness is reduced, the surface state is changed, the influence of the surface on the size of vortex is reduced, and the testing precision is improved; meanwhile, specific distribution points are matched, accurate resistivity data can be obtained, the operation process is simple, the surface state of the wafer can be improved, and the method is suitable for resistivity tests of conductive silicon carbide wafers with different sizes and thicknesses.
2. According to the method for testing the resistivity of the cut conductive silicon carbide wafer, disclosed by the application, the cleaning sequence and concentration of the solution mainly comprising acid liquor are limited, absolute ethyl alcohol is firstly used as an initial cleaning solution, organic residues and dust on the surface of the wafer can be removed, the surface is purified, the oxide and oxide layer on the surface of the wafer can be effectively removed by using hydrofluoric acid with limited concentration, the surface pollution is reduced without seriously corroding the surface of the wafer, the damage is avoided, metal ions and other impurities on the surface of the wafer can be removed by using hydrochloric acid with limited concentration, the purity of further wafers is improved, the influence of moisture on the wafer can be reduced by using ultrapure water with limited conductivity, the moisture residue and ion pollution are avoided, and the accuracy of the test is improved; finally, after multi-stage chemical cleaning, ultrasonic waves are used for cleaning the wafer, so that tiny pollution on the surface, which is difficult to clean, can be further removed, the cleaning effect is more thorough, and the absolute ethyl alcohol is used as an ultrasonic medium, so that the wafer is not damaged;
if the cleaning is performed by using alkali liquor with limited concentration, metal ions on the surface can be effectively chelated without seriously corroding the surface of the wafer, and damage is avoided.
3. According to the method for testing the resistivity of the cut conductive silicon carbide wafer, the chemical reaction rate can be accelerated by limiting the specific temperature and time and matching the cleaning solution with the limited concentration, so that the reaction of pollutants and cleaning liquid can be accelerated, the cleaning efficiency can be improved, and the cleaning effect can be maximized on the premise of no damage.
4. According to the method for testing the resistivity of the cut conductive silicon carbide wafer, provided by the application, by innovatively arranging the 73-point test method, on one hand, the resistivity in the polar axis and polar angle directions can be better reflected, the resistivity of the whole surface of the wafer can be accurately represented, the resistivity of each region of the wafer can be comprehensively tested, the uniformity and distribution of the resistivity of the wafer can be evaluated according to the test result, and an accurate basis is provided for judging the quality of the wafer; on the other hand, the influence of local surface conditions on the test result can be eliminated, a more accurate average resistivity value of the wafer is obtained, richer and more detailed resistivity information is provided, the change trend and the local difference of the surface resistivity of the wafer are revealed, and finally a more accurate basis is provided for judging the quality of the wafer.
Drawings
The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description serve to explain the application and do not constitute a limitation on the application. In the drawings:
fig. 1 is a graph showing wafer roughness comparisons before and after a cleaning process according to the present application.
Fig. 2 is a schematic diagram of 73 point location distribution according to an embodiment of the present application.
Fig. 3 is a graph comparing wafer roughness atomic force microscopy before wafer cleaning after dicing according to the present application and after wafer roughness atomic force microscopy after wafer cleaning according to example 1.
Fig. 4 is a graph showing resistivity measurements of wafers before and after the wafer cleaning process after dicing according to the present application.
FIG. 5 is a graph of resistivity after treatment of comparative example 1.
FIG. 6 is a graph of resistivity after treatment of comparative example 2.
FIG. 7 is a plot of the dot profile and the resistivity test after processing in comparative example 3.
Detailed Description
The present application is described in detail below with reference to examples, but the present application is not limited to these examples.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. The reagents or materials used in the present application may be purchased in conventional manners, and unless otherwise indicated, they may be used in conventional manners in the art or according to the product specifications. In addition, any methods and materials similar or equivalent to those described herein can be used in the methods of the present application. The preferred methods and materials described in this patent are illustrative only.
Example 1
A method of testing resistivity of a cut conductive silicon carbide wafer, comprising the steps of:
a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank containing an organic solvent, an acid solution and water, cleaning the silicon carbide wafer, performing ultrasonic treatment in an ultrasonic machine filled with the organic solvent, and drying the silicon carbide wafer;
b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer, and finally obtaining the average value of thickness data;
c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points according to point location distribution, testing the probe twice on each point location during testing, and finally drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value.
In the step a, four acid-base tanks are used, absolute ethyl alcohol, hydrofluoric acid, hydrochloric acid and ultrapure water are respectively filled, a basket for loading wafers sequentially passes through the four acid-base tanks, and finally, ultrasonic waves are carried out in an ultrasonic machine filled with the absolute ethyl alcohol. The hydrofluoric acid with the mass percent concentration of 2% and the hydrochloric acid with the mass percent concentration of 85% are used in the step a, and the conductivity of the ultrapure water is below 2 mu S/cm.
The temperature of the solution in each acid-base tank is 75 ℃, and the basket stays in each acid-base tank for 5min. The ultrasonic power is 140W, and the ultrasonic time is 5min; the drying method is to wipe the surface of the wafer clean by using clean non-woven fabrics, and put the wafer into an ultra-clean room for testing. In the step c, the surface of a sample wafer operation table for resistivity test is wiped clean by alcohol, the silicon surface is required to face upwards when a wafer is placed, and after the wafer is placed, the average thickness of the wafer is input, wherein the unit is mu m, and the unit is accurate to the next decimal point.
Fig. 1 is a schematic diagram showing wafer roughness comparison before and after processing, wherein the upper diagram is before processing, and the lower diagram is after processing in example 1. The specific surface roughness pairs before and after treatment are shown in fig. 3, which is the result of the test using an atomic force microscope. The roughness before cleaning was 200nm and after cleaning by this example was 60nm.
In the step c, the resistivity is measured by adopting a 73-point test method, 8 concentric circles with the radius of 8mm, 16mm, 24mm, 32mm, 40mm, 48mm, 56mm and 64mm are outwards formed by taking the center of the wafer as the circle center, and meanwhile, radial lines with the circle center outwards formed at intervals of 20 degrees are intersected with each concentric circle. Taking the circle center as a first locus, sequentially selecting an intersection point as a measurement locus on a minimum concentric circle at intervals of one radial line, selecting 9 intersection points as measurement loci on each concentric circle, and taking the measurement loci of adjacent concentric circles not on the same radial line for 73 points in total. As shown in particular by the dot distribution in fig. 2.
As shown in fig. 4, and the maximum minimum and average values are counted. Fig. 4 compares the resistivity data before and after the cleaning process, and it can be seen that more accurate and comprehensive resistivity data is obtained after the cleaning process of example 1.
Example 2
A method of testing resistivity of a cut conductive silicon carbide wafer, comprising the steps of:
a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank in which an organic solvent, acid liquor and water are placed, cleaning the silicon carbide wafer, performing ultrasonic treatment in the organic solvent, and drying the silicon carbide wafer;
b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer, and finally obtaining the average value of thickness data;
c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points according to point location distribution, testing the probe twice on each point location during testing, and finally drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value.
In the step a, four acid-base tanks are used, absolute ethyl alcohol, hydrofluoric acid, hydrochloric acid and ultrapure water are respectively filled, a basket for loading wafers sequentially passes through the four acid-base tanks, and finally, ultrasonic waves are carried out in an ultrasonic machine filled with the absolute ethyl alcohol. The hydrofluoric acid with the mass percent concentration of 4% and the hydrochloric acid with the mass percent concentration of 87% are used in the step a, and the conductivity of the ultrapure water is below 2 mu S/cm.
The temperature of the solution in each acid-base tank is 70 ℃, and the basket stays in each acid-base tank for 5min. The ultrasonic power is 150W, and the ultrasonic time is 4min; the drying method is that a nitrogen gun is used for drying, and the air is put into an ultra-clean room to be tested. In the step c, the surface of a sample wafer operation table for resistivity test is wiped clean by alcohol, the silicon surface is required to face upwards when a wafer is placed, and after the wafer is placed, the average thickness of the wafer is input, wherein the unit is mu m, and the unit is accurate to the next decimal point.
In the step c, the resistivity is measured by adopting a 73-point test method, 8 concentric circles with the radius of 8mm, 16mm, 24mm, 32mm, 40mm, 48mm, 56mm and 64mm are outwards formed by taking the center of the wafer as the circle center, and meanwhile, radial lines with the circle center outwards formed at intervals of 20 degrees are intersected with each concentric circle. Taking the circle center as a first locus, sequentially selecting an intersection point as a measurement locus on a minimum concentric circle at intervals of one radial line, selecting 9 intersection points as measurement loci on each concentric circle, and taking the measurement loci of adjacent concentric circles not on the same radial line for 73 points in total.
Example 3
A method of testing resistivity of a post-conductivity silicon carbide wafer, comprising the steps of:
a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank in which an organic solvent, alkali liquor and water are placed, cleaning the silicon carbide wafer, performing ultrasonic treatment in the organic solvent, and drying the silicon carbide wafer;
b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer, and finally obtaining the average value of thickness data;
c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points according to point location distribution, testing the probe twice on each point location during testing, and finally drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value.
In the step a, three acid-base tanks are used, absolute ethyl alcohol, sodium hydroxide solution and ultrapure water are respectively filled, a basket for loading wafers sequentially passes through the three acid-base tanks, and finally, the ultrasonic wave is carried out in an ultrasonic machine filled with the absolute ethyl alcohol. The sodium hydroxide solution with the mass percent concentration of 45% is used in the step a, and the conductivity of the ultrapure water is below 2 mu S/cm. The temperature of the solution in each acid-base tank is 75 ℃, and the basket stays in each acid-base tank for 5min. The ultrasonic power is 160W, and the ultrasonic time is 3min; the drying method is to wipe the surface of the wafer clean by using clean non-woven fabrics, and put the wafer into an ultra-clean room for testing. In the step c, the surface of a sample wafer operation table for resistivity test is wiped clean by alcohol, the silicon surface is required to face upwards when a wafer is placed, and after the wafer is placed, the average thickness of the wafer is input, wherein the unit is mu m, and the unit is accurate to the next decimal point.
In the step c, the resistivity is measured by adopting a 73-point test method, 8 concentric circles with the radius of 8mm, 16mm, 24mm, 32mm, 40mm, 48mm, 56mm and 64mm are outwards formed by taking the center of the wafer as the circle center, and meanwhile, radial lines with the circle center outwards formed at intervals of 20 degrees are intersected with each concentric circle.
Taking the circle center as a first locus, sequentially selecting an intersection point as a measuring locus on a minimum concentric circle at intervals of one radial line, selecting 9 intersection points as measuring loci on each concentric circle, and taking the measuring loci of adjacent concentric circles not on the same radial line for 73 loci in total.
Comparative example 1
Comparative example 1 differs from example 1 in that: only 5% hydrofluoric acid was used in comparative example 1.
The resistivity data in fig. 5 is 5% hydrofluoric acid treated, and the selected wafer is adjacent to the wafer in example 1, as can be seen by the more non-uniform resistivity after treatment, and less efficient.
Comparative example 2
Comparative example 2 differs from example 1 in that: comparative example 2 the hydrofluoric acid having a concentration of 10% by mass and the hydrochloric acid having a concentration of 50% by mass were used in step a. The selected wafer was the wafer adjacent to that of example 1, and the resistivity after processing as shown in fig. 6 still differed significantly from that of example 1.
Comparative example 3
Comparative example 3 differs from example 1 in that: the measurement points in comparative example 3 were measured by other means, as shown in the left graph of fig. 7, and also were 73 points, and unlike in example 1, the centers of circles formed radial lines at 22.5 ° intervals outwards in order, 8 points for each concentric circle, and 16 points for the outermost circle. The selected wafer is the wafer adjacent to the wafer in example 1, and the resistivity edge after processing is larger as shown in the right-hand graph of fig. 7.
Experimental example
The untreated wafer was tested with example 1 and comparative examples 1-3 according to conventional test methods to obtain average resistivity and variance data as shown in table 1.
Table 1 average resistivity and variance data table
As can be seen from the above table, the average resistivity of example 1 is the smallest and the variance is the smallest. It was demonstrated that the method of example 1 gave more accurate and uniformly distributed resistivity values with high accuracy.
As can be seen from the drawings, the cleaning method and the measurement point location defined by the application have good effect on the surface treatment of the wafer finally, are favorable for accurate subsequent measurement, can obtain the resistivity data of the whole silicon carbide wafer, can comprehensively evaluate the resistivity distribution and uniformity of each area of the wafer, and provide more accurate basis for judging the quality of the wafer.
Comparative example 1, in which the treatment was performed with a single acid, had a general cleaning effect on wafers, and was liable to affect the accuracy of the post-measurement; the acid concentration adopted in comparative example 2 is beyond the range defined by the application, so that excessive etching is easily caused on the surface of the wafer, and the measurement result is affected; the point location distribution in comparative example 3 cannot fully embody the wafer resistivity finally, and it is difficult to provide accurate basis for final judgment.
The above description is only an example of the present application, and the scope of the present application is not limited to the specific examples, but is defined by the claims of the present application. Various modifications and variations of the present application will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the technical idea and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. A method of testing resistivity of a cut conductive silicon carbide wafer, comprising the steps of:
a. and (3) sectional cleaning: placing the cut silicon carbide wafer in a flower basket, sequentially soaking the silicon carbide wafer in an acid-base tank in which an organic solvent, acid liquor or alkali liquor and water are placed, cleaning the silicon carbide wafer, performing ultrasonic treatment in an ultrasonic machine filled with the organic solvent, and drying the silicon carbide wafer;
b. using an FRT surface type tester to test the thickness of a plurality of points on the surface of the wafer and obtaining the average value of thickness data;
c. and inputting the average thickness of the wafer by using a non-contact resistivity tester, setting test points by using 73-point test point bit distribution, testing the probe twice on each point during test, drawing a resistivity distribution diagram of the whole wafer surface, and counting the maximum value, the minimum value and the average value.
2. The method for testing the resistivity of the cut conductive silicon carbide wafer according to claim 1, wherein four acid-base tanks are used in the step a, absolute ethyl alcohol, hydrofluoric acid, hydrochloric acid and ultrapure water are respectively filled in the four acid-base tanks, and a basket for loading the wafer sequentially passes through the four acid-base tanks and finally is subjected to ultrasonic treatment in an ultrasonic machine filled with the absolute ethyl alcohol.
3. The method for testing resistivity of cut conductive silicon carbide wafer according to claim 2, wherein the hydrofluoric acid with a mass concentration of 2-5% and the hydrochloric acid with a mass concentration of 85-88% are used in the step a, and the conductivity of the ultrapure water is below 2 μs/cm.
4. The method for testing the resistivity of cut conductive silicon carbide wafers according to claim 1, wherein three acid-base tanks are used in the step a, absolute ethyl alcohol, potassium hydroxide or sodium hydroxide solution and ultrapure water are respectively filled in the three acid-base tanks, and a basket for loading the wafers sequentially passes through the three acid-base tanks and finally is subjected to ultrasonic treatment in an ultrasonic machine filled with the absolute ethyl alcohol.
5. The method for testing resistivity of cut conductive silicon carbide wafers according to claim 4, wherein the potassium hydroxide or sodium hydroxide solution having a concentration of 45 to 50% by mass is used in the step a, and the conductivity of ultrapure water is 2 μs/cm or less.
6. The method of testing the resistivity of cut conductive silicon carbide wafers of claim 1 wherein the temperature of the solution in each acid-base tank is 70-80 ℃ and the basket stays in each acid-base tank for at least 5 minutes.
7. The method of testing the resistivity of a cut conductive silicon carbide wafer of claim 4 wherein the ultrasonic power is 140-160W, the ultrasonic frequency is 10-50kHz, and the ultrasonic time is 3-5min;
the drying method is to wipe clean the surface of the wafer with clean non-woven fabrics or blow-dry with a nitrogen gun, and put the wafer into an ultra-clean room to be tested.
8. The method of claim 1, wherein in step c, the surface of the wafer table is cleaned with alcohol, the wafer is placed with the silicon facing upwards, and the average thickness of the wafer is input after the wafer is placed, in μm, to the decimal point.
9. The method of claim 1, wherein the resistivity of the cut conductive silicon carbide wafer is measured by a 73-point test in the step c, wherein 8 concentric circles with the radii of 8mm, 16mm, 24mm, 32mm, 40mm, 48mm, 56mm and 64mm are formed outwards by taking the center of the wafer as the center of the circle, and the center of the circle outwards forms radial lines which are sequentially spaced by 20 ° to intersect each concentric circle.
10. The method of claim 9, wherein the center of a circle is a first locus, one intersection point is selected as a measurement locus by sequentially separating a radial line on a smallest concentric circle, 9 intersection points are selected as measurement loci on each concentric circle, and the measurement loci of adjacent concentric circles are not on the same radial line.
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