CN115825682A - Method for detecting deep energy level defect of detector-grade high-purity germanium single crystal - Google Patents
Method for detecting deep energy level defect of detector-grade high-purity germanium single crystal Download PDFInfo
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Abstract
A method for detecting deep level defects of a detector-grade high-purity germanium single crystal comprises the following steps: the detector-grade high-purity germanium single crystal is a p-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the head of the p-type germanium single crystal to carry out carrier concentration and dislocation density detection respectively, and DLTS sample wafers are taken from the head of the residual crystal of the p-type germanium single crystal; processing; sputtering a dot tin film on the front surface of the DLTS sample wafer to be used as a Schottky electrode, connecting the back surface of the DLTS sample wafer with a tin foil to form a copper sheet, wherein the outer contour of the surface of the copper sheet is larger than that of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and the area of the part is more than ten times that of the dot tin film, so that a detection sample is formed; and (3) detection: and (3) contact detection, if the contact between the Schottky electrode and the ohmic electrode is not a problem, carrying out normal-temperature IV curve detection, if the detection sample forms Schottky contact, carrying out DLTS spectrum signal detection, and if the DLTS spectrum signal is good, starting complete low-temperature DLTS detection to obtain a DLTS spectrum.
Description
Technical Field
The disclosure relates to the field of germanium, and more particularly to a method for detecting deep level defects of a detector-grade high-purity germanium single crystal.
Background
The high-purity germanium single crystal material is the highest material in germanium series products with the highest technical difficulty in preparation, has the purity of 13N, and is a core material for manufacturing a high-purity germanium detector. Compared with other detectors, the high-purity germanium detector has incomparable advantages of good energy resolution, high detection efficiency, strong stability and the like, becomes indispensable instrument and equipment for nuclear physics, particle physics, inspection and quarantine, biomedicine and national defense safety, and has wide market application prospect.
DLTS (Deep Level Transient Spectroscopy) is an important technical means for researching and detecting semiconductor impurities, defect Deep levels, interface states and the like in the field of semiconductors.
However, the DLTS detection belongs to non-standard detection, and different detection samples need to be designed for different materials to ensure that an effective detection result can be obtained. At present, no report is available for detecting deep level defects by adopting DLTS equipment aiming at detector-grade high-purity germanium single crystals, so that a detection method for the deep level defects of the detector-grade high-purity germanium single crystals is required to be developed.
Disclosure of Invention
In view of the problems in the background art, the present disclosure is directed to a method for detecting deep level defects of a detector-grade high-purity germanium single crystal, which can detect deep level defects of a detector-grade high-purity germanium single crystal.
Therefore, the method for detecting the deep level defects of the detector-grade high-purity germanium single crystal comprises the following steps: s1, sampling: the detector-grade high-purity germanium single crystal is a p-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the head of the p-type germanium single crystal to respectively detect the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the p-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the p-type germanium single crystal is less than 10000cm -2 Then, taking a DLTS sample wafer at the head of the residual crystal of the p-type germanium single crystal; s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying; s3, preparing an electrode: sputtering a dot tin film on the front surface of the DLTS sample wafer, wherein the dot tin film is used as a Schottky electrode, the back surface of the DLTS sample wafer is connected with a copper sheet by using a tin foil, the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, and the outer contour of the surface of the copper sheet is larger than that of the DLTS sample waferThe surface outline of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times of the area of the dot tin film; thereby forming a test sample; and S4, detecting, namely putting a detection sample into a sample stage of DLTS detection equipment, enabling a positive probe of the sample stage to be in contact with the Schottky electrode of the detection sample, enabling a negative probe of the sample stage to be in contact with the part, exceeding the outer contour of the surface of the DLTS sample wafer, of the copper sheet, then performing contact detection to determine whether the Schottky electrode is in contact with the ohmic electrode or not, performing normal-temperature IV curve detection if the Schottky electrode is not in contact with the ohmic electrode, performing DLTS spectrum signal detection if the detection sample forms Schottky contact, and starting complete low-temperature DLTS detection to obtain a DLTS spectrum if the DLTS spectrum signal is good.
Therefore, the method for detecting the deep level defects of the detector-grade high-purity germanium single crystal comprises the following steps: s1, sampling: the detector-grade high-purity germanium single crystal is an n-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the tail of the n-type germanium single crystal to respectively detect the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the n-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the n-type germanium single crystal is less than 5000cm -2 Then, a DLTS sample wafer is taken from the tail part of the residual crystal of the n-type germanium single crystal; s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying; s3, preparing an electrode: sputtering a dot gold film on the front surface of the DLTS sample wafer, and then carrying out annealing heat treatment, wherein the dot gold film is used as a Schottky electrode, the back surface of the DLTS sample wafer is connected with a copper sheet by a tin foil, the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, the surface outline of the copper sheet is larger than the surface outline of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times of that of the dot gold film; thereby forming a test sample; s4, detection: putting a detection sample into a sample table of DLTS detection equipment, wherein a positive probe of the sample table is contacted with a Schottky electrode of the detection sample, and a negative probe of the sample tableAnd (3) the needle is contacted with the part of the copper sheet, which exceeds the surface outline of the DLTS sample sheet, and then contact detection is carried out to determine whether the contact between the Schottky electrode and the ohmic electrode is in a problem, if the contact between the Schottky electrode and the ohmic electrode is not in a problem, normal-temperature IV curve detection is carried out, if the detection sample forms Schottky contact, DLTS spectrum signal detection is carried out, and if the DLTS spectrum signal is good, complete low-temperature DLTS detection is carried out to obtain a DLTS spectrum.
The beneficial effects of this disclosure are as follows: based on the two detection methods for detecting the deep level defect of the detector-grade high-purity germanium single crystal, the detection of the deep level defect of the detector-grade high-purity germanium single crystal can be realized.
Drawings
Fig. 1 is a graph showing an IV curve for a p-type germanium single crystal that is acceptable at room temperature in example 1.
Fig. 2 is a graph of the IV curve at normal temperature of comparative example 1 in which the schottky electrode and the ohmic electrode for the p-type germanium single crystal were not annealed.
FIG. 3 is a graph of DLTS spectrum signals for p-type germanium single crystals that pass at 160K in example 1.
Fig. 4 is a graph of DLTS spectral signals for a p-type germanium single crystal at 160K for comparative example 1.
Fig. 5 is a graph of DLTS spectrum signal at 160K for comparative example 2 where the area of the portion of the tin foil covering and contacting the back surface of the DLTS sample sheet for p-type germanium single crystal was five times the area of the dome tin film.
FIG. 6 is a graph of DLTS spectra in the range of 10K to 160K for p-type high single crystals of example 1.
FIG. 7 is a graph of DLTS spectra for comparative example 2 for the range of 10K-160K for p-type high single crystals.
FIG. 8 is a graph of DLTS spectrum signals for n-type germanium single crystals that pass at 160K in example 2.
Fig. 9 is a graph of DLTS spectra for the 10K-160K range for n-type high purity germanium of example 2.
Detailed Description
[ method for detecting deep level defects of detector-grade high-purity germanium single crystal-p-type germanium single crystal ]
The method for detecting the deep level defects of the detector-grade high-purity germanium single crystal aiming at the p-type germanium single crystal comprises the following steps:
s1, sampling: the detector-grade high-purity germanium single crystal is a p-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the head of the p-type germanium single crystal to respectively detect the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the p-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the p-type germanium single crystal is less than 10000cm -2 Then, taking a DLTS sample wafer at the head of the residual crystal of the p-type germanium single crystal;
s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying;
s3, preparing an electrode: sputtering a dot tin film on the front surface of the DLTS sample wafer, wherein the dot tin film is used as a Schottky electrode, the back surface of the DLTS sample wafer is connected with a copper sheet by a tin foil, the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, the surface outline of the copper sheet is larger than that of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times of that of the dot tin film, and then annealing is carried out, so that a detection sample is formed;
s4, detection: putting a detection sample into a sample stage of DLTS detection equipment, contacting a positive electrode 5 probe of the sample stage with a Schottky electrode of the detection sample, contacting a negative electrode probe of the sample stage with a part of a copper sheet exceeding the surface outline of a DLTS sample sheet, then carrying out electrode contact detection to determine whether the contact between the Schottky electrode and an ohmic electrode is problematic, if the contact between the Schottky electrode and the ohmic electrode is not problematic, carrying out normal-temperature IV curve detection, and if the detection sample forms Schottky contact, carrying out DLTS spectrum confidence
And (4) detecting, if the DLTS spectrum signal is good, starting to perform complete low-temperature DLTS detection to obtain a 0DLTS spectrum.
In one embodiment, in step S1, the Hall sample wafer has a sampling specification of (8-12 mm) × (8-12 mm) × (1-2 mm), the dislocation sample wafer has a sampling specification of the entire cross-section of the head portion of the p-type germanium single crystal × (3-5 mm), and the DLTS sample wafer has a sampling specification of (15-20 mm) × (15-20 mm) × (3-5 mm).
5 in step S1, the carrier concentration of the hall coupon is detected by HL9900 of Toho Technology, usa, the four corners of the hall coupon are pressed with tin particles, annealed to form a good ohmic contact, and then an IV test is performed on HL9900, and after no problem, a low temperature hall test is performed to determine the carrier concentration. Wherein the annealing heat treatment specifically comprises the following steps: placing into a 7N nitrogen annealing furnace at 300-400 deg.C for 20-30min.
0 in step S1, the dislocation density is that after the dislocation sample wafer is milled and polished to be flat and smooth on both sides by a milling machine,
polishing to a mirror surface, cleaning with pure water, putting the dislocation sample wafer into a constant temperature corrosive liquid at 5-15 ℃ for corrosion for 5-10min, and detecting on a metallographic microscope. The etching solution is hydrofluoric acid, nitric acid, 10% copper nitrate = 2.
Similarly, in one embodiment, in step S2, the etching solution used for etching is hydrofluoric acid, nitric acid 5, 10% copper nitrate = 1.
In step S3, in one embodiment, the dot tin film has a diameter of 1-2mm and a thickness of 100-200nm corresponding to the sampling specification of the DLTS sample (i.e., (15-20 mm) × (15-20 mm) × (3-5 mm), and the tin foil takes the same profile as the DLTS sample (i.e., (15-20 mm) × (15-20 mm)) to completely contact and cover the back surface of the DLTS sample, and the thickness of the tin foil is 30-50 μm.
0 in step S3, the area of the portion of the tinfoil covering and contacting the back surface of the DLTS sample is ten times or more the area of the dome tin film, and the DLTS spectrum signal can be efficiently obtained in step S4, see the comparison between fig. 3 and 5.
In the step S3, by adding the copper sheet, the outer contour of the surface of which is larger than that of the DLTS sample sheet, on one hand, the protection of the copper sheet on the tin foil is increased, so that the stability of the ohmic electrode is enhanced, on the other hand, the resistance to the vibration of the helium cooling table from a low temperature is increased in the complete DLTS detection process, and the stability of the contact between the tin foil and the back surface of the DLTS sample sheet is improved. The size of the outer contour of the surface of the copper sheet is enough to meet the requirement that a negative probe of the sample table is in contact with the part of the copper sheet, which exceeds the outer contour of the surface of the DLTS sample table, and the thickness of the copper sheet is enough to ensure that the copper sheet has certain integral hardness so as to resist deformation caused by the vibration of the helium cooling table at low temperature. Specifically, the thickness of the copper sheet is 0.5-1mm.
In one embodiment, in step S3, the back surface of the DLTS sample is connected to the copper sheet by tin foil, and the method includes: and (3) placing tin foil between the back surface of the DLTS sample wafer and the copper sheet with a cleaning glove, and extruding the DLTS sample wafer and the copper sheet from two sides by hands to connect the DLTS sample wafer, the tin foil and the copper sheet together.
In step S3, the germanium sheet is brought into better contact with the schottky electrode and the ohmic electrode by an annealing process, and the IV curve maintains the diode characteristics, as shown by comparing fig. 1 and fig. 2.
In one embodiment, in step S3, the annealing is: the DLTS sample wafer sputtered with the tin film faces upwards, the copper sheet is arranged below the tin foil, and the DLTS sample wafer is placed in a 7N nitrogen annealing furnace at the temperature of 300-400 ℃ for 20-30min.
Note that, in step S3, since the dot tin film and the tin foil are both made of tin, the entire annealing process may be performed once, thereby saving the detection time and improving the detection efficiency.
In step S4, the electrode contact test is performed directly using the DLTS device' S own function. In the method for detecting the deep-level defects of the detector-grade high-purity germanium single crystal, the DLTS equipment is a digital deep-level transient spectrometer DLTS of Sula Technologies, USA, and the DLTS equipment can linearly display that the capacitance value of a test sample is stabilized within 1%, namely, the contact between a Schottky electrode and an ohmic electrode is determined to be free of problems.
In step S4, a normal temperature IV curve test is performed, and if the IV curve of the test sample is non-linear (for example, fig. 1), the schottky contact is formed.
In step S4, the DLTS spectrum signal detection is performed at the maximum point of the low-temperature range of the complete low-temperature DLTS detection, for example, if the low-temperature range is 10 to 160K, the DLTS spectrum signal detection is performed at 160K, which is convenient for directly continuing to perform the complete low-temperature DLTS detection under the condition that the DLTS spectrum signal obtained by the DLTS spectrum signal detection is good, so that the complete low-temperature DLTS detection does not need to wait or readjust to the maximum point of the low-temperature range as a starting point to start, thereby saving the detection time and improving the detection efficiency.
In step S4, the DLTS spectrum signal is good by whether the spectrum signal graph of the DLTS output forms a good exponential curve, and the thinner the line of the exponential curve, the better the spectrum signal of the DLTS, as shown in fig. 3, for example.
In step S4, the low-temperature range of the complete low-temperature DLTS spectrum detection is provided by the DLTS device itself, the sample stage of the DLTS of the digital deep level transient spectrometer DLTS of Sula Technologies, usa has a helium cooling stage with a temperature adjustable and connected with a compressor, and the low-temperature range of the complete low-temperature DLTS spectrum detection is 10K to 160K.
[ method of detecting deep level defects of a detector-grade high-purity germanium single crystal-n-type germanium single crystal ]
The method for detecting the deep level defect of the detector-grade high-purity germanium single crystal aiming at the n-type germanium single crystal comprises the following steps:
s1, sampling: the detector-grade high-purity germanium single crystal is an n-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the tail part of the n-type germanium single crystal for respectively detecting the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the n-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the n-type germanium single crystal is less than 5000cm -2 Then, a DLTS sample wafer is taken from the tail part of the residual crystal of the n-type germanium single crystal;
s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying;
s3, preparing an electrode: sputtering a dot gold film on the front surface of the DLTS sample wafer, and then carrying out annealing heat treatment, wherein the dot gold film is used as a Schottky electrode; connecting the back surface of the DLTS sample wafer with a copper sheet by using a tin foil, wherein the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, the surface outline of the copper sheet is larger than that of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times of that of the dot gold film, and then annealing treatment is carried out, so that a detection sample is formed;
s4, detection: and (2) placing a detection sample into a sample stage of DLTS detection equipment, wherein a positive probe of the sample stage is in contact with a Schottky electrode of the detection sample, a negative probe of the sample stage is in contact with a part of the copper sheet, which exceeds the surface outline of the DLTS sample sheet, then performing electrode contact detection to determine whether the contact between the Schottky electrode and the ohmic electrode is in problem, if the contact between the Schottky electrode and the ohmic electrode is not in problem, performing normal-temperature IV curve detection, and if the detection sample forms Schottky contact, performing DLTS spectrum signal detection, and if the DLTS spectrum signal is good, starting to perform complete low-temperature DLTS detection to obtain a DLTS spectrum.
Likewise, in one embodiment, in step S1, the Hall sample wafer has a sampling specification of (8-12 mm) × (8-12 mm) × (1-2 mm), the dislocation sample wafer has a sampling specification of the entire cross-section of the tail of the n-type germanium single crystal × (3-5 mm), and the DLTS sample wafer has a sampling specification of (15-20 mm) × (15-20 mm) × (3-5 mm).
Similarly, in step S1, the carrier concentration of the hall coupon was measured by HL9900 of Toho Technology, usa, and tin particles were pressed at four corners of the hall coupon, annealed to form a good ohmic contact, and then subjected to an IV test on HL9900, and after no problem, a low-temperature hall test was performed to determine the carrier concentration. Wherein the annealing heat treatment specifically comprises the following steps: placing into a 7N nitrogen annealing furnace at 300-400 deg.C for 20-30min.
Similarly, in step S1, the dislocation density is measured by milling the two sides of the dislocation sample wafer with a milling machine to be smooth, polishing to a mirror surface, cleaning with pure water, etching the dislocation sample wafer in a 5-15 ℃ constant temperature etching solution for 5-10min, and then detecting on a metallographic microscope. The etching solution is hydrofluoric acid, nitric acid, 10% copper nitrate = 2.
Similarly, in one embodiment, in step S2, the etching solution used for etching is hydrofluoric acid: nitric acid: 10% copper nitrate = 2.
In step S3, in one embodiment, the diameter of the dot gold film is 1-2mm and the thickness is 100-200nm, and the tin foil takes the same profile as the DLTS sample (i.e., (15-20 mm) × (15-20 mm)) to completely contact and cover the back surface of the DLTS sample, corresponding to the sampling specification of the DLTS sample (i.e., (15-20 mm) × (15-20 mm) × (3-5 mm)).
In step S3, the area of the portion of the foil covering and contacting the back surface of the DLTS sample is ten times or more the area of the dome gold film, and the DLTS spectrum signal can be efficiently obtained in step S4.
Similarly, in step S3, by adding the copper sheet, the outer contour of the surface of which is larger than that of the DLTS sample sheet, on one hand, the protection of the copper sheet on the tin foil is increased, so that the stability of the ohmic electrode is enhanced, on the other hand, the resistance to the vibration of the helium cooling table from a low temperature is increased in the complete DLTS detection process, and the stability of the contact between the tin foil and the back surface of the DLTS sample sheet is improved. The size of the outer contour of the surface of the copper sheet can meet the requirement that a negative electrode probe of the sample table is in contact with the part, exceeding the outer contour of the surface of the DLTS sample table, of the copper sheet, and the thickness of the copper sheet can ensure that the copper sheet has certain overall hardness so as to resist deformation caused by vibration of the low-temperature helium cooling table. Specifically, the thickness of the copper sheet is 0.5-1mm.
Likewise, in one embodiment, in step S3, the back surface of the DLTS sample is connected to the copper sheet by tin foil as follows: and (3) placing tin foil between the back surface of the DLTS sample wafer and the copper sheet with a cleaning glove, and extruding the DLTS sample wafer and the copper sheet from two sides by hands to connect the DLTS sample wafer, the tin foil and the copper sheet together.
In step S3, the germanium sheet is brought into better contact with the schottky electrode and the ohmic electrode through annealing heat treatment and annealing treatment, and the IV curve maintains the diode characteristics. However, since the dot gold film and the tin foil are different materials, in step S3, the dot gold film is sputtered and then annealed, and then a copper sheet is connected to the back surface of the DLTS sample sheet with the tin foil and then annealed.
In one embodiment, in step S3, the annealing heat treatment is: and (3) putting the DLTS sample wafer with the sputtered dot gold film with the front side facing upwards into a 7N nitrogen annealing furnace for annealing at the temperature of 1100-1150 ℃ for 20-30min.
In one embodiment, in step S3, the annealing process is: and (3) enabling the dot gold film of the DLTS sample wafer to be upward, placing the copper sheet below the tin foil, and putting the DLTS sample wafer into a 7N nitrogen annealing furnace at the temperature of 300-400 ℃ for 20-30min.
Likewise, in step S4, the electrode contact test is performed directly using the DLTS device' S own function. In the method for detecting the deep-level defects of the detector-grade high-purity germanium single crystal, DLTS equipment is a digital deep-level transient spectrometer DLTS of Sula Technologies, USA, and the DLTS equipment can linearly display that the capacitance value of a test sample is stabilized within 1%, namely, the contact between a Schottky electrode and an ohmic electrode is determined without problems.
Similarly, in step S4, a normal temperature IV curve test is performed, and if the IV curve of the test sample is non-linear, it is indicated that a schottky contact is formed.
Similarly, in step S4, the DLTS spectrum signal detection is performed at the maximum point of the low temperature range of the complete low temperature DLTS detection, for example, if the low temperature range is 10 to 160K, the DLTS spectrum signal detection is performed at 160K, which is convenient for directly continuing to perform the complete low temperature DLTS detection under the condition that the DLTS spectrum signal obtained by the DLTS spectrum signal detection is good, so that the complete low temperature DLTS detection does not need to wait or readjust to the maximum point of the low temperature range as a starting point to start, thereby saving the detection time and improving the detection efficiency.
Similarly, in step S4, the DLTS spectrum signal is good by whether the spectrum signal graph of the DLTS output forms a good exponential curve, and the thinner the line of the exponential curve, the better the spectrum signal of the DLTS, as shown in fig. 8, for example.
Similarly, in step S4, the low-temperature range of the complete low-temperature DLTS spectrum detection is provided by the DLTS device itself, the sample stage of the DLTS of the digital deep level transient spectrometer DLTS of Sula Technologies in usa has a helium cooling stage with a temperature adjustable connected with a compressor, and the low-temperature range of the complete low-temperature DLTS spectrum detection is 10K-160K.
[ test ]
Example 1
The method for detecting the deep level defects of the detector-grade high-purity germanium single crystal aiming at the p-type germanium single crystal comprises the following steps:
s1, sampling:
the detector-grade high-purity germanium single crystal is a p-type germanium single crystal, a Hall sample wafer and a dislocation sample wafer are taken from the head of the p-type germanium single crystal to be respectively subjected to carrier concentration and dislocation density detection, the sampling specification of the Hall sample wafer is 10mm multiplied by 2mm, and the sampling specification of the dislocation sample wafer is the thickness of the whole cross section multiplied by 4mm of the head of the p-type germanium single crystal; the carrier concentration of the Hall sample wafer is detected by HL9900 of Toho Technology company in America, tin particles are pressed at four corners of the Hall sample wafer, annealing heat treatment is carried out to form good ohmic contact, then IV test is carried out on the HL9900, and after no problem exists, low-temperature Hall detection is carried out to determine the carrier concentration, wherein the annealing heat treatment specifically comprises the following steps: placing in a 7N nitrogen annealing furnace at 350 deg.C for 25min; the dislocation density is that a milling machine is used for milling and grinding the two sides of a dislocation sample wafer to be flat and smooth, then the dislocation sample wafer is polished to a mirror surface, the dislocation sample wafer is cleaned by pure water, the dislocation sample wafer is put into a constant temperature corrosive liquid with the temperature of 10 ℃ for corrosion for 10min, and then the detection is carried out on a metallographic microscope, wherein the corrosive liquid is hydrofluoric acid, nitric acid and 10% copper nitrate = 1 (volume ratio);
if the carrier concentration of the Hall sample wafer of the p-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the p-type germanium single crystal is less than 10000cm -2 Taking a DLTS sample wafer at the head of the residual crystal of the p-type germanium single crystal, wherein the sampling specification of the DLTS sample wafer is 18mm multiplied by 4mm;
s2, processing:
carrying out surface grinding, polishing and corrosion (the corrosive liquid is hydrofluoric acid: nitric acid: 10% copper nitrate =2 = 1 (volume ratio)) on the DLTS sample wafer to a mirror surface, cleaning with pure water, and drying by blowing;
s3, preparing an electrode:
sputtering a dot tin film on the front surface of the DLTS sample wafer, wherein the dot tin film is 1.5mm in diameter and 150nm in thickness, the dot tin film is used as a Schottky electrode and is provided with a cleaning glove, a tin foil is placed between the back surface of the DLTS sample wafer and a copper sheet, the DLTS sample wafer and the copper sheet are squeezed by hands from two sides, and the DLTS sample wafer, the tin foil and the copper sheet are connected together, so that the back surface of the DLTS sample wafer is connected with the copper sheet by the tin foil, the tin foil takes the same contour as the DLTS sample wafer (namely 18mm multiplied by 18mm to be completely contacted and cover the back surface of the DLTS sample wafer), the thickness of the tin foil is 40 mu m, the surface outline of the copper sheet is 10mm larger than the surface outline of the DLTS sample wafer, the thickness of the copper sheet is 0.75mm, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and then annealing is carried out: the front side of the DLTS sample wafer sputtered with the tin film faces upwards, the copper sheet is arranged below the tin foil, and the DLTS sample wafer is placed in a 7N nitrogen annealing furnace at the temperature of 350 ℃ for 25min, so that a detection sample is formed;
s4, detection:
and (2) placing a detection sample into a sample stage of DLTS detection equipment, contacting a positive probe of the sample stage with a Schottky electrode of the detection sample, contacting a negative probe of the sample stage with a part of the copper sheet exceeding the surface outline of the DLTS sample sheet, and then carrying out electrode contact detection to determine whether the contact between the Schottky electrode and an ohmic electrode is in a problem, wherein the electrode contact test is directly carried out by utilizing the self-function of the DLTS equipment. In the method for detecting the deep-level defects of the detector-grade high-purity germanium single crystal, DLTS equipment is a digital deep-level transient spectrometer DLTS of Sula Technologies, USA, and the DLTS equipment can linearly display that the capacitance value of a test sample is stabilized within 1%, namely, the contact between a Schottky electrode and an ohmic electrode is determined to be free of problems;
if the contact between the Schottky electrode and the ohmic electrode is not problematic, performing normal-temperature IV curve detection by using DLTS equipment, and if the IV curve of a detection sample is nonlinear, indicating that Schottky contact is formed;
if the detected sample forms Schottky contact, DLTS equipment carries out DLTS spectrum signal detection, the DLTS spectrum signal detection is carried out at the maximum value point 160K of the low-temperature range of complete low-temperature DLTS detection, and the DLTS spectrum signal is well carried out through whether a spectrum signal diagram output by DLTS forms a good exponential curve or not, wherein a sample platform of a DLTS of a digital deep level transient spectrometer of Sula Technologies company in the United states is provided with a helium cooling platform with adjustable temperature connected with a compressor, and the low-temperature range of the complete low-temperature DLTS spectrum detection is 10K-160K;
if the DLTS spectrum signal is good, the DLTS equipment starts to perform complete low-temperature DLTS detection with the low temperature range of 10-160K so as to obtain a DLTS spectrum.
Comparative example 1
The same procedure as in example 1 was repeated, except that annealing was not conducted in step S3.
Comparative example 2
The same procedure as in example 1 was repeated except that the size of the tin foil was 5 times the area of the dot film in step S3.
Fig. 1 and fig. 2 show the results of normal temperature IV curve detection performed by the DLTS device in step S4 in example 1 and comparative example 1, respectively, and it can be seen from the comparison between fig. 1 and fig. 2 that in example 1, the germanium sheet is better contacted with the schottky electrode and the ohmic electrode by annealing, and the IV curve maintains the diode characteristics; whereas comparative example 1 did not employ annealing, the non-linearity of the IV curve was not good. Further, fig. 3 and fig. 4 respectively show the detection results of the DLTS spectrum signals in step S4 of example 1 and comparative example 1, and it is seen from the comparison between fig. 4 and fig. 3 that the DLTS spectrum signals in the subsequent step S4 cannot see the exponential curve because the step S3 of comparative example 1 does not adopt annealing, and thus the complete low-temperature DLTS spectrum detection cannot be performed.
Fig. 3 and 5 show the detection results of the DLTS spectrum signals in step S4 of example 1 and comparative example 2, respectively, and from the comparison of fig. 3 and 5, the area of the portion of the tin foil of fig. 5 covering and contacting the back surface of the DLTS sample is 5 times the area of the dot tin film, although the trend of the exponential curve can be seen, the line of the exponential curve is very thick.
Fig. 6 shows the DLTS spectrum of example 1, which clearly reveals a clear and well-defined peak representing a deep level defect. Fig. 7 gives the DLTS spectrum of comparative example 2. Based on the comparison of fig. 3 and 5, and further based on the comparison of fig. 6 and 7, the DLTS spectrum further obtained had few and insignificant peaks due to the difference in the DLTS spectrum signal of comparative example 2.
Example 2
The method for detecting the deep level defect of the detector-grade high-purity germanium single crystal aiming at the n-type germanium single crystal comprises the following steps:
s1, sampling:
the detector-grade high-purity germanium single crystal is an n-type germanium single crystal, a Hall sample wafer and a dislocation sample wafer are taken from the tail of the n-type germanium single crystal to be respectively subjected to carrier concentration and dislocation density detection, the sampling specification of the Hall sample wafer is 10mm multiplied by 2mm, and the sampling specification of the dislocation sample wafer is the thickness of the whole cross section multiplied by 4mm of the tail of the n-type germanium single crystal; the carrier concentration of the Hall sample wafer is detected by HL9900 of Toho Technology company in America, tin particles are pressed at four corners of the Hall sample wafer, annealing heat treatment is carried out to form good ohmic contact, then IV test is carried out on the HL9900, and after no problem exists, low-temperature Hall detection is carried out to determine the carrier concentration, wherein the annealing heat treatment specifically comprises the following steps: placing in a 7N nitrogen annealing furnace at 350 deg.C for 25min; the dislocation density is that a milling machine is used for milling and grinding the two sides of a dislocation sample wafer to be flat and smooth, then the dislocation sample wafer is polished to a mirror surface, the dislocation sample wafer is cleaned by pure water, the dislocation sample wafer is put into a constant temperature corrosive liquid with the temperature of 10 ℃ for corrosion for 10min, and then the detection is carried out on a metallographic microscope, wherein the corrosive liquid is hydrofluoric acid, nitric acid and 10% copper nitrate = 1 (volume ratio);
if the carrier concentration of the Hall sample wafer of the n-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the n-type germanium single crystal is less than 5000cm -2 Taking a DLTS sample wafer at the tail part of the residual crystal of the n-type germanium single crystal, wherein the sampling specification of the DLTS sample wafer is 18mm multiplied by 4mm;
s2, processing: carrying out surface grinding, polishing and corrosion (the corrosive liquid is hydrofluoric acid: nitric acid: 10% copper nitrate =2 = 1 (volume ratio)) on the DLTS sample wafer to a mirror surface, cleaning with pure water, and drying by blowing;
s3, preparing an electrode:
sputtering a dot gold film on the front surface of the DLTS sample wafer, wherein the diameter of the dot gold film is 1.5mm, the thickness of the dot gold film is 150nm, and then performing annealing heat treatment, wherein the annealing heat treatment comprises the following steps: placing the DLTS sample wafer with the dot gold film sputtered upwards in a 7N nitrogen annealing furnace for annealing at 1125 ℃ for 25min, wherein the dot gold film is used as a Schottky electrode; the method comprises the following steps of putting tin foil between the back surface of a DLTS sample wafer and a copper sheet, pressing the DLTS sample wafer and the copper sheet from two sides by hands to connect the DLTS sample wafer, the tin foil and the copper sheet together, connecting the copper sheet with the tin foil on the back surface of the DLTS sample wafer, taking the tin foil with the same contour as the DLTS sample wafer (namely 18mm multiplied by 18mm to completely contact and cover the back surface of the DLTS sample wafer), wherein the thickness of the tin foil is 40 mu m, the surface contour of the copper sheet is 10mm larger than the surface contour of the DLTS sample wafer, the thickness of the copper sheet is 0.75mm, and the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode and then annealing treatment is carried out, wherein the annealing treatment is as follows: enabling a dot gold film of the DLTS sample wafer to face upwards, enabling a copper sheet to be arranged below a tin foil, and putting the DLTS sample wafer into a 7N nitrogen annealing furnace at the temperature of 350 ℃ for 25min to form a detection sample;
s4, detection:
and (2) placing a detection sample into a sample stage of DLTS detection equipment, contacting a positive probe of the sample stage with a Schottky electrode of the detection sample, contacting a negative probe of the sample stage with a part of the copper sheet exceeding the surface outline of the DLTS sample sheet, and then carrying out electrode contact detection to determine whether the contact between the Schottky electrode and an ohmic electrode is in a problem, wherein the electrode contact test is directly carried out by utilizing the self-function of the DLTS equipment. In the method for detecting the deep-level defects of the detector-grade high-purity germanium single crystal, DLTS equipment is a digital deep-level transient spectrometer DLTS of Sula Technologies, USA, and the DLTS equipment can linearly display that the capacitance value of a test sample is stabilized within 1%, namely, the contact between a Schottky electrode and an ohmic electrode is determined to be free of problems;
if the contact between the Schottky electrode and the ohmic electrode is not problematic, performing normal-temperature IV curve detection by using DLTS equipment, and if the IV curve of a detection sample is nonlinear, indicating that Schottky contact is formed;
if the detection sample forms Schottky contact, DLTS equipment carries out DLTS spectrum signal detection, the DLTS spectrum signal detection is carried out at the maximum value point 160K of the low-temperature range of complete low-temperature DLTS detection, and the DLTS spectrum signal is well carried out through whether a spectrum signal diagram output by DLTS forms a good exponential curve, wherein a sample platform of a DLTS of a digital deep level transient spectrometer of Sula Technologies company in the United states is provided with a helium cooling platform with adjustable temperature connected with a compressor, and the low-temperature range of the complete low-temperature DLTS spectrum detection is 10K-160K;
if the DLTS spectrum signal is good, the DLTS equipment starts to perform complete low-temperature DLTS detection with the low temperature range of 10-160K so as to obtain a DLTS spectrum.
Fig. 8 shows the DLTS spectrum signal detection result in step S4 of embodiment 2. Fig. 9 shows the DLTS spectrum obtained in step S4 of example 2.
Claims (10)
1. A method for detecting deep level defects of a detector-grade high-purity germanium single crystal comprises the following steps:
s1, sampling: the detector-grade high-purity germanium single crystal is a p-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the head of the p-type germanium single crystal to respectively detect the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the p-type germanium single crystal is less than 2E10cm -3 And dislocation density of dislocation sample wafer of p-type germanium single crystal is less than 10000cm -2 Then, taking a DLTS sample wafer at the head of the residual crystal of the p-type germanium single crystal;
s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying;
s3, preparing an electrode: sputtering a dot tin film on the front surface of the DLTS sample wafer, wherein the dot tin film is used as a Schottky electrode, the back surface of the DLTS sample wafer is connected with a copper sheet by using a tin foil, the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, the surface outline of the copper sheet is larger than that of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times that of the dot tin film; thereby forming a test sample;
s4, detecting, namely placing a detection sample into a sample stage of DLTS detection equipment, contacting a positive probe of the sample stage with a Schottky electrode of the detection sample, contacting a negative probe of the sample stage with a part of a copper sheet, which exceeds the outer contour of the surface of a DLTS sample sheet, then performing contact detection to determine whether the contact between the Schottky electrode and an ohmic electrode is problematic, if the contact between the Schottky electrode and the ohmic electrode is not problematic, performing normal-temperature IV curve detection, if the detection sample forms Schottky contact, performing DLTS spectrum signal detection, and if the DLTS spectrum signal is good, starting to perform complete low-temperature DLTS detection to obtain a DLTS spectrum.
2. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S1, the Hall sample wafer has a sampling specification of (8-12 mm) × (8-12 mm) × (1-2 mm), the dislocation sample wafer has a sampling specification of the entire cross-section of the head portion of the p-type germanium single crystal × (3-5 mm) and the DLTS sample wafer has a sampling specification of (15-20 mm) × (15-20 mm) × (3-5 mm).
3. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S3, the back surface of the DLTS sample sheet is connected to the copper sheet by tin foil: and (3) placing tin foil between the back surface of the DLTS sample wafer and the copper sheet with a cleaning glove, and extruding the DLTS sample wafer and the copper sheet from two sides by hands to connect the DLTS sample wafer, the tin foil and the copper sheet together.
4. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S1, the sampling specification of the DLTS sample wafer is (15-20 mm) × (15-20 mm) × (3-5 mm);
in step S3, the dot tin film has a diameter of 1-2mm and a thickness of 100-200nm, and the tin foil takes the same profile as that of the DLTS sample sheet (15-20 mm). Times.15-20 mm) to completely contact and cover the back surface of the DLTS sample sheet, and has a thickness of 30-50 μm.
5. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S3, the annealing is: the DLTS sample wafer sputtered with the tin film faces upwards, the copper sheet is arranged below the tin foil, and the DLTS sample wafer is placed in a 7N nitrogen annealing furnace at the temperature of 300-400 ℃ for 20-30min.
6. A method for detecting deep level defects of a detector-grade high-purity germanium single crystal comprises the following steps:
s1, sampling: the detector-grade high-purity germanium single crystal is an n-type germanium single crystal, hall sample wafers and dislocation sample wafers are taken from the tail of the n-type germanium single crystal to respectively detect the carrier concentration and the dislocation density, and if the carrier concentration of the Hall sample wafers of the n-type germanium single crystal is less than 2E10cm -3 And the dislocation density of the dislocation sample wafer of the n-type germanium single crystal is less than 5000cm -2 Then, a DLTS sample wafer is taken from the tail part of the residual crystal of the n-type germanium single crystal;
s2, processing: grinding, polishing and corroding the surface of the DLTS sample wafer to a mirror surface, cleaning with pure water and drying;
s3, preparing an electrode: sputtering a dot gold film on the front surface of the DLTS sample wafer, and then carrying out annealing heat treatment, wherein the dot gold film is used as a Schottky electrode, the back surface of the DLTS sample wafer is connected with a copper sheet by a tin foil, the tin foil at least partially covers and contacts the back surface of the DLTS sample wafer, the surface outline of the copper sheet is larger than the surface outline of the DLTS sample wafer, the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is used as an ohmic electrode, and the area of the part of the tin foil covering and contacting the back surface of the DLTS sample wafer is more than ten times of that of the dot gold film; thereby forming a test sample;
s4, detection: and (2) placing a detection sample into a sample stage of DLTS detection equipment, contacting a positive probe of the sample stage with a Schottky electrode of the detection sample, contacting a negative probe of the sample stage with a part of the copper sheet, which exceeds the surface outline of the DLTS sample sheet, and then carrying out contact detection to determine whether the contact between the Schottky electrode and the ohmic electrode is problematic, if the contact between the Schottky electrode and the ohmic electrode is not problematic, carrying out normal-temperature IV curve detection, and if the detection sample forms Schottky contact, carrying out DLTS spectrum signal detection, and if the DLTS spectrum signal is good, starting to carry out complete low-temperature DLTS detection to obtain a DLTS spectrum.
7. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S1, the Hall sample wafer has a sampling specification of (8-12 mm) × (8-12 mm) × (1-2 mm), the dislocation sample wafer has a sampling specification of the thickness of the entire cross section of the tail of the n-type germanium single crystal × (3-5 mm), and the DLTS sample wafer has a sampling specification of (15-20 mm) × (15-20 mm) × (3-5 mm).
8. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S3, the back surface of the DLTS sample sheet is connected to the copper sheet by tin foil: and (3) placing tin foil between the back surface of the DLTS sample wafer and the copper sheet with a cleaning glove, and extruding the DLTS sample wafer and the copper sheet from two sides by hands to connect the DLTS sample wafer, the tin foil and the copper sheet together.
9. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S1, the sampling specification of the DLTS sample wafer is (15-20 mm) × (15-20 mm) × (3-5 mm);
in step S3, the dot gold film has a diameter of 1-2mm and a thickness of 100-200nm, and the foil is (15-20 mm). Times. (15-20 mm) the same contour as the DLTS sample so as to completely contact and cover the back surface of the DLTS sample, and has a thickness of 30-50 μm.
10. The method of detecting deep level defects in a detector-grade high-purity germanium single crystal according to claim 1,
in step S3, the annealing heat treatment is: placing the DLTS sample wafer with the sputtered dot gold film with the front side facing upwards into a 7N nitrogen annealing furnace for annealing at 1100-1150 ℃ for 20-30min;
in step S3, the annealing process is: the dot gold film of the DLTS sample wafer is upward, the copper sheet is arranged below the tin foil, and the DLTS sample wafer is placed into a 7N nitrogen annealing furnace at the temperature of 300-400 ℃ for 20-30min.
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