CN114544745A - Detection method for distribution of trace impurity elements in high-purity GaN single crystal - Google Patents

Abstract

The invention relates to the technical field of material detection, and discloses a detection method for the distribution of trace impurity elements in high-purity GaN single crystals, which comprises the following steps: step 1, placing a GaN single crystal sample to be tested on an objective table in a sample chamber; step 2, vacuumizing the sample chamber, and introducing carrier gas to increase the air pressure of the sample chamber to atmospheric pressure; vacuumizing, introducing the carrier gas to atmospheric pressure again, and repeating for several times; and 3, introducing carrier gas into the sample chamber, keeping stable airflow to continuously purge the sample chamber, introducing ICP torch flame, detecting the mass-to-charge ratio of each element to be detected, and counting until the mass spectrum signal of the element to be detected is stable and then is used as a blank value. The method does not need strong acid, strong alkali and digestion equipment, is green and environment-friendly, does not need special processing for samples, is convenient and quick to detect, has low lower limit of measurement, less interference and is sensitive and accurate; the method can be directly used for measuring the content of the impurity elements of the high-purity GaN and measuring the distribution plane (three-dimensional) of the impurity elements; the limitation caused by chemical digestion of the sample is completely avoided.

Description

Detection method for distribution of trace impurity elements in high-purity GaN single crystal

Technical Field

The invention relates to the field of material detection, in particular to a detection method for the distribution of trace impurity elements in high-purity GaN single crystals.

Background

Gallium nitride is a third-generation semiconductor material, and has the characteristics of large forbidden band width, high thermal conductivity, high temperature resistance, radiation resistance, acid and alkali resistance, high strength, high hardness and the like. The GaN device has high breakdown electric field, high thermal conductivity, electron saturation rate obviously higher than that of other semiconductor materials, and excellent radiation resistance, and is very suitable for manufacturing high-temperature, high-frequency and high-power electronic devices. In addition, the optical band gap is wider, so that the material can be used for preparing blue-green light and ultraviolet light emitting devices, short-wavelength lasers, microwave power devices and the like. However, impurities in GaN seriously affect the quality of semiconductor devices, and thus are important for the detection and control of impurity elements in high-purity GaN single crystals.

At present, for the detection method of impurity elements in high-purity GaN single crystals, a glow discharge mass spectrometry, a secondary ion mass spectrometry and an inductively coupled plasma mass spectrometry are generally adopted. The existing methods have advantages respectively, but have disadvantages respectively, for example, the detected impurity element types are not comprehensive, the space resolution detection can not be carried out, or the direct solid sample injection detection can not be carried out, and the practical requirements can not be met.

Glow discharge mass spectrometry (GD-MS) is the most effective means for directly analyzing trace and ultra-trace elements of solid conductive materials, and has been widely applied to analysis of various high-purity metals, alloys and other materials in recent years. However, the following problems also exist for measuring the impurity concentration and distribution of a GaN single crystal wafer:

1) the forbidden band width of GaN is larger (3.4eV), the resistivity is higher under the condition of no doping, the conductivity is poorer, and the GD-MS is inconvenient to directly detect.

2) GD-MS adopts Ar ion bombardment to await measuring the surface of the sample, and the bombardment region is about 1 centimetre generally in the diameter, so can't detect the plane distribution of impurity concentration in the GaN single crystal piece.

Secondary Ion Mass Spectrometry (SIMS) requires detection in an ultra-high vacuum (<10-6Pa) environment, the equipment is very expensive and the test time is long, making detection cost prohibitive.

Inductively coupled plasma mass spectrometry (ICP-MS) adopts solution sample injection, and a sample needs to be dissolved into a liquid solution for detection; high-purity GaN is an insoluble compound with high melting point, high boiling point and acid and alkali resistance, various common acids are difficult to digest at normal temperature and normal pressure or under microwave conditions, and high-purity GaN is easily polluted by chemical reagents and the like in the dissolving process, so that even under the alkali melting condition, an alkali fusing agent which is several times or tens times of that of a sample is required to be added, and acid which is several times of that of the sample is also required to be added for neutralization, the sample preparation process is complex, the reagent (impurity) blank is high, the interference factors are many, and the detection of trace or trace impurities in the high-purity GaN is very difficult. Therefore, the method has great limitations and cannot be used for measuring trace impurity elements of high-purity GaN, and the method cannot detect the planar (or three-dimensional) distribution of the impurity elements of the single crystal epitaxial layer because a sample is completely dissolved into a solution.

In order to solve the above problems, the present application proposes a method for detecting the distribution of trace impurity elements in a high purity GaN single crystal.

Disclosure of Invention

Objects of the invention

In order to solve the technical problems in the background technology, the invention provides a detection method for the distribution of trace impurity elements in high-purity GaN single crystals, strong acid, strong alkali and digestion equipment are not needed, the method is green and environment-friendly, a sample does not need to be specially processed, the detection is convenient and quick, the lower limit of the determination is low, the interference is less, and the sensitivity and the accuracy are high; the method can be directly used for measuring the content of the impurity elements of the high-purity GaN and measuring the distribution plane (three-dimensional) of the impurity elements; the limitation caused by chemical digestion of the sample is completely avoided.

(II) technical scheme

In order to solve the above problems, the present invention provides a method for detecting the distribution of trace impurity elements in a high purity GaN single crystal, comprising the steps of:

step 1, placing a GaN single crystal sample to be detected on an objective table in a sample chamber;

step 2, vacuumizing the sample chamber, and introducing carrier gas to increase the air pressure of the sample chamber to atmospheric pressure; vacuumizing, introducing the carrier gas to atmospheric pressure again, and repeating for several times;

step 3, introducing carrier gas into the sample chamber, keeping stable gas flow to continuously purge the sample chamber, introducing ICP torch flame, detecting mass-to-charge ratio count of each element to be detected, taking the mass-to-charge ratio count as a blank value after mass spectrum signals of the element to be detected are stable, and entering the next step;

step 4, drawing a calibration curve:

in a pulse mode, adjusting a laser to focus on the surface of a GaN standard sample which is quantitatively doped, and measuring the mass-to-charge ratio count of impurity elements; the number of the quantitatively doped series GaN standard samples is generally not less than three, the steps 1-3 are repeated, and a calibration curve for measuring impurity elements is drawn by linear fitting;

step 5, sample testing:

keeping the working condition of a GaN standard sample to be tested, focusing laser on the surface of the GaN single crystal sample to be tested, observing the position of a laser spot through a CCD camera, calibrating by using a coordinatometer, and dividing the sample into M multiplied by N plane (xy) regions to be tested;

step 6, adjusting laser power:

injecting laser to the 1 st test area of the GaN monocrystal to generate vaporized sample atoms to be tested, blowing the vaporized sample atoms into an ICP torch tube by carrier gas, ionizing the sample atoms, and then introducing the sample atoms into a mass spectrometer to test the mass-to-charge ratio count of the elements to be tested; the ablation action is repeated longitudinally (z) under the same laser ablation condition at the same plane position according to the requirement, and the mass-to-charge ratio counting of the impurity elements is repeated for K times; then, the lens is adjusted to focus the laser to 2 nd to M multiplied by N test areas, and the measurement is carried out according to the same mode to obtain the xyz three-dimensional distribution (M multiplied by N multiplied by K data sets) of the GaN single crystal trace impurities.

Preferably, in step 2, this is repeated 3 times so that the vacuum chamber is finally filled with positive pressure.

Preferably, in the step 2, after the mechanical pump is vacuumized, the air pressure of the sample chamber is 1-5 pa.

Preferably, in the step 2, the carrier gas is argon or helium.

Preferably, in the step 3, the flow rate of the carrier gas is in the range of 0.5-1L/min.

Preferably, in the step 4, the laser is an ArF excimer laser, the center wavelength is 193nm, the maximum energy of a single pulse is 240mJ, and the pulse frequency is 1 to 20 Hz.

Preferably, in step 5, the planar resolution of the laser spot is at least 5 microns.

Preferably, the step 6 includes:

step 601: when the longitudinal denudation action K is 1, obtaining the plane (xy) distribution of the content of the impurity elements on the surface of the GaN single crystal;

step 602: when M ═ N ═ K, the sample single point impurity content was obtained.

Preferably, the purity of the carrier gas is 99.999% or more.

The technical scheme of the invention has the following beneficial technical effects:

1. the element in the sample is vaporized by means of high-energy laser acting on the surface of the sample, so that the problem of secondary pollution caused by conventional solution sample preparation of ICP-MS is avoided, and the problem that GD-MS analysis cannot be directly carried out due to poor conductivity of GaN is solved; the sample chamber is simplified by means of carrier gas purging, an ultrahigh vacuum environment is not required, the equipment is simple and cheap, and the problems of high cost and high detection cost of SIMS equipment are solved.

2. Micro-area analysis of sample impurities can be performed by virtue of the advantage of laser energy focusing, and the surface distribution of the impurities can be obtained by scanning laser spots; the laser power is adjusted to strip in the depth direction in a certain area, so that the impurity depth distribution of the area can be obtained, and meanwhile, the idea is developed for component detection of other similar single crystal materials.

3. The test method has the advantages of high detection speed and high analysis precision.

Drawings

FIG. 1 is a flow chart of a method for detecting the distribution of trace impurity elements in a high purity GaN single crystal according to the present invention.

FIG. 2 is a diagram showing an implementation of the method for detecting the distribution of trace impurity elements in a high purity GaN single crystal according to the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings in conjunction with the following detailed description. It should be understood that the description is intended to be exemplary only, and is not intended to limit the scope of the present invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.

Example 1

The method for measuring the surface distribution of the trace impurities in the GaN single crystal wafer comprises the following steps:

step 1, placing a GaN single crystal wafer to be tested on an objective table in a sample chamber;

step 2, closing the valve 1, opening the valve 2, vacuumizing the sample chamber to 3pa by using a mechanical pump, closing the valve 2, and introducing high-purity argon (the purity is more than 99.999%) to increase the air pressure of the sample chamber to the atmospheric pressure; vacuumizing to 3pa again, introducing argon to atmospheric pressure again, repeating the steps for 3 times, filling the vacuum chamber with argon of more than one atmospheric pressure, closing the valve 2, and closing the mechanical pump;

step 3, opening a valve 1, introducing argon into the sample chamber, keeping a stable gas flow of 1L/min to continuously purge the sample chamber, introducing the gas flow into an ICP torch flame, detecting the mass-to-charge ratio count of each element to be detected until the mass-to-charge ratio signal of the element to be detected is stable and is used as a blank value, and entering the next step;

step 4, drawing a calibration curve: an ArF excimer laser with a center wavelength of 193nm, a single pulse energy of 90mJ and a pulse frequency of 5Hz was used. And adjusting laser spots to focus on the surface of the quantitatively doped GaN standard sample in a pulse mode, and measuring the mass-to-charge ratio of the impurity elements. Selecting three standard GaN single crystal samples quantitatively doped with silicon and oxygen, repeating the steps 1-3, and drawing an impurity element determination calibration curve by linear fitting;

step 5, sample testing: keeping the working condition of a GaN standard sample to be tested, focusing laser on the surface of the GaN single crystal sample to be tested, observing the position of a laser spot through a CCD camera, calibrating by using a coordinatometer, and dividing the sample into 10 multiplied by 10 planar regions to be tested;

step 6, adjusting laser power, enabling laser to be incident on the 1 st test region of the GaN single crystal, generating vaporized sample atoms to be tested, purging and introducing the vaporized sample atoms into an ICP torch tube by carrier gas, ionizing the sample atoms, and then introducing the sample atoms into a mass spectrometer to test the mass-to-charge ratio count of elements to be tested; and adjusting a lens to focus laser to 2 nd to 10 multiplied by 10 test regions, and measuring according to the same mode to obtain xy plane distribution of trace impurities of the GaN single crystal.

Example 2:

the depth distribution determination of the trace impurities in the GaN single crystal wafer comprises the following steps:

step 1, placing a GaN single crystal wafer to be tested on an objective table in a sample chamber;

step 2, closing the valve 1, opening the valve 2, vacuumizing the sample chamber to 3pa by using a mechanical pump, closing the valve 2, and introducing high-purity argon (the purity is more than 99.999%) to increase the air pressure of the sample chamber to the atmospheric pressure; vacuumizing to 3pa again, introducing argon to atmospheric pressure again, repeating the steps for 3 times, filling the vacuum chamber with argon of more than one atmospheric pressure, closing the valve 2 and closing the mechanical pump;

step 3, opening a valve 1, introducing argon into the sample chamber, keeping a stable gas flow of 1L/min to continuously purge the sample chamber, introducing the gas flow into an ICP torch flame, detecting the mass-to-charge ratio count of each element to be detected until the mass-to-charge ratio signal of the element to be detected is stable and is used as a blank value, and entering the next step;

step 4, drawing a calibration curve: an ArF excimer laser with a center wavelength of 193nm, a single pulse energy of 120mJ and a pulse frequency of 8Hz was used. Adjusting laser spots to focus on the surface of the quantitatively doped GaN standard sample in a pulse mode, measuring the mass-to-charge ratio count of impurity elements, selecting three types of quantitatively doped silicon and oxygen standard GaN single crystal samples, repeating the steps 1-3, and drawing an impurity element measurement calibration curve by adopting linear fitting.

Step 5, sample testing: keeping the working condition of a GaN standard sample to be tested, focusing laser on the surface of a GaN single crystal sample to be tested, observing the position of a laser spot through a CCD camera, and adjusting the spot to the position to be tested on the surface of the single crystal;

step 6, adjusting laser power, enabling laser to be incident on a test area, generating vaporized sample atoms to be tested, purging and introducing the vaporized sample atoms into an ICP torch tube by carrier gas, ionizing the sample atoms, and then introducing the sample atoms into a mass spectrometer to test the mass-to-charge ratio count of the elements to be tested; and (3) at the same position, using the same laser ablation condition, longitudinally repeating the ablation action along the depth direction of the wafer, and detecting the mass-to-charge ratio of the impurity elements in the same mode for 10 times in total to obtain the depth distribution of the trace impurities of the GaN monocrystal.

The method has the advantages that the elements in the sample are vaporized by means of the action of high-energy laser on the surface of the sample, the problem of secondary pollution caused by conventional solution sample preparation of ICP-MS is avoided, and the problem that GD-MS analysis cannot be directly carried out due to poor conductivity of GaN is solved; the sample chamber is simplified by means of carrier gas purging, an ultrahigh vacuum environment is not required, the equipment is simple and cheap, and the problems of high cost and high detection cost of SIMS equipment are solved; micro-area analysis of sample impurities can be performed by virtue of the advantage of laser energy focusing, and the surface distribution of the impurities can be obtained by scanning laser spots; the laser power is adjusted to strip in the depth direction in a certain area, so that the impurity depth distribution of the area can be obtained, and meanwhile, the idea is developed for component detection of other similar single crystal materials; the Element XR high-resolution mass spectrometer widely applied at present and produced by ThermoFisher company is adopted, and the test method has the advantages of high detection speed and high analysis precision.

It is to be understood that the above-described embodiments of the present invention are merely illustrative of or explaining the principles of the invention and are not to be construed as limiting the invention. Therefore, any modification, equivalent replacement, improvement and the like made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. Further, it is intended that the appended claims cover all such variations and modifications as fall within the scope and boundaries of the appended claims or the equivalents of such scope and boundaries.

Claims (9)

1. A detection method for the distribution of trace impurity elements in high-purity GaN single crystals is characterized by comprising the following steps:

step 1, placing a GaN single crystal sample to be tested on an objective table in a sample chamber;

step 2, vacuumizing the sample chamber, and introducing carrier gas to increase the air pressure of the sample chamber to atmospheric pressure; vacuumizing, introducing the carrier gas to atmospheric pressure again, and repeating for several times;

step 3, introducing carrier gas into the sample chamber, keeping stable airflow to continuously purge the sample chamber, introducing ICP torch flame, detecting mass-to-charge ratio counts of elements to be detected until mass spectrum signals of the elements to be detected are stable and then serve as blank values, and entering the next step;

step 4, drawing a calibration curve:

in a pulse mode, adjusting a laser to focus on the surface of a GaN standard sample which is quantitatively doped, and measuring the mass-to-charge ratio count of impurity elements; the number of the quantitatively doped series GaN standard samples is generally not less than three, the steps 1-3 are repeated, and a calibration curve for measuring impurity elements is drawn by linear fitting;

step 5, sample testing:

keeping the working condition of a GaN standard sample to be tested, focusing laser on the surface of the GaN single crystal sample to be tested, observing the position of a laser spot through a CCD camera, calibrating by using a coordinatometer, and dividing the sample into M multiplied by N plane (xy) regions to be tested;

step 6, adjusting laser power:

injecting laser to the 1 st test area of the GaN monocrystal to generate vaporized sample atoms to be tested, blowing the vaporized sample atoms into an ICP torch tube by carrier gas, ionizing the sample atoms, and then introducing the sample atoms into a mass spectrometer to test the mass-to-charge ratio count of the elements to be tested; the ablation action is repeated longitudinally (z) under the same laser ablation condition at the same plane position according to the requirement, and the mass-to-charge ratio counting of the impurity elements is repeated for K times; then, the lens is adjusted to focus the laser to 2 nd to M multiplied by N test areas, and the measurement is carried out according to the same mode to obtain the xyz three-dimensional distribution (M multiplied by N multiplied by K data sets) of the GaN single crystal trace impurities.

2. The method for detecting the distribution of trace impurity elements in a high purity GaN single crystal according to claim 1, wherein in step 2, the process is repeated 3 times so that the vacuum chamber is filled with positive pressure last.

3. The method for detecting the distribution of the trace impurity elements in the high-purity GaN single crystal according to claim 1, wherein in the step 2, after the mechanical pump is vacuumized, the air pressure of the sample chamber is 1-5 pa.

4. The method for detecting the distribution of trace impurity elements in a high-purity GaN single crystal according to claim 1, wherein in step 2, the carrier gas is argon or helium.

5. The method as claimed in claim 1, wherein in said step 3, the flow rate of the carrier gas is in the range of 0.5 to 1L/min.

6. The method according to claim 1, wherein in step 4, the laser is an ArF excimer laser with a center wavelength of 193nm, a single pulse with a maximum energy of 240mJ and a pulse frequency of 1-20 Hz.

7. The method for detecting the distribution of trace impurity elements in a high purity GaN single crystal according to claim 1, wherein in step 5, the planar resolution of the laser spot is at least 5 μm.

8. The method for detecting the distribution of the trace impurity elements in the high-purity GaN single crystal according to claim 1, wherein the step 6 comprises:

step 601: when the longitudinal denudation action K is 1, obtaining the plane (xy) distribution of the content of the impurity elements on the surface of the GaN single crystal;

step 602: when M ═ N ═ K, the sample single point impurity content was obtained.

9. The method as claimed in claim 4, wherein the purity of the carrier gas is 99.999% or more.

Images