Test method for measuring resistivity of monocrystal silicon - In-line four-point probe and direct current two-point probe method
1 Scope
This standard specifies the test method for measuring resistivity of monocrystal silicon by in-line four-point probe and direct current two-point probe method.
This standard is applicable to the measurement of resistivity of monocrystal silicon, in which, in-line four-point probe method is applicable to the p-type monocrystal silicon with a resistivity of 7×10-4~8×103Ω·cm and n-type monocrystal silicon with a resistivity of 7×10-4~1.5×104Ω·cm; direct current two-point probe method is applicable to the round, square or rectangular monocrystal silicon with an uniform cross-sectional area (the ratio of sample length to the maximum cross-sectional dimension is not less than 3:1) with a resistivity of 1×10-3~1×104Ω·cm. This document may be used as a reference for the test of monocrystal silicon with a resistivity other than those specified above.
2 Normative references
The following referenced documents are indispensable for the application of this standard. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 1550 Test methods for conductivity type of extrinsic semiconducting materials
GB/T 14264 Semiconductor materials -Terms and definitions
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 14264 apply.
4 Test conditions
Test shall be carried out at an environment temperature of 23±5℃ and a relative humidity of not greater than 65%.
5 Interference factors
5.1 Light may have an influence on the measured resistivity, therefore the test should be carried out in a dark environment or a light shield as possible unless the sample to be tested is insensitive to the surrounding light.
Note: The influence of light is more significant for samples with a resistivity of greater than 103Ω·cm.
5.2 The test apparatus placed near the high-frequency interference source may cause stray current in the sample due to AC interference, which may cause errors in measured resistivity, so the apparatus in this case shall be provided with electromagnetic shielding.
5.3 The sample should not have a too large electric field intensity so as to avoid minority carrier injection which may lead to a decrease in resistivity for samples with high resistivity and long life. The influence of minority carrier injection on resistivity may be obtained by repeated testing at low current, and no significant change in resistivity in repeated testing indicates that the minority carrier injection has little influence. The change in resistivity shall not be greater than ±0.5% if the test is carried out at a current of 2 or 1/2 times of an appropriate current.
5.4 Temperature has an influence on the measured resistivity, therefore the environment temperature shall be kept stable during the test. The reference temperature is 23±0.5℃, and the test results at other temperatures (18~28℃) may be corrected appropriately. It is suggested that the environment temperature during arbitration test be 23±0.5℃.
5.5 The probe vibration will cause a change in contact resistance. In this case, the apparatus and sample shall be equipped with a vibration isolation device, or the equipment shall be equipped with a vibration prevention device.
5.6 As the type and pressure of the probe head have an influence on the test results, the probe with an appropriate type and pressure shall be selected according to the shape of the sample during the test.
5.7 The interference factors for in-line four-point probe method include:
a) too large current or too long period of current introduction during test may improve the temperature of the sample test area, so the current should be as small as possible during the test, and the current introduction period in each test should be as short as possible. If the resistivity changes with the increase of current introduction period, it means that the sample is hot, in this case, a radiator should be used to keep the sample at the test temperature for enough time so as to reach temperature equilibrium;
b) the thickness is required to be tested according to 6.4.3 during arbitration test. Under general conditions, test users may determine the allowable thickness tolerance according to actual needs;
c) the radial resistivity of monocrystal silicon is not uniform and the sample has finite boundary, therefore the contact between the probe and the sample may have an influence on the measured resistivity. In arbitration test, the probe shall be within a range of 0.25mm from the sample center and the probe spacing shall be 1.59mm.
5.8 The interference factors for direct current two-point probe method include:
a) the test result by direct current two-point probe method will only represent the mean resistivity of a certain test section of the crystal if the resistivity of the sample is non-uniform, and the resistivity of the wafer cut from the monocrystal silicon is not relevant to the resistivity of monocrystal silicon measured by direct current two-point probe method;
b) presence of slight fracture (generally invisible to the naked eyes) or other mechanical damage in the sample, if any, may lead to a wrong resistivity test result;
c) more than one conductivity type in the whole crystal of the sample may lead to a wrong resistivity test result.
6 In-line four-point probe method
6.1 Principle
Four probes arranged in a straight line are pressed vertically on a flat sample surface which is approximately semi-infinite, when DC current flows into semiconductor sample from Probe 1 and Probe 4, based on the point source superposition principle, the potential at Probe 2 and Probe 3 is the sum of the potential generated by current source at Probe 1 and Probe 4, and the potential difference between Probe 2 and Probe 3 is a function of current source intensity, sample resistivity and probe coefficient. Direct current I is introduced into the sample between Probe 1 and Probe 4, and the potential difference V generated between Probe 2 and Probe 3 is measured. The resistivity is calculated using Equation (1) according to the measured current and potential difference. See Figure 1 for the schematic diagram. The resistivity of wafer sample shall be corrected using the correction factor according to the ratio of the thickness and the diameter to the mean probe spacing.
(1)
where,
ρ——the resistivity, Ω·cm;
S——the probe spacing, cm;
V——the measured potential difference, mV;
I——the measured current, A.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Test conditions
5 Interference factors
6 In-line four-point probe method
7 Direct current two-point probe method
