Measuring semiconductor doping using constant surface potential corona charging
An example method of characterizing a semiconductor sample includes measuring an initial value, V in , of a surface potential at a region of a surface of the semiconductor sample, biasing the semiconductor sample to have a target surface potential value (V 0 ) of 2V or less, and depositing a monitored amount of corona charge (ΔQ 1 ) on the region of the surface after adjusting the surface potential to the target value. The method also includes measuring a first value, V 1 , of the surface potential at the region after depositing the corona charge, determining the first change of surface potential (ΔV 1 =V 1 −V 0 ), and determining the first capacitance value C 1 =ΔQ 1 /ΔV 1 , and characterizing the semiconductor sample based on V 0 , V 1 , ΔV 1 , ΔQ 1 and C 1 .
1. A method of characterizing a semiconductor sample, the method comprising:
(i) measuring an initial value of a surface potential at a region of the semiconductor sample;
(ii) applying a bias voltage to the semiconductor sample via a voltage source electrically coupled to a surface of the semiconductor sample so that the semiconductor sample has a target surface potential value of two volts or less;
(iii) depositing a dose of corona charge on the region of the surface while applying the bias voltage to the semiconductor sample, wherein the amount of corona charge is monitored during the deposition;
(iv) measuring a further value of the surface potential at the region after depositing the dose of corona charge and removing the bias voltage from the semiconductor sample;
(v) determining an incremental value of surface potential equal to a difference between the values of the surface potential, without the bias voltage applied to the semiconductor sample, measured before and after depositing the dose of corona charge;
(vi) determining a surface space charge capacitance value of the semiconductor sample equal to a ratio of the dose of corona charge to the incremental value of the surface potential;
(vii) repeating steps (ii) through (vi) k times to provide k corona charge values, k incremental values of surface potential, and k surface space charge capacitance values, wherein k is an integer greater than 1 and sufficient to achieve a target doping monitoring depth of the semiconductor sample; and
(viii) characterizing the semiconductor sample based on the initial value of the surface potential, the k further values of the surface potential, the k corona charge doses, the k incremental values of the surface potential, and the k surface space charge capacitance values.
2. The method of claim 1 , wherein the k corona charge doses are corrected by a calibration function F(V, I) to obtain k corresponding charge density values under a probe used for measuring the surface potential.
3. The method of claim 2 , where each of the k charge density values are used to determine a corresponding corrected space charge capacitance equal to a ratio of the corresponding charge density value to the corresponding incremental value of the surface potential.
4. The method of claim 3 , where a corrected net corona charge density equal to a sum of the k charge density values and the corrected space charge capacitances are used to determine a doping density of the semiconductor sample.
5. The method of claim 4 , wherein a quality of the calibration function is determined using a capacitance charge factor equal to a product of the corrected space charge capacitance and the corresponding corrected net charge density value.
6. The method of claim 1 , further comprising performing a charge density calibration using a semiconductor calibrating sample with a known doping density over a distance W under a surface of the semiconductor calibrating sample.
7. The method of claim 1 , wherein a polarity of the corona charging is such that it creates a depletion surface space charge region in the semiconductor sample.
8. The method of claim 7 , wherein the semiconductor sample is an n-type semiconductor and the corona charge is deposited using a negative charging polarity.
9. The method of claim 7 , wherein the semiconductor sample is a p-type semiconductor and the corona charge is deposited using a positive charging polarity.
10. The method of claim 1 , wherein characterizing the semiconductor sample comprises determining a doping density and/or a doping profile.
11. The method of claim 1 , wherein the semiconductor sample comprises a wide bandgap semiconductor.
12. The method of claim 1 , wherein the semiconductor sample comprises a semiconductor selected from the group consisting of SiC, GaN, ZnO, ZnS, and ZnSe.
13. The method of claim 1 , wherein the surface potential measurements are performed using a non-contact vibrating probe.
14. The method of claim 1 , wherein the surface potential measurements are performed using a capacitive electrode.
15. The method of claim 1 , wherein the target surface potential is 0.5 volts or less.
16. The method of claim 1 , wherein the target surface potential is approximately zero volts.
17. The method of claim 1 , wherein the deposited corona charge is photo-neutralized and removed from the semiconductor surface using illumination with light of photon energy sufficient to generate excess carriers in the semiconductor sample.
18. The method of claim 17 , further comprising repeating characterization of the semiconductor sample after photo-neutralizing the deposited corona charge prior to each repetition.