Wide bandgap semiconductor characterization based on capacitance characteristics acquired using corona surface charge neutralization by UV radiation pulses
A method of characterizing a wide-bandgap semiconductor sample includes: depositing a corona charge on a surface of the sample; measuring a surface voltage at the region; irradiating the region with a series of ultraviolet (UV) radiation pulses to neutralize the deposited charge, wherein the increments of neutralized corona charge are linear with the pulse duration; measuring the surface voltage at the region after each UV radiation pulse and determining an average voltage in the pulse, and an incremental change of the surface voltage; and calculating a capacitance-voltage (C-V) characteristic for the region based on a series of capacitance values and surface voltage (V) values.
1 . A method of characterizing a wide-bandgap semiconductor sample, the method comprising:
depositing a corona charge on a surface of the semiconductor sample in the dark to bias a region of the semiconductor sample to depletion;
measuring a surface voltage at the region in the dark after depositing the corona charge;
irradiating the region with a series of ultraviolet (UV) radiation pulses to neutralize the deposited corona charge in a series of incremental steps, each comprising a UV radiation wavelength, λ, a photon flux, Φ, and a pulse duration, Δt p corresponding to a linear corona charge neutralization range, wherein the increments of neutralized corona charge, ΔQ, are linear with the pulse duration, Δt p ;
measuring the surface voltage at the region in the dark before and after each UV radiation pulse and determining an average voltage in the UV radiation pulse, and an incremental change of the surface voltage, ΔV, corresponding to the UV radiation pulse;
calculating a capacitance-voltage (C-V) characteristic for the region based on a series of capacitance values and surface voltage (V) values, the capacitance (C) values being determined for each UV radiation pulse based on a ratio
Δ
t
p
Δ
V
for the corresponding UV radiation pulse and a calibration constant f cal relating a neutralized charge increment ΔQ to the pulse duration for specific UV radiation photon flux, Φ, as ΔQ=f cal ·Δt p ; and
determining one or more electrical parameters for the semiconductor sample at the region based on the capacitance-voltage (C-V) characteristic.
2 . The method of claim 1 , wherein calculating the capacitance-voltage (C-V) characteristic comprises determining a capacitance (C) value for each UV radiation pulse according to a relationship:
C=f cal ·Δt p /ΔV.
3 . The method of claim 1 , wherein the calibration constant f cal is equal to 1 and the capacitance (C) values are determined in relative units as C rel =Δt p /ΔV and values of the one or more electrical parameters are determined in relative units.
4 . The method of claim 3 , wherein the values of the one or more electrical parameters in relative units are determined at multiple regions on the semiconductor sample.
5 . The method of claim 4 , wherein the values of the one or more electrical parameters are determined at nine, 12, or 49 regions of the semiconductor sample.
6 . The method of claim 2 , wherein the calibration constant f cal is experimentally determined for the specific UV radiation photon flux, Φ, and the calibration constant f cal determination comprises using a reference calibration corona charge using a known reference arbitrary unit capacitance or a reference known doping concentration.
7 . The method of claim 1 , wherein the semiconductor sample is a wafer comprising a SiC, GaN, AlGaN, or AlGaN/GaN HEMT structure.
8 . The method of claim 1 , wherein the UV radiation length λ, is 240 nm or less.
9 . The method of claim 1 , wherein the photon flux, Φ, is in a range from 5×10 12 to 10 14 photons per cm 2 .
10 . The method of claim 1 , wherein the pulse duration, Δt p , is in a range from 0.5 milliseconds to 10 milliseconds.
11 . The method of claim 1 , wherein the semiconductor sample comprises an AlGaN/GaN HEMT structure and the one or more electrical parameters comprises a pinch-off voltage of the AlGaN/GaN HEMT structure determined based on an arbitrary unit C rel .
12 . A system for acquiring capacitance-voltage characteristics according to the method of claim 1 , comprising: a corona charge source; a noncontact surface voltage measurement probe; a pulsed UV radiation source; a UV detector arranged to monitor a photon flux from the pulsed UV radiation source; a moveable chuck configured to support the semiconductor sample relative to the corona charge source, the noncontact surface voltage measurement probe, and the pulsed UV radiation source; and a computer controller in communication with the corona charge source, the noncontact surface voltage measurement probe, and the pulsed UV radiation source and programmed to cause the system to perform measurements acquiring data of surface voltage increments and average voltage V values in a sequence of UV radiation pulses and to calculate capacitance-voltage (C-V) characteristics and to determine electrical parameters of the semiconductor sample.
13 . A system for characterizing semiconductor doping in a wide bandgap semiconductor sample, the system comprising:
a surface voltage measurement probe;
a corona charge source;
a UV radiation source;
a moveable wafer chuck configured to support the semiconductor sample relative to the surface voltage measurement probe, the corona charge source, and the UV radiation source; and
a computer controller in communication with the surface voltage measurement probe, the corona charge source, the UV radiation source, and the moveable wafer chuck, the computer controller being programmed to cause the system to:
(i) deposit, using the corona charge source, a corona charge on a surface of the semiconductor sample in the dark to bias a region of the semiconductor sample to depletion;
(ii) measure, using the surface voltage measurement probe, a surface voltage at the region in the dark after depositing the corona charge;
(iii) irradiate, using the UV radiation source, the region with a series of ultraviolet (UV) radiation pulses to neutralize the deposited corona charge in a series of incremental steps, each comprising a short UV radiation wavelength, λ, a photon flux, Φ, and a pulse duration, Δt p corresponding to a linear corona charge neutralization range, wherein increments of neutralized corona charge, ΔQ, are linear with the pulse duration, Δt p ;
(iv) measure, using the surface voltage measurement probe, the surface voltage at the region in the dark before and after each UV radiation pulse and determining an average voltage in the UV radiation pulse, and an incremental change of the surface voltage, ΔV, corresponding to the UV radiation pulse;
(v) calculate a capacitance-voltage (C-V) characteristic for the region based on a series of capacitance (C) values and surface voltage (V) values, the capacitance (C) values being determined for each UV radiation pulse based on a ratio
Δ
t
p
Δ
V
for the corresponding UV radiation pulse and a calibration constant f cal relating a neutralized charge increment ΔQ to the pulse duration for specific UV radiation photon flux, Φ, as ΔQ=f cal ·Δt p ; and
(vi) determine one or more electrical parameters for the semiconductor sample at the region based on the capacitance-voltage (C-V) characteristic.
14 . The system of claim 13 , wherein the UV radiation source is arranged to irradiate the region at a position different from the position under the surface voltage measurement probe.
15 . The system of claim 14 , further comprising a moving stage supporting the moveable wafer chuck and the computer controller is programmed to cause the stage to move the region between the surface voltage measurement probe and the UV radiation source.
16 . The system of claim 13 , wherein the UV radiation source is arranged to illuminate the region while the region is positioned under the surface voltage measurement probe.
17 . The system of claim 16 , wherein the computer controller is programmed to cause the system to irradiate the region while simultaneously monitoring neutralization induced surface voltage decay at the region.
18 . The system of claim 16 , wherein the surface voltage measurement probe comprises a nontransparent electrode and the UV radiation source is arranged to direct radiation at a non-normal angle to the surface of the semiconductor sample at the region.
19 . The system of claim 13 , wherein the surface voltage measurement probe is a non-contact Kelvin probe.
20 . The system of claim 13 , wherein the UV radiation source is configured to provide a photon flux in a range from 5×10 12 to 10 14 photons per cm 2 .
21 . The system of claim 13 , wherein the UV radiation source is configured to emit radiation at a wavelength of 240 nm or less.