APPARATUS AND METHOD FOR REAL TIME MEASUREMENT OF SUBSTRATE TEMPERATURES FOR USE IN SEMICONDUCTOR GROWTH AND WAFER PROCESSING

• US 20090177432A1
• Filed: 04/17/2008
• Published: 07/09/2009
• Est. Priority Date: 10/09/2003
• Status: Active Grant

• Current Assignee: k-Space Associates, Inc.
• Original Assignee: k-Space Associates, Inc.
• Inventors: Williams, Jason, Clarke, Roy, Barlett, Darryl, Perry, Douglas, Taylor, Charles A. II
• Granted Patent: US 7,837,383 B2
• Time in Patent Office: Days
• US Class Current: 702/134
• CPC Class Codes: C23C 16/46 characterised by the method used for heating the substrate C23C16/48, C23C16/50 take precedence
• CPC Class Codes: C23C 16/52 Controlling or regulating the coating process C23C16/45557, C23C16/279 take precedence
• CPC Class Codes: G01J 3/024 using means for illuminating a slit efficiently (e.g. entrance slit of a spectrometer or entrance face of fiber)
• CPC Class Codes: G01J 3/0286 Constructional arrangements for compensating for fluctuations caused by temperature, humidity or pressure, or using cooling or temperature stabilization of parts of the device; Controlling the atmosphere inside a spectrometer, e.g. vacuum
• CPC Class Codes: G01J 3/0291 Housings; Spectrometer accessories; Spatial arrangement of elements, e.g. folded path arrangements
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 5/0003 for sensing the radiant heat transfer of samples, e.g. emittance meter
• CPC Class Codes: G01J 5/0007 of wafers or semiconductor substrates, e.g. using Rapid Thermal Processing
• CPC Class Codes: G01J 5/0821 Optical fibres
• CPC Class Codes: G01J 5/60 using determination of colour temperature

Abstract

The invention is an optical method and apparatus for measuring the temperature of semiconductor substrates in real-time, during thin film growth and wafer processing. Utilizing the nearly linear dependence of the interband optical absorption edge on temperature, the present method and apparatus result in highly accurate measurement of the absorption edge in diffuse reflectance and transmission geometry, in real time, with sufficient accuracy and sensitivity to enable closed loop temperature control of wafers during film growth and processing. The apparatus operates across a wide range of temperatures covering all of the required range for common semiconductor substrates.

Claims

1. A method for determining the temperature of a semiconductor material by spectral analysis in an environment where there are light signals from wanted and unwanted sources, said method comprising the steps of:

a) providing a semiconductor material;

b) interacting light signals with the semiconductor material to produce diffusely scattered light;

c) collecting light in a spectrometer to produce spectra data by resolving light signals into discrete wavelength components of particular light intensity, the light containing both diffusely scattered light from the semiconductor material along with a component of unwanted light signals;

d) identifying an absorption edge region in the spectra data;

e) deriving a band edge wavelength value as a function of the identified absorption edge region;

f) inferring a temperature of the semiconductor material based on the derived band edge wavelength value;

g) and subtracting the unwanted light component from the spectra data before said step of deriving a band edge wavelength to create preprocessed spectra, whereby the temperature of a semiconductor material can be determined without modulating the wanted light signal prior to said collecting step.

2. The method of claim 1 wherein said step of subtracting the unwanted light component includes determining a point of interest wavelength within the spectra data using a derivative calculation.

3. The method of claim 2 wherein said step of determining the point of interest wavelength includes the steps of:

a) calculating a 1^st derivative of the spectra data;

b) identifying a peak feature of the 1^st derivative within the absorption edge region;

c) making a linear fit to the absorption edge region at the wavelength position of the 1^st derivative peak;

d) extrapolating the linear fit to determine a wavelength position for subtraction of the unwanted light component.

4. The method of claim 2 wherein said step of determining a point of interest wavelength includes the steps of:

a) calculating a 2^nd derivative of the spectra data;

b) identifying a peak feature of the 2^nd derivative within the absorption edge region;

c) using the spectra intensity value at the 2^nd derivative peak, or the intensity value just prior to the 2^nd derivative peak, as the unwanted light component to subtract.

5. The method of claim 1 wherein said step of deriving the band edge wavelength value includes the steps of:

a) calculating a 1^st derivative of the preprocessed spectra;

b) identifying a peak feature of the 1^st derivative within the absorption edge region;

c) making a linear fit to the absorption edge region at the wavelength position of the 1^st derivative peak;

d) extrapolating the linear fit to determine the bandage wavelength.

6. The method of claim 1 wherein said step of deriving a band edge wavelength value includes:

a) calculating a 2^nd derivative of the preprocessed spectra;

b) identifying a peak feature of the 2^nd derivative within the absorption edge region;

c) using the 2^nd derivative peak wavelength position as the band edge wavelength.

7. The method of claim 1 further including the step of constructing a calibration function of band edge wavelength versus inferred semiconductor material temperature, and wherein said step of inferring a temperature of the semiconductor material includes correlating the band edge wavelength value to a temperature using a calibration function.

8. The method of claim 7 wherein said step of constructing a calibration function includes collecting spectra data from semiconductor materials at predetermined temperatures.

9. A method for determining the temperature of a semiconductor material via spectral analysis in an environment where there are light signals from wanted and unwanted sources, said method comprising the steps of:

h) providing a semiconductor material;

i) interacting light signals with the semiconductor material to produce diffusely scattered light;

j) collecting light in a spectrometer to produce spectra data by resolving light signals into discrete wavelength components of particular light intensity, the light containing both diffusely scattered light from the semiconductor material along with a component of unwanted light signals;

k) identifying an absorption edge feature in the spectra data;

l) ignoring a predetermined level of light deemed noise based on experimental conditions;

m) clipping the spectra data;

n) dividing a reference lamp spectrum from the collected light to remove any unwanted features introduced by a lamp; and

o) removing unwanted light from the spectra data to create preprocessed spectra.

10. The method of claim 9 further including the steps of:

p) creating a flat line up to the wavelength with the minimum value by setting a minimum intensity value; and

q) subtracting the minimum intensity value from the spectra data to establish a data point offset.

11. The method of claim 9 wherein said step of clipping the spectra data includes removing anomalies in the spectra data beyond the absorption edge and providing a consistent wavelength position for normalizing the spectra data.

12. The method of claim 9 wherein said step of removing unwanted light includes using a derivative calculation.

13. The method of claim 12 wherein said step of using a derivative calculation includes smoothing the spectra data to enhance broad features and remove narrow features.

14. The method of claim 13 wherein said step of using a derivative calculation includes determining a point of interest within the derivative.

15. The method of claim 14 wherein said step of determining the point of interest wavelength includes the steps of:

a) calculating a 1^st derivative of the spectra data;

b) identifying a peak feature of the 1^st derivative within the absorption edge region;

c) making a linear fit to the absorption edge region at the wavelength position of the 1^st derivative peak;

d) extrapolating the linear fit to determine a wavelength position for subtraction of the unwanted light component.

16. The method of claim 14 wherein said step of determining a point of interest wavelength includes the steps of:

a) calculating a 2^nd derivative of the spectra data;

b) identifying a peak feature of the 2^nd derivative within the absorption edge region;

c) using the spectra intensity value at the 2^nd derivative peak, or the intensity value just prior to the 2^nd derivative peak, as the unwanted light component to subtract.

17. The method of claim 9 further including the steps of:

r) further smoothing the spectra data to enhance broad features and remove narrow features;

s) computing a band edge wavelength value; and

t) inferring a temperature of the semiconductor material based on the computed band edge wavelength value.