Method of etching or depositing a thin film
A method of plasma etching or plasma deposition of a target layer of material in or onto a sample comprising a further layer of material, the method comprising: during a process of plasma etching or plasma deposition of the target layer of material: directing light of a first wavelength at the sample; measuring the intensity of light of the first wavelength reflected by the sample; directing light of a second wavelength at the sample; and measuring the intensity of light of the second wavelength reflected by the sample; determining, based on the intensities of light reflected by the sample, an endpoint of the process of plasma etching or plasma deposition of the target layer of material; and ending the process of plasma etching or plasma deposition of the target layer of material based on the determined endpoint.
1 . A method of plasma etching or plasma deposition of a target layer of material in or onto a sample comprising a further layer of material, the method comprising:
during a process of plasma etching or plasma deposition of the target layer of material:
directing light of a first wavelength at the sample;
measuring the intensity of light of the first wavelength reflected by the sample;
directing light of a second wavelength at the sample; and
measuring the intensity of light of the second wavelength reflected by the sample;
determining, based on the intensities of light reflected by the sample, an endpoint of the process of plasma etching or plasma deposition of the target layer of material;
ending the process of plasma etching or plasma deposition of the target layer of material based on the determined endpoint; and
wherein determining the endpoint of the process of plasma etching or plasma deposition of the target layer of material comprises taking a ratio of the two measured intensities,
wherein the first wavelength corresponds to a region of a reflectance spectrum of the target layer, or the further layer of material, without a peak or trough, such that the first wavelength provides a reference signal with which to compare the intensity of light reflected by the second wavelength; or
wherein the second wavelength corresponds to a region of a reflectance spectrum of the target layer, or the further layer of material, without a peak or trough, such that the second wavelength provides a reference signal with which to compare the intensity of light reflected by the first wavelength.
2 . A method according to claim 1 , wherein the first wavelength is at a peak or trough in the reflectance of the target layer or of the further layer of material.
3 . A method according to claim 2 , wherein the first wavelength is in the range of 280 nm to 340 nm.
4 . A method according to claim 1 , wherein the second wavelength is at a peak or trough in the reflectance of the target layer or of the further layer of material.
5 . A method according to claim 4 , wherein the second wavelength is in the range of 340 nm to 390 nm.
6 . A method according to claim 1 , wherein determining the endpoint of the process of plasma etching or plasma deposition of the target layer of material comprises determining the reflectance of the sample at the first and second wavelengths.
7 . A method according to claim 6 , wherein determining the reflectance of the sample at the first and second wavelengths comprises, for each wavelength, taking the ratio of the intensity of light of said wavelength reflected by the sample to the intensity of light of said wavelength directed at the sample.
8 . A method according to claim 6 , wherein determining the endpoint of the process of plasma etching or plasma deposition of the target layer of material comprises taking a ratio of the determined reflectance of the sample at the first wavelength to the determined reflectance of the sample at the second wavelength.
9 . A method according to claim 1 , wherein one of the first and second wavelengths corresponds to a trough in an emission spectrum of a plasma used in the process of plasma etching or plasma deposition of the targe layer of material.
10 . A method according to claim 1 , wherein one or both of the light of the first wavelength and the light of the second wavelength directed at the sample are provided by a plasma used in the process of plasma etching or plasma deposition of the target layer of material.
11 . A method according to claim 1 , wherein the method comprises a calibration step of measuring the intensity of light of the first and second wavelengths reflected by the sample at the start of the process of plasma etching or plasma deposition of the target layer of material.
12 . A method according to claim 1 , wherein determining, based on the intensities of light reflected by the sample, an endpoint of a process of plasma etching the target layer of material comprises determining the thickness of the target layer of the sample at the start of the plasma etching process.
13 . A method according to claim 1 , wherein the endpoint is used to end the process of plasma etching or plasma deposition of the target layer of material at a predetermined residual thickness.
14 . A method according to claim 13 , wherein the predetermined residual thickness is 10 nm or less.
15 . A method etching a target layer of material to a predetermined residual thickness according to claim 13 , wherein, prior to the process of etching the target layer of material, the method comprises an earlier step of etching the target layer of material to a first residual thickness.
16 . A plasma processing apparatus configured to perform the steps of claim 1 , the apparatus comprising:
a plasma processing chamber;
at least two optical emitters;
at least two optical detectors; and
at least one optical port for coupling the at least two optical emitters and the at least two optical detectors to the inside of the plasma processing chamber.