Apparatus and method for real-time measurement of thin film layer thickness and changes thereof

• US 5,450,205 A
• Filed: 05/28/1993
• Issued: 09/12/1995
• Est. Priority Date: 05/28/1993
• Status: Expired due to Term

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Dalton, Timothy J., Sachs, Emanuel M., Sawin, Herbert H., Conner, William T.
• Primary Examiner(s): Pham, Hoa Q.
• Application Number:
  US08/070,118
• Time in Patent Office: 837 Days
• Field of Search: 356/381, 356/382, 356/355, 356/357, 356/345, 356/445, 250/560, 156/601, 156/612, 156/626, 156/627
• US Class Current: 356/632
• CPC Class Codes: G01B 11/0675 using interferometry
• CPC Class Codes: H01J 37/32935 Monitoring and controlling tubes by information coming from the object and/or discharge

Abstract

A new technique has been developed to measure etching or deposition rate uniformity in situ using a CCD camera which views the wafer during plasma processing. The technique records the temporal modulation of plasma emission or laser illumination reflected from the wafer; this modulation is caused by interferometry as thin films are etched or deposited. The measured etching rates compare very well with those determined by Helium-Neon laser interference. This technique is capable of measuring etching rates across 100-mm or larger wafers. It can resolve etch rate variations across a wafer or within a die. The invention can also be used to make endpoint determinations in etching operations as well as measuring the absolute thickness of thin films.

Claims

1. An apparatus for measuring change in the thickness of a thin film on a substrate supported on a support in the presence of electromagnetic plasma emission radiation emitted throughout a volume of gas, the apparatus comprising:

a. spaced away from said support, and on the opposite side of said volume of gas that emits said plasma emission, an array of means for sensing plasma emission radiation reflected from the thin film, the array providing an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film;

b. filter means for transmitting plasma emission radiation of at least one selected range of wavelengths to said array of sensing means;

c. means for focusing plasma emission radiation reflected from said film, said focusing means comprising an iris and arranged between said thin film and said array such that an image of a region of said film is focused onto said array;

d. means for storing a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to plasma emission radiation transmitted through said filter means and in response to no other significant illumination, reflected from said film; and

data processing means for comparing the data signals for at least one sensing means of the array over a portion of said time period, and from the comparison, determining the change of the thickness of the film over said portion of said time period at the region of film focused upon said at least one sensing means of the array.

2. The apparatus of claim 1, further comprising means for measuring the length of the time period over which data signals that have been compared have been generated, and data processing means for using the measured time and the change of the film thickness to determine the rate of change of the thickness of the film at the region of film during the period of time.

3. The apparatus of claim 1, further comprising means for displaying symbols that correspond to the determined change of film thickness.

4. The apparatus of claim 1, said substrate residing in a walled chamber, said apparatus further comprising, through a wall of said chamber, a transparent means for transmitting plasma emission radiation of said selected range of wavelengths, reflected from said film to said array, and which transparent means is smaller in its largest dimension than the largest dimension of said region of said thin film to be imaged onto said array.

5. The apparatus of claim 4, further wherein the largest dimension of said transparent means is less than three quarters of the largest dimension of said thin film.

6. The apparatus of claim 5, further wherein the largest dimension of said transparent means is less than one half of the largest dimension of said thin film.

7. The apparatus of claim 1, said filter means comprising means for transmitting a first selected range of wavelengths of plasma emission radiation to said array of sensing means while blocking other ranges of wavelengths of radiation, and subsequently for transmitting at least a second, different selected range of wavelengths of plasma emission radiation to said array while blocking other ranges of wavelengths of radiation.

8. The apparatus of claim 7, said filter means comprising means for transmitting at least a third, fourth and fifth different selected range of wavelengths of plasma emission radiation at different times to said array while blocking other ranges of wavelengths of plasma emission radiation.

9. The apparatus of claim 7, said data processing means further comprising means for determining the reflectivity of the film for said at least two selected ranges of wavelengths based on the intensity of the plasma emission radiation focused upon said array.

10. The apparatus of claim 9, said data processing means further comprising means for comparing said reflectivity to a predetermined set of correlations between reflectivity and film thickness, to determine the thickness of said film.

11. The apparatus of claim 1, said array comprising at least one hundred individual means for sensing electromagnetic radiation.

12. The apparatus of claim 11, said array comprising a CCD.

13. The apparatus of claim 1, further comprising means for synchronizing said signals generated by said array to any periodic fluctuation in said plasma emission radiation caused by phenomena not under analysis.

14. The apparatus of claim 13, where said phenomenon causing fluctuations is a fluctuating magnetic field.

15. An apparatus for collecting information regarding the change in the thickness of a thin film being reduced in thickness on a substrate supported on a support in the presence of plasma emission radiation emitted throughout a volume of gas, the apparatus comprising:

a. spaced away from said support, and on the opposite side of said volume of gas that emits said plasma emission, an array of means for sensing plasma emission radiation reflected from the thin film, the array providing an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film;

b. filter means for transmitting plasma emission radiation of at least one selected range of wavelengths to said array of sensing means;

c. means for focusing plasma emission radiation reflected from said film, said focusing means arranged between said thin film and said array such that an image of a region of said film is focused onto said array; and

d. means for storing a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to plasma emission radiation transmitted through said filter means and in response to no other significant illumination, reflected from said film.

16. The apparatus of claim 15, further comprising means for displaying said time sequence of data signals in operator perceivable symbols.

17. The apparatus of claim 15, further comprising data processing means for analyzing said time sequence of data signals to determine if individual components of said time sequence conform to a predetermined relationship.

18. The apparatus of claim 15, said array comprising a CCD.

19. A method for determining when a layer of a thin film has been completely removed by a thickness reduction process in the presence of plasma emission radiation emitted throughout a volume of gas at a plurality of locations over the area of said thin film, comprising the steps of:

a. reflecting said plasma emission radiation from said thin film, in the absence of any other significant illumination of said thin film, during the time said film is being reduced in thickness;

b. focusing at least one selected range of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing plasma emission radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;

c. generating a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to plasma emission radiation focused on said array;

d. correlating the amplitude of said data signals with the time during which said signals were generated;

e. identifying a time periodic pattern in the amplitude of said data signals;

f. at selected time intervals, comparing the rate of change of said amplitude of said data signals with said periodic pattern; and

g. determining that said film has been removed if said rate of change of said amplitude of said signals departs from said periodic pattern.

20. The method of claim 19, said array comprising a CCD.

21. A method for determining the rate of change of the thickness of a thin film to which is being applied a process of changing film thickness in the presence of plasma emission radiation emitted throughout a volume of gas at a plurality of locations over the area of said thin film, said method comprising the steps of:

a. reflecting plasma emission radiation from said thin film, in the absence of any other significant illumination of said film, during the time said film is being changed in thickness;

b. focusing at least one selected range of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing electromagnetic radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film, said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;

c. generating a time sequence of data signals corresponding to the signals generated by the array of sensing means over a period of time in response to radiation focused on said array;

d. correlating the amplitude of said data signals with the time during which said signals were generated;

e. identifying a periodicity in the rate of change of the amplitude of said data signals; and

f. determining the rate of change of the thickness of said film by relating said periodicity to said selected range of wavelengths.

22. The method of claim 21, further comprising the steps of:

a. generating a time sequence of images of said thin film using said time sequence of data signals;

b. from said time sequence of images, identifying a plurality of locations over the area of said thin film and conducting said steps of identifying a periodicity and determining the rate of change at each of said plurality of locations.

23. The method of claim 22, further comprising the step of generating an image of said film showing said rate of change at said locations at a selected time.

24. The method of claim 21, said process of changing film thickness comprising a film thickness reduction process.

25. The method of claim 21 said process of changing film thickness comprising a film thickness addition process.

26. The method of claim 21, further comprising the step of synchronizing the generation of said time sequence of data signals to any periodic fluctuation in said plasma emission radiation caused by phenomena not under analysis.

27. The method of claim 26, where said phenomenon causing fluctuations is a magnetic field.

28. A method for determining the thickness of a thin film at a plurality of locations over the area of said thin film, said method comprising the steps of:

a. emitting plasma emission radiation throughout a volume of gas and reflecting said plasma emission radiation from said thin film, in the absence of any other significant illumination of said film, during the time said film is being changed in thickness;

b. focusing at least two selected ranges of wavelengths of said plasma emission radiation reflected from said film onto an array of means for sensing plasma emission radiation which provides an individually recoverable signal for each sensing means of the array, each signal corresponding to a region of the film said array being located on the opposite side of said volume of gas that emits said plasma emission from said film;

c. generating a set of data signals corresponding to the signals generated by the array of sensing means in response to radiation of said selected at least two ranges of wavelengths focused on said array;

d. correlating the amplitudes of said data signals with the wavelength of said plasma emission radiation from which said signals were generated;

e. comparing said correlation of the amplitudes to a predetermined correlation between amplitudes and film thickness; and

f. determining the thickness of said film by said comparison.

29. The method of claim 28, said array comprising a CCD.