Methods and apparatuses for etch profile optimization by reflectance spectra matching and surface kinetic model optimization

• US 10,303,830 B2
• Filed: 05/04/2018
• Issued: 05/28/2019
• Est. Priority Date: 02/08/2016
• Status: Active Grant

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Tetiker, Mehmet Derya, Sriraman, Saravanapriyan, Bailey, III, Andrew D., Paterson, Alex, Gottscho, Richard A.
• Primary Examiner(s): Ngo, Brian
• Application Number:
  US15/972,063
• Publication Number:
  US 20180260509A1
• Time in Patent Office: 389 Days
• Field of Search: 716 51, 716 52, 716 53, 716 54, 716 55
• CPC Class Codes: G01B 11/002 for measuring two or more coordinates
• CPC Class Codes: G01B 2210/56 Measuring geometric parameters of semiconductor structures, e.g. profile, critical dimensions or trench depth
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G03F 1/70 Adapting basic layout or design of masks to lithographic process requirements, e.g., second iteration correction of mask patterns for imaging
• CPC Class Codes: G03F 1/80 Etching
• CPC Class Codes: G03F 1/84 Inspecting
• CPC Class Codes: G03F 7/00 Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor using photoresist structures for special production processes, see the relevant places, e.g. B44C, H01L, e.g. H01L21/00, H05K
• CPC Class Codes: G06F 30/367 Design verification, e.g. using simulation, simulation program with integrated circuit emphasis [SPICE], direct methods or relaxation methods
• CPC Class Codes: G06F 30/39 Circuit design at the physical level physical level design for reconfigurable circuits G06F30/347

Abstract

Disclosed are methods of optimizing a computer model which relates the etch profile of a feature on a semiconductor substrate to a set of independent input parameters (A), via the use of a plurality of model parameters (B). In some embodiments, the methods may include modifying one or more values of B so as to reduce a metric indicative of the differences between computed reflectance spectra generated from the model and corresponding experimental reflectance spectra with respect to one or more sets of values of A. In some embodiments, calculating the metric may include an operation of projecting the computed and corresponding experimental reflectance spectra onto a reduced-dimensional subspace and calculating the difference between the reflectance spectra as projected onto the subspace. Also disclosed are etch systems implementing such optimized computer models.

Claims

1. A computer implemented method of optimizing a computer model which relates etch profiles of features on semiconductor substrates to a set of independent input parameters, the method comprising:

(a) identifying values for one or more model parameters to be optimized, wherein the model parameters are used in executing the computer model;

(b) receiving experimental reflectance spectra generated from optical measurements of one or more semiconductor substrates etched using an experimental etch process performed using values of the set of independent input parameters;

(c) generating, by using a computer processor, computed reflectance spectra by executing the computer model using the values for the set of independent input parameters specified in (b) and values of the model parameters identified in (a); and

(d) modifying, by using a computer processor, the values of the one or more model parameters identified in (a) and repeating (c) with the modified values of the one or more model parameters so as to reduce a metric indicative of the differences between the experimental reflectance spectra received in (b) and corresponding computed reflectance spectra generated in (c) with respect to the values of the set of independent input parameters, thereby producing modified values for the one or more model parameters for use in the computer model which relates etch profiles of features on semiconductor substrates to the set of independent input parameters.

2. The method of claim 1, wherein at least some of the computed reflectance spectra are generated by a process comprising:

(i) generating a computed etch profile represented by a series of etch profile coordinates using the model;

(ii) from the computed etch profile generated in (i), generating a computed reflectance spectrum by simulating the reflection of electromagnetic radiation off of said computed etch profile.

3. The method of claim 1, wherein:

the experimental reflectance spectra received in (b) comprise reflectance spectra corresponding to a sequence of etch times representing different durations of etch processes; and

the computed reflectance spectra generated in (c) comprise reflectance spectra computed from the model so as to correspond to the sequence of etch times in (b).

4. The method of claim 3, wherein the experimental reflectance spectra are received in (b) from optical measurements taken during ongoing etch processes at the sequence of etch times.

5. The method of claim 4, wherein consecutive etch times over at least a portion of the sequence of etch times are separated by 0.01-1 second.

6. The method of claim 4, wherein at least some of the experimental reflectance spectra received in (b) were adjusted based on comparisons with optical measurements taken with respect to, and after the conclusion of, substrate etch processes of various durations.

7. The method of claim 6, wherein the optical measurements corresponding to the concluded etch processes of various duration were taken after the corresponding etched substrates were removed from the processing chambers in which they were etched.

8. The method of claim 1, further comprising repeating (d).

9. The method of claim 8, further comprising further repeating (d) until a substantially local minimum in error with respect to the one or more model parameters is obtained.

10. The method of claim 1, wherein the computer model calculates local etch rates at a grid of points representing the etch profile of the feature on the semiconductor substrate as a function of time.

11. The method of claim 10, wherein the one or more model parameters include reaction rate constants, reactant and product sticking coefficients, and/or reactant and product diffusion constants.

12. The method of claim 1, further comprising identifying the set of independent input parameters by performing PCA.

13. The method of claim 12, wherein the PCA is performed with respect to concatenated vectors of independent input parameters and corresponding measured etch profiles.

14. The method of claim 1, further comprising etching a semiconductor substrate using or adjusting a set of etch conditions determined using the computer model with the modified values of the one or more model parameters.

15. An optimized computer model comprising a non-transitory computer readable medium on which is provided computer executable instructions encoding a computer model, which relates etch profiles of features on semiconductor substrates to the set of independent input parameters, configured with the modified values for the one or more model parameters, wherein the computer model was optimized by operations (a)-(d) of claim 1.

16. A computer implemented method of approximately determining the profile of a feature on a semiconductor substrate after the feature has been etched by an etch process, the method comprising:

specifying test values for the set of independent input parameters corresponding to the etch process; and

generating, by a computer processor, an etch profile using the optimized computer model of claim 15 with the specified test values for the set of independent input parameters.

17. A method of determining a set of values for a set of independent input parameters for an etch process which will approximately yield a desired etch profile of a feature on a semiconductor substrate after the feature is etched by said etch process, the method comprising:

(a) specifying test values for the set of independent input parameters corresponding to the etch process;

(b) generating a computed etch profile using the optimized computer model of claim 15 with the specified set of test values for the independent input parameters;

(c) computing a metric indicative of the difference between the desired etch profile and the computed etch profile; and

(d) modifying one or more values for the set of independent input parameters specified in (a) so as to reduce the difference between desired and computed etch profiles as ascertained by repeating (b)-(c).

18. The method of claim 17, further comprising:

(e) repeating (d) until a substantially local minimum in error with respect to the values for the set of independent input parameters selected in (d) is obtained.

19. A system for processing semiconductor substrates, the system comprising:

an etcher apparatus for etching semiconductor substrates whose operation is adjusted by a set of independent input parameters; and

a controller for controlling the operation of the etcher apparatus, the controller comprising a processor and a memory;

wherein;

the memory stores an etched feature profile model optimized by operations (a)-(d) of claim 1; and

the processor is configured to use the etched feature profile model stored in the memory to compute an etched feature profile from a set of values for the set of independent input parameters.

20. The system of claim 19, wherein the controller adjusts the operation of the etcher apparatus by varying one or more values of the set of independent input parameters in response to the computed etched feature profile.

21. The system of claim 20, wherein the set of independent input parameters whose values are varied in response to the computed etched feature profile include one or more parameters selected from:

RF plasma frequency and RF plasma power level.

22. The system of claim 19, wherein the etcher apparatus comprises:

a processing chamber;

a substrate holder for holding a substrate within the processing chamber;

a plasma generator for generating a plasma within the processing chamber, the plasma generator comprising an RF power supply;

one or more valve-controlled process gas inlets for flowing one or more process gases into the processing chamber; and

one or more gas outlets fluidically connected to one or more vacuum pumps for evacuating gases from the processing chamber.

23. The system of claim 22, wherein the controller is configured to adjust the frequency and/or the power level of the RF power supply to modify characteristics of the plasma in the processing chamber in response to the computed etched feature profile.

24. The system of claim 22, wherein the controller is configured to operate the one or more valve-controlled process gas inlets to adjust the flow rates of one or more process gases into the processing chamber in response to the computed etched feature profile.

25. The system of claim 22, wherein the controller is configured to adjust a temperature and/or a pressure within the processing chamber in response to the computed etched feature profile.

26. The method of claim 1, wherein the computer model enables development of etch process parameters, wherein the computer model is optimized with the modified values, as produced in (d), for the one or more model parameters.

27. The method of claim 1, wherein the computer model enables development of lithography masks for etch processes, wherein the computer model is optimized with the modified values, as produced in (d), for the one or more model parameters.

28. The optimized computer model of claim 15, wherein the computer executable instructions further comprise instructions for developing lithography masks for etch processes.

29. The optimized computer model of claim 15, wherein the computer executable instructions further comprise instructions for developing etch process parameters.