Method for controlling a recess etch process

• US 7,399,711 B2
• Filed: 11/01/2002
• Issued: 07/15/2008
• Est. Priority Date: 08/13/2002
• Status: Expired due to Fees

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Perry, Andrew J., Venugopal, Vijayakumar C.
• Primary Examiner(s): Goudreau; George A.
• Application Number:
  US10/286,409
• Publication Number:
  US 20040087041A1
• Time in Patent Office: 2,083 Days
• Field of Search: 438/7, 438/8, 438/9, 438/16, 438/714, 216/60
• US Class Current: 438/714
• CPC Class Codes: G01B 11/0616 of coating
• CPC Class Codes: G01B 11/0625 with measurement of absorption or reflection
• CPC Class Codes: G01B 11/0683 measurement during deposition or removal of the layer
• CPC Class Codes: G01N 21/8422 Investigating thin films, e.g. matrix isolation method

Abstract

A method of controlling a recess etch process for a multilayered substrate having a trench therein and a column of material deposited in the trench includes determining a first dimension from a surface of the substrate to a reference point in the substrate by obtaining a measured net reflectance of at least a portion of the substrate including the trench, computing a modeled net reflectance of the portion of the substrate as a weighted incoherent sum of reflectances from n≧1 different regions constituting the portion of the substrate, determining a set of parameters that provides a close match between the measured net reflectance and the modeled net reflectance, and extracting the first dimension from the set of parameters; computing an endpoint of the process as a function of the first dimension and a desired recess depth measured from the reference point; and etching down from a surface of the column of material until the endpoint is reached.

Claims

1. A method of controlling a recess etch process, comprising:

for a multilayered substrate having a trench therein and a column of material deposited in the trench, determining a first dimension from a surface of the substrate to a reference point in the substrate by;

obtaining a measured net reflectance spectrum of at least a portion of the substrate including the trench;

computing a modeled net reflectance spectrum of the portion of the substrate as a weighted incoherent sum of reflectances from n ≧

1 different regions constituting the portion of the substrate;

determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum; and

extracting the first dimension from the set of parameters;

computing an endpoint of the recess etch process as a function of the first dimension and a desired recess depth measured from the reference point; and

etching down from a surface of the column of material until the endpoint is reached.

2. The method of claim 1, wherein obtaining the measured net reflectance spectrum comprises illuminating the portion of the substrate with a normal incident light beam.

3. The method of claim 1, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k ≧

1 laterally-distinct areas constituting the region.

4. The method of claim 3, wherein each laterally-distinct area is modeled as a thin-film stack.

5. The method of claim 4, wherein computing the modeled net reflectance spectrum comprises modeling the substrate as having a nominally polarization-independent reflectance.

6. The method of claim 1 wherein determining the set of parameters comprises calculating a least squares difference error metric between the measured net reflectance spectrum and the modeled net reflectance spectrum and finding the set of parameters that minimizes the error metric.

7. The method of claim 6, Further comprising amplifying an effect of a change in the first dimension on the error metric.

8. The method of claim 7, wherein computing the modeled net reflectance spectrum comprises receiving as input a set of initial guesses for the set of parameters.

9. The method of claim 1, wherein the endpoint is based on a combination of broadband-reflectometry and an interferometric endpoint approach.

10. The method of claim 9, wherein computing the endpoint comprises computing a fringe count required to reach the endpoint.

11. The method of claim 10, wherein etching down comprises counting interference fringes evolved from the portion of the substrate during the etching and stopping the etching when the interference fringes evolved from the portion of the substrate have reached the fringe count.

12. The method of claim 1, further comprising determining a second dimension from the surface of the substrate to the surface of the column of material.

13. The method of claim 12, wherein determining the second dimension comprises extracting the second dimension from the set of parameters.

14. The method of claim 13, wherein computing the endpoint further comprises adjusting the endpoint by an amount proportional to the second dimension.

15. The method of claim 1, further comprising planarizing the surface of the substrate prior to determining the first dimension.

16. The method of claim 1, further comprising removing any native oxide buildup on the surface of the substrate prior to determining the first dimension.

17. A method of controlling a recess etch process, comprising:

planarizing a surface of a multilayered substrate having a trench therein and a column of material deposited in the trench;

after planarizing, determining a first dimension from the surface of the substrate to a reference point in the substrate by;

obtaining a measured net reflectance spectrum of at least a portion of the substrate including the trench;

computing a modeled net reflectance spectrum of the portion of the substrate as a weighted incoherent sum of reflectances from n ≧

1 different regions constituting the portion of the substrate, wherein the reflectance of each of the n different regions is a weighted coherent sum of reflected fields from k ≧

1 laterally-distinct areas constituting the region;

determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum; and

extracting the first dimension from the set of parameters;

computing an endpoint of the recess etch process as a function of the first dimension and a desired recess depth measured from the reference point; and

etching down from a surface of the column of material until the endpoint is reached.

18. The method of claim 17, further comprising determining a second dimension from the surface of the substrate to the surface of the column of material, wherein determining the second dimension comprises extracting the second dimension from the set of parameters, and wherein computing the endpoint further comprises adjusting the endpoint by an amount proportional to the second dimension.

20. The method of claim 17 wherein the weighted incoherent sum of reflectances is

R =w₁(λ

₀)|E₁|²+w₂(λ

₀|E₂|²+. . . +w_n(λ

₀)|E_n|²

where R is the net reflectance measured, E_nare the individual incoherently adding field terms, and w<sub>n(λ

0</sub>) are the weighting factors for the incoherently adding terms.

21. The method of claim 17 wherein the weighted coherent sums of reflected fields is

E₁ =a ₁(λ

₀)E_cl+a₂(λ

₀)e_cl+...+a_k(λ

₀)E_ck

where a₁(λ

₀) are the weighting factors for coherently adding field terms E_ck.

19. A method of controlling a recess etch process, comprising:

for a multilayered substrate having a trench therein and a column of material deposited in the trench, determining a first dimension from a surface of the substrate to a reference point in the substrate and a second dimension from the surface of the substrate to a surface of the column of material by;

obtaining a measured net reflectance spectrum of at least a portion of the substrate including the trench;

computing a modeled net reflectance spectrum of the portion of the substrate as a weighted incoherent sum of reflectances from n ≧

1 different regions constituting the portion of the substrate;

determining a set of parameters that provides a close match between the measured net reflectance spectrum and the modeled net reflectance spectrum; and

extracting the first and second dimensions from the set of parameters;

computing an endpoint of the recess etch process as a function of the first and second dimensions and a desired recess depth measured from the reference point; and

etching down from a surface of the column of material until the endpoint is reached.