Selection and use of representative target subsets

Patent metadata

Field	Value
Publication number	US-10025756-B2
Application number	US-201414508469-A
Country	US
Kind code	B2
Filing date	Oct 7, 2014
Priority date	Jun 28, 2013
Publication date	Jul 17, 2018
Grant date	Jul 17, 2018

Abstract

Methods and respective modules which reduce sample size and measurement duration of metrology parameters by selecting a relatively small subset of measured targets to represent a distribution of parameter measurements of a large number of targets. The subset is selected by sampling a substantially equal number of measurements from each of a selected number of quantiles of the distribution. The methods and modules allow identification of targets which represent correctly the whole target measurement distribution. The methods and modules optimize quantiles and sample size selections, using accuracy scores and estimations of the robustness of the selections. Sampling and selections may be carried out iteratively to reach specified criteria that match the results which can be derived when considering the whole distribution.

First claim

What is claimed is:

1. A method comprising:
defining a representation criterion;
acquiring one or more measurements of an N number of targets;
selecting a subset n of the N number of targets, wherein the subset n of the N number of targets includes a smaller number of targets than the N number of targets;
selecting one or more quantiles q based on a distribution of the one or more measurements of the N number of targets;
sampling a selected number of targets from each quantile q of the distribution, wherein the selected number of targets is equal to or proportional to the ratio between the values n and q;
calculating at least one accuracy score for the sampled selected number of targets equal to or proportional to the ratio between the values n and q to quantify an amount the sampled selected number of targets equal to or proportional to the ratio between the values n and q represent the distribution of the one or more measurements of the N number of targets;
reiterating at least one of the sampling the selected number of targets equal to or proportional to the ratio between the values n and q, the selecting of the subset n, the selecting of the number of quantiles q, or the calculating the at least one accuracy score until the at least one accuracy score is below the defined representation criterion;
selecting a subset m of the N number of targets after the calculated at least one accuracy score is below the defined representation criterion, wherein the subset m of the N number of targets includes a smaller number of targets than the N number of targets;
acquiring one or more measurements of the subset m of the N number of targets;
determining one or more correctable terms based on the one or more measurements of the subset m of the N number of targets; and
adjusting one or more sample selection criterion utilized by a metrology tool based on the one or more correctable terms,
wherein at least one of the selecting the subset n, the selecting the number of quantiles q, the sampling the selected number of targets equal to or proportional to the ratio between the values n and q, or the calculating at least one accuracy score is carried out by at least one computer processor.

2. The method of claim 1 , further comprising:
calculating a robustness score for the subset n based on the at least one accuracy score for the subset n corresponding to the sampled number of selected targets equal to or proportional to the ratio between the values n and q.

3. The method of claim 2 , wherein the robustness score is related to a variance of the at least one accuracy score.

4. The method of claim 2 , wherein the at least one wafer includes a plurality of wafers, wherein the one or more measurements of the N number of targets are carried out with respect to the plurality of wafers.

5. The method of claim 4 , wherein the subset n is selected for a first wafer of the plurality of wafers, wherein the selecting the number of quantiles q and the sampling of the selected number of targets equal to or proportional to the ratio between the values n and q are carried out based on the robustness score calculated for at least a second wafer of the plurality of wafers.

6. The method of claim 4 , wherein the selecting the subset n of the N number of targets and the reiterating at least one of the sampling the n/q number of targets or the selecting of the subset n and the number of quantiles q are carried out based on the plurality of wafers.

7. The method of claim 1 , wherein the sampling of the selected number of targets equal to or proportional to the ratio between the values n and q is random.

8. The method of claim 1 , wherein the sampling the selected number of targets equal to or proportional to the ratio between the values n and q is deterministic, wherein the deterministic sampling is based on the at least one accuracy score.

9. The method of claim 1 , wherein the sampled selected number of targets equal to or proportional to the ratio between the values n and q are selected based on a median of a distribution of the respective at least one accuracy score, wherein the median yields a distribution of representation criterions smaller than a selected representation criterion limit.

10. The method of claim 1 , wherein the one or more measurements of the N number of targets are based on at least one of one or more metrology parameters, one or more metrology measurements acquired from the one or more metrology parameters, one or more metrology quality merits, one or more correctable terms acquired from the one or more metrology parameters using a metrology model, or one or more residuals of metrology parameters acquired from the metrology model and one or more target production process parameters.

11. The method of claim 1 , wherein the one or more measurements of the N number of targets are based on, along at least one measurement direction, to at least one of an overlay, a tool induced shift, or a measurement quality merit.

12. The method of claim 1 , wherein the one or more measurements of the N number of targets relate to at least one of: a scanner dose or a scanner focus.

13. The method of claim 1 , wherein the one or more measurements relate to an overlay acquired from a metrology overlay model, wherein one or more overlay signature measurements are separately captured from different zones on the at least one wafer.

14. The method of claim 1 , further comprising:
carrying out one or more additional measurements on the selected subset n of the N number of targets.

15. The method of claim 1 , wherein the one or more measurements of the N number of targets are based on one or more residuals of metrology parameters acquired from a metrology model, wherein the distribution of the one or more residuals is a Gaussian distribution, wherein the metrology model is an Ordinary Least Squares (OLS) overlay model.

16. The method of claim 1 , further comprising:
incorporating one or more target characteristics of the N number of targets during the selecting the subset n of the N number of targets.

17. The method of claim 16 , wherein the one or more target characteristics comprise:
spatial information including at least one of an inter-field position, an intra-field location, or a radius.

18. The method of claim 1 , further comprising:
removing one or more outliers prior to at least one of the sampling the selected number of targets equal to or proportional to the ratio between the values n and q, the selecting of the subset n, or the selecting of the number of quantiles q.

19. The method in claim 1 , wherein the one or more correctable terms reduce at least one of a sample size selection or a measurement duration of the metrology tool.

20. A method comprising:
acquiring one or more measurements of an N number of targets of at least one wafer;
performing one or more calculations on the one or more measurements of the N number of targets;
selecting a subset m of an N number of targets based on the performed one or more calculations, wherein the subset m of the N number of targets includes a smaller number of targets than the N number of targets, wherein the subset m represents a distribution of the one or more metrology parameters of the N number of targets, wherein the subset m of the N number of targets is selected by sampling a selected number of one or more measurements from each of a selected number of quantiles q of the distribution of the one or more measurements of the N number of targets, wherein the selected number of the one o

Assignees

• Kla Tencor Corp

Inventors

• Klein Dana
• Jug Sven

Classifications

• G06F17/18 Primary

  for evaluating statistical data {, e.g. average values, frequency distributions, probability functions, regression analysis (forecasting specially adapted for a specific administrative, business or logistic context G06Q10/04)} · CPC title

• G05B19/41875

  characterised by quality surveillance of production · CPC title

• G03F7/70633

  Overlay, i.e. relative alignment between patterns printed by separate exposures in different layers, or in the same layer in multiple exposures or stitching · CPC title

• Y02P90/22

  Cross-Sectional Technologies · mapped topic

• Y02P90/02

  Total factory control, e.g. smart factories, flexible manufacturing systems [FMS] or integrated manufacturing systems [IMS] · CPC title