Methods and systems to calibrate reticle thermal effects
A method of reducing effects of heating and/or cooling a reticle in a lithographic process includes conditioning the reticle to adjust an initial temperature of the reticle to a predetermined temperature, reducing stress in the reticle to reduce parasitic thermal effects, calibrating a reticle heating model by exposing the reticle and a non-production substrate to a dose of radiation, and processing a production substrate by exposing the reticle and a production substrate to a dose of radiation based on the reticle heating model. The method can increase calibration accuracy and speed of the reticle heating model, reduce conditioning times of the reticle, reduce stress in the reticle, avoid rework of production substrates, and increase throughput, yield, and accuracy.
1 . A method comprising:
conditioning a reticle to adjust an initial temperature of the reticle to a predetermined temperature;
exposing the reticle and a non-production substrate to a zero dose of radiation to reduce stress in the reticle to reduce parasitic thermal effects;
calibrating a reticle heating model by:
exposing the reticle and the non-production substrate to a non-zero dose of radiation;
measuring a reticle shape deformation; and
calculating a reticle temperature.
2 . The method of claim 1 , wherein:
the conditioning comprises measuring a reticle alignment between the reticle and the non-production substrate to determine when the reticle has reached the predetermined temperature; and
the measuring the reticle alignment is based on one or more alignment marks on the reticle.
3 . The method of claim 1 , wherein:
the conditioning comprises measuring a reticle shape deformation of the reticle to determine when the reticle has reached the predetermined temperature;
the measuring the reticle shape deformation is based on one or more edge alignment marks on the reticle; and
the conditioning further comprises converting the measured reticle shape deformation to a reticle temperature using a finite element model (FEM).
4 . The method of claim 1 , wherein the conditioning comprises using a fixed amount of production substrates to determine when the reticle has reached the predetermined temperature.
5 . The method of claim 1 , wherein:
the conditioning comprises using decision-based and/or machine learning to determine when the reticle has reached the predetermined temperature; and
the using decision-based and/or machine learning comprises using a regression, a local regression, a non-parametric local regression, a kernel regression, a multivariate adaptive regression, regression trees, a Gaussian process regression, a support vector regression, splines, smoothing splines, nearest neighbors, a neural network, an adaptive window, Kalman filtering, or a linear quadratic estimation, or a combination thereof.
6 . The method of claim 1 , wherein the conditioning comprises using key performance indicators (KPIs) based on a reticle alignment and/or a reticle shape deformation to determine when the reticle has reached the predetermined temperature.
7 . The method of claim 1 , wherein:
the conditioning comprises heating and/or cooling the reticle in a conditioning slot to flow gas over the reticle;
the predetermined temperature is 22° C.±0.2° C.; and
the reducing stress comprises removing the reticle from a reticle stage to a turret.
8 . The method of claim 1 , wherein the calibrating comprises inline real-time calibration of the reticle heating model based on one or more non-production substrates and/or one or more non-production lots.
9 . The method of claim 1 , wherein:
the calibrating comprises evaluating the reticle heating model for each reticle alignment (RA) between the reticle and a plurality of non-production substrates in a non-production lot;
the evaluating comprises updating a parameter x of a lithographic process by the following:
x
new
=
x
old
+
γ
·
(
x
old
-
RA
results
)
where γ is a gain value and configured to filter out noise; and/or
the evaluating comprises evaluating the reticle alignment (RA) of each of the plurality of non-production substrates until a convergence of at least 90% is reached.
10 . The method of claim 1 , wherein the reticle heating model comprises one or more modal deformations describing a relationship between inputs and distortions resulting from the inputs to reduce noise in the reticle heating model.
11 . The method of claim 1 , further comprising:
predicting distortions of the reticle in a lithographic apparatus based on the reticle heating model and inputs in a lithographic process, wherein the inputs in the lithographic process comprise a dose of radiation from a radiation source, a reticle temperature, or a number of production substrates in a production lot, or a combination thereof; and
determining a correction in the lithographic process based on the predicted distortions of the reticle, wherein the correction is a correction of an alignment of a production substrate relative to the reticle.
12 . A lithographic apparatus comprising:
an illumination system configured to illuminate a reticle;
a projection system configured to project an image of the reticle onto a substrate; and
a controller configured to reduce effects of heating and/or cooling the reticle in a lithographic process, the controller configured to:
condition the reticle in the lithographic process to adjust an initial temperature of the reticle to a predetermined temperature,
expose the reticle and a non-production substrate to a zero dose of radiation to reduce stress in the reticle to reduce parasitic thermal effects, and
calibrate a reticle heating model by:
exposing the reticle and non-production substrate to a non-zero dose of radiation,
measuring a reticle shape deformation, and
calculating a reticle temperature.
13 . A non-transitory computer readable medium program comprising computer readable instructions configured to cause a processor to:
condition a reticle in a lithographic process to adjust an initial temperature of the reticle to a predetermined temperature,
expose the reticle and a non-production substrate to a zero to a zero dose of radiation to reduce stress in the reticle to reduce parasitic thermal effects, and
calibrate a reticle heating model by:
exposing the reticle and non-production substrate to a non-zero dose of radiation,
measuring a reticle shape deformation, and
calculating a reticle temperature.