Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1998-06-26
2001-05-08
Heckler, Thomas M. (Department: 2787)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
Reexamination Certificate
active
06230069
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the manufacture of discrete parts using model predictive control, more specifically, to a system and method for controlling the manufacture of semiconductor wafers using model predictive control.
BACKGROUND OF THE INVENTION
Many manufacturing operations involve the manufacture of discrete parts. Semiconductor fabrication includes the fabrication of discrete parts, such as runs or batches of wafers, each of which includes one or more wafers fabricated using similar processing. One challenge in semiconductor fabrication is controlling equipment inputs from run to run. The challenge in run-to-run control stems from a lack of real-time information about process states and output states while processing a given wafer or group of wafers and variable input states of incoming wafers.
Chemical-mechanical polishing (CMP) is a common and rapidly growing process used in the fabrication of semiconductor wafers for planarizing silicon dioxide as well as other types of layers on semiconductor wafers. Chemical mechanical polishing typically utilizes an abrasive slurry disbursed in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action. A typical chemical mechanical polishing tool includes a rotatable circular platen or table on which a polishing pad is mounted and a polishing device is positioned above the pad. The polishing device includes one or more rotating carrier heads to which wafers can be secured typically through the use of vacuum pressure. In use, the platen is rotated and an abrasive slurry is disbursed onto the polishing pad. Once the slurry has been applied to the polishing pad, a downforce is applied to each rotating carrier head to press its wafer against the polishing pad. As the wafer is pressed against the polishing pad, the surface of the wafer is mechanically and chemically polished. In a manufacturing operation, the usual adjustment parameter or tool input is polishing time (though in some operations, carrier downforce is input as well). Other parameters, such as table speed and carrier downforces are fixed for the process.
As semiconductor devices are scaled down, the importance of run-to-run control increases. In particular, it becomes increasingly important to control tool outputs as variations in tool outputs deleteriously impact subsequent fabrication steps and degrade device performance. In CMP, for example, tool outputs, such as post-polish thicknesses of polished layers, must be accurately controlled as variations in post-polish thicknesses can, for example, significantly degrade subsequent processing steps, such as lithography.
Conventional run-to-run control of manufacturing tools, such as CMP tools, typically involves the use of Exponentially Weighted Moving Average (EWMA) controllers. EWMA controllers typically use a linear regression process model such as:
y
k
=B*u
k|k−1
+c
k|k−1
+e
k
[1]
Where y
k
is the output at batch k, B is the process gain, u
k|k−1
is the input at batch k calculated from information up through batch k−1, c
k|k−1
is the estimate for the intercept, and e
k
is unknown process noise entering the system. Typically, the system gain and the initial value of the intercept is modeled a priori from designed experiments.
The intercept is typically updated recursively by an observer of the form:
c
k|k−1
=&lgr;*(
y
k−1
−B*u
k−1|k−2
)+(1−&lgr;)*
c
k−1|k−2
[2]
where &lgr; is the exponential weighting factor, or tuning parameter, of the observer. The weighting factor &lgr; takes a value between 0 and 1 and is chosen based on the desired properties of the observer. Using the updated intercept, the input for batch k (u
k|k−1
) is determined from the following relationship:
u
k|k−1
=(
T−c
k|k−1
)/
B
[3]
where T is a target output thickness.
Other controllers, such as predictor-corrector controllers (PCC), have been suggested for run-to-run control. PCC uses a second exponential filter to forecast the trend in the estimated intercept in an attempt to predict how the intercept will change in the future, while the standard EWMA controller simply assumes the intercept will remain constant. The additional observer equation of the PCC is of the form:
&dgr;
c
k|k−1
=&ggr;*(
y
k
−B*u
k|k−1
−c
k|k−1
)+(1−&ggr;)*
&dgr;c
k−1|k−2
[4]
where &dgr;c
k|k−1
is the smoothed trend of the intercept. After this modification, the model prediction equation then becomes:
&ggr;
k
=B*u
k|k−1
+c
k|k−1
[5]
with the new prediction for the intercept given by:
c
k|k−1
=c
k|k−1
+&dgr;c
k|k−1
[6]
Despite the use of EWMA and PCC controllers, variations in tool output still significantly impact semiconductor fabrication and device performance. The significance of the impact is also growing as a result of the ever decreasing size of semiconductor devices. Consequently, semiconductor manufacturers seek systems and methods for more accurately controlling the manufacture of semiconductor wafers.
SUMMARY OF THE INVENTION
The present invention provides a system and method for controlling the manufacture of semiconductor wafers using model predictive control. In accordance with one embodiment, a tool output of the manufacturing tool is determined based on a first wafer run. Using the tool output, a tool input for a subsequent wafer run is determined by minimizing an optimization equation being dependent upon a model which relates tool output to tool process state and tool process state to tool input and previous tool process state. The tool input is then provided to the manufacturing tool for processing a second wafer run. In this manner, processing by the tool or tool age is taken into account in determining the tool input for a subsequent run. This can reduce variations in tool output from run-to-run and improve the characteristics of the ultimately formed semiconductor devices. The tool may, for example, be a chemical mechanical polishing tool with the tool input being polishing time and the tool output being a post-polish wafer layer thickness associated with CMP tool for a run.
The above summary of the present invention is not intended to describe each illustrated embodiment or implementation of the present invention. The Figures and the detailed description which follow more particularly exemplify these embodiments.
REFERENCES:
patent: 5298110 (1994-03-01), Schoenborn et al.
patent: 5408405 (1995-04-01), Mozumder et al.
patent: 5519605 (1996-05-01), Cawlfield
patent: 5526293 (1996-06-01), Mozumder et al.
patent: 5609136 (1997-03-01), Tuken
patent: 5655951 (1997-08-01), Meikle et al.
patent: 5665199 (1997-09-01), Sahota et al.
patent: 5695601 (1997-12-01), Kodera et al.
patent: 5740033 (1998-04-01), Wassick et al.
patent: 0 643 344 A1 (1995-03-01), None
Boning, D. et al., “Practical Issues in Run by Run Process Control”, IEEE/SEMI Advanced Semiconductor Manufacturing Conference, pp. 201-208 (Copyright 1995).
Boning, D.S. et al., “Run by Run Control of Chemical-Mechanical Polishing”,IEEE Transactions on Components, Packaging and Manufacturing Technology—Part C.,19(4):307-311 (Oct. 1996).
Butler, S.W. et al., “Supervisory Run-to-Run Control of Polysilicon Gate Etch Using In Situ Ellipsometry”,IEEE Transactions on Semiconductor Manufacturing,7(2):193-201 (May 1994).
Castillo, E.D. et al., “Run-to-Run Process Control: Literature Review and Extensions”,Journal of Quality Technology,29(2):184-196 (Apr. 1997).
Hunter, J.S. “The Exponentially Weighted Moving Average”,Journal of Quality Technology,18(4):203-210 (Oct. 1986).
Ingolfsson, A.
Campbell William Jarrett
Mullins James Anthony
Toprac Anthony John
Advanced Micro Devices , Inc.
Crawford PLLC
Heckler Thomas M.
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