Semiconductor device manufacturing: process – Including control responsive to sensed condition – Optical characteristic sensed
Reexamination Certificate
1999-09-30
2001-07-24
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Including control responsive to sensed condition
Optical characteristic sensed
C156S345420, C216S059000, C216S060000, C438S009000, C438S014000, C438S710000
Reexamination Certificate
active
06265231
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to plasma etch processes, and more particularly to method and apparatus for process control of the etch process via valve position monitoring.
In the fabrication of integrated circuits, the removal of various layers of materials formed on a substrate to define device patterns is commonly accomplished by means of an etching process. Etching techniques in use include wet, or chemical etching, and dry, or plasma etching. The latter technique is typically dependent upon the generation of reactive species from process gases that are impinged on the surface of the material to be etched. A chemical reaction takes place between the material and these species and the gaseous reaction product is then removed from the surface.
With reference to
FIG. 1
, creating plasma for use in manufacturing or fabrication processes typically begins by introducing various process gases into a plasma chamber
10
of a plasma reactor, generally designated
12
. These gases enter the chamber
10
through an inlet
13
and exit through an outlet
15
. A workpiece
14
, such as an integrated circuit wafer is disposed in the chamber
10
help upon a chuck
16
. The reactor
12
also includes a plasma density production mechanism
18
(e.g. an inductive coil). A plasma-inducing signal, supplied by a plasma inducing power supply
20
is applied to the plasma density production mechanism
18
. A top portion
22
, constructed of a material transmissive to radiation such as ceramic or quartz, is incorporated into the upper surface of the chamber
10
. The top portion
22
, allows for efficient transmission of radiation from the coil
18
to the interior of the chamber
10
. This radiation in turn excites the gas molecules within the chamber generating a plasma
24
. The generated plasma
24
is useful in etching layers from a wafer or for depositing layers upon a wafer as is well known in the art.
An important consideration in all etch processes is control of the extent to which the wafer is etched and determining a time, referred to as the endpoint, at which to end the process. Common methods for monitoring the etch process include spectroscopy and interferometry. In the spectroscopic method, the composition of the species in the plasma chamber
10
are monitored. In the interferometric method, a light is directed through a viewing window
25
onto an area of the wafer undergoing etching within the plasma chamber
10
. The intensity of the light reflected from the wafer is detected and recorded as a function of time and/or wavelength. Due to the changing optical path through the layer being etched, varying interference patterns are detected and analyzed to determine etch rate, film thickness and the process endpoint.
In an etch process, the total pressure in the plasma chamber
10
is the sum of the pressures from the gas species being delivered and pressures from the etch by-products generated. The gas species pressures are constant due to the nature of the etch recipe.
The pressure due to etch by-products changes as the amount of by-products changes. In order for the plasma chamber pressure to remain constant, as required by the etch recipe, a pressure control valve changes position to compensate for the pressure changes. By monitoring the position of the pressure control valve, information regarding the constituent species in the chamber can be determined.
A specific application of the etch process is an in-situ cleaning process of the plasma chamber
10
. A polymerizing oxide etch process is commonly used to etch the oxide films on the substrate. This process leaves polymer within the chamber. The in-situ cleaning process is then carried out to remove the polymer from the inside surfaces of the plasma chamber
10
and thereby clean the inside surfaces. Conventionally this is a timed process, particularly when the number of optical channels available for observing the chamber is limited or none are available. The time set is normally exaggerated to ensure that all of the polymer is etched in a worst case scenario. Overshooting in a timed cleaning process leads to the over-cleaning of the plasma chamber which can cause hardware erosion.
It would be desirable therefore to provide a process control method and apparatus that accurately detects the endpoint of an in-situ cleaning process and thereby overcomes the aforementioned disadvantages of the prior art methods and apparatus.
SUMMARY OF THE INVENTION
The present invention provides a process control method and apparatus via pressure control valve position monitoring for endpointing an in-situ plasma chamber cleaning operation. The invention also finds applicability in endpointing other etch processes as further described hereinbelow.
More particularly, in one embodiment of the invention, a computer implemented method comprises monitoring the pressure control valve position during an in-situ chamber cleaning process and determining an endpoint of the process based upon the monitored position. In another embodiment, a computing system includes a system process having logic for monitoring the pressure control valve position and determining an endpoint based upon the monitored position. In yet another embodiment, a computer program for endpointing an in-situ chamber cleaning process includes a code segment that monitors the pressure control valve position and a code segment that determines the endpoint based upon the monitored position.
The method and apparatus of the present invention provide for an endpoint to the in-situ cleaning process which reduces the over-cleaning of the plasma chamber. Additionally, the method and apparatus of the invention eliminates the necessity of predetermining an end time to the cleaning process and thereby provides for a single cleaning process which automatically determines the process endpoint. Throughput of the etching tool is improved as overshoot times are no longer needed. Finally, the method and apparatus of the present invention allows for monitoring the repeatability of the endpoint detection of in-situ cleaning processes to thereby detect problems with the operation of the etching tool.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings.
REFERENCES:
patent: 5391252 (1995-02-01), Taylor
patent: 5536359 (1996-07-01), Kawada et al.
patent: 5685912 (1997-11-01), Nizhizaka
Hitchman, M.L., Eichenberger, V. A simple method of end-point determination for plasma etching. Journal of Vacuum Science and Technology, vol. 17, No. 6, Nov.-Dec. 1980.
Roland, J.P., Marcoux, P.J., Ray, G.W., Rankin, G.H. Endpoint detection in plasma etching. Journal of Vacuum Science and Technology, vol. 3, No. 3, May-Jun. 1985, pp. 681-686.
Lam Research Corporation
Oppenheimer Wolff & Donnelly LLP
Powell William
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