Method and apparatus for controlling the quality of a...

Adhesive bonding and miscellaneous chemical manufacture – Differential fluid etching apparatus – With microwave gas energizing means

Reexamination Certificate

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C216S085000, C216S093000, C134S111000, C134S010000

Reexamination Certificate

active

06203659

ABSTRACT:

TECHNICAL FIELD
The present invention broadly relates to processes and apparatus for fabricating semiconductor devices, such as wafers, and deals more particularly with a method and apparatus for sensing and controlling the quality of a photoresist stripper bath used to strip photoresist materials applied to the surface of the wafer.
BACKGROUND OF THE INVENTION
In order to fabricate semiconductor devices, such as semiconductor wafers used in integrated circuits, a number of various processes are used to form circuit features and conductive paths on the wafer substrate. One such process involves photolithography wherein a photosensitive material referred to as a photoresist is applied to the face of the substrate, and is subsequently exposed to light through a mask possessing features related to the circuit paths to be formed. Following such exposure, the un-exposed portions of the photoresist, i.e. those covered by the mask, are removed to form the desired conductive paths. The photoresist material is removed by subjecting the exposed photoresist coating to a specialized acid stripper, typically in the form of a bath. The photoresist layer is actually a mixture of a photoresist material combined with a chosen polymer and chemically held together by an organic bond.
As the photoresist stripper bath is used to process successive batches of wafers, the stripped, photoresist material builds up in the stripper bath, thus diluting the concentration of the photoresist stripper acid, and reducing its effectiveness accordingly. In order to solve this problem, the photoresist stripper acid is re-circulated through a filter which filters out the unwanted photoresist materials, thus maintaining the stripper acid above a desired concentration threshold.
In spite of the use of the filtering system mentioned above, the photoresist stripper acid concentration level sometime falls below the desired threshold level for any of a number of reasons, including reduction in the effectiveness of the filter due to residue buildup or other factors, or even complete failure of the filter. In the past, there has been no means by which an operator could be alerted to the fact that the stripper acid concentration had fallen below a threshold level. In other words, there has not previously been a means for monitoring or detecting, on a real time basis, the stripper acid concentration level. As a result, one or more batches of the wafers are not properly processed, thus resulting in defective wafers which in turn reduce throughput and yield in the fabrication process. Accordingly, there is a clear need in the art for a method and apparatus for controlling the quality of a photoresist stripper bath which overcomes each of deficiencies of the prior art mentioned above.
BRIEF DESCRIPTION OF THE INVENTION
According to one aspect of the invention, apparatus is provided for controlling the quality of a liquid photoresist stripper bath wherein the stripper quality is ordinarily degraded by the accumulation of photoresist materials accumulated in the bath. The apparatus includes filter means for filtering the photoresist materials accumulated in the bath, a re-circulating line for delivering the photoresist stripper in the bath to the filter means and for returning the photoresist stripper from the filter means to the bath, and means for sensing the concentration of the photoresist materials present in the bath. The sensing means preferably comprises a source of light energy in a desired range of wavelengths, such as the infrared range (i.e., wavelength=2~15 &mgr;m), and a photosensor for sensing the level of infrared light passing through the photoresist stripper contained in the bath. The infrared light source and infrared detector are preferably mounted on opposite sides of the re-circulating line such that the flow of stripper bath passing through the line is continuously monitored, on a real time basis. The apparatus further includes control means which compares the detected level of infrared light with a threshold level corresponding to a selected concentration level of the photoresist materials contained in the bath.
According to a second aspect of the invention, apparatus is provided for sensing the concentration of photoresist materials contained in a photoresist stripper system of the type including a bath of a photoresist stripper acid used to strip photoresist materials from a semiconductor device during fabrication thereof, a filter for filtering the photoresist materials from the stripper bath and a re-circulating line for delivering the photoresist stripper from the bath to the filter means and for returning the filtered photoresist stripper from the filter means to the bath. The apparatus comprises means for irradiating the stripper with light energy having a wavelength at least partially absorbed by a property of the photoresist materials, and means for detecting the light energy passing through the stripper and originating from the irradiating means, the photoresist material functioning to attenuate the intensity of the light energy passing through the stripper, the intensity of the detected light being related to the concentration of the photoresist material and the stripper.
According to a third aspect of the invention, a method is provided for sensing the concentration of photoresist materials contained in a bath of photoresist stripper used to strip photoresist material from a semiconductor device during fabrication thereof, comprising the steps of: passing the stripper through a line re-circulating the stripper from the bath, back to the bath; passing light energy through a section of the line such that a quantity of the stripper in the line is irradiated with the light energy; and, detecting the light energy passing through the line, the intensity level of the detected light energy being related to the concentration of the photoresist materials contained in the stripper.
The method further includes the steps of comparing the level of intensity detected in step (C) with a threshold value, and issuing an alarm when the level of intensity detected in step (C) falls below the threshold value.
Accordingly, it is a primary object of the present invention to provide real time monitoring and control of the quality of a photoresist stripper acid bath used to fabricate semiconductor devices.
A further object of the invention is to provide a method and apparatus as mentioned above which senses the concentration level of a desired photoresist materials contained in the bath.
A still further object of the invention is to provide a method and apparatus as aforementioned, wherein a relatively simple, inexpensive sensing means is used to sense the concentration of the photoresist materials.
A further object of the invention is to provide a method and apparatus mentioned above which senses the concentration level of photoresist materials contained in the bath without the need for physically contacting the bath or immersing sensors within the bath.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.


REFERENCES:
patent: 4778532 (1988-10-01), McConnell et al.
patent: 4908676 (1990-03-01), Bedell et al.
patent: 5671760 (1997-09-01), Nakagawa et al.
patent: 6013156 (2000-01-01), Holbrook et al.

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