Radiation imagery chemistry: process – composition – or product th – Including control feature responsive to a test or measurement
Reexamination Certificate
1999-10-29
2001-05-29
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Including control feature responsive to a test or measurement
C250S492200
Reexamination Certificate
active
06238830
ABSTRACT:
TECHNICAL FIELD
The present invention generally relates to semiconductor processing, and in particular to a system and method for monitoring and controlling the temperature within a photoresist in conjunction with a maskless lithography process.
BACKGROUND OF THE INVENTION
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller features sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as comers and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, etc.) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Due to the extremely fine patterns which are exposed on the photoresist, nonuniform heating of the photoresist during pattern formation can negatively impact the goal of achieving uniformity in the critical dimensions of various features. Small changes in the time/temperature history of the photoresist can substantially alter image sizes, resulting in lack of image line control. A uniform time/temperature history of the photoresist is especially important with chemically amplified photoresists because image size control may be drastically affected by only a few degrees difference in temperature. This is because a substantial portion of the exposure reaction in such resists are driven thermally. Therefore if different portions of the resist are being exposed at varying temperature levels, the amount of exposure and therefore the resulting patterns generated subsequently using the resist as a mask will also vary undesirably.
It is therefore desirable to have a system and/or method which substantially reduces or eliminates temperature variations in a resist during the pattern generation process.
SUMMARY OF THE INVENTION
The present invention is directed toward a system and method of monitoring a temperature of the resist during pattern generation and provides dynamic feedback control to one or more writing tools in order to maintain the resist temperature either below a threshold temperature or within a preferred temperature range. According to one aspect of the present invention, the resist is doped with a temperature sensitive material which undergoes a transformation as a function of temperature. For example, such a material may be a temperature sensitive fluorophore which produces fluorescence having a magnitude of which is a function of the resist temperature. The resist temperature is then monitored by monitoring the transformation of the temperature sensitive material within the resist, for example, by monitoring the amount of fluorescence across the resist.
Based upon the in-situ monitoring, the resist temperature may be accurately and quickly ascertained and such temperature data is used to control the one or more writing tools being used in the lithography process. For example, if the temperature at one location in the resist exceeds a predetermined temperature threshold, the write rate of the writing tool at that particular location is reduced to thereby reduce the resist temperature thereat. Correspondingly, if the resist temperature at a location in the resist falls below another predetermined threshold, the write rate of the writing tool at the location may be increased.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
REFERENCES:
patent: 5504338 (1996-04-01), Marrian et al.
patent: 5618760 (1997-04-01), Soh et al.
patent: 5784157 (1998-07-01), Gorfinkel et al.
Rangarajan Bharath
Singh Bhanwar
Templeton Michael K.
Advanced Micro Devices
Eschweiler & Associates LLC
Young Christopher G.
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