Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1999-08-27
2001-05-01
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C250S559300
Reexamination Certificate
active
06225639
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of semiconductor manufacturing, and more particularly, this invention relates to the field of analyzing a semiconductor surface using line width metrology for monitoring a patterned transfer process.
BACKGROUND OF THE INVENTION
Photoresist features are measured using a scanning electron microscope (SEM) or other line width metrology device to determine if the desired feature size is within a specified range. The line width metrology device typically performs a single measurement, which specifies the size or scale at a single point on a feature's vertical wall. This process is often used in integrated circuit manufacturing before performing a patterning step, often a plasma etch, to determine the quality of the photo-lithographic process. If the quality is inadequate, the resist is stripped and the lithography is reworked.
As device features get smaller, this type of evaluation brought about by a scanning electron microscope or other line width metrology device becomes increasingly important. A reworking of lithography processes is costly and limits the efficient use of expensive equipment in semiconductor manufacturing.
Also, in the semiconductor industry, critical dimension metrology is used with the scanning electron microscope or other intensity trace to determine a width before and after an etching process. Typically, a specific algorithm is picked to determine where on the scanning electron microscope trace that forms an amplitude modulated waveform a position is used to determine the two edges that measure the critical dimension. This typically is an arbitrary method associated with increasingly poor predictive capabilities. For example, much of the method could be based on an inspector's intuition or experience. Thus, the predictive capabilities of the metrology are limited by the intuition and experience of the engineer or inspector making the algorithm determination. The predictive value of the comparison of line width between different technologies, fabrication plants and various companies in the industry are limited by the large variation and the choices of etch detection algorithms used by different metrologists in the industry.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method of monitoring a patterned transfer process in the manufacture of a semiconductor device that is not limited by the intuition and experience of an engineer making an algorithm determination to determine edges in the critical dimension measurement.
In accordance with the present invention, the method of the present invention monitors a patterned transfer process in the manufacture of a semiconductor device. The method comprises the step of scanning across patterned features formed on a semiconductor layer to be etched for generating a first amplitude modulated waveform intensity signal. The first amplitude modulated waveform intensity signal is sampled to extract a first measurement population of critical dimension measurements. The patterned features are etched. The method further comprises the step of scanning across the etched patterned features for generating a second amplitude modulated waveform intensity signal. The method comprises the step of then sampling the second amplitude modulated waveform intensity signal to extract a second measurement population of critical dimension measurements. The first and second population of critical dimension measurements are then cross-correlated to obtain correlation values of the etching process.
In one aspect of the present invention, the method comprises the step of deriving a curve of outer line width and inner line spacing for the first and second amplitude modulated waveform intensity signals. The method also comprises the step of forming a patterned photoresist layer over a nitride layer that has been formed over a silicon semiconductor layer. The nitride layer is etched to expose a pattern of the silicon semiconductor layer. The etched nitride layer is then scanned for generating the first amplitude modulated waveform intensity signal. In a further aspect of the present invention, the etched silicon semiconductor layer is etched and the patterned silicon semiconductor layer is scanned for generating the second amplitude modulated waveform intensity signal.
In still another aspect of the present invention, the method comprises the step of sampling about ten to about twenty times across the patterned features in about 5% to about 10% increments for obtaining the population of critical dimension measurements. The method also comprises the step of generating first and second amplitude modulated waveform signals with a scanning electron microscope.
In still another aspect of the present invention, the first and second amplitude modulated waveform signals can be generated with a semiconductor stylus measurement tool.
In still another aspect of the present invention, the method can store the correlation values of the etching process within a database for use in monitoring subsequent etching on other samples of other semiconductor layers to be etched. A second semiconductor layer to be etched can also be scanned for generating an amplitude modulated waveform intensity signal of the second semiconductor layer to be etched. The anticipated etching process results can be determined based on the stored correlation values.
REFERENCES:
patent: 4600839 (1986-07-01), Ichihashi et al.
patent: 4751384 (1988-06-01), Murakoshi et al.
patent: 4767926 (1988-08-01), Murakoshi et al.
patent: 5807761 (1998-09-01), Coronel et al.
Adams Thomas E.
Frederick Thomas S.
Jessen Scott
McIntosh John M.
Vartuli Catherine
Agere Systems Guardian Corp.
Allen, Dyer, Doppelt, Milbrah & Gilchrist, P.A.
Le Que T.
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