Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-02-12
2003-11-04
Picard, Leo (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C438S009000, C204S192330
Reexamination Certificate
active
06643559
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention lies in the field of semiconductor technology and relates to a method for monitoring a semiconductor fabrication process for processing a substrate.
A multiplicity of fabrication processes are used in fabricating and processing semiconductor substrates to form integrated semiconductor circuits therein. Deposition processes and etching processes for patterning layers that are applied on a substrate are mentioned as examples. These fabrication processes must be monitored, in principle, since, because of their complexity, unnoticed disturbances or poorly adapted process conditions can lead to defectively fabricated semiconductor circuits. To be able to efficiently carry out this monitoring, there is generally a desire to characterize the fabrication process through real-time analysis of specific measurement quantities that are determined during the fabrication process to thereby be able to make a regulating intervention, if appropriate.
Possible methods for monitoring fabrication processes are disclosed, for example, in U.S. Pat. No. 5,877,032, which describes a method for determining the end point of a plasma etching process, in which the detected optical emission of the plasma is used for determining the end point. The background to this approach is the fact that, during etching processes, a layer situated on a substrate is etched through and the underlying substrate is uncovered in the process. The interaction between the etching gas and the uncovered substrate can be demonstrated spectroscopically as a change in the emission spectrum of the plasma. In accordance with U.S. Pat. No. 5,877,032, this change is compared with a multiplicity of predetermined reference curves and the end point of the plasma etching process is inferred from the comparison.
U.S. Pat. No. 5,739,051 likewise discloses a method for determining the end point of a plasma etching process, in which the optical emission of the plasma is likewise used for determining the end point. Emission lines that are characteristic of the interaction between the etching gas and the substrate are used for the assessment.
However, very often it is difficult to extract the measurement quantity that is characteristic of the etching process from the multiplicity of available spectra or else from other measurement quantities. Therefore, U.S. Pat. No. 5,658,423 proposes a method based on so-called principal component analysis, in which the temporal development of the entire emission spectrum from about 240 to 600 nanometers is used for the end point analysis. Using principal component analysis, the volume of data obtained is reduced to a few so-called base patterns and the temporal development thereof is used for detecting the end point. As a result of this, the detection of the end point is no longer based on the assessment of a single emission wavelength, but on the change in the entire available spectrum. In principle, however, this approach also requires that reference values be provided for comparison with the currently measured measurement quantities.
In U.S. Pat. No. 5,737,496, an attempt is made to avoid the last-mentioned problem, in particular, by using a neural network. The neural network is trained using a multiplicity of determined measurement quantities, so that it can subsequently be used for decision-making with regard to the end point identification. It has been shown, however, that neural networks often learn incorrect signals and patterns, so that an incorrect interpretation can occur. Erroneous training of the neural network arises, for example, through a change in the emission spectra because of aging phenomena of the sensors or because of chamber contamination that occurs. Therefore, U.S. Pat. No. 5,864,773 proposes a so-called virtual sensor system, in which these changes are taken into account before the measurement quantities are actually assessed. As a result, the intention is to produce a virtual sensor that is free of chamber-specific or process-specific fault effects. Since it is necessary to have recourse to the operating personnel's experiences in this case, too, unexpectedly occurring faults and changes cannot automatically be taken into account.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for monitoring a semiconductor fabrication process for processing a substrate which overcomes the above-mentioned disadvantages of the prior art methods of this general type.
In particular, it is an object of the invention to provide a method for monitoring a semiconductor fabrication process for processing a substrate which enables the fabrication process to be monitored reliably and in a manner that is, as far as possible, free from faults. Even more particularly, the method serves for determining the end point of the fabrication process.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for monitoring a plasma process that includes steps of:
using a first model to determine an end point of a first plasma process that is performed in a plasma;
defining the first model with an algorithm, with a termination criterion, and with at least one predetermined measurement quantity that can be determined during the first plasma process and that is based on an intensity of at least one predetermined emission wavelength of the plasma;
configuring the algorithm such that when the algorithm is applied to the predetermined measurement quantity that is determined, the algorithm provides a decision quantity which, upon comparison with the termination criterion, serves for determining the end point of the first plasma process;
performing the first plasma process by using a plasma-excited gas in a plasma chamber, by introducing a substrate, which will be treated, into the plasma chamber, and by allowing the substrate to interact with the plasma-excited gas in the plasma chamber;
during the first plasma process, determining the predetermined measurement quantity for the first model to thereby obtain a measured quantity;
applying the algorithm of the first model to the measured quantity and determining the decision quantity;
comparing the decision quantity with the termination criterion prescribed by the first model and terminating the first plasma process when the termination criterion is met;
using a second model for comparatively determining the end point of the first plasma process;
defining the second model with an algorithm, with a termination criterion, and with at least one predetermined measurement quantity that can be determined during the first plasma process and that is based on an intensity of at least one predetermined emission wavelength of the plasma;
using an additional monitoring function for continuously assessing the first model and the second model;
if the end point that was determined with the second model has a higher significance than the end point that was determined with the first model, then using the second model to determine an end point of a second plasma process succeeding the first plasma process;
measuring intensities of a plurality of emission wavelengths of the plasma during the first plasma process;
using the intensities of the plurality of the emission wavelengths as measurement quantities and continuously storing the measurement quantities in a data processing system;
also using the data processing system for identifying the end point of the first plasma etching process;
performing the first plasma process as a plasma etching process and providing the plasma-excited gas as a dry etching gas that etches at least parts of the substrate;
providing the substrate with an insulating layer; and
etching contact holes using the plasma etching process.
In accordance with an added feature of the invention, the method includes: using the second model during the second plasma process; performing the second plasma process in a plasma; using a third model for comparatively determining the end point of the second plasma process; defining t
Greenberg Laurence A.
Kosowski Alexander
Locher Ralph E.
Picard Leo
Stemer Werner H.
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