Coating apparatus – With indicating – testing – inspecting – or measuring means
Reexamination Certificate
1997-08-29
2001-03-06
Mills, Gregory (Department: 1763)
Coating apparatus
With indicating, testing, inspecting, or measuring means
C118S713000, C156S345420
Reexamination Certificate
active
06197116
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a plasma processing technique for use in fabricating semiconductor devices and, more particularly to a plasma processing system for processing wafers, etc., by the use of plasma, a process monitoring method, and method for fabricating a semiconductor device.
2. Description of the Related Art
Plasma processing systems use a reactive gas plasma excited by radio frequency electric power to etch a thin film on a surface of a substrate or deposit a thin film on a surface of a wafer by generated ions and radicals, and are widely used in processes for fabricating semiconductor devices.
A conventional plasma processing system will be explained with reference to a parallel plate reactive ion etching system shown in FIG.
8
.
An upper electrode
62
and a lower electrode
64
are positioned opposite to each other in a vacuum chamber
60
for plasma processing. A wafer
66
to be etched is mounted on the lower electrode
64
. A radio frequency electric power supply
70
for generating a plasma
68
between the upper electrode
62
and the lower electrode
64
is applied between the upper and the lower electrodes
62
,
64
through impedance matching unit
72
. The vacuum chamber
60
includes a flow rate controller
74
for introducing a required rate of an etching gas, and a gas pressure controller
76
. The radio frequency electric power supply
70
, the flow rate controller
74
and the gas pressure controller
76
are connected to a computer for system control
78
.
Then, the operation of the conventional plasma processing system will be explained.
First, a wafer
66
to be processed is mounted on the lower electrode
64
in the vacuum chamber
60
, and then an internal pressure of the vacuum chamber
60
is reduced to a required pressure.
Next, an etching gas is introduced into the vacuum chamber
60
through the flow rate controller
74
while an internal pressure of the vacuum chamber
60
is maintained constant by the gas pressure controller
76
.
Then, in this state a radio frequency is applied between the upper electrode
62
and the lower electrode
64
to generate a plasma
68
between the electrodes. The operating frequency supplied by the radio frequency electric power supply
70
is, e.g., 13.56 MHz.
Thus, the film on the wafer
66
mounted on the lower electrode
64
is etched by ions and radicals in the plasma into a required pattern.
For the etching, usually etching conditions (system control parameters), such as a radio frequency electric power, a gas pressure, and gas flow rate, are set in the computer for system control
78
, so that associated controller separately retain set values.
However, a plasma condition, which affects properties of an etching process, such as etching rate, etc., is determined by the so-called condition setting, in which set values, as of radio frequency electric power, gas pressure, gas flow rate, etc., are variously changed to investigate the relationship between the set conditions and etching rate, uniformity, selectivity and processed profile, etc., and the set conditions are adjusted so that characteristics obtained by the plasma processing, e.g., etching rate, etching uniformity, selectivity, processed profile etc. become as required, whereby mass production conditions are determined.
That is, a plasma condition is determined by correlation among a radio frequency electric power, a gas pressure, a gas flow rate, etc., and by separately controlling respective plasma parameters a plasma condition cannot be directly controlled. Accordingly, the conventional plasma processing system in which a radio frequency electric power, a gas pressure, a gas flow rate, etc., are separately controlled by the associated controller controlled by the computer for system control
78
cannot suitably control the plasma condition.
In the usual plasma processing system, for ends of TAT (turnaround time) improvement, etc., characteristics provided by processing are periodically checked by a line operator for in-line administration, but wafers are not checked one-by-one as to whether or not the processing is normally conducted.
As a result, it is accordingly impossible to check changes of processing characteristics, such as etching characteristics, caused by transient changes of the electrode surfaces and wall of the vacuum chamber
60
caused by increased numbers of processed wafers, fluctuation and troubles of the controller for various controls, etc., cannot be quickly checked at their occurrences. A number of defective wafers are often produced.
Even when etching is conducted, and changes of etching characteristics are found on wafers, causes for the changes cannot be identified, and the system is often forced to be stopped for a long period of time.
This also happens in plasma processing systems for film deposition systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a plasma processing system which can realtime monitor fluctuation and transient changes of plasma processing characteristics to thereby provide higher fabrication yields and productivity.
The above-described object is achieved by a plasma processing system comprising: a measuring unit for measuring an electric signal reflecting a plasma condition; a model expression memory for storing a model expression for relating a value of the electric signal with a plasma processing characteristic; a computing unit for substituting the value of the electric signal measured by the measuring unit into the model expression read from the model expression memory to compute a predicted value of the plasma processing characteristic; and a diagnosing unit for diagnosing a condition of a plasma based on the predicted value of the plasma processing characteristic. The plasma processing system of this structure permits a condition of a plasma to be estimated by substituting realtime measured electric signals into a model expression, whereby when a change of plasma processing characteristics occurs, the operator can immediately know it. Accordingly, an occurrence of a large number of defective wafers can be precluded. The model expression permits a balance of a plurality of parameters to be related with the plasma characteristics to monitor the condition of the plasma at once in place of monitoring parameters of respective electric signals, e.g., current, voltage, phase, etc., whereby a cause for an abnormality of the system can be easily investigated.
In the above-described plasma processing system it is preferable that the plasma processing system further comprises an endpoint detector for detecting an endpoint of the plasma processing, based on the electric signal; and in which the computing unit computes actually measured value of the plasma processing characteristic, based on an endpoint information detecting by the endpoint detector, and the diagnosing unit diagnoses the condition of the plasma, based on difference between the predicted value and the actually measured value. By further providing unit for giving actually measured values, based on comparison of the actually measured values with the predicted values, it can be easily judged whether or not the plasma processing has been conducted in accordance with the model expression.
In the above-described plasma processing system it is preferable that the diagnosing unit decides whether or not plasma processing is continued, based on a diagnose result of the condition of the plasma. Occurrence of a large number of defective wafers processed outside a prescribed plasma condition can be prevented.
In the above-described plasma processing system it is preferable that the plasma processing system further comprises a controller for controlling the condition of the plasma, based on the predicted value so that the plasma processing characteristic is substantially constant. Wafers can be processed with suitable plasma processing characteristics.
In the above-described plasma processing system it is preferable that the measuring unit measures as the elect
Alejandro Luz
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Mills Gregory
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