Method of detecting end point of process, end point...

Details Method of detecting end point of process, end point... Method of detecting end point of process, end point...

1998-09-25

2001-12-04

Hilten, John S. (Department: 2854)

Data processing: measuring, calibrating, or testing

Measurement system in a specific environment

Electrical signal parameter measurement system

36, 36

Reexamination Certificate

active

06327540

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a method of detecting an end point of a process such as a manufacture process and a test process, a device to be used in the method, a computer memory product in which a computer program for executing the method is stored, and a chemical mechanical polishing apparatus provided with the device for detecting an end point of a process.
In the case where a semiconductor device such as a LSI and a VLSI is to be manufactured by using a wafer in which plural films are stacked on a silicon substrate, it is necessary to planarize the film surface of a desired layer in order to realize the higher circuit integration of the semiconductor device. The usage of a chemical mechanical polishing (hereinafter refereed to as the CMP) apparatus has been proposed for this purpose.
In a CMP apparatus, a polishing cloth impregnated with a polishing solution such as an alkaline colloidal silica solution is allowed to be in contact with the surface of a wafer with an appropriate force applied, and the polishing cloth is driven to be rotated, so that the film surface of the wafer can be planarized through composite functions of chemical etching using the alkaline solution and mechanical polishing using the colloidal silica. The end point of the polishing process by using the CMP apparatus has been conventionally detected by repeatedly measuring the thickness of the film with the CMP apparatus temporarily halted. Therefore, it disadvantageously takes a long time to planarize plural wafers. Accordingly, Japanese Patent Application Laid-Open No. 8-306648 (1996) discloses the following apparatus as a countermeasure.
FIG. 1
is a block diagram for showing the structure of an end point detector disclosed in Japanese Patent Application Laid Open No. 8-306648 together with the structure of a CMP apparatus. In
FIG. 1
, a reference numeral
32
denotes a polishing table in the shape of a bottomed cylinder. A polishing cloth
31
impregnated with a polishing solution is stretched over the opening of the polishing table
32
, so as to be in contact with the surface of a wafer W in which plural films are stacked on a silicon substrate. At the center of the bottom of the polishing table
32
, the output axis of a DC motor
34
is vertically provided. The DC motor
34
has power terminals
35
and
36
, with the power terminal
36
connected with a positive terminal of a power supply
37
and the power terminal
35
connected with a negative terminal of the power supply
37
through a switch
38
.
The power terminals
35
and
36
of the-DC motor
34
are also connected with an analyzer
41
for analyzing a frequency characteristic of an electric signal. The analyzer
41
analyzes a frequency characteristic of a noise signal appearing at the power terminals
35
and
36
of the DC motor
34
, and supplies a result of the analysis to a level discriminating circuit
42
. In the noise signal, different frequency components appear in accordance with the materials of the respective films of the wafer W.
In the level discriminating circuit
42
, specific frequency components appearing in polishing the respective films of the wafer W by the CMP apparatus are previously set. The level discriminating circuit
42
generates time series data at levels of the specific frequency components on the basis of the results of the analysis supplied with time by the analyzer
41
, detects the timing of a peak in the generated time series data, and supplies a peak detection signal to a control circuit
39
. The control circuit
39
turns the switch
38
on in response to the peak detection signal, thereby halting the polishing of the wafer W by the CMP apparatus.
In the end point detector described in Japanese Patent Application Laid-Open No. 8-306648, however, the analysis of the frequency characteristic takes a long time because the frequency characteristic of the noise signal appearing at the power terminals of the DC motor is analyzed by the analyzer. Therefore, there arises a problem that the polishing speed of the CMP apparatus should be set low. Furthermore, it is necessary to previously determine the specific frequencies corresponding to the materials of plural films through tests to be previously set in the level discriminating circuit, which is disadvantageously troublesome. In addition, the analyzer for analyzing the frequency characteristic is disadvantageously expensive.
BRIEF SUMMARY OF THE INVENTION
The present invention was devised to overcome the aforementioned conventional problems, and the object of the invention is providing a method of detecting an end point of a process by which an end point can be detected in a shorter period of time at a lower cost without previously conducting plural tests; an end point detector used in the method; a computer memory product in which a computer program for the method is recorded; and a chemical mechanical polishing apparatus provided with the end point detector.
Specifically, in the method of this invention of detecting an end point of a process on the basis of time series data obtained by measuring, with time, a physical quantity changing in accordance with proceeding of the process, every time the time series data of a previously set time region are obtained, first time series data corresponding to a part of the time series data and second time series data delayed from the first time series data by a predetermined delay time are extracted from the time series data, correlation between the first time series data and the second time series data is calculated, and an end point of the process is discriminated on the basis of a result of calculation.
Furthermore, the device for detecting an end point of a process of this invention comprises a memory for storing the time series data; extracting means for extracting, from the memory, the first time series data and the second time series data; calculating means for calculating correlation between the first time series date and the second time series data; and discriminating means for discriminating an end point of the process on the basis of calculation by the calculating means.
Moreover, in the computer memory product of this invention is recorded a program including program code means for causing a computer to store the time series data in a memory; program code means for causing the computer to extract, from the memory, the first time series data and the second time series data; program code means for causing the computer to calculate correlation between the first time series data and the second time series data; and program code means for causing the computer to discriminate an end point of the process on the basis of a result of calculation.
Furthermore, the chemical mechanical polishing apparatus of this invention comprises a table for placing an object to be polished; a polishing table disposed to oppose the table and provided with a polishing cloth; a motor mounted on the table and/or the polishing table for causing a relative movement between the table and the polishing table; the device having the aforementioned structure for detecting an end point of a process in which a physical quantity changes in accordance with proceeding of the process; and control means for controlling the motor to halt chemical mechanical polishing when the device for detecting an end point detects the end point of the process.
According to the invention, the time series data are obtained by measuring with time the physical quantity changing in accordance with the proceeding of the process. For example, in the case where the invention is applied to a chemical mechanical polishing apparatus, in which the surface of a wafer is polished by contacting and moving the polishing cloth and the wafer relatively with supplying slurry, a current supplied to a motor for relatively moving the cloth and the wafer is periodically measured, thereby obtaining the time series data.
With plural time regions defined by dividing the time axis into a predetermined time duration, every time the time series data of

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