Dry etching endpoint detection system

Details Dry etching endpoint detection system Dry etching endpoint detection system

1998-12-14

2001-03-27

Mills, Gregory (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Delaminating processes adapted for specified product

Delaminating in preparation for post processing recycling step

C156S345420, C216S060000, C216S067000, C216S059000, C438S714000, C356S072000

Reexamination Certificate

active

06207008

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to endpoint detection during dry etching processes such as plasma assisted discharge processing operations. More particularly, the present invention relates to a method and apparatus for such dry etching endpoint detection.
2. Description of the Related Art
A number of etching methods have been utilized in semiconductor device fabrication processes, employing plasma discharges and charged particles produced by such discharges. These etching methods by plasma or dry etch methods have been used more and more widely in device fabrication.
During device fabrication processes, a device portion to be etched typically comprises a layer of a first material disposed on top of a layer of a second different material, with certain portions of the first material exposed to plasma through a mask. The device portion is then subjected to plasma etching. The aim of the plasma etching process is to etch away portions of the first material until the second material is exposed, without etching any of the second material. Therefore, it is critical to determine when the plasma etching process should be terminated.
One of the known methods for monitoring the etching of these layers is to monitor the intensity of the light emission from the plasma discharge. Many processes have particular spectral lines or regions which originate from some chemical constituents in the plasma such as reactant species or plasma etch products. By monitoring the intensity at the wavelength characteristic of these species in the plasma, the concentration of those species in the plasma can be determined, which is directly related to the etching processes.
For example, there is disclosed a method in Japanese Laid-Open Patent Application No. 59-94423, in which (1) the intensity of light emission from certain reaction products is monitored, (2) the second derivatives of the intensity is then calculated with time and (3) an endpoint is determined when the value of the second derivative exceeds a predetermined threshold level.
In this method, however, there have been found several shortcomings such as, for example, fluctuations with time in the light emission intensity which is extracted from a reaction etching chamber, thereby resulting in noises included in the intensity signals. These noises originate from several sources depending, for example, on the method used to generate the plasma and the kind of material to be etched.
When the light emission to be extracted is passing through the material to be etched, emitted light is affected by interference depending on the wavelength of the light thereby resulting in noise occurring in the outputted intensity signals, which will be detailed hereinbelow.
FIG. 3
is a schematic block diagram, illustrating major portions of a known plasma etching system. The etching system includes a reaction chamber
1
, a body
16
placed therein to be etch treated, a suitable evacuating apparatus (not shown) attached thereto through a connection
2
, and a gas feeding system (not shown) also attached thereto through a connection
3
to supply gaseous materials appropriate for the processing. The body
16
is disposed generally on top of a substrate
16
a.
Also provided within the reaction chamber
1
are lower and upper electrodes
4
and
5
, having broad faces. These broad faces of the electrodes are placed spaced apart horizontally to form a parallel plate reactor. The lower electrode
4
is supplied with power, generally in the radio-frequency (RF) range, by a power source
6
and serves as a support for the body
16
to be treated. The upper electrode
5
is maintained at ground potential.
Still further, the reaction chamber
1
includes a window
9
provided on a side wall portion thereof, for extracting the light emission which is produced within the chamber
1
by the interaction between the plasma and the body
16
being treated. A fiber optic cable
10
links the window
9
to a spectrometer
11
, where the intensity of the extracted light emission at appropriate wavelengths is obtained and transformed further to signal outputs according to the detected intensity.
A shown in
FIG. 3
, the window
9
has been typically located on the side wall portion of the reaction chamber
1
above the horizontal plane which is defined by the surface of the body
16
, and on the same side of the chamber
1
at which plasma processing is taking place. The light emission extracted from the window
9
may therefore include several components such as (1) a component I
0
which originates from the plasma region
8
between the electrodes, (2) another component I
R
which originates from the reflection by the inner walls of the reaction chamber
1
and (3) still another component I
&thgr;
caused by the reflection from the body
16
being treated, which is assumed to be transparent in the spectral wavelength of the measurements.
Since the component I
&thgr;
results from the interference of (1) light reflected by the surface of the body
16
and (2) light reflected by the interface between the body
16
and the underlying substrate
16
a
, as illustrated in
FIG. 4
, the component I
&thgr;
reflected by the body
16
has an intensity variation with peak intensities under the condition
2
h·
(
n
2
2
−n
1
2
·sin
2
&thgr;)±&lgr;
0
/2=
m·&lgr;
0
  (1)
(m=1,2,3, . . . )
with h being a thickness of the body
16
,
n
1
a refractive index of the reaction chamber ambience,
n
2
a refractive index of the body
16
,
&thgr; an angle between a reflected light beam and the normal of the surface of the body
16
, and
&lgr;
0
a wavelength of light to be detected.
The value h in the above equation (1) decreases as the etching process proceeds, thereby resulting in a periodic change in the emission intensity over time. Accordingly, the amount of change in thickness h
0
, corresponding to one intensity peak to the next in the I
&thgr;
versus time curve, is expressed by
h
0
=&lgr;
0
/{2(
n
2
2
−n
1
2
·sin
2
&thgr;)}  (2).
This results in the period &tgr; for the aforementioned periodic change as
&tgr;=
h
0
/R
  (3)
in which R is an etching rate.
As an exemplary illustration, an etching process is assumed in a case where a body
16
composed of a polysilicon layer is etch treated under the following conditions; n
1
1.0, n
2
5.05, &thgr; 60° and &lgr;
0
426 nanometers. With an etch rate of 300 nanometers/second, &tgr; is found to be 8.56 seconds.
The aforementioned periodic change in intensity gives rise to concomitant changes in the second derivative values of the light emission intensity which is utilized for determining the endpoints in the aforementioned example. When these changes exceed a predetermined value, this may result in erroneous endpoint detection.
Several methods have been disclosed to obviate the above-mentioned difficulties, such as, for example, by eliminating the periodic changes or fluctuations. For example, Japanese Laid-Open Patent Application No. 1-226154 discloses several methods, in which an additional “external” means such as a low-pass filter, phase adjusting unit or input signal controller is additionally incorporated in a signal processing circuitry to smooth the fluctuation with time, to thereby eliminate the above periodic changes.
By “external” is meant that this process attempts to eliminate the change after the extraction of light emission or in the course of the signal processing, instead of eliminating it before the extraction or during the collection of light emission inside the chamber. With these methods, the aforementioned difficulties may be obviated to some extent.
Referring to
FIG. 5
, the above-mentioned method will be exemplified hereinbelow for the case of a plasma etching system with signal processing units incorporating a low-pass filter
20
.
The plasma etching system including the reaction chamber is illustrated and described above with respect to FIG.
3
. Accordingly, the various portions of
FIG. 5
which a

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