Method of through-etching substrate

Details Method of through-etching substrate Method of through-etching substrate

2002-02-28

2004-11-23

Deo, Duy-Vu (Department: 1765)

Semiconductor device manufacturing: process

Chemical etching

Combined with coating step

C438S709000, C438S710000, C438S714000, C438S717000, C438S719000

Reexamination Certificate

active

06821901

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of through-etching a substrate, which is an important technique in manufacturing a three-dimensional microelectromechanical system (MEMS).
2. Description on the Related Art
A microelectromechanical system (MEMS) is referred to as an ultra-small system or a system made of ultra-small machine parts of several micrometers or several millimeters. Also, the MEMS is an integrated microelement that is coupled with electric machine parts and mechanical machine parts and manufactured via batch-type process techniques used in manufacturing semiconductor integrated circuits.
Today, use of the MEMS has been rapidly spreading because it is a compact, portable, and efficient thermodynamic energy system. In particular, a lot of interest is centered on developing the structure, functions, and techniques of manufacturing a three-dimensional (3-D) MEMS that is a multi-layered structure of several silicon substrates, each having a recess region and a penetration region of a regular form. For example, techniques of through-etching a silicon substrate have been continuously developed.
A lot of effort to develop the technique of through-etching a substrate has been undertaken by the Gas Turbine Laboratory of Massachusetts Institute of Technology (MIT) since 1995. For example, the recent trends regarding techniques of through-etching a substrate are introduced by Ravi Khanna et al. of MIT in a report entitled “Microfabrication Protocols for Deep Reactive Ion Etching and Wafer-Level Bonding” [
Sensors
, April 2001]. Also, an example of a method of through-etching a substrate applied to a power MEMS is disclosed in a report entitled “Demonstration of a Microfabricated High-Speed Turbine Supported on Gas Bearings” written by Luc. G. Frechette et al. of MIT [
Solid
-
State Sensor and Actuator Workshop
, June 2000]. Further, an example of a method of through-etching a substrate applied to micro gas turbine is disclosed in a report entitled “A Six-Wafer Combustion System for a Silicon Micro Gas Turbine Engine” [Amit Mehra et al.,
Journal of Microelectromechanical Systems
, vol. 9, No. 4, December 2000].
FIGS. 1 through 5
are cross-sectional diagrams explaining a conventional method of through-etching a substrate used in the MEMS, which is disclosed in “Microfabrication Protocols for Deep Reactive Ion Etching and Wafer-Level Bonding” introduced by Ravi Khanna et al. of MIT [
Sensors
, April 2001].
Referring to
FIG. 1
, a photoresist layer
12
is formed on a wafer substrate
10
to be etched. Next, a photoresist pattern, which exposes a portion of the wafer substrate
10
, is formed by performing an exposure process and a developing process, which are generally adopted during a process of manufacturing semiconductor devices, on the wafer substrate
10
having the photoresist layer
12
.
Referring to
FIG. 2
, with the photoresist pattern as an etching mask, a portion of the wafer substrate
10
is dry etched to form a recess region
10
a
of a trench shape in the wafer substrate
10
. Then, the photoresist pattern
12
is stripped to be removed.
Referring to
FIG. 3
, in order to penetrate the recess region
10
a
, the side of the wafer substrate
10
having the recess region
10
a
is adhered to a handling wafer
20
via a photoresist layer
14
. Preferably, the handling wafer
20
is formed of a hard material such as quartz or silicon.
The reason why the handling wafer
20
is used during the through-etching of the wafer substrate
10
is to prevent helium gas from leaking into an etching chamber. In detail, the wafer substrate
10
to be etched is loaded onto a stage installed at a central lower portion of the etching chamber and then is dry etched using plasma. At this time, in order to cool the heat generated in the wafer substrate
10
, helium gas, which is cooled to a predetermined temperature, is introduced into the stage to reach the bottom of the wafer substrate
10
. However, when a hole is formed at a portion of the wafer substrate
10
that is passed through, the introduced helium gas leaks into the etching chamber, thereby polluting the etching chamber and changing the etching process conditions. Therefore, the handling wafer
20
is used to prevent the leakage of the helium gas into the etching chamber.
After adhering the wafer substrate
10
to the handling wafer
20
, a photoresist layer
16
, as shown in
FIG. 4
, is formed on the side opposite to the wafer substrate
10
having the recess region
10
a
. Then, as described above, the exposure and developing processes are performed on the photoresist layer
16
to form a photoresist pattern exposing a portion that includes the recess region
10
a
of the wafer substrate
10
. Next, a combination of the wafer substrate
10
having the photoresist pattern and the handling wafer
20
, is loaded onto the stage of the etching chamber. Then, with the photoresist pattern as an etching mask, the wafer substrate
10
is dry etched using plasma so as to be through-etched.
Then, referring to
FIG. 5
, after through-etching, the combination of the wafer substrate
10
and the handling wafer
20
is unloaded from the etching chamber, the handling wafer
20
is detached from the wafer substrate
10
, and then the photoresist layers
14
and
16
are stripped to be removed.
The conventional method of through-etching a wafer substrate using a handling wafer, however, has the following problems:
i) resist burning may occur. That is, bubbles may form in the photoresist layer
14
positioned between the wafer substrate
10
and the handling wafer
20
during a plasma process;
ii) wafer breakage occurs. As shown in the “A” portions of
FIG. 4
, plasma ions hit the surface of the handling wafer
20
, rebound therefrom at the end of the process of through-etching the wafer substrate
10
, and then hit the sidewalls of the wafer substrate
10
again. As a result, the sidewalls of holes formed in the wafer substrate
10
are damaged;
iii) structure erosion occurs. The handling wafer
20
made of silicon or quartz has such a low heat conductivity that the etched wafer substrate
10
cannot be sufficiently cooled by helium gas. Thus a specific portion of the etched wafer substrate
10
is etched rapidly as if it would corrode; and
iv) a lot of time is spent on detaching the handling wafer
20
from the wafer substrate
10
. Acetone is used to detach the handling wafer
20
from the wafer substrate
10
. However, since the handling wafer
20
was fast-coupled with the wafer substrate
10
, several hours are lost in separating the handling wafer
20
from the wafer substrate
10
.
SUMMARY OF THE INVENTION
To solve the above problems, it is a first object of the present invention to provide a method of through-etching a substrate that is simplified and only uses general techniques that are used in manufacturing semiconductor devices, without adhering a handling wafer to a wafer substrate.
It is a second object of the present invention to provide a method of through-etching a substrate, adopting a material of high heat conductivity rather than a handling wafer of low heat conductivity, by which cooling gas is prevented from leaking during through-etching, thereby sufficiently cooling the etched wafer substrate.
It is a third object of the present invention to provide a method of through-etching a substrate, adopting a material of high electric conductivity rather than a handling wafer of low electric conductivity, by which the flow of ions can be kept to be regular during a plasma dry etching process, thereby preventing the breakage of the sidewalls of an etched wafer substrate.
It is a fourth object of the present invention to provide a method of through-etching a substrate, by which after through-etching the substrate, all unnecessary layers except for the substrate are rapidly removed to shorten the processing time.
To achieve an aspect of the above objects, there is provided a method of through-etching a substrate, including fo

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