Method for wet etching and wet etching apparatus

Details Method for wet etching and wet etching apparatus Method for wet etching and wet etching apparatus

2002-08-12

2004-04-06

Goudreau, George A. (Department: 1763)

Etching a substrate: processes

Nongaseous phase etching of substrate

Relative movement between the substrate and a confined pool...

C438S745000, C438S747000

Reexamination Certificate

active

06716365

ABSTRACT:

CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-252861 filed on Aug. 23, 2001.
BACKGROUND OF THE INVENTION
The present invention relates to a method for wet etching and a wet etching apparatus for the method. The method and the apparatus are especially preferably used for manufacturing a diaphragm-type semiconductor sensor chip.
As shown in
FIGS. 4A and 4B
, a diaphragm-type semiconductor sensor chip
2
such as a pressure sensor has a recess
2
a
, and a thin film layer
1
a
, which functions as a diaphragm and is located at the bottom of the recess
2
a
. The sensor chip
2
also includes components such as a sensing element for measuring a physical quantity, transistors making up a circuit for processing an electric signal from the sensing element, and electrodes for electric connection, which are located on the lower surface of the thin film layer
1
a
in the vertical direction of FIG.
4
B.
In a proposed manufacturing process for the diaphragm-type semiconductor sensor chip
2
, a plurality of semiconductor sensor chips
2
are formed in a semiconductor wafer
1
, as shown in
FIGS. 3A and 3B
, and the wafer
1
is divided into the semiconductor sensor chips
2
, as shown in
FIGS. 4A and 4B
. The wafer
1
has an active surface and a back surface. The two surfaces face in the opposite direction. The thin film layer
1
a
and components are located on the active surface. The recess
2
a
is formed by selectively etching the wafer
1
using an etchant such as potassium hydroxide aqueous solution from the back surface, which is masked by a mask
3
shown in FIG.
4
B. The geometric dimensions of the diaphragm are determined by the size of the recess
2
a.
As shown in
FIG. 5
, a proposed etching apparatus
11
includes a base member
12
, a gasket
13
, a vacuum chuck cylinder
14
, an etching bath cylinder
15
, and a lid
16
. The base member
12
is roughly in the shape of a disk. For etching the wafer
1
, the wafer
1
is placed on the base member
12
such that the back surface faces upward, as viewed in FIG.
5
. The gasket
13
, which is attached to the inner surface of the etching bath cylinder
15
, seals the periphery of the back surface of the wafer
1
. The etching bath cylinder
15
is tightly fixed to the base member
12
by vacuuming the inner space of the vacuum chuck cylinder
14
. The wafer
1
is clamped between a projection of the base member
12
and the gasket
13
at the periphery of the wafer
1
, as viewed in FIG.
5
. An etching chamber
17
, which is defined by the wafer
1
as a bottom, the gasket
13
and the etching bath cylinder
15
as a sidewall, and the lid
16
as a lid, is formed, as shown in FIG.
5
.
The back surface of the wafer
1
is etched by the etchant when the etchant is supplied into the etching chamber
17
. The lid
16
includes an etchant supply port
16
a
, a rinsing water supply port
16
b
, and a drain
16
c
. Deionized water (DIW) is used as the rinsing water. The lid
16
also includes a stirrer
18
for agitating the etchant, a heater
19
for heating the etchant, and an electrode
20
for stopping the etching electrochemically.
However, in the etching using the proposed etching apparatus
11
, if there is a defect in the thin film layer
1
a
, as shown in
FIG. 6
, the etchant leaks out of the etching chamber
17
through the defect when the etchant reaches the thin film layer
1
a
. The leaking etchant etches the sensing element, the transistors, and the electrodes on the thin film layer
1
a
. Even in the case that a wafer is thinned by the etching using the proposed etching apparatus
11
, if there is a crack in a thinned part of the wafer, the etchant leaks out of the etching chamber
17
through the crack and the active surface of the wafer is undesirably etched.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above aspects with a first object to provide a method for wet etching, with which an etchant is prevented from leaking out of an etching chamber through a defect or a crack generated in a wafer. A second object is to provide a wet etching apparatus for the method. A third object is to provide a method for manufacturing a diaphragm-type semiconductor sensor chip using the method for wet etching and the wet etching apparatus.
In the present invention, a wafer, a first surface of which is protected by a protective film, is mounted on a base member such that the first surface faces the base member. An etching bath cylinder, to which a gasket for sealing the periphery of the wafer on a second surface that is opposite to the first surface is attached, is placed on the wafer. An etching chamber is formed by vacuum chucking with a vacuum chuck cylinder in an etching pot. Nitrogen gas is supplied from a high pressure gas supply source to a hermetic room, which is formed by the base member and the wafer, while being regulated by a pressure regulator. The pressure regulator includes a water reservoir, a decompressing room having an orifice, a first balance tube, and a second balance tube. The wafer is etched while a pressure higher than that applied to the second surface from an etchant is put on the protective film by the nitrogen gas. Therefore, the etchant is prevented from intruding into the hermetic room because the active surface is protected by the protective film and the protective film is supported by nitrogen gas in the hermetic room.


REFERENCES:
patent: 3960623 (1976-06-01), Gantley
patent: 5578167 (1996-11-01), Sooriakumar et al.
patent: 5874365 (1999-02-01), Tomita et al.
patent: 5956142 (1999-09-01), Muller et al.
patent: 6171437 (2001-01-01), Shimizu et al.
patent: 6547641 (2003-04-01), Zuniga et al.
patent: 2001-053054 (2001-02-01), None

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