Etching a substrate: processes – Etching of semiconductor material to produce an article...
Reexamination Certificate
1999-10-13
2001-09-18
Powell, William A. (Department: 1765)
Etching a substrate: processes
Etching of semiconductor material to produce an article...
C216S024000, C216S041000, C216S079000, C438S739000, C438S743000
Reexamination Certificate
active
06290858
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a manufacturing method for a micromechanical device having an anchoring region provided on a substrate, in which a part of the device, located over the substrate, is anchored, such as, for example, an acceleration sensor or an actuator in the form of a swiveling mirror. Other examples include chemical sensors and passive components in the form of coils, nozzles, etc.
BACKGROUND INFORMATION
Micromechanical devices, which are customarily integrated with analyzing circuits, are used, for example, in automobile manufacturing, machine controls and regulators, as well as in many areas of consumer electronics. For all areas it is essential that the components used and the respective analyzing circuits be cost-effective, reliable and highly functional.
Although the present invention is applicable in principle to any micromechanical device, the present invention elucidated with reference to a micromechanical swiveling mirror.
Micromechanical swiveling mirrors are used, for example, as switching elements in optical telecommunication technology, scanning elements for deflecting a laser beams for bar code recognition or area monitoring, or marking tools.
Using low-stress electroplating, micromechanical swiveling mirrors can be manufactured without warping, in particular, with respect to the mirror surfaces. Such metallic micromechanical components are usually manufactured using LIGA technology, 3D deep lithography or add-on methods.
In particular, the latter add-on, or additive, methods allow the size of the micromechanical arrangements and thus their price to be reduced, opening up new application possibilities. Inexpensive, reliable and durable micromechanical devices result. Additive methods also allow freely movable metallic structures to be created on any desired substrate, such as a silicon substrate, a glass substrate or a ceramic substrate.
Additive methods also allow large, unperforated surfaces to be exposed, so that solid mirror surfaces with dimensions of up to a few millimeters can be manufactured. This method can be mastered inexpensively and well as single-layer electroplating. Multiple electroplating can also be performed in order to manufacture the anchoring regions and the mirror surfaces or suspensions separately, for example. Large swiveling angles can be obtained using sacrificial layers of suitable thicknesses.
Electroplated metal structures normally contain an anchoring region provided on a substrate, in which a part of the corresponding device located over the substrate, for example, a structure that is freely movable over the substrate, is anchored in order to bond it mechanically and/or electrically to the substrate. The substrate should be understood as the base in the general sense.
FIGS. 3
a
-
3
g
show cross-sectional views of the process steps of a manufacturing method according to the present invention for a micromechanical device.
In
FIGS. 3
a
-
3
g
,
10
denotes a substrate with an operating circuit after final processing, which has a passivation layer
15
with an open terminal pad
20
embedded therein. A sacrificial layer in the form of a first photoresist layer is denoted with
25
; an adhesive layer in the form of a sputtered electroplating start layer (plating base) is denoted with
30
; a second photoresist layer is denoted with
40
; a silicon dioxide layer is denoted with
50
; a third photoresist layer is denoted with
60
and an electroplated layer in the form of a nickel plating is denoted with
35
.
The point of departure for manufacturing the micromechanical device according to the first embodiment of the present invention is the finished operating circuit with passivation layer
15
and open terminal pad
20
.
As
FIG. 3
a
shows, in a first step a first photoresist layer is applied as a sacrificial layer
25
and structured so that terminal pad
20
is exposed. This terminal pad
20
is used as the plating base for the anchoring region of the micromechanical device to be manufactured. First photoresist layer
25
can advantageously be used both for opening terminal pad
20
and as a sacrificial layer if terminal pad
20
must be initially opened in passivation layer
15
.
As
FIG. 3
b
shows, in a next step adhesive layer
30
is sputtered on in the form of an electroplating start layer (plating base). In this embodiment, this is a conductive layer made of chromium-copper. Chromium is responsible for the adhesion of first photoresist layer
25
under it; copper is used as the starting layer for the subsequent step of electrodeposition.
As
FIG. 3
c
shows, an approximately 15&mgr; thick second photoresist layer
40
is applied on adhesive layer
30
by centrifugation and set at temperatures typically around 200° C.
Subsequently an approximately 600 nm thick silicon dioxide layer
50
is deposited on second photoresist layer
40
using plasma CVD (chemical vapor phase deposition). Silicon dioxide layer
50
is subsequently used as a hard mask for structuring second photoresist layer
40
under it and is structured for this purpose by a photolithographic process using a third photoresist layer
60
and by subsequent plasma etching, as shown in
FIG. 3
d.
After overetching silicon dioxide layer
50
, trench etching of second photoresist layer
40
is performed using an anisotropic plasma etching process. The resulting structure is shown by
FIG. 3
e.
In the polymer negative form thus obtained, formed by second photoresist layer
40
, a several micrometers thick nickel layer is electrodeposited. This results in the comb structure illustrated in
FIGS. 3
f
and
3
g
. It should be noted that the individual areas of second electrodeposited layer
35
are connected in areas that are not visible in this cross sectional representation.
Subsequently silicon dioxide layer
50
is removed by wet chemical etching and the polymer negative form of structured second photoresist layer
40
is removed by dry chemical etching.
A selective wet chemical etching of adhesive layer
30
and etching of the sacrificial layer in the form of first photoresist layer
25
in plasma follows, resulting in the structure shown in
FIG. 3
g
. Removal of sacrificial layer
25
in the form of the first photoresist layer is an isotropic etching process, with the photoresist under nickel combs
35
being completely removed.
The result is a micromechanical device with freely movable structures that can be operated as a capacitor, as
FIG. 3
g
shows.
The drawback in the customary manufacturing processes is the fact that the anchoring regions must have a lateral design thickness of typically 30 &mgr;m×30 &mgr;m, since considerable lateral underetching occurs as adhesive layer
30
(plating base) is removed by selective wet chemical etching. This considerably limits the design options.
SUMMARY OF THE INVENTION
The manufacturing method according to the present invention has the advantage over conventional methods in that it allows anchoring regions for additive structures with a minimum size of typically 4 &mgr;m×4 &mgr;m and a spacing of typically 3 &mgr;m to be implemented. This is an improvement by a factor of 7.5 compared to conventional manufacturing methods. It allows novel component layout principles to be implemented using additive methods, with only one mask plane being added, in contrast with the customary method.
The basic idea of the present invention is that the anchoring regions of the adhesive layer are configured as quasi-insular regions, only having a thin web for electrical connection to the rest of the adhesive layer. This results in a lateral overgrowth of the adhesive layer during the growth of the electroplated layer and prevents subsequent underetching when the adhesive layer is removed overgrowth is implemented by forming a mask prior to electrodeposition on the adhesive layer that is structured so that the anchoring region and an overgrowth region adjacent thereto remain unmasked.
According to an advantageous embodiment of the present invention, a sacrificial layer is formed on the sub
Elsner Bernhard
Hirtreiter Josef
Kenyon & Kenyon
Powell William A.
Robert & Bosch GmbH
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