U.S. patent application number 09/975125 was filed with the patent office on 2003-04-10 for silicon pressure micro-sensing device and the fabrication process.
Invention is credited to Chiang, Kuo-ning, Lin, Chune-te, Lin, Ji-cheng, Peng, Chih-tang, Shie, Jin-shown, Yu, Shih-han.
Application Number | 20030068838 09/975125 |
Document ID | / |
Family ID | 25522720 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030068838 |
Kind Code |
A1 |
Shie, Jin-shown ; et
al. |
April 10, 2003 |
SILICON PRESSURE MICRO-SENSING DEVICE AND THE FABRICATION
PROCESS
Abstract
The invention is a silicon pressure micro-sensing device and the
fabrication process thereof. The silicon pressure micro-sensing
device includes a pressure chamber, and is constituted of a P-type
substrate with a taper chamber and an N-type epitaxial layer
thereon. On the N-type epitaxial layer are a plurality of
piezo-resistance sensing units which sense deformation caused by
pressure. The fabrication pressure of the silicon pressure
micro-sensing device includes a step of first making a plurality of
holes on the N-type epitaxial layer to reach the P-type substrate
beneath. Then, by an anisotropic etching stop technique, in which
etchant pass through the holes, a taper chamber is formed in the
P-type substrate. Finally, an insulating material is applied to
seal the holes, thus attaining the silicon pressure micro-sensing
device that is able to sense pressure differences between two ends
thereof.
Inventors: |
Shie, Jin-shown; (Hsin Chu,
TW) ; Lin, Ji-cheng; (Hsin Chu, TW) ; Lin,
Chune-te; (Hsin Chu, TW) ; Peng, Chih-tang;
(Hsin Chu, TW) ; Yu, Shih-han; (Hsin Chu, TW)
; Chiang, Kuo-ning; (Hsin Chu, TW) |
Correspondence
Address: |
MARTINE & PENILLA, LLP
710 LAKEWAY DRIVE
SUITE 170
SUNNYVALE
CA
94085
US
|
Family ID: |
25522720 |
Appl. No.: |
09/975125 |
Filed: |
October 9, 2001 |
Current U.S.
Class: |
438/50 ;
257/414 |
Current CPC
Class: |
B81B 2203/0127 20130101;
B81C 2201/016 20130101; B81C 2201/014 20130101; G01L 9/0054
20130101; B81B 2203/0315 20130101; B81B 2201/0264 20130101; B81C
1/00182 20130101 |
Class at
Publication: |
438/50 ;
257/414 |
International
Class: |
H01L 021/00; H01L
029/82 |
Claims
What is claimed is:
1. A fabrication process for a silicon pressure micro-sensing
device, comprising the steps of: (1) preparing of a P-type (100)
substrate with an N-type epitaxial layer on its surface; (2)
forming a plurality of piezo-resistance units, a passivation, and a
plurality of device pads on said N-type epitaxial layer; (3)
performing a deep-etching process to form a plurality of holes,
which pass through said N-type epitaxial layer to the P-type (100)
substrate thereunder; (4) performing an etching stop process, in
which an etchant go through said plurality of holes to remove
silicon of the P-type (100) substrate beneath said N-type epitaxial
layer, and form a taper chamber in said P-type (111) substrate; (5)
applying an insulating material on said N-type epitaxial layer to
seal said plurality of holes, attaining the silicon pressure
micro-sensing device.
2. The fabrication process for silicon a pressure micro-sensing as
described in claim 1, further comprising a step of forming a
venthole for said taper chamber to have an open access to
exterior.
3. A silicon pressure micro-sensing device comprising: an N-type
epitaxial layer comprising: a plurality of piezo-resistance sensing
units, for sensing pressure, in said N-type epitaxial layer; a
passivation, for preventing inappropriate etching from etchant in
the process, on an upper surface of said N-type epitaxial layer; a
plurality of device pads formed on an upper surface of the
passivation and connected to leads of an external circuit; a
plurality of holes which go through said N-type epitaxial layer and
passivation and act as passages for the etchant; and an insulating
membrane on the upper surface of said passivation to seal said
plurality of holes; and a P-type (100) substrate with a taper
chamber and on a lower surface of said N-type epitaxial layer.
4. The silicon pressure micro-sensing device as described in claim
3, wherein said P-type (100) substrate further comprises a venthole
at a bottom part of said taper chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of Invention
[0002] The invention relates to a silicon pressure micro-sensing
device and the fabrication process thereof, which require only a
single substrate without any adhesion, and the fabrication for
difficulty-free taper chamber meets.
[0003] 2. Related Art
[0004] The history of pressure sensor development using silicon
substrate as the base material is long-standing. Its sensing
principle is based on the piezo-sensitivity of silicon. That is,
when a resistor made by silicon substrate encounters pressure or
deformation, the value of resistance thereof changes accordingly.
In order to enhance the sensitivity to increasing deformation
caused by pressure, a membrane structure is generally constructed
to sustain a pressure difference on both ends. A piezo-resistance
unit is preferably placed onto the area with the most membrane
deformation, to attain the highest degree of sensitivity.
[0005] A piezo-resistance sensing unit made from monocrystalline
silicon has the following advantages: (1) the sensing unit can be
manufactured by semiconductor fabrication; (2) the membrane can be
formed by a conventional anisotropic etching technique using bulk
micro-machining technology. In addition, if the popular
electro-chemical-etching-stop technique is utilized to implement
the bulk micro-machining, a P-type silicon can be removed leaving
an N-type silicon, thus forming an N-type stress membrane on a
surface of the unit; (3) as a result of the membrane and the
substrate being made from the same silicon, residual stress is
unlikely to be present between the two, therefore the accuracy and
yield of the product are both elevated. Micro pressure-sensing
devices have for a long time mostly been produced by backside bulk
micro-machining.
[0006] FIG. 1 shows a structure of a conventional sensing device.
The conventional sensing device includes: a substrate 13, a
membrane 14, and piezo-resistance sensing units 15. Anisotropic
etching that starts upward from the bottom of the substrate 13 and
narrows with a particular angle to the membrane 14 forms the
conventional sensing unit. The particular angle is formed because
the included angle between the inclined crystal plane (111) for
etching stop and a horizontal plane is 54.7.degree.. In accordance
with this geometric structure, in order to obtain a larger area of
the stress membrane 14, the bottom area of the substrate 13 is
necessarily comparatively larger. This results in unnecessary
silicon substrate loss in the substrate 13, causing a comparatively
low yield; especially for a large-sized substrate that has a larger
thickness as well as larger bottom openings, not only is more
silicon substrate wasted, but the anisotropic etching process time
is also prolonged, and these factors increase the cost.
[0007] In order to minimize substrate waste and increase the yield
for each wafer, U.S. Pat. No. 6,038,928 discloses a structure
formed by a front-side bulk micro-machining process.
[0008] FIG. 2 shows the structure of the sensing unit in the U.S.
Pat. No. 6,038,928. Its fabrication process includes the following
steps: First, a taper chamber 26 is formed on a silicon substrate
23 by conventional anisotropic etching, and then adhered to a
P-type substrate 27 with an N-type epitaxial layer by wafer
adhesion technology. Next, making use of the
electrochemical-etching-stop technique to etch away the P-type
substrate 27 situated on top of the epitaxial layer and leaving an
N-type epitaxial membrane 24, obtains an adhered wafer 28 with an
inner chamber. Then, piezo-resistance sensing units 25 and metal
lines (not shown) are formed by semiconductor fabrication and
finally a structure for a pressure-sensing unit is obtained. In
order to allow the taper chamber 26 an open access to the exterior;
the back of the silicon substrate 23 is etched to form an opening
29. The taper chamber 26 of a die formed by front-side bulk the
micro-machining process contracts downwards, therefore the needed
supporting area on the sensing unit periphery is consequently much
smaller.
[0009] Referring to FIG. 3, if the aforesaid membrane is in the
shape of a square with each side length thickness of the wafer
thickness at 400 .mu.m, and the reserved width at the supporting
periphery being 250 .mu.m, the area of a conventional unit with
back-side opening is hence approximately 265% larger than that of a
unit with front-side opening. Naturally the number of sensing dies
output per wafer decreases with the same percentage.
[0010] Although the front-side bulk micro-machining process has the
advantage of reducing the area of the device, nevertheless, the
fabrication process in the U.S. Pat. No. 6,038,928 essentially puts
the costly substrate adhesion process into practice, which doubles
the amount of wafer usage and implements two copious bulk
micro-machining etching processes, with not only the cost
increased, but defects during adhesion, which also cause a drop in
production yield. In addition, the wafer after adhesion has a
chamber structure, which may meet many unpredicted fabrication
difficulties when a high temperature fabrication process required
for making a piezo-resistance device is further performed.
SUMMARY OF THE INVENTION
[0011] In view of the need to improve the aforesaid prior art, one
object of the invention is to provide a silicon pressure
micro-sensing device and the fabrication process thereof, in which
a front-side bulk micro-machining process is utilized to make the
size of the required dies smaller than those processed by prior art
processes.
[0012] Another object of the invention is to provide a silicon
pressure micro-sensing device and the fabrication process thereof,
in which the membrane taper chamber is made by a single substrate
and requires no adhesion of two substrates. Thus, the amount of
material used is decreased and the fabrication process is
simplified so that the cost is significantly reduced.
[0013] A further object of the invention is to provide a silicon
pressure micro-sensing device and the fabrication process thereof,
in which the taper chamber and the sealed membrane are both
processed at low temperature. Therefore, it is unnecessary to
adjust the conventional fabrication process of piezo-resistance
sensing units, leaving no impediments in the fabrication
process.
[0014] The fabrication process of the silicon pressure
micro-sensing device of the invention includes the following steps.
First, a P-type (100) substrate with an N-type epitaxial layer
thereon is prepared. Then, a plurality of piezo-resistance sensing
units, a passivation, and a plurality of device pads are formed on
the N-type epitaxial layer. Next, a deep-etching process is
performed to the N-type epitaxial layer to form a plurality of
holes, which pass through the N-type epitaxial layer to the P-type
(100) substrate thereunder. It is followed by performing an
etching-stop technique, in which an etchant goes through the holes
to remove silicon of the P-type (100) substrate below the N-type
epitaxial layer substrate, thus forming a taper chamber in the
P-type (111) substrate. Finally, an insulating material is applied
onto the N-type epitaxial layer to seal a plurality of holes and
attain the desired silicon pressure micro-sensing device.
[0015] The silicon pressure micro-sensing device of the invention
includes an N-type epitaxial layer which includes: a plurality of
piezo-resistance units in the N-type epitaxial layer, for sensing
pressure; a passivation formed on the N-type epitaxial layer, for
preventing inappropriate etching from an etchant in the fabrication
process; a plurality of device pads formed on the passivation and
connected to the leads of an exterior circuit; a plurality of
holes, which pass through the N-type epitaxial layer and the
passivation so as to act as passages for the etchant; and an
insulating membrane on the passivation to seal the plurality of
holes. And the silicon pressure micro-sensing device also includes
a P-type (100) substrate on a lower surface of the N-type epitaxial
layer. It is a substrate with a taper chamber.
[0016] The aforesaid and other objects, characteristics, and
advantages of the present invention, are illustrated more precisely
by the detailed descriptions of the preferred embodiments
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows the structure of a prior art sensing unit.
[0018] FIG. 2 shows the structure of a sensing unit in U.S. Pat.
No. 6,038,928.
[0019] FIG. 3 shows the difference of wafer required by prior art
and the U.S. Pat. No. 6,038,928.
[0020] FIGS. 4(a) to (f) are schematic diagrams showing fabrication
steps of the silicon pressure micro-sensing device of the
invention.
[0021] FIGS. 5(a) to 5(b) are schematic diagrams showing the
structure of a plurality of holes.
[0022] FIGS. 6(a) and (b) are sectional schematic diagrams showing
the taper chamber of the invention based on FIG. 5(b) viewing from
line AA'.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] FIGS. 4(a) to (f) are schematic diagrams showing the
fabrication steps of the silicon pressure micro-sensing device of
the invention.
[0024] FIG. 4(a) shows a P-type (100) substrate 42 with an N-type
epitaxial layer 41 thereon.
[0025] Referring to FIG. 4(b), a plurality of piezo-sensing units
44, a plurality of device pads 48, and a passivation 43 are formed
on the N-type epitaxial layer 41 by conventional semiconductor
fabrication processes.
[0026] Referring to FIG. 4(c), a deep-etching process is utilized
to form pluralities of holes 45, which pass through to the P-type
substrate 42 beneath the N-type epitaxial layer 41.
[0027] Referring to FIG. 4(d), an etching stop process is carried
out to have the etchant go through a plurality of holes 45 to
remove silicon of the P-type (100) substrate 42. Because the
etchant possesses the characteristics of anisotropic etching, the
taper chamber 46 in a shape of an inverted pyramid is formed along
the crystal plane (111).
[0028] Referring to FIG. 4(e), a photosensitive polyamide membrane
47 is formed on the passivation 43 by spin on. Then, polyamide in
the device pad 48 is removed by photolithography, so as to
accommodate further testing and bonding processes. During the spin
on process, due to factors such as contained air in the chamber and
surface tension of the polyamide, the applied polyamide membrane
does not sag or leak through the fine holes 45 to the taper chamber
46 thereunder. This step is to seal the plurality of holes 45 of
the N-type epitaxial layer 41, so that upper and lower parts of the
substrate achieve air-tightness. It should be noted that the
polyamide as the sealing material mentioned above is only one of
examples. In other cases, spin-on-glass (SOG) or silicone can also
be used.
[0029] Referring to FIG. 4(f), after the above processes are
completed, the pointed end at the bottom of the taper chamber 46 of
the P-type (100) 27 is made to have an open access to exterior and
acts as a venthole 49, which contributes to gauge pressure.
[0030] The aforesaid fabrication processes of the silicon pressure
micro-sensing device are all low temperature fabrication processes,
therefore it is unnecessary to vary general conditions of the
fabrication process for piezo-resistance sensing units, and creates
no impediments to its fabrication.
[0031] In order to form the taper chamber 46 shown in FIG. 4(d)
while be able to keep most of the N-type epitaxial layer 41, the
holes 45, as shown in FIG. 5, have to possess the following
attributes: (1) the number of holes must be plural; (2) the
plurality of holes 45 must be close enough, so that initial tiny
taper chambers from individual openings are able to connect with
each other and continuously expand to become a larger taper
chamber, until the largest single taper chamber 46 is formed
circumscribing the outmost holes. Such a mechanism of etching and
then extending is a characteristic of silicon wafer anisotropic
etching. Referring to FIG. 5(b), each circumscribed square 53a of
hole 45 overlaps with another circumscribed square 53b to form a
larger square 53.
[0032] FIGS. 6(a) to (b) are sectional schematic diagrams showing
the taper chamber of the invention based on FIG. 5(b) viewing from
line AA'. By an etching stop process, the etchant through a
plurality of holes 45 removes silicon of the P-type (100) substrate
42 thereunder. The initial shape etched is in the form of a cone.
Referring to FIG. 6(a), due to the anisotropic etching
characteristic possessed by the etchant, an acute angle is
developed between the crystal planes (111) of the cones etched, and
the cones become tetragonal tapers 46a. When two adjacent
tetragonal tapers meet, the two crystal planes (111) thereof create
an obtuse angle .theta., which is not exempted from being etched;
hence the tetragonal taper 46a becomes an even larger tetragonal
taper 46b. At this point, only an acute angle is present between
the crystal planes (111) of the largest taper chamber and the
etching is therefore stopped. As shown in FIG. 6(b), adjacent
tetragonal tapers 46a become a larger tetragonal taper 46b, so that
etching is proceeds until the formation of the largest taper
chamber is achieved.
[0033] FIG. 4(e) shows the structure of the first embodiment of the
silicon pressure micro-sensing device of the present invention. The
silicon pressure micro-sensing device includes: an N-type epitaxial
layer 41, a P-type (100) substrate 42, a passivation 43, a
plurality of piezo-resistance sensing units 44, a plurality of
holes 45, a taper chamber 46, a membrane 47, and a plurality of
device pads 48.
[0034] The P-type (100) substrate 42 is a base of the silicon
pressure micro-sensing device with the taper chamber 46. The N-type
epitaxial layer 41 is on the upper surface of the P-type (100)
substrate 42. The pluralities of piezo-resistance sensing units 44
are in the N-type epitaxial layer 41, to sense pressure. The
passivation 43 is formed on the upper surface of the N-type
epitaxial layer 41, to avoid inappropriate etching from the etchant
in the fabrication process. The plurality of device pads 48 are
formed on the upper surface of the passivation 43, and are
connected to leads of an external circuit (not shown). The
plurality of holes 45 pass through the N-type epitaxial layer 41
and the passivation 43, and are passages for the etchant so as to
carry out the etching-stop process. The membrane 47 is formed on
the upper surface of the passivation 43 and seals the holes 45 to
have the taper chamber 46 an air-tight isolation.
[0035] FIG. 4(f) shows the structure of the second embodiment of
the silicon pressure micro-sensing device of the invention. The
silicon pressure micro-sensing device includes: an N-type epitaxial
layer 41, a P-type (100) substrate 42, a passivation 43, a
plurality of piezo-resistance sensing units 44, a plurality of
holes 45, a taper chamber 46, a membrane 47, a plurality of device
pads 48, and a venthole 49.
[0036] In order to simplify the illustration, the following solely
distinguishes the differences between the first embodiment and the
second embodiment. In the second embodiment, the venthole 49 is
added to the bottom of the taper chamber 46, for measuring
pressure.
[0037] While the invention has been particularly described, in
conjunction with specific preferred embodiments, it is evident that
many alternatives, modifications and variations will be apparent to
those skilled in the art in light of the foregoing description. It
is therefore contemplated that the appended claims will embrace any
such alternatives, modifications and variations as falling within
the true scope and spirit of the invention.
* * * * *