U.S. patent application number 10/536890 was filed with the patent office on 2006-06-29 for method for making a planar suspended microstructure, using a sacrificial layer of polymer material and resulting component.
Invention is credited to Catherine Maeder-Pachurka, France Michel, Philippe Robert, Nicolas Sillon.
Application Number | 20060138076 10/536890 |
Document ID | / |
Family ID | 25166401 |
Filed Date | 2006-06-29 |
United States Patent
Application |
20060138076 |
Kind Code |
A1 |
Robert; Philippe ; et
al. |
June 29, 2006 |
Method for making a planar suspended microstructure, using a
sacrificial layer of polymer material and resulting component
Abstract
Production process of a flat suspended micro-structure using a
sacrificial layer of polymer material and component obtained
thereby The process successively comprises deposition of a
sacrificial layer (2) of polymer material, deposition, on at least
a part of the substrate (1) and of the front face of the
sacrificial layer (2), of an embedding layer (6), the thickness
whereof is larger than that of the sacrificial layer (2), and
planarization so that the front faces of the sacrificial layer (2)
and of the embedding layer (6) form a common flat surface. A
formation layer (3) of a suspended structure (5) is deposited on
the front face of the common flat surface. Planarization can
comprise chemical mechanical polishing and etching of the embedding
layer (6). Etching of the sacrificial layer (2) can be performed by
means of a mask formed on the front face of a layer of polymer
material eliminated during the planarization step.
Inventors: |
Robert; Philippe; (Grenoble,
FR) ; Michel; France; (Sassenage, FR) ;
Maeder-Pachurka; Catherine; (June, FR) ; Sillon;
Nicolas; (Fontaine, FR) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Family ID: |
25166401 |
Appl. No.: |
10/536890 |
Filed: |
December 18, 2003 |
PCT Filed: |
December 18, 2003 |
PCT NO: |
PCT/FR03/03789 |
371 Date: |
October 3, 2005 |
Current U.S.
Class: |
216/11 ;
216/37 |
Current CPC
Class: |
B81B 2203/0118 20130101;
G01R 1/06716 20130101; H01L 2924/01075 20130101; H01L 2924/181
20130101; B81C 2201/0125 20130101; H01R 13/24 20130101; H05K 3/4092
20130101; H01L 2924/12042 20130101; H01L 2924/01046 20130101; H01L
2924/3025 20130101; H01L 2924/0103 20130101; B33Y 80/00 20141201;
H01L 2924/01079 20130101; H01L 2924/12042 20130101; H01L 2924/01029
20130101; G01R 1/07342 20130101; G01R 3/00 20130101; H01L
2924/01015 20130101; H01L 2924/01072 20130101; H01L 2924/01033
20130101; H01L 24/72 20130101; H01L 2924/01074 20130101; H05K
7/1069 20130101; H01R 12/52 20130101; G01R 1/06733 20130101; H01L
2924/01023 20130101; G01R 1/0483 20130101; G01R 1/06727 20130101;
H01L 2924/01005 20130101; H01L 2924/01011 20130101; H01L 2924/01024
20130101; H01L 2924/01027 20130101; H01L 2924/14 20130101; G01R
1/06711 20130101; B81C 1/00611 20130101; H01L 2924/01006 20130101;
H01L 2924/01042 20130101; B81C 2201/0108 20130101; H01L 2924/01013
20130101; H01L 2924/01078 20130101; H01L 23/4822 20130101; H01L
2924/01082 20130101; H01L 2924/181 20130101; H01R 13/2407 20130101;
H01L 2924/01057 20130101; H01L 2924/00 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
216/011 ;
216/037 |
International
Class: |
B44C 1/22 20060101
B44C001/22 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 27, 2001 |
US |
09/795772 |
Claims
1.-7. (canceled)
8. Production process of an integrated micro-system type component,
comprising a flat suspended micro-structure, using a sacrificial
layer of polymer material deposited on a substrate and having side
walls confining the flat suspended structure, process successively
comprising a planarization step, a deposition step of a formation
layer of the suspended structure, an etching step of at least one
opening of the formation layer up to the level of the front face of
the sacrificial layer and a dry etching step of the sacrificial
layer, process comprising, between deposition of the sacrificial
layer and the planarization step, a deposition step, on at least a
part of the substrate and of the front face of the sacrificial
layer, of an embedding layer presenting a larger thickness than the
thickness of the sacrificial layer, so that, after the
planarization step, the front faces of the sacrificial layer and of
the embedding layer form a common flat surface, the formation layer
of the suspended structure being deposited on the front face of the
common flat surface.
9. Production process according to claim 8, wherein the
planarization step comprises chemical mechanical polishing.
10. Production process according to claim 8, wherein the
planarization step successively comprises a chemical mechanical
polishing sub-step of the embedding layer and an etching sub-step
of the embedding layer so that the front faces of the sacrificial
layer and of the embedding layer form a common flat surface.
11. Production process according to claim 8, wherein the side walls
of the sacrificial layer are confined by etching by means of a mask
formed on the front face of a layer made from polymer material by
deposition, lithography and etching of a temporary layer,
deposition of the embedding layer being performed on the assembly
formed by the sacrificial layer and the mask, the mask being
eliminated in the course of the planarization step.
12. Production process according to claim 11, wherein the
planarization step comprises an etching step of the mask.
13. Production process according to claim 8, wherein, the component
comprising salient elements on the substrate, the process
successively comprises, before deposition of the sacrificial layer,
deposition on at least one zone of the substrate designed to be
covered by the sacrificial layer and comprising salient elements,
of a base layer presenting a larger thickness than the thickness of
the salient elements, and an additional planarization step, by
chemical mechanical polishing, of the base layer so that the front
faces of the base layer and of the salient elements form a common
flat surface.
14. Component, produced by the process according to claim 8,
wherein the two faces of the formation layer of the suspended
structure are totally flat.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to a production process of an
integrated micro-system type component, comprising a flat suspended
micro-structure, using a sacrificial layer of polymer material
deposited on a substrate and having side walls confining the flat
suspended structure, process successively comprising a
planarization step, a deposition step of a formation layer of the
suspended structure, an etching step of at least one opening of the
formation layer up to the level of the front face of the
sacrificial layer and a dry etching step of the sacrificial
layer.
STATE OF THE ART
[0002] Many integrated micro electro-mechanical systems (MEMS)
comprise flat suspended micro-structures. This is for example the
case of suspended volume actuators, sensors, switches, variable
capacitors, inductors or acoustic wave resonators. In
micro-technology or microelectronics, suspended micro-structures
are achieved by the use of a sacrificial layer. The conventional
steps for obtaining a suspended micro-structure are represented, in
simplified form, in FIGS. 1 to 5. In a first step represented in
FIG. 1, a layer 2a is deposited on a substrate 1. The layer 2a is
typically made of polymer material, silicon oxide or tungsten. The
second step, represented in FIG. 2, consists in lithographing and
etching the layer 2a so as to form a sacrificial layer 2 covering a
part of the substrate 1 whereon the suspended structure has to be
formed. Then, in a third step represented in FIG. 3, a formation
layer 3 of the suspended structure is deposited on the substrate 1
and on the sacrificial layer 2. The formation layer 3 can be
conducting or dielectric or formed by a stack of several different
layers. The fourth step, represented in FIG. 4, consists in
lithographing and etching the formation layer 3 up to the level of
the front face of the sacrificial layer, so as to confine the
suspended structure 5 by openings 4 in the formation layer 3. In a
fifth step, represented in FIG. 5, the sacrificial layer is removed
by dry etching or wet etching so as to form a free space between
the substrate and the suspended structure 5, thus releasing the
suspended structure.
[0003] The material forming the sacrificial layer is chosen so that
etching thereof is selective with respect to the material for
achieving the micro-structure. For example the sacrificial layer
can be made of silicon oxide (SiO.sub.2) and the suspended
structure can be made of polysilicon. A second combination
comprises a sacrificial layer made of polymer material and a
suspended structure made of SiO.sub.2. A third possibility consists
in using a sacrificial layer of polymer material and a suspended
structure made of metal. The use of a sacrificial layer that is
removed by wet etching, for example SiO.sub.2 in a hydrofluoric
acid (HF) based bath, gives rise to sticking problems of the
structures in the removal step. This problem is generally
associated with capillarity effects and surface forces.
Consequently, a sacrificial layer of polymer material that is
easily removed by plasma etching, for example of the oxygen plasma
type, is increasingly used. As this etching is performed dry,
sticking problems are eliminated.
[0004] The geometric shape and cross-sectional profile of the
suspended structure has great consequences on buckling or
displacement of the suspended structure according to an external
excitation (electric, thermal, acceleration, pressure, etc . . .
).
[0005] The profile of the suspended structure 5, in a plane
perpendicular to FIG. 5, is perfectly defined in the lithography
step. Its profile in the plane of FIG. 5 on the other hand depends
on the bottom layers, and in particular on the sacrificial layer on
which the suspended structure is built. In the case of use of a
sacrificial layer of polymer material, the profile is very often
greatly accentuated by the creep of the material when annealing is
performed. However the exact profile of the suspended structure has
repercussions on checking of the system. Ondulations of the
micro-structure, caused by the shape of the sacrificial layer, in
fact make the stiffness of the final device and its deformation
according to the excitation conditions difficult to know. The space
comprised between the suspended structure and the substrate is also
influenced by the outline. Moreover, the embedding of the
micro-structure depends on the tilt of the suspended structure,
which also depends on the profile. Not knowing the exact profile
leads to a large discrepancy between simulations and experimental
measurements of the device and to risks of stress concentrations at
the embeddings and on the mobile structure. Especially, this makes
the devices extremely sensitive to process variations.
[0006] In order to be able to check the profile of the final
suspended structure better, it is recommendable to include a
sacrificial layer planarization step. However, polymers are
materials which are very difficult to planarize. Chemical
mechanical polishing (CMP) tests show very mediocre results, for
example tear-off of the resin when polishing, irregularity of
planarization or incrustation of colloidal silica (contained in the
CMP planarization product) in the polymer, then occurring when the
sacrificial layer is removed.
[0007] Other dry planarization tests (planarization on abrasive
film) also gave mediocre results. A good rectification of the
polymer was obtained, but at the price of a very large number of
scratches on the plane of the chip and tear-offs on the polymer
pads, as well as incrustation of the abrasive material in the
polymer.
[0008] U.S. Pat. Nos. 6,361,402 and 6,150,274 propose polymer
planarization processes. However, these processes do not provide a
simple solution. Moreover, these processes are not suitable for all
types of polymer (photosensitive resin, polyimide, etc . . . ) and
for all the annealing conditions of these polymers. Indeed, in
certain cases, the polymer may have to be annealed at a higher
temperature than its temperature of use, for example by annealing
at 300.degree. C. of a photosensitive resin the temperature of use
whereof is conventionally less than 200.degree. C., to enable a
plasma enhanced chemical vapor deposition (PECVD) process to be
used at 300.degree. C. on the polymer. These thermal treatments may
lead to the polymer being denatured and make it almost impossible
to planarize. In a general manner, and in particular when they are
annealed at high temperature, polymers are very sensitive to
tearing and tend to trap the abrasive compounds contained in the
planarization products which are deposited under the mobile
structure when the removal step is performed.
OBJECT OF THE INVENTION
[0009] The object of the invention is to remedy these shortcomings
and, more particularly, to provide flat suspended structures using
a planarized polymer sacrificial layer.
[0010] According to the invention, this object is achieved by the
fact that the process comprises, between deposition of the
sacrificial layer and the planarization step, a deposition step, on
at least a part of the substrate and of the front face of the
sacrificial layer, of an embedding layer presenting a larger
thickness than the thickness of the sacrificial layer, so that,
after the planarization step, the front faces of the sacrificial
layer and of the embedding layer form a common flat surface, the
formation layer of the suspended structure being deposited on the
front face of the common flat surface.
[0011] According to a preferred embodiment, the planarization step
successively comprises a chemical mechanical polishing sub-step of
the embedding layer and an etching sub-step of the embedding layer
so that the front faces of the sacrificial layer and of the
embedding layer form a common flat surface.
[0012] According to a development of the invention, the side walls
of the sacrificial layer are confined by etching by means of a mask
formed on the front face of a layer made from polymer material by
deposition, lithography and etching of a temporary layer,
deposition of the embedding layer being performed on the assembly
formed by the sacrificial layer and the mask, the mask being
eliminated in the course of the planarization step.
[0013] According to another development of the invention, the
component comprising salient elements on the substrate, the process
successively comprises, before deposition of the sacrificial layer,
deposition on at least one zone of the substrate designed to be
covered by the sacrificial layer and comprising salient elements,
of a base layer presenting a larger thickness than the thickness of
the salient elements, and an additional planarization step, by
chemical mechanical polishing, of the base layer, so that the front
faces of the base layer and of the salient elements form a common
flat surface.
[0014] According to a component achieved by a process according to
the invention, the two faces of the formation layer of the
suspended structure are totally flat.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] Other advantages and features will become more clearly
apparent from the following description of particular embodiments
of the invention given as non-restrictive examples only and
represented in the accompanying drawings, in which:
[0016] FIGS. 1 to 5 represent a process, according to the prior
art, for achieving a component comprising a suspended
structure.
[0017] FIGS. 6 to 11 represent different steps of a particular
embodiment of a process according to the invention.
[0018] FIGS. 12 to 14 represent steps of another particular
embodiment of a process according to the invention.
[0019] FIGS. 15 to 19 represent steps of a third particular
embodiment of a process according to the invention.
[0020] FIGS. 20 to 23 represent steps of a fourth particular
embodiment of a process according to the invention.
DESCRIPTION OF PARTICULAR EMBODIMENTS
[0021] FIG. 6 represents a sacrificial layer 2 arranged on a
substrate 1. The side walls 10 of the sacrificial layer 2 have been
confined by lithography and etching, as in FIG. 2. The flat
suspended structure designed to be formed on the sacrificial layer
2 is confined by the side walls 10 of the sacrificial layer 2. FIG.
7 represents a deposition step, on at least a part of the substrate
and of the front face of the sacrificial layer 2, of an embedding
layer 6 presenting a larger thickness than the thickness of the
sacrificial layer. Typically the thickness of the embedding layer 6
is 1.7 times greater than the thickness of the sacrificial layer 2.
The embedding layer 6 must be arranged in such a way as to envelop
the sacrificial layer 2 and to prevent lateral displacement of the
sacrificial layer 2. The embedding layer 6 can cover and surround
the sacrificial layer 2 totally. It can also only cover a limited
strip of the sacrificial layer 2 and extend, at the ends of this
strip, onto the adjacent zones of the substrate 1, on each side of
the sacrificial layer 2. The material of the embedding layer 6 must
be a material enabling a planarization process to be used, in
particular of the CMP type, for example SiO.sub.2, silicon nitride
or aluminium. As represented in FIG. 8, a planarization step of the
whole of the embedding layer 6 and of the sacrificial layer 2 is
performed so that the front faces of the sacrificial layer 2 and of
the embedding layer 6 form a common flat surface. The planarization
step must be stopped as soon as the front face of the sacrificial
layer 2 is completely uncovered. In this way, the fluctuations of
thickness of the sacrificial layer 2 are evened out and the
sacrificial layer 2 and the embedding layer 6 form a common flat
surface. Continuing the planarization step beyond this limit
increases the risk of damaging the quality of the surface of the
sacrificial layer 2 and of degrading the flatness.
[0022] FIG. 9 represents a deposition step of a flat formation
layer 3 for formation of the suspended structure on the front face
of the common flat surface of the sacrificial layer 2 and the
embedding layer 6. Unlike the prior art (FIG. 3), deposition of the
formation layer 3 is performed on a single plane. A fourth step,
represented in FIG. 10, consists in etching at least one opening 4
in the formation layer 3 up to the level of the front face of the
sacrificial layer 2. Then, in a fifth step represented in FIG. 11,
dry etching of the sacrificial layer 2 is performed. The flat
formation layer 3 then forms the flat suspended structure 5.
[0023] A component achieved by the process according to the
invention comprises a formation layer 3 of the suspended structure
5 presenting two flat faces, the front face and the back face
arranged on the embedding layer 6.
[0024] The planarization step can comprise chemical mechanical
polishing (CMP) and, in particular, consists only in chemical
mechanical polishing. A process of the CMP type consists, in known
manner, in holding the object to be planarized against a wetted
rotary polishing plate in a polishing bath containing abrasives and
an acid or alkaline solution. The abrasives are typically
aluminium- or silicon-base particles. The layer to be planarized is
thus chemically modified by the liquid and then removed by the
particles of the abrasive. Applying a CMP type process directly on
the sacrificial layer 2 is liable to damage the sacrificial layer
2, even in the presence of an embedding layer 6, in particular by
incrustation of residues of the abrasive.
[0025] In another particular embodiment of the process of the
invention, represented in FIGS. 12 to 14, contact of the
sacrificial layer with the polishing bath is avoided. The initially
deposited embedding layer 6 in fact presents a thickness about 1.7
times greater than the thickness of the sacrificial layer 2 (FIG.
12), and the planarization step comprises a chemical mechanical
polishing sub-step enabling a flat surface of the embedding layer 6
(FIG. 13) to be obtained, and an etching sub-step of the embedding
layer 6 uncovering the sacrificial layer 2 so that the front faces
of the sacrificial layer 2 and of the embedding layer 6 form a
common flat surface (FIG. 14).
[0026] In another particular embodiment of a process according to
the invention, represented in FIGS. 15 to 19, initial etching of
the sacrificial layer 2 is performed by means of a mask 7
previously formed on the front face of the sacrificial layer 2 by
deposition, lithography and etching of a temporary layer (FIG. 15).
The temporary layer can be made of dielectric or metal material
(for example chromium, aluminium, etc . . . ). The typical
thickness of the temporary layer is comprised between 10 and 50
nanometers. As represented in FIG. 16, the mask 7 enables the side
walls 10 of the sacrificial layer 2 to be confined. Deposition of
the embedding layer 6 is then performed on the assembly formed by
the sacrificial layer 2 and the mask 7 (FIG. 17). The complete
planarization step is then performed in two sub-steps. A first
planarization sub-step can be performed by a CMP type process,
without any risk of damaging the sacrificial layer 2, because the
sacrificial layer 2 is protected by the mask 7 (FIG. 18). A second
planarization sub-step consists in eliminating the mask 7,
preferably by dry or wet etching, as represented in FIG. 19. The
fabrication process of the suspended structure can then be
continued by the steps represented in FIGS. 9 to 11, described
above.
[0027] If the component comprises salient elements 8 on the
substrate 1, as represented in FIG. 20, the process for producing
the suspended structure can comprise additional steps before
deposition of the sacrificial layer 2. In a particular embodiment
illustrated in FIG. 21, a base layer 9 is deposited on the
substrate 1 and on the salient elements 8 so as to completely fill
the zones arranged between the salient elements 8. The base layer 9
presents a larger thickness than the thickness of the salient
elements (typically 1.7 times greater). The next step is
planarization by chemical mechanical polishing of the base layer 9
so that the front faces of the base layer 9 and of the salient
elements 8 form a common flat surface (FIG. 22) able to act as
substrate for deposition of the sacrificial layer 2 (FIG. 23). If
there is a risk of the salient elements 8 being damaged during the
planarization step, planarization of the CPM type is performed
followed by etching up to the level of the front face of the
salient elements 8.
[0028] The process is suitable for any type of sacrificial layer
polymer (photosensitive resin, polyimide, PMMA, etc . . . ) and is
independent from any treatment of the sacrificial layer polymer
(polymer strongly or weakly annealed or even not annealed, annealed
in UV, having undergone an ion implantation, etc . . . ). The
process enables any geometry of the sacrificial layer to be
achieved (narrow, broad, thick, thin, rectangular, round, etc.
shape). There are no risks of scratching on the sacrificial layer
and the substrate, nor are there any risks of tear-off of the
sacrificial layer during the planarization step, the sacrificial
layer at no time extending beyond the embedding layer.
[0029] Application of an etching sub-step during the planarization
step (FIGS. 12 to 14) and/or the use of a temporary layer (mask 7)
on the sacrificial layer 2 (FIGS. 15 to 19) moreover enables any
risk of damage of the sacrificial layer 2 by the abrasives to be
eliminated.
[0030] In the case where thermal treatment of the sacrificial layer
is necessary (for example when the technological component
fabrication steps comprise high temperature steps, i.e. at a higher
temperature than the polymer deposition temperature), this will
preferably be performed before the polymer etching step to prevent
creep of the latter.
* * * * *