U.S. patent application number 09/992939 was filed with the patent office on 2002-05-09 for method for producing a micromechanical structure and a micromechanical structure.
Invention is credited to Rudhard, Joachim.
Application Number | 20020055253 09/992939 |
Document ID | / |
Family ID | 7662625 |
Filed Date | 2002-05-09 |
United States Patent
Application |
20020055253 |
Kind Code |
A1 |
Rudhard, Joachim |
May 9, 2002 |
Method for producing a micromechanical structure and a
micromechanical structure
Abstract
A method for producing a micromechanical structure, and a
micromechanical structure having a movable structure and a
stationary structure made of silicon. In the method for producing
the micromechanical structure, in one process step, a superficial
metal-silicide layer is produced in the movable structure and/or
the stationary structure.
Inventors: |
Rudhard, Joachim;
(Leinfelden-Echterdingen, DE) |
Correspondence
Address: |
KENYON & KENYON
ONE BROADWAY
NEW YORK
NY
10004
US
|
Family ID: |
7662625 |
Appl. No.: |
09/992939 |
Filed: |
November 5, 2001 |
Current U.S.
Class: |
438/672 |
Current CPC
Class: |
B81B 3/0008 20130101;
B81C 2201/112 20130101; B81B 3/0086 20130101; B81B 2201/0235
20130101 |
Class at
Publication: |
438/672 |
International
Class: |
H01L 021/44 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2000 |
DE |
1 00 55 421.0 |
Claims
What is claimed is:
1. A method for producing a micromechanical structure, comprising:
introducing trenches into a silicon layer for forming at least one
movable structure and at least one stationary structure from the
silicon layer, the movable structure being movable relative to the
stationary structure; after introducing the trenches, depositing a
metal layer on side walls of the trenches; after depositing the
metal layer, carrying out a thermal treatment by which metal of the
metal layer forms a metal silicide with silicon of the silicon
layer; and subsequently carrying out an etching process which
removes the metal of the metal layer and does not remove the metal
silicide.
2. The method according to claim 1, wherein the metal layer is
composed of one of titanium, zirconium, hafnium, vanadium,
chromium, niobium, tantalum, molybdenum, tungsten, cobalt, nickel,
palladium and platinum.
3. The method according to claim 1, wherein the silicon layer is
composed of one of polycrystalline silicon and monocrystalline
silicon.
4. The method according to claim 1, wherein the silicon layer is
arranged on a sacrificial layer.
5. The method according to claim 4, wherein the sacrificial layer
is arranged on a support, the support being composed of one of
silicon and glass.
6. The method according to claim 1, wherein the thermal treatment
is carried out at a temperature between 400.degree. and 800.degree.
C.
7. A micromechanical structure comprising: at least one stationary
structure; and a movable structure movable relative to the
stationary structure, wherein the movable structure and the
stationary structure are composed substantially of silicon, and
wherein at least one of the movable structure and the stationary
structure has a superficial metal-silicide layer.
Description
BACKGROUND INFORMATION
[0001] Methods for producing a micromechanical structure or
micromechanical structures are already known, in which a movable
silicon structure and a stationary silicon structure are provided
which are movable relative to one another.
SUMMARY OF THE INVENTION
[0002] The method according to the present invention for producing
a micromechanical structure, and the micromechanical structure of
the present invention have the advantage that superficial,
conductive metal-silicide layers are provided. Electrostatic
surface charges on the micromechanical structures can be prevented
by these conductive metal-silicide layers. Adhesion of the
micromechanical structures to one another is thereby also
reduced.
[0003] The metals indicated are especially suitable for forming
metal-silicide layers. Both polycrystalline and monocrystalline
silicon is suitable as material for the structures. The method can
be used particularly easily in connection with producing silicon
structures on sacrificial layers, particularly on a support.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 shows a first method step for producing a
micromechanical structure.
[0005] FIG. 2 shows a second method step for producing a
micromechanical structure.
[0006] FIG. 3 shows a third method step for producing a
micromechanical structure.
[0007] FIG. 4 shows a fourth method step for producing a
micromechanical structure.
[0008] FIG. 5 shows a fifth method step for producing a
micromechanical structure.
[0009] FIG. 6 shows a sixth method step for producing a
micromechanical structure.
[0010] FIG. 7 shows a top view of a micromechanical structure.
DETAILED DESCRIPTION
[0011] FIG. 1 shows a cross-section through a silicon layer 1 that
is arranged by way of a sacrificial layer 2 on a support 3. The
layer thicknesses shown here are not true to scale. Typically,
silicon layer 1 is between 2 and approximately 30 .mu.m thick.
Layer thicknesses on the order of magnitude of a few micrometers
are usually used for sacrificial layer 2. For support 3, usually
boards (plates) having a thickness of more than 500 .mu.m are used,
since only in this way is a sufficient mechanical stability of the
entire construction provided.
[0012] Silicon layer 1 can be made both of polycrystalline silicon
and of monocrystalline silicon. For sacrificial layer 2, any
material is suitable which can be etched selectively with respect
to the silicon of layer 1. A typical material for a sacrificial
layer 2 is, for example, silicon oxide or phosphorus silicate
glass. Support 3 should, above all, ensure a stable mechanical
construction. Customary materials for support 3 are, for example,
silicon, silicon oxide or ceramic materials.
[0013] A preferred construction is made of a silicon wafer for
support 3, a sacrificial layer of silicon oxide and a
polycrystalline silicon layer 1.
[0014] Applied on the top side of silicon layer 1 is a masking 4
which, in FIG. 1, is already patterned. Patterned masking 4 is used
to introduce a structure into silicon layer 4 in an etching step.
Metals, silicon oxide, silicon nitride, photo-resist or a
multilayer build-up of these materials are suitable as materials
for masking 4. In the following etching step, an etch attack of
silicon layer 1 takes place only where it is not covered by masking
4.
[0015] FIG. 2 shows the result of such an etching step used on the
layer construction according to FIG. 1. By etching in using an
anisotropic etching process, which in particular forms vertical
etching flanks, trenches 5 have been introduced into silicon layer
1. Trenches 5 subdivide silicon layer 1 into individual structures
6.
[0016] Anistropic plasma etching methods based on
fluorine-containing gas mixtures are particularly suitable for
structuring silicon layer 1. Such methods are capable of producing
vertical etching flanks for trenches 5.
[0017] In a further processing step, a metal layer 7 is now
deposited. This is shown in cross-section in FIG. 3. As FIG. 3
shows, metal layer 7 is deposited in such a way that a more or less
uniform deposition results on the entire surface of structures 6
and in trenches 5. In this context, metals are used for metal layer
7 which, by way of a thermal treatment, are able to form a metal
silicide with the silicon of silicon layer 1. For example, the
metals titanium, zirconium, hafnium, vanadium, chromium, niobium,
tantalum, molybdenum, tungsten, cobalt, nickel, palladium and
platinum are suitable. These metals are able to form metal
silicides which exhibit good electrical conductivity. For example,
a particularly suitable material is platinum.
[0018] Metal layer 7 must be deposited in such a way that as good a
covering as possible results both on the edges and on the vertical
side walls of structures 6. In this context, a suitable thickness
of metal layer 7 can lie between a few nanometers to several 100
nanometers. Suitable deposition methods are, for example, physical
methods such as sputtering or vapor deposition of metal layers.
Furthermore, metal layer 7 can also be implemented by chemical
methods such as the CVD (chemical vapor deposition) method.
[0019] In a next process step, a metal silicide is now formed. This
is shown in FIG. 4. The metal silicide is formed by a thermal
treatment, in that the layer construction according to FIG. 3 is
exposed to a temperature between, for example, 400.degree. C. and
800.degree. C. Naturally, the selection of the temperature also
depends upon the metal used for metal layer 7. For platinum, a
temperature between 400.degree. C. and 800.degree. C. is
sufficient. This thermal process can be carried out for a few
minutes or a few hours depending upon the temperature and the
material for the metal. As can be seen in FIG. 4, a superficial
metal-silicide layer 8 forms where the metal of metal layer 7 is in
direct contact with the silicon of structures 6. In this context, a
part of superficial metal layer 7 is used up, or, if metal layer 7
is very thin, this metal layer is completely converted into metal
silicide. Since the top side of silicon structures 6 is still
covered with masking layer 4, no metal-silicide layer forms in this
region. Since in the lower region of trenches 5, metal layer 7 lies
on sacrificial layer 2, no metal silicide forms there either.
[0020] As a next processing step, metal layer 7 is now etched
selectively with respect to metal-silicide layer 8. The chemical
properties of metals and metal silicides differ markedly. It is
therefore possible, by suitable chemicals, to dissolve metal layer
7 in an etching medium, while the metal-silicide layer is not
dissolved by the etching medium. For example, when using platinum
for metal layer 7, this platinum layer can be etched by hot aqua
regia (nitrohydrochloric acid), while at the same time, the
corresponding metal silicide (platinum silicide) is not attacked by
this etching medium. By dipping the layer construction according to
FIG. 4 into hot aqua regia, metal layer 7 can thus be selectively
removed, and metal-silicide layers 8 remain on the surface of
silicon structures 6. The result of this etching process is shown
in cross-section in FIG. 5. As can be seen there, silicon
structures 6 now have vertical side walls which are provided with a
metal-silicide layer 8. Masking layers 4, which likewise were not
attacked by the etching medium, are still arranged on the top side.
For example, in the case of platinum, silicon oxide is a
correspondingly suitable masking material for masking 4. It can
also be seen in FIG. 5 that no metal layer 7 whatsoever has
remained on the structure.
[0021] FIG. 6 shows the result of a further processing step, the
etching of sacrificial layer 2; the etching is carried out in such
a way that only middle silicon structure 6 is undercut, that is to
say, sacrificial layer 2 is completely removed underneath this
structure. However, sacrificial layer 2 remains in both silicon
structures 6 situated to the right and to the left. Thus, a
central, movable silicon structure 10 is produced which is arranged
between two stationary silicon structures 11. Silicon structures 10
and 11 have vertical side walls whose surfaces are provided with a
metal-silicide layer 8.
[0022] FIG. 7 shows, by way of example, a top view of a
micromechanical element which has such a movable silicon structure
10 between two stationary silicon structures 11. Also shown
schematically is a line of intersection VI-VI which corresponds
roughly to FIG. 6. FIG. 6 corresponds only approximately to line of
intersection VI-VI, since in FIG. 6, stationary structures 11 to
the right and to the left are not shown completely, but are only
shown cut off. The reason for this is that the extension of
stationary structures 11 to the right and to the left in FIG. 6
would have to be shown considerably larger, which can no longer be
reasonably depicted graphically.
[0023] FIG. 7 shows here a top view of a micromechanical element,
in which a movable structure 10 is arranged between two stationary
structures 11. As can be seen, movable structure 10 is joined to a
bearing block 12. Stationary structures 11 and bearing block 12 are
joined to an underlying support 3 by remnants of a sacrificial
layer 2 (which cannot be seen in the top view of FIG. 7). However,
movable structure 10 is not joined to underlying support 3. Because
of its geometrical dimension, here especially as a long, thin
tongue, movable structure 10 is so designed that it is movable
relative to substrate 3, and thus also relative to stationary
structures 11, by a force influence. Such structures are usable,
for instance, as acceleration sensors.
[0024] In the case of such micromechanical structures having
movable elements and stationary elements, the use of the material
silicon is not completely without its problems, since the material
silicon is a semi-conductive material. When working with such
semi-conductive materials, superficial electrostatic charges cannot
be completely ruled out. Such electrostatic surface charges
generate forces between the micromechanical structures,
particularly when the distances between the structures are small.
Because of the poor conductivity of silicon, such electrostatic
surface charges can only poorly equalize. Furthermore, when working
with micromechanical structures, adhesion of the structures to one
another again is always observed. By using a superficial
metal-silicide layer, the conductivity of the silicon structures is
reduced at least in the area on the surface. The surface charges
can be reduced more easily, since they can now move easily both on
the surface and into the depth of the silicon. Surface charges are
thus reduced by this measure. In addition, this measure has proven
to be capable of reducing adhesion of the micromechanical
structures to one another.
* * * * *