U.S. patent application number 09/858092 was filed with the patent office on 2001-11-15 for electronic microcomponent of the variable capacitor or microswitch type, and process for fabricating such a component.
This patent application is currently assigned to Memscap. Invention is credited to Basteres, Laurent, Bouchon, Eric, Campo, Alain, Charrier, Catherine, Imbert, Guy, Valentin, Francois.
Application Number | 20010040250 09/858092 |
Document ID | / |
Family ID | 8850211 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040250 |
Kind Code |
A1 |
Charrier, Catherine ; et
al. |
November 15, 2001 |
Electronic microcomponent of the variable capacitor or microswitch
type, and process for fabricating such a component
Abstract
Process for fabricating electronic components, of the variable
capacitor or microswitch type, comprising a fixed plate (1) and a
deformable membrane (20) which are located opposite each other,
which comprises the following steps, consisting in: depositing a
first metal layer on an oxide layer (2), said first metal layer
being intended to form the fixed plate; depositing a metal ribbon
(10, 11) on at least part of the periphery and on each side of the
fixed plate (1), said ribbon being intended to serve as a spacer
between the fixed plate (1) and the deformable membrane (20);
depositing a sacrificial resin layer (15) over at least the area of
said fixed plate (1); generating, by lithography, a plurality of
wells in the surface of said sacrificial resin layer; depositing,
by electrolysis, inside the wells formed in the sacrificial resin
(15), at least one metal region intended to form the deformable
membrane (20), this metal region extending between sections of the
metal ribbon (10, 11) which are located on each side of said fixed
plate (1); removing the sacrificial resin layer (15).
Inventors: |
Charrier, Catherine; (Saint
Martin D'heres, FR) ; Bouchon, Eric; (Saint Egreve,
FR) ; Campo, Alain; (Sillans, FR) ; Imbert,
Guy; (Grenoble, FR) ; Valentin, Francois;
(Veurey Voiroize, FR) ; Basteres, Laurent;
(Grenoble, FR) |
Correspondence
Address: |
WALL, MARJAMA & BILINSKI
101 S. Salina St., Suite 400
SYRACUSE
NY
13202
US
|
Assignee: |
Memscap
|
Family ID: |
8850211 |
Appl. No.: |
09/858092 |
Filed: |
May 15, 2001 |
Current U.S.
Class: |
257/300 ;
438/238 |
Current CPC
Class: |
B81B 2201/018 20130101;
B81C 1/00158 20130101; B81C 2201/0109 20130101; H01H 1/0036
20130101; B81B 3/007 20130101; B81B 2203/0127 20130101; H01G 5/16
20130101; B81B 2203/0307 20130101; B81C 2201/0197 20130101; B81B
2203/033 20130101 |
Class at
Publication: |
257/300 ;
438/238 |
International
Class: |
H01L 021/8234 |
Foreign Application Data
Date |
Code |
Application Number |
May 15, 2000 |
FR |
00 06142 |
Claims
1. A process for fabricating electronic microcomponents, of the
variable capacitor or microswitch type, comprising a fixed plate
(1) and a deformable membrane (20) which are located opposite each
other, which comprises the following steps, consisting in:
depositing a first metal layer on an oxide layer (2), said first
metal layer being intended to form the fixed plate; depositing a
metal ribbon (10, 11) on at least part of the periphery and on each
side of the fixed plate (1), said ribbon being intended to serve as
a spacer between the fixed plate (1) and the deformable membrane
(20); depositing a sacrificial resin layer (15) over at least the
area of said fixed plate (1); generating, by lithography, a
plurality of wells in the surface of said sacrificial resin layer;
depositing, by electrolysis, inside the wells formed in the
sacrificial resin (15), at least one metal region intended to form
the deformable membrane (20), this metal region extending between
sections of the metal ribbon (10, 11) which are located on each
side of said fixed plate (1); removing the sacrificial resin layer
(15).
2. The process as claimed in claim 1, wherein the oxide layer (2)
is deposited on an integrated circuit.
3. The process as claimed in claim 1, wherein the oxide layer (2)
is made of quartz.
4. The process as claimed in claim 1, wherein the first metal layer
intended to form the fixed plate is inserted into a recess (3)
formed in the oxide layer (2).
5. The process as claimed in claim 1, wherein the first metal layer
includes an extension (5) associated with a connection pad (6).
6. The process as claimed in claim 1, wherein the ribbon (10, 11)
is present along the periphery of the fixed plate (1), on two
opposed sides of the latter.
7. The process as claimed in claim 1, wherein the ribbon consists
of a succession of individual segments.
8. The process as claimed in claim 1, wherein the sacrificial resin
layer (15) partly covers the peripheral ribbon (10, 11).
9. The process as claimed in claim 1, which also includes a step
consisting in etching the oxide layer in order to form one or more
anchoring grooves (8, 9) intended to accommodate part of the
peripheral ribbon (10, 11).
10. The process according to claim 1, which also includes a step
consisting in etching the oxide layer in order to form one or more
anchoring grooves (8, 9) intended to accommodate part of the ends
of the deformable membrane (20).
11. The process as claimed in either of claims 9 and 10, wherein
the anchoring groove (8, 9) has a width (w) about twice the
thickness of the deformable membrane (20).
12. The process as claimed in claim 11, wherein the anchoring
groove (8, 9) has a depth (d) more than one and a half times its
width (w).
13. The process as claimed in claim 1, which furthermore includes a
step consisting, after the fixed plate has been deposited, in
depositing a film (6) of a dielectric, intended to prevent the
deformable membrane from bonding to said fixed plate.
14. The process as claimed in claim 1, which furthermore includes a
step consisting, after the sacrificial resin (15) has been removed,
in producing, on the upper face of the deformable membrane or
membranes, raised regions (25) capable of modifying the moment of
inertia of the surface of the deformable membrane so as to produce
membranes with programmed deformation.
15. The process as claimed in claim 14, wherein the raised features
are longitudinal ribs (25).
16. The process as claimed in claim 1, wherein the metal used both
for producing the fixed plate and the deformable membrane is chosen
from the group comprising copper, chromium, nickel and alloys
including these metals.
17. A microcomponent of the variable capacitor or microswitch type,
comprising: a fixed metal plate (1) inserted into an oxide layer
(2); at least two metal ribbons (10, 11) located peripherally and
on each side of said fixed plate (1); at least one deformable metal
membrane (20) located opposite said fixed plate (20) and resting at
its two ends on the two metal ribbons.
18. The microcomponent as claimed in claim 17, which is located on
the upper face of an integrated circuit.
19. The microcomponent as claimed in claim 17, wherein the
deformable membrane (20) has, on its upper face, raised features
(25) intended to modify its moment of inertia of the surface.
20. The microcomponent as claimed in claim 17, wherein the fixed
plate (1) is covered with a film (6) of a dielectric intended to
prevent the deformable membrane (20) from bonding to the fixed
plate (1).
21. The microcomponent as claimed in claim 17, which includes
anchoring grooves (8, 9) formed in the oxide layer (2) and located
outside the fixed plate, said grooves (8, 9) being filled with a
portion of the spacer ribbons (10, 11) and/or with the deformable
membrane (20).
22. The microcomponent as claimed in claim 17, wherein the metal
constituting the fixed plate and the movable membrane is chosen
from the group comprising copper, nickel and chromium.
23. The microcomponent as claimed in claim 17, wherein the cross
section of the deformable membrane (20) varies over the length of
said deformable membrane.
Description
TECHNICAL FIELD
[0001] The invention relates to the field of microelectronics, and
especially to the field of microsystem components. It relates more
particularly to microcomponents of the variable microcapacitor or
microswitch type which integrate a membrane that can deform under
the action of electrostatic forces. It also relates to a particular
process allowing such microcomponents to be obtained, which proves
to be greatly advantageous over the existing processes.
PRIOR ART
[0002] It is known that the microcomponents of the microcapacitor
or microswitch type have a fixed plate and a movable membrane which
are separated by a volume whose dimensions can vary, especially for
example when a continuous potential difference exists between the
fixed plate and the deformable membrane.
[0003] By subjecting the fixed plate and the movable membrane to a
particular potential difference, it is thus possible to vary the
nominal value of the capacitance according to the desired
application.
[0004] In certain situations, it is also possible to ensure that
the movable membrane moves sufficiently close to the fixed plate to
make contact. The component is then used as a microswitch.
[0005] Microcomponents of this type are generally obtained by using
techniques associated with surface micromachining. Conventionally,
such a membrane is obtained by processes carried out at high
temperature, above 400.degree. C., and more generally above the
temperatures that can be withstood by a finished semiconductor
without any risk of its functionalities being too greatly
modified.
[0006] A component typically consists of a stack of thin layers,
with the following conventional structure. A first layer
constitutes the fixed plate of the capacitor. This layer may be
made of polysilicon of the first level when the technologies used
are compatible with semiconductor processing methods. This
polysilicon layer is deposited on an oxide or nitride layer. In the
document Darrin J. Young and Bernhard E. Boser "A
Micromachine-Based RF Low-Noise Voltage-Controlled Oscillator",
IEEE 1997 Custom Integrated Circuits Conference, May 1997, pp.
431-434, microcomponents were also described in which the fixed
plate is made of aluminum.
[0007] The layer that has to provide the future volume between the
fixed plate and the movable plate is made of a sacrificial material
deposited on top of the layer forming the fixed plate by any
process compatible with the type of microcomponent that it is
desired to produce. Thus, this material may conventionally be
silicon dioxide (SiO.sub.2) or a derivative compound which will be
removed by acid etching.
[0008] The upper layer, forming the deformable plate of the
microcomponent is conventionally made of polysilicon obtained by
LPCVD (low-pressure chemical vapor deposition) and is doped
sufficiently to reduce its resistivity. Certain techniques propose
a conductive coating placed on top of the polysilicon in order to
decrease the apparent resistivity thereof. This movable plate is
anchored to the substrate through vias, that is to say holes etched
in the oxide and/or the sacrificial film. This movable and
deformable plate may also be slightly textured by features etched
partially in the oxide or sacrificial film before the latter is
deposited. This texturing gives the lower face of the movable plate
a certain relief and limits the area of contact between the fixed
plate and the movable plate in the case in which they touch. Thus,
any bonding phenomena are avoided.
[0009] In order to dissolve the sacrificial layer by chemical
etching, or any process allowing isotropic etching, it is essential
for the layer constituting the movable plate to also be pierced
over its entire area in the form of regular and repeated patterns
allowing the dissolving solution to pass.
[0010] A major drawback of this type of process is that the
deposition of the polysilicon layer requires the use of a
high-temperature technique which is not compatible with deposition
on semiconductor layers whose functionalities run the risk of being
significantly modified or degraded by heat. It is therefore
impossible with this kind of technique to produce microcomponents
directly on existing integrated circuits by a "post-processing"
technique.
[0011] The invention therefore aims to overcome these various
drawbacks.
SUMMARY OF THE INVENTION
[0012] The invention therefore relates to a process for fabricating
electronic microcomponents of the variable capacitor or microswitch
type, comprising a fixed plate and a deformable membrane which are
located opposite each other.
[0013] This process comprises the following steps, consisting
in:
[0014] depositing a first metal layer of complex shape on an oxide
layer, said first metal layer being intended to form the fixed
plate;
[0015] depositing a metal ribbon, forming a border, on at least
part of the periphery and on each side of the fixed plate, said
ribbon being intended to serve as a spacer between the fixed plate
and the deformable membrane;
[0016] depositing a sacrificial resin layer over at least the area
of said fixed plate;
[0017] generating, by lithography, a plurality of wells in the
surface of said sacrificial resin layer;
[0018] depositing, by electrolysis, inside the wells formed in the
sacrificial resin, at least one metal region intended to form the
deformable membrane, this metal region extending between sections
of the metal ribbon which are located on each side of said fixed
plate;
[0019] removing the sacrificial resin layer.
[0020] In other words, the process according to the invention
allows production of deformable membranes produced by electrolysis,
which process is carried out at room temperature. This therefore
allows the microcomponent to be placed on various substrates,
including integrated circuits.
[0021] Thus, in a first family of applications, the process
according to the invention may be implemented using, as oxide
layer, a quartz layer in order to form components incorporating
only microcapacitors or microswitches.
[0022] In another type of application, the process may be
implemented using, as oxide layer, an oxide layer deposited on an
integrated circuit so that the microcapacitors or microswitches may
be placed directly on top of the integrated circuit and can
interact with functional regions of the integrated circuit, thereby
limiting as far as possible the influence of the connection system
since these microcomponents are closer to the integrated circuit.
High integrated density is also achieved.
[0023] In practice, the first metal layer intended to form the
fixed plate of the microcomponent is advantageously inserted into a
recess formed in the oxide layer. In other words, the fixed metal
plates may be obtained by a "damascene" metallization process. This
allows particularly reliable components to be obtained, since they
are strong and vibration-resistant. Furthermore, by virtue of the
excellent flatness of the layers obtained by this process, it is
possible to superpose several layers without building up
topological irregularities. The subsequent operations are thus
facilitated.
[0024] In practice, the first metal layer forming the fixed plate
advantageously includes an extension associated with a connection
pad mounted on or inside the oxide layer. This connection pad
allows the microcomponent to be linked either to the subjacent
integrated circuit or to other parts of an electronic circuit.
[0025] According to another characteristic of the invention, the
spacer ribbon is present along the periphery of the fixed plate, on
two opposed sides of the latter. The segments of this ribbon then
serve to support the ends of the deformable membranes.
[0026] In practice, the spacer ribbon may consist of a continuous
band, or even advantageously of a succession of individual
segments, present only in the regions receiving the ends of the
deformable membranes.
[0027] In practice, the sacrificial resin layer is advantageously
deposited in such a way that it partly covers the peripheral spacer
ribbon. In this way, when the deformable membrane is deposited on
top of the sacrificial resin layer, the region where it joins the
spacer ribbon has breaks in slope, facilitating flexure of the
deformable membrane.
[0028] In practice, the process according to the invention
advantageously also includes a step consisting in etching the oxide
layer in order to form one or more anchoring grooves intended to
accommodate part of the peripheral ribbon, or else part of the ends
of the deformable membrane. This anchoring groove is located
directly outside the peripheral ribbon, or else partly beneath the
peripheral ribbon. This groove accommodates part of the peripheral
ribbon or else part of the membrane in order to ensure that it is
deeply anchored in the substrate, thereby increasing the robustness
of the microcomponent.
[0029] In practice, it has been determined that the anchoring is
satisfactory when the groove advantageously has a width about twice
the thickness of the deformable membrane and that, complementarily,
the depth of the groove is more than one and a half times its
width.
[0030] According to another characteristic of the invention, the
process may furthermore include a step consisting, after the fixed
plate has been deposited, in depositing a film of dielectric,
intended to prevent the deformable membrane from bonding to the
fixed plate. Thus, direct contact between the fixed plate and the
deformable plate, which could cause these two plates to bond
together, and therefore damage the microcomponent, is avoided. The
value of the capacitance per unit area may, furthermore, be
improved if the dielectric constant of the additional film is
greater than that of air.
[0031] According to another characteristic of the invention, it is
possible to complete the process according to the invention by
adding an additional step consisting, after the sacrificial resin
has been removed, in producing, on the upper face of the deformable
membrane or membranes, raised regions capable of modifying the
moment of inertia of the surface of the deformable membrane so as
to produce membranes with programmed deformation. This is because,
as already mentioned, the modification in the capacitance of the
microcomponent may arise from modification in the spacing of the
deformable membrane with respect to the fixed membrane when the
latter are subjected to a DC voltage component. It is therefore
possible, by virtue of this arrangement, to adapt the deformation
of the deformable membrane, and therefore the variation in the
capacitance, to a variation in the DC component to which the
microcomponent is subjected.
[0032] In practice, the raised features produced on the membranes
may advantageously be longitudinal ribs.
[0033] In practice, the metals used to produce the various plates
may advantageously be chosen from the group comprising, especially,
copper, chromium, nickel and alloys including these metals.
Different metals may be used to produce the plates and the spacer
ribbon. The choice of the various materials and of the various
electrolysis conditions makes it possible to accurately establish
the internal stresses in the deformable membrane.
[0034] By virtue of this characteristic, it is possible to give the
deformable membrane a cross section which varies over its
length.
BRIEF DESCRIPTION OF THE FIGURES
[0035] The manner in which the invention is realized and the
advantages which stem therefrom will become clearly apparent from
the description of the method of implementation which follows,
supported by the appended figures in which:
[0036] FIG. 1 is a top view of a microcomponent produced according
to the process of the invention, illustrated after the fixed plate
has been deposited;
[0037] FIG. 2 is a sectional view of FIG. 1 in the direction of the
arrows II-II';
[0038] FIG. 3 is a top view of the microcomponent according to the
invention illustrated after the anchoring grooves have been
etched;
[0039] FIG. 4 is a sectional view of FIG. 3 in the direction of the
arrows III-III';
[0040] FIG. 5 is a top view of the microcomponent produced
according to the invention after the spacer ribbons have been
deposited;
[0041] FIG. 6 is a sectional view of FIG. 2 in the direction of the
arrows IV-IV';
[0042] FIG. 7 is a top view of a microcomponent during production
according to the invention, after the sacrificial resin layer has
been deposited;
[0043] FIG. 8 is a sectional view of FIG. 7 in the direction of the
arrows VIII-VIII';
[0044] FIG. 9 is a top view of the microcomponent according to the
invention, illustrated after the deformable plate has been
deposited; and
[0045] FIG. 10 is a sectional view of FIG. 9 in the direction of
the arrows X-X'.
MANNER OF REALIZING THE INVENTION
[0046] As already stated, the invention relates to a process
allowing microcomponents, such as micro-capacitors or
microswitches, to be produced. By using electrolysis steps not
requiring high temperatures, it is possible to implement this
process of producing the microcomponents either directly on quartz
layers or directly on pre-existing integrated circuits.
[0047] Since the implementation of the process may be carried out
on both these types of support, the internal structure of the
substrate on which the microcomponent according to the invention is
produced will not be described below.
[0048] Thus, as shown in FIG. 1, the first series of steps in the
process consists in producing a fixed plate (1) on a substrate (2).
The substrate (2) may either be a quartz layer, if a microcomponent
is produced independently of an integrated circuit, or else the
oxide layer obtained, for example, by PECVD (plasma-enhanced
chemical vapor deposition), typically with a thickness of a few
microns, which covers an integrated circuit.
[0049] To produce the fixed plate (1), the process starts with the
production of a well (3) by etching into the oxide layer (2). Next,
a metal growth sublayer (4), typically made of a copper/titanium
alloy, is deposited on the oxide layer (2) and the well (3).
[0050] The well produced has a shape encompassing both that of the
fixed plate (1) and that of an extension (5) forming the voltage
lead to the fixed plate (1). This voltage lead (5) may be extended
by a pad (7) allowing it to be connected to the microcomponent.
[0051] Next, copper is deposited electrolytically on top of the
growth sublayer (4). The metal used for the electrolysis is
preferably copper, chosen for its low resistivity. The electrolysis
is continued until the copper layer (1) has a thickness sufficient
to fill the well (3) made in the oxide layer (2).
[0052] Next, as illustrated in FIGS. 1 and 2, the copper layer (1)
is planarized, allowing it to be given a surface finish with a very
high flatness.
[0053] Next, a dielectric layer (6) is deposited, typically PECVD
silicon oxide or nitride. This oxide film (6) has the minimum
thickness for preventing the phenomena of the deformable membrane
bonding to the fixed plate (1). Interposing this oxide film (6)
slightly increases the capacitance of the capacitor which will be
formed with the movable plate, if the dielectric constant of this
film is greater than that of air.
[0054] Next, as illustrated in FIGS. 3 and 4, the substrate layer
(2) is etched by a conventional lithographic etching process making
it possible to create a peripheral anchoring groove (8, 9). In
general, this groove has a width (w) about twice the thickness of
the future upper deformable membrane. The depth (d) of this groove
(8, 9) is at least one and a half times its width (w).
[0055] Next, a new growth sublayer (14) is deposited on the surface
of the entire region of the microcomponent. By lithographic
etching, this growth sublayer is covered except in the regions for
producing the peripheral borders, so as to create growth regions
for the electrolysis of the peripheral ribbon (see FIG. 5). This
ribbon (10, 11) is then formed by electrolysis. This ribbon (10,
11) may be made of a material identical to or different from that
serving for the fixed plate (1) and for the movable plate,
depending on the result desired. In the embodiment illustrated, the
ribbon (10) is located between the groove (8) and the boundary (13)
of the fixed plate (1), but in certain situations it is conceivable
for this peripheral ribbon(10, 11) to be partly embedded within the
anchoring groove (8).
[0056] Moreover, the embodiment illustrated in FIG. 5 shows a
peripheral ribbon located on either side of the fixed plate (1) and
consisting of a single band (10, 11) on each side. If it is desired
to produce several deformable membranes on top of a single common
fixed plate (1), the metal ribbon may then be segmented into as
many portions as necessary.
[0057] Next, as illustrated in FIGS. 7 and 8, a sacrificial resin
(15) is deposited with a thickness, close to 2 micrometers,
corresponding approximately to the gap which will exist between the
fixed plate (1) and the deformable membrane. Typically, this resin
has a thickness approximately equal to that of the peripheral
ribbon (10, 11). Of course, this thickness value is given by way of
example, and it may be tailored according to the geometry
associated with the applications. The material used for this resin
is among the materials conventionally used in microelectronics.
[0058] Next, an electrolytic growth sublayer is deposited on top of
the sacrificial resin layer (15), the exposed part of the ribbon
(10, 11) and the anchoring grooves (8, 9). This layer is typically
made of titanium or chromium, chosen for its capability of adhering
to silica. The process then continues with a lithographic step in
order to cover this growth sublayer and to leave it exposed only at
the necessary places on the sacrificial resin layer (15) and at the
peripheral ribbon (10, 11) and anchoring groove (8, 9).
[0059] Next, an electrolysis step is carried out allowing the
deformable membrane (20) to be produced on top of the remaining
growth sublayer. The choice of metal used depends on the stresses
required for the stiffness of the membrane.
[0060] The process then continues with the removal of the
sacrificial resin layer and of the growth sublayer covered
beforehand by the lithographic etching.
[0061] As illustrated in FIG. 9, the movable membrane (20) has,
vertically in line with the border of the fixed plate, indentations
(21-24) defining an aperture for passage of the substances used for
dissolving the resin. These indentations are especially useful if
several deformable membranes are placed side by side. In the case
of a microcomponent having only one movable membrane of large
dimensions, it is then pierced by holes or indentations over a
major part of its surface in order to allow flow of the substances
needed to dissolve the sacrificial resin.
[0062] Next, according to another characteristic of the invention,
a second resin is deposited on top of the deformable membrane. This
second resin may be exposed in certain characteristic regions in
order to reveal certain regions of the deformable plate (20)
itself. In these regions, it is then possible by an additional
electrolysis operation to form beams (25) whose stiffness is added
to and combined with those of the deformable membrane. Thus, the
moment of inertia of the surface is modified, thereby modifying the
membrane deformation law.
[0063] Advantageously, these additional beams (25) have a thickness
possibly up to 30 microns and may be made, for example, of nickel.
Next, the additional resin deposited on top of the deformable
membrane (20) is removed.
[0064] Of course, the various thicknesses and the dimensions and
choice of materials used depend on the technological constraints of
the desired applications and are not limited to the valid ones
described above. Thus, it is possible to obtain capacitors whose
capacitance can vary between a few tens of femtofarads and a few
tens of picofarads. Depending on the application, the gap may be up
to a few micrometers. Of course, these values are given by way of
example and they may vary depending on the types of components
produced and on their applications.
[0065] It is apparent from the foregoing that the process according
to the invention has many advantages and especially:
[0066] the possibility of producing a capacitor of variable
capacitance, whose gap, or the distance between its fixed plate and
its variable plate, is particularly uniform, making the component
very precise;
[0067] the possibility of using microcomponents such as a
microswitch for applications operating in the radio frequency range
(from 100 megahertz to 5 gigahertz), the use of low-resistivity
metals, such as copper or gold, proving to be advantageous with
regard to insertion losses of the metal/metal contact,
[0068] for applications in the high-frequency range (from 5
gigahertz to 100 gigahertz), the use of a dielectric interlayer
making it possible to obtain a capacitive contact, without any risk
of causing bonding between the movable membrane and the fixed
membrane;
[0069] the possibility of producing a plurality of variable
capacitors sharing the same fixed plate;
[0070] the use of relatively low temperatures, allowing the process
to be carried out directly on integrated circuits without any risk
of modifying the functionalities of said circuits; and
[0071] the possibility of modifying the mechanical structure of the
deformable membrane in order to adapt its deformation law to the
desired application.
* * * * *