U.S. patent application number 13/066835 was filed with the patent office on 2011-08-25 for method for applying a layer to a substrate.
Invention is credited to Christoph Kleinlogel, Felix Mayer.
Application Number | 20110207333 13/066835 |
Document ID | / |
Family ID | 41089322 |
Filed Date | 2011-08-25 |
United States Patent
Application |
20110207333 |
Kind Code |
A1 |
Mayer; Felix ; et
al. |
August 25, 2011 |
Method for applying a layer to a substrate
Abstract
A semiconductor wafer (10) is structured such that fine
structures (3), such as membranes, bridges or tongues, with a
thickness d<<D are formed, wherein D designates the thickness
of the semiconductor wafer (10). Then particles of a desired
material are applied. A temporal or spatial temperature gradient is
generated in the semiconductor wafer (10), e.g. by progressive
heating. In such a heating process the fine structures heat up more
quickly and become hotter than the remaining wafer because they
have a smaller heat capacity per area and cannot carry off heat as
quickly. In this manner, the fine structures can be heated to a
temperature that allows a sintering of the particles. For coating
the semiconductor wafer (10) is brought into a reactor (11). A
precursor compound of a metal is provided and fed to the reactor
(11), where a reaction takes place during which the metal is
transformed to a final compound and is deposited in the form of
particles on the semiconductor wafer (10).
Inventors: |
Mayer; Felix; (Stafa,
CH) ; Kleinlogel; Christoph; (Zurich, CH) |
Family ID: |
41089322 |
Appl. No.: |
13/066835 |
Filed: |
April 26, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11791549 |
May 12, 2009 |
7955645 |
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PCT/CH05/00691 |
Nov 23, 2005 |
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13066835 |
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60656501 |
Feb 25, 2005 |
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Current U.S.
Class: |
438/758 ;
257/E21.211 |
Current CPC
Class: |
C23C 16/453 20130101;
C23C 16/481 20130101; B81B 2201/0214 20130101; B81C 1/00373
20130101; B81B 2203/0127 20130101; C23C 16/04 20130101; C23C 16/46
20130101; C23C 16/407 20130101; G01N 27/128 20130101 |
Class at
Publication: |
438/758 ;
257/E21.211 |
International
Class: |
H01L 21/30 20060101
H01L021/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 2004 |
CH |
1937/04 |
Claims
1-12. (canceled)
13. A method for applying a layer of a material on a substrate
comprising the steps of arranging the substrate in a reactor,
providing a precursor compound comprising a metal and feeding the
precursor compound to the reactor, feeding a compound Y to the
reactor, carrying out a reaction inside the reactor in which the
metal of the precursor compound is transformed to a final
compound.
14. The method of claim 13 wherein the final compound forms
particles and wherein the particles on the substrate are
sintered.
15. The method of claim 13 wherein the precursor compound is fed to
the reactor as a suspension.
16. The method of claim 13 wherein the substance Y comprises oxygen
or nitrogen and the final compound comprises an oxide or nitride
composition of the metal.
17. The method of claim 13 wherein the precursor compound comprises
a chloride or fluoride compound.
18. (canceled)
19. The method of claim 13 wherein the precursor compound is
deposited on the substrate and then reacts with the substance
Y.
20. The method of claim 13 wherein the precursor compound reacts
with the substance Y prior to hitting the substrate, whereby the
final compound is formed, wherein the final compound then hits the
substrate, and in particular wherein the final compound hits the
substrate in the form of solid particles or droplets.
21. The method of claim 13 wherein a flame synthesis is carried out
in the reactor, in which the final compound is generated, and in
particular wherein the substrate is heated by the flame
synthesis.
22. The method of claim 13 wherein the precursor compound is
introduced into the reactor by means of a nozzle and wherein an
electric voltage is applied between the nozzle and the
substrate.
23. The method of claim 13 wherein the particles have a diameter of
not more than 100 nm, in particular not more than 10 nm.
24. The method of claim 13 wherein the layer on the substrate is at
least partially polarized by applying an electric or magnetic
field.
25. The method of claim 13 wherein the substrate comprises
integrated heaters, which are heated during deposition, and in
particular wherein the integrated heaters are arranged in or at the
structures.
26. The method of claim 13 wherein the substrate is heated by means
of heated particles and/or by means of a gas and/or plasma and/or a
flame.
27. The method of claim 13 comprising the steps of synthesizing
said final compound or material in a flame during a flame pyrolysis
process and heating said substrate by said flame.
28. The method of claim 13 wherein the substrate is brought into
contact with a cooling device.
29. The method of claim 13 wherein said substrate is a
semiconductor wafer.
30. The method of claim 13 further comprising the step of
manufacturing one or more sensors, in particular substance sensors,
from said substrate.
31. The method of claim 13 comprising the step of applying a mask
over said substrate for structuring said layer.
32. The method of claim 13 comprising the steps of applying several
layers on said substrate.
33. The method of claim 13 comprising the steps structuring the
substrate in such a manner that structures of a thickness
d<<D are formed at or on the substrate, wherein D is a
thickness of said substrate, and applying particles of the material
to said substrate and heating the substrate for generating a
spatial or temporal temperature gradient in the substrate such that
the structures reach a higher temperature T than non-structured
regions of the substrate.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
[0001] This application claims the priority of Swiss patent
application 01937/04, filed 24 Nov. 2004, as well as of U.S.
provisional application Ser. No. 60/656,501, filed 25 Feb. 2005,
the disclosure of both of which is incorporated herein by reference
in its entirety.
TECHNICAL FIELD
[0002] The invention relates to a method for applying a layer of a
material on a substrate, in particular a semiconductor wafer.
[0003] 1. Background Art
[0004] Applying layers, in particular sintered layers, on
semiconductor wafers and other substrates is of interest for a
plurality of applications. For example, substance sensors requiring
a sintered layer of SnO.sub.2 as active layer are known. It has
been found, however, that it is not easy to carry out a suited
sintering process on a semiconductor wafer. In particular, circuits
etc. integrated in the wafer can be damaged during sintering.
[0005] 2. Disclosure of the Invention
[0006] Hence it is an object to provide a method of this type that
allows efficient manufacturing of such layers. This object is
achieved by the independent claims.
[0007] In a first aspect of the invention the substrate is being
structured, namely in such manner that fine structures, such as
membranes, bridges, tongues or porous regions having a thickness
d<<D are formed (advantageously by means of removing
material), wherein D designates the thickness of the substrate.
Then particles of the desired material are deposited and a temporal
or spatial temperature gradient is created within the substrate
before, during or after depositing the particles, namely in such a
way that the fine structures reach a higher temperature than the
rest of the substrate. The term "temporal temperature gradient" is
used to express that the temperature changes in time.
[0008] For example, the substrate is increasingly heated for this
purpose, e.g. by irradiation or by bombardment by hot material from
the outside. In such a heating process, fine structures are being
heated more quickly and become hotter than the rest of the
substrate since they have a smaller heat capacity per area and
cannot carry off heat as easily. In this manner, the fine
structures can be heated to a temperature T that allows an
efficient deposition and, where applicable, a sintering of the
particles, while the temperature T' in the rest of the substrate
remains lower. This offers, on the one hand, the possibility to
deposit or sinter particles depending on the position on the
substrate, e.g. only in the region of the fine structures but not
on the remaining regions of the substrate. On the other hand, it
allows to use higher deposition or sintering temperatures at which
the electronic circuits e.g. located in other regions of the
substrate would be damaged.
[0009] The term "structured regions" is, in the following, being
used for those regions of the substrate where there are thermally
insulated structures of said thickness d<<D, while the term
"unstructured regions" designates those regions where no such
structures are present.
[0010] The structures advantageously comprise at least two free
surfaces, the distance between which corresponds at most to the
thickness d. "Free surfaces" is to be understood as designating
surfaces in the thermal sense, i.e. the free surfaces abut against
a medium that has a thermal conductivity and heat capacity much
smaller that the one of the used semiconductor. The medium is
advantageously gas or vacuum. For such structures, the heat loss
while heating is small such that they become hot quickly.
[0011] In a second aspect of the invention a layer, advantageously
a structured layer, of a material on a substrate is manufactured by
introducing the semiconductor layer into a reactor. A precursor
compound of a metal is provided and fed to the reactor.
Furthermore, a substance Y is fed to the reactor. A chemical
reaction takes place in the reactor, during which the metal is
transformed to a final compound and is deposited on the substrate
in the form of particles.
[0012] This procedure allows the direct coating of a substrate with
particles of the desired final compound.
[0013] The reaction for transforming the metal to the final
compound can take place on the substrate, e.g. if the precursor
(e.g. in dissolved state) is deposited on the substrate and then
reacts with the substance Y. The reaction can, however, also take
place prior to deposition if the precursor reacts with the
substance Y prior to hitting the substrate, whereupon the final
compound is formed, which then hits the substrate e.g. in solid
form or as droplets.
[0014] Advantageously, the substance Y comprises oxygen or nitrogen
and the final compound comprises an oxide and/or nitride compound
of the metal.
[0015] The metal can be a pure metal or a mixture of several
metals.
[0016] Advantageously a flame synthesis takes place in the
reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The invention will be better understood and objects other
than those set forth above will become apparent when consideration
is given to the following detailed description thereof. Such
description makes reference to the annexed drawings, wherein:
[0018] FIG. 1 a sectional view of a substance sensor with a
measuring layer of tin oxide ceramics,
[0019] FIG. 2 the schematic representation of a first embodiment of
the coating method,
[0020] FIG. 3 the schematic representation of a second embodiment
of the coating method, and
[0021] FIG. 4 the schematic representation of a third embodiment of
the coating method.
MODES FOR CARRYING OUT THE INVENTION
[0022] At first, a preferred embodiment of the invention is
described for the example of a substance sensor. In a second part
of the description, advantageous further embodiments are then
shown.
[0023] FIG. 1 shows a substance sensor with a semiconductor
substrate 1 and a measuring layer 2. The measuring layer 2 is
arranged on a thin membrane 3 or bridge, which spans an opening 4
in the semiconductor substrate 1, on the top side of the substrate.
The opening 4 extends through the substrate 1 to its bottom side. A
heating is arranged in membrane 3, by means of which the measuring
layer 2 can be heated to approximately 200-400.degree. C., as well
as two electrodes, by means of which the electrical resistance of
the measuring layer can be determined. Arranging the measuring
layer 3 on the membrane has the advantage that the desired
operating temperature can be reached with comparatively low
electrical power.
[0024] A sensor of the type shown in FIG. 1 is known, per se, to
the person skilled in the art. It is based on the principle that
the electric resistance of measuring layer 2 changes under the
influence of certain gases, such as CO, CO.sub.2 or
carbohydrates.
[0025] Measuring layer 3 consists e.g. of ceramics of tin oxide
(SnO.sub.2) with contributions of magnesium oxide or other
additions or dopants, such as platinum and/or palladium. It should
be porous for being sufficiently sensitive.
[0026] Evaluation electronics can be integrated on semiconductor
substrate 1, which electronics carry out at least a preprocessing
or a complete processing up to digitization of the measured
resistance values.
[0027] In the following, a procedure for manufacturing such devices
is described.
[0028] As usual in semiconductor technology, the sensor of FIG. 1
is manufactured together with a plurality of further, identical
sensors on a semiconductor wafer.
[0029] For this purpose, a semiconductor wafer 10, as it is shown
in FIG. 2, is first processed by means of conventional procedures.
In particular, a plurality of membranes 3 or other fine structures,
such as webs or bridges, are manufactured on the top side of the
wafer. The fine structures or membranes 3 are arranged over
openings 4, which extend through semiconductor wafer 10 to its
bottom side.
[0030] For manufacturing the membranes 3, one or more coatings of
e.g. silicon oxide or silicone nitride, combined, if necessary,
with conducting layers, are applied, in per se known manner, to the
top side of the wafer, and then the wafer is etched off
anisotropically from the bottom side in the region of the openings
4, such that the coatings remain and form the membranes 2.
Furthermore, advantageously, the further required components are
also integrated on the top side of semiconductor wafer 10, such as
electrodes for contacting the measuring layer 2, conductors,
contact pads and, where applicable, processing electronics,
advantageously in CMOS technology.
[0031] The semiconductor wafer 10 manufactured in this way
therefore comprises structured regions (namely the membranes 3)
with a thickness d between e.g. 1 and 50 .mu.m, while, otherwise,
the thickness of the wafer is e.g. some 100 .mu.m.
[0032] In a next step the measuring layer 2 is applied. For this
purpose the semiconductor wafer 10 structured in the previous step
is introduced into a reactor 11, as it is e.g. shown in FIG. 2.
[0033] An apparatus 12 for carrying out flame synthesis or flame
pryrolysis is arranged in reactor 11. It consists e.g. of several
concentric tubes 13-15. An inflammable gas is introduced through an
outer tube 13. A dispersion gas is introduced through a next inner
tube 14 and a precursor compound is introduced through an innermost
tube 15.
[0034] The precursor compound is e.g. a compound that comprises the
metal for the coating, such as SnCl.sub.4 or an organometallic
compound. The precursor compound can, if it is liquid of gaseous,
be provided directly. It can, however, also be provided as a
solution. Both variants are possible for SnCl.sub.4. Advantageously
the precursor compound is fed to the reactor in the form of a
suspension.
[0035] The dispersion gas can e.g. comprise oxygen, or also be an
inert gas. The dispersion gas serves to nebulize the precursor
compound.
[0036] The inflammable gas from tube 13 is ignited such that a
flame 16 is formed. In this flame the precursor compound is
transformed to a final compound, in the present case tin oxide
(SnO.sub.2) by reaction with oxygen. The oxygen can originate, as
mentioned above, from the dispersion gas or be fed separately, e.g.
through tube 13 together with the inflammable gas, or through a
separate feed.
[0037] The final compound forms droplets or particles 18, which are
deposited on semiconductor wafer 10.
[0038] At the same time the wafer 10 is subjected to a temporal
temperature gradient by being heated by flame 16 and/or another
heat source, such as an infrared lamp 20, from the outside and
changing its temperature in time-dependent manner. During this, the
thin structures of the wafer 10, i.e. the membranes 3, are heating
up much faster than the thick regions. For example, a temperature T
of e.g. above 600.degree. C. can in this way be reached in the
region of the membranes 3, while the temperature T' at the top side
of the thick regions does not yet exceed 200.degree. C. In this
manner, the particles 18 can e.g. be subjected to a temperature
sufficient for sintering or adhesion in the region of membrane 3,
but not outside the membranes 3. The heat sources are switched of
or reduced in power before the top side of the thick regions
reaches as high temperatures as the thin regions of the
semiconductor wafer.
[0039] By means of this procedure, an adhesion or even sintering of
the particles 18 is achieved in the region of the thin structures,
while the particles hitting the thick regions of the wafer adhere
and are sintered only weakly or not at all.
[0040] In a next step the semiconductor wafer 10 can be removed
form reactor 11. The excessive particles on the thick regions of
the wafer are, if necessary, removed, e.g. by washing.
[0041] An alternative coating procedure is shown in FIG. 3. Also in
this case, the semiconductor wafer 10 is first structured and then
introduced into a reactor 11. In reactor 11, a nebulizer 22 is
provided, by means of which the precursor material is nebulized and
applied as droplets 18' to a first side of the semiconductor wafer
10. At the same time, a reaction substance Y, such as oxygen, is
fed to the reactor through a further nozzle 23.
[0042] The semiconductor wafer is irradiated from a second side by
means of a infrared heat source 20 and thereby subjected to a
temporal temperature gradient such that the thin structures or
membranes 3 are heating up more quickly than the thick regions of
the wafer 10. This procedure is time controlled in such a way that,
during the arrival of the particles 18', the thin structures have a
substantially higher temperature than the topside of the thick
regions of the wafer 10.
[0043] In particular in the hot regions a reaction between the
reaction gas Y, e.g. oxygen, and the precursor material, which e.g.
again comprises SnCl.sub.4, takes place, such that tin oxide in the
form of more or less solid particles is formed. The temperature in
the thin structures is advantageously adjusted such that the
particles sinter to each other at the same time.
[0044] Also in this case, the process is stopped before the
temperature in the thicker regions of wafer 10 becomes too high.
Then wafer 10 is taken out of reactor 11 and the excessive
particles are removed.
[0045] Instead of the two said procedures, other methods can be
used for generating particles, e.g. a laser pyrolysis procedure as
described in U.S. Pat. No. 6,200,674.
[0046] To heat up semiconductor wafer 10, the heat content of the
particles 18 or droplets 18' can be used in addition to or instead
of heat source 20 if the amount and temperature of the particles 18
or droplets 18' is sufficient for this purpose. Heat can also be
fed to the semiconductor wafer, additionally, or alternatively, by
means of a hot gas, plasma, ion bombardment or by other means, e.g.
by means of the flame 16 of the embodiment of FIG. 2.
[0047] By subjecting the semiconductor safer 10 to a temporal
temperature gradient, e.g. by continuously increasing its
temperature by feeding thermal energy from the outside, higher
temperatures are reached in the region of the fine structures or
membranes 3 of the embodiments described above than in the other
regions of the wafer. Specifically this is achieved by supplying
the thermal energy via the surface of waver 10 into the same, e.g.
by means of electromagnetic radiation of by bombardment with hot or
energy rich particles, molecules, atoms or ions. With this, the
fine structures at the surface of the wafer 10 can be heated easily
because of their low mass and, at the same time, the heat is not
carried of well because of the low thickness of the structures.
[0048] Alternatively or in addition to using a temporal temperature
gradient, a local increase of the temperatures in the fine
structures can also be achieved in temporal equilibrium with only
spatial temperature gradients, as it is schematically shown in FIG.
4. Here, again, a particle source 26 is provided, which is e.g.
formed by a flame synthesis apparatus 12 according to FIG. 2, a
nebulizer 22 with subsequent chemical transformation according to
FIG. 3, or a laser pyrolysis apparatus according to U.S. Pat. No.
6,200,674. The product of the particle source 26 is deposited on
the top side of semiconductor wafer 10. At the same time,
semiconductor 10 is heated by a heating device 20 e.g. by means of
electromagnetic radiation, namely advantageously from the side at
which deposition takes place. Semiconductor wafer 10 is placed on a
cooled table 28 with its bottom side. With the exception of the
regions of the openings 4, semiconductor wafer 10 is in thermal
contact with table 28. This arrangement leads to a higher
temperature in the region of the fine structures or membranes 3
than in the remaining regions of the wafer, even if the arrangement
is in temporal equilibrium.
[0049] Hence, a local heating of the fine structures or membranes 3
can also be achieved if only a temporal temperature gradient is
generated in semiconductor wafer 10, especially if the heat is
carried off from the wafer by bringing it in contact with a cooling
device (e.g. table 28). For a strong effect it should be observed
that the fine structures or membranes 3 are not in direct contact
with the cooling device.
[0050] To heat the fine structures or membranes 3, it is also
possible to provide heaters in the form of integrated thin
conductive strips, which carry a current from an external current
source during sintering.
[0051] Furthermore, the side of semiconductor wafer 10 facing the
particle source 26 can be provided with a mask that makes a
deposition of particles outside the desired regions more
difficult.
[0052] On the other hand, semiconductor 10 can be provided with a
coating, in particular in the region of the fine structures or
membranes 3, which promotes the deposition of the particles. For
example, a material can be used for this purpose that exceeds its
glass temperature at the temperatures reigning during deposition or
sintering and becomes soft or liquid and enters a close bond with
the deposited material.
[0053] Tin oxide has been named in the above embodiments as a final
compound or material for the particles. Depending on application,
however, a plurality of further materials can be used, such as
magnesium oxide, aluminum oxide, cerium oxide or zircon oxide, i.e.
advantageously oxygen compounds of a metal. Other metal compounds,
however, can be used as well, such as nitride compounds.
Nonmetallic compounds are possible, too.
[0054] In the methods mentioned above a precursor compound is
converted to a final compound in reactor 11. The precursor compound
can e.g. be a chloride, nitride and or fluoride compound of a
metal, such as SnCl.sub.4, SnCl.sub.2 or MgCl.sub.2 or MgF.sub.2 or
an organometallic compound. The reaction for converting the metal
compound into the final compound can either take place before
arrival of the precursor compound on the semiconductor wafer 10 or
afterwards.
[0055] For producing acentric ceramics that e.g. have piezoelectric
properties, pyroelectric properties, nonlinear optical properties
of second order, or other properties that require a macroscopic
acentricity of the ceramics, the ceramics can be polarized by means
of an electric or magnetic field during deposition or sintering,
e.g. by using the arrangement of FIG. 3. Acentric, piezoelectric
ceramics can e.g. be used to integrate SAW filters or piezoelectric
actuators on semiconductor wafer 10.
[0056] The particles used in the present case are advantageously
nanoparticles with diameters smaller than 100 nm, in particular
smaller than 10 nm, such that they can take advantage of the
melting point reduction that is observed for small particles.
[0057] Semiconductor wafer 10 is advantageously a silicon wafer,
but other semiconductor materials can be used as well.
[0058] The invention is especially suited for manufacturing
substance sensors with measuring layers of metal oxide ceramics,
e.g. for the detection of nitrogen oxides, carbohydrates, carbon
monoxide, or carbon dioxide. As mentioned, it is also possible to
manufacture devices with piezoelectric ceramics. Further
applications are e.g. the integration of chemically active
structures (e.g. catalytic structures) on semiconductor
substrates.
[0059] The deposited material can be a pure substance, a doped
substance of a mixture of several substances.
[0060] As mentioned, the deposited material can be sintered. It is
also possible to vary the degree of sintering over the deposited
layer thickness, e.g. by first depositing at higher temperature for
improved adhesion with the substrate such that the bottommost layer
is sintered strongly, while the degree of sintering decreases for
higher layers.
[0061] It is also possible to deposit several layers of coatings,
which e.g. differ in their degree of sintering, doping and/or
composition.
[0062] It is also possible to use, as fine structures in
semiconductor wafer 10, needles, hole structures with thin
separating walls or porous regions in or on semiconductor wafer 10
instead of membranes, bridges and webs.
[0063] The coating can, as mentioned, be structured by choosing the
parameters of the process such that the particles only are
deposited in the hot regions (i.e. in the region of the fine
structures) of the semiconductor wafer 10. It is, however, as
mentioned, also possible to achieve a structuring by means of a
mask alone, which is applied to semiconductor wafer 10 prior to
coating and which hinders or promotes depositing in certain
regions. Finally, it is also possible to use a combination of both
structuring methods.
[0064] The present invention, though especially suited for
semiconductor wafers, can be applied for depositing layers on other
types of substrates, such as ceramics or glasses.
[0065] While there are shown and described presently preferred
embodiments of the invention, it is to be distinctly understood
that the invention is not limited thereto but may be otherwise
variously embodied and practiced within the scope of the following
claims.
* * * * *