U.S. patent application number 14/903961 was filed with the patent office on 2016-07-07 for method for locating devices.
The applicant listed for this patent is SOITEC. Invention is credited to Chrystelle Lagahe Blanchard, Marcel Broekaart, Ionut Radu.
Application Number | 20160197006 14/903961 |
Document ID | / |
Family ID | 49546458 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160197006 |
Kind Code |
A1 |
Broekaart; Marcel ; et
al. |
July 7, 2016 |
METHOD FOR LOCATING DEVICES
Abstract
The disclosure relates to a process for locating devices, the
process comprising the following steps: a) providing a carrier
substrate comprising: a device layer; and alignment marks; b)
providing a donor substrate; c) forming a weak zone in the donor
substrate, the weak zone delimiting a useful layer; d) assembling
the donor substrate and the carrier substrate; and e) fracturing
the donor substrate in the weak zone so as to transfer the useful
layer to the device layer; wherein the alignment marks are placed
in cavities formed in the device layer, the cavities having an
aperture flush with the free surface of the device layer.
Inventors: |
Broekaart; Marcel; (Theys,
FR) ; Radu; Ionut; (Crolles, FR) ; Blanchard;
Chrystelle Lagahe; (Crolles, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOITEC |
Bernin |
|
FR |
|
|
Family ID: |
49546458 |
Appl. No.: |
14/903961 |
Filed: |
June 24, 2014 |
PCT Filed: |
June 24, 2014 |
PCT NO: |
PCT/FR2014/051568 |
371 Date: |
January 8, 2016 |
Current U.S.
Class: |
438/401 |
Current CPC
Class: |
H01L 2223/54426
20130101; H01L 23/544 20130101; H01L 2924/0002 20130101; H01L
27/14687 20130101; H01L 21/76254 20130101; H01L 2924/0002 20130101;
H01L 2924/00 20130101 |
International
Class: |
H01L 21/762 20060101
H01L021/762; H01L 23/544 20060101 H01L023/544 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 15, 2013 |
FR |
1301697 |
Claims
1. A process for locating devices after transfer of a useful layer,
the process comprising the following steps: a) providing a carrier
substrate comprising: a device layer comprising a free surface; and
alignment marks; b) providing a donor substrate; c) forming a weak
zone in the donor substrate, the weak zone delimiting a useful
layer; d) assembling the donor substrate and the carrier substrate;
and e) fracturing the donor substrate in the weak zone so as to
transfer the useful layer to the device layer; wherein the
alignment marks are placed in cavities formed in the device layer,
the cavities having an aperture flush with the free surface of the
device layer.
2. The process according to claim 1, in which the assembly step d)
comprises a direct bonding step executed in an environment at a
pressure below 20 mbars.
3. The process according to claim 2, wherein the cavities extend
into the carrier substrate.
4. The process according to claim 3, wherein the alignment marks
are placed at the bottom of the cavities.
5. The process according to claim 4, wherein the device layer
comprises devices distributed over an entire extent of the device
layer.
6. The process according to claim 4, wherein an opaque layer is
present on the useful layer before the assembly step d).
7. The process according to claim 6, wherein the opaque layer
comprises at least one material selected from the following group:
tungsten, titanium, tungsten silicide, titanium silicide, nickel
silicide, nickel silicide and platinum.
8. The process according to claim 4, wherein the step c) of forming
the weak zone is executed by implanting at least one of the species
selected from the following group: hydrogen and helium.
9. The process according to claim 4, wherein the fracturing step e)
comprises a heat treatment executed at a temperature between
200.degree. C. and 500.degree. C.
10. The process according to claim 1, wherein the thickness of the
useful layer is smaller than 8000 .ANG..
11. The process according to claim 1, wherein the useful layer
comprises sublayers of different doping.
12. The process according to claim 10, wherein the thickness of the
userful layer is smaller than 5000 .ANG..
13. The process according to claim 1, wherein the cavities extend
into the carrier substrate.
14. The process according to claim 1, wherein the alignment marks
are placed at the bottom of the cavities.
15. The process according to claim 1, wherein the device layer
comprises devices distributed over an entire extent of the device
layer.
16. The process according to claim 1, wherein an opaque layer is
present on the useful layer before the assembly step d).
17. The process according to claim 1, wherein the step c) of
forming the weak zone is executed by implanting at least one of the
species selected from the following group: hydrogen and helium.
18. The process according to claim 1, wherein the fracturing step
e) comprises a heat treatment executed at a temperature between
200.degree. C. and 500.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a national phase entry under 35 U.S.C.
.sctn.371 of International Patent Application PCT/FR2014/051568,
filed Jun. 24, 2014, designating the United States of America and
published in English as International Patent Publication WO
2015/007971 A1 on Jan. 22, 2015, which claims the benefit under
Article 8 of the Patent Cooperation Treaty and under 35 U.S.C.
.sctn.119(e) to French Patent Application Serial No. 1301697, filed
Jul. 15, 2013, the disclosure of each of which is hereby
incorporated herein in its entirety by this reference.
TECHNICAL FIELD
[0002] This disclosure relates to a process for locating devices
after transfer of a useful layer to a carrier substrate.
BACKGROUND
[0003] A prior-art process for locating devices after transfer of a
useful layer 8 to a carrier substrate 1, as illustrated in FIG. 1A,
comprises the following steps: [0004] a0) Providing a carrier
substrate 1 comprising: [0005] A front side 2; [0006] A back side 3
parallel to the front side 2; and [0007] A device layer 4 placed on
the front side 2, the device layer 4 comprising alignment marks 5;
[0008] b0) Providing a donor substrate 6; [0009] c0) Forming a weak
zone 7 in the donor substrate 6, the weak zone 7 delimiting a
useful layer 8; [0010] d0) Assembling the donor substrate 6 and the
carrier substrate 1; and [0011] e0) Fracturing the donor substrate
6 in the weak zone 7 so as to transfer the useful layer 8 to the
device layer 4.
[0012] The device layer 4 comprises devices such as transistors,
(npn or pnp) junctions, interconnections and any other structure.
The useful layer 8 generally comprises an opaque semiconductor
layer.
[0013] After the fracturing step e0), the useful layer 8 masks the
devices of the device layer 4 and the alignment marks 5.
[0014] The main drawback of this process is that the alignment
marks 5 are no longer accessible or observable.
[0015] Therefore, such as shown in FIG. 1B, which illustrates a
common practice, apertures 9 (or holes) must be produced in the
useful layer 8 in order to expose the alignment marks 5.
[0016] The process for forming the apertures 9 generally comprises
a photolithography step, followed by an etching step.
[0017] The photolithography step is intended to define the shape
and position of the apertures 9 in the useful layer 8. However,
this step, carried out with no reference point other than the edge
of the carrier substrate 1, has a precision of +/-100 .mu.m.
Therefore, the alignment marks 5 can be localized only to within
+/-100 .mu.m. The apertures 9 must thus have a side length (i.e., a
width) of about 250 .mu.m. Such a side length consumes too much
space, and is unacceptable.
[0018] One aim of the disclosure is, therefore, to provide a
simpler process for locating devices after transfer of a useful
layer 8, allowing smaller apertures to be formed than with
prior-art techniques.
BRIEF SUMMARY
[0019] This disclosure aims to remedy the aforementioned drawbacks,
and relates to a process for locating devices after transfer of a
useful layer, the process comprising the following steps: [0020] a)
providing a carrier substrate comprising: [0021] a device layer
comprising a free surface; and [0022] alignment marks; [0023] b)
providing a donor substrate; [0024] c) forming a weak zone in the
donor substrate, the weak zone delimiting a useful layer; [0025] d)
assembling the donor substrate and the carrier substrate; and
[0026] e) fracturing the donor substrate in the weak zone so as to
transfer the useful layer to the device layer.
[0027] The alignment marks are placed in cavities formed in the
device layer, the cavities having an aperture flush with the free
surface of the device layer. The alignment marks are placed so as
to make it possible to locate the devices.
[0028] The useful layer may be formed from a set of sublayers. The
useful layer is generally opaque and, therefore, masks the device
layer after step e).
[0029] The cavities have walls, and the volume delimited by the
walls of a cavity and its aperture makes up the volume of the
cavity.
[0030] By "alignment marks placed in cavities," is meant that the
alignment marks are placed in the volume of the cavities.
[0031] The presence of through-holes in the useful layer has been
observed after the fracturing step e), and in positional
correspondence with the cavities. The holes thus extend through the
cavities into the useful layer, so that the alignment marks are
visible from the free surface of the useful layer.
[0032] Thus, the devices of the device layer may be located from
the free surface of the useful layer.
[0033] Furthermore, it is not necessary to execute fabrication
steps specific to the formation of holes in the useful layer. The
holes are automatically formed in the positions of the cavities at
the moment of the transfer of the useful layer.
[0034] According to one method of implementation, the assembly step
d) comprises a direct bonding step executed in an environment at a
pressure below 20 mbars.
[0035] Thus, it has been observed that the through-holes in the
useful layer have a shape that corresponds to the aperture of the
cavities. Therefore, the through-holes in the useful layer do not
encroach beyond the aperture of the cavities.
[0036] According to one method of implementation, the cavities
extend as far as into the carrier substrate.
[0037] According to one method of implementation, the alignment
marks are placed at the bottom of the cavities.
[0038] According to one method of implementation, the device layer
comprises devices regularly distributed over the entire extent of
the device layer.
[0039] According to one method of implementation, an opaque layer
is present on the useful layer before the assembly step d).
[0040] According to one method of implementation, the opaque layer
comprises at least one material selected from the following group:
tungsten, titanium, tungsten silicide, titanium silicide, nickel
silicide, nickel silicide and platinum.
[0041] According to one method of implementation, step c) of
forming the weak zone is executed by implanting at least one of the
species selected from the following group: hydrogen and helium.
[0042] According to one method of implementation, the fracturing
step e) comprises a heat treatment executed at a temperature
between 200.degree. C. and 500.degree. C.
[0043] According to one method of implementation, the thickness of
the useful layer is smaller than 8000 .ANG. and preferably smaller
than 5000 .ANG..
[0044] According to one method of implementation, the useful layer
comprises sublayers of different doping.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] Other features and advantages will become apparent from the
following description of methods of implementation of a process for
locating devices according to the disclosure, which are given by
way of nonlimiting example and with reference to the appended
drawings, in which:
[0046] FIGS. 1A and 1B are schematic representations of a structure
obtained with a process for locating devices according to prior-art
techniques;
[0047] FIG. 2 is a schematic representation of a process for
locating devices according to one embodiment of the disclosure;
[0048] FIG. 3 is a schematic representation of the structure
obtained with the process for locating devices according to a
second embodiment of the disclosure; and
[0049] FIG. 4 is a schematic representation of the process for
locating devices according to one embodiment of the disclosure.
DETAILED DESCRIPTION
[0050] For the various methods of implementation, the same
references will be used for elements that are identical or that
provide the same function, for the sake of simplicity of the
description.
[0051] FIGS. 2 and 3 schematically illustrate a process for
locating devices.
[0052] To facilitate the illustration, the respective thicknesses
of the various layers are not shown to scale.
[0053] Step a) of the process for locating devices comprises
providing a carrier substrate 10 comprising a front side 20 and a
back side 30 parallel to the front side 20.
[0054] The carrier substrate 10 may comprise a bulk substrate on
which a device layer 40 is formed on the front side 20 of the
carrier substrate 10.
[0055] The bulk substrate may consist of any material
conventionally used in the microelectronics, optics,
optoelectronics and photovoltaic industries.
[0056] In particular, the bulk substrate may comprise at least one
material selected from the following group: silicon, silicon
carbide, silicon germanium, glass, a ceramic and a metal alloy.
[0057] The device layer 40 comprises devices, such as electronic
devices (for example transistors, junctions, etc.),
interconnections and/or metalized zones.
[0058] The devices are formed using techniques well known to those
skilled in the art.
[0059] The devices may be regularly distributed over the entire
extent of the device layer 40.
[0060] Cavities 90 are formed in the device layer 40. The cavities
90 are open and comprise an aperture flush with the free surface of
the device layer 40.
[0061] The cavities 90 comprise walls. The walls of the cavity 90
and the aperture of the cavity 90 delimit the volume of the cavity
90.
[0062] Advantageously, the cavities 90 may extend as far as into
the carrier substrate 10.
[0063] Alignment marks 50 are placed in the volume of the cavities
90, and the alignment marks 50 are away from the aperture of the
cavities 90.
[0064] The alignment marks 50 are placed so as to make it possible
to precisely locate the devices of the device layer 40.
[0065] Alignment marks 50 are conventionally used to align
photolithography masks.
[0066] The alignment marks 50 may take the form of crosses,
chevrons or interference patterns, or any other form liable to
allow the precise location of the devices to be determined.
[0067] In this respect, those skilled in the art will find a
technical description of the alignment or photolithography masks in
Fundamentals of Microfabrication: The Science of Miniaturization,
2.sup.nd ed., Marc J. Madou, Nanogen, Inc., San Diego, Calif.
[0068] Advantageously, the alignment marks 50 are placed at the
bottom of the cavities 90.
[0069] Step b) of the process for locating devices comprises
providing a donor substrate 60.
[0070] The donor substrate 60 may be made of any material
conventionally used in the microelectronics, optics,
optoelectronics and photovoltaic industries.
[0071] In particular, the donor substrate 60 may comprise at least
one material selected from the following group: silicon, silicon
carbide and silicon germanium.
[0072] The donor substrate 60 may comprise a semiconductor
material.
[0073] Step c) of the process for locating devices may comprise
forming a weak zone 70 in the donor substrate 60.
[0074] The donor substrate 60 comprises a first surface. The weak
zone 70 and the first surface of the donor substrate 60 delimit a
useful layer 80 intended to be transferred to the device layer
40.
[0075] The weak zone 70 may be obtained by implanting atomic
species. The weakening implantation may be carried out with a
single species (for example, hydrogen or helium), but may also be
carried out with a plurality of sequentially implanted species (for
example, hydrogen and helium).
[0076] Advantageously, the hydrogen is implanted with an energy of
between 20 and 70 keV, and a dose of between 4.times.10.sup.16 and
6.times.10.sup.16 atoms/cm.sup.2.
[0077] The helium may be implanted with an energy of between 20 and
70 keV, and a dose of between 0.5.times.10.sup.16 and
3.times.10.sup.16 atoms/cm.sup.2.
[0078] In some embodiments, the useful layer 80 may have a
thickness smaller than 8000 .ANG. and preferably smaller than 5000
.ANG..
[0079] Step d) of the process for locating devices may comprise
assembling the donor substrate 60 and the carrier substrate 10.
[0080] In some embodiments, the assembly step d) may be executed by
direct bonding.
[0081] The assembly may be executed by bringing the useful layer 80
into direct contact with the device layer 40. The assembly is
executed so as to preserve, at least in part, the volume of the
cavities 90. Therefore, the presence of cavities 90 generates
unbonded zones.
[0082] The assembly step d) may comprise a direct bonding step
executed in an environment at a pressure below 20 mbar (2000
Pa).
[0083] Such as illustrated in FIG. 4, an intermediate layer 100 may
be placed on the useful layer 80 before the assembly step d).
[0084] The intermediate layer 100 may be an opaque layer placed on
the useful layer 80.
[0085] The opaque layer may comprise at least one material selected
from the following group: tungsten, titanium, tungsten silicide,
titanium silicide, nickel silicide, nickel silicide and
platinum.
[0086] Step e) of the method for locating devices comprises
fracturing the donor substrate 60 in the weak zone 70 so as to
transfer the useful layer 80 to the device layer 40.
[0087] Thus, after step e), the useful layer 80 masks the
devices.
[0088] If an opaque layer has been formed on the useful layer 80
prior to the assembly step d), the opaque layer is then located
intermediate between the useful layer 80 and the device layer 40
after the fracturing step.
[0089] Advantageously, the fracturing step e) may comprise a heat
treatment executed at a temperature between 200.degree. C. and
500.degree. C.
[0090] Particularly advantageously, after the fracturing step e),
the presence of through-holes has been observed in the useful layer
80, and the opaque layer in the case where the latter is
present.
[0091] Moreover, the through-holes in the useful layer 80 are in
positional correspondence with the cavities 90, so that the
through-holes extend the cavities 90 into the useful layer 80.
[0092] Furthermore, the aperture of each cavity 90 is inscribed in
the aperture of a hole of the useful layer 80.
[0093] In embodiments in which step d) comprises direct bonding
executed in an environment at a pressure below 20 mbar (2000 Pa),
each through-hole in the useful layer 80 may have an aperture that
corresponds to the aperture in the cavity 90 into which it extends,
such as illustrated in FIG. 3.
[0094] The presence of these holes in the useful layer 80 is
advantageously capitalized upon to expose the alignment marks 50
placed in the cavities 90.
[0095] Thus, it is possible to locate the devices masked by the
useful layer 80.
* * * * *