Semiconductor wafer and method for producing the same

Details Semiconductor wafer and method for producing the same Semiconductor wafer and method for producing the same

2001-09-20

2004-08-03

Pham, Long (Department: 2814)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Responsive to electromagnetic radiation

C438S222000, C438S406000, C438S458000

Reexamination Certificate

active

06770507

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a bonded semiconductor wafer having a layered structure alternately stacked with semiconductor layers and insulator layers in two cycles or more and to a novel manufacturing process therefor.
BACKGROUND ART
In the technical progress in miniaturization of LSI (Large Scale Integrated circuit) devices in recent years, more perfect isolation, a higher operating speed and higher performance have been pursued and attention has been given to an SOI (Silicon-On-Insulator) wafer as material satisfying such demands.
There has been known a wafer bonding process as one of the manufacturing techniques for an SOI wafer. As a technique utilizing this bonding process, a so-called ion implantation separation process (also called a Smart-Cut (a registered trade mark) process) has been developed, which is described in JP A 93-211128.
This ion implantation separation process is a technique wherein an oxide film is formed on at least one of two silicon wafers, hydrogen gas ions or rare gas ions are implanted into one silicon wafer through an upper surface thereof to form a micro-bubble layer (an enclosed layer) within the interior of the one silicon wafer, thereafter the ion implanted surface is put into close contact with the other wafer with the oxide film interposed therebetween, then heat treatment (separation heat treatment) is applied to the wafers in close contact to separate the one wafer in such a manner that the contact portion is partly left in a state of a thin film at the micro-bubble layer performing as a cleavage plane (a separation plane), and heat treatment (bonding heat treatment) is further applied to the other wafer with the thin film left thereon to reinforce bonding between the surfaces in close contact and thereby manufacture an SOI wafer.
In this process, an SOI wafer is obtained with relative ease in which the separated surface is a good mirror surface and the SOI layer is very high in uniformity. This process is also advantageous in that a raw material can be effectively used since one wafer partly removed by separation can be reused. Furthermore, this process makes it possible that two silicon wafers can be bonded directly with each other without an oxide film interposed therebetween, not limited to the case where two silicon wafers are bonded together, the ion implanted silicon wafer is bonded to an insulator wafer having a different thermal expansion coefficient such as of quartz, silicon carbide and alumina, or by selecting a material other than silicon as a wafer to be ion implanted, a bonded wafer having a thin film of the material can be manufactured.
With the advent of the ion implantation separation process, there is solved a problem of film thickness uniformity which is the greatest problem in a bonded semiconductor wafer, and it has been possible to manufacture a bonded SOI wafer with a film thickness uniformity as excellent as 1 nm or less in film thickness standard deviation across a surface of the SOI layer. This process has made possible application of a bonded SOI wafer to an LSI such as a CMOS as a leading device, which requires an SOI layer in the form of an ultra-thin film and excellent film thickness uniformity, in addition to its conventional applications to a BiCMOS and a power IC.
While an SOI wafer to be used in the above-mentioned applications is of a structure including a single SOI layer formed on a buried oxide film, the applicant of the present application has proposed a technique in a previous application (JP A 99-316154) that the ion implantation separation process is adopted to form a bonded semiconductor wafer alternately stacked with two kinds of layers having different refractive indexes such as a combination of an SOI layer and a buried oxide film in two cycles or more and the bonded silicon wafer is utilized in an optical functional device.
This technique is to cultivate a field where the bonded semiconductor wafer is utilized in an optical functional device such as a waveguide, an optical communication modulator, an optical detector or a laser, and very useful. Especially, an SOI wafer having the simplest two cycle layered structure in such layered structures makes advantageously possible that an upper SOI layer is utilized in fabrication of an LSI while an lower SOI layer is utilized as an optical waveguide or a wiring layer, thereby facilitating three-dimensional wiring.
Description will be given of examples of prior art steps for manufacturing a bonded semiconductor wafer having a two cycle layered structure by use of the ion implantation separation process on the basis of
FIGS. 4 and 5
.
FIG. 4
is a flow chart showing an example of a prior art manufacturing process for a bonded semiconductor wafer.
FIG. 5
is a flow chart showing another example of a prior art manufacturing process for a bonded semiconductor wafer.
In
FIG. 4
, first of all, there are prepared a semiconductor wafer A having an insulator film or an insulator layer
10
a
on a surface thereof and a semiconductor wafer B having no insulator film on a surface thereof. Hydrogen (or rare gas) ions are implanted into the wafer A to form a micro-bubble layer
12
a
in the interior of the wafer A. The wafer A with the micro-bubble layer
12
a
is bonded to the wafer B with the insulator film
10
a
interposed therebetween at room temperature to form a bonded wafer
15
.
When the bonded wafer
15
is heat treated, cracking occurs in the wafer A at the micro-bubble layer
12
a
due to strain to form an SOI wafer
16
with a one cycle layered structure in which the insulator layer
10
a
and a semiconductor layer
14
a
are formed on the wafer B. As opposed to the SOI wafer
16
with a one cycle layered structure, there is further prepared a wafer C having an insulator film or an insulator layer
10
b
on a surface thereof, hydrogen (or rare gas) ions are implanted into the wafer C to form a micro-bubble layer
12
b
in the interior of the wafer C. The wafer C with the micro-bubble layer
12
b
is bonded to the SOI wafer
16
at room temperature to form a bonded wafer
17
.
When the bonded wafer
17
is heat treated, cracking occurs in the wafer C at the micro-bubble layer
12
b
to form an SOI wafer
18
with a two cycle layered structure in which the insulator layer
10
b
and the semiconductor layer
14
b
constituting the second cycle layered structure are formed on the first cycle layered structure (the insulator layer
10
a
and the semiconductor layer
14
a
) of the SOI wafer
16
.
In another example of a prior art process shown in
FIG. 5
, a manufacturing process goes according to the same steps as in
FIG. 4
till the first cycle layered structure is formed on a wafer B and as opposed to the SOI wafer
16
there is further prepared a wafer C having an insulator film or an insulator layer
10
b
on a surface thereof In this prior art example, hydrogen (or rare gas) ions are implanted into the SOI wafer
16
to form a micro-bubble layer
12
c
in the interior of the SOI wafer
16
instead of ion implantation on the wafer C in FIG.
4
.
Then, the SOI wafer
16
is bonded to the wafer C with the insulator film
10
b
interposed therebetween at room temperature to form a bonded wafer
17
. When the bonded wafer
17
is heat treated, cracking occurs in the wafer C due to strain at the micro-bubble layer
12
c
, and the insulator layer
10
b
and a semiconductor layer
14
c
are further formed in addition to the one cycle layered structure (the insulator layer
10
a
and the semiconductor layer
14
a
) of the SOI wafer
16
to complete an SOI wafer
18
having a two cycle layered structure.
As described above, in any of the manufacturing processes of
FIGS. 4 and 5
, there are necessarily repeated two times the hydrogen (or rare gas) ion implantation step and the bonding step, respectively. Furthermore, at least two heat treatment steps are required for separation heat treatment, and when separation heat treatment and bonding heat treatment are separately performed, further heat treatment steps are added.
In manufacturi

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