Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates
Reexamination Certificate
1999-02-16
2002-01-29
Lebentritt, Michael S. (Department: 2812)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
C438S466000, C438S477000, C438S759000
Reexamination Certificate
active
06342433
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite member, its separation method and a preparation method of a semiconductor substrate, particularly to a composite member having inside a fragile structure with a low mechanical strength, its separation method and a preparation method of a semiconductor substrate. The present invention is particularly suitable for a preparation method of a substrate (SOI substrate) having an SOI (semiconductor on insulator) structure as a type of semiconductor substrate.
2. Related Background Art
A device using the SOI substrate has various advantages which cannot be attained by an ordinary Si substrate. For example, the advantages are as follows:
(1) a dielectric is easily separated, and the device is suitable for high integration;
(2) the device is superior in resistance to rays;
(3) a floating capacity is small, and high speed operation of elements is realized;
(4) a well process is unnecessary;
(5) latch-up can be prevented; and
(6) a complete depletion type field-effect transistor can be formed by thinning films.
Since the SOI structure has various advantages as described above, researches concerning its forming method have been advanced these several decades. Known as a conventional SOI technique is an SOS (silicon on sapphire) technique for forming Si on a single-crystal sapphire substrate by hetero epitaxial growth in CVD (chemical vapor deposition) method. The SOS technique has been evaluated as most matured SOI technique, but has not been put to practical use because of a large amount of crystal defects caused by lattice mismatching in an interface of an SI layer and a base sapphire substrate, mixture of aluminum constituting the sapphire substrate into the Si layer, substrate price, delay in area enlargement, and for other reasons.
Following the SOS technique, an SIMOX (separation by ion implanted oxygen) technique has appeared. Concerning the SIMOX technique, various methods have been developed aiming at reduction of the crystal defects or reduction of manufacture cost. Examples of the methods include a method of injecting oxygen ions to a substrate to form an embedded oxide layer; a method of bonding two wafers via an oxide film, polishing or etching one of the wafers, and leaving a thin single-crystal Si layer on the oxide film; a method of implanting hydrogen ions into a predetermined depth from a surface of an Si substrate with an oxide film formed thereon, bonding with the other substrate, leaving a thin single-crystal Si layer on the oxide film by heating or another treatment, and peeling off the bonded substrate (other substrate); and the like.
A new SOI technique has been disclosed in Japanese Patent No. 2,608,351 or U.S. Pat. No. 5,371,037. In the technique, a first substrate obtained by forming a non-porous single-crystal layer on a single-crystal semiconductor substrate with a porous layer formed thereon is bonded on a second substrate and these substrates are bonded, then unnecessary portions are removed, so that the non-porous single-crystal layer is transferred to the second substrate. The technique is superior in that the SOI layer has a superior film thickness uniformity, a crystal defect density of the SOI layer can be reduced, the SOI layer has a good surface flatness, a manufacture device with expensive and special specifications is unnecessary and that SOI substrates having SOI films in the range of about several 10 nm to 10 &mgr;m can be manufactured with the same manufacture device.
Furthermore, the present applicant has disclosed a technique in Japanese Patent Application Laid-open No. 7-302889, in which after first and second substrates are bonded, the first substrate is separated from the second substrate without being collapsed, a surface of the separated first substrate is then smoothed, and a porous layer is formed thereon again, so that the first substrate is reused. An example of the proposed method will be described with reference to
FIGS. 12A
to
12
C. After a surface layer of a first Si substrate
1001
is made porous to form a porous layer
1002
, a single-crystal Si layer
1003
is formed on the layer
1002
, and the single-crystal Si layer and a main surface of a second Si substrate
1004
separate from a first Si base substrate are bonded to each other via an insulating layer
1005
(FIG.
12
A). Thereafter, a wafer bonded via the porous layer is divided (FIG.
12
B), and the porous Si layer exposed to the surface of a second Si base substrate is selectively removed to form an SOI substrate (FIG.
12
C). The first Si substrate
1001
can be reused by removing the remaining porous layer therefrom.
In the invention disclosed in Japanese Patent Application Laid-open No. 7-302889, the substrate is separated using the property that the structure of the porous silicon layer is more fragile than a non-porous silicon. Since the substrate once used in preparation of the semiconductor substrate can be used again in preparation of the semiconductor substrate, the cost of the semiconductor substrate can effectively be reduced. Moreover, in the technique, since the first substrate can be used without being wasted, the manufacture cost can largely be reduced. Additionally, the manufacture process is advantageously simple.
Examples of the method for separating the first and second base substrates (base plates) include pressurizing, pulling, shearing, wedge insertion, thermal treatment, oxidization, vibration application, wire cutting, and the like. Additionally, the present inventors have proposed a separation method in Japanese Patent Application No. 9-75498 or U.S. patent application Ser. No. 047,327 filed on Mar. 25, 1998, in which fluid is sprayed to a separation area. Gas and/or liquid is used as the fluid, and especially a water jet using a liquid mainly composed of water is preferable. In the method, at the time of separating, water not only cuts a bonded face but also uniformly enters a gap-between the first and second bases, so that a relatively uniform separating pressure can be applied to the entire separation face. Moreover, in the method, different from the case where gas is not used, particles can be washed away without being scattered. The method is superior in these two respects to the separation method by the wedge insertion. Especially, when the mechanical strength of the separation area is set lower than that of the bonded place, only the fragile portion is ruptured, collapsed or removed by spraying the fluid flow to the separation area, and another strong portion can advantageously be left without being collapsed.
However, when the water jet or another fluid is used to separate the bonded composite member by spraying the fluid to a side face of a composite member, especially around a side face of the separation area, there is a case where the fluid flow cannot easily break or cut the separation area because the separation area has an excessive strength. In this case, the composite member can be separated by raising a fluid pressure, but if the pressure is excessively raised, cracks advance inward from the side face of the bonded base. In the midst, one or both of the separated base substrates may be cracked by the pressure of the fluid injected to the separation area. Therefore, yield is lowered in the separating process. To avoid this, there is provided a method of further lowering the mechanical strength of the separation area to form a more fragile structure. If the structure is excessively fragile, however, a problem is caused that the separation area is broken and cannot be bonded or that the separation area is broken to generate particles as contaminants during heating, cleaning, or handling the base substrate otherwise in a process of preparing the composite member.
Moreover, when separation is performed in another method without using the fluid, basically the similar problem is caused. Therefore, the yield in the separating process may be lowered.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a composite me
Ohmi Kazuaki
Sakaguchi Kiyofumi
Yanagita Kazutaka
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Lebentritt Michael S.
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