Silicon epitaxial wafer and its manufacturing method

Details Silicon epitaxial wafer and its manufacturing method Silicon epitaxial wafer and its manufacturing method

2000-12-19

2002-10-01

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Forming from vapor or gaseous state

With decomposition of a precursor

C117S094000, C117S097000, C117S106000, C117S935000, 14

Reexamination Certificate

active

06458205

ABSTRACT:

TECHNICAL FIELD
This invention relates to a silicon epitaxial wafer obtained by forming a silicon single-crystal thin film on a silicon single-crystal substrate and a production process therefor.
BACKGROUND ART
A silicon epitaxial wafer obtained by forming a silicon single-crystal thin film in vapor phase growth on a silicon single-crystal substrate, in general, has been produced according to a process as described next: First, a silicon single crystal ingot produced by means of a FZ (floating zone) method, a CZ (Czochralski) method or the like is sliced into wafers with a saw blade. A wafer obtained in slicing is chamfered along peripheral edges, followed by lapping on both sides thereof and furthermore, the wafer receives a chemical etching treatment on all the surfaces thereof. The wafer after the chemical etching receives is further mirror-polished by means of a chemical-mechanical polishing processing and thereafter, proceeds to a vapor phase growth step for forming a silicon single-crystal thin film thereon. Note that the chemical etching treatment is to remove a surface strained layer of a silicon single-crystal wafer caused by mechanical processings in preceding steps such as slicing, lapping and others. Generally speaking, the chemical etching treatment is performed by immersing the silicon single-crystal wafer in an acid etching liquid such as a nitric acid/hydrofluoric acid aqueous solution, wherein a etching removal (which is defined as the sum of decreases in thickness at both sides of a wafer) thereof amounts to the order of from 20 &mgr;m to 40 &mgr;m.
In the mean time, a processing technique for a silicon single-crystal wafer has achieved a tremendous progress in aspects of improvement on qualities such as crystallinity, accuracy in shape and dimensions, keeping pace with development of a semiconductor fabrication technique including an integrated circuit related technique for LSI as a primary part. On the other hand, however, insofar as fabrication of discrete semiconductor devices represented by a transistor and a diode is concerned, a strong demand for cost reduction and a short delivery time of the wafer from the view point of a processing technique thereof has been built up rather than improvement on qualities, though being attached with great importance in the field of integrated circuit devices.
It is accordingly an object of the invention is to provide a silicon single epitaxial wafer that can be produced with smaller mandays at low cost and a production process therefor.
DISCLOSURE OF INVENTION
A silicon epitaxial wafer of the invention provided for achieving the above described object is characterized by that a silicon single-crystal thin film is formed on a chemically etched silicon single-crystal substrate with a surface glossiness of 95% or higher. Furthermore, a production process for a silicon epitaxial wafer of the invention has a characteristic procedure in which a silicon single-crystal thin film with a surface glossiness of 95% or higher is formed in vapor phase on a chemically etched substrate obtained by chemically etching a to-be-treated silicon single-crystal substrate. Herein, the term “glossiness” means a specular glossiness defined in paragraph 3.1 of JIS Z8741 (1962). A surface glossiness of a silicon single-crystal substrate whose surface has been mirror-polished by a chemical-mechanical polishing processing, which is described above, is almost 100%.
In a conventional production process for a silicon epitaxial wafer, a silicon single-crystal thin film was formed on a substrate having received steps of chemical etching and mirror-polishing in this order, while in the invention, a silicon single-crystal thin film is formed direct on a chemically etched substrate. That is, in the invention, by deleting a mirror-polishing step, a time required for all the process can be effectively shortened, which largely contributes to reduction in production cost of a silicon epitaxial wafer and improvement on production efficiency thereof, with the result that a reduced wafer price at a user's end and a short delivery time are ensured.
Furthermore, a production process for a silicon epitaxial wafer of the invention has a major feature that a surface glossiness of a silicon epitaxial wafer obtained by forming a silicon single-crystal thin film on a chemically etched substrate is 95% or higher. This is because of the following reasons: That is, when a chemical etching treatment of an etching removal of from 20 &mgr;m to 40 &mgr;m that has been generally performed with an acid etching liquid such as a nitric acid/hydrofluoric acid aqueous solution is applied to a wafer to produce a chemically etched substrate, a silicon single-crystal thin film formed on a front main surface of such a chemically etched substrate has a poor surface glossiness, resulting in a problem in an exposure processing of a photolithographic step performed after formation of the silicon single-crystal thin film, since in the exposure processing, an auto-alignment operation of a transfer pattern thereon is poorly performed. The problem is considered to be caused by inability of correct reading of a pattern on the substrate in auto-alignment (the pattern is formed in a lithographic step and a diffusion step in advance) due to reduction in glossiness.
The inventors of the invention have, however, attained through serious research conducted by them findings that a surface glossiness of a chemically etched substrate can be dramatically improved by increasing a etching removal compared with a normal practice; To be concrete, for example, in a case of an n-type chemically etched substrate, a surface glossiness of the chemically etched substrate can be increased to 95% or higher with an etching removal of 60 &mgr;m or more. Moreover, when a silicon single-crystal thin film is formed on a chemically etched substrate having such a dramatically increased surface glossiness, a glossiness of a front main surface of a silicon epitaxial wafer obtained can be ensured to be 95% or higher and the above described auto-alignment processing on the silicon epitaxial wafer in a photolithographic step can be performed with no trouble.
In the mean time, a technical concept, itself, of simply forming a silicon single-crystal thin film direct on a chemically etched substrate is of a known technique, as disclosed in, for example, FIG. 2 of JP-A-91-295235 and FIG. 5 of JP-A-92-122023. In the published documents, however, neither disclosure is found on values of glossiness of a main surface of a wafer before and after formation of a silicon single-crystal film thereon, nor is description or suggestion is available about influence of a surface glossiness exerted on a lithographic step as described above. In addition, both of the techniques adopt mirror-polishing after formation of a silicon single-crystal thin film as a last resort for achieving improved flatness of a front main surface of the as-grown silicon single-crystal thin film, which suggests that no sufficient flatness is achieved without the mirror-polishing. If mirror-polishing is added in any way as a process step after formation of a silicon single-crystal thin film, it is apparent that no effect of reduction in mandays, which is an object of the invention, can be attained at all. In contrast to the conventional practices, according to the invention, an etching removal of a chemically etched substrate is controlled so as to sufficiently increase a glossiness on a front main surface thereof and thereby, a surface glossiness of an as-grown silicon single-crystal thin film thereon can be 95% or higher; therefore, an additional mirror-polishing, which has been adopted in a conventional practice, is not required in any way.


REFERENCES:
patent: 5340437 (1994-08-01), Erk et al.
patent: 5976983 (1999-11-01), Miyazaki et al.
patent: 6294469 (2001-09-01), Kulkarni et al.
patent: 4-357106 (1992-12-01), None
Japanese Patent Office, Japanese Patent Provisional Publication No.: 4-122023, Date of Publication: Apr. 22, 1992, Application No.: 2-243474, Filin

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