Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates – Subsequent separation into plural bodies
Reexamination Certificate
2000-02-01
2002-04-23
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
Subsequent separation into plural bodies
Reexamination Certificate
active
06376332
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composite member and separating method therefor, a bonded substrate stack and separating method therefor, a transfer method for transfer layer, and an SOI substrate manufacturing method.
2. Description of the Related Art
A substrate (SOI substrate) having an SOI (Silicon On Insulator) structure is known as a substrate having a single-crystal Si layer on an insulating layer. A device using this SOI substrate has many advantages that cannot be achieved by ordinary Si substrates. Examples of the advantages are as follows.
(1) The integration degree can be increased because dielectric isolation is easy.
(2) The radiation resistance can be increased.
(3) The operating speed of the device can be increased because the stray capacitance is small.
(4) No well step is necessary.
(5) Latch-up can be prevented.
(6) A complete depletion type field effect transistor can be formed by thin film formation.
Since an SOI structure has the above various advantages, researches have been made on its formation method for several decades.
As one SOI technology, the SOS (Silicon On Sapphire) technology by which Si is heteroepitaxially grown on a single-crystal sapphire substrate by CVD (Chemical Vapor Deposition) has been known for a long time. This SOS technology once earned a reputation as the most matured SOI technology. However, the SOS technology has not been put into practical use to date because, e.g., a large amount of crystal defects are produced by lattice mismatch in the interface between the Si layer and the underlying sapphire substrate, aluminum that forms the sapphire substrate mixes in the Si layer, the substrate is expensive, and it is difficult to obtain a large area.
Attempts have recently been made to realize the SOI structure without using any sapphire substrate. The attempts are roughly classified into two methods.
In the first method, the surface of a single-crystal Si substrate is oxidized, and a window is formed in the oxide film (SiO
2
layer) to partially expose the Si substrate. Single-crystal Si is epitaxially grown laterally using the exposed portion as a seed, thereby forming a single-crystal Si layer on SiO
2
(in this method, an Si layer is deposited on an SiO
2
layer).
In the second method, a single-crystal Si substrate itself is used as an active layer, and an SiO
2
layer is formed on the lower surface of the substrate (in this method, no Si layer is deposited).
As a means for realizing the first method, a method of directly epitaxially growing single-crystal Si in the horizontal direction from the single-crystal Si layer by CVD (CVD), a method of depositing amorphous Si and epitaxially growing single-crystal Si laterally in the solid phase by annealing (solid phase epitaxial growth), a method of irradiating an amorphous silicon layer or a polysilicon layer with a focused energy beam such as an electron beam or laser beam to grow a single-crystal Si layer on an SiO
2
layer by melting recrystallization (beam annealing), or a method of scanning band-shaped melting regions by a rod-like heater (zone melting recrystallization) is known.
All of these methods have both advantages and disadvantages and many problems of controllability, productivity, uniformity, and quality, and therefore have not been put into practical use in terms of industrial applications. For example, CVD requires sacrifice oxidation to form a flat thin film. Solid phase epitaxial growth is poor in crystallinity. In beam annealing, the process time required to scan the focused beam and controllability for beam superposition or focal point adjustment pose problems. Zone melting recrystallization is the most matured technique, and relatively large-scaled integrated circuits have been fabricated on a trial basis. However, since a number of crystal defects such as a subboundary undesirably remain, minority carrier devices cannot be created.
As the above second method, i.e., as the method without using the Si substrate as a seed for epitaxial growth, the following four techniques can be used.
As the first technique, an oxide film is formed on a single-crystal Si substrate having a V-shaped groove formed in the surface by anisotropic etching. A polysilicon layer having nearly the same thickness as that of the single-crystal Si substrate is deposited on the oxide film. After this, the single-crystal Si substrate is polished from the lower surface, thereby forming, on the thick polysilicon layer, a substrate having a single-crystal Si region surrounded and dielectrically isolated by the V-shaped groove. With this technique, a substrate having satisfactory crystallinity can be formed. However, there are problems of controllability and productivity in association with the process of depositing polysilicon as thick as several hundred micron or the process of polishing the single-crystal Si substrate from the lower surface to leave the isolated Si active layer.
The second technique is SIMOX (Separation by Ion Implanted Oxygen). In this technique, oxygen ions are implanted into a single-crystal Si substrate to form an SiO
2
layer. In this technique, to form an SiO
2
layer in a substrate, oxygen ions must be implanted at a dose of 10
18
(ions/cm
2
) or more. This implantation takes a long time to result in low productivity and high manufacturing cost. In addition, since a number of crystal defects are generated, the quality is too low to manufacture minority carrier devices.
As the third technique, an SOI structure is formed by dielectric isolation by oxidizing a porous Si layer. In this technique, an n-type Si island is formed on the surface of a p-type single-crystal Si substrate by proton ion implantation (Imai et al., J. Crystal Growth, vol. 63, 547 (1983)) or epitaxial growth and patterning. This substrate is anodized in an HF solution to convert only the p-type Si substrate around the n-type Si island into a porous structure. After this, the n-type Si island is dielectrically isolated by accelerated oxidation. In this technique, since the Si region to be isolated must be determined before the device process, the degree of freedom in device design is limited.
As the fourth technique, an SOI structure is formed by bonding a single-crystal Si substrate to another thermally oxidized single-crystal Si substrate by annealing or an adhesive. In this technique, an active layer for forming a device must be uniformly thin. More specifically, a single-crystal Si substrate having a thickness of several hundred micron must be thinned down to the micron order or less.
To thin the substrate, polishing or selective etching can be used.
A single-crystal Si substrate can hardly be uniformly thinned by polishing. Especially, in thinning to the submicron order, the variation range is several ten %. As the wafer size becomes large, this difficulty becomes more pronounced.
Selective etching is effective to uniformly thin the substrate. However, the selectivity ratio is as low as about 10
2
, the surface planarity after etching is poor, and the crystallinity of the SOI layer is unsatisfactory.
A transparent substrate represented by a glass substrate is important in forming a contact sensor as a light-receiving element or a projection liquid crystal display device. To realize highly precise pixels (picture elements) having higher density and resolution for the sensor or display device, a high-performance driving element is required. For this purpose, a demand has arisen for a technique of forming a single-crystal Si layer having excellent crystallinity on a transparent substrate.
However, when an Si layer is deposited on a transparent substrate represented by a glass substrate, only an amorphous Si layer or a polysilicon layer is obtained. This is because the transparent substrate has an amorphous crystal structure, and the Si layer formed on the substrate reflects the disorderliness of the crystal structure of the transparent substrate.
The present applicant has disclosed a new SOI technology in Japanese Patent Laid-Open No. 5-21338. In t
Kurisu Hirokazu
Ohmi Kazuaki
Sakaguchi Kiyofumi
Yanagita Kazutaka
Morgan & Finnegan L.L.P.
Whitmore Stacy
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