Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-07-25
2004-06-08
Osele, Mark A. (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S345420, C438S458000
Reexamination Certificate
active
06746559
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for separating a composite member, separated members, and a semiconductor substrate and its production method.
2. Related Background Art
The formation of a single crystal Si semiconductor layer on an insulating surface of a substrate is widely known as a semiconductor on insulator (SOI) technique, and many efforts have been made to research this technique because devices produced using the SOI technique have many advantages that cannot be achieved by bulk Si substrates used to fabricate normal Si integrated circuits.
The use of the SOI technique provides the following advantages:
(1) The dielectric separation can be easily made to attain high integration.
(2) Radiation resistance is excellent.
(3) The stray capacity is reduced to attain high speed.
(4) The well formation process can be omitted.
(5) Latch-up can be prevented.
(6) The thickness can be reduced to provide a fully depleted field effect transistor.
To achieve the many advantages of the device, methods for forming SOI structures have been researched for decades. One of such known methods is SOS (silicon on sapphire) in which Si is heteroepitaxially formed by CVD (chemical vapor deposition) on a single crystal sapphire substrate. This technique has been successful as the maturest SOI technique, but its applications are limited by a large amount of crystal defects due to the misalignment of lattices in the interface between an Si layer and a sapphire substrate, by the mixture of aluminum from the sapphire substrate into the Si layer, and in particular, by the high costs of the substrate and the still insufficient the enlargement of area of the device. More recently, an attempt has been made to implement an SOI structure without the sapphire substrate. This attempt can be roughly classified into the following two methods.
1. After the surface of an Si single crystal substrate is oxidized, a window is made in the oxidized film to expose a part of the surface of the Si substrate, and this part is used as a seed to allow a horizontal epitaxial growth to form an Si single crystal layer on the SiO
2
(in this case, an Si layer is deposited on SiO
2
).
2. The Si single crystal substrate is used as an active layer and SiO
2
is formed under this layer (this method does not require an Si layer to be deposited).
Known means for realizing the above method 1 include a method for allowing the direct horizontal epitaxial growth of single crystal layer Si using CVD, a method of depositing amorphous Si and allowing its horizontal epitaxial growth in a solid phase by thermal treatment, a method of irradiating an amorphous or polycrystal Si layer with converging energy beams such as electron or laser beams, and allowing a single crystal layer to grow on SiO
2
by means of melting recrystallization, and a method of using a bar-like heater to scan a molten area in such a way that the scanning trace appears like a band (zone melting recrystallization). Although these methods have both advantages and disadvantages, they still have many problems in terms of their controllability, productivity, uniformity, and quality and none of them have been put to industrially practical use. For example, the CVD method requires sacrificial oxidization to provide flat films. The solid phase growth method provides poor crystallinity. The beam anneal method has problems in terms of the time required for converging-beam scanning, and control of the superposition of beams, and focusing. Among them, the zone melting recrystallization method is maturest and has been used to produce relatively-large-scale integrated circuits on an experimental basis, but it still causes a large amount of crystal defects such as sub-grains to remain in the device, thereby failing to fabricate minor-carrier devices and to provide sufficiently excellent crystals.
The above method 2 that does not use the Si substrate as a seed for epitaxial growth includes the following four methods.
(1) An oxide film is formed on an Si single crystal substrate with a V-shaped groove etched anisotropically in its surface, a polycrystal Si layer is deposited on the oxide film so as to be as thick as the Si substrate, and then an Si single crystal region surrounded by the V-shaped groove so as to be separated dielectricly is formed on the thick polycrystal Si layer by polishing from the rear surface of the Si substrate. This method provides excellent crystallinity but the steps for depositing polycrystal Si by a thickness of several hundred microns and polishing the single crystal Si substrate from its rear surface to leave only the separated Si active layer have problems in terms of controllability and productivity.
(2) SIMOX (Separation by Ion-Implemented Oxygen) that forms an SiO
2
layer in an Si single crystal substrate by means of oxygen ion implantation and that is the presently maturest technique due to its excellent compatibility with the Si process. To form an SiO
2
layer, however, 10
18
ions/cm
2
or more of oxygen ions must be implanted, resulting in the need for a large amount of time for the implantation, thereby leading to reduced productivity. In addition, the costs of wafers are high. Furthermore, this method cause a large amount of crystal defects to remain in the device and does not industrially provide a sufficient quality to fabricate minor-carrier devices.
(3) A method for forming an SOI structure by dielectric separation through the oxidization of porous Si. In this method, an N-type Si layer is formed like an island on a surface of a P-type Si single crystal substrate by proton-ion implantation (Imai et al., J. Crystal Growth, vol. 63, 547 (1983)) or by epitaxial growth and patterning. Only the P-type Si substrate is made porous by an anodization method using an HF solution in such a way that the porous region surrounds the Si island from the surface, and the N-type Si island is then oxidized at a high speed for dielectric separation. In this method, the separating Si region is determined prior to the device step, thereby limiting the degree of freedom of device design.
(4) A method for forming an SOI structure using thermal treatment or an adhesive to bond an Si monocrystal substrate on a different Si single crystal substrate that is thermally oxidized is attracting attention. This method requires an active layer for a device to be formed as a uniformly thin film. That is, the thickness of a several-hundred-micron-thick Si single crystal substrate must be reduced to the order of micron or less.
The following two methods can be used to provide a thinner film.
1) Thickness reduction by polishing
2) Thickness reduction by selective etching
The polishing in 1) cannot provide uniformly thin films easily. In particular, if the thickness is reduced to the order of submicron, the thickness variation will be several tens %, resulting in a serious problem for providing uniformity. The difficulty in achieving uniformity further increases with increasing size of the substrate.
In addition, although the etching in 2) is supposed to be effective in providing uniform thin films, it has the following problems.
The selection ratio is at most 10
2
and is insufficient.
The surface obtained after etching is bad.
The crystallinity of the SOI layer is bad due to the use of ion implantation or epitaxial or heteroepitaxial growth on a high concentration B-doped Si layer.
A semiconductor substrate formed by bonding requires two substrates, one of which is mostly uselessly removed and disposed of through polishing and etching, thereby wasting limited global resources. Thus, SOI with bonding presently has many problems in terms of its controllability, uniformity, and costs.
In addition, generally due to the disorder of the crystal structure of a light-transmissive substrate represented by glass, a thin film Si layer deposited on the substrate can only form an amorphous layer or a polycrystal layer based on the disorder of substrates, and therefore high-performance devices cannot be produced.
Ohmi Kazuaki
Sakaguchi Kiyofumi
Yanagita Kazutaka
Yonehara Takao
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