Semiconductor device manufacturing: process – Bonding of plural semiconductor substrates
Reexamination Certificate
1999-12-17
2001-02-13
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Bonding of plural semiconductor substrates
C438S107000, C438S938000
Reexamination Certificate
active
06187653
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention is directed to processes for fabricating devices, such as photodetector devices, in which two crystalline substrates with different crystal lattices are bound together.
2. Description of the Related Art
Processes for fabricating certain semiconductor devices require that two wafers, each having a crystal lattice that is different from the other, be bound together. For example crystalline III-V substrates (e.g. substrates of Indium Phosphide (InP) and Indium Gallium Arsenide (InGaAs)) substrates are bound to crystalline silicon substrates to fabricate photodetectors. Such devices are described in Hawkins, A., et al., “Silicon heterointerface photodetector,”
Appl. Phys. Lett.,
Vol. 68:26, pp. 3692-3694 (1996) (hereinafter Hawkins et al.). As used herein, III-V substrates are semiconductor compounds in which one of the elements is from column III of the Mendeleef Periodic Table and one of the elements is from column V of that Table.
Hawkins et al. describe a process for fabricating avalanche photodetector devices in which a silicon wafer is fused directly to an InGaAs surface of an indium phosphide (InP) substrate. In the Hawkins et al. process, an InGaAs surface is epitaxially grown on the InP substrate. The bonding surface of the silicon wafer is an epitaxial silicon layer grown on an n+ substrate with a shallow p-type implant at the surface. After bonding, the InP substrate is subsequently removed leaving only the InGaAs layer and the other thin device layers bound to the silicon substrate. The bonding is performed by pressing the surfaces of the two substrates together for 20 minutes at 650° C. in an H
2
atmosphere.
U.S. Pat. No. 5,207,864 describes low temperature fusion of dissimilar semiconductors. In the case in which both wafers are compound semiconductors, the wafers are lightly pressed together and left at a temperature at which one of the compositions can atomically rearrange at the interface. In the case in which one of the wafers is silicon, the wafers are pushed together in a strong acid. The wafers are adhered together with Van der Waals forces. Thereafter, they are pressed together and anealed at a temperature at which the non-silicon composition can atomically rearrange.
The quality of the semiconductor devices depends on, among other things, the quality of the silicon-InGaAs interface. Accordingly, a process for forming a high quality interface between the two different surfaces is desired.
SUMMARY OF THE INVENTION
The present invention is a process for bonding together two substrates (typically semiconductor wafers) each substrate having a crystal lattice structure that is different from the other. The invention is further directed to a process for device fabrication in which a first is substrate with a first crystal lattice structure is bound to a second substrate with a second crystal lattice structure. In the context of the present invention, a difference in lattice constant that is greater than about 0.1 percent qualifies as a different crystal lattice.
In the process of the present invention, a first substrate is placed in physical contact with a second substrate. A flexible membrane is placed in physical contact with the contacted first substrate and second substrate. Pneumatic force is applied to the flexible membrane for a sufficient time in order for an attractive force to develop between the two substrates. This attractive force, referred to herein as Van der Waals force, develops sufficiently when the substrates are held together for about five to about thirty minutes.
Subsequent conventional processing steps can be used to form a desired device from the attractively bonded substrates. For example, after the two substrates are Van der Waals' bonded together, a portion of one of the substrates is typically removed prior to device fabrication. For example, in the context of the photodetector devices previously described, it is desired to bond a silicon substrate to a III-V device layers such as InGaAs device layers formed on a III-V semiconductor substrate (e.g. an InP substrate). The bulk of either the first substrate or the second substrate is etched away after the substrates are Van der Waals bound together. Only one or more discrete, thin layers formed on the removed substrate remain bound to the other substrate. In order to ensure that the desired device layer(s) remain, an etch stop layer is formed on the III-V substrate. After the bulk of one substrate is removed leaving only the layer(s) formed thereon bound to the other substrate, the structure is heated to a temperature sufficient to induce a covalent bond between the device layer(s) and the other substrate.
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Hui Sanghee Park
Levine Barry Franklin
Pinzone Christopher James
Thomas Gordon Albert
Lucent Technologies - Inc.
Mathews, Collins Shepherd & Gould P.A.
Niebling John F.
Simkovic Viktor
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