Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Graded composition
Reexamination Certificate
1998-05-22
2001-07-10
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Graded composition
C438S048000, C438S098000, C438S233000
Reexamination Certificate
active
06258616
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to semiconductor devices, and in particular, to a semiconductor device having a non-alloyed ohmic contact to a buried doped semiconductor layer. It also relates to a method for making such devices.
BACKGROUND OF THE INVENTION
Semiconductor devices are used in a vast assortment of equipment including computers and communication systems. Many of these semiconductor devices have multilayered structures that include semiconductive layers of dissimilar doping. Separate ohmic contacts are frequently made to the different layers of the device.
It is often desirable that the ohmic contacts of the device be produced without subsequent heating. Such ohmic contacts are referred to as being “non-alloyed”. Methods for producing non-alloyed ohmic contacts to doped semiconductor surface layers are well known in the art. See, U.S. Pat. No. 5,013,685 to Chiu et al. which is incorporated herein by reference. They are used in semiconductor devices which are susceptible to damage caused by heat.
Photonic semiconductor devices such as vertical-cavity surface emitting lasers and modulators are particularly susceptible to heating during subsequent semiconductor processing. These devices employ highly reflective mirrors made from gold films or silver capped gold films which form laser cavities or produce reflective modulation. These gold and silver films are most effective when applied directly to the surfaces of pristine semiconductor layers (semiconductor surfaces that have not been subjected to heating) without using base layers of chromium or titanium. When used without the base layers, the gold and silver films can buckle when heated. Buckling of these films reduces their reflectivity and leads to reliability problems.
This heat susceptibility presents major obstacles in the fabrication of photonic semiconductor devices. It is desirable to apply the mirrors early in the fabrication process so that they can be used as masks in self-aligned processing steps. But ohmic contacts must be formed at the end and typically at least one ohmic contact must be made to a buried doped semiconductor layer.
Unfortunately, there are no known processes for fabricating non-alloyed ohmic contacts to buried doped semiconductor layers of semiconductor devices. Since buried alloyed contacts are typically fabricated at about 420° C., buckling of the gold or silver mirror films frequently occurs when the second ohmic contacts are fabricated.
Accordingly, a need exists for a method of producing a non-alloyed contact to a buried doped layer of a semiconductor device.
SUMMARY
An improved semiconductor device comprises a buried doped layer of semiconductor material and a non-alloyed contact to the buried doped layer. The non-alloyed contact is made ohmic by the presence of an underlying delta-doped monolayer. The semiconductor device is made by placing a stop-etch layer on top of a buried doped layer and forming at least one delta-doped monolayer in either the stop-etch layer or the buried doped layer. Layers of semiconductor material disposed above the stop-etch layer are removed with an etchant to define an active region of the semiconductor device. The stop-etch layer prevents the etchant from removing the delta-doped monolayer. A non-alloyed metal film is then deposited over the delta-doped monolayer to form an ohmic contact to the buried doped layer.
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Cunningham John Edward
Goossen Keith Wayne
Lee Granvill D
Lucent Technologies - Inc.
Mathews, Collins Shepherd & Gould P.A.
Smith Matthew
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