Semiconductor device manufacturing: process – Coating with electrically or thermally conductive material – To form ohmic contact to semiconductive material
Reexamination Certificate
2002-01-18
2004-03-02
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Coating with electrically or thermally conductive material
To form ohmic contact to semiconductive material
C438S738000, C438S936000
Reexamination Certificate
active
06699778
ABSTRACT:
BACKGROUND OF THE INVENTION
2
Field of the Invention
The invention relates to masking techniques for producing semiconductor components, particularly a BH laser diode. In the production of III-V semiconductor components, masking steps are usually used to structure the surface of a sample. The surface of the sample is partially covered with a mask, for instance a mask made of SiO
2
as an amorphous material. The sample material is then removed in the region that is not covered by the mask by an etching step (a dry or wet chemical process).
The term “sample” refers to any material that is structured in the course of manufacturing semiconductor components.
For instance, a BH (Buried Heterostructure) laser diode includes a structured active layer, with dry etching techniques (e.g. reactive ion etching) and/or wet chemical techniques being used for structuring.
The disadvantage of this procedure is that, in order to remove the SiO
2
mask from the surface or to structure the active layer of the BH laser diode, the sample must be removed from the epitaxy apparatus, thereby exposing the sample to air-borne contaminants and oxygen. The contamination is particularly bad in structures containing aluminum, because this exhibits a high bonding affinity to oxygen. Because such structures are highly significant to semiconductor laser production, the contamination in ex-situ techniques is particularly problematic.
It is also necessary to add an expensive wet chemical treatment process to dry etching techniques for BH laser diode fabrication, in order to remove the regions of the semiconductor material where ex-situ damage occurs. In a InGaAsP/InP system, etching solutions containing bromine are usually used, which may adversely affect the long-term stability of the BH laser diodes.
Furthermore, in the selective epitaxy technique used in BH laser diode fabrication, it is impossible to prevent the mask material, for instance SiO
2
or SiN, from getting into the epitaxy apparatus. At high temperatures, there is a chance that this mask material may additionally contaminate the wafer.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a masking method for producing semiconductor components, particularly a BH laser diode, that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that provides a method for easily removing the mask from semiconductor material and applying additional layers in situ during the manufacture of semiconductor components.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of producing a structure for semiconductor components. The first step of the method is applying a mask made of at least one mask material to a sample in a masking step. The next step is selecting the composition of the mask material to control the etch rate. The next step is at least partially etching the mask during an etching step.
In accordance with a further object of the invention, the etching step lasts for a set period of time.
The mask can be at least partly dissolved during an etching step by selecting the etch rate in the etching step based upon the composition and/or nature of the mask material. Thus, a masking and further processing of the sample can be performed in-situ in the epitaxy apparatus. In this way, a kind of self-dissolving mask can be created, given which the etch rate is expediently selected in such a way that the mask is gone from the sample at the end of the etching step, or the underlying layer is etched.
It is particularly advantageous to utilize a III-V semiconductor material, namely a monocrystalline III-V semiconductor material.
It is also advantageous if at least one mask material is Ga
x
In
1-y
As
y
P
1-y
, AlGaInAs, or InGaAlP. These materials can be is removed in a highly controlled fashion by etching the sample.
It is particularly advantageous if the creation of a structure on and/or in the mask, specifically by lithography, is followed by an etching step with tertiary butyl chloride (TBCl) as the etching agent. This etching agent is appreciably milder than the halogenic hydrogen compounds (e.g. HCl) commonly used in in-situ methods. Thus, noble steel parts, for instance parts of the epitaxy apparatus, valves, or pipes, are not attacked. Moreover, the etch rate of this agent is particularly easy to control. In this way, a “self-etching mask” can be created, which is removable from the sample in-situ. The mask can be at least partly dissolved during etching, which saves a substantial amount of processing time.
It is advantageous that the etching step can be accomplished in the same device in which the structure has been applied in and/or on the sample.
Advantageously, at least one epitaxial layer, particularly a guard layer, is applied to the surface in situ after the etching step. The in-situ overgrowth prevents contamination and saves valuable processing time.
The doping type of the overgrowth layers is expediently complementary to the doping type of a substrate for the semiconductor component. It is also advantageous if the band gap to at least one overgrowth layer is larger than the band gap of the active layer of the semiconductor component.
In an advantageous development of the inventive method, at least one surface-wide etching of a ridge for a BH laser diode is completed in situ in the epitaxy device during the etching step. This way, a significant production step can be accomplished in situ.
Upon completion of the method, the emerging semiconductor structure can be expediently applied in a semiconductor component, particularly a BH laser.
In a particularly efficient production of a BH laser diode, an etching step with TBCl serves specifically for creating the ridge structure, and a subsequent epitaxy step is completed for the overgrowth. The etching step and the overgrowth step are accomplished in situ in the same epitaxy device (without the sample leaving the epitaxy device), so that the production process is particularly efficient and free of contamination.
An epitaxy step for generating a base structure can be expediently provided before the etching step.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a masking technique for producing semiconductor components, particularly a BH laser diode, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
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K. Imanaka et al.: ,,A novel technique to fabricate GaInAsP/InP buried heterostructure laser diodes, Appl. Phys. Lett. vol. 44, No. 10, May 15, 1984, pp. 975-977.
J.R. Lothian et al.: “Mask erosion during dry etching of deep features in III-V semiconductor structures”, Semiconductor Science and Technology, vol. 7, No. 9, Sep. 1992, pp. 1199-1209.
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Baumeister Horst
Borchert Bernd
Gessner Roland
Veuhoff Eberhard
Wenger Gundolf
Everhart Caridad
Greenberg Laurence A.
Infineon - Technologies AG
Mayback Gregory L.
Stemer Werner H.
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