Method of cleaving a semiconductor wafer including...

Semiconductor device manufacturing: process – Semiconductor substrate dicing

Reexamination Certificate

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C438S462000

Reexamination Certificate

active

06225193

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a method of cleaving a semiconductor wafer, and in particular to a method of cleaving a semiconductor wafer to form microelectronic and optoelectronic devices.
BACKGROUND OF THE INVENTION
Semiconductor wafers for semiconductor and optoelectronic applications are conventionally separated into individual dice by cleaving along a preferential crystal orientation. Cleaving is promoted by forming scribe lines or edge nicks in the material to generate a fracture location. Compound III-V semiconductor materials are commonly used in the fabrication of integrated circuits and optoelectronic devices, e.g. lasers and optical amplifiers. Such optoelectronic devices conventionally have a Fabry-Perot cavity wherein high quality cleaved end surfaces serve as the cavity mirrors. Alternatively, distributed feedback (DFB) or distributed Bragg reflector (DBR) type lasers, or other devices such as semiconductor Mach Zehnder modulators may also require optical quality cleaved facets. There may be as many as 10,000 devices on a 1″ diameter wafer. After defining device structures, the semiconductor wafer is separated into individual elements by cleaving. A high yield at the cleaving stage is critical.
The wafer is usually cleaved into quarters which are subsequently cleaved into bars wherein each bar contains a plurality of side-by-side devices. These bars are then cleaved to separate the individual elements.
The cleaving process is traditionally a manual operation with a skilled operator using a probe to initiate crack propagation within either a scribed laser bar or a wafer quarter. This is labour intensive process and the yield of good devices is often dependent on the skill and ability of the operator. Further, as new and different laser structures are introduced into production or as production volumes increase more operators are required to meet the increased workload. It is difficult to control and ensure the consistency of a purely manual skill, even with a small workforce. As extra staff is introduced to the operation, additional training and close monitoring is required.
Accordingly, there is a need in the industry for alternative methods of cleaving semiconductor wafers which would avoid manual operation and provide high yield of laser devices with high quality cleaved facets.
SUMMARY OF THE INVENTION
Thus, the present invention seeks to provide a method of cleaving a semiconductor wafer which would avoid or reduce the afore-mentioned problems.
Therefore, according to a first aspect of the present invention there is provided a method of cleaving a semiconductor wafer, comprising the steps of:
selectively masking a semiconductor wafer;
ion implanting unmasked regions of the wafer to a pre-determined depth;
annealing the wafer to cause exfoliation of the material from the implanted regions.
The dose of ion implantation, the depth of ion penetration, and the rate and temperature of the annealing are determined so as to cause exfoliation, and separation of the material from the implanted regions, thereby patterning the material, by ion induced selective area exfoliation. Voids form in the implanted region during annealing at the predetermined depth and cause explosive exfoliation, causing cleavage of the material along boundaries of the implanted regions, as will be described in detail below.
Advantageously, the step of masking comprises providing a mask having edges parallel to natural cleavage planes of the semiconductor material, to facilitate cleavage to form optical quality sidewall facets. The mask may be removed before of after annealing, as required.
Typical ions for the ion implantation step are the light ions of hydrogen or helium or isotopes thereof. Inert gases, e.g neon or its isotopes, are an alternative choice.
Preferably, annealing comprises rapid thermal annealing to cause exfoliation. Other known annealing processes may be used which provide the required heating rate and temperature to cause exfoliation. Annealing of the material is performed, for example, by rapid thermal annealing, furnace annealing, annealing by use of electron beams, ion beams, or laser beams, or a combination of annealing processes. All of these methods provide thermal heating of the material up to a required temperature causing exfoliation.
The appropriate selection of masks and implantation provides the desired exfoliation of the material and cleaving of the wafer to form sidewall-facets.
Typical materials selected for the mask may include metals, e.g. gold, nickel or aluminum; dielectrics, e.g. silicon dioxide or silicon nitride; organic materials, e.g. photoresist; or a combination thereof.
The materials used for the mask must be thick enough to stop the implanted ions, robust enough to withstand the implantation without significant deformations and preferably allows required control of an edge profile of the mask. Preferably, the mask is defined by use of photo-lithography, etching and lift-off techniques. The mask may be removed by plasma ashing, chemical etching, mechanical polishing, or ion etching, depending on the masking material selected, the processes being well known in the semiconductor industry. The mask may be removed either before or after the annealing, as required.
The steps of masking and implanting may be repeated a number of times before performing the step of annealing to cause exfoliation and cleaving of the wafer to form sidewall-facets. That is, masking and implanting with different ions, energies and doses in different areas of the sample may be performed several times before the annealing. A mask may be removed after each implantation, or, alternatively, all the masks may be removed together either before or after the annealing step. Similarly to the above, the steps of masking, implanting and annealing may be repeated as many times as needed, with annealing after each implantation to remove regions of the wafer by exfoliation. Several implantations may be used for different patterns.
According to another aspect of the invention there is provided a method of cleaving a semiconductor wafer to define optoelectronic devices, comprising the steps of:
forming an optoelectronic device structure in the surface of the wafer;
selectively masking the semiconductor wafer with a mask having edges parallel to natural cleavage planes of the semiconductor material;
ion implanting unmasked regions of the wafer with ions to a pre-determined depth;
annealing the wafer to cause exfoliation of the material from the implanted regions.
The method above provides defining of optoelectronic devices on the wafer, for example, optoelectronic devices including laser devices, having active regions formed on the wafer. Annealing causes exfoliation of the material from the implanted regions, with cleaving of the material to form sidewall-facets. The mask has straight edges parallel to natural cleavage planes of the semiconductor material, which facilitates cleaving to form high quality facets.
Preferably, the ions penetrate into the wafer below the active region, and thus cause separation of the optoelectronic device structures, for example laser devices formed in the surface of the wafer. The patterned structure remaining on the wafer after exfoliation forms a first set of laser devices. The collected pieces of exfoliated material may form a second set of laser devices, with sidewall-facets serving as laser facets for each set. The orientation of sidewall-facets depends on orientation of the direction of ion implantation with respect to the crystallographic directions, i.e. cleavage planes, of the wafer, for example, to form vertical facets or facets inclined at a pre-determined angle.
Advantageously after cleaving, the laser devices may further be tested, the testing of the first set of laser structures being performed on the wafer. Further steps of the method may include coating laser facets of the first set of laser devices, and detaching laser devices of the first set from the wafer.


REFERENCES:
patent: 4824800 (1989-04-01), Takano
pate

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