Semiconductor device manufacturing: process – Chemical etching – Altering etchability of substrate region by compositional or...
Reexamination Certificate
1999-08-19
2001-03-06
Powell, William (Department: 1765)
Semiconductor device manufacturing: process
Chemical etching
Altering etchability of substrate region by compositional or...
C216S062000, C216S087000, C438S690000, C438S715000
Reexamination Certificate
active
06197697
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method of patterning brittle materials, and in particular to a method of patterning semiconductor materials.
BACKGROUND OF THE INVENTION
Patterning of the materials used in the semiconductor industry is one of the major steps in fabrication of microelectronic devices, integrated circuits and optoelectronic devices including semiconductor lasers. Conventionally known methods of patterning comprise selectively masking a semiconductor material with a photoresist or any other masking material, followed by etching. Known etching methods include selective wet chemical etching, or dry etching, e.g. plasma and reactive ion etching. (E.g., see Van Nostrand's Scientific Encyclopedia, 7th Edition, Ed. by Douglas and Glenn Considine, NY, 1989, pp. 1851-1852.) Anisotropic etching processes are known for defining microscopic structures of sub-micron dimensions.
Nevertheless, there are limitations associated with known etching processes, for example, in etching multilayer structures of different materials, because etchants are material specific and often only one layer of a particular material can be etched with a specific etchant. Thus etching through several layers of different materials may require numerous steps and be time consuming and costly. Control of etch rates, sidewall and perimeter profiles may present challenges requiring careful control of etch parameters, which is also necessary to reduce unwanted etch damage, and etch residues and edge distortions and provide reproducible and consistent etch processes. Etching of deep structures may be time consuming, or require multiple steps. Endpoint control is required to prevent underetching and overetching, undercutting and other distortions. Etchants may include hazardous or reactive materials requiring special handling expense for safe handling, and high purity materials to prevent contamination of sensitive semiconductor structures. Furthermore, there are some materials which cannot be readily etched using conventional techniques, e.g. some dielectrics such as lithium fluoride, lithium niobate.
Therefore a need exists for development of alternative methods for patterning brittle materials, and particularly semiconductor materials, which would for example avoid multiple step etching for patterning through multi-layer structures, and allow rapid deep patterning, and be applicable to an extended list of materials.
SUMMARY OF THE INVENTION
Thus, the present invention seeks to provide a method of patterning brittle materials, including semiconductors, which avoids or reduces the above-mentioned problems.
Therefore, according to a first aspect of the present invention there is provided a method of patterning a brittle material, comprising the steps of: selectively masking the material; implanting unmasked regions of the material with ions to a pre-determined depth; annealing to cause exfoliation of the material from the implanted regions.
Thus a method of patterning brittle materials such as semiconductors, ceramics, etc., is provided for a wide range of applications.
The dose of ion implantation, the depth of ion penetration, and the rate and temperature of 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.
Typical ions suitable for the implantation step are the light ions of hydrogen or helium or isotopes thereof, or an inert gas of neon or its isotopes, depending on the material to be patterned. Annealing of the material may be performed by, for example, rapid thermal annealing, furnace annealing, annealing by use of electron beams, ion beams, or laser beams. These methods provide thermal heating of the material up to a required temperature causing exfoliation and separation of the implanted regions as will be described in more detail below. This method of patterning is applicable to a crystalline or non-crystalline material, provided the material is sufficiently brittle to cleave during exfoliation. Exfoliation occurs when the implanted ions lead to the formation of pressurized voids within the material thus initiation cleavage, preferably along natural cleavage planes of the material. For multi-layered semiconductor structures, the method may allow for patterning through several layers of the structure at the same time when the ions are implanted below the multi-layered structure. The mask may be removed either before or after the annealing step. Typical depths of patterning semiconductor materials according to the above method may range from about a few nanometers to about tens of micrometers depending on the application, and the lateral dimensions of exfoliated pieces may range from a few micrometers to several centimeters. The method is thus potentially applicable to a wide range of materials and structures including for example applications in semiconductor processing for integrated circuits and optoelectronic devices.
More complex patterns may be defined with multiple masking steps and implantation steps. For example, masking and implantation may be repeated a number of times before performing annealing to cause exfoliation. Multiple implants with different ions, energies and doses in different areas of the sample may be made before the annealing and exfoliation. Masks may be removed before or after annealing, as required. Alternatively, multiple exfoliation steps may be performed sequentially. The mask may be removed before or after the annealing step.
Multiple implantations at different energies may be performed through the same mask for deep patterning of the material, the mask being removed either before or after the annealing step. The step of annealing may be a multi-stage process, wherein multiple annealing is performed, each subsequent annealing being performed at a higher temperature than the previous one, with the temperature of last stage annealing being performed at the temperature required for exfoliation.
For crystalline materials, when edges of masks are oriented along certain crystallographic directions of the material, exfoliation occurs along natural cleavage planes and results in the formation of high quality sidewall facets of the exfoliated material and of the complimentary patterned material remaining at the boundaries of exfoliated regions.
Typical materials for the mask include metals, e.g. gold, nickel or aluminum; dielectrics e.g. silicon dioxide or silicon nitride; organic materials e.g. conventional photoresists, or a combination thereof. Materials used for the mask must be thick enough to stop the implanted ions, robust enough to withstand the implantation without significant deformations, and allow definition of a required edge profile of the mask. Preferably, the mask is defined by use of photo-lithography, etching and lift-off techniques. Masks may be removed by suitable processes being well known in the semiconductor industry, for example, plasma ashing, chemical etching, mechanical polishing, or ion etching.
To facilitate exfoliation of the material along pre-determined boundaries, the method may further include a step of forming trenches at the boundaries and along the perimeter of the material to be exfoliated.
Preferably, these trenches are formed by etching, or, alternatively, by the method of patterning of the present invention. Conveniently, the depth of trenches is equal to or deeper than the depth of patterning of the material.
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Considine, D. and G., ed, Van Nostrand's Scientific Encyclopedia, 7thEdition, New York, 1989, pp. 1849-1854.
Kaminsky, M., “Plasma Contamination and Wall Erosion in Thermonuclear Reactors”, IEEE Transactions on Nuclear Science, vol. NS-18, No. 4, Aug. 1971, pp. 208-217.
Kaminsky, M., et al, “Radiation Blistering of Polycrystalline Niobium by Helium-Ion
Este Grantley Oliver
Mitchell Ian Vaughan
Shepherd Frank Reginald
Simpson Todd William
Donnelly Victoria
Nortel Networks Limited
Powell William
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