CA1104909A - Enhancing epitaxy and preferred orientation - Google Patents
Enhancing epitaxy and preferred orientationInfo
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- CA1104909A CA1104909A CA356,882A CA356882A CA1104909A CA 1104909 A CA1104909 A CA 1104909A CA 356882 A CA356882 A CA 356882A CA 1104909 A CA1104909 A CA 1104909A
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Abstract
ABSTRACT OF THE DISCLOSURE
An array of oriented artificial relief features or artificial point defects embraced by parallel planes on a substrate surface influence the orientation of solid films during the course of their growth on the substrate surface. There may be multiple sets embraced in generally parallel planes at an angle to each other that is an integral multiple of 30°. Although there are many important technological opportunities for the application of preferred orientation and epitaxial films, particularly in electronic, acoustic and optical devices, with a few notable exceptions, such films have not been consistently obtained with suffi-cient quality or in a sufficient number of combinations and orientations to meet the requirements.
An array of oriented artificial relief features or artificial point defects embraced by parallel planes on a substrate surface influence the orientation of solid films during the course of their growth on the substrate surface. There may be multiple sets embraced in generally parallel planes at an angle to each other that is an integral multiple of 30°. Although there are many important technological opportunities for the application of preferred orientation and epitaxial films, particularly in electronic, acoustic and optical devices, with a few notable exceptions, such films have not been consistently obtained with suffi-cient quality or in a sufficient number of combinations and orientations to meet the requirements.
Description
CH/rc BACKGROUND OF THE INVE~NTION
This invention relates in general to improving the crystallographic quality of solid films grown on the surfaces of solid substrates, and more particularly to enhancing epitaxy or preferred orientation to provide rel~tlvely large area thin ~ilms regularly oriented by means of a practical process.
Much of modern technology makes use of thin solid films on the surfaces of solid substrates. A number of me~hods have been used to deposit such thin films including ~hermal evapora-tion, DC sputtering, rf sputtering, ion beam deposition, chemical va~or deposi-tion, plating, molecular-~e~m deposition and depositicn from the liquid phase.
The structure of thin films can be amorphous (that is, the atoms of the film are not arranged in àny crystalline order), polycry~talline (that is, the film is composed of many small regions, in each of which the atoms are arranged in a regular crystalline order, but the small regions have no mutual alignment of their crystallographic axes), preferred orientation (that is, the film is composed of many small regions, in each of which the atoms are arranged in a regular crystalline order, and one or more of the crystalline axes of the majority of said small regions are parallel), or epitaxial tthat is, the film is pre-dominantly of a single crystallographic orientation). A thin film can be the same material (that is, the same element or compound~ as the substrate, or it can differ in chemical composi-tion from the substrate. If the film is epitaxial, the former is called "homoepitaxy" and the latter "heteroepitaxy''.
In general, techniques for obtaining high quality amorphous and polycrystalline films (particularly metals) axe well developed and well understood. However, techniques for obtaining high quality epitaxial films and films of preferred orientation are severely limited, and only a limited number of combinations of overlayex film and substrate have been achieved.
This invention relates in general to improving the crystallographic quality of solid films grown on the surfaces of solid substrates, and more particularly to enhancing epitaxy or preferred orientation to provide rel~tlvely large area thin ~ilms regularly oriented by means of a practical process.
Much of modern technology makes use of thin solid films on the surfaces of solid substrates. A number of me~hods have been used to deposit such thin films including ~hermal evapora-tion, DC sputtering, rf sputtering, ion beam deposition, chemical va~or deposi-tion, plating, molecular-~e~m deposition and depositicn from the liquid phase.
The structure of thin films can be amorphous (that is, the atoms of the film are not arranged in àny crystalline order), polycry~talline (that is, the film is composed of many small regions, in each of which the atoms are arranged in a regular crystalline order, but the small regions have no mutual alignment of their crystallographic axes), preferred orientation (that is, the film is composed of many small regions, in each of which the atoms are arranged in a regular crystalline order, and one or more of the crystalline axes of the majority of said small regions are parallel), or epitaxial tthat is, the film is pre-dominantly of a single crystallographic orientation). A thin film can be the same material (that is, the same element or compound~ as the substrate, or it can differ in chemical composi-tion from the substrate. If the film is epitaxial, the former is called "homoepitaxy" and the latter "heteroepitaxy''.
In general, techniques for obtaining high quality amorphous and polycrystalline films (particularly metals) axe well developed and well understood. However, techniques for obtaining high quality epitaxial films and films of preferred orientation are severely limited, and only a limited number of combinations of overlayex film and substrate have been achieved.
-2- ~
AA MIT P0~
CH/rc In most cases, films exhibit a high concentration of crystalline defects [S. T. Picraux, G. T. Thomas, '1Correlation of ion channeling and electron microscopy results in the evaluation of heteroepitaxial silicon" J. Appl. Phys. vol 44, pp 594-602 (1973)].
In some cases, high temperatures are required to ac'hieve epitax~
or preferred orientation, and differences in thernal expansion between film and substrate lead to high stresses and sometimes to cracking when samples are cooled to room temperature. Although there are many importan~ technological opportunities for the application of preferred orientation and epitaxial films, particularly in electronic, acoustic, and optical devices, with a ~ew notable exceptions, such films have not been consistently obtained with su~'ficient quality or in a su~icient number of com~inations and orientations to meet the requirements.
Present or conventional methods for obtaining preferred orientation and epitaxial film growth are based on choosing a combination of deposition parameters (such as substrate composi-tion and orientation, deposition method, deposition rate, temperature and pressure) such that the nucleation and growth processes which take place at a microscopic level on the sub-strate surface favor the growth of the desired fi]m or:ientation.
The fundamental difficulty with this approach is that :it is not always possible to control or reproduce all the factors which affect film nucleation and growth. Moreover, this approach limits the number of epitaxial combinations and orientations.
i It is an important object of this invention to overcome the shortcomings of conventional methods for producing epitaxial ;' - and preferred orientation films and directly influence in a controllable manner the nucleation, growth and orientation of films grown on solid surfaces.
It is another object of -~his invention to control the crystallographic orientation of thin films grown on solid CH/rc 12/28/76 surfaces in accordance with the preceding object.
It is a :Eurther obiect of this invention to achieve one or more of the preceding Gbjects while reducing the density and magnitude of defects in crystalline thin films grown on solid surfaces.
- It is a further object of this invention to achieve one or more of the preceding objects while obtaining epitaxial or preferred orientation films at moderate temperatures and there-by avoid stresses induced by differences in thermal expansion between film and substrate.
This invention results from the discovery that the phenomena of nuclcation, growth, a~d changes in crystallographic orientation that occur during the early stages of film formation on solid surfaces can be influenced and controlled by means of arti~
ficial surface relief structures and point defécts. It is well known that naturally occurring defects such as steps or point defects on crystal surfaces can act as nucleation sites for deposited material. Some indication of the effects of arrAys of point defects on the nucleation and growth of epitaxial films can be found in the work of Distler et al LG. I. Distler, "Epitaxy as a Matrix Replicating Process", Thin Solid Films, vol.32, pp. 157-162 (1976); G. I. Distler, V. P. Vlasor, V. M. Kaneosky, "Orientational and Long Range Effects in Epitaxy", Thin Solid Films, vol. 33, pp. 287-300 (1976)] whb observed that naturally occurring point defects on solid surfaces act as nucleation sites.
Distler et al further suggest that the point defects on a surface naturally occur in some form of matrix or lattice and that the orientational effects in epitaxy and crystallization in general are due to the existence of the lattice of point defects.
" .
SU~M`ARY QF THE INVENTION
According to the lnvention intentionally create at pre-determined locations on a solid surface an array of artificial surface relief steps or artificial point defects and thereby control in a predetermined way the process of film formation and growth.
rrhe creation of a regular array of surface relief steps or point defects on a solid surface in order to enhance the crystallographic quality of thin solid films grown on said surface is in direct contradic-tion to conventional methods of thin film growth. Conventional methods attemp-t to remove, to the fullest extent possible, any natural surface relief steps or point defects. This is usually done by polishing or etch-ing the surface prior to film growth.
I~le invention includes a process of preparing an array of artiEicial defects such as surface relief steps or point defects at predetermined locations on a solid surface, and a process for depositing material onto the solid surface in such a way that the crystallographic orientation of the deposited material is controlled by the array of surface relief steps or point defects, more particularly, by the geo-metric arran~ement of ad~acent defects~ :
The geometric pattern of the surface relief struc-ture or array of point defects that will be effective for a given combination of overlayer film and substrate and a given deposition method depends on the exact mechanisms of nuclea- .
tion and growth operable for that combination and deposition method~ r~he geometric pattern will in general ~e a simple grating or grid with repeating elements spaced by distances of the order of 1/~ ~m or less, although in some cases, a re-peat distance of 1 ~m is adequater The depth of -the surface : relief struc-ture can vary from less than one nanometer to of the order of one micrometer~ ~referably, there are sets of steps and/or point defects with each set embraced by a plane generally perpendicular to the substra-te surface ancL generally parallel to a plane embracing another set with the angle between intersecting planes being preferably an integral multiple of 30 or ~/6 radians.
According to a further broad aspect of the present invention, there is provided a method of enhancing epitaxy and preferred orientation, which method includes the steps of intentionally forming at predetermined locations a plurality of artificial defects at the surface of an amorphous solid substrate. The artificial defec-ts are selected from the group consisting of (1) artificial point defects and (2) artificial surface relief structure. Thereafter, a film is deposited on the surface to form a substantially epitaxial or preferred orientation layer in the film hav:ing crystallo-graphic orientation controlled by the geometric arrangement of adjacent artificial defects.
According to a further broad aspect of the present invention there is provided a device comprising a solid substrate having a surface with artificial defects selected from the group consisting of (1) artificial point defects and (2) artificiaL relief structure. A film is provided on the surface including a substantially preferred orientation layer having crystallographic orientation influenced by adjacent ones of the artificial defects. The separation between adjacent ones of the artificial defects is sufficiently small so that both artificial defects in a pair of adjacent ones contribute to influencing the crystallographic orientation~
~ umerous other features, objects and advantages of the invention will become apparent from ~' ' ,: , ,. .. . ~ .
AA MIT ~6 CH/rc the following specification when read in connection with the accompanying drawing in which:
BRIEF DESCRIPTION OF T-IIE DR~WING
FIG. 1 is a fragmentary sectional view of a solid coated with a thin film;
FIG. 2 is a com~ined block-sect:ional view illustrating the use of soft x-rays for forming a cont:rolled relief pattern in a solid substrate according ta the invention;
FIG. 3 is a sectional view of the relief pa~tern thus formed;
FIG. ~ is a sectional view illustrating the relief , s-tructure following etching;
; FIG. 5 is a combined block-pictorial representation of ~ means or depositing a thin layer on the solid substrate with ion beam sputtering; and FIG. 6 is a greatly enlarged perspective view of a solid substrate formed with regularly spaced steps according to .,~
the invention suitable ~or receiving an épitaxial or preferred orientatlon layer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS -With reference now to the drawing and ~ore particu-larly FIGS. 1-4, there is illustrated a method for creating a relief structure on the surface of a solid according to the invention. The solid 1 is coated with a radiation sensitive polymer film 2 (commonly called a "resist") as seen in the fragmentary sectional view of FIG. 1. An example of such a film would be polymethyl methacryl.ate. This film may then be exposed by x-ray lithography (Patent 3,743,842 (July 3, 1973) "X-ray Lithographic Apparatus and Process" H. I. Smith, D. L. Spears, E. Stern) as depicted in FIG. 2. The mask 3 consists of a membrane 4 which i9 relatively transparent to x-rays7 and an absorber 5, which is formed into a pattern of periodic or quasi-periodic elements, such as a grating or grid. Soft: x-rays 6 AA MIT Pu~
CH/rc 12/28/7~
from source 7 pass through the mask 3, thereby casting a shadow of the absorber pattern 5 on the radiation sensitive polymer 2.
After exposure, a reliPf pattern is created in the radiation sensitive polymer by a development step. In the case of polymethyl methacrylate, development may be accomplished, for example in a solution of 40% methyl isolutyl ketane and 60%
isopropyl alcohol, which removes those regions of the polymer directly exposed to the soft x-ray radiat:ion. Those regions of the polymer 2 which were protected from the full intensity of the x-ray radiation by the obstruction of absorber pattern 5 remain undissolved and hence stand in relief, as depicted in FIG. 3.
Many other radiation sensitive polymers and developing methods could be substituted within the principlesof the invention.
The pattern can be exposed in the radiation sensitive polymer film by a number of other methods including photolithog-raphy, electron beam lithography, and holographic methods. X-ray lithography is particularly well suited because of its capability of exposing patterns with linewidths of lOOOA and less with sharp vertical sidewalls. It is estimated that a resolution of 50A is possible wi~h x-r~y lithography, using the Carbon K x-ray at 44.7A wavelength.
Polymer relief structures can also be created by in-site polymerization.
Following creation of the polymer rellef structure 8, the solid substrate 1 is etched and the polymer is removed, thereby leaving a relief structure 9 on the surface of the solid as seen in FIG. 4. The method of etching depends on the chemical nature of the solid and the resistance of the poly~er to various etching environments. For example, with PMMA as the polymer relief pattern, reIief structures with sharp vPrtical sidewalls can be etched into SiO2 substrates by a reactive ion etching process.
While steep ve~tical sidewalls are preferred, the principles of the invention are applicable to discont:inuities _7_ .. . . .. . .
.
~ ~4~
formed by sloping sidewalls, including those formed by under-cutting. Alternatively, ion beam etching, wet chemical etch-ing or gaseous plasma etching could be used for etching.
Another approach to creating a relief structure on sio2 is to deposit sio2 or SiO, or a mixture of the two, over the polymer relief structure, and then dissolve the polymer in a suitable organic solvent. This leaves a relief structure of the sio2, sio or mixture of the two on the sur-face~ To convert the ~-relief structure to a high quality sio2, the substrate can be baked in an oxygen oven at or near 1000C.
An array of artificial point defects can be created on the substrate surface by exposing it to radiation in some pattern. For example, a high energy finely focused electron beam can be scanned in an appropriate pattern ovex the sample surface creating lines of point defects. Alternatively, ion bombardment through a mask could be employed to create a pat-tern of defects. High energy photons could also be used.
Following the creation of the artificial relief structure or array of de~ects on the solid surface, material is deposited on top of it to form a thin film. The relief structure or array of defects has the effect of controlling the nucleation and/or growth of the film, thereby resulting in a film with a determined crystallographic orientation and low defect density. Many methods can be used to deposit thin film material on the solid with surface relief structures or array of point defects. These include evaporation, rf sputtering, DC sputtering, ion bearn sputtering, chemical vapor deposition, molecular beam deposition, plating and deposition from the liquid phase. Ion beam sputtering as depicted in ~IG. S has been used, and the material deposited was germanium on sio2 substrate, a substance of amorphous material. An ion source 10 emits an ion beam 11 which impinges , ~
on target 12 of the material to be deposited. The material 13 sputtered from the target 12 deposits on the substrate 1 with surface relief structure 9.
While the invention is useful for making devices w.ith thin films 0-3 microns thick, the invention is also use-ful for growing larger crystals. The initial thin film may then function as a seed and larger crystals grown using con-ventional crystal growing techniques~
Referring to FIG. 6, there is shown a greatly magni-fied perspective view of a substrate regularly stepped accord-ing to the invention ready for receiving an epitaxial or pre-ferred orientation surface layer. There are sets of steps each embraced by a plane parallel to the plane embracing another set of steps. Intersecting embracing planes intersect at an angle of 90 or ~/2 radians, an integral multiple of 30 or ~/6 radians~ The planes might also intersect at an angle of 60 or ~/3 radians, also an integral multiple of 30 or ~/6 radians. It is also preferred that separation between adjacent parallel embracing planes be less than 1 micronr typically being 500 Angstroms as shown in FIG. 6 or 1/20 micron. The artificial step or point defect depth is prefer- ~:
ably within the range of 1 atom to 1/2 micron. . `
There has been described novel structure and tech- :
niques for providing epitaxial and preferred orientation films of relatively large area with an economically practical repeat-able process, It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific structure and techniques disclosed herein without departing from the inventive concepts. Consequently, the in- :
vention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed _ 9 _ rl~ :
by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of -the appended claims.
This is a division of Canadian patent application serial number 298,810 filed March 13, 1978.
AA MIT P0~
CH/rc In most cases, films exhibit a high concentration of crystalline defects [S. T. Picraux, G. T. Thomas, '1Correlation of ion channeling and electron microscopy results in the evaluation of heteroepitaxial silicon" J. Appl. Phys. vol 44, pp 594-602 (1973)].
In some cases, high temperatures are required to ac'hieve epitax~
or preferred orientation, and differences in thernal expansion between film and substrate lead to high stresses and sometimes to cracking when samples are cooled to room temperature. Although there are many importan~ technological opportunities for the application of preferred orientation and epitaxial films, particularly in electronic, acoustic, and optical devices, with a ~ew notable exceptions, such films have not been consistently obtained with su~'ficient quality or in a su~icient number of com~inations and orientations to meet the requirements.
Present or conventional methods for obtaining preferred orientation and epitaxial film growth are based on choosing a combination of deposition parameters (such as substrate composi-tion and orientation, deposition method, deposition rate, temperature and pressure) such that the nucleation and growth processes which take place at a microscopic level on the sub-strate surface favor the growth of the desired fi]m or:ientation.
The fundamental difficulty with this approach is that :it is not always possible to control or reproduce all the factors which affect film nucleation and growth. Moreover, this approach limits the number of epitaxial combinations and orientations.
i It is an important object of this invention to overcome the shortcomings of conventional methods for producing epitaxial ;' - and preferred orientation films and directly influence in a controllable manner the nucleation, growth and orientation of films grown on solid surfaces.
It is another object of -~his invention to control the crystallographic orientation of thin films grown on solid CH/rc 12/28/76 surfaces in accordance with the preceding object.
It is a :Eurther obiect of this invention to achieve one or more of the preceding Gbjects while reducing the density and magnitude of defects in crystalline thin films grown on solid surfaces.
- It is a further object of this invention to achieve one or more of the preceding objects while obtaining epitaxial or preferred orientation films at moderate temperatures and there-by avoid stresses induced by differences in thermal expansion between film and substrate.
This invention results from the discovery that the phenomena of nuclcation, growth, a~d changes in crystallographic orientation that occur during the early stages of film formation on solid surfaces can be influenced and controlled by means of arti~
ficial surface relief structures and point defécts. It is well known that naturally occurring defects such as steps or point defects on crystal surfaces can act as nucleation sites for deposited material. Some indication of the effects of arrAys of point defects on the nucleation and growth of epitaxial films can be found in the work of Distler et al LG. I. Distler, "Epitaxy as a Matrix Replicating Process", Thin Solid Films, vol.32, pp. 157-162 (1976); G. I. Distler, V. P. Vlasor, V. M. Kaneosky, "Orientational and Long Range Effects in Epitaxy", Thin Solid Films, vol. 33, pp. 287-300 (1976)] whb observed that naturally occurring point defects on solid surfaces act as nucleation sites.
Distler et al further suggest that the point defects on a surface naturally occur in some form of matrix or lattice and that the orientational effects in epitaxy and crystallization in general are due to the existence of the lattice of point defects.
" .
SU~M`ARY QF THE INVENTION
According to the lnvention intentionally create at pre-determined locations on a solid surface an array of artificial surface relief steps or artificial point defects and thereby control in a predetermined way the process of film formation and growth.
rrhe creation of a regular array of surface relief steps or point defects on a solid surface in order to enhance the crystallographic quality of thin solid films grown on said surface is in direct contradic-tion to conventional methods of thin film growth. Conventional methods attemp-t to remove, to the fullest extent possible, any natural surface relief steps or point defects. This is usually done by polishing or etch-ing the surface prior to film growth.
I~le invention includes a process of preparing an array of artiEicial defects such as surface relief steps or point defects at predetermined locations on a solid surface, and a process for depositing material onto the solid surface in such a way that the crystallographic orientation of the deposited material is controlled by the array of surface relief steps or point defects, more particularly, by the geo-metric arran~ement of ad~acent defects~ :
The geometric pattern of the surface relief struc-ture or array of point defects that will be effective for a given combination of overlayer film and substrate and a given deposition method depends on the exact mechanisms of nuclea- .
tion and growth operable for that combination and deposition method~ r~he geometric pattern will in general ~e a simple grating or grid with repeating elements spaced by distances of the order of 1/~ ~m or less, although in some cases, a re-peat distance of 1 ~m is adequater The depth of -the surface : relief struc-ture can vary from less than one nanometer to of the order of one micrometer~ ~referably, there are sets of steps and/or point defects with each set embraced by a plane generally perpendicular to the substra-te surface ancL generally parallel to a plane embracing another set with the angle between intersecting planes being preferably an integral multiple of 30 or ~/6 radians.
According to a further broad aspect of the present invention, there is provided a method of enhancing epitaxy and preferred orientation, which method includes the steps of intentionally forming at predetermined locations a plurality of artificial defects at the surface of an amorphous solid substrate. The artificial defec-ts are selected from the group consisting of (1) artificial point defects and (2) artificial surface relief structure. Thereafter, a film is deposited on the surface to form a substantially epitaxial or preferred orientation layer in the film hav:ing crystallo-graphic orientation controlled by the geometric arrangement of adjacent artificial defects.
According to a further broad aspect of the present invention there is provided a device comprising a solid substrate having a surface with artificial defects selected from the group consisting of (1) artificial point defects and (2) artificiaL relief structure. A film is provided on the surface including a substantially preferred orientation layer having crystallographic orientation influenced by adjacent ones of the artificial defects. The separation between adjacent ones of the artificial defects is sufficiently small so that both artificial defects in a pair of adjacent ones contribute to influencing the crystallographic orientation~
~ umerous other features, objects and advantages of the invention will become apparent from ~' ' ,: , ,. .. . ~ .
AA MIT ~6 CH/rc the following specification when read in connection with the accompanying drawing in which:
BRIEF DESCRIPTION OF T-IIE DR~WING
FIG. 1 is a fragmentary sectional view of a solid coated with a thin film;
FIG. 2 is a com~ined block-sect:ional view illustrating the use of soft x-rays for forming a cont:rolled relief pattern in a solid substrate according ta the invention;
FIG. 3 is a sectional view of the relief pa~tern thus formed;
FIG. ~ is a sectional view illustrating the relief , s-tructure following etching;
; FIG. 5 is a combined block-pictorial representation of ~ means or depositing a thin layer on the solid substrate with ion beam sputtering; and FIG. 6 is a greatly enlarged perspective view of a solid substrate formed with regularly spaced steps according to .,~
the invention suitable ~or receiving an épitaxial or preferred orientatlon layer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS -With reference now to the drawing and ~ore particu-larly FIGS. 1-4, there is illustrated a method for creating a relief structure on the surface of a solid according to the invention. The solid 1 is coated with a radiation sensitive polymer film 2 (commonly called a "resist") as seen in the fragmentary sectional view of FIG. 1. An example of such a film would be polymethyl methacryl.ate. This film may then be exposed by x-ray lithography (Patent 3,743,842 (July 3, 1973) "X-ray Lithographic Apparatus and Process" H. I. Smith, D. L. Spears, E. Stern) as depicted in FIG. 2. The mask 3 consists of a membrane 4 which i9 relatively transparent to x-rays7 and an absorber 5, which is formed into a pattern of periodic or quasi-periodic elements, such as a grating or grid. Soft: x-rays 6 AA MIT Pu~
CH/rc 12/28/7~
from source 7 pass through the mask 3, thereby casting a shadow of the absorber pattern 5 on the radiation sensitive polymer 2.
After exposure, a reliPf pattern is created in the radiation sensitive polymer by a development step. In the case of polymethyl methacrylate, development may be accomplished, for example in a solution of 40% methyl isolutyl ketane and 60%
isopropyl alcohol, which removes those regions of the polymer directly exposed to the soft x-ray radiat:ion. Those regions of the polymer 2 which were protected from the full intensity of the x-ray radiation by the obstruction of absorber pattern 5 remain undissolved and hence stand in relief, as depicted in FIG. 3.
Many other radiation sensitive polymers and developing methods could be substituted within the principlesof the invention.
The pattern can be exposed in the radiation sensitive polymer film by a number of other methods including photolithog-raphy, electron beam lithography, and holographic methods. X-ray lithography is particularly well suited because of its capability of exposing patterns with linewidths of lOOOA and less with sharp vertical sidewalls. It is estimated that a resolution of 50A is possible wi~h x-r~y lithography, using the Carbon K x-ray at 44.7A wavelength.
Polymer relief structures can also be created by in-site polymerization.
Following creation of the polymer rellef structure 8, the solid substrate 1 is etched and the polymer is removed, thereby leaving a relief structure 9 on the surface of the solid as seen in FIG. 4. The method of etching depends on the chemical nature of the solid and the resistance of the poly~er to various etching environments. For example, with PMMA as the polymer relief pattern, reIief structures with sharp vPrtical sidewalls can be etched into SiO2 substrates by a reactive ion etching process.
While steep ve~tical sidewalls are preferred, the principles of the invention are applicable to discont:inuities _7_ .. . . .. . .
.
~ ~4~
formed by sloping sidewalls, including those formed by under-cutting. Alternatively, ion beam etching, wet chemical etch-ing or gaseous plasma etching could be used for etching.
Another approach to creating a relief structure on sio2 is to deposit sio2 or SiO, or a mixture of the two, over the polymer relief structure, and then dissolve the polymer in a suitable organic solvent. This leaves a relief structure of the sio2, sio or mixture of the two on the sur-face~ To convert the ~-relief structure to a high quality sio2, the substrate can be baked in an oxygen oven at or near 1000C.
An array of artificial point defects can be created on the substrate surface by exposing it to radiation in some pattern. For example, a high energy finely focused electron beam can be scanned in an appropriate pattern ovex the sample surface creating lines of point defects. Alternatively, ion bombardment through a mask could be employed to create a pat-tern of defects. High energy photons could also be used.
Following the creation of the artificial relief structure or array of de~ects on the solid surface, material is deposited on top of it to form a thin film. The relief structure or array of defects has the effect of controlling the nucleation and/or growth of the film, thereby resulting in a film with a determined crystallographic orientation and low defect density. Many methods can be used to deposit thin film material on the solid with surface relief structures or array of point defects. These include evaporation, rf sputtering, DC sputtering, ion bearn sputtering, chemical vapor deposition, molecular beam deposition, plating and deposition from the liquid phase. Ion beam sputtering as depicted in ~IG. S has been used, and the material deposited was germanium on sio2 substrate, a substance of amorphous material. An ion source 10 emits an ion beam 11 which impinges , ~
on target 12 of the material to be deposited. The material 13 sputtered from the target 12 deposits on the substrate 1 with surface relief structure 9.
While the invention is useful for making devices w.ith thin films 0-3 microns thick, the invention is also use-ful for growing larger crystals. The initial thin film may then function as a seed and larger crystals grown using con-ventional crystal growing techniques~
Referring to FIG. 6, there is shown a greatly magni-fied perspective view of a substrate regularly stepped accord-ing to the invention ready for receiving an epitaxial or pre-ferred orientation surface layer. There are sets of steps each embraced by a plane parallel to the plane embracing another set of steps. Intersecting embracing planes intersect at an angle of 90 or ~/2 radians, an integral multiple of 30 or ~/6 radians~ The planes might also intersect at an angle of 60 or ~/3 radians, also an integral multiple of 30 or ~/6 radians. It is also preferred that separation between adjacent parallel embracing planes be less than 1 micronr typically being 500 Angstroms as shown in FIG. 6 or 1/20 micron. The artificial step or point defect depth is prefer- ~:
ably within the range of 1 atom to 1/2 micron. . `
There has been described novel structure and tech- :
niques for providing epitaxial and preferred orientation films of relatively large area with an economically practical repeat-able process, It is evident that those skilled in the art may now make numerous uses and modifications of and departures from the specific structure and techniques disclosed herein without departing from the inventive concepts. Consequently, the in- :
vention is to be construed as embracing each and every novel feature and novel combination of features present in or possessed _ 9 _ rl~ :
by the apparatus and techniques herein disclosed and limited solely by the spirit and scope of -the appended claims.
This is a division of Canadian patent application serial number 298,810 filed March 13, 1978.
Claims (29)
1. A method of enhancing epitaxy and preferred orienta-tion which method includes the steps of intentionally forming at predetermined locations a plurality of artificial defects at the surface of an amorphous solid substrate, said artifi-cial defects being selected from the group consisting of (1) artificial point defects and (2) artificial surface relief structure, and thereafter depositing a film on said surface to form a substantially epitaxial or preferred orientation layer in said film having crystallographic orientation controlled by the geometric arrangement of adjacent artificial defects.
2. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 1 and further including the step of maintaining the separation between rows of artificial defects substantially equal.
3. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 1 and further including the step of establishing said artificial defects in intersecting rows.
4. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 3 and further including the step of maintaining the separation between parallel rows substan-tially equal.
5. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 1 and further including the step of forming artificial point defects among said artificial defects.
6. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 1 and further including the step of forming artificial steps among said artificial defects.
7. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 6 and further including the step of spacing said artificial steps substantially equidistant.
8. A method for enhancing epitaxy and preferred orienta-tion in accordance with claim 6 and further including the step of forming artificial steps that are substantially orthogonal to the first-mentioned artificial steps.
9. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 1 and further including the step of forming said artificial defects with the dimension of each defect in a direction perpendicular to the substrate surface being within the range of 1 atom to 1/2 micron.
10. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 3 and further including the step of establishing said artificial defects in rows that intersect at an angle that is an integral multiple of .pi./6 radians.
11. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 3 and further including the step of forming artificial point defects among said artificial defects.
12. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 3 and further including the step of forming artificial steps among said artificial defects.
13. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 6 wherein said steps have substantially vertical walls.
14. A method of enhancing epitaxy and preferred orienta-tion in accordance with claim 6 wherein said steps have sloping walls.
15. A method of enhancing epitaxy and preferred orienta-tion which method includes the steps of intentionally forming at predetermined locations a plurality of artificial defects at the surface of anamorphous solid substrate, said artificial defects being selected from the group consisting of (1) arti-ficial point defects and (2) artificial surface relief struc-ture, and thereafter depositing a film on said surface to form a substantially preferred orientation layer in said film having crystallographic orientation influenced by the geometric arrangement of adjacent ones of said artificial defects, the separation between adjacent ones of said artificial defects being sufficiently small so that both artificial defects in a pair of adjacent ones contribute to influencing said crystallo-graphic orientation.
16. A method of enhancing epitaxy and preferred orienta-tion which method includes the steps of intentionally forming at predetermined locations a plurality of artificial defects at the surface of an amorphous solid substrate, said artificial defects being selected from the group consisting of (1) artificial point defects and (2) artificial surface relief structure, and thereafter depositing a film on said surface to form a substantially preferred orientation layer in said film having crystallographic orientation influenced by the geometric arrangement of adjacent ones of said artificial defects.
17. A method of enhancing preferred orientation in accordance with claim 15 and further including subjecting the film and substrate to conditions for enhancing the orienting influence of said artificial defects.
18. A method of enhancing preferred orientation in accordance with claim 17 wherein said conditions comprises environmental conditions.
19. A method of enhancing preferred orientation in accordance with claim 18 wherein said conditions include conditions selected from the group consisting of (1) placing said film and substrate in a plating solution, (2) placing said film and substrate in an environment of reactive gases at elevated temperatures, (3) placing said film and substrate within a solvent medium, and (4) placing said film and substrate in a solution that invades the said film, softens it, or otherwise enhances the mobility of molecules in the film.
20. A method of enhancing preferred orientation in accordance with claim 17 wherein said conditions include delivering energy to said film.
21. A method of enhancing preferred orientation in accordance with claim 20 and further including the step of subjecting the film to elevated temperature.
22. A method of enhancing preferred orientation in accordance with claim 16 and further including subjecting the film and substrate to conditions for enhancing the orien-ting influence of said artificial defects.
23. A method of enhancing preferred orientation in accordance with claim 22 wherein said conditions comprise environmental conditions.
24. A method of enhancing preferred orientation in accordance with claim 23 wherein said conditions include conditions selected from the group consisting of (1) placing said film and substrate in a plating solution, (2) placing said film and substrate in an environment of reactive gases at elevated temperatures, (3) placing said film and substrate within a solvent medium, and (4) placing said film and substrate in a solution that invades the said film, softens it, or otherwise enhances the mobility of molecules in the film.
25. A method of enhancing preferred orientation in accordance with claim 22 wherein said conditions include delivering energy to said film.
26. A method of enhancing preferred orientation in accordance with claim 25 and further including the step of subjecting the film to elevated temperature.
27. A method in accordance with claim 15 wherein said artificial surface relief structure comprises structure having a preselected shape bounded by substantially planar facets.
28. A method of enhancing preferred orientation in accordance with claim 15 wherein said artificial defects comprise material different from that of said substrate.
29. A device comprising a solid substrate having a surface with artificial defects selected from the group consisting of (1) artificial point defects and (2) artificial relief structure, and a film on said surface including a substantially preferred orientation layer having crystallo-graphic orientation influenced by adjacent ones of said artificial defects, the separation between adjacent ones of said artificial defects being sufficiently small so that both artificial defects in a pair of adjacent ones contribute to influencing said crystallographic orientation.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA356,882A CA1104909A (en) | 1978-03-13 | 1980-07-23 | Enhancing epitaxy and preferred orientation |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA298,810A CA1102223A (en) | 1978-03-13 | 1978-03-13 | Enhancing epitaxy and preferred orientation |
| CA356,882A CA1104909A (en) | 1978-03-13 | 1980-07-23 | Enhancing epitaxy and preferred orientation |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1104909A true CA1104909A (en) | 1981-07-14 |
Family
ID=25668666
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA356,882A Expired CA1104909A (en) | 1978-03-13 | 1980-07-23 | Enhancing epitaxy and preferred orientation |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1104909A (en) |
-
1980
- 1980-07-23 CA CA356,882A patent/CA1104909A/en not_active Expired
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