CA1249071A - Direct writing of refractory metal lines for use in integrated circuit devices - Google Patents
Direct writing of refractory metal lines for use in integrated circuit devicesInfo
- Publication number
- CA1249071A CA1249071A CA000521384A CA521384A CA1249071A CA 1249071 A CA1249071 A CA 1249071A CA 000521384 A CA000521384 A CA 000521384A CA 521384 A CA521384 A CA 521384A CA 1249071 A CA1249071 A CA 1249071A
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- CA
- Canada
- Prior art keywords
- silicon
- refractory metal
- approximately
- atmosphere
- present
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/26—Bombardment with radiation
- H01L21/263—Bombardment with radiation with high-energy radiation
- H01L21/268—Bombardment with radiation with high-energy radiation using electromagnetic radiation, e.g. laser radiation
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
- H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
- H01L21/32051—Deposition of metallic or metal-silicide layers
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
- H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
- H01L21/768—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics
- H01L21/76838—Applying interconnections to be used for carrying current between separate components within a device comprising conductors and dielectrics characterised by the formation and the after-treatment of the conductors
- H01L21/76877—Filling of holes, grooves or trenches, e.g. vias, with conductive material
- H01L21/76879—Filling of holes, grooves or trenches, e.g. vias, with conductive material by selective deposition of conductive material in the vias, e.g. selective C.V.D. on semiconductor material, plating
Abstract
DIRECT WRITING OF REFRACTORY METAL LINES FOR USE
IN INTEGRATED CIRCUIT DEVICES
ABSTRACT OF THE DISCLOSURE
Laser beams are employed for direct writing of micron-sized refractory metal lines at a speed of several centimeters per second on silicon surfaces.
Tungsten metal lines are selectfully deposited on silicon surfaces using laser induced chemical vapor deposition. Smooth tungsten lines with a length of a few centimeters and with a line width of between 2 and 15 microns are obtainable on silicon surfaces by employing argon lasers with focused spot sizes of approximately 20 microns. The process is particularly useful in the construction of custom integrated circuits, in the placement of discretionary conductors in integrated circuits, in mask correction, and in the correction of defects in large scale integrated circuitry and liquid crystal displays.
IN INTEGRATED CIRCUIT DEVICES
ABSTRACT OF THE DISCLOSURE
Laser beams are employed for direct writing of micron-sized refractory metal lines at a speed of several centimeters per second on silicon surfaces.
Tungsten metal lines are selectfully deposited on silicon surfaces using laser induced chemical vapor deposition. Smooth tungsten lines with a length of a few centimeters and with a line width of between 2 and 15 microns are obtainable on silicon surfaces by employing argon lasers with focused spot sizes of approximately 20 microns. The process is particularly useful in the construction of custom integrated circuits, in the placement of discretionary conductors in integrated circuits, in mask correction, and in the correction of defects in large scale integrated circuitry and liquid crystal displays.
Description
RD 16,146 DIRECT WRITING OE_REFRACTORY METAL LINES FOR USE
IN INTEGRATED CIRCUIT DEVICES
The present invention is generally re]ated to a method for direct writing of micron-size, refractory metal lines on a silicon surface at a speed of several cm/sec. More particularly, the present invention relates to laser induced chemical vapor deposition of tungsten on silicon surfaces~ The method of the present invention is particularly useful for post-process formation of conductive interconnection lines in integrated circuits.
In the fabrication of large scale and very large scale integrated circuits, it is often desirable to be able to make discretionary electrical connections between various parts of the substrate.
There are several reasons for performing this operation. For example, in yate arrays, customization is generally effected by severing interconnection lines. This may be done with a focused laser or electrically by passing a sufficiently large current through a fusable link. However, it would also be desirable to be able to customize gate arrays and the like through the formation of conductive links rather than by cutting them. Likewisej in the fabrication of liquid crystal display devices, yield problems can result, partlcularly in such displays which are large RD 16 ,146 and/ or matrix addressed. DefectS in such devices o~ten take the form oE open connections along gate lines or data lines. In such cases, whole lines of the display may be rendered non-functional. More generally~ conductive lines which exhibit step profiles as they cross over other lines, are particularly susceptible to open circuit defects. It is therefore seen that in certain cases it would be very desirable to provide a customized conductive interconnection which bridges the broken or degraded circuit connection. Likewise, in the manufacture of very large scale integrated circuit chips (VLSI), fabrication yields are not always as high as desired.
Some of the defects that occur in such processing may be corrected by the inclusion of micron sized metal connecting lines added in a customized fashion to correct discovered defects, particularly open circuit defects. In short, interest in direct writing of metal structures using devices such as laser beams has been driven by the impetus Eor providing discretionary interconnections in VLSI and packaging applications.
Other applications include water or mask fault correction, yield enhancements, localized masking, and coating~ and fabrication of customery circuits.
Ehrlich and Tsao have reported the fabrication of poly-silicon stxuctures having submicron dimensions by means of a pyrolytic process employing SiC14 vapor and hydrogen vapor using an argon laser. See ~Applied Physics Letters"~
30 Volume 44, page 267 (1984). Efforts in other directions have employed thermal chemical vapor deposition systems in which hydrogen is used to form tungsten films in accordance with the following reduction reaction:
WE'6 + 3H2 -~ W + 6HF (1) ~0 RD 16,146 The reduction mechanism of tungsten hexa-fluoride (WF6) in the presence of hydrogen has been studied extensively. See J. F. Berkeley, A. Brenner~
and W. E. Reed in "Journal of Electrochemical Society"
Volume 114~ page 701 (1967). See also W. A~ Bryant in "Journal of Electrochemical Society" Volume 125, page 153~ (1978). In these efforts, hydrogen has been employed as a gas for the reduction of tungsten hexafluoride. However, the utili~ation of hydrogen as a reducing atmosphere produces certain disadvantages in laser induced direct writing of refractory metal lines on silicon surfaces. For example, because a gas phase reaction is involved in the reaction kinetics, the resolution could be limited at high writing speeds. While the precise reasons for all of the reaction phenomena that occur in hydrogen reduction reactions of this type are not well understood, it is generally thought that participation of the hydrogen in the reaction rather than direct surface participation is a factor in limiting the resolution.
Moreover, utilization of hydrogen reduction with lasers generally does not result in the formation of metal lines with a surface morphology as smooth as that produced using only surface reduction reaction.
Summary of the Invention -In accordance with a preferred embodiment of the present invention, a process for depositing refractory metal on a silicon surface compri~ses the steps of disposing the silicon surface in an atmosphere compressing a gaseous refractory metal compound such as tungsten hexafluoride. The silicon surface is then heated in this atmosphere with a focused beam of electromagnetic radiation such as a laser. The heating occurs along a prescribed path at a temperature which is sufficient to heat the surface so as to initiate a surface reduction reaction in RD 16,146 which refractory metal is reduced and deposited on or in place of the silicon sur~ace. In a preferred embodiment of the present invention, smooth tungsten lines with lengths of a few centimeters and with line widths of between about 2 and about 15 microns, are deposited on a silicon surface using an argon laser with a power of about 50 milliwatts and with a focused spot size of approximately 20 microns (full-width, half-maximum). It is noted that the deposition of the present invention may be performed on a crystalline, polycrystalline, or amorphous silicon surfaceO The processing is preferably performed in a vacuum chamber with a partial gas pressure of WF6 in the range of from 1 to 100 torr in a buffer gas of argon at a partial pressure of about 1 a-tmosphere. The deposited refractory metal layer ls typically between approximately 100 and 1000 angstroms thick. In the process of the present invention, the silicon surface itself acts as the reducing ayent for the metal
IN INTEGRATED CIRCUIT DEVICES
The present invention is generally re]ated to a method for direct writing of micron-size, refractory metal lines on a silicon surface at a speed of several cm/sec. More particularly, the present invention relates to laser induced chemical vapor deposition of tungsten on silicon surfaces~ The method of the present invention is particularly useful for post-process formation of conductive interconnection lines in integrated circuits.
In the fabrication of large scale and very large scale integrated circuits, it is often desirable to be able to make discretionary electrical connections between various parts of the substrate.
There are several reasons for performing this operation. For example, in yate arrays, customization is generally effected by severing interconnection lines. This may be done with a focused laser or electrically by passing a sufficiently large current through a fusable link. However, it would also be desirable to be able to customize gate arrays and the like through the formation of conductive links rather than by cutting them. Likewisej in the fabrication of liquid crystal display devices, yield problems can result, partlcularly in such displays which are large RD 16 ,146 and/ or matrix addressed. DefectS in such devices o~ten take the form oE open connections along gate lines or data lines. In such cases, whole lines of the display may be rendered non-functional. More generally~ conductive lines which exhibit step profiles as they cross over other lines, are particularly susceptible to open circuit defects. It is therefore seen that in certain cases it would be very desirable to provide a customized conductive interconnection which bridges the broken or degraded circuit connection. Likewise, in the manufacture of very large scale integrated circuit chips (VLSI), fabrication yields are not always as high as desired.
Some of the defects that occur in such processing may be corrected by the inclusion of micron sized metal connecting lines added in a customized fashion to correct discovered defects, particularly open circuit defects. In short, interest in direct writing of metal structures using devices such as laser beams has been driven by the impetus Eor providing discretionary interconnections in VLSI and packaging applications.
Other applications include water or mask fault correction, yield enhancements, localized masking, and coating~ and fabrication of customery circuits.
Ehrlich and Tsao have reported the fabrication of poly-silicon stxuctures having submicron dimensions by means of a pyrolytic process employing SiC14 vapor and hydrogen vapor using an argon laser. See ~Applied Physics Letters"~
30 Volume 44, page 267 (1984). Efforts in other directions have employed thermal chemical vapor deposition systems in which hydrogen is used to form tungsten films in accordance with the following reduction reaction:
WE'6 + 3H2 -~ W + 6HF (1) ~0 RD 16,146 The reduction mechanism of tungsten hexa-fluoride (WF6) in the presence of hydrogen has been studied extensively. See J. F. Berkeley, A. Brenner~
and W. E. Reed in "Journal of Electrochemical Society"
Volume 114~ page 701 (1967). See also W. A~ Bryant in "Journal of Electrochemical Society" Volume 125, page 153~ (1978). In these efforts, hydrogen has been employed as a gas for the reduction of tungsten hexafluoride. However, the utili~ation of hydrogen as a reducing atmosphere produces certain disadvantages in laser induced direct writing of refractory metal lines on silicon surfaces. For example, because a gas phase reaction is involved in the reaction kinetics, the resolution could be limited at high writing speeds. While the precise reasons for all of the reaction phenomena that occur in hydrogen reduction reactions of this type are not well understood, it is generally thought that participation of the hydrogen in the reaction rather than direct surface participation is a factor in limiting the resolution.
Moreover, utilization of hydrogen reduction with lasers generally does not result in the formation of metal lines with a surface morphology as smooth as that produced using only surface reduction reaction.
Summary of the Invention -In accordance with a preferred embodiment of the present invention, a process for depositing refractory metal on a silicon surface compri~ses the steps of disposing the silicon surface in an atmosphere compressing a gaseous refractory metal compound such as tungsten hexafluoride. The silicon surface is then heated in this atmosphere with a focused beam of electromagnetic radiation such as a laser. The heating occurs along a prescribed path at a temperature which is sufficient to heat the surface so as to initiate a surface reduction reaction in RD 16,146 which refractory metal is reduced and deposited on or in place of the silicon sur~ace. In a preferred embodiment of the present invention, smooth tungsten lines with lengths of a few centimeters and with line widths of between about 2 and about 15 microns, are deposited on a silicon surface using an argon laser with a power of about 50 milliwatts and with a focused spot size of approximately 20 microns (full-width, half-maximum). It is noted that the deposition of the present invention may be performed on a crystalline, polycrystalline, or amorphous silicon surfaceO The processing is preferably performed in a vacuum chamber with a partial gas pressure of WF6 in the range of from 1 to 100 torr in a buffer gas of argon at a partial pressure of about 1 a-tmosphere. The deposited refractory metal layer ls typically between approximately 100 and 1000 angstroms thick. In the process of the present invention, the silicon surface itself acts as the reducing ayent for the metal
2~ containing gas. For example, the utilization of tungsten hexafluoride produces the following chemical reaction:
2 WF6 + 3 Si -~2 W + 3SIF4 12) In laser-beam-induced chemical vapor deposition processes, the reaction typically ~akes places over a period from several seconds to as short a time as a few milliseconds, the time being controlled by the scanning speed and the spot size of the laser beam. The deposition conditions may be controlled by varying the laser power, scanning speed, and gas pressure.
Accordingly, it is an object of the present invention to provide a method for direct writing of refractory metal lines on si~icon surfaces.
RD 16,146 It is a further object of the present invention to provide a method for discretionary and custom formation of interconnection metal lines on electrical circuit chips.
It is also an object of the present invention to provide a method for increasing the yield in various semiconductor manufacturing processes including the production of VLSI semiconductor circuit chips and liquid crystal display devices.
It is yet another object of the present invention to provide a method or formation of interconnections in electronic circuit packaging applications.
It is a still further object of the present invention to provide a method for correcting semiconductor chip masks.
Lastly, but not limited hereto, it is an object of the present invention to provide correction means for wafer or chip mask faults and to enhance the 0 yield of semiconductor fabrication processes.
Description of the Figures The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof r may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure lA illustrates a cross-sectional side elevation view of a pair of metal structures on a substrate which are to be electrically connected by a conductive material in accordance with the process of the present invention;
Figure lB illustrates a cross-sectional side 7.~
RD 16,145 elevation vi.ew of the substrate of Figure lA in which a polysilicon or amorphous silicon layer has been added;
Figure lC i.llustrates a cross-sectional side elevation view of the substrate of Figure lB being treated in accordance with the process of the present invention by means of a focused electromagnetic radiation beam moving from left ot right from point A
to point B;
Figure lD illustrates the method of the present invention as in Figure lC but with the focused beam having traversed the desired writing line distance.
Figure lE illustrates a cross-sectional side elevation view of the interconnection structure formed in Figure lD by the process of the present invention after which layer 15 has been removed, such as by selective etching~
Detailed Description of the Invention In using laser-induced micro-chemistry for electronic material processing and device fabrication, there are basically two approaches, namely, deposition induced by pyrolytic or photolytic reactions which are : effected directly by laser radiation and deposition effected by those surface conditions which can be modified by laser radiation. The latter processes include, for example, modification of catalytic reactions or nucleation barriers by radiation to enhance or inhihit the subsequent growth of films.
The process described in the present application is directed to the utilization of pyrolysis reactions induced by focused electromagnetic radiation~
particularly that produced by laser energy. In a preferred embodiment of the present invention r the process employs a reduction reaction of tungsten hexafluoride by a silicon surface induced by localized RD l~rl46 heating using a focused laser beam. The laser beam spot size is typically between about 10 and about 20 microns in width. Since such pyrolytic processes are highly dependent upon local temperature, the reaction rate is strongly effected by non-linear temperature conditions such as those produced by a focused laser beam. For example, if the temperature profile induced by an incident beam is Gaussian, it is seen that the actual width of the line drawn is significantly srnaller than the beam profile itself. For example, the temperature profile induced by a Gaussian beam might be described by the following equation:
I(r) = ~O exp(-9.5 r /Ro ), (3) where Ro is a characteristic width.
lS Because the reaction rate is dependent upon the temperature which is highly non-linear t line widths much smaller than rO microns can be produced.
Another interesting property observed in a micro-chemical processl induced by heat sources of micron dimensions, is enhancement of the available reaction flux. The reaction rate in a heterogeneous reaction at a gas-solid interface is generally limited either by diffusion of reactants and/or diffusion of products, or by reaction rates on the solid surface.
The reactant flux channeled into the reaction zone increases at high pressure as dimensions of a reacting zone decrease to a small ~alue compared with gas diffusion distances. on the other hand, for an extended heated surface, the reaction flux at a high pressure is usually limited by gas phase diffusion.
From geometrical scale considerations, net reaction rates in a micro-chemical process induced by a focused laser beam can be several orders of magnitude faster 3f ~
~ D 16,146 than those observed in a diEfusion-limited case such as a furnace. For instance, a reaction flux of 1 x 1021 cm .sec is available at a pressure of 100 torr for a 10 micron Eoc:used Gaussian beam. The reaction flux reduces to a value of 1 x 1019 cm 2.sec 1 for a Gaussian beam of 1 millimeter dimension. It is therefore seen that the method of the present invention can provide rapid line writing speeds on the order of several centimeters per second. SUch parameters are important for production line throughput considerations.
Specific attention is now directed to Figures lA-lE in which one embodiment of the present method is illustrated. In particular, Figure lA
illustrates metallic islands or conductive strips 11 and 12 which are to be connected with a refractory metal conductor. Metal paths 11 and 12 typically exist as part of a metallization pattern formed on an integrated circuit chip or similar device which is generically illustrated by substrate 10. While conductive elements 11 and 12 are shown as lying in the same plane, it is important to note that ~or the purposes of the present invention, the method described herein is not restricted to that situation.
In one embodiment of the present invention, silicon layer 15 is deposited on the structure shown in Figure lA. Silicon material 15 may comprise crystalline, polycrystalline, or amorphous silicon material~ However, because low process temperatures are generally desirable, layer 15 typically comprises amorphous silicon or polysilicon rather than crystalline silicon which is usually associated with higher temperature processing.
One embodi~ent of the process of the present inve~tion is particularly illustrated in Figure lC in which it is seen that focused radiation beam 18 moves RD 16~146 . g _ between points A and B/ as shown. This provides localized laser induced heating of layer 15. Since heating occurs in an atmosphere comprising a reactive gaseous refractory metal compound, heated silicon in layer 15 reacts in accordance with Equation (2) to convert a portion of the silicon layer along the line traversed to tungsten while at the same time forming gaseous silicon tetrafluoride. It is also noted that molybdenum hexafluoride may be similarly employed to deposit molybdenum. Figure lC also illustrates the fact that material 16 to the left of laser beam 18 has been converted in accordance with the present invention and that material 17 to ~he right of the laser beam, but to the left of point B, yet remains to be treated.
EXAMPLES
FIGURE lD illustrates the state of the substrate at the end of the laser writing step.
Unconverted amorphous silicon may then be removed as by etching, e.g. in a KOH solution. The result is shown in Figure lE.
Micron-size fine tungsten lines with a minimum line width of 1 micron have been deposited at a speed of several centimeters per second on a crystalline silicon surfaces scanned ~ith a focused argon laser beam having an approximately 20 micron spot size at a power of approximately 5 watts in a reaction chamber containing cun~sten hexafluoride at a partial pressure of 50 torr and an inert buffer gas of argon at a partial pressure of about 1 atmosphere.
The resistivity of the deposited lines was measured to be less than 1 milliohm/centimeter.
In another example of the method of the present invention, a tungsten film with a thickness of over approximately 100 nanometers was deposited on an amorphous silicon layer, which, in turn, was deposited r~
RD 16 ,146 on a silicon dioxide substrate in a reaction chamber containing tungsten hexafluoride at a partial pressure oE 50 torr and argon gas at a partial pressure of 1 atmosphere. Both CW, YAG and pulsed frequency-doubled YAG lasers may be employed.
It is noted that in the present invention, it is generally desirable to heat the si;Licon surface to a temperature between approxlmately 350C and approximately 550C. It is also noted that excessively high temperatures should be avoided because of the tendency for the formation of tungsten silicide. It is also noted that while laser beams are preferably employed for inducing localized heating, other focusable radiant energy sources are also employable. It is also noted that a faster scanning rate is made possible by the method of the present invention.
From the above, it should be appreciated that the method of the present invention produces direct writing of micron sized refractory metal lines on silicon surfaces at a relatively high speed. It is also seen that the present invention exhibits high resolution and takes advantage of the non-linear temperature dependence of chemical reaction rates to produce narrow lines. It is also seen that the method of the present invention provides a mechanism for writing thin lines having appropriate electrical resistivity without contamination by various impurities. It is also seen that the present invention permits the formation of conductive lines even in areas where traversal of step differences in integrated circuits is necessary. It is also seen that the process of the present invention fulfills the objectives stated above.
While the invention has been described in detail herein, in accordance with certain preferred , RD 16,146 embodiments thereof, many modifications and changes therein may be efected by those skilled in the art.
Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
:~ : : : : : : :
: ,~
: :
`: : : :: : :
:
:
.
2 WF6 + 3 Si -~2 W + 3SIF4 12) In laser-beam-induced chemical vapor deposition processes, the reaction typically ~akes places over a period from several seconds to as short a time as a few milliseconds, the time being controlled by the scanning speed and the spot size of the laser beam. The deposition conditions may be controlled by varying the laser power, scanning speed, and gas pressure.
Accordingly, it is an object of the present invention to provide a method for direct writing of refractory metal lines on si~icon surfaces.
RD 16,146 It is a further object of the present invention to provide a method for discretionary and custom formation of interconnection metal lines on electrical circuit chips.
It is also an object of the present invention to provide a method for increasing the yield in various semiconductor manufacturing processes including the production of VLSI semiconductor circuit chips and liquid crystal display devices.
It is yet another object of the present invention to provide a method or formation of interconnections in electronic circuit packaging applications.
It is a still further object of the present invention to provide a method for correcting semiconductor chip masks.
Lastly, but not limited hereto, it is an object of the present invention to provide correction means for wafer or chip mask faults and to enhance the 0 yield of semiconductor fabrication processes.
Description of the Figures The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof r may best be understood by reference to the following description taken in connection with the accompanying drawings in which:
Figure lA illustrates a cross-sectional side elevation view of a pair of metal structures on a substrate which are to be electrically connected by a conductive material in accordance with the process of the present invention;
Figure lB illustrates a cross-sectional side 7.~
RD 16,145 elevation vi.ew of the substrate of Figure lA in which a polysilicon or amorphous silicon layer has been added;
Figure lC i.llustrates a cross-sectional side elevation view of the substrate of Figure lB being treated in accordance with the process of the present invention by means of a focused electromagnetic radiation beam moving from left ot right from point A
to point B;
Figure lD illustrates the method of the present invention as in Figure lC but with the focused beam having traversed the desired writing line distance.
Figure lE illustrates a cross-sectional side elevation view of the interconnection structure formed in Figure lD by the process of the present invention after which layer 15 has been removed, such as by selective etching~
Detailed Description of the Invention In using laser-induced micro-chemistry for electronic material processing and device fabrication, there are basically two approaches, namely, deposition induced by pyrolytic or photolytic reactions which are : effected directly by laser radiation and deposition effected by those surface conditions which can be modified by laser radiation. The latter processes include, for example, modification of catalytic reactions or nucleation barriers by radiation to enhance or inhihit the subsequent growth of films.
The process described in the present application is directed to the utilization of pyrolysis reactions induced by focused electromagnetic radiation~
particularly that produced by laser energy. In a preferred embodiment of the present invention r the process employs a reduction reaction of tungsten hexafluoride by a silicon surface induced by localized RD l~rl46 heating using a focused laser beam. The laser beam spot size is typically between about 10 and about 20 microns in width. Since such pyrolytic processes are highly dependent upon local temperature, the reaction rate is strongly effected by non-linear temperature conditions such as those produced by a focused laser beam. For example, if the temperature profile induced by an incident beam is Gaussian, it is seen that the actual width of the line drawn is significantly srnaller than the beam profile itself. For example, the temperature profile induced by a Gaussian beam might be described by the following equation:
I(r) = ~O exp(-9.5 r /Ro ), (3) where Ro is a characteristic width.
lS Because the reaction rate is dependent upon the temperature which is highly non-linear t line widths much smaller than rO microns can be produced.
Another interesting property observed in a micro-chemical processl induced by heat sources of micron dimensions, is enhancement of the available reaction flux. The reaction rate in a heterogeneous reaction at a gas-solid interface is generally limited either by diffusion of reactants and/or diffusion of products, or by reaction rates on the solid surface.
The reactant flux channeled into the reaction zone increases at high pressure as dimensions of a reacting zone decrease to a small ~alue compared with gas diffusion distances. on the other hand, for an extended heated surface, the reaction flux at a high pressure is usually limited by gas phase diffusion.
From geometrical scale considerations, net reaction rates in a micro-chemical process induced by a focused laser beam can be several orders of magnitude faster 3f ~
~ D 16,146 than those observed in a diEfusion-limited case such as a furnace. For instance, a reaction flux of 1 x 1021 cm .sec is available at a pressure of 100 torr for a 10 micron Eoc:used Gaussian beam. The reaction flux reduces to a value of 1 x 1019 cm 2.sec 1 for a Gaussian beam of 1 millimeter dimension. It is therefore seen that the method of the present invention can provide rapid line writing speeds on the order of several centimeters per second. SUch parameters are important for production line throughput considerations.
Specific attention is now directed to Figures lA-lE in which one embodiment of the present method is illustrated. In particular, Figure lA
illustrates metallic islands or conductive strips 11 and 12 which are to be connected with a refractory metal conductor. Metal paths 11 and 12 typically exist as part of a metallization pattern formed on an integrated circuit chip or similar device which is generically illustrated by substrate 10. While conductive elements 11 and 12 are shown as lying in the same plane, it is important to note that ~or the purposes of the present invention, the method described herein is not restricted to that situation.
In one embodiment of the present invention, silicon layer 15 is deposited on the structure shown in Figure lA. Silicon material 15 may comprise crystalline, polycrystalline, or amorphous silicon material~ However, because low process temperatures are generally desirable, layer 15 typically comprises amorphous silicon or polysilicon rather than crystalline silicon which is usually associated with higher temperature processing.
One embodi~ent of the process of the present inve~tion is particularly illustrated in Figure lC in which it is seen that focused radiation beam 18 moves RD 16~146 . g _ between points A and B/ as shown. This provides localized laser induced heating of layer 15. Since heating occurs in an atmosphere comprising a reactive gaseous refractory metal compound, heated silicon in layer 15 reacts in accordance with Equation (2) to convert a portion of the silicon layer along the line traversed to tungsten while at the same time forming gaseous silicon tetrafluoride. It is also noted that molybdenum hexafluoride may be similarly employed to deposit molybdenum. Figure lC also illustrates the fact that material 16 to the left of laser beam 18 has been converted in accordance with the present invention and that material 17 to ~he right of the laser beam, but to the left of point B, yet remains to be treated.
EXAMPLES
FIGURE lD illustrates the state of the substrate at the end of the laser writing step.
Unconverted amorphous silicon may then be removed as by etching, e.g. in a KOH solution. The result is shown in Figure lE.
Micron-size fine tungsten lines with a minimum line width of 1 micron have been deposited at a speed of several centimeters per second on a crystalline silicon surfaces scanned ~ith a focused argon laser beam having an approximately 20 micron spot size at a power of approximately 5 watts in a reaction chamber containing cun~sten hexafluoride at a partial pressure of 50 torr and an inert buffer gas of argon at a partial pressure of about 1 atmosphere.
The resistivity of the deposited lines was measured to be less than 1 milliohm/centimeter.
In another example of the method of the present invention, a tungsten film with a thickness of over approximately 100 nanometers was deposited on an amorphous silicon layer, which, in turn, was deposited r~
RD 16 ,146 on a silicon dioxide substrate in a reaction chamber containing tungsten hexafluoride at a partial pressure oE 50 torr and argon gas at a partial pressure of 1 atmosphere. Both CW, YAG and pulsed frequency-doubled YAG lasers may be employed.
It is noted that in the present invention, it is generally desirable to heat the si;Licon surface to a temperature between approxlmately 350C and approximately 550C. It is also noted that excessively high temperatures should be avoided because of the tendency for the formation of tungsten silicide. It is also noted that while laser beams are preferably employed for inducing localized heating, other focusable radiant energy sources are also employable. It is also noted that a faster scanning rate is made possible by the method of the present invention.
From the above, it should be appreciated that the method of the present invention produces direct writing of micron sized refractory metal lines on silicon surfaces at a relatively high speed. It is also seen that the present invention exhibits high resolution and takes advantage of the non-linear temperature dependence of chemical reaction rates to produce narrow lines. It is also seen that the method of the present invention provides a mechanism for writing thin lines having appropriate electrical resistivity without contamination by various impurities. It is also seen that the present invention permits the formation of conductive lines even in areas where traversal of step differences in integrated circuits is necessary. It is also seen that the process of the present invention fulfills the objectives stated above.
While the invention has been described in detail herein, in accordance with certain preferred , RD 16,146 embodiments thereof, many modifications and changes therein may be efected by those skilled in the art.
Accordingly, it is intended by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.
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Claims (15)
1. A process for depositing refractory metal on a silicon surface, said process comprising the steps of:
disposing said silicon surface in an atmosphere of at least one gaseous refractory metal compound, said compound being capable of reduction by silicon; and heating said silicon surface in said atmosphere with a focused beam of electromagnetic radiation along a prescribed path, to a temperature sufficient to initiate surface reduction in which said refractory metal is reduced and deposited in place of at least some of said silicon in said surface.
disposing said silicon surface in an atmosphere of at least one gaseous refractory metal compound, said compound being capable of reduction by silicon; and heating said silicon surface in said atmosphere with a focused beam of electromagnetic radiation along a prescribed path, to a temperature sufficient to initiate surface reduction in which said refractory metal is reduced and deposited in place of at least some of said silicon in said surface.
2. The process of claim 1 in which said silicon surface is selected from the group consisting of crystalline silicon, polycrystalline silicon, and amorphous silicon.
3. The process of claim 1 in which said heating is performed by a focused laser beam.
4. The process of claim 3 in which said laser beam is produced by a YAG laser.
5. The process of claim 3 in which said laser beam is focused to a spot approximately 20 microns in diameter.
6. The process of claim 1 in which said gaseous refractory metal compound is selected from the group consisting of tungsten hexafluoride and molybdenum hexafluoride.
7. The process of claim 1 in which said gaseous refractory metal compound is present at a partial pressure of between approximately 1 and approximately 100 torr.
8. The process of claim 7 in which said gaseous refractory metal compound is present at a partial pressure of approximately 100 torr.
9. The process of claim 1 in which said silicon surface is heated to a temperature between approximately 350°C and 550°C.
10. The process of claim 1 in which said temperature is insufficient to initiate formation of refractory metal silicides.
11. The process of claim 1 in which said atmosphere in which said silicon surface is disposed also includes an inert buffer gas.
12. The process of claim 11 in which said buffer gas comprises argon.
13. The process of claim 12 in which said argon is present at a partial pressure of approximately 1 atmosphere.
14. A process for electrically connecting electrical conductors disposed on a substrate, said method comprising the steps of:
disposing a layer of silicone over said substrate and said conductors;
disposing said coated substrate in an atomosphere comrpising at least one gaseous refractory metal compound; and heating said silicon surface in said atmosphere with a focused beam of electromagnetic radiation along a prescribed path between said conductors, said heating being sufficient to raise the temperature of said silicon surface so as to initiate surface reduction in which said refractory metal is reduced and deposited so as to form a conductive path between said conductors.
15. The process of claim 14 further
disposing a layer of silicone over said substrate and said conductors;
disposing said coated substrate in an atomosphere comrpising at least one gaseous refractory metal compound; and heating said silicon surface in said atmosphere with a focused beam of electromagnetic radiation along a prescribed path between said conductors, said heating being sufficient to raise the temperature of said silicon surface so as to initiate surface reduction in which said refractory metal is reduced and deposited so as to form a conductive path between said conductors.
15. The process of claim 14 further
Claim 15 continued:
including the step of removing unreacted silicon from said silicon layer.
including the step of removing unreacted silicon from said silicon layer.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79987885A | 1985-11-20 | 1985-11-20 | |
| US799,878 | 1985-11-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1249071A true CA1249071A (en) | 1989-01-17 |
Family
ID=25176997
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000521384A Expired CA1249071A (en) | 1985-11-20 | 1986-10-24 | Direct writing of refractory metal lines for use in integrated circuit devices |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS62188342A (en) |
| CA (1) | CA1249071A (en) |
| DE (1) | DE3639080A1 (en) |
| FR (1) | FR2590408A1 (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3730644A1 (en) * | 1987-09-11 | 1989-03-30 | Baeuerle Dieter | METHOD FOR THE PRESENTED STRUCTURED DEPOSITION OF MICROSTRUCTURES WITH LASER LIGHT |
| DE4401612A1 (en) * | 1994-01-20 | 1995-07-27 | Resma Gmbh | Conductive region prodn. in or on ceramic workpiece |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS60245227A (en) * | 1984-05-21 | 1985-12-05 | Seiko Instr & Electronics Ltd | Pattern film forming method |
-
1986
- 1986-10-24 CA CA000521384A patent/CA1249071A/en not_active Expired
- 1986-11-14 DE DE19863639080 patent/DE3639080A1/en not_active Withdrawn
- 1986-11-17 FR FR8615923A patent/FR2590408A1/en not_active Withdrawn
- 1986-11-18 JP JP27309386A patent/JPS62188342A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS62188342A (en) | 1987-08-17 |
| DE3639080A1 (en) | 1987-05-21 |
| FR2590408A1 (en) | 1987-05-22 |
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