GB2212819A

GB2212819A - Laser chemical vapor deposition

Info

Publication number: GB2212819A
Application number: GB8827836A
Authority: GB
Inventors: Tushar Shashikant Chande
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1987-11-30
Filing date: 1988-11-29
Publication date: 1989-08-02
Also published as: GB8827836D0; JPH01212770A; FR2623820A1; IT1227653B; IT8822803A0; DE3840042A1

Description

RD-18,215 LASER CHEMICAL VAPOR DEPOSITION The present invention relates to

laser chemical vapor deposition systems.

221281 -9 The conventional process of chemical vapor deposition (CVD) is, generally, the process by which a gaseous chemical reactant is deposited on and bonded to a substrate material. Techniques for performing the conventional CVD process are well known and successfully employed in the semiconductor chip fabrication art, e.g. As part of VLSI microfabrication, as well as in the metallurgical art where it is employed to deposit a layer of material having desirable properties onto a substrate material. Exemplary of such a metallurgical application is the deposition of oxides or nitrides onto a steel or titanium substrate to improve the surface properties thereof. Laser-chemical vapor deposition (LCVD) is a process in which a laser beam facilitates the deposition of the chemical reactant onto the substrate and is also well known in the art.

Figure I illustrates an LCVD system 100 exemplary of prior art techniques for the performance of LCVD. A workpiece 102 is positioned within a sealed environment reaction chamber 104. The chamber includes a reactant gas inlet port 106, a gas outlet port 108 and a pressure gauge for indicating the pressure within the chamber. The chamber further includes a window 112 suitable for the RD-18,215 transmission therethrough of a laser beam and an observation window 114 for viewing the workpiece being subjected to the LCVD process. A laser 116 generates a laser beam 118 which is collimated by means not shown. The collimated beam is directed toward and focused through window 112 by suitable optical means diagrammatically represented as a mirror 120 and a focussing lens 122. The focused portion 124 of the laser beam is directed onto the workpiece. In operation, chamber 104 is evacuated, via outlet port 108, and the gaseous chemical reactant to be deposited onto the surface of workpiece 102 is subsequently introduced through inlet 106. Typically, enough gaseous reactant is introduced into the chamber of the LCVD system to establish a static atmosphere of sufficient concentration to support the deposition process, the pressure registered by gauge 110 providing an indication of the concentration of the gaseous reactant within the chamber. Focussed laser beam 124 is directed onto those portions of the workpiece surface (substrate) where it is desired to deposit the gaseous reactant. Redirection of the focused laser beam onto different portions of the substrate - may be accomplished by movement of the optical components, such as mirror 120. As is known in the art, the deposition onto the substrate occurs either by a process of photolysis in which the laser beam causes the molecules of the gaseous reactant to disso ciate and react with the substrate material or by a process of pyrolysis in which the laser beam heats the substrate and the gaseous reactant reacts directly therewith.

The prior art technique of LCVD illustrated in

Figure 1 and described hereinabove suffers a number of dis advantages. One primary disadvantage derives from the limitation of having to introduce the focused laser beam through window 112. Such windows are costly since they must RD-18,215 be fabricated from a material that is highly transmissive to the laser beam being employed in order to minimize beam attenuation. Further, the window must have sufficient strength to withstand the pressure (positive or negative) within the chamber. In practice, the chemical reactant is known to deposit on such windows and thereby degrade window transmissibility. One technique known in the art for minimizing such deposition on the window is to heat the window. However, it has been found that such window heating can cause distortion of the window and therefore distortion of the focused laser beam transmitted therethrough. It would therefore be desirable to provide apparatus for performing LCVD which does not require use of such a window to enable introduction of the laser beam into the reaction chamber.

A second primary disadvantage experienced with the above described and illustrated prior art LCVD technique is the limited ability to control the concentration of gaseous reactant proximate the substrate onto which it is being deposited. Both conventional CVD and LCVD techniques rely on controlling the rate of flow or pressure of the-gaseous reactant in the reaction chamber to influence the reactant concentration in the region of deposition. Such methods of controlling the concentration of gaseous reactant within thechamber are inherently inaccurate since they only serve to 2S maintain some average gaseous concentration wiihin the chamber as a whole. Close control of the concentration of gaseous reactant in the immediate vicinity of the region of deposition is very difficult to achieve using such methods. It would therefore be further desirable to provide apparatus for performing LCVD in which the gaseous reactant concentration in the region of deposition can be closely controlled.

RD-18,215 An additional disadvantage of the prior art LCVD technique is the limited flexibility in redirecting the focused laser beam onto different portions of the substrate. As indicated above, such redirection is accomplished in prior art LCVD apparatus 100 by manipulation of the optical apparatus external to the chamber. Clearly, the degree of freedom in such redirection is constrained by the cross-sectional area bf window 112 and the ability to effectively focus the laser beam onto different areas of the sub- strate. It would therefore be additionally desirable to provide LCVD apparatus having substantial freedom of relative movement between the focused laser beam and the workpiece.

A further disadvantage of the prior art LCVD technique derives from the nonuniform intensity profile experienced in the focused spot of the laser beam. Such nonuniformity of the intensity profile may be attributed to variations within the laser resonator-itself resulting from fluctuations in input power and cooling water flow, vibra- tion of optical elements, etc. Where LCVD proceeds by the above noted pyrolysis mechanism, nonuniform heating of the substrate portion onto which the focused beam is directed results and corresponds to the nonuniform intensity profile of the focused beam spot. Disadvantageously, such non- uniform heating results in variations in reaction rate within the heated beam spot and, hence, nonuniformity of the thickness of material deposited on the substrate. Further, where a pulsed laser beam is employed to perform LCVD, the difference in intensity profile of successive beam pulses may result in corresponding nonuniformities in the deposited material. It would therefore be yet further desirable to provide LCVD apparatus in which both the nonuniformity in i t RD-18,215 beam intensity profile and intensity profile differences between successive beam pulses are minimized.

Aspects of the present invention seek to provide laser chemical vapor deposition (LCVD) systems and apparatus which are not subject to various ones of the aforementioned problems and disadvantages.

One aspect of the present invention seeks to provide LCVD system and apparatus which does not require transmitting the laser beam through a window into a reaction chamber.

A further aspect of the present invention seeks to provide LCVD system and apparatus in which the concentration of the gaseous reactant proximate the substrate onto which it is being deposited can be closely controlled.

An additional aspect Of the present invention seeks to provide LCVD system and apparatus in which there is substantial flexibility in redirecting the laser beam over different portions of the substrate onto which the gaseous reactant is to be deposited.

Yet another aspect of the present invention seeks to provide LCVD system and apparatus in which nonuniformity of intensity profile in the focused beam spot is minimized.

Yet a further aspect of the present invention seeks to provide LCVD system and apparatus in which variations of intensity profile observed in successive beam pulses generated by a pulsed laser is minimized.

An illustrative apparatus in accordance with the invention for performing laser chemical vapor deposition RD-18,215 (LCVD) of a gaseous chemical reactant onto a workpiece using a laser beam comprises an optical f iber for transmitting the laser beam and suitable optical,components for injecting the laser beam into an input end of the optical fiber for transmission therethrough. The LCVD apparatus further comprises means for deploying the gaseous reactant in the vicinity of a predetermined region of the workpiece where it is desired to deposit the gaseous reactant and an output coupler for focusing the laser beam emitted at an output end of the fiber. In an embodiment in which deposition of the gaseous reactant proceeds by the pyrolysis process, the beam is focused onto at least a portion of the workpiece predetermined region so that the gaseous reactant is deposited thereon. In another embodi- ment in which it is desired to deposit the reactant by means of the photolysis process, the output coupler is oriented so that the beam is focused onto a portion of the gaseous reactant proximate the workpiee predetermined region.

In several embodiments, the gas deploying means comprises a nozzle, coupled to the output coupler, for flowing the gaseous reactant into the immediate vicinity of the workpiece predetermined region. Control of the flow of gaseous reactant to the nozzle enables control of the concentration of reactant to be deposited.

In several illustrative embodiments of the present invention, the apparatus further comprises a sealed environment reaction chamber for containing the workpiece and output coupler. The optical fiber penetrates a wall of the chamber through a first opening therein so that the input and output fiber ends are respectively outside and inside the chamber. The first opening in the wall is sealed around the optical fiber to maintain the sealed chamber environment. The chamber includes a second 1 RD-18,215 wall opening for the introduction of gaseous reactant and a third opening in the wall for evacuating the chamber or removing gaseous reactant therefrom. Where the gas deploying means comprises the nozzle, means such as tubing is provided for directing the gaseous reactant from the second opening to the nozzle. In an embodiment in which the output coupler, positioned within the chamber, is provided without the nozzle, a suitable concentration of gaseous reactant may be established in the vicinity of the workpiece predeter- mined region, following chamber evacuation, by flowing the gaseous reactant through the chamber via the second and third wall openings or by establishing a static atmosphere of the reactant by introduction through the second opening while closing off the third opening. It is preferred herein that the apparatus additionally comprise mechani- cal means for controllably moving the output coupler and workpiece relative to one another so that the gaseous reactant can be controllably deposited on different portions of the workpiece surface.

In a further illustrative embodiment of the present invention, the laser beam is split into first and second beams which are transmitted through first and second optical fibers to first and second output couplers, respectively, within the reaction chamber. In this manner, the LCVD process can be simultaneously conducted at two different locations on the workpiece. It is noted that in all embodi ments of the present invention, the use of optical fiber to transmit the laser beam to the proximity of the workpiece obviates the above described prior art problems deriving from beam introduction through a window in the reaction chamber wall.

1 RD- 18, 2 15 The invention will be better understood from a consideration of the following illustrative description in conjunction with the drawing figuresi, in which:

Figure I illustrates a laserchemical vapor deposition (LCVD) system exemplary of prior art LCVD techniques;

Figure 2 illustrates an LCVD system constructed in accordance with a first embodiment of the present invention; Figure 3 illustrates an LCVD system constructed in accordance with a second embodiment of the present invention; Figure 4 illustrates an LCVD system constructed in accordance with a third embodiment of the present invention; and Figure 5 illustrates an LCVD system constructed in accordance with a fourth embodiment of the present invention.

Referring now to the drawings, Figure 2 illus trates a laser chemical vapor deposition (LCVD) system 200 constructed in accordance with a first illustrated embodi ment of the present invention. System 200 as illustrated is especially adapted to perform LCVD by the process of pyroly sis, i.e. by-heating of the substrate onto which the gaseous reactant is to be deposited. System 200 comprises a power laser 202 for generating a laser beam 204 suitable for performing LCVD. Power lasers generating laser beams having an average power in the range of 5 watts to 1500 watts are X t RD-18,215 -g- generally suitable for such applications. Laser types suitable for performing LCVD include neodymium:yttrium aluminum-garnet (Nd:YAG), neodymium-doped glass, ruby, argon-ion lasers and some excimer lasers such as a xenon chloride excimer laser. LCVD can be successfully practiced, both in the prior art and in embodiments of the present invention, using either a pulsed or continuous wave laser.

Laser beam 204 is collimated by apparatus, not.shown, within laser 202. Beam 204 is focused by focusing lens 206, which for clarity is shown partially cut away, onto an input end 208 of an optical fiber 210. The beam is so focused on the fiber input end for the purpose of injecting the beam into the fiber for transmission therethrough. The input end of the optical fiber is held in'alignment with the focused laser beam by a fiber input coupler 212. The portion of input coupler 212 that actually holds the fiber is preferably constructed as a split block of a material that is substantially transparent to the laser beam focused onto the input end of the fiber. For example, materials such as quartz or Luciteg are suitably transparent for use with an Nd:YAG or neodymium-doped glass laser. The split block is preferably held in a mechanical positioning device with three degrees of linear freedom and two tilt degrees of freedom. A commercially available fiber holder suitable for use with Nd:YAG lasers, is manufactured by Melles-Grist Corporation of Irvine, California as Model No. 07-HFO-002.

Fiber 210 is preferably constructed with a quartz core and may have a diameter as small as 0.2mm. The technique preferred herein for injecting a power laser beam into the input end of an optical fiber for transmission therethrough is disclosed in commonly assigned U.S. Patents 4,676,586 (Jones et al.) and 4,681,396 (Jones), both of which are incorporated-in their entirety herein by RD-18,215 reference. While the beam injection techniques taught in the above incorporated Jones and Jones et al. patents are primarily directed to the injection of a high power laser beam (2SO watts average power or greater), those techniques are equally applicable to enable the successful injection of a lower power laser beam into an optical fiber for trans mission therethrough. In accordance with the techniques taught in the above incorporated Jones and Jones et al.

patents, it is assumed herein that input end 208 of fiber 210 has been properly prepared for beam injection, that the focal length of lens 206 is properly selected to achieve a cone angle less than twice the numerical aperture of the fiber and that the size of the focused spot of laser beam 204 on fiber input end 208 has a smaller diameter than that of the fiber core.

LCVD system 200 further includes a reaction chamber 214 constructed to maintain a sealed environment within. A stage 216 is positioned within chamber 214 for supporting a workpiece or substrate 218 onto a surface 220 of which a gaseous chemical reactant is to be deposited.

Optical fiber 210 penetrates into chamber 214 through an opening 222 in the wall thereof, that opening being suitably sealed around the fiber to maintain the sealed environment within the chamber. It is preferred herein to enclose the portion of the optical fiber within the chamber in a protec tive jacket (not shown), such as Polyflows or rubber tubing, in order to protect the fiber from potentially degrading effects of the gaseous reactant. An output end 224 of the optical fiber is terminated in an output coupler 226. A focusing portion 228 of the output coupler includes a fiber support block 230 for holding the fiber output end in alignment with a lens 232 mounted in the output coupler for collimating a diverging portion 234 of laser beam 204 RD-18,215 emitted from the end of the fiber. A lens 236 is mounted in the output coupler and aligned with lens 232 and fiber 224 to receive a collimated portion 238 of the laser beam and focus the collimated portion into a focused portion 240.

The focused portion may be directed to fall incident on a portion of workpiece surface 220 where it is desired to deposit the gaseous reactant. Block 228 need only be constructed to rigidly hold the fiber end in alignment with lenses 232 and 234 and need not be transparent to the laser beam, as was preferred for input coupler 212. Focusing portion 228 is constructed to maintain the components therein in rigid alignment and of a material, such as stainless steel or aluminum, not subject to degradation by the gaseous reactant being deposited on the workpiece.

is The gaseous reactant is deployed in the vicinity of a predetermined region of workpiece surface 220, where it is desired to deposit the gaseous reactant, by a nozzle portion 242 of output coupler 226. Nozzle portion 242 and focusing portion 228 of output coupler 226 may be con structed as a single unit or they may be constructed as separate units for screw engagement therebetween as illust rated in Figure 2. Nozzle portion 242 receives the gaseous reactant via tubing connections, e.g. rubber tubing, to openings in the wall of chamber 214. With respect to the nozzle portion of the output coupler, nozzles used in standard welding techniques such as tungsten inert gas (TIC) and oxyacetylene welding are readily adapted for use herein as the output coupler nozzle portion. While the gaseous reactant may be composed of any number of different gases, two different gases are assumed to compose the gaseous reactant in illustrated system 200 and so nozzle portion 242 is connected to two openings 244 and 246 in the chamber wall via flexible gas delivery tubes 248 and 250. The gases are RD-18,215 delivered through the tubes via valves 252 and 254 to enable control of the flow rate of each gas delivered to the nozzle portion via the tubes and, thereby, the concentration of gaseous reactant proximate surface 220. It is noted that multiple gases may be premixed external to the reaction chamber and the gaseous mixture introduced through one of the tubes. The nozzle portion thus enables the gaseous reactant to be directed onto the portion of workpiece surface 220 where the focused laser beam falls incident.

Chamber 214 additionally includes an opening 256, controlled by a valve 258, for evacuating the chamber or removing gaseous reactants that have been introduced through the nozzle portion via openings 244 and 246. Arrows are provided in Figure 2 proximate openings 244, 246 and 256 to is indicate the contemplated flow direction of gas at each opening. A pressure gauge 260 is installed on chamber 214 to measure and indicate pressure within. Chamber 214 is also necessarily fitted with a sealing access door, not shown, to enable insertion/removal of a workpiece and of output coupler 226. While not shown in Figure 2, system 200 additionally includes means for mechanically moving, in a controlled fashion, the output coupler and stage relative to one another. Depending on the size of chamber 214, adequate movement may be achieved by simply enabling movement of the output coupler while holding the stage rigid.

In operation, chamber 214 is initially evacuated through opening 256 while valves 252 and 254 are closed.

Then, laser 202 generates laser beam 204 which is focused onto the input end of optical fiber 210 and transmitted therethrough. The diverging beam emitted from the output end of the fiber is collimated and focused by the focusing portion of the output coupler. The output coupler is posi tioned so that the focused beam falls incident on at least 1 4 RD-18,215 portion of the predetermined region of workpiece surface-220 where it is desired to deposit the gaseous reactant. The gaseous reactant is deployed in the vicinity of the prede termined region through nozzle portion 242 which receives the gases composing the gaseous reactant, via valves 252 and 254, through the chamber walls and the gas delivery tubes.

The portion of workpiece surface 220 onto which the focused laser beam falls incident is heated sufficiently to result in bonding thereto, and hence deposition, of the gaseous reactant. The ability to manipulate valves 252 and 254 as well as the delivery of the gaseous reactant to the proxim ity of the laser beam focal point enables close control of the gaseous reactant concentration in the predetermined region on the workpiece surface. Valve 2S8 may remain closed to build up a concentration of the gaseous reactant within the chamber or it may be opened to remove the reac tant after it is introduced through the nozzle portion of the output coupler. The pressure reading on pressure gauge 260 provides an indication of the concentration of gaseous reactant within the chamber.

Figure 3 shows an LCVD system 300 constructed in accordance with a second illustrated embodiment of the present invention in which deposition is conducted by the photolysis process. The apparatus comprising system 300 is generally identical to that of system 200 and is labeled with like reference numerals. System 300 differs from system 200 in the orientation of output coupler 226 relative to surface 220 of the workpiece and in the selection of a focussing lens 302, for use in the output coupler, having a longer focal length than lens 236 described above with respect to system 200. As seen in Figure 3, the output coupler is positioned.so that an axis 304 of the focused laser beam is disposed nearly parallel to surface 220. As RD-18,215 briefly described above and known in the art, deposition by -the photolysis process proceeds from the dissociation of the molecules composing the gaseous reactant. This dissociation results from absorption by the gas molecules of sufficient laser energy to cause the dissociation. Sufficient laser energy to cause such molecular dissociation is available at the focal point of the focused beam and for some distance to either side thereof along axis 304, depending on the nature of the gaseous reactant and the power of the laser beam.

Selection of a long focal length for lens 302 enables disposition of the beam focal point proximate a greater portion of workpiece surface 220.

In the operation of system 300, the gaseous reactant is deployed proximate the laser beam focal point through the nozzle portion of the output coupler. The gaseous reactant-absorbs sufficient energy in the proximity of the beam focal point to dissociate. Some portion of the dissociated molecules bind to the portion of workpiece surface 220 proximate thereto. Thus by moving output coupler 226 over surface 220, the deposition process can proceed in a controlled fashion. It will be recognized by those skilled in the art that the optimal distance of the focal point of the focused beam from the workpiece surface will, in order to support the photolysis process, depend on the nature of the deposition being performed, i.e. gaseous reactant composition, substrate material, laser beam proper ties, etc. Further and also subject to the nature of the deposition, the angle at which axis 304 of beam 300 is disposed relative to the workpiece surface may be varied with successful results.

Figure 4 shows an L= system 400 constructed in accordance with g third illustrated embodiment of the present invention in which the nozzle portion of the optical RD- 18, 2 15 -is- coupler is dispensed with. As in the case of system 200, system 400 is adapted to perform LCVD by the pyrolysis process. Thus, system 400 includes the same elements as system 200, labeled with the same reference numerals as in Figure 2, for generating the laser beam and transmitting it via optical fiber 210 to the output coupler. Since the output coupler consists only of the focusing portion, it is labeled with the reference numeral 228. The output coupler is positioned within a reaction chamber 402 which is other- wise identical to chamber 214 of LCVD system 200 except that instead of openings 244 and 246, chamber 402 is fitted with an opening 404 preferably positioned adjacent workpiece 218 mounted on stage 216. Opening 404 is fitted with a valve 406 to control the flow therethrough of gaseous reactant into chamber 402.

In the operation of system 400, valve 406 is initially closed and chamber 402 is evacuated through opening 256 via valve 258. Then, the LCVD system is oper ated in either of two modes. In a first one of the modes, valve 258 is closed and, with valve 406 opened, gaseous reactant is introduced into the chamber through opening 404 until a static atmosphere of sufficient concentration of gaseous reactant is established therein to support deposi tion. Pressure gauge 260 may serve as an indication of the relative concentration of the gaseous reactant within the chamber. Then, by focusing the laser beam onto the predetermined region of workpiece surface 220, deposition occurs. In a second operating mode of system 400, following evacuation of chamber 402, gaseous reactant is introduced through 30 opening 404 and simultaneously removed through opening 256, so that a forced flow of gaseous reactant is established through the chamber. By appropriately locating openings 256 and 404, this forced flow can be directed through the RD-18,215 vicinity of the predetermined region of workpiece surface 220 where it is desired to deposit the reactant. The location of opening 404 adjacent the workpiece, in Figure 4, is intended to schematically illustrate an appropriate location for the introduction of the gaseous reactant so that its flow is appropriately directed over the workpiece. It is assumed with respect to system 400 that the output coupler and stage may.be moved relative to one another to achieve flexibility in controllably directing the laser beam over the workpiece surface. It is noted that while one opening 404 is provided in system 400 for the introduction of the gaseous reactant, the operation of system 400 is not limited to the introduction of a single gas as the gaseous reactant. Multiple gases composing the gaseous reactant may be combined externally to opening 404 prior to introduction therethrough. Alternatively, other openings may be located -proximate opening 404 to enable the separate introduction of other reactant gases.

A fourth illustrated embodiment of the present invention is shown in Figure 5 wherein an LCVD system 500 employs a beam splitter 502 to split a collimated laser beam 504 generated by laser apparatus 506. Beam 504 is thereby split into two portions 508 and 510 which are respectively focused by focusing lenses 512 and 514 onto the input ends of optical fibers 516 and 518 for transmission therethrough.

The input ends of the fibers are respectively held by fiber input couplers 519 and 520 which are each constructed in like manner to block 212 of system 200. Fibers 516 and 518 penetrate a sealed reaction chamber 521 through openings 522 and 524, these openings being appropriately sealed around the fibers respectively passing therethrough to maintain the sealed environment of the chamber.

f RD-18,215 1 Within the chamber, a workpiece 526 is mounted on a support stage 528. An output end of each fiber 516 and 518 is respectivelyterminated in an output coupler 530 and 532. The construction of each output coupler 530, 532 is substantially identical to that of output coupler 226 in system 200. Output coupler 530 is connected via gas delivery tubes 534 and 536 to chamber wall openings 538 and 540, respectively, to receive gaseous reactant therefrom. Valves 542 and 5 44 control the flow of gas introduced through 10 openings 538 and 540. Similarly, output coupler 532 is connected to chamber wall openings 546 and 548 via gas delivery tubes 550 and 552, respectively, to receive gaseous reactant. Valves 554 and 556 control the flow of gas introduced through openings 546 and 548, respectively. An 15 additional opening 558, fitted with a valve 560, is provided in the chamber wall to enable evacuation of the chamber and removal of gaseous reactant therefrom. In the operation of LCVD system 500, following evacuation of chamber 521, beam 504 is split into two beams 20 508 and 510 which are respectively transmitted through fibers 516 and 518 to be focused onto predetermined regions of a surface 562 of workpiece 526. By means not shown, both output couplers can be independently controllably moved relative to surface 562 so that gaseous reactant introduced through the nozzle portion of each output coupler is deposited in controlled fashion onto the surface by the pyrolysis process. While not illustrated in Figure 5, one or both of the output couplers can be oriented relative to the workpiece predetermined regions to cause deposition thereon by the photolysis process.

With respect to each embodiment of the present invention illustrated and described hereinabove, the laser beam used to perform LCVD is introduced into the reaction RD- 18, 2 15 chamber by means of an optical fiber. As.a result, the embodiments of the present invention do not reguire introduction of the laser beam through a window in the chamber wall as requ ired by the above described prior art LCVD technique and therefore do not suffer the above-described problems associated with the window. Those embodiments of the present invention employing the nozzle portion of the output coupler enjoy the ability to carefully control the disposition and concentration of the gaseous reactant proximate the portion of the substrate onto which the reactant is to be deposited. With respect to all embodiments of the present invention disclosed hereinabove, the ability to move the output coupler relative to the workpiece within the chamber enables substantial flexibility in redirecting the focused laser beam over different areas of the workpiece surface. Such movement can be achieved while appropriately maintaining the beam focal point in a desired orientation relative to the workpiece surface. This flexibility in redirecting the focused beam is a substantial improvement over the above described prior art LCVD system in which the window and external optics greatly constrain the ability to redirect the laser beam over the workpiece surface.

As indicated above, a problem experienced with prior art LCVD systems is the uneven deposition of the gaseous reactant due to a nonuniform intensity profile occurring in the focused beam spot. As a result of transmission through an optical fiber, the nonuniform intensity profile of a beam is made substantially more uniform. It is further noted hereinabove, that where a pulsed laser beam is employed, pulse-to-pulse intensity profile differences may result in nonuniformity of deposition. It is also a property of transmission through an optical fiber that such pulse-to-pulse intensity profile differences are minimized.

RD-18,215 Effects of beam transmission through optical fiber on nonuniform intensity profile in the focused beam spot and on pulse-to-pulse intensity profile differences are disclosed in a paper entitled "Observed Intensity Profiles of a 400 Watt Nd:YAG Laser Beam Transmitted Through an Optical Fiber" by T. Chande et al., Proceedings of the 1987 International Congress on the Application of Lasers and Electro-Optics, November 9-11, 1987, published by the Laser Institute of America, that paper being incorporated in its entirety herein by reference. Thus, in all embodiments of the present invention disclosed hereinabove, the transmission of the laser beam through an optical fiber obviates these prior art problems related to beam intensity profile.

While the output coupler utilized in the LCVD apparatus described hereinabove is schematically illustrated as comprising simple plano-convex lenses for collimating and focusing the laser beam emitted by the optical fiber, the invention is not so limited. The output coupler may be constructed with other types and combinations of lenses, well known in the art, suitable for collimating and focusing the fiber emitted beam. Further, such lenses may be selected to form a focused beam spot of a predetermined shape that may have utility in a particular LCVD application. While the operation of the output coupler in LCVD 25 systems 200, 300 and 500 illustrated and described hereinabove is conducted within a reaction chamber, the invention is not so limited. A sufficient flow of gaseous reactant may be introduced through the nozzle portion of the output coupler so as to purge the volumetric space, proximate the workpiece predetermined region, of other gaseous elements. As a result, deposition of the gaseous reactant onto the workpiece predetermined region may proceed outside the sealed environment of a reaction chamber. Such practice of RD-18,215 the present invention outside a reaction chamber may be enhanced by use of a nozzle portion on the output coupier that enables introduction of an inert shielding gas such as used in conventional welding techniques. Such a nozzle 5 portion would flow the gaseous reactant proximate the workpiece predetermined region while also flowing the shielding gas to surround the gaseous reactant and thereby isolate it from contamination by the external environment. One limitation on such practice of LCVD without a reaction chamber is the noxious nature of some gaseous reactants.

LCVD system 300 of the present invention is illustrated and described hereinabove for the practice of LCVD by the photolysis process and the output coupler employed therein includes the nozzle portion. The invention is, however, not so limited. Practice of LCVD by the photolysis process in accordance with the present invention may be successfully practiced with only the focusing portion of the output coupler. In such a case, the gaseous reactant would be deployed in the proximity of the workpiece predetermined region by means of either establishing a static atmosphere of the reactant within the reaction chamber or establishing a forced flow of the gaseous reactant through the chamber, such as described above for the operation of illustrated system 400 LCVD system 500 illustrated and described herein above, comprises a beam splitter for splitting the laser beam generated by a single laser. The invention is, how ever, not so limited. In lieu of the single laser and beam splitter, two separate lasers may be employed to generate laser beams for injection into optical fibers 516 and 518.

In such a case, the lasers may be respectively selected to generate laser beams at wavelengths that facilitate the type of deposition process being performed, i.e. pyrolysis or k_ RD-18,215 photolysis. More generally, through the use of multiple lasers, beam splitters and optical fibers, a variety of combinations for performing LCVD will occur to those skilled in the art.

While a preferred embodiment has been illustrated and described herein,it will be obvious that numerous modifications, changes, variations, substitutions and equivalents, in whole or in part, will now occur to those skilled in the art without departing from the spirit and scope contemplated by the invention. Accordingly, it is intended that the invention herein be limited only by the scope of the appended claims.

RD-18,215

Claims

CLAIMS:

1. Apparatus for performing laser chemical vapor deposition of a gaseous chemical reactant onto a workpiece using a laser beam generated by a laser, comprising:

an optical fiber for transmitting the laser beam; means for injecting the laser beam into a first input end of said optical fiber for transmission there through; means for deploying the gaseous reactant in the vicinity of a predetermined region of the workpiece where it is desired to deposit the gaseous reactant; and output coupling means for focussing the laser beam emitted at a second output end of said fiber onto at least a portion of the predetermined region of the workpiece so that the gaseous reactant is deposited thereon.

15.

2. The apparatus of claim 1 wherein said gas deploying means comprises gas delivery means, coupled to said output coupling means, for flowing the gasegus reactant onto the portion of the workpiece predetermined region where the focused laser beam falls incident.

3. The apparatus of claim I further including a reaction chamber constructed to maintain a sealed environ ment within; said optical fiber penetrating a wall of said chamber through a first opening therein so that said first and second fiber ends are respectively outside and inside said chamber, said first opening being sealed around said - fiber to maintain the sealed environment within said cham- ber; and j i.

RD-18,215 said gas deploying means comprising means for introducing the gaseous reactant into said chamber; so that said output coupling means can be positioned within said chamber to focus the laser beam onto the workpiece predetermined region.

4. The apparatus of claim 3 wherein the gaseous reactant is introduced into said chamber to establish a static atmosphere thereof in the vicinity of the workpiece predetermined region.

5. The apparatus of claim 3, said gas introducing means comprising: a second opening in said chamber wall for the introduction of the gaseous reactant therethrough; and a third opening in said chamber wall for the removal of the gaseous reactant introduced through said second wall opening; so that by simultaneously introducing and removing the gaseous reactant respectively via said second and third wall openings, a forced flow of the gaseous reactant through said chamber can be established In the vicinity of the workpiece predetermined region.

6. The apparatus of claim 3 wherein said gas deploying means comprises nozzle means, coupled to said output coupling means, for flowing the gaseous reactant onto the portion of the workpiece predetermined region where the focused laser.beam falls incident; a second opening in said chamber wall for intro duction of the gaseous reactant therethrough; and RD-18,215 means for directing the gaseous reactant introduced through said second wall opening to said nozzle means.

7. The apparatus of claim 3 further including means for controllably moving said output coupling means and the workpiece relative to one another so that the focused laser beam can be directed onto different portions of the workpiece predetermined region.

8. Apparatus for performing laser chemical vapor deposition of a gaseous chemical reactant onto a workpiece using a laser beam generated by a laser, comprising:

an optical fiber for transmitting the laser beam; means for injecting the laser beam into a first input end of said optical fiber for transmission therethrough; means for deploying the gaseous reactant in the vicinity of a predetermined region of the workpiece where it is desired to deposit the gaseous reactant; and output coupling means for focussing the laser beam emitted at a second output end of said fiber onto a portion of the gaseous reactant proximate the workpiece predetermined region so that the gaseous reactant is deposited thereon by a photolysis process.

9. The apparatus of claim 8 wherein said gas deploying means comprises nozzle means, coupled to said output coupling means, for flowing the gaseous reactant proximate a focal point of the focused laser beam.

9 RD-18,215 10. The apparatus of claim 8 further including a reaction chamber constructed to maintain a sealed environment within; said optical fiber penetrating a wall of said chamber through a first opening therein so that said first and second fiber ends are respectively outside and inside said chamber, said first opening being sealed around said fiber to maintain the sealed environment within said chamber; and said gas deploying means comprising means for introducing the gaseous reactant into said chamber; so that said output coupling means can be positioned within said chamber to focus the laser beam onto the portion of the gaseous reactant proximate the workpiece predetermined region.

11. The apparatus of claim 10 wherein the gaseous reactant is introduced into said chamber to establish a static atmosphere thereof in the vicinity of the workpiece predetermined region.

12. The apparatus of claim 10, said gas introducing means comprising: a second opening in said chamber wall for the introduction of the gaseous reactant therethrough; and a third opening in said chamber wall for the removal of the gaseous reactant introduced through said second wall opening; so that by simultaneously introducing and removing the gaseous reactant respectively via said second and third wall openings, a forced flow of the gaseous reactant through said chamber can be established in the vicinity of the workpiece predetermined region.

1 RD-18,215 13. The apparatus of claim 10 wherein said gas deploying means comprises nozzle means, coupled to said output coupling means, for flowing the gaseous reactant proximate a focal point of the focused laser beam; a second opening in said chamber wall for intro duction of the gaseous reactant therethrough; and means for directing the gaseous reactant intro duced through said second wall opening to said nozzle means.

14. The apparatus of claim 10 further including means for controllably moving said output coupling means and the workpiece relative to one another so that the focused laser beam can be directed onto different portions of the workpiece predetermined region.

1S. Apparatus for performing laser chemical vapor deposition of a gaseous chemical reactant onto a workpiece using a laser beam generated by a laser, comprising:

a reaction chamber constructed to maintain a sealed environment within; an optical fiber for transmitting the laser beam; means for injecting the laser beam into a first input end of said optical fiber for transmission there- through; output coupling means for focussing the laser beam emitted at a second end of said fiber; said optical fiber penetrating a wall of said chamber through an opening therein so that said first and second fiber ends are respectively outside and inside said chamber, said opening being sealed around said fiber to maintain the sealed environment within said chamber; 1 RD-18,215 means for supporting the workpiece within said chamber, said output coupling means being positioned within said chamber so that the focused laser beam falls incident onto at least a portion of a predetermined region of the workpiece where it is desired to deposit the gaseous reactant; nozzle means, coupled to said output coupling means, for flowing the gaseous reactant onto the portion of the workpiece predetermined region onto which the focused laser beam falls incident so that the gaseous reactant is deposited thereon; means for introducing the gaseous reactant through a second opening in said chamber wall and directing the introduced gaseous reactant to said nozzle means; and means for controllably moving said output coupling means and the workpiece relative to one another so that the focused laser beam can be directed onto different portions of the workpiece predetermined region.

16. A laser chemical vapor deposition (LCVD) system for depositing a gaseous chemical reactant onto a a laser for generating a laser beam suitable for performing LCVD; a reaction chamber constructed to maintain a sealed environment within; an optical fiber for transmitting the laser beam; means for injecting the laser beam into a first input end of said optical fiber for transmission there- through; output coupling means for focussing the laser beam emitted at a second end of said fiber; _ RD-18,215 said optical fiber penetrating a wall of said chamber through an opening therein so that said first and second fiber ends are respectively outside and inside said chamber, said opening being sealed around said fiber to maintain the sealed environment within said chamber; means for supporting the workpiece within said chamber, said output coupling means being positioned within said chamber so that the focused laser beam falls incident onto at least a portion of a predetermined region of the workpiece where it is desired to deposit the gaseous reactant; nozzle means, coupled to said output coupling means, for flowing the gaseous reactant onto the portion of the workpiece predetermined region onto which the focused laser beam falls incident so that the gaseous reactant is deposited thereon; means for introducing the gaseous reactant through a second opening in said chamber wall and directing the introduced gaseous reactant to said nozzle means; and 20 means for controllably moving said output coupling means and the workpiece relative to one another so that the focused laser beam can be directed onto different portions of the workpiece predetermined region. 17. Apparatus for performing laser chemical vapor deposition of a gaseous chemical reactant onto a workpiece using at least two laser beams, comprising:

a reaction chamber constructed to maintain a sealed environment within; a first optical fiber for transmitting a first one of the laser beams; a second optical fiber for transmitting-a second one of the laser beam; w.

1 RD-18,215 first injecting means for injecting the first laser beam into an input end of said first optical fiber for transmission therethrough; second injecting means for injecting the second laser beam into an input end of said second optical fiber for transmission therethrough; first output coupling means for focusing a first laser beam emitted at an output end of said first optical fiber; second output coupling means for focusing the second laser beam emitted at an output end of said second optical fiber; said first and second optical fibers penetrating a wall of said chamber so that the input and output ends of both said first and second optical fibers are respectively outside and inside said chambei, the penetration of each said first and second optical fiber into said chamber being adapted to maintain the sealed environment within said chamber; means for deploying the gaseous reactant in the vicinity of predetermined regions of the workpiece where it is desired to deposit the gaseous reactant; and means for supporting the workpiece within said chamber, said first and second output coupling means respec- tively being positioned within said chamber so that the focused first and second laser beams are respectively directed at predetermined orientations relative to the workpiece predetermined regions to result in the deposit of the gaseous reactant thereon.

18. The apparatus of claim 17 wherein the first and second laser beams are respectively generated by first and second lasers to have respective distinct first and second wavelengths; RD-18,215 said first output coupling means positioned so that the first focused beam falls incident onto one ofthe workpiece predetermined regions and results in the deposit of the gaseous reactant thereon by a pyrolysis process; said second output coupling means positioned so that the second focused beam is directed onto a portion of the gaseous reactant proximate one of the workpiece predetermined regions and results in the deposition of the gaseous reactant thereon by a photolysis process; and the first and second laser beam wavelengths being selected to respectively facilitate the pyrolysis and photolysis processes.

19. The apparatus of claim 17 further including means for splitting a laser beam into two laser beams; and said beam splitting means splitting a third laser beam generated by a laser into the first and second laser beams.

20. Apparatus for performing laser chemical vapor deposition substantially as hereinbefore described with reference to Figure 2 or Figure 3 or Figure 4 or Figure 5 of the accompaning drawings.

Published 1989 at The PatentOffioe. State House, 66171 High Holborn, LondonWClR 4TP. Further oopies may be obtained1rom The Patent Onloe. Sales Branch, St Iftry Cray, Orpington, Kent BR5 3RD. Printed by MultiPlex techniques ltd, St Mary Cray, Kent, Con. 1/87