Patent Number: 061335770
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The detailed description set forth below in connection with the appended drawings is intended as description of the presently preferred embodiment of the invention and is not intended to represent the only form in which the present invention may be constructed or utilized. The description sets forth the functions and the sequence of steps for constructing and operating the invention in connection with the illustrated embodiment. It is to be understood, however, that the same or equivalent functions and sequences may be accomplished by different embodiments that are also intended to be encompassed within the spirit and scope of the invention. The extreme ultra-violet photolithography system for facilitating production of semi-conductor components having geometries of 10 nm and smaller of the present invention is illustrated in FIGS. 1-11, which depict a presently preferred embodiment thereof. Referring now to FIG. 1, the extreme ultra-violet photolithography system generally comprises a converging-diverging nozzle 10 from which gas 11 flows, at a supersonic velocity, toward diffuser 12 which captures a substantial portion of the flowing gas 11. The converging-diverging nozzle 10 and the diffuser 12, as well as the collecting and focusing optics 29 and the work piece, i.e., integrated circuit chip(s) being fabricated, are all preferably disposed within a common vacuum chamber 40, so as to facilitate integrated circuit fabrication utilizing photolithography. As described in detail below, the diffuser 12 reduces the velocity of the flowing gas 11, while simultaneously increasing the pressure thereof. Gas flows from the diffuser 12 via conduit 13 to compressor 14, which preferably comprises a 0.71 hp compressor. The compressor 14 compresses, i.e., increases the pressure of, the gas 11 such that it may be recycled to the converging-diverging nozzle 10 and thus used repeatedly to produce extreme ultra-violet light. Gas flows from the compressor 14 to heat exchanger 16, preferably a 64.1 btu/min heat exchanger for removing heat from the compressed gas. According to the preferred embodiment of the present invention, the temperature of the gas entering the heat exchanger 16 is approximately 610.degree. K and the temperature of the gas exiting the heat exchanger 16 is approximately 300.degree. K. The gas exiting the heat exchanger 16 is communicated via conduit 17 to the converging-diverging nozzle 10 where a stagnation pressure of 6,079 torr is developed. Stagnation pressure is defined herein as that gas pressure when no flow occurs. Referring now to FIG. 2 also, the converging-diverging nozzle 10 more particularly comprises a pressure plenum 18 into which the compressed gas from the heat exchanger 16 flows. The converging-diverging nozzle 10 further comprises a converging portion 20 and a diverging portion 22. The converging-diverging nozzle 10 is configured so as to accelerate the gas flowing therethrough to a supersonic velocity, preferably above Mach 2, preferably approximately Mach 3. The diverging portion 22 preferably has a generally rectangular cross-section and is preferably configured such that the length, Dimension L, is substantially greater than the width, Dimension W, thereof. This configuration provides a high aspect ratio which facilitates the exposure of a substantial portion of the flowing gas to the radiated energy beam and which provides a short path for extreme ultra-violet light stimulated thereby through the flowing gas. Referring now to FIGS. 1 and 3, the diffuser 12 generally comprises an opening which corresponds generally in size and configuration to that of the widest portion of the diverging portion of the converging-diverging nozzle 10. Thus the opening of the diffuser has a length which is preferably slightly longer than the length of the converging-diverging nozzle 10 and has a width which is preferably slightly longer than the width of the converging-diverging nozzle, so as to capture a substantial portion of the gas flowing from the converging-diverging nozzle 10. Those skilled in the art will appreciate that various different configurations of the diffuser 12 are suitable. The diffuser decreases in cross-sectional area from the opening 30 thereof to the coupling end 32 thereof, at which the fluid conduit 13 attaches. As discussed in detail below, the cross-sectional area of the diffuser 12 optionally increases again, from the narrowest portion thereof, so as to define a throat. Such tapering or narrowing of the cross-sectional area of the diffuser 12 provides a gradual slowing of the gasses captured thereby, while minimizing the occurrence of undesirable regurgitation which might otherwise occur. Optionally, one or more knife edges are formed in or proximate the diffuser 12, so as to aid in the deceleration of the gasses entering the opening 30. According to the preferred embodiment of the present invention, the periphery of the opening 30 of the diffuser 12 is formed as a first knife edge 31. Additional concentric generally rectangular knife edges 33 and 35 are disposed within the opening 30 of the diffuser 12 and mounted thereto via any suitable means. Knife edge struts may optionally be utilized to mount the second 33 and third 35 concentric rectangular knife edges in place within the opening 30 of the diffuser 12. Those skilled in the art will appreciate that various different numbers and configurations of such knife edges may be utilized to effect generation of shocks which tend to decrease the velocity of the supersonic gas while simultaneously increasing the pressure thereof within the diffuser 12. Isobaric pressure profiles of the gas flowing from the converging-diverging nozzle 10 are provided in FIG. 1. As shown, the radiated energy beam, an electron beam according to the preferred embodiment of the present invention, is directed into that portion of the flowing gas 11 proximate the converging-diverging nozzle 10, so as to enhance the efficiency of the present invention. This is better shown in FIG. 4 which illustrates the relative positions of the electron beam 23 and the flowing gas 11 in perspective. A portion of the extreme ultra-violet light 27 whose emission is stimulated from the flowing gas 11 by the radiated energy beam 23 is collected and focused by collecting and focusing optics 29, which direct the extreme ultra-violet light onto a work piece, i.e., an integrated circuit component being fabricated, as desired. According to the preferred embodiment of the present invention, a vacuum pump, preferably that vacuum pump 36 utilized to evacuate the vacuum chamber 40 within which the gas 11 flows and within which the photolithographic process is performed, evacuates a substantial portion of the gas 11 which is not captured by the diffuser 12 and provides that gas 11 back to the converging-diverging nozzle 10, preferably via the compressor 14 and heat exchanger 16, so as to facilitate recycling thereof. Referring now to FIG. 4, in operation a gas, preferably a noble gas such as argon, helium, or xenon, or a combination thereof, flows at a supersonic velocity from the converging-diverging nozzle 18 when a pressurized supply thereof is provided to the converging-diverging nozzle 18 via gas conduit 17. Sufficient pressure is provided by compressor 14 to achieve the desired gas flow speed. A radiated energy beam, preferably an electron beam, is directed through the supersonic gas flow 11 at a position which minimizes the transmission of the resulting extreme ultra-violet light through the gas 11, thereby mitigating undesirable absorption thereof. A substantial portion of the flowing gas 11 is captured by the diffuser 12 and recycled. A substantial portion of the gas not captured by the diffuser 12 is evacuated from the vacuum chamber 40 via vacuum pump 36 and recycled. At least a portion of the extreme ultra-violet light 27 emitted due to the interaction of the radiated energy beam 23 with the supersonic gas 11 is collected and focused by collecting and focusing optics 29 so as to facilitate photolithography therewith. Thus, according to the present invention, contamination of the collecting and focusing optics 29, as well as any other sensitive surfaces within the vacuum chamber 40, is mitigated. Such contamination is mitigated since supersonic flow of the gas 11 tends to force all of the gas particles, i.e., molecules, atoms, ions, electrons, etc., into the diffuser 12, thereby substantially mitigating the amount of such particles floating freely within the vacuum chamber 40 and capable of coming into contact with such sensitive items. The present invention takes advantage of the gas dynamic properties of the supersonic jet to direct any debris generated during the plasma formation into the diffuser, and thus away from the collection and focusing optics 29, as well as the rest of the photolithography system. The efficiency of the present invention is enhanced by minimizing the amount of gas 11 through which the generated extreme ultra-violet light 27 must pass. As those skilled in the art will appreciate, extreme ultra-violet light is readily absorbed (and thus attenuated) by the noble gasses from which its emission is stimulated. Thus, it is very desirable to minimize the distance through which the extreme ultra-violet light 27 must travel through such gas. This is accomplished by positioning the radiated energy beam 23 close to the surface of the flowing gas 11, preferably by positioning the radiated energy beam 23 proximate the converging-diverging nozzle 10 where the gas flow has a comparatively narrow cross-sectional area and comparatively high density. Thus, according to the present invention, the high density gas region is confined to nearly the same volume as that occupied by the radiated energy beam. Thus, extreme ultra-violet light generated thereby is not required to travel through a substantial portion of the high density gas after leaving the area where stimulated emission occurs. The high aspect ratio configuration of the converging-diverging nozzle tends to maximize the volume of flowing gas available for interaction with the radiated energy beam, while simultaneously minimizing the volume of flowing gas which attenuates the stimulated extreme ultra-violet light. As those skilled in the art will appreciate, the higher the velocity of the flowing gas 11, the smaller the mass flow thereof which will diverge or turn away from the gas flow, i.e., jet, when surrounded by the very low pressure of the vacuum chamber. Any such flow which diverges from the gas jet into the high vacuum surrounding the gas jet must ultimately be pumped out against a very high adverse pressure ratio, which adds substantially to the cost of manufacturing and maintaining the system. Even more important, the gas that diverges from the gas jet becomes a potential contaminant for the collecting and focusing optics and also becomes an undesirable attenuating mass for the extreme ultra-violet light which is produced by the interaction of the radiated energy beam and the gas flow. Further, by converting a significant portion of the kinetic energy of the flowing gas 11 into pressure, the need to increase the pressure of the gas via the compressor 14 is reduced, thereby facilitating operation with a smaller capacity and less expensive compressor 14. Referring now to FIGS. 5 and 6, the generally rectangular concentric knife edges 33, 35 of FIG. 3 are shown in further detail. Each generally concentric knife edge 33, 35 preferably comprises a body 37 and a bevel 39. As those skilled in the art will appreciate, it is the purpose of each knife edge 31, 33, and 35 to produce a shock wave, similar in nature to the sonic boom shock wave associated with supersonic aircraft, which defines a region of increased pressure within the diffuser 12, and thus facilitates reduction of the speed of the flowing gas 11 and simultaneously facilitates an increase in the pressure thereof. Referring now to FIG. 8, the converging-diverging nozzle is optionally configured as a cap 10a which is specifically sized and shaped to fit a standard pulse generator. Thus, the cap 10a comprises a body 50 which is sized to be received within the exit orifice of a pulse generator and a flange 52 which functions as a stop to limit insertion of the body 50 into the exit orifice. A rectangular boss 54 has a rectangular opening 56 formed therein. The converging-diverging bore 58 of the nozzle is formed in a continuous or co-extensive manner in the body 50, flange 52, and boss 54. Such construction facilitates easy removal and replacement of the converging-diverging nozzle 10a, particularly when a standard pulse generator is utilized. Referring now to FIG. 9, a preferred cross-sectional profile of a nozzle orifice is shown. The nozzle comprises a converging region 60 which decreases to form a neck 62 and then increases in cross-sectional area to form the diverging region 64 thereof. The exit plane 66 is that plane of the nozzle flush with the end thereof, i.e., the outer opening thereof. Referring now to FIG. 10, the cross-sectional profile of the diffuser is shown. According to the present invention, the diffuser tapers or converges from the entry plane 70 to define a converging portion 72 thereof. At the end of the converging portion 72 a neck 74 is formed and the diffuser may then optionally diverge or increase in cross-sectional area so as to form a diverging portion 76. As those skilled in the art will appreciate, the velocity of the flowing gas 11 decreases within the converging portion 72, while the pressure thereof simultaneously increases. Referring now to FIG. 11, the calculated density field for a xenon extreme ultra-violet light source jet and diffuser is shown. Gas 11a from within the converging-diverging nozzle exits therefrom at the exit plane 66 to form gas jet 11b. The gas jet 11b enters the diffuser at the entry plane 70 thereof. Within the diffuser 12 first oblique shocks 80 are formed due to the knife edge(s) 31 defined by the opening 30 of the diffuser 12. The oblique shocks 80 interact to form perpendicular shock 82 downstream therefrom. Second oblique shocks 84 are formed as the flowing gas interacts with the internal walls of the diffuser. The second oblique shocks 84 interact with one another so as to form perpendicular shock 86. Third oblique shocks 88 are formed in a similar manner downstream from the second oblique shocks 84. As those skilled in the art will appreciate, each shock defines a high pressure region within which the flowing gas slows. In this manner a plurality of knife edges may be utilized to form shocks so as to effect slowing of the gas flow and increasing the pressure thereof. It is understood that the exemplary method and apparatus for producing extreme ultra-violet light described herein and shown in the drawings represents only a presently preferred embodiment of the invention. Indeed, various modifications and additions may be made to such embodiment without departing from the spirit and scope of the invention. For example, various sizes, shapes, crosssectional configurations, etc. of the nozzle and diffuser are contemplated. It must further be appreciated that various different configurations of the radiated energy beam, other than circular as shown, may be utilized. For example, the radiated energy beam 23 may alternatively be elliptical, square, rectangular, triangular, etc. It is generally desirable that the radiated energy beam 23 be comparable in cross-sectional area to that portion of the flowing gas 11 proximate the converging-diverging nozzle 10, so as to minimize the amount of gas 11 through which stimulated extreme ultra-violet light 27 must flow. Further, it must be appreciated that the method and apparatus for producing extreme ultra-violet light according to the present invention may be utilized in a variety of different applications, and is not limited to use in photolithographic applications. Further, it must also be appreciated that the general method and apparatus of the present invention may alternatively be utilized to produce wavelengths of electromagnetic radiation other than extreme ultra-violet, and thus is not limited to the production of extreme ultra-violet light. Thus, these and other modifications and additions may be obvious to those skilled in the art and may be implemented to adapt the present invention for use in a variety of different applications.