The present invention refers to a maskless method and device for patterning high-resolution images directly on photolithographic layers with a massively-parallel beam array. This device is intended for use in the fabrication of semiconductor devices, microelectronics, Microsystems, thin-film devices, flat screens, and the structuring of masks and substrates for microlithographic applications.
Photolithography is a technique for transferring images onto semiconductor or other substrates. There are two fundamental types of photolithography systems. A first type, referred to as image-projection lithography, uses master patterns, referred to as masks or reticles, and a projection system for projecting the image on the mask on a substrate. A second type of system, referred to as a maskless or direct-write system, forms images directly onto the substrate by scanning (or “writing”) beams of light on the substrate. Maskless systems are used to generate the masks for the image-projection lithography. However, systems with masks are generally faster and better suited for high-volume commercial applications than the direct-write systems.
In image-projection lithography, an image formed on a mask is transferred to a substrate by a projection device. In one type of image-projection system, known as a wafer stepper, the entire mask pattern is projected onto the substrate at once, patterning one portion of the substrate. The mask is then moved (“stepped”) relative to the substrate, and another portion of the substrate is patterned. In another type of lithographic projection apparatus, known as a step-and-scan apparatus, portions of the substrate are irradiated by progressively scanning the mask with a projection beam while synchronously scanning the substrate parallel to this direction. In both types of systems, an image is projected onto a photosensitive layer, referred to as a resist, layered on the surface of the substrate. Each mask includes a pattern corresponding to a layer of circuit components or interconnects to be formed on the substrate. A number of patterns are exposed and processed to build up the three-dimensional structure of an integrated circuit.
After exposure, the resist is developed leaving only a selected pattern of resist on the wafer corresponding to the exposed image. Since resists “resist” etching of the substrate below them, the pattern developed in the resist is transferred to the substrate by a subsequent etch step. The resist may be of a positive or negative type, which refers to the fact that the exposed resist may selectively remain on the wafer or be removed from the wafer in the development step.
Unfortunately, due to decreasing design rules and the wide use of RET (Resolution Enhancement Techniques) such as OPC (Optical Proximity Correction) and PSM (Phase Shift Masks), the masks used in image-projection systems have become increasingly difficult and expensive to make. Since many masks are needed to form the multiple patterns required to manufacture an integrated circuit, the time delay in making the masks and the expense of the masks themselves is a significant cost in the manufacture of semiconductors. This is especially so in the case of smaller volume devices, where the cost of the masks cannot be amortized over a large number of devices. Thus, it is desirable to provide a fast apparatus for making semiconductor chips while eliminating the need for expensive masks. It is also desirable to improve the obtainable resolution of optical lithography. Further, such a device may be useful for directly patterning a small number of substrates, such as runs of prototype devices, and for making masks.
A method to improve the resolution obtainable with conventional masks is described in UV thermoresists: sub-100-nm imaging without proximity effects, Gelbart, Dan, Karasyuk, Valentin A., Creo Products Inc., Proc. SPIE Vol. 3676, p. 786-793, Emerging Lithographic Technologies III, Yuli Vladimirsky; Ed. 6/1999. In this method, microlens arrays are used in combination with image-projection systems to break the image into an array of high-resolution spots that are scanned between pulses in a conventional stepper, forming a complete image. Since the spots are separated one from another, such systems eliminate optical proximity effects. With a combination of a thermal photoresist, this method provides for improved resolution with conventional masks. However, it still requires the use of a mask or reticle.
A method that eliminates the need for masks has been proposed in “A Microlens Direct-Write Concept for Lithography,” Davidson, Mark, SPIE VOL. 3048, PP. 346-355, 1997 (Spectel Company, Mountain View Calif.). In this system microlens arrays have been proposed for use in direct-write systems in combination with parallel light beams for the purpose of obtaining high resolution and higher throughput. A beam splitter produces an array of parallel beams which are individually modulated by an array of piezoelectric discs in a parallel-array Michelson interferometer modulator. The modulated beams are imaged by a microlens array onto a substrate in a multi-spot grid pattern.
Another direct-write lithography employing a microlens arrays is described in “Microlens scanner for microlithography and wide-field confocal microscopy,” U.S. Pat. No. 6,133,986 issued to Kenneth C. Johnson Oct. 17, 2000. In this system a parallel array of modulated beans is provided by a Digital Micromirror Device (DMD), described by J. B. Samsell in “An Overview of the Performance Envelope of Digital Micromirror Device (DMD) Based Projection Display Systems,” Society for Information Display 1994 International Symposium (San Jose, Jun. 12-17, 1994). Each beam is imaged through a corresponding element in a microlens array onto a substrate in a multi-spot grid pattern.
Although both the Davidson and the Johnson systems eliminate the need for masks, they do not improve the resolution obtainable from optical based lithography. Accordingly, it is desirable to provide a practical, maskless, direct-write system with improved resolution and throughput for improved mask making and wafer lithography.
The present invention provides a high resolution and high data-rate direct-write spot grid array lithography system suitable for fast mask making and wafer lithography. According to the present invention, an image is exposed on a substrate by scanning a two-dimensional array of optical beams across the substrate. The image is formed by selectively modulating the optical beams the beam array is scanned across to the substrate. In alternative embodiments, Spatial Light Modulators provide for grey level modulation, in which intermediate level of signals, other than “on” and “off” are available. One such modulator is available from Franhaufer Institute, Dresden, Germany, and is referred to as a Cantilever Beam Micromirror Spatial Light Modulator. Another method for providing grey level modulation is described by Davidson, Mark, SPIE VOL. 3048, PP. 346-355, 1997 cited above. This method uses Michelson interferometer to generate gray level modulation. As described herein, “on” and “off” modulation is a special case of grey level modulation, in which only two gray levels, “0” and “1” are possible. Resolution is enhanced by shaping each of the selected optical beams to provide a narrowed main lobe thus defining a narrowed beam. The narrowed beams are then focused to small spots on the substrate, which is layered with a resist (also known as a photoresist). Undesired exposure resulting from side lobes of the narrowed beams is prevented by preventing the side lobes from exposing the resist with energy above its exposure threshold. This is implemented by the use of a thermal photoresist and an exposure strategy and device architecture which provide time for portions of the resist which have been exposed to side lobes to cool down before such portions might be exposed to further exposure. This exposure strategy further includes a scanning technique that provides sufficient time between exposures of adjacent points on the resist for the resist to cool between consecutive exposures.
The present invention provides lithography method comprising the steps of generating a array of substantially parallel light beams; modulating a plurality of light beams out of the array of the substantially parallel light beams corresponding to a predefined image to be recorded on a resist; shaping each light beam to provide a narrowed light beam having a narrowed main lobe and corresponding side lobes; and translating the resist relative to the array of narrowed light beams along an axis slightly rotated from the normal axis of the array such that a desired image is exposed on the resist in a staggered multiple-raster slanted scan pattern. The use of the narrowed beams provides an advantage of improved resolution.
The present invention provides lithography method and an apparatus employing a memoryless photoresist. As used herein, a memoryless thermal photoresist (or more generally, a limited response period photoresist) is characterized by the fact that it does not integrate energies of consecutive exposures, as long as none of them exceed a threshold, and there is time period (or sufficient cool-down time) between them. The class of thermal photoresists is an example of memoryless photoresists.
The present invention provides lithography method and an apparatus using a scanning and exposure strategy for supressing side lobes of the scanning beams, resulting in a significant improvement in resolution.
The present invention provides a lithography method and an apparatus using scanning techniques that provide sufficient time between exposures of adjacent points on the resist for the resist to cool between consecutive exposures. The present invention provides lithography method and an apparatus utilizing improved scanning techniques that include a high density of spots in a reduced field-of-view for improving the overall throughput of the system by reducing the time lost to scanning off-substrate areas.
The present invention provides lithography method including the step of detecting mechanical misalignments of the movable stage and providing on-the-fly correction in the direct-write optics.
The present invention provides a lithography method and an apparatus comprising a light source for providing and modulating a two-dimensional array of parallel optical beams for irradiating a substrate layered with a resist, the modulation of optical beams corresponding to an pattern to be imaged on the resist; a beam shaper interposed between the light source and the resist for narrowing each of the optical beams; focusing optics for forming a spot-grid array corresponding to a portion of the image; and a movable stage for introducing a relative movement between the resist and the focusing optics. The printer thus records a pattern on the resist resulting from an interaction of the resist with the narrowed modulated optical beams, and prevents recording resulting from an interaction of side lobes.
Advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent like elements throughout, and wherein:
a and 6b illustrate cross-sections of optical beams processed by the printer of the present invention.
In the first embodiment of the present invention, programmable Spatial Light Modulator (“SLM”) 104, illustrated in both
Beam shaper 110, illustrated in
Conventionally, beam shapes are chosen which minimize the amplitudes of the side lobes. In the present invention, a narrower main lobe results from ring apertures with higher weights to the aperture circumference than would be used in a Gaussian aperture. However, such a narrowed beam shape results in substantial side lobes. Improved resolution is obtained in accordance with the present invention by effectively using the narrowed beams in combination with an exposure strategy prevents the resist from being permanently affected by exposure from side lobes. As will be explained more fully below, undesired patterning from these side lobes is prevented by advantageously utilizing a thermal resist and an appropriate exposure strategy.
In an alternative embodiment of the present invention, the memoryless resist is used with a beam as illustrated in
Referring again to
Focusing optics 114 may be a single array of lenses, or multiple arrays arranged in series, as per conventional optical techniques, so the optical paths of the individual lens elements from the separate arrays form a compound lens. Such an arrangement results in arrays of compound lenses having a higher numerical aperture than can be obtained with arrays of single lenses. Such compound micro-lens arrays can be mechanically assembled by stacking individual lens arrays, or manufactured by, for example, well-known MEMS (micro-electro mechanical systems) manufacturing techniques.
As illustrated in
Substrate 120 is layered with a resist 122 which is of a thermal type and irreversibly changes solubility or etch rate when a threshold temperature has been reached. Further, resist 122 is of the type that does not respond to previous partial exposures, provided that sufficient cool-down time is provided. Such thermal resists are one example of a “memoryless” resist, which refers to the fact that the resist is not affected by cumulative partial exposures. The exposure strategy and device architecture of the present invention are matched to the shape of the beams such that resist 122 does not record the side lobes of beams 106. This strategy includes:
The exposure strategy includes the use of a staggered multiple-raster slanted-scan pattern. The narrowed optical beams in the optical beam array scan substrate 120 along adjacent but staggered scan paths such that adjacent spots on substrate 120 are exposed at different times. These time differences are selected in accordance with the exposure strategy to ensure that overlapping side lobe exposures do not permanently pattern the resist 122.
More specifically, substrate 120 is carried on mechanical stage 130, and translated in the y-direction. The array of beams 106 is slightly rotated (or “slanted”) relative to the y-axis. The beam array is formed in a rectangular grid pattern in a number of rows and columns. Stage 130 is translated in the y-direction which results in each beam being scanned along a line parallel to the y-axis of the stage. The offsets of the beams across the x-axis of stage 130 is such that as substrate 120 is translated relative to the beam array in the scan direction y, the spots exposed by the beams leaves no gaps in the pattern on substrate 120. As the stage is further translated, the beams each expose spots in interlaced lines to fill in the complete image on substrate 120.
A second interlaced scanning technique is illustrated in FIG. 4A. In this second slanted-scan technique, a pattern corresponding to a 3×5 beam array is illustrated. The beam array includes 3 columns (A, B and C) and five rows (1, 2, 3, 4 and 5). Each beam is identified by it column and row position. For example, the beam array in its initial position includes beams A1, B1, C1, A2, B2, C2, etc. The beam array is slanted relative to the y-axis, which is the axis along which the beam array is translated relative to substrate 120 by stage 130. The beam array is slanted relative to the y-axis such that spot Al is positioned one/half pixel-width past spot B1 in the y-direction and such that the first beam on column B (beam B1) is displaced one/half pixel-width from the last beam in column A (beam A5) in the x-direction. One exposure is made, exposing the spots in the initial position, which will again be designated with the subscript 1. That is, one spot grid array including spots A11, B11, C11, A21, B21, and C21 etc. are exposed in a first exposure. Stage 130 is then moved in the y-direction by stage 130 so that the beams expose positions translated one pixel-width along the y-axis and a second exposure is made. This second exposure will expose a grid array including A12, B12, C12, A22, B22, and C22 etc. As can be readily appreciated, since the vertical rows of the final pattern on substrate 120 are offset by one-half pixel width from their nearest neighbor and each row in the final pattern is also offset by one-half a pattern from its nearest neighbor, a tightly packed pattern results. Further, as can be seen, adjacent positions on substrate 120 are not simultaneously exposed, which makes this exposure technique suitable for use with memoryless resists and narrowed beams characterized by side lobes.
Either a continuous light source or a pulsed light source may be used for these scanning techniques. However, if a continuous light source is used it is possible that the resist may not cool down sufficiently between exposure of consecutive pixels formed by each beam and illumination from side lobes may accumulate, resulting in a loss of resolution in the y direction. To avoid this loss of resolution, SLM 104 may be used to blank the beams between two consecutive pixels.
One consideration of using large spot-grid arrays is that of field-of view (FOV). In particular, in the simple slanted-scan technique illustrated in
Increasing the density of the beam array requires decreasing the pitch (“P”), the cross-scan distance between the beams. However, to create a complete but non-overlapping traces on substrate 120 with a slanted scan, it is necessary that distance between adjacent scan lines (“d”) equal the product of the pitch (“P”) and N, where N is the number of beams is a column.
d=P*N
To reduce the spacing between adjacent scan lines further would result in overwriting of the spots of one beam by another unless a different scanning technique is implemented. One embodiment of the present invention includes such a technique, which is referred to as interleaving. A number of interleaving techniques exist, corresponding to integer numbers (I) greater than 1.
A first interleaved exposure pattern (corresponding to I=2) is illustrated in
A second interleaved exposure pattern (corresponding to I=3) is illustrated in
Other interleaved techniques can be constructed. For example, in a case characterized by I=4, the stage is translated 4 pixel widths each exposure and the beams are aligned along vertical columns spaced one-fourth of a pixel width apart. In the general case, the beam array is tilted such that the x-axis separation between the paths of lens in consecutive rows is only a fraction (1/I) of the pixel width (p). For example, referring to
As can be readily appreciated from comparing of
In general, in interleaved patterns it is preferable that the light source is a pulsed laser source (such as an Excimer laser or Q laser) or that the SLM be capable of high speed switching so that the beams can be quickly blanked between sequent exposures and blurring does not occur between spots as the stage is repositioned. Alternatively, SLM 104 can appropriately blank all beams.
One other interleave pattern is illustrated in FIG. 5C.
In an alternative embodiment of the present invention, illustrated in
An alternative configuration for the present invention is illustrated in FIG. 8. In this embodiment, light source 805 comprises a pulsed laser light source. The laser light is collimated by lens 810 and reflected from half-silvered mirror 815 onto a 1 k by 1 k pixel reflective spatial light modulator 820. Reflective spatial light modulator 820 comprises an array of micromirrors, such as a Model DMD available from Texas Instruments of Dallas, Tex. Light from each SLM element (also called a pixel) in the “on” state are focused and re-collimated by optical system 830 onto a corresponding element of beam shaper 840. An aperture stop 460 is placed at the focus of optical system 830 so as to block light from the SLM elements in “off” states that are deflected. A further advantage of using the optical system 830 and aperture 460 is the reduction in stray light and a subsequent improvement in the signal-to-noise in the system. Light from SLM elements in “on” states passes through aperture stop 460. Microlens array 845 focuses the selected narrowed beams from beam shaper 410 onto resist 850, which is placed upon movable stage 855.
Movable stage 855 must be capable of providing accurate linear motion, such as can be obtained from a conventional interferometer-controlled stage with linear motors, commercially available from Anorad Corporation of New York.
To correct for any residual inaccuracy such as that created by mechanical vibrations of the stage, a compensator for compensating for inaccuracies in the stage's movement is introduced. Referring to
According to one embodiment of the present invention shown in
To obtain good results when practicing the spot array concept of the present invention, close tolerances on the linearity of the optics is important—both for the focusing optics 114 and for the de-magnification optical elements 150. The optical spots 107 must be located on an exactly rectilinear grid with very exact distances between the spots. For example, in a grid 1000 rows deep, the thousandth row spot of column n must pass accurately near the location which was viewed by the first row's spot of column n−1. Assuming a desired accuracy of {fraction (1/10)}th of a pixel, this implies linearity of one tenth of a pixel over the length of the FOV. Where the lens pitch is equal to 100 pixels, the linearity requirement is therefore 1:10E6 (1000 rows *100 pixels pitch/0.1 pixel tolerance=10E6). This requirement for extreme accuracy is problematic if mechanical vibrations are present.
The present invention can be practiced by employing conventional materials, methodology and equipment. Accordingly, the details of such materials, equipment and methodology are not set forth herein in detail. In the previous descriptions, numerous specific details are set forth, such as specific materials, structures, chemicals, processes, etc., in order to provide a thorough understanding of the present invention. However, it should be recognized that the present invention may be practiced without resorting to the details specifically set forth. In other instances, well known processing structures have not been described in detail, in order not to unnecessarily obscure the present invention.
Only exemplary embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.
This application claims priority from the U.S. provisional application No. 60/331,029 filed on Nov. 7, 2001.
Number | Name | Date | Kind |
---|---|---|---|
3617125 | Sobottke | Nov 1971 | A |
3861804 | Lehmbeck | Jan 1975 | A |
3877801 | MacGovern | Apr 1975 | A |
3973953 | Montgomery | Aug 1976 | A |
3973954 | Bean | Aug 1976 | A |
4272186 | Plummer | Jun 1981 | A |
4353628 | Berman | Oct 1982 | A |
4377753 | Mir | Mar 1983 | A |
4455485 | Hosaka et al. | Jun 1984 | A |
4464030 | Gale et al. | Aug 1984 | A |
4465934 | Westerberg et al. | Aug 1984 | A |
4498742 | Uehara | Feb 1985 | A |
4619508 | Shibuya et al. | Oct 1986 | A |
4668080 | Gale et al. | May 1987 | A |
4680855 | Yamazaki et al. | Jul 1987 | A |
4727381 | Bille et al. | Feb 1988 | A |
4950862 | Kajikawa | Aug 1990 | A |
5027132 | Manns et al. | Jun 1991 | A |
5085977 | Sugawara et al. | Feb 1992 | A |
5121160 | Sano et al. | Jun 1992 | A |
5148322 | Aoyama et al. | Sep 1992 | A |
5166508 | Davis et al. | Nov 1992 | A |
5242803 | Noguchi | Sep 1993 | A |
5282088 | Davidson | Jan 1994 | A |
RE34634 | Konno et al. | Jun 1994 | E |
5327223 | Korth | Jul 1994 | A |
5345336 | Aoyama et al. | Sep 1994 | A |
5386266 | Kang | Jan 1995 | A |
5387961 | Kang | Feb 1995 | A |
5412200 | Rhoads | May 1995 | A |
5436114 | Itoo et al. | Jul 1995 | A |
5436725 | Ledger | Jul 1995 | A |
5452054 | Dewa et al. | Sep 1995 | A |
5463200 | James et al. | Oct 1995 | A |
5486851 | Gehner et al. | Jan 1996 | A |
5495279 | Sandstrom | Feb 1996 | A |
5495280 | Gehner et al. | Feb 1996 | A |
5517279 | Hugle et al. | May 1996 | A |
5539568 | Lin et al. | Jul 1996 | A |
5543919 | Mumola | Aug 1996 | A |
5552820 | Genovese | Sep 1996 | A |
5595857 | Fukuda et al. | Jan 1997 | A |
5631721 | Stanton et al. | May 1997 | A |
5635976 | Thuren et al. | Jun 1997 | A |
5659420 | Wakai et al. | Aug 1997 | A |
5659429 | Kudo | Aug 1997 | A |
5669800 | Ida et al. | Sep 1997 | A |
5691541 | Ceglio et al. | Nov 1997 | A |
5700627 | Ida et al. | Dec 1997 | A |
5777342 | Baer | Jul 1998 | A |
5900637 | Smith | May 1999 | A |
5936713 | Paufler et al. | Aug 1999 | A |
5982552 | Nakama et al. | Nov 1999 | A |
6002466 | Brauch et al. | Dec 1999 | A |
6060224 | Sweatt et al. | May 2000 | A |
6061185 | Cullman et al. | May 2000 | A |
6133986 | Johnson | Oct 2000 | A |
6177980 | Johnson | Jan 2001 | B1 |
6188519 | Johnson | Feb 2001 | B1 |
6248988 | Krantz | Jun 2001 | B1 |
6259550 | Gottfried-Gottfried et al. | Jul 2001 | B1 |
6285488 | Sandstrom | Sep 2001 | B1 |
6301000 | Johnson | Oct 2001 | B1 |
6333508 | Katsap et al. | Dec 2001 | B1 |
6335783 | Kruit | Jan 2002 | B1 |
6373619 | Sandstrom | Apr 2002 | B1 |
6379867 | Mei et al. | Apr 2002 | B1 |
6392752 | Johnson | May 2002 | B1 |
6399261 | Sandstrom | Jun 2002 | B1 |
6424404 | Johnson | Jul 2002 | B1 |
20020054284 | De Jager et al. | May 2002 | A1 |
20020163629 | Switkes et al. | Nov 2002 | A1 |
20030030014 | Wieland et al. | Feb 2003 | A1 |
Number | Date | Country |
---|---|---|
0368482 | Oct 1989 | EP |
0485803 | Oct 1991 | EP |
0486316 | Nov 1991 | EP |
0558781 | Mar 1992 | EP |
0707237 | Oct 1995 | EP |
0759578 | Aug 1996 | EP |
2223861 | Aug 1989 | GB |
57181549 | Apr 1981 | JP |
57191628 | Nov 1982 | JP |
5818622 | Feb 1983 | JP |
59127017 | Jul 1984 | JP |
05224396 | Feb 1992 | JP |
WO 9705526 | Jul 1996 | WO |
WO 9734171 | Feb 1997 | WO |
WO 9734171 | Sep 1997 | WO |
WO 9812603 | Sep 1997 | WO |
WO 0042618 | Jan 2000 | WO |
Number | Date | Country | |
---|---|---|---|
20030123040 A1 | Jul 2003 | US |
Number | Date | Country | |
---|---|---|---|
60331029 | Nov 2001 | US |