Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/0816—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements
  • G02B26/0833—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light by means of one or more reflecting elements the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70283—Mask effects on the imaging process
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70283—Mask effects on the imaging process
  • G03F7/70291—Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70216—Mask projection systems
  • G03F7/70358—Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70425—Imaging strategies, e.g. for increasing throughput or resolution, printing product fields larger than the image field or compensating lithography- or non-lithography errors, e.g. proximity correction, mix-and-match, stitching or double patterning
  • G03F7/70475—Stitching, i.e. connecting image fields to produce a device field, the field occupied by a device such as a memory chip, processor chip, CCD, flat panel display
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/70—Microphotolithographic exposure; Apparatus therefor
  • G03F7/70691—Handling of masks or workpieces
  • G03F7/70791—Large workpieces, e.g. glass substrates for flat panel displays or solar panels

Definitions

• a critical and common factor in the above applications is the need for a large-area patterning system that is capable of providing the required resolution over the entire substrate with high processing throughput.
• the patterning technology used determines not only the ultimate performance of the product (e.g., pixel density in a display, minimum device geometry in a chip, or interconnect density in a packaging module), but also the economics of the entire manufacturing process through such key factors as throughput and yield.
• a contact printer for substrate exposure consists of a fixture to align and hold the board (i.e., the substrate) in contact with the mask, which is then illuminated with high-intensity light to transfer the mask image to the board.
• Systems that can handle boards as large as 610 mm x 915 mm (24" x 36") are commercially available.
• a wide range of resolution capabilities is available in contact printers for different applications -- from below a micron for semiconductor device fabrication to roughly 100 microns and larger for printed circuit board applications.
• a desirable feature of contact printing systems is high throughput; however, the required use of contact masks contains a number of disadvantages.
• the process of designing and constructing a mask places a significant drag on the time required to build electronic module prototypes.
• the process of fabricating an electronic module involves the imaging of different layers and requires a different mask for each layer.
• the time required for switching and aligning masks as well as the expense of maintaining an array of masks for the production of a single electronic module represents a significant fraction of the cost of integrated circuit (IC) manufacturing. Eliminating the need for masks would reduce the long development time and minimize the high costs associated with IC production.
• Projection printing also requires the use of masks.
• masking technology leads to many problems: use of masks does not allow for rapid prototyping of electronic modules; a different mask is required for subsequent layers of an electronic module, adding considerably to the expense of manufacturing; and the production capability of large-area masks does not meet all the current industry requirements for precision and accuracy at low cost and on fast schedules.
• the entire board can be directly patterned.
• CAD computer aided design
• the offered resolution varies from 13-25 ⁇ m for printed circuit board patterning to under a micron for systems designed for semiconductor applications. Since transfer of the pattern information in a scanning- spot direct-write tool takes place in a slow, bit-by-bit serial mode, typical processing times for such systems can range from 2 minutes to several hours per sq. ft., depending upon the resolution and the complexity of the pattern data.
• Direct-write systems avoid the problems associated with using masks, they are extremely slow because transfer of the pattern information takes place in a bit-by-bit serial mode. Due to the large number of pixels (-10 8 - 10 10 ) that must be written on an electronic module, typical processing times with such systems are unacceptably long for cost-effective volume manufacturing. Direct-write systems, therefore, are best suited for applications such as mask fabrication and prototyping.
• DMD Deformable micromirror device
• the Deformable Micromirror Device is an optomechanical system which acts as a spatial light modulator that works in the reflective mode.
• the device consists of an array of hinged micromirrors which fit on a chip, each micromirror having the capability of tilting in two different rotations about an axis.
• micromirrors tilt in one direction, they may reflect radiation through an optical system, for imaging; thus these micromirrors are described as turned “on.”
• Micromirrors that tilt in the other direction reflect radiation so that it does not pass through the optical system. These mirrors are turned “off.”
• the set of micromirror devices arranged in an array is the object of an imaging system where the "on” mirrors form the bright pixels of the object while the "off” mirrors form the dark pixels.
• DMD Micromirror Device
• One embodiment of the invention disclosed integrates the seamless scanning system with Deformable Micromirror Device (DMD) technology, while another embodiment uses the seamless scanning system with Liquid Crystal Light Valve (LCLV) technology.
• DMD Deformable Micromirror Device
• LCLV Liquid Crystal Light Valve
• the invention is a maskless patterning system which is capable of imaging electronic modules by delivering high resolution over a large image field, with high exposure throughput. It is the object of the invention to eliminate the need for masks in the imaging of patterns on electronic modules, through the use of seamless scanning and a spatial light modulator that is directly addressed by a control system. Another object of the invention is to retain choice of light source, including laser and halogen lamp, and choice of spatial light modulator, including a deformable micromirror device (DMD) and an array of liquid crystal light valves (LCLVs).
• DMD deformable micromirror device
• LCLVs liquid crystal light valves
• Another object of the invention is to enable patterning of substrate panels that are several times greater in size than is currently possible. For a given panel size, processing throughput is increased substantially, at the same time that high resolution is maintained over the entire substrate.
• a feature of the invention is to achieve seamless scanning through electronically programming the spatial light modulator.
• the DMD or LCLV array is configured to reflect or transmit an image with a particular intensity profile, part of which may be integrated with the intensity profile of an overlapping, adjacent scan.
• Another feature of the invention is that the entire spatial light modulator may be illuminated so as to allow the modulator itself to generate the intensity profile characteristic of a scanning hexagonal field.
• An advantage of the invention is that it corrects for image reversal with the stream of data that is loaded onto the spatial light modulator, thus obviating the need for image reversing optics.
• Another advantage of the invention is its versatility, which enables it to be used in the production of several high-volume electronic products.
• a further advantage of the invention is that it eliminates the shortcomings of conventional contact, projection, and direct-writing systems.
• FIG. 1 is a schematic presentation of an embodiment of the invention wherein the spatial light modulator is a deformable micromirror device (DMD).
• DMD deformable micromirror device
• FIG. 2 is a schematic presentation of a prior art imaging system which uses a conventional mask.
• FIG. 3 is a diagram of hexagonal overlap seamless scanning according to the prior art imaging system of U.S. Pat. No. 4,924,257.
• FIG. 4 is a semi-schematic diagram of one micro-mechanical element of a DMD array.
• FIG. 5 shows an illumination pattern on a DMD chip which allows for seamless scanning.
• FIG. 6 is a chart showing how light gradients are applied in complementary fashion to achieve seamless optical scanning.
• FIG. 7 is shows how adjacent optical image fields are exposed in a complementary fashion.
• FIG. 8 is a stylized drawing showing how the tiling effect is eliminated by complementary scans.
• FIG. 9 is a schematic presentation of an embodiment of the invention wherein the spatial light modulator is a liquid crystal light valve (LCLV).
• LCLV liquid crystal light valve
• the substrate is scanned as shown in FIG. 1 along, say, the y-axis.
• control system 7 feeds a stream of pixel selection data to the DMD array 3, thus causing the micromirror elements to tilt in the correct orientation.
• the illuminated pixel pattern imaged onto the substrate 5 by the radiation source thus represents an instantaneous snapshot of the set of micromirrors at that moment in time.
• the pixel selection data stream configuring the DMD array 3 must be synchronized with the motion of the scanning stage 6.
• the radiation illuminating the DMD array 3 must also be pulsed or shuttered at a repetition rate that is synchronized with the micromirrors on the DMD array 3 and the scanning stage 6.
• the DMD pixels will already be reset by the pixel selection data to generate a different pattern when imaged to the substrate 5.
• the stage 6 is moved by a suitable amount along an orthogonal axis (x- axis), following which another scan is generated along the y-axis, and so on.
• the duration of the illuminating pulse of light, ⁇ t is determined by the following expression: ⁇ t-v « ⁇ y (1 ) where v is the velocity of the stage 6 moving the substrate 5, and ⁇ y is the desired minimum feature size of the projection system 4. If the pulse duration is too large, then the generated image will be blurred. It is possible to compensate for a longer pulse duration by reducing the velocity of the stage. While this reduces the throughput of the system, it could be a lower cost option. Conventional excimer laser systems have pulse durations on the order of 10 - 40 ns. If the substrate is scanned at 250 mm/s, then the product ⁇ t-v would be about 0.01 ⁇ m. This is more than adequate for an imaging system with a desired minimum feature size of 1 ⁇ m.
• a continuous wave (CW) source If a continuous wave (CW) source is used, then the radiation source must be shuttered at the appropriate frequency and with the proper duty cycle to meet the condition given in equation (1) above.
• CW continuous wave
• the stage 6 velocity must be reduced to much less than 4 mm/s, assuming that pixel selection data can be fed to the spatial light modulator at 4 kHz. While this represents a system which would have much lower throughput, it would also be a lower cost system.
• seamless scanning patterning technology has been used with masking technology to expose a desired pattern on an electronic module.
• this invention eliminates the need for a mask, a preliminary description of seamless scanning when used with a conventional mask will nevertheless aid in understanding the maskless nature of this invention.
• the means by which this invention eliminates masking technology is discussed more fully later, in the subsection entitled Spatial Light Modulator. Thus, the description which immediately follows describes how the seamless scanning technology has been demonstrated when used with a mask.
• the substrate stage 10 scans the substrate 8 across its hexagonal exposure region so as to traverse the length of the substrate in the direction of the scan.
• the mask stage 11 scans the mask 9 across its hexagonal illuminated region.
• both stages 10 and 11 move in a direction orthogonal to the scan direction.
• a new scan is generated by precise movements of the substrate stage 10 and mask stage 11 in the same manner as before.
• the effective scan width and the illumination source system 12 are designed with such characteristics that in combination, they produce a transition, from one scan to the next, that is "seamless" and free from non-uniformities in intensity.
• a spatial light modulator is incorporated to function as a kind of programmable mask, which makes the invention suitable for rapid prototyping, flexible manufacturing, and mask making. Two preferred embodiments of the spatial light modulator are described below.
• the micromirror operates in binary digital mode or in trinary digital mode.
• DMD arrays that function in trinary digital mode have three possible states: “on,” “off,” or “flat.”
• each micromirror 25 When operating, each micromirror 25 is twisted to the “on” or “off” state; however, when no power is applied to the array it relaxes to the flat state. Thus, in operation, each micromirror stays latched in an "on” or “off” position until a new piece of data is loaded from the memory cell.
• each pulse that illuminates the DMD array 3 and is imaged onto the substrate 5 will illuminate a different part of the substrate.
• the DMD 3 operates so that the entire array of micromirrors can be reconfigured for each pulse to form the correct image on the substrate 5.
• the projection lens assembly 4 is of a conventional design with all refractive elements, it will form a reversed image of the DMD 3 on the substrate 5.
• special reversing optics were required to correct for image reversal resulting from the projection lens. This invention, however, does not require an image reversing system to properly orient the image on the substrate.
• the desired image is digitized and loaded onto the DMD array as a stream of data in such a sequence that it corrects for image reversal.
• the invention also eliminates the need for a scanning translation stage for the mask assembly required by the prior art seamless scanning technology.
• the physical footprint of the overall lithography system is thus reduced, as are alignment and handling constraints.
• constraints on the translation stage are also significantly reduced.
• the DMD performs the role played by the mask in a FIG. 2 imaging projection system by means of the control system, which dynamically addresses the micromirrors for each position of the stage.
• the desired image on the substrate is digitized and fed to the DMD array as a stream of data in a similar fashion as used in direct-write systems or parallel by pixel group for faster setting.
• a difference between the invention and conventional direct-write methods is that the parallel processing power of the DMD can be utilized to project images of more than 1 million pixels per frame at a rate that can be greater than several kiloHertz.
• existing direct-write systems are typically 1000 times slower, because they relay data in a slow, bit by bit fashion.
• the substrate 5 is illuminated by a beam pattern 31.
• the illuminated pattern imaged onto the substrate 5 at any given moment represents a particular orientation of the DMD array 3.
• the stage 6 has moved by an amount that is a fraction of the width of the illumination beam 31.
• Each point of the substrate 5 that is to be patterned is illuminated by several different pulses as the stage 6 carries the substrate 5 through the illumination beam pattern 31. This effect integrates the energy along the scan direction and improves the uniformity of the delivered dose along that axis.
• the number of pulses that illuminates a certain point on the substrate 5 is determined by the repetition rate of the laser, the speed of the stage 6, and the size of the illumination area. It is desirable to have a certain minimum number of pulses to illuminate each point on the substrate 5 in order to achieve a uniform integrated dose along the scan direction. It is possible to increase the number of pulses illuminating each point by decreasing the stage 6 speed, but this also reduces the throughput of the system so this is not desirable. In principle it could be achieved by increasing the repetition rate of the laser, but, in practice, this can be difficult. With this invention, it is possible to have more than one spatial light modulator in the object field of the reduction lens 4 to increase the number of pulses illuminating each point of the substrate 5.
• the same data stream can be fed to each of the spatial light modulator arrays with a temporal delay between the streams determined by the physical separation between the edges of the arrays.
• This added flexibility is a powerful feature of this invention, making it easier to design lithography tools to meet the industry's demands.
• the stage 6 moves in a direction orthogonal to the y-direction scan, i.e., in the x direction. Control of the displacement of the stage 6 in the x-direction is important to maintaining seamless exposure from one scan to the next. If the intensity profile across each scan (in the x-direction) were constant, then the stage 6 would have to move in the x-direction by an amount exactly equal to the scan width.
• stitching errors can be eliminated through the use of a hexagonal illumination pattern (see also FIG. 3). That is, one could illuminate the DMD 3 with a beam whose transverse profile is that of a hexagon which transcribes the array of micromirrors, as shown in FIG. 5. Thus, in FIG. 5, shaded area 32 depicts the laser illumination area on the DMD array 3.
• other polygonal illumination geometries may be used, such as trapezoids and parallelograms. It is also possible to illuminate the entire DMD array and use the array itself to generate the intensity profile characteristic of, for example, a scanning hexagonal field. Using this method, seamless joining of scans is achieved through electronic programming of the micromirror elements. The elements are individually programmed in such a way as to provide a uniform intensity profile across adjacent scans.
• an adjacent scan 42 When an adjacent scan 42 is generated, it partially overlaps the previous scan 43, as illustrated in FIG. 7, along area 44, the region of partial overlap. Uniform intensity across the width of the adjacent scans is achieved by integrating the intensities of the edge profiles, as shown in FIGS. 8 and 9.
• micromirrors are unlikely to be "on” full-time, because they are needed to generate a pattern on the substrate -- not to illuminate the entire board, as described above.
• the micromirrors must therefore be programmed to flip "on” or “off” so that the DMD array reflects the appropriate image onto the moving substrate.
• LCLV Liquid Crystal Light Valve
• a liquid crystal light valve is an electro-optic device which is programmable and has an array of optically active pixels that can be directly addressed by a control system.
• the pattern of modulation that is desired to be sent through the LCLV's output beam is a digital image that has been stored and is fed to the LCLV as a stream of data.
• the transmission through the liquid crystal medium is modulated, and the modulation is transferred to a beam of radiation transmitted through the light valve to create the pattern which is to be imaged on the substrate.
• the individual pixels are either transmissive or opaque.
• the transmissive pixels of the LCLV embodiment are functionally analogous to the micromirrors of the DMD embodiment (described above) that are tilted in the "on" position, because they allow radiation to be imaged on a point of the substrate.
• the opaque pixels of the LCLV embodiment are the functional equivalent of the "off" micromirrors of the DMD embodiment, because they do not allow radiation to pass through the system for imaging.
• micromirrors on the DMD that are in the "off” position prevent radiation from passing through the imaging system by deflecting the radiation out of the imaging path.
• FIG. 10 is a schematic illustration of the embodiment of the invention that uses the LCLV 45.
• the primary difference between FIG. 10 and FIG. 1 other than the choice of spatial light modulator (i.e., the LCLV 45), is the fact that the LCLV embodiment shown in FIG. 10 enables radiation leaving the radiation source 1 to pass through the LCLV for transmission to the projection lens 4, whereas in the DMD embodiment shown in FIG. 1 , radiation leaving the source 1 for imaging is reflected by the DMD 3 toward the projection lens 4.
• the lithography system disclosed herein has applicability in the fabrication and manufacturing of diverse electronic and opto-electronic products.
• the invention eliminates the need for masks, it is ideally suited for rapid prototyping and flexible manufacturing of electronic modules.
• it is particularly useful for mask making, because of the quick turnaround of corrections if the mask pattern does not fit the task in all respects.
• it provides the capability to pattern large substrates, even continuous substrates such as flat panel displays (FPDs), while maintaining high resolution and high throughput.
• FPDs flat panel displays
• the spatial light modulator can simulate a mask of unlimited size. This is an important advantage for the production of large FPDs, where the production and handling of large-area masks has represented a significant cost barrier to large FPD production. Also, with its continuous scanning movement and its unique exposure field, the invention can pattern boards of arbitrarily large sizes at fast exposure rates, due to the seamless overlap between adjacent scans. The critical stitching requirements of conventional step-and-repeat tools are thus eliminated. Furthermore, the invention achieves microelectronic patterning significantly faster than focused-beam direct- write systems, which transfer pattern information in a bit-by-bit serial mode. Instead, the invention uses high parallel-processing power to generate any possible pattern, while maintaining high resolution over a large image field.
• the maskless, large-area, high-throughput lithography system fills a critical need in the manufacturing of numerous electronic products required in diverse applications, such as flat-panel displays, printed circuit boards, and semiconductor ICs.

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• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

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• 1996
  • 1996-07-25 WO PCT/US1996/012240 patent/WO1998004950A1/fr not_active Ceased
  • 1996-07-25 EP EP96925490A patent/EP0914626A4/fr not_active Ceased

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