Optical: systems and elements – Mirror – Plural mirrors or reflecting surfaces
Reexamination Certificate
1999-01-23
2001-11-06
Henry, Jon (Department: 2872)
Optical: systems and elements
Mirror
Plural mirrors or reflecting surfaces
C359S224200, C359S291000, C355S035000, C355S053000, C355S067000
Reexamination Certificate
active
06312134
ABSTRACT:
TECHNICAL FIELD
This invention relates to high-throughput lithography systems, and, more particularly, this invention relates to a maskless lithography system that provides large-area, seamless patterning using a spatial light modulator capable of being directly addressed by a control system.
BACKGROUND ART
High-throughput lithography systems are advantageous in the manufacture of many electronic and opto-electronic products, which require fabrication of millions of microscopic structures on a single large substrate. Such structures may be in the form of active devices, such as the transistors in an electronic display or in a semiconductor integrated circuit, or may be in the form of passive patterns, such as the metal interconnect network in a multichip packaging module or in a printed circuit board. The large substrate can be a display panel, a silicon wafer, or a board. The pattern feature sizes in these diverse products, which shall be referred to as electronic modules, range from sub-micron for semiconductor chips to multi-microns for displays and packaging products. The substrate size requirements vary from a few square centimeters for small modules to a few square feet for large displays.
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.
Conventional lithographic techniques that use masking technology involve a multi-step process which includes the photographic definition of patterns on optical masks which are used to impart these patterns onto the surfaces of individual substrates. The major exposure technologies used currently in patterning of electronic modules can be classified into three general categories:
(1) contact printing systems;
(2) conventional and step-and-repeat projection systems; and
(3) focused-beam laser direct-writing systems. Each of these will be briefly described below.
(1) Contact Printing Systems
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×915 mm (24″×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.
Furthermore, contact printing requires that, during exposure, the film or glass mask and the resist-coated board be brought in contact or near-contact. Good contact is difficult to produce over a large area. Poor contact, or a proximity gap, results in limited resolution. Frequent contact between the mask and the board causes generation of defects on the board which results in lower yields and causes reduction of the mask life, which leads to higher overall costs. In addition, variations in the gap cause feature size errors.
For certain electronic modules, such as flat panel displays (FPDs), the module size can be up to several square feet, requiring masks which are just as large. The technology to manufacture the masks themselves is a real impediment to manufacturing large-area FPDs. Eliminating the dependency on masks would sidestep this barrier; easing the difficulty of making the mask itself would be a great step forward.
(2) Projection Printing Systems
A wide variety of projection imaging systems are routinely used in fabrication of various electronic modules. Typically, a projection lens with a 1:1 magnification is used for imaging the mask pattern on the board. The illumination system uses a 1-2 kW mercury-xenon arc lamp, a heat-filtering mirror that filters away wavelengths in the visible and infrared regions, and a condenser to direct the radiation to the mask. All projection printing systems suffer from the limitation that there exists a trade-off between the resolution and the maximum image field size of the projection lens. For example, whereas 25 &mgr;m resolution can be obtained over approximately a 100 cm square field, the imaging area for 1 &mgr;m resolution must be limited to a field diameter no larger than 1-2 cm. For larger areas the total imaging field must be broken up into segments which then must be imaged one at a time in a step-and-repeat fashion, thereby limiting the available throughput. Most step-and-repeat systems use reduction imaging, typically with a 2:1, 5:1 or 10:1 ratio. Generally, systems with larger reduction ratios provide higher resolution, but also lower throughput.
Projection printing also requires the use of masks. As described above for contact printing systems, 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.
In addition, conventional projection imaging systems, due to fundamental lens-design considerations governing their performance, are forced to make a trade-off between resolution and image field size. This trade-off necessitates step-and-repeat imaging, in which significantly lower throughputs are obtained than by full-field contact printing. Lower throughputs result because each step involves the operations of load, unload, align, settle and focus. Step-and-repeat imaging also leads to higher costs due to the requirement of several masks and the errors introduced in stitching the different fields together.
The overlap or gap errors due to stitching the different fields together, usually referred to as “tiling,” can be eliminated by complementary overlapping polygonal scans as described by a coinventor in U.S. Pat. No. 4,924,257, K. Jain, Scan And Repeat High Resolution Projection Lithography System, May 8, 1990.
U.S. Pat. No. 5,477,304, K. Nichi, Projection Exposure Apparatus, issued Dec. 19, 1995, uses a rectangular scanning aperture with a variable field stop, and uses orthogonally-moving mask stage and substrate stage to form a number of varying rectangles, in a tile pattern on a circular wafer.
Other systems use extensive shutter and blind components to form a useful exposure aperture, but still require a mask. See, as examples, U.S. Pat. No. 5,477,410, Projection Exposure Apparatus, issued Dec. 5, 1995, Nishi, and U.S. Pat. No. 5,227,839, Small Field Scanner, issued Jul. 13, 1993, Allen.
(3) Focused-Beam Direct-Writing Systems
A focused-beam direct-writing system uses a blue or UV laser in a raster scanning fashion to expose all the pixels, one at a time, on the substrate. The laser beam is focused on to the resist-coated boar
Dunn Thomas J.
Hoffman Jeffrey M
Jain Kanti
Anvik Corporation
Henry Jon
King Carl C.
LandOfFree
Seamless, maskless lithography system using spatial light... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Seamless, maskless lithography system using spatial light..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Seamless, maskless lithography system using spatial light... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2586927