Additional info also available from JMAR's home page at:
jmar.com and jmar.com
ADDITIONAL INFORMATION ON SEMICONDUCTOR LITHOGRAPHY
This "Additional Information" is provided in response to the numerous requests that JMAR continues to receive from shareholders and potential investors for more details on JMAR's X-ray lithography program and the relationship between it and advanced lithography programs being conducted elsewhere.
Overview
Lithography is one of the most critical elements in the production of semiconductor integrated circuits (IC's). It is a photographic process which uses precision light sources to copy intricate computer-generated electronic circuit designs onto the semiconductor chips. Lithography systems are often categorized by the characteristics of their light sources.
Optical Lithography
Systems using light beams which can be focused by optical lenses or directed by reflective mirror-like elements are usually referred to as "optical" lithography systems. Today's commercial production lithography is performed by optical systems employing ultraviolet light sources such as excimer lasers or precision arc lamps. They produce 0.248 micron or 0.365 micron light, respectively, to expose photosensitive resist material placed on the semiconductor wafers located beneath masks containing the circuit patterns. These systems are currently limited to minimum feature sizes approximately equal to the wavelength of their light sources (i.e., approximately 0.25 microns), although more expensive complex optical techniques and light sources are under development in an attempt to extend optical lithography to smaller feature sizes.
Requirements For Advanced Microcircuits
The Department of Defense, through the Defense Advanced Research Projects Agency (DARPA)and the Army Research Laboratory, is developing state-of-the-art electronic systems to support future military needs. These systems require low-power, high-performance integrated circuits that are one to two generations beyond those based on the 0.25 micron feature sizes in production, today.
New methods for patterning are required to produce these advanced circuits. Such technology is a fundamental enabler for all levels of advanced military integrated circuit development and production.
It will also make possible the manufacture of entire new generations of much higher performance and more compact products for the commercial marketplace, including telephones, computers, fax machines, electronic games, auto electronics and more.
The system being developed by the Department of Defense on the contract announced in JMAR's January 13, 1998 news release will use X-rays instead of light rays to transfer circuit patterns having feature sizes as small as 0.13 microns, and below. The three methods believed capable of generating these feature sizes are discussed below.
E-Beam/I-Beam Lithography
The first method is through the use of either electron or ion beam-writing tools. Current systems utilize direct-write techniques. While capable of generating very small feature sizes they appear to be limited to circuit feature writing speeds adequate for mask-making but too slow for cost-effective IC circuit production. Most high performance circuits have more than twenty levels in them and a production facility generally requires a throughput of at least thirty wafers per hour per machine to be commercially viable. Some time ago, Lucent Technologies announced that it is developing a "projection" electron beam lithography system, named "Scalpel", with the goal of meeting high throughput production requirements. The viability of this technical approach appears to be dependent upon Lucent's ability to overcome certain technical hurdles, especially those involving development of practical masks.
Extreme Ultraviolet (EUV) Lithography
The second method involves the use of very low energy, laser-generated X-rays originally referred to as "soft" X-rays, but more recently re-named "extreme ultraviolet" or "EUV". Though still in its infancy, EUV lithography has made important strides in recent years as a result of advancements in the art of X-ray optics technology pioneered by Lawrence Livermore National Laboratories (LLNL). Recently, Intel Corporation announced a new initiative to develop this technology for
serious consideration as an alternative for future lithography applications. Currently, the mainline approach of the Intel/LLNL EUV program is based on the use of 0.013 micron light produced by advanced solid state lasers.
One of the attractive aspects of using EUV light as a lithography source is the eventual potential for utilizing LLNL's advanced optics technology to focus the EUV light from relatively low powered laser sources to generate circuit features finer than those that could be made by other optical lithography approaches. JMAR believes that, although there is good future potential for EUV lithography, much technology development remains before it can be seriously considered for insertion into future IC production lines.
Since 1992, JMAR's laser systems have been used to produce EUV light for lithography research applications - initially under contract from Sandia National Laboratories and, subsequently, as part of an earlier LLNL/Intel consortium to lay the technical foundation for the current EUV program. JMAR's PXS is routinely capable of producing the EUV light that will eventually be required by future EUV lithography systems. As EUV process technology matures JMAR expects to play a more active role as a supplier of high performance EUV sources. However, much process development work is required before EUV technology will approach the already demonstrated capability of current X-ray lithography technology which is the third method for producing 0.13 micron and smaller feature sizes. Today, that technology uses the 0.001 micron light generated by synchrotrons to produce circuits much smaller than 0.18 microns.
X-ray Lithography (XRL)
X-ray systems work the same way as optical systems except that they use X-ray sources instead of ultraviolet light sources and operate without the need for expensive and complex optical components required by all "optical" lithography techniques. The primary challenge facing the industry today is the lack of availability of low-cost equipment for producing the X-rays needed to expose the resist.
Synchrotron XRL
Presently, there are two different methods for producing the X-rays used in X-ray lithography (XRL). The first is the synchrotron which generates very high intensities of 0.001 micron light. During the past several years, consortiums led by IBM in the U.S. and by Mitsubishi and others in Japan, have demonstrated the feasibility of the X-ray lithography process using synchrotrons. Synchrotrons are powerful X-ray sources that can produce enough X-rays to feed several steppers simultaneously. However, they are also very expensive to install and to operate and, to be cost effective, require major changes in the overall semiconductor fab process architecture. For example, to feed all of the advanced steppers with a single X-ray source it is essential that all of the steppers be in one location.
For many IC manufacturers such an arrangement may be inconsistent with optimum efficiency of their overall production operations. Accordingly, most integrated circuit manufacturers, including those that could afford their own separate synchrotrons, have been reluctant to make the needed changes in their processes.
Point Source XRL
The second method for producing X-rays is called a "Point Source". They are much smaller and much less expensive than synchrotrons and are designed to produce enough X-rays to power a single stepper. With its patented picosecond X-ray source (PXS), JMAR has become a pioneering leader in the X-ray point source field. The PXS is a very compact X-ray light source that uses JMAR's proprietary all-solid-state lasers to generate the lithography X-rays. As the laser beam strokes its metallic target, bursts of X-rays are produced which are channeled through the mask to create circuit patterns in the photoresist coated on the semiconductor.
"To date, the industry's delay in adopting X-ray lithography (XRL) on a large scale appears to be centered on the high cost and inflexibility of the large synchrotrons now being used to produce X-rays in today's XRL systems", commented Richard Foster, President of JMAR Technology Co., JMAR's R&D Division. "JMAR's system is designed specifically to overcome these challenges. We believe that the PXS will give the industry a cost effective X-ray source that operates at atmospheric pressure, is no larger than current optical lithography sources, and which will produce circuit sizes 0.13 microns and smaller."
JMAR's Point Source XRL Program
The two major elements of Point Source Systems are the X-ray source and the mask-to-wafer alignment systems. During 1998 JMAR expects, subject to DARPA's approval, to integrate its laser-driven Picosecond X-ray Source ("PXS") with an aligner being developed under other DARPA programs to transfer computer-generated circuit patterns onto semiconductor wafers. The PXS system to be built under the new contract includes both pulse generating and amplifier lasers based on JMAR's proprietary Britelight™ laser technology to produce 30 to 90 watts of the type of X-rays required for optimum lithographic exposures. The PXS system also includes an X-ray source chamber containing thin metallic source tapes, drive units, debris control systems and X-ray collimation components as they become available, as well as an X-ray mask alignment interface capability with all required electronic, mechanical and other subsystems necessary to connect the source with the aligners currently under development.
Inquiries regarding the applicability of JMAR's proprietary compact, high power x-ray sources to a range of industrial, scientific and medical applications should be faxed to Mr. Richard Foster at (619)535-1835.
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