On April 7, 2013 Yehiel Gotkis commented on my recent March 20, report on SPIE Activities (scroll down to my prior post) which spoke to developments in EUV lithography and related process issues. Yehiel questioned why my comments did not include discussion of Direct Write E-beam Lithography. Burn Lin of TSMC recently presented a status update on DWEB lithography at SPIE Advanced Lithography IV which prompts further discussion of this complementary lithographic technology. My response to Yehiel's comments follow:
Thank you for your observations on e-beam lithography. In my opinion direct write e-beam technology continues to demonstrate its value as an important component in the mix of lithography strategies used in both current and future semiconductor production. In addition to my recent blog comments on EUV, I made a brief reference to direct imprint, multiple e-beam and Directed Self Assembly (DSA) as supplemental alternatives to EUV lithography. My omission of commentary on e-beam technology was not intended to minimize its importance or viability in the semiconductor manufacturing market place. If there is limited success with the further increase of EUV source output power the extended dose/exposure times will enhance the competitive viability of e-beam lithography for HVM (High Volume Manufacturing).
As the semiconductor market evolves there will be niche markets for application specific lithography technologies which are best able to address process problems unique to newly emerging segments of the semiconductor industry. Currently, industry interest is focused on resolving EUV lithography HVM issues as evidenced by recent investments in ASML by Intel, TSMC and Samsung. Is direct write e-beam an HVM alternative to EUV or 193 nm lithography? For High Volume Manufacturing of RAM memory, many MPUs and other high volume commodity products the answer is probably no, not at this time, but events change quickly. This observation in no way disqualifies e-beam from other market segments where it has real value. In the 1980s IBM had a production line called QTAT (I'm sure the QTAT example has been cited many times). This was a Quick Turn Around Time direct write e-beam production line which supplemented the traditional optical lithography line. As explained to me by IBM years ago, one of the intended purposes of QTAT was to enable the IBM sales and marketing team to respond quickly to customer orders which were time sensitive. Traditional sales activity hand off to the wafer fab involves the strategic scheduling of fab assets to accommodate work flow determined by the mix of products in the factory. Often times this scenario represented multiple customers with specific, time sensitive delivery requirements. In most cases this work flow was efficiently scheduled on the optical lithography line where production costs were minimized. However, on occasion the fab would receive a time sensitive order which could not be easily integrated into the mix scheduled for optical production. These orders were sometimes routed through QTAT. In addition to the many standard photo mask sets in place at the IBM wafer fab, much of the product line was also replicated on the direct write e-beam system computers. When there was a resource conflict for use of the optical lithography line, the work flow could be diverted to the e-beam line. It was a simple matter to down load the e-beam lithography patterns with out concern for the time consuming loading and qualifying mask sets. It's probable that in most situations this was more cost and time efficient than work flow disruption of the optical line or loosing time sensitive orders to competition.
In today's foundry environment, direct write e-beam can provide a similar quick turn around back up capability on the production line. In addition to the significant evolution of e-beam lithography capabilities over the years recent renewed interest in complementary lithography support might also be reflective of the historic value of the QTAT concept. The ability to develop new products without concern for mask design/fabrication and optical lithography hardware can be very influential as the cost of nanometer scale production escalates.
It is rumored that direct imprint lithography systems are currently in use at a major flash memory manufacturer where complex, high cost products are being produced. In the absence of HVM EUV and given the added costs and complexities of 193 nm double patterning, direct imprint lithography can also become a contender for many niche applications.
Next generation nanometer scale lithography technology continues to evolve. Mapper, KLA-Tencor, JEOL, Multibeam,
PARAM, and Vistec are all engaged in research which pushes the envelope in both development labs and production fabs. Many industry actions and decisions will be keyed upon successful scaling of EUV power output, mask and resist issues. With regard to e-beam direct write systems, it's interesting to note that the full complement of current MEMS technology is being leveraged to create the electrostatic lens systems that enable some multiple e-beam lithography systems with their precision. A technology shake out is in progress.
Direct write e-beam lithography has its own set of advantages and technology node issues worthy of further discussion. I plan to report on e-beam lithography more expansively in the coming weeks.
Semiconductor Industry Consultant
The Technology High Ground