Special Issue on Precision and Ultraprecision Positioning

<jats:p>I have been the chairman of the technical committee of ultraprecision positioning at the Japan Society of Precision Engineers (JSPE) from 1993 to 1997. In November 2008, the 3rd International Conference on Positioning Technology (ICPT) was held in Shizuoka, Japan. After the conference I together with Dr. Sadaji Hayama, an adviser of the journal editorial board, asked by mail the most significant presenters and members of the technical committee of ultraprecision positioning if they are willing to contribute their papers for this special issue. As a result, we received more than 20 manuscripts, among which 2 development reports, 2 reviews, and 14 papers have been selected for publication in this journal. The contents of these papers relate mainly to the nano/subnanometer positioning technology, new control methods for ultraprecision positioning, guide way for precision positioning, positioning for ultraprecision machining, new hard disk drive method, etc. I would like to express my sincere gratitude to the authors for their interesting papers on this issue and I also would like to deeply thank all the reviewers and editors for their invaluable effort.</jats:p><jats:p>1. Demarcation Between Precision Positioning and Ultraprecision Positioning The Technical Committee of Ultraprecision Positioning (TCUP) has had a poll on Ultraprecision and Ultraprecision technology to the randomly selected members of Japan Society for Precision Engineers (JSPE) every four years since 1986 [1]. Results indicate that most respondents felt that the maximum allowable positioning error and image resolution was 1 µm for precision positioning and 10 nm for ultraprecision positioning. After 2004, most respondents appeared to view 0.1 nm as the demarcation line between the precision positioning and ultraprecision positioning.</jats:p><jats:p>2. Know-How for Achieving Ultraprecision Positioning The champion device in ultraprecision positioning is always the stages of demagnification exposure devices for semiconductors. The exposure method using stages have advanced from 1980s steppers shown in Fig. 1(a) to today's scanning stages with the increasement of LSI capacity in achieving higher processing as shown in Fig. 1(b). The stepper consists of X and Y stages.</jats:p><jats:p>The XY stages in the 1980s consisted of a DC servomotor, either a ball or sliding screw plus a linear guide way consisting of either rollers or a slide guide. Current scanning type consists of a linear motor and pneumatic hydrostatic guide way (Fig. 1(b)). Reticle and wafer stages travel in opposite directions and the relative positioning error is about 1 nm.</jats:p><jats:p>Ultraprecision positioning of sub-µm accuracy is now achieved either by an AC servomotor and a ball screw or by using a linear motor. subsection</jats:p><jats:p>2.1. Achieving high positioning resolution and accuracy with less than 0.1 µm generally depends on three factors: newpage</jats:p><jats:p>(1) Displacement sensors for feed-back</jats:p><jats:p>(2) Mechanical structure</jats:p><jats:p>(3) Control, including software Ultraprecision positioning is possible only when these three factors are well coordinated.</jats:p><jats:p>(1) Displacement Sensors Ultra-precision positioning requires high-performance displacement sensors. About 10 sensor manufacturers in Japan alone currently achieve resolution under 1 nm [3]. To achieve higher resolution, laser interferometers must operate in thermostatic chambers controlling or monitoring temperature, humidity, and atmospheric pressure. Great effort is required to minimize or eliminate air turbulence and inhomogeneous atmosphere temperatures in the laser beam path. To achieve nm level resolution, operations must be conducted in a vacuum.</jats:p><jats:p>Linear encoders, although somewhat less accurate than laser interferometers, are used in over 50% for ultraprecision positioning devices in Japan and their market share continues to grow, according to the 2006 TCUP poll. Analog sensor performance in detecting microscopic displacement is steadily improved. The technical level of precision positioning device is often assessed by how the designer considers Abbe's principle.</jats:p><jats:p>(2) Mechanical Structure Overall structural rigidity should be maximized to ensure monolithic construction. Semiconductor aligners used in exposure are made from ceramics with a high specific rigidity, i.e., the quotient of Young's modulus divided by specific gravity.</jats:p><jats:p>1990s arguments pitting linear actuators against ball screws subsided as their specific advantages and domains of preferred use became established. Linear guide ways using steel balls or rollers are becoming cheaper, and their accuracy and other aspects of performance are improving.</jats:p><jats:p>When stage movement is reversed, friction generated by preloads as nonlinear spring behavior which is caused by elastic deformation of balls and race ways over the moving stroke of several te ...