Patent Number: 052689514
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENT The scanning method in accordance with this invention avoids distortion errors by means of the steps as follows: 1. A collimating first mirror has the capability of altering the source to mirror location and/or grazing angle of incidence. PA0 2. A flat second mirror is capable of a scanning motion by translation with an optional accompanying change in the grazing angle of incidence. This invention employs a scanning method which greatly reduces or eliminates mirror scanning errors while presenting the possibility of producing a constant distortion (zero to some value determined by mask/wafer overlay distortion correction), a minimum of flux change throughout vertical scanning, and a nearly constant x-ray beam profile during scanning. The technique is independent of collimating mirror surface form. Alternative Mirror Scanning Method The alternative scanning method requires a second, flat, grazing incidence mirror M2 which is placed after the first, collimating, mirror M1. FIGS. 1A-1C illustrate the basic principle involved in maintaining collimation and performing vertical scanning by shifting the flat collimating mirror M1 parallel to the exposure field or along the input beam to the flat second mirror M2 (to minimize the length of the second mirror M2). The x-ray radiation beam 10 from source S is reflected over a range shown by beams 12 and 14 from the first mirror M1 and reflected by second mirror M2 as beams 16 and 18 which are directed at exposure field EF. Combinations of both shifts are not shown but are obvious. This method has existing analogs in conventional optics. Less obvious is the capability of this two mirror system M1 and M2 to allow some adjustment of the Xphase and Zphass errors at the mask during exposure scanning, independently, allowing independent control of (gap dependent) printing distortion in the vertical and horizontal directions. This capability is an important feature of this invention. Xphase adjustments may be made by modifications of the location of collimating mirror M1 (along and/or perpendicular to the beam path), mirror grazing angle, or combinations thereof. Changes in Zphase usually accompany the changes in Xphase produced, most noticeably in the mean value of the Xphase at the top and bottom of the exposure field while changes in Zphase in the horizontal direction are much smaller, often negligible. FIG. 1B shows the second mirror M2 of FIG. 1A making a linear vertical shift vertical to the path of x-ray beam 19 with mirror M2 moving to higher position M2' along the direction of scan 21 with x-ray beam 19 reflecting twice, at different times, from the collimating mirror M2, M2' as top and bottom beams 20 and 22 corresponding to the respective positions of mirror M2, M2'. FIG. 1C shows the second mirror M2 of FIG. 1A making a linear shift parallel to the path of x-ray beam 19 with mirror M2" moving along the direction of scan 23 to position M2'" with x-ray beam 19 reflecting from the collimating mirror M2",M2'" as top and bottom beams 20' and 22' corresponding to the respective positions of mirror M2", M2'". FIGS. 2A and 2B show the Zphase error introduced by altering the grazing angle of the collimating first mirror M1 with Zphase correction by the second flat mirror M2. By altering the grazing angle of the flat mirror M1 and shifting the mirror M1 as shown in FIGS. 2A and 2B, the mean Zphase of the rays 28, 30 in FIG. 2A and 30' in FIG. 2B arriving at the mask may be altered to a desired value, usually zero. In FIG. 2B, exposure scanning is accomplished by shifting the mirror M2 as shown in FIGS. 1A-1C. By this method the Zphase errors introduced by modifying the first mirror M1 are reduced to only the small horizontal component. FIG. 3 illustrates altering the grazing angle of the flat mirror M2 between positions M2' and M2" while it is scanned so a deliberate Zphase error may be introduced at the mask. This error is introduced solely by the second flat mirror M2. The distortion correction capability of this system is primarily a function of the gap and the specific design of the first, collimating, mirror. Typically, increasing the source to mirror distance for the first mirror allows larger phase changes to be made with position modification before adverse image effects are noted, such as nonlinear Xphase within the exposure field, or unacceptably large Zphase errors in the horizontal direction for a given Xphase error. Increasing the source to mirror distance also reduces the flux gathered from the source per unit length of horizontal exposure field, reducing throughput. These effects are engineering trade-offs, and performance of the scanning operations is not degraded by the scanning second mirror. The introduction of a second reflecting surface into the beam path reduces the flux available for exposure, requiring longer exposure times, and yielding lower system throughput. While this invention has been described in terms of the above embodiment(s), those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.