Step-and-repeat projection microlithographic systems used in the microelectronics industry achieve important advantages, notably including extremely high quality. However, such systems also have major disadvantages. These include very low throughputs, and very high capital costs for the systems.
It would be a distinct benefit to the industry if a projection microlithographic system could be created that is characterized by high throughput and relatively low capital cost, yet still achieves a large part of the quality of step-and-repeat systems.
One significant reason why step-and-repeat systems are commonly used is that the substrates can shrink as the result of process steps. Shrinkage can be caused by such factors as the firing of the substrates, or the putting down of thin layers of materials on the substrates. Such layers may create stresses which pull on the substrates in such manner as to shrink them. Although both types of shrinkage are dimensionally small, they can create significant errors in the microelectronics components being fabricated. Step-and-repeat systems compensate for the shrinkage, and so reduce or eliminate these errors.
Prior art related to projection microlithography has often involved Dyson projection or imaging systems. These 1-to-1 systems are well known to create important advantages. They have not, however, been previously so constructed or used as to achieve to a high degree (if at all), and/or in a high quality way, the following:
(1) a large field size, such as 60 mm by 60 mm, with high quality, and with (for example) a 10-inch diameter primary mirror, so that throughput is massively increased; PA1 (2) large air gaps between the prisms (or mirrors) of the Dyson system, and the object and image planes thereof, in combination with a magnification adjustment element that is disposed in one of these air gaps and employed to compensate for such factors as the above-indicated shrinkage of the substrates; PA1 (3) an image plane that is parallel to the object plane, and an image that has the same orientation as the object, so that continuous scanning can be practically and effectively performed; PA1 (4) correction for the three near-UV spectral lines of mercury (365 nm, 405 nm, and 436 nm wavelengths) for the whole field, thus permitting much transfer of power from a mercury light source to the substrate, and correction for the alignment wavelength (577 nm) at the central, reduced, field; PA1 (5) a high numerical aperture (NA) for a 1-to-1 system, with consequent good resolution, and a large field size under these conditions; PA1 (6) magnification compensation or adjustment with very low distortion at all settings, and magnification compensation or adjustment with very little change in modulation transfer function at all settings; PA1 (7) Dyson system elements that are selected, constructed and located to perform functions including (a) correction of field aberrations, (b) correction of chromatic aberrations--with consequent good image quality over the large field and even with the large air gaps, and (c) reduction of astigmatism; PA1 (8) An adjustment mechanism for effecting very small adjustments in the positions of the prisms in order to aid in achieving precise registry or superposition of a point or small line in the projected image during one scan of a scanning projection microlithography system, in comparison to the image of the same point or line during the next scan.