Towards ultimate optical lithography with NXT:1950i dual stage immersion platform

Abstract

Optical lithography, currently being used for 45-nm semiconductor devices, is expected to be extended further towards the 32-nm and 22-nm node. A further increase of lens NA will not be possible but fortunately the shrink can be enabled with new resolution enhancement methods like source mask optimization (SMO) and double patterning techniques (DPT). These new applications lower the k1 dramatically and require very tight overlay control and CD control to be successful. In addition, overall cost per wafer needs to be lowered to make the production of semiconductor devices acceptable. For this ultimate era of optical lithography we have developed the next generation dual stage NXT:1950i immersion platform. This system delivers wafer throughput of 175 wafers per hour together with an overlay of 2.5nm. Several extensions are offered enabling 200 wafers per hour and improved imaging and on product overlay.The high productivity is achieved using a dual wafer stage with planar motor that enables a high acceleration and high scan speed. With the dual stage concept wafer metrology is performed in parallel with the wafer exposure. The free moving planar stage has reduced overhead during chuck exchange which also improves litho tool productivity.In general, overlay contributors are coming from the lithography system, the mask and the processing. Main contributors for the scanner system are thermal wafer and stage control, lens aberration control, stage positioning and alignment. The back-bone of the NXT:1950i enhanced overlay performance is the novel short beam fixed length encoder grid-plate positioning system. By eliminating the variable length interferometer system used in the previous generation scanners the sensitivity to thermal and flow disturbances are largely reduced. The alignment accuracy and the alignment sensitivity for process layers are improved with the SMASH alignment sensor. A high number of alignment marker pairs can be used without throughput loss, and furthermore the GridMapper functionality which is using the inter-die and intra-die scanner capability can reduce overlay errors coming from mask and process without productivity impact.In this paper we will present the main design features and discuss the system performance of the NXT:1950i system, focusing on the improvements made in overlay and productivity. We will show data on imaging, overlay, focus and productivity supporting the 3X-nm node and we will discuss next improvement steps towards the 2X-nm node.

Measurement technologies for precision positioning

“…As laser interferometer measurements are based on the optical wavelength of the laser, uncompensated changes in the refractive index of air in the optical path lead to measurement noise and error. In addition, frequent high acceleration and de-acceleration of wafer stages cause unwanted air flow and cause non-uniformity in air pressure/temperature/humidity/ composition [25,187], and thus contribute to repeatability error and noise. It has been experimentally demonstrated that the 2D encoder solution can achieve 0.2 nm measurement noise (3s), in comparison to 0.8 nm measurement noise (3s) by laser interferometers [25].…”

“…In addition, frequent high acceleration and de-acceleration of wafer stages cause unwanted air flow and cause non-uniformity in air pressure/temperature/humidity/ composition [25,187], and thus contribute to repeatability error and noise. It has been experimentally demonstrated that the 2D encoder solution can achieve 0.2 nm measurement noise (3s), in comparison to 0.8 nm measurement noise (3s) by laser interferometers [25]. Another advantage of the 2D planar encoder solution is that it is less expensive than laser interferometer solutions which provide six-axis position feedback.…”

Improving Equipment Defectivity Specifications Through Chip Yield Modeling: A Case Study for Immersion Lithography

“…Defect data was collected from more than 700 wafers during Factory Acceptance Tests (FAT) from more than 70 NXT:1950i dual stage immersion scanners [4]. The defect detection scheme [5] included printing 45-nm lines and 55-nm spaces onto 300-mm wafers (full wafer coverage).…”

Ultra-precision engineering in lithographic exposure equipment for the semiconductor industry

“…Only recently, it became possible to design a planar encoder system with a sufficient resolution to operate as the long-range measurement system of a wafer scanner as schematically shown in figure 15 [11]. Its main advantage is the short path through air of less than 15 mm, reducing the thermal sensitivity by a factor of 100 to DL/L = 10 −8 per degree Celsius.…”