Step and Flash Imprint Lithography (SFIL) is an attractive low-cost method for printing sub-100 nm geometries. Relative to other imprinting processes, SFIL has the advantage that the template is transparent thereby facilitating conventional overlay techniques. In addition, the imprint process is performed at low pressures and room temperature, which minimizes magnification and distortion errors. Since SFIL is a 1X lithography technique, the template masks will require very good layer-to-layer overlay accuracy for multiple level device fabrication. To fabricate a transparent SFIL template, processing techniques familiar to existing binary phase shift mask fabrication are utilized. However, in order to fabricate the sub-100 nm features necessary for SFIL templates, thinner resist and chromium are necessary. Initial resolution tests have resulted in features sizes down to ~20 nm with the non-chemically amplified resist, ZEP520. Template to template overlay of <15 nm (mean + 3σ) can be achieved if the template fabrication procedure consists of a single 1” template exposed in the center of a 6” × 6” × 0.25” quartz blank.
As semiconductor device requirements approach the 70 nm lithography node the development and implementation of a next-generation lithography (NGL) technology and the associated masks becomes of paramount importance. We have been developing Extreme Ultraviolet Lithography (EUVL) mask materials and processes. Fabrication of these masks includes the deposition and patterning of an EUV absorber stack. An understanding of the effect of pattern transfer on image placement is required due to the stringent image placement requirements for NGL masks. This article reports the measurement results of image placement caused by the pattern transfer of resist through final image for a candidate EUVL absorber stack using both bright field and dark field patterned 6025 (6” × 6” × 0.25”) masks.
To determine stress related image distortion for EUV masks, an EUV stack consisting of SiON, TaSiN, and Cr was deposited onto Mo/Si coated mask blanks (6025 format) provided by Lawrence Livermore National Laboratory (LLNL). Both dark field and bright field masks were built and the pattern image placement was measured after e-beam lithography and after every etch process. Analysis of the data sets provided the resultant pattern transfer induced image displacement.
The Semiconductor Industry Association (SIA) has placed stringent requirements on Next Generation Lithography mask critical dimension (CD) control. A new chemically amplified (CA) positive resist, Shipley XP2040D was evaluated for mask making application. This resist exhibited an extraordinary post exposure bake (PEB) sensitivity, less than 0.6 nm/ degree(s)C, along with a sub-50 nm resolution. The PEB stability in ambient was larger than 4.5 hours and the line-edge-roughness (LER) was less than 2.9 nm.
A negative tone, chemically amplified deep ultraviolet resist, Shipley<SUP>R</SUP> UVN30, has been evaluated for use in NGL mask fabrication and direct write applications. This resist displayed excellent exposure latitude and resolution for both dense and isolated features. At optimum conditions 50 nm isolated lines and 60 nm dense lines resolved in a 300 nm thick film. Exposure dose latitude was 32%. Resist coat shelf life tests produced CD variations of 5 nm after 1 week and 10 nm after 3 months. A 66 hour post exposure bake delay in vacuum produced a 9 nm CD variation. PEB temperature sensitivity was 3 nm per degree Celsius. By selecting appropriate process conditions exposure latitude and resolution were optimized while decreasing linearity and line edge roughness performance. This paper reviews the test conditions for performing the optimization experiments and discuses the potential of using this resist for both advanced mask fabrication and direct write application.
We report on the comparison of defect printability experimental results with at-wavelength defect inspection and printability modeling at extreme ultraviolet (EUV) wavelengths. Two sets of EUV masks were fabricated with nm- scale substrate defect topographies patterned using a sacrificial layer and dry-etch process, while the absorber pattern was defined using a subtractive metal process. One set of masks employed a silicon dioxide film to produce the programmed defects, whereas the other set used chromium films. Line-, proximity- and point-defects were patterned and had lateral dimensions in the range of 0.2 micrometer X 0.2 micrometer to 8.0 micrometer X 1.5 micrometer on the EUV reticle, and a topography in the range of 8 nm - 45 nm. Substrate defect topographies were measured by atomic force microscopy (AFM) before and after deposition of EUV-reflective Mo/Si multilayers. The programmed defect masks were then characterized using an actinic inspection tool. All EUVL printing experiments were performed using Sandia's 10x- reduction EUV Microstepper, which has a projection optics system with a wavefront error less than 1 nm, and a numerical aperture of 0.088. Defect dimensions and exposure conditions were entered into a defect printability model. In this investigation, we compare the simulation predictions with experimental results.