E-beam direct writing, one node ahead of advanced optical lithography, can be a time and cost effective option for early device and technology development as well as for fast prototyping. Because of the device complexity only a variable-shaped e-beam writer combined with sensitive chemically amplified resists (CAR) can be considered for this approach. We evaluated various pCARs and nCARs of all major suppliers for our goal to structure DRAMs of the 50nm node using the Leica SB350 e-beam writer. The most promising samples were selected for a process optimization by variation of bake and development conditions. Finally, one resist of each tonality met the most of our specifications like dense lines and contact holes resolution, sensitivity and vacuum stability.
A resolution of 45nm dense lines has been be realized in a 100nm thick commercial available positive tone chemically amplified resist (pCAR) using the Leica SB350 variable shaped beam writer. On the basis of this resist process and by optimization of photomask blank material as well as by adaptation of chrome and quartz etching processes, a nanoimprint template technology has been developed which enables patterning of 50nm dense lines. The sensitivity of the selected pCAR as well as the performance of the implemented dynamical stage control of the Leica pattern generator, facilitates an acceptable throughput even for complex pattern. We characterized the templates in terms of feature profile, CD linearity and pattern fidelity. The final imprinting of different pattern proved the applicability of the manufactured stamps for the nanoimprint technology.
An initial Nanoimprint template manufacturing process using a state-of-the-art mask front end line has been developed. The process flow is based on conventional 6025 photomask blanks and known basic process steps for chrome and quartz etching. While these etching processes have been slightly adapted, a comprehensive investigation of chemically amplified resists for this purpose was done. We were able to identify a pre-commercial pCAR enabling to approach the 50nm dense line resolution using the Leica SB350 variable shaped beam e-beam writer. We characterized profile, CD-linearity, CD-uniformity and placement accuracy of the nanoimprint templates. The final imprinting of different pattern proved the applicability of the manufactured stamps for the nanoimprint technology.
An increasingly tighter set of mask specifications requires new equipment, process improvements, and improved e-beam resist materials. Resist profiles, footing behavior and line edge roughness (LER) have strong impacts on CD-uniformity, process bias and defect control. Additionally, the CD stability of e-beam resists in vacuum contributes to the final CD-uniformity as a systematic error. The resolution capability of the resist process is becoming increasingly important for slot contact like features, which are expected to be applied as clear assist features in contact hole layers at the sub 100nm technology node (1x)1. Three e-beam sensitive pCAR resists from different vendors were investigated in terms of resolution and pattern quality, PED stability, PEB sensitivity, dose latitude, CD-uniformity and line edge roughness. As reported here, all three pCARs showed improvements in all of these areas. Future work with these pCAR resists will focus on defect density, PCD, and CD uniformity.
Recently developed positive tone CARs (pCAR) and negative tone CARs (nCAR) have been evaluated for mask making using a 50kV e-beam pattern generator. We determined a screening method considering the most important parameters for example resolution, profile, delay influences, line edge roughness (LER), which was identically applied for all investigated resist samples. The screening was accomplished on 6025 chrome blanks using a state-of-the-art mask line. Some of the investigated resists have shown promising progress in terms of straight profile, of reduced footing, of lower line edge roughness and of an almost insensitive influence of the post exposure delay. Unfortunately, all the improvements were not unified in one sample.
With shrinking feature sizes there is a growing demand for improved uniformity values and defect levels especially for aqueous develop during photomask processing. Standard nozzle systems with discrete dispense channels for applying the developer medium onto the photomask surface may cause non-uniformities. This results in characteristic imprints in CD-uniformity reflecting the nozzle design used during the develop process step. These can lead on the one hand to an increased number and various types of defects and on the other hand to variations in CD-uniformity. A new puddle nozzle design for the STEAG HamaTech's ASP5500 has been developed to address this issue. Instead of discrete dispense holes the developer medium is applied onto the substrate surface by a full-width film. This media film is applied uniform across the substrate and has low impact onto the photomask surface. By combining the new nozzle design with gas-less high volume dispense pumps a very uniform and defect-free dispense can be achieved. The uniformity and defect performance of the new film nozzle will be presented and compared to a standard dispense nozzle system. The study has been done on masks with Chemically Amplified Resist (CAR).