Douglas E. Benoit

Etching processes and characteristics for the fabrication of refractory x-ray masks

Refractory x-ray masks for a wide variety of pattern types were fabricated using tantalum silicon as the absorber material. Both positive (Shipley UVIII®) and negative (Shipley SNR200®) chemically amplified electron beam resists were exposed and the patterns transferred into a silicon oxynitride hardmask. The amorphous TaSi absorber was then etched using a Cl2/O2 reactive ion etch (RIE). From a mask manufacturing standpoint, the challenge is etching the wide variety of feature types that commonly occur in device processing. The overall etch process was characterized for the formation of both freestanding lines (using negative electron beam resist) and narrow trenches (using positive resist). RIE lag, feature shape dependence, and cross-mask uniformity in the etch bias were characterized for feature sizes down to 125 nm. The etch process has been implemented in a pilot line environment and is being used to produce product masks.

UVIII-positive chemically amplified resist optimization

A highly sensitive resist is required for the fabrication of x-ray membrane masks (1X) using electron-beam lithography. Current products require precise control of 175 nm critical dimensions with test features of 100 to 125 nm. UVIII, a chemically amplified positive resist designed for DUV processes, also functions as an electron-beam resist with sensitivities of 12 to 30 (mu) C/cm2, depending upon the bake parameters. This paper discusses the process and demonstrates the capability of the resist on membranes. The post-apply bake (PAB) and post-expose bake (PEB) affect the resist sensitivity and process latitude of UVIII. The process was defined using a statistically designed experiment (DOE) to optimize the PAB and PEB conditions. The figures of merit included resist sensitivity, dose latitude and resolution. When the patterning process was defined, the etch processes were developed for both the SiON hardmask and TaSi absorber. Features as small as 100 nm have been successfully transferred from UVIII resist into the TaSi membrane with critical dimension (CD) uniformity of less than 20nm 3(sigma) within a mask. The process latitude, high resolution, and excellent CD uniformity indicate the UVIII resist is compatible with the manufacturing environment required for the fabrication of x-ray membrane masks.

Characterization of oxynitride hard mask removal processes for refractory x-ray mask fabrication

Silicon oxynitride removal processes are characterized for incorporation into the refractory x-ray mask fabrication sequence as the hardmask removal step. It is essential that his process not alter final image placement, one of the most critical parameters affecting x-ray mask performance. In this paper, we show that 10:1 buffered HF causes large image placement movement when used on refractory x-ray masks. This is because etching in HF has deleterious effects on TaSi, resulting in highly compressive film stress. Materials analysis indicates the presence of hydrogen in the TaSi films after being exposed to HF, which is most likely affecting the film stress. Alternative processes being investigated include using a more dilute 100:1 buffered HF solution and a CHF3 plasma dry-etch chemistry. Both of these options completely remove the SiON hardmask without causing any significant image placement movement and result in high quality refractory x-ray masks.

Advanced refractory-metal and process technology for the fabrication of x-ray masks

This paper provides an in-depth report of the advanced materials and process technology being developed for x-ray mask manufacturing at IBM. Masks using diamond membranes as replacement for silicon carbide are currently being fabricated. Alternate tantalum-based absorbers, such as tantalum boron, which offer improved etch resolution and critical dimension control, as well as higher x-ray absorption, are also being investigated. In addition to the absorber studies, the development of conductive chromium- based hard-mask films to replace the current silicon oxynitride layer is being explored. The progress of this advanced-materials work, which includes significant enhancements to x-ray mask image-placement performance, will be outlined.

Etch characteristics of various materials in ethanolamine etchants

Abstract Data for the etch rates of passivating and non-passivating films are presented for the anisotropic etchant ethanolamine-gallic acid-water. Thesedataidentifyusefulmasking and conductive layers for

UVN2-negative chemically amplified resist optimization for x-ray mask fabrication

A resist process has been defined, characterized and optimized using Shipley UVN2 chemically amplified negative resist for the fabrication of x-ray membrane masks using electron-beam lithography. Advanced masks require precise control of 150 nm critical dimensions with test features of 100 and 125 nm. UVN2, a chemically amplified negative resist designed for DUV processes, also functions as an electron- beam resist wit sensitivities of 10 to 20 (mu) C/cm2 depending upon the bake parameters. This paper discusses the process and demonstrates the capability of the resist on membrane masks. Post-apply bake (PAB) and post-expose (PEB) affect the resist sensitivity and process latitude of UVN2. The resists process was defined by using a statistically designed experiment to optimize the PAB and PEB conditions. The figures of merit included resist sensitivity, dose latitude, resist thinning and resolution. Once the patterning process was defined, the etch processes and optimized, features as small as 100 nm have been successfully transferred from the UVN2 resist into the tantalum-silicon membrane with critical-dimension uniformity of less than 15nm 3(sigma) within a mask. The process latitude, resolution, and excellent CD uniformity result obtained for UVN2 resist are consistent with the manufacturing requirements for the fabrication of x-ray membrane masks.

X-ray mask image-placement studies at the Microlithography Mask Development Center

A continuing trend in X-ray lithography is the requirement for high accuracy masks. Image placement, or the ability to pattern images in the correct locations, is one of the most critical requirements. It is driven by a number of parameters, including the electron-beam lithography system and precision of the metrology system. Also, because the X-ray mask substrate consists of a thin membrane, it is very susceptible to the stresses of the resist film, absorber material, and plating base. An extensive analysis of the contributors to image placement was performed to determine the relative contribution of each. This analysis highlighted those contributors which caused the largest distortions and which, therefore, presented the most opportunities for improvement. Several changes were then implemented which resulted in a 50 percent overall improvement to placement of the X-ray mask images. The experimental design and detailed results are discussed.

Development of a membrane-etch wet station for x-ray masks

This paper describes the evolution of a simple recirculating etch station into a successful x-ray mask membrane-etch station. The manufacturing etch station consists of a large, heated mix tank in which she ethanolamine solution is brought to reaction temperature. The etchant is then pumped into a smaller heated process tank and is continuously recirculated through a filter between the two tanks. Up to 50 substrates can be processed during one product run. Both tanks and wetted parts are made of Teflon. Salient features of the membrane-etch station include dual Pyrex reflux columns, a nitrogen blanket throughout the systems to prevent oxygen infiltration, special high-temperature Teflon and Gore-tex seals for the mix and process tank lids, and a Teflon filter in the recirculating line between the mix and process tanks. Subsequent tooling improvements included improving the thermal sensors and installing more powerful heaters. Tool qualification tests have demonstrated the membrane-etch station ready for manufacturing use. The manufacturing etch station has increased our etch capacity by almost an order of magnitude and is currently being used to produce silicon membranes for x-ray mask substrates.