Resist Thickness Uniformity Research Articles

Chemical–Mechanically Planarized Cross-Type Josephson Junctions in Nb-Al-AlOx-Nb Technology

Fabrication of devices composed of Josephson junctions in trilayer technology is usually compromised by the topography of the subjacent layers. If the structures of subsequent layers traverse steps, several adverse effects arise. Lithography may be impaired because of issues with resist thickness uniformity and focus depth, and the superconducting ampacity of the Nb wiring is reduced. Various methods have been tried to planarize perturbing structures. In this contribution, we address a few of the challenges of chemical mechanical polishing. The proposed improvements are based on the well-established IPHT cross-type junction technology.

Inedible cellulose-based biomass resist material amenable to water-based processing for use in electron beam lithography

An electron beam (EB) lithography method using inedible cellulose-based resist material derived from woody biomass has been successfully developed. This method allows the use of pure water in the development process instead of the conventionally used tetramethylammonium hydroxide and anisole. The inedible cellulose-based biomass resist material, as an alternative to alpha-linked disaccharides in sugar derivatives that compete with food supplies, was developed by replacing the hydroxyl groups in the beta-linked disaccharides with EB-sensitive 2-methacryloyloxyethyl groups. A 75 nm line and space pattern at an exposure dose of 19 μC/cm2, a resist thickness uniformity of less than 0.4 nm on a 200 mm wafer, and low film thickness shrinkage under EB irradiation were achieved with this inedible cellulose-based biomass resist material using a water-based development process.

On control of resist film uniformity in the microlithography process

A novel approach to improve photoresist thickness uniformity after the conventional spin-coating and softbake process is proposed in this paper. Using an array of thickness sensors, a multizone programmable bakeplate, and model-based control techniques, the temperature distribution of the bakeplate is manipulated in real-time to reduce photoresist thickness non-uniformity. To prevent the decomposition of photoactive compound in the photoresist, the bakeplate temperature is constrained. We have experimentally obtained a repeatable improvement in resist thickness uniformity from wafer-to-wafer and across each wafer. Thickness non-uniformity of less than 10 A ̊ has been obtained. On average, there is a 10× improvement in the thickness uniformity as compared to conventional softbake process.

Resist film uniformity in the microlithography process

With the trends toward smaller feature size, one of the challenge is to control the resist thickness and uniformity to a tight tolerance in order to minimize thin film interference effects on the critical dimensions. In this paper, we propose a new approach to improve resist thickness control and uniformity through the soft-bake process. Using an array of thickness sensors, a multizones bakeplate and a sliding mode control algorithm, the temperature distribution of the bakeplate is manipulated in real-time to reduce the resist thickness nonuniformity. The sliding mode control algorithm is implemented in a cascaded control structure so that the bake temperature is constrained. This is to prevent decomposition of the photoactive compound in the resist. We have experimentally demonstrated an improvement in the resist thickness uniformity across individual wafers and from wafer-to-wafer. The cascaded control structure using a sliding mode control algorithm provides a simpler and faster implementation of the thickness control strategy and makes it more suitable for real-time application. There is about 75 times reduction in the computation time and a resist thickness nonuniformity of less than 10 /spl Aring/ is achieved.

Real-time predictive control of photoresist film thickness uniformity

With the trends toward larger wafer size and the linewidth going below 100 nm, one of the challenges is to control the resist thickness and uniformity to a tight tolerance in order to minimize the thin-film interference effect on the critical dimension. In this paper, we propose a new approach to improve resist thickness control and uniformity through the softbake process. Using an array of thickness sensors, a multizone bakeplate, and advanced control strategy, the temperature distribution of the bakeplate is manipulated in real time to reduce resist thickness nonuniformity. The bake temperature is also constrained to prevent the decomposition of a photoactive compound in the resist. We have experimentally obtained a repeatable improvement in resist thickness uniformity from wafer-to-wafer and across individual wafers. Thickness nonuniformity of less than 10 /spl Aring/ has been obtained. On average, there is 10 /spl times/ improvement in the thickness uniformity as compared to conventional softbake process.

ON CONTROL OF RESIST FILM UNIFORMITY IN THE MICROLITHOGRAPHY PROCESS

A new approach to improve resist thickness uniformity through the softbake process is proposed. Using in-situ thickness measurements, a multi-zone bakeplate and sliding mode control algorithm, the temperature distributions of the bakeplate is manipulated in real-time to reduce the resist thickness non-uniformity. Constraints on the bakeplate temperature are imposed to prevent the decomposition of photoactive compound in the resist. Hence the sliding mode control is implemented in a cascaded control structure. The resist thickness non-uniformity is reduced to less than 10 angstroms across individual wafers and from wafer-to-wafer.

Critical dimension control optimization methodology on shallow trench isolation substrate for sub-0.25 μm technology gate patterning

The impact of shallow trench isolation (STI) chemical mechanical polishing on gate critical dimension (CD) control for submicron technology was studied. The CD depends on the STI process scheme, whether it is recessed or elevated STI. We investigated the surface topography for both STI schemes at different stages of patterning and how it affected the CD control. Surface topography affected organic bottom antireflective coating (BARC) and resist thickness uniformity, led to variation in the effective exposure dose and caused CD nonuniformity across the wafer [C. A. Mack, Appl. Opt. 25, 1958 (1986)]. We used an atomic force microscope surface scan to study substrate topographical variations. The solution is to optimize BARC and resist thickness by using simulations of topographical swing curves and CD error contour plot. Excellent agreement was found between simulation and experimental results.