Very thick photoresist layers were patterned by contact ultraviolet ͑UV͒ lithography. In a following microelectrodeposition step the generated resist patterns were molded and three-dimensional ͑3D͒ microstructures were fabricated directly onto system surfaces. The new technology, called 3D UV-microforming, consists of an advanced resist preparation process, an UV lithographic step, resist development, a molding procedure by electrodeposition, and finally stripping and cleaning for finishing the structures. It enables the low-cost fabrication of a wide variety of microcomponents for many different uses. During resist preparation, layers up to 200 m thickness were obtained. By using a standard UV mask aligner as an exposure tool followed by immersion development, thick resist layers up to 100 m could be patterned in a single step on preprocessed silicon wafers. Repeated exposure and development were successfully used for structuring resist layers of up to 200 m thickness. Using AZ 4000 series photoresist, the resolution is also limited by mechanical stability. For lines and spaces in 15-m-thick resist a minimum width of 3 m for the resist was found to be necessary to overcome the fabrication process. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88°could be fabricated. The resist patterns used were molded by pulse or by direct current electroplating. For microsystem applications some metals and alloys were deposited. Three-dimensional microcomponents were fabricated as samples for demonstrating the new technique. The technique allows the use of materials with interesting properties, ones that could not be provided by standard processes.
Articles you may be interested inAg2Te/As2S3: A high-contrast, top-surface imaging resist for 193 nm lithography J.Interest in thick photoresist applications is steadily growing. Besides the bump fabrication and wire interconnect technology, the process of patterning thick layer photoresists by UV lithography is specially qualified for applications in micro electro mechanical systems. Specialized equipment and new photoresists have been developed or are under development to cope with the new challenges in the field of preparing extremely thick photoresist layers, to plan the process of patterning these thick resists, and to deal with the difficulties of the following galvanoplating step. A technology called three-dimensional ͑3D͒ UV-microforming was developed, consisting of a resist preparation process for very thick photoresists ͑positive or negative tone͒, UV lithographic steps, resist development, moulding procedures by galvanodeposition, and finally stripping and cleaning for finishing the structures. A minimum width of 3 m for the resist bars was found to be necessary to withstand the fabrication process of lines and spaces in 15 m thick resist. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88°could be fabricated. The resist patterns were moulded by using electroplating. For microsystem applications metals and alloys can be deposited into the resist patterns. 3D UV-microforming, a combination of UV patterning of thick layer resists and galvanoplating, enables the low-cost fabrication of a wide variety of micro components for many different users.
Interest in thick photoresist applications is steadily growing. Besides the bump fabrication and Wire Interconnect Technology (WIT), the process of patterning thick layer photoresists by UV lithography is specially qualified for applications in Micro Electro Mechanical Systems (MEMS). Specialised equipment and new photoresists have been developed or are under development to cope with the new challenges in the field of preparing extremely thick photoresist layers, the process of patterning these thick resists, and to deal with the difficulties of the following galvanoplating step.As one of the most critical steps in thick photoresist processing, the baking procedure was investigated. Two positive tone photoresists (AZ 4562, ma-P VlOO) were processed by means of three different baking methods: air-forced oven, ramped hotplate, and JR radiation. Furthermore, combinations between the methods were tested. It could be shown that JR baking is advantageous compared to the other methods with respect to process duration and energy consumption. Compared to edge steepness, resolution, edge loss, and surface roughness, all methods deliver nearly same results. A minimum width of 2 -3 m for the resist bars was found to be necessary to withstand the fabrication process of lines and spaces in about 15 pm thick resist. For thicker layers high aspect ratios of more than 10 as well as steep edges of more than 88 could be fabricated. The resist patterns can be moulded by using electroplating.
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