Photoresists thin film fabrication

Photoresist A photoimaging material, generally applied as a thin film, whose local solubility properties can be altered photochemically. A subsequent development step produces an image which is useful for the fabrication of microelectronic devices (e.g., integrated circuits). 

The metal-RIE process is used in the fabrication of Al interconnects on chips. In this process, a blanket thin film of Al (or Al alloys, like Al—Cu, Al—Si) is deposited and then etched in a reactive plasma (RIE) through a photoresist stencil. After RIE, a... 

Novel o-quinone diazides have been the subject of several patents for applications as positive photoresists or in lithography. Thin-film composite membranes with pendant diazoketone groups have been synthesized. The resulting membranes can be modified photochemically after fabrication. 

Metal-RIE process was/is used in the fabrication of Al inter-coimects on chips." This process is depicted in four steps in Fig. 2. The first step in the metal-RIE process is sputter deposition of a blanket thin film of Al (or Al alloys, such as Al-Cu, Al-Si) over a planerized dielectric (e.g., silicon dioxide). In the next step, the unwanted metal is etched away by reactive ion etching (RIE) through a photoresist mask. The features produced this way are separated, electrically isolated, metal Al conductor lines. In the RIE process chemicaly active ions such as F or Cl bombard the Al surface and form volatile aluminum fluorides or chlorides, which are then pumped away in the vacuum system. After etcliing, a dielectric is deposited in such a fashion that it fills the gaps between the lines as well as above them. In the last step, the dielectric is planarized using the chemical mechanical polishing (CMP) technique. ... 

An alternative approach to the complicated photoresist systems could be the application of APD (ablative photodecomposition), where a strong absorbance at the irradiation wavelength is one of the conditions for successful ablation. A logical approach to the use of APD as a dry etching technique in microlithography is the development of polymers designed for APD. This is especially true for photolithographic applications that do not require a submicron resolution, such as thin film transistor (TFT) fabrication for liquid crystal displays (LCD) which require a resolution around 1 pm. 

Microelectronics device fabrication entails lithography in order to transfer a layout pattern onto the surface of a substrate, such as a silicon wafer. In this technique, the surface of a Si wafer is oxidized, typically at 800-1200 °C in steam or dry oxygen, to form a thin layer of silicon oxide as shown in the upper left portion of Figure 1.23. Then, a thin film of a polymer known as a photoresist is deposited on the oxide layer. This material is sensitive to ultraviolet radiation but resistant to chemical attack by etchants and, in some cases, to electrons and x-rays. A photomask, which comprises a glass... 

Fig. 11 Thin-film parylene-based microelectrode with embedded microfluidic channel. The pary-lene is structured in a reactive-ion etch. The photoresist serves as a sacrificial material, and it defines the channel shape. As with the polyimide fabrication process, the silicon substrate serves as a mechanical support during fabrication, and the parylene probe is removed in the last step. In this injection test, ink is passed through the microfluidic channel [67] - Reproduced by permission of The Royal Society of Chemistry...

A hybrid BCB-silicon neural implant with embedded microfluidic channels has been fabricated and tested in acute recordings [70]. A thin layer of silicon was used to add mechanical stiffness to the implant. The fabrication process is based on SOI technology, where the device layer of the wafer was the 2-, 5-, or 10-iim silicon backbone of the BCB structure. The microfluidic channels were made with a sacrificial photoresist layer. Cytotoxicity tests of BCB have demonstrated its biocompatibility in glial and fibroblast cell culture [71] and using brain slice culture [72]. A summary of several microfabricated thin-film electrodes is presented in Table 1. 

The most widely used technique for producing thin films of polymeric material is spin coating from solution. This technique is widely used in microelectronics fabrication to produce thin films of photoresist for photolithographic processes (Chapter 2). For this application, the thickness and uniformity of the photoresist must be accurately controlled, and to this end precision spin-coating machines have been developed offering accurate acceleration and spin speeds typically between 1000 and 10000revmin The requirement of polymeric thin films for optical purposes are very similar, and spin-coating techniques have been used to produce exceptionally low-loss structures [139]. 

The semiconductor fabrication process is cyclic, (a) First, a thin film is deposited on the wafer surface using thin-fihn deposition teeh-niques. (b) A uniform photosensitive polymer (photoresist) is then deposited and (c) exposed to light from a mask that contains the pattern that is desired on the thin film, (d) The photoresist is developed to obtain the desired pattern, (e) The pattern in the photoresist is then transferred to the thin film using an etching technique, and the photoresist is removed. Figure 1.1 shows a cross section of the wafer at each step. This cycle is repeated for each new layer, with some processes requiring as many as 20 to 30 cycles. 

Figure 1.1 The semiconductor fabrication process, (a) Thin-film deposition (yellow), (b) photoresist deposition (blue), (c) photolithography (mask clear and opaque red arrows), (d) photoresist development, and (e) etching to transfer the pattern in the photoresist into the thin film. See color plate section.

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