Polysilicon thin films

Kitahara, K. Yamazaki, R. Kurosawa, T. Nakajima, K. Moritani, A. 2002. Analysis of stress in laser-crystallized polysilicon thin films by Raman scattering spectroscopy. Jpn. J. Appl. Phys. 41 5055-5059. 

The polymerase chain reaction is the prevalent method for DNA amplification. Much effort has been made to integrate PCR chambers on microchips to carry out amplifications of DNA molecules prior to their analysis. For instance, PCR was first achieved on a Si-based reaction chamber (25 or 50 pL) integrated with a polysilicon thin-film (2500-A-thick) heater for the amplification of the GAG gene sequence (142 bp) of HIV (cloned in bacteriophage M13) [997]. 

Transparent glass-ceramics of the Si02-Al203-Li20 system are used to produce color filter substrates for polysilicon thin-film-transistor liquid crystal displays for laptop color PCs. Nippon Electric Glass Co., Ltd., Japan,... 

Epi-seal encapsulation developed by Kenny et al. at Stanford University consists of a 20 50-p,m thick epitaxially grown polysilicon encapsulation layer covered by 4 ttm passivation oxide. Aluminum partially covers the encapsulation to form electrical interconnects [109], Investigation on the hermeticity and diffixsion behaviors of epi-seal wafer-scale polysilicon thin-film encapsulation revealed that hermeticity of the encapsulation is gas species specific hydrogen and helium easily travel in and out of the encapsulation, but nitrogen and argon do not [110],... 

Cuscuna M, BonfigUetti A, Carluccio R, Mariucci L, Mectirini F, Pecora A, Stanizzi M, Valetta A, Fortunato G (2002) A novel fabrication process for polysilicon thin film transistors with source/drain contacts formed by deposition tmd lift-off of highly doped layers. Solid-State Elektron 46 1351-1358... 

The tin oxide thin film was patterned by reactive ion etching (RIE) using either SiCl or 1% H2 in N2 as the etch gas. The polysilicon contact holes were opened by wet-chemical etching in buffered hydrofluoric acid (BHF). A double-layer metallization (Cr -50 nm plus A1 -1 pm) was done by electron beam evaporation to form the electrical interconnection (Figure 1c). 

Here, 41 indicates the thin film transistors, 51 the substrate, 43 a dielectric layer, 49 polysilicon gates, 50 gate electrodes, 55 contact plugs, 56 bottom electrodes, 53 the planarization layer, 54 the mercury cadmium telluride layer and 57 the top electrode layer. The planarization layer is formed from silicon oxide, silicon nitride, silicon oxide nitride or from a polyimide. The planarization layer may be formed as a double or triple layer. 

When we consider silicon films, on the other hand, the nature of the solid deposit is crucial to the behavior of the film. Depending on deposition conditions, we can deposit amorphous, polycrystalline, or single crystal films. As was noted in Chapter 1, the morphology of polycrystalline films can be complex. In the present section, we will review some aspects of polysilicon (poly) thin films deposited by CVD. The final section of this chapter will be devoted to epitaxial silicon thin films. 

For high information-content displays, active-matrix (AM) pixel addressing provides improved display performance and reduced power consumption. In active matrix addressing each individual pixel is controlled by one or more thin-film transistors (TFTs). To date, most AM OLED displays have used polysilicon TFTs as the active elements, because they can provide sufficient current at low voltages and acceptable device dimensions, and they are capable of integrated drive electronics... 

To reduce expense, efforts are made to exploit integrated thin film technologies. For example, arrays have been produced via thin film deposition of the pyroelectric onto a sacrificial layer, e.g. a suitable metal or polysilicon, which is then selectively etched away. Thermal isolation of the pyroelectric element is achieved through engineering a gap between it and the ROIC silicon wafer. Yias in the supporting layer permit electrical connections to be made between the detector and the wafer via solder bonds. Imaging arrays have been produced in this way incorporating sputtered PST and sol-gel formed PZT films. 

Tungsten peel Tungsten does not adhere to quartz and even thin films tend to peel leading to unacceptable particle counts. Although this could potentially be solved by first depositing an adhesion layer like polysilicon, the high stress values of thick tungsten films will soon cause... 

Figure 5.2.1 shows a photograph of an integrated surface-micromachined accelerometer, and Figure 5.2.2 is a close-up of the surface-micromachined polysilicon MEMS structure near the center of Figure 5.2.1. The structural material is 3 pm thick polysilicon and the IC process is bipolar and CMOS (BiCMOS) with thin film resistors. This structure thus combines bipolar transistors, CMOS, precision laser-trimmed resistors, and mechanical polysilicon [4],...

For discrete micromechanical devices that do not include integrated electronics, the situation is different Platinum is an excellent choice for sensors based on a thermal measurement principle and is used in very high volumes, for example, in the air mass flow sensor chip produced at Bosch. Here, a platinum thin film serves as both a heater and a temperature sensor on a thin dielectric membrane consisting of silicon oxide and silicon nitride. The advantages of platinum as a thin film for thermal sensors compared to, for example, polysilicon are as follows ... 

Given the birth of MEMS from the IC industry, the dominant material used in the early devices was silicon. The use of silicon as a substrate and structural material, and the use of polysilicon as a thin film structural material, has continued to the present day for several reasons. The microfabrication techniques for silicon are highly developed and flexible, the microfabrication equipment has been designed for silicon, the properties of silicon are very well known and can be tightly controlled, silicon has excellent mechanical properties, and silicon has an insulating native oxide that can be used as a sacrificial layer. Other thin film materials that are commonly used in MEMS include silicon nitride, metals, and conventional polymers, such as polyimide. 

Laghla Y, Sched E (1997) Optical study of undoped, B or P-doped polysilicon. Thin Solid Films 306 67-73... 

---