Doping wafer fabrication process

A schematic view of the cold cathode fabrication process is shown in Fig. 10.18. The cold cathode is fabricated by low pressure chemical vapor deposition (LPCVD) of 1.5 pm of non-doped polysilicon on a silicon wafer or a metallized glass substrate. The topmost micrometer of polysilicon is then anodized (10 mA cnT2, 30 s) in ethanoic HF under illumination. This results in a porous layer with inclusions of larger silicon crystallites, due to faster pore formation along grain boundaries. After anodization the porous layer is oxidized (700 °C, 60 min) and a semi-transparent (10 nm) gold film is deposited as a top electrode. 

The fabrication process is illustrated in Figure 5.16, the details of which can be found elsewhere.25 As before, a 3-inch n-type doped silicon wafer was used for the fabrication of the cantilever structure. Firstly, a layer of silicon dioxide... 

These processes are considerably more complex in actual CMOS fabrication. First, the lower layers of a CMOS stmcture typically have a twin-tub design which includes both PMOS and NMOS devices adjacent to each other (see Fig. 3b). After step 1, a mask is opened such that a wide area is implanted to form the -weU, followed by a similar procedure to create the -weU. Isolation between active areas is commonly provided by local oxidation of sihcon (LOCOS), which creates a thick field oxide. A narrow strip of lightly doped drain (LDD) is formed under the edges of the gate to prevent hot-carrier induced instabiUties. Passivation sidewalls are used as etch resists. A complete sequence of fabrication from wafer to packaged unit is shown in Figure 10. 

Test samples were fabricated by Si and Ge monohydrides pyrolysis in the gas mixture at the total pressure of 35-40 Pa with monogerman to monosilane volume ratio of 0.001-0.002. Temperature of the process was not higher than 680°C. P-doped silicon wafers (100) were used as substrates. Before the pyrolysis process we have oxidized the surface of some silicon wafers in dry oxygen in order to form thin silicon dioxide layer. In addition dysprosium and yttrium oxides were also formed on the wafer surface for other samples by the process of their deposition and following oxidation. 

In order to support the ever-shrinking device dimensions, a dry etching technique was developed to replace wet chemical etching for high-fidelity pattern transfer by Irving and co-workers ° in 1971 in a process that involved the use of a CF4/O2 gas mixture to etch silicon wafers. Molecular beam epitaxy, developed also in 1971 by Cho, offers the advantage of near-perfect vertical control of composition and doping down to atomic dimensions, and is now applied extensively in the fabrication of photonic devices and quantum effect devices. ... 

Electrical measurement of the dielectric constant is done through the fabrication of metal—oxide—semiconductor capacitor structures, where the ULK serves as the dielectric of the capacitor. A doped Si wafer is used as the substrate, on which the ULK film is deposited. This ULK film is subjected to CMP, say, or any other process whose impact on ULK characteristics needs to be quantified. An aluminum film is deposited on the backside of the Si wafer to form one of the capacitor contacts. Using a shadow mask, aluminum dots of varying diameters are evaporated onto the surface of the ULK film, to form the other terminal of the capacitor. Each aluminum dot is probed to measure its capacitance (at about 100 kHz). Evaporation through a shadow mask allows for the formation of metal contacts without altering the dielectric further— as would be the case if reactive-ion-etch were used to form the contacts. (It should be noted that more complex process flows can be used to eliminate concerns such as dot-size variation, the effect of probe-tip impact on the dielectric being tested, etc.) The results of electrical measurement of the k-value increase post-CMP of the variety... 

Ion implantation has become the dominant doping technique, particularly in the fabrication of bipolar-CMOS devices and in the formation of shallow junctions. Laser ablation sampling coupled with ICP-MS was applied recently to the determination of total dopant dose. Since this technique spatially and temporally separates the sampling and ionization steps, it has the potential to produce more quantitative results than SIMS for trace elements in a given matrix. Wafer surface analysis can also be used to monitor the contamination induced hy different process steps. The importance, in terms of contamination contrihution, of the chamber components used for film deposition and ion implantation was demonstrated, as was the effect of cleaning bath solution purity. ... 

IBC detector array production utilizes many of the capabilities discussed above for readouts as well as facilities specific to detector fabrication. HTC has devdoped custom IBC detector modeling software to predict the performance of various detector layer doping profiles. Profiles yidding the desired performance are grown epitaxially in HTC s custom epi reactors. These epitaxial wafers are then processed into detector arrays in the same processing lab as the readouts. 

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