Doped silicon films

The solution-processed doped silicon films described above (baked at 500 °C for 2 hr) exhibited high electrical resistivity (greater than 300 Qcm), which is the measurement limit of the instrument we used. To lower the resistivity, we tried an additional rapid thermal annealing (RTA) of the film prepared from the copolymerized solution with 1 wt% phosphorus concentration. In this RTA, the SiC plate on which the sample was placed was irradiated with infrared (IR) light from a 1-kW IR lamp. The RTA conditions were 600 °C for 2 hr, 650 °C for 20 min, 700 °C for 5 min, and 750 °C for 5 min these temperatures were that of the SiC plate, and the temperature of the Si film is estimated to be several dozens of degrees lower than that. 

Figure 5.18 shows the relationship between the resistivity and phosphorus concentration of the initial solution for the film formed from various solutions and heated under the same polycrystallizing RTA conditions (750 °C for 5min). As the initial phosphorus concentration increases, the resistivity decreases down to 2.1mQcm. The film formed from a l-wt% postpolymerization addition solution and the film formed from a 0.01-wt% copolymerized solution exhibit almost the same resistivity, which is reasonable since the two films have almost the same amount of phosphorus atoms, as shown in Fig. 5.16. To apply these doped-silicon films to the source and drain regions of poly-Si TFTs, the initial concentration of 0.1-1 wt% will be sufficient in the case of the copolymerized solution for this heating condition.

Similar depth profiles are routinely done for phosphorus and arsenic-doped silicon films. 

Among the most commonly used indicator dyes for doping silicone films are ruthenium(II) complexes with polyazaheterocyclic chelating hgands [33] and metallo-porphyrins [104]. These compounds possess unique photochemical and photophysical characteristics such as large separation between the absorption and emission bands and... 

Polysilicon is a contraction of polycrystalline silicon, (in contrast with the single-crystal epitaxial silicon). Like epitaxial silicon, polysilicon is also used extensively in the fabrication of IC s and is deposited by CVD.f l it is doped in the same manner as epitaxial silicon. Some applications of poly silicon films are ... 

Tanaka, H. et al. 2007. Spin-on n-type silicon films using phosphorous-doped polysilane. Jpn. J. Appl. Phys. 46 L886-L888. 

Doped silicon, conductivity in, 23 35 Doped/undoped electrochromic organic films, 6 580-582 Dope-dyeing, 9 197 Dope-making process, in acrylic fiber solution spinning, 11 204 Dope solids, in air gap spinning, 11 209 Doping, 23 838—839 calcium, 23 842-844 conducting polymers, 7 528-529... 

According to the macropore formation mechanisms, as discussed in Section 9.1, the pore wall thickness of PS films formed on p-type substrates is always less than twice the SCR width. The conductivity of such a macroporous silicon film is therefore sensitive to the width of the surface depletion layer, which itself depends on the type and density of the surface charges present. For n-type substrates the pore spacing may become much more than twice the SCR width. In the latter case and for macro PS films that have been heavily doped after electrochemical formation, the effect of the surface depletion layer becomes negligible and the conductivity is determined by the geometry of the sample only. The conductivity parallel to the pores is then the bulk conductivity of the substrate times 1 -p, where p is the porosity. 

For homogeneously doped silicon samples free of metals the identification of cathodic and anodic sites is difficult. In the frame of the quantum size formation model for micro PS, as discussed in Section 7.1, it can be speculated that hole injection by an oxidizing species, according to Eq. (2.2), predominantly occurs into the bulk silicon, because a quantum-confined feature shows an increased VB energy. As a result, hole injection is expected to occur predominantly at the bulk-porous interface and into the bulk Si. The divalent dissolution reaction according to Eq. (4.4) then consumes these holes under formation of micro PS. In this model the limited thickness of stain films can be explained by a reduced rate of hole injection caused by a diffusional limitation for the oxidizing species with increasing film thickness. 

Microelectronic devices on silicon chips are typically made from layers of n-type and p-type silicon. Films of silica act like the plastic sheath on copper cable, since silica is insulating. A layer of p-type silicon back to back with a layer of n-type, called a p-n junction, allows a current moving across the junction to flow in one direction but not the reverse. This one-way behaviour is the fundamental characteristic of a device called a diode. Early diodes in electronics were made from metal plates sealed inside evacuated glass tubes, which could be seen glowing in the innards of old radio sets. Diodes made from doped silicon can be much smaller and more robust since they are made from solid materials, they are components of solid-state electronics. 

Osenbach, J. W. Sodium diffusion in plasma-deposited amorphous oxygen-doped silicon-nitride (alpha-SiON H) films. Journal of Apphed Physics 63, 4494—4500 (1988). 

The specific application of a material generally determines the particular structure desired. For example, hydrogenated amorphous silicon is used for solar cells and some specialized electronic devices (10). Because of their higher carrier mobility (see Carrier Transport, Generation, and Recombination), single-crystalline elemental or compound semiconductors are used in the majority of electronic devices. Polycrystalline metal films and highly doped polycrystalline films of silicon are used for conductors and resistors in device applications. 

Chemical and phase purity are not always desirable. For example, H- and N-doped silicon carbide films behave as high temperature semiconductors, while silicon carbonitride glasses offer properties akin to glassy carbon with room temperature conductivities of 103 2 cm-118. Additional reasons for targeting materials that are not chemically or phase pure stem from the desire to control microstructural properties. 

PECVD of silicon nitride has been of commercial importance since 1976.1 The original motivation was to find a final passivation layer for an integrated circuit that would replace the doped silicon dioxide films then in use. The latter were not reliable enough to permit packaging of integrated circuits in plastic. Silicon nitride was recognized as a better final passivation film, but the only available technique for its deposition was the high-temperature thermal process. Since it had to cover an aluminum final metallization layer that would melt at 600°C, this clearly could not work. The solution was to use PECVD at 350° to 400°C. 

Many questions remain. It will have to be shown that the doped resistivity can be as good as conventional doped LPCVD films. Also, the role of species other than silicon has to be clarified (i.e., hydrogen, noble gases). 

As noted earlier in Chapter 3, epitaxial silicon films deposited by CVD can be affected by autodoping. If diffusion of the doping species is excessive, the film is not a useful one. Therefore, quite a lot of effort has been spent to accurately measure the distribution of dopant through the film thickness. 

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