Etching doping effect

Since doping affects the etch rate of polysilicon, we investigated the etch rate characteristics of each gas used in the etch process (Table 1). We discovered that, the polysilicon etch rate with SF6 was independent of doping effects. To minimize the isotropic etch characteristics of SF6 in the B.T step(3), we used HBr, which is a well known polymer forming gas, with a SF6 HBr ratio of 1 0.75. With this new process, vertical profiles were obtained after the B.T step, in both types of polysilicon. At the end of the B.T step, the remaining polysilicon thickness in the n-type was comparable to the p-type and was less than the amount of polysilicon after the B.T step In the conventional process (Fig. 2-a 2-b). Also, the later the EP in the M.E step, the thinner was the remaining polysilicon in the p-type, thus... 

Pure Chemical F-Atom Etching of Silicon Flamm Formulas and Doping Effect... 

Houle F A 1986 A reinvestigation of the etch products of silicon and XeF2 doping and pressure effected. Appl. Phys. 60 3018-27... 

Yarmoff J A and McFeely F R 1988 Effect of sample doping level during etching of silicon by fluorine atoms Phys. Rev. B 38 2057-62... 

Doping of the siHcon can have a large effect on the etch rate, and layers of different materials such as Si02 and Si N can have different etch rates. Eor pressure sensors, thin diaphragms of Si or related materials are etched into the wafer (see Pressure measurements). 

The etch rate of highly p-doped silicon (> 1019 cm4) is found to be reduced by orders of magnitude compared to the etch rate of low doped or highly doped n-type silicon of (100) orientation. This effect is shown in Fig. 2.3 for KOH note that the etch rate is significantly affected by the amount of dissolved oxygen... 

The study in Ref. 74 followed essentially the same deposition procedure as before, but on Cr-plated steel (compared with steel in the previous studies see Sec. 9.2.1 for an explanation of the effect of Cr plating based on the poor electro-catalytic activity of Cr) and with a CuCliKCN etch at 90°C (the reason for this specific etch was not explained). These modifications led to improved PEC response, which was further improved using As-doped CdS, deposited by adding AsCE to the deposition bath. 

Heavily doped (>1018/cm3) n-type Si and poly-Si etch faster in Cl- and F-containing plasmas than do their boron-doped or undoped counterparts (103a, 105, 111, 112). Because ion bombardment is apparently not required in these cases, isotropic etch profiles (undercutting) in n + poly-Si etching often occur. Although the exact mechanisms behind these observations are not completely understood, enhanced chemisorption (103b, 111) and space charge effects on reactant diffusion (112) have been proposed. 

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