Problem 3. Doping a Semiconductor The following chemical scheme is used to introduce P-atoms as a...

 

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Problem 3. Doping a Semiconductor The following chemical scheme is used to introduce P-atoms as a dopant into a semiconductor - a silicon chip. POCI3 Cl POCI 3 vapor P P SiO2 + P(s) CVD coating Si wafer Si(s)+2POCI3(g) SiO2(s) + 3Cl2 + 2P(s) P-rich layer (source) z=0- CAS. Si (sink) Figure 27.2 Phosphorous doping of a silicon wafer. The doping process occurs at 1100 C. The initial concentration of P-atoms is 0. The concentration of P-atoms at the surface by decomposition of POCI3 is 2.5 X1020 P cm-3 The concentration of Si-atoms in the wafer is 5 x 1022 atoms-Si cm. The diffusion constant of P in Si is 6.5 X10-17 m2 s1 at 1100 C. The target P content for the proper electronic properties is at least 0.005 P atoms per 100 Si atoms. The area of the silicon chip is 2.0 X106 m. a) After one hour, what will the thickness of the film be, if the target concentration is 1% of the surface value? b) Estimate the total number of P-atoms that diffuse into the Si wafer during this 1 hr period. Problem 3. Doping a Semiconductor The following chemical scheme is used to introduce P-atoms as a dopant into a semiconductor - a silicon chip. POCI3 Cl POCI 3 vapor P P SiO2 + P(s) CVD coating Si wafer Si(s)+2POCI3(g) SiO2(s) + 3Cl2 + 2P(s) P-rich layer (source) z=0- CAS. Si (sink) Figure 27.2 Phosphorous doping of a silicon wafer. The doping process occurs at 1100 C. The initial concentration of P-atoms is 0. The concentration of P-atoms at the surface by decomposition of POCI3 is 2.5 X1020 P cm-3 The concentration of Si-atoms in the wafer is 5 x 1022 atoms-Si cm. The diffusion constant of P in Si is 6.5 X10-17 m2 s1 at 1100 C. The target P content for the proper electronic properties is at least 0.005 P atoms per 100 Si atoms. The area of the silicon chip is 2.0 X106 m. a) After one hour, what will the thickness of the film be, if the target concentration is 1% of the surface value? b) Estimate the total number of P-atoms that diffuse into the Si wafer during this 1 hr period.