Crystalline silicon contains 5 times 10^22 atoms/cm^3. When a wafer is doped the

Question

Crystalline silicon contains 5 times 10^22 atoms/cm^3. When a wafer is doped the dopant atom replaces a silicon atom in the lattice. What is the ratio of dopant atoms to silicon lattice sites for the following doping levels? Express in terms of % dopant and parts per million (ppm/billion(ppb)/trillion(ppt). Example: 5 times 10^14 dopant atoms/cm^3 = 0.000001% dopant or 10 ppb dopant 5 times 10^15 dopant atoms/cm^3 2.5 times 10^16 dopant atoms/cm^3 5 times 10^18 dopant atoms/cm^3 5 times 10^20 dopant atoms/cm^3

Explanation / Answer

given: silicon atoms = 5 *10^22 atoms/cm^3

1 million=10^6

1 billion =10^9

1 trillion =10^12

1 % = 0.01

% of dopant=(dopant atoms) / (silicon atoms)

a.% of dopant=(5*10^15) / (5*10^22)=10^-7=0.00001 % of dopant=100/(10^9)=100 parts per billion(ppb)=0.1 parts per million=100000 parts per trillion

b.% of dopant=(2.5*10^16) / (5*10^22)=0.5*10^-6=0.00005 % of dopant=500 ppb=0.5 ppm= 500000ppt

c.% of dopant=(5*10^18) / (5*10^22)=10^-4=0.01 % of dopant=10^5 ppb=100 ppm=10^8 ppt

d.% of dopant =(5*10^20) / (5*10^22)=10^-2= 1% of dopant =10^7 ppb=10^4 ppm=10^10 ppt

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