Question

5.147 Silicon nitride, SizN4, is a material that is used in computer chips as an insulator. Silicon nitride can be pre. pared according to the chemical equation 3SiH (g) + 4NH3(g) →SizN4(g) + 12H2(g) If you wanted to prepare a surface film of SizN_(s) that had an area of 9.0 mm2 and was 4.0 X 10-mm thick, what volume of SiH, gas would you need to use at 1.0 X 10-5 torr and 775 K? The density of SizN, is 3.29 g/cm?.

Answer 1

We want to prepare a film of Siz N4 (32 I that had area of Imm² and thickness of 4410-5 mm 50, Volume of S13 M4 - Used in film = Area (A)X thickness (t) _ V= Axt = 9 x 4x10-5 mm 3 so, Volume = 3.6x10-4 mm3 Imm3 = 1073) = 3.6x10-4 x 10-3 cm3 cm = 3.6 410-7 cm 3 and density of Sl₃ N4 = 3.29 gm/cm3 and density (dl) = mass (m) Volumelv so mass of Sig Ng = d x v = 3.29 x 3.6% 10- 2 11.844x10-7.

and Molar mass of Sia Nx= 3x28 + 4x14. = 140 golman t son moles of S13 N4 = Given mass (m) Molay mars 11.844 x 10-7 140 = 8.46x109 mol from the reaction, | 3 Si H4(9) + 4 NH3tof 5 Sty Netol + 12 Hz (9) Alcto sto chiometry + Foy 1 mol Of Sig NA we need 3 mol of Siltu and we have 8.46 x 10-9 moles of Sjana

Required moly of Si Hy = 348.46x10^9 ___= 25.38 X10-9 moly

from ideal gas equation, | PV = HRI] p- pressure pressure 1 V- Volume T-temperowie na molé R = 0.0821 atm-L molek - goy Constant

P= 1:0910-5 tory 1: 1 am = 760 form x 10-5 atm 760 *2005 T=775k n = 25.38 x 10-9 met 30, Volume Sihy = nRT 25.38X10-9 x 0.0821 x 775 4760 1 x lors - 129.73 so, volume of SiHy wrequired 1 122.732