3.155J/6,152J Microelectronic Processing Technology Fall Term. 2003 Quiz 2 With SOLUTIONs Dec.3,2003 vaporation and sputter deposition [151 1. a)In the plasma of a sputter deposition system, consider an argon atom that is ionized during a collision in the plasm 1) Express the ratio of the acceleration of the liberated electron to that of the argon ion in terms of m and m, the mass of the ion and electron; give the numerical value of this ratio, and say in which direction each species accelerates )31 11) Over a given mean free path, one of the particles will achieve a much higher speed. Explain how that affects the potential (voltage)of the plasma relative to that of either electrode? [31 111) In argon(atomic number A =40)sputtering from a target composed of equal parts of tungsten(A= 184)and aluminum(A 27), would the deposited layer more likely turn out richer in Wor AI?[3 b)Answer these items with either"" or"evaporation"or"both 1) Which deposition method affords better step coverage? [21 11) Which deposition method is more likely to have ballistic transport ng deposited? [21 111) Which method is more likely to be used for deposition of an epitaxial single crystal film? [2] 1. a) i)a=F/m, hence alecto aon_= M/m; electron accelerates toward anode, ion 11) Over a given mean free path, electron achieves a much hi gher speed and thus travels much farther than the ion. Since most of these particles are created in the plasma(some a generated at the cathode), more electrons than ions leave the plasma and as a result, the plasma is at a positive potential relative to either electrode 111) Argon ions are much more effective at transferring energy to species having similar masses(mM/m+M, so the sputtering yield for Al is much greater than that for tungsten in argon ion sputtering b) 1) sputtering; species approach substrate from a greater distribution of angles i1)evaporation; much lower pressure gives longer mena free path chan ii) evaporation; film can be cleaner because of lower background pressure I mber, and hence fewer defects available to upset periodicit Interconnects 25 2. Two different metals, tungsten(W) and copper(Cu) are to be used for interconnects on given IC. [12 a) Which of these metals is more likely to be used for local interconnects? [211 3.155J/6.152J Microelectronic Processing Technology Fall Term, 2003 Quiz # 2 With SOLUTIONS Dec. 3, 2003 Evaporation and sputter deposition [15] 1. a) In the plasma of a sputter deposition system, consider an argon atom that is ionized during a collision in the plasma. i) Express the ratio of the acceleration of the liberated electron to that of the argon ion in terms of M and m, the mass of the ion and electron; give the numerical value of this ratio, and say in which direction each species accelerates.) [3] ii) Over a given mean free path, one of the particles will achieve a much higher speed. Explain how that affects the potential (voltage) of the plasma relative to that of either electrode? [3] iii) In argon (atomic number A = 40) sputtering from a target composed of equal parts of tungsten (A = 184) and aluminum (A = 27), would the deposited layer more likely turn out richer in W or Al? [3] b) Answer these items with either “sputtering” or “evaporation” or “both”. i) Which deposition method affords better step coverage? [2] ii) Which deposition method is more likely to have ballistic transport of the species being deposited? [2] iii) Which method is more likely to be used for deposition of an epitaxial single crystal film? [2] 1. a) i) a =F/m, hence aelecton/aion = M/m ; electron accelerates toward anode , ion toward cathode. ii) Over a given mean free path, electron achieves a much higher speed and thus travels much farther than the ion. Since most of these particles are created in the plasma (some a generated at the cathode), more electrons than ions leave the plasma and as a result, the plasma is at a positive potential relative to either electrode. iii) Argon ions are much more effective at transferring energy to species having similar masses (mM /[m + M]), so the sputtering yield for Al is much greater than that for tungsten in argon ion sputtering. b) i) sputtering; species approach substrate from a greater distribution of angles. ii)evaporation; much lower pressure gives longer mena free path. iii) evaporation; film can be cleaner because of lower background pressure I chamber, and hence fewer defects available to upset periodicity. Interconnects [25] 2. Two different metals, tungsten (W) and copper (Cu) are to be used for interconnects on a given IC. [12] a) Which of these metals is more likely to be used for local interconnects? [2]