Patent ID: 7427519

Claim:
A method of detecting an end point of a plasma etching process for etching a first layer on a second layer that comprises a material different from that of the first layer, wherein the first layer produces a first etching product and the second layer produces a second etching product, the method comprising: collecting time-dependent intensity [I j=1 to m (t)] of a number “m” (m≧1) of spectral line(s) of the first etching product in an emission spectrum of the plasma and time-dependent intensity [I i=1 to n (t)] of a number “n” (n≧1) of spectral line(s) of the second etching product in the emission spectrum, wherein “m+n≧3” is satisfied; calculating, in real time, one index of Lm ⁡ ( t ) ⁡ [ = ∏ i = 1 , j = 1 n , m ⁢ ⁢ I i ⁡ ( t ) I j ⁡ ( t ) ] , Ls ⁡ ( t ) ⁡ [ = ∑ i = 1 , j = 1 n , m ⁢ ⁢ I i ⁡ ( t ) I j ⁡ ( t ) ] , Lm′(t) {=d[Lm(t)]/dt} and Ls′(t) {=d[Ls(t)]/dt} and plotting the same with the time; and identifying at least one etching end-point from the plot of the one index with the time.