Patent ID: 6859754

Claim:
A statistical process control (SPC) method for a post-stage process which is related to a pre-stage process, said SPC method comprising: collecting a plurality of pre-stage measurements during said pre-stage process; collecting a plurality of post-stage measurements during said post-stage process, said plurality of post-stage measurements corresponding to said plurality of pre-stage measurements; evaluating an equation for approaching a relation between said plurality of post-stage measurements and said plurality of pre-stage measurements; calculating a post-stage variance based on said equation, said post-stage variance being independent of a fluctuation of said plurality of pre-stage measurements; and monitoring said post-stage process of mass production by an upper control limit and a lower control limit, wherein said upper control limit is equal to said equation plus half order of said post-stage variance and said lower control limit is equal to said equation minus half order of said post-stage variance.