The stopping power of photo-resist is an important parameter to define the photoresist thickness. In this paper, we have developed a novel method to the stopping power of the photo-resist. This method is to directly determine the implantation profile in the photo-resist using secondary ion mass spectrometry (SIMS) due to its excellent sensitivity and high depth resolution. We have obtained the depth distribution of dopants, such as boron, arsenic, phosphorous and indium, in the photo-resist using CAMECA Wf SIMS machine. The results obtained with the novel method are straightforward and unambiguous, compared to the conventional method. The safe photo-resist thickness has been optimized based on the SIMS results.