Are you looking for a combined neurology/IM residency program or either one of these?
You will only get a generic response here because you have nothing on your resume so far. However as an FMG you will need a combination of above average USMLE step 1 and 2 and significant research experience.
I don't think that a masters in science would improve your odds on its own. However, if that's the only way for you to be exposed to research, then go ahead and do it.
Alternatively, take the USMLE and ace it then apply for research for postgrad research opportunities here in the US. I know a number of FMGs who did a year or two research at well-known institutions and eventually they were able to match neurology, and they matched well.
Good luck