Scholarships for Ph.D
Normally, if you're doing a PhD in the United States—at least in the sciences and engineering—you shouldn't have to worry about having a scholarship. The department or advisor should be responsible for paying your tuition as well as a stipend for your living expenses. So there aren't a lot of "scholarships" in the same sense as for undergraduate study. However, while there are fellowships which provide "portable" funds for graduate study, these tend to have stringent citizenship requirements, and I can't ever recall seeing one for which Indian students were eligible.

Your best bet is probably just to apply to the graduate programs in which you're interested, and see if they have funds to support your graduate work.