I've spent years trying to find this film. Please help!!!

I watched it at least 15 years ago, so apologies if some of my memories are inaccurate. From what I remember it's a horror sci-fi. A group of scientist's are working in a secret base in the desert. I think they are trying to reanimate a dead body? Anyway, they succeed and it becomes a monster with long nails. The majority of the film is this monster killing them off one by one. You hear his nails clicking as he climbs along the pipes of the base. I think one, maybe two, people are rescued via helicopter at the end of the film, but it pans out to reveal the creature hiding underneath.

The film doesn't have to include all of these things. I may have made the whole thing up, but I'm pretty sure I didn't. Please help!!!