Scanning tunneling microscope (STM) has recently demonstrated its potential application as a powerful tool for nanometer-scale surface modification. We have successfully fabricated new types of diamond-coated STM tips by using microwave plasma chemical vapor deposition (MPCVD). The reactant is a gaseous mixture of methane and hydrogen, sometimes adding oxygen. While natural diamond is a good insulator, the electrical conductivity of diamond-coated tips made by MPCVD technique is always high enough for STM experiments. These tips are quite stable, hard enough to make machining on metal or other solid surfaces in nanometer scale. We have applied the diamond coated STM tip to so-called controlled machining on the metallic surfaces, such as gold, silver, and platinum films, and even polycrystal platinum, single crystal nickel, and palladium. Further investigations, including the results caused by different tips, applications for nanometer-scale processing and engineering, etc., have been discussed. This technique might become a potential useful tool for nanometer science and technology in the future.