Method for forming microcrystalline semiconductor film and method for manufacturing semiconductor device

A seed crystal including mixed phase grains having high crystallinity with a low grain density is formed under a first condition, and a microcrystalline semiconductor film is formed over the seed crystal under a second condition which allows the mixed phase grains in the seed crystal to grow to fill a space between the mixed phase grains. In the first condition, the flow rate of hydrogen is 50 times or greater and 1000 times or less that of a deposition gas containing silicon or germanium, and the pressure in a process chamber is greater than 1333 Pa and 13332 Pa or less. In the second condition, the flow rate of hydrogen is 100 times or greater and 2000 times or less that of a deposition gas containing silicon or germanium, and the pressure in the process chamber is 1333 Pa or greater and 13332 Pa or less.