"Higher power" is an Alcoholics Anonymous thing, which has been rationalized by the group to include atheism and agnosticism, although not all atheists and agnostics are on board with that (Cf. Secular Organizations for Sobriety, Rational Recovery). In Freemasonry, you're looking for the "Supreme Being," the God of "that religion in which all men agree" which is an attempt at universalism from a 18th century cultural Christian perspective. While that concept has been harmonized with Buddhism, Hinduism, various Neopaganisms, and many other religions that aren't a natural fit, atheism remains explicitly called out as something that's incompatible in the ritual used in the Anglo-American Masonic tradition. Adogmatic or Liberal Freemasonry admits atheists (and sometimes women!), but they're much fewer in number outside Latin America and Continental Europe and unrecognized by the larger Anglo-American faction.
The disqualification of atheism is because it is a materialist anti-belief, where the necessary condition is that any faith of others is wrong, which makes it the essence of choosing to have an irreconcilable difference. They literally identify as adversaries to the faithful.
If you've ever seen a dog scramble to take food and wolf it down without a sense of consequences because the food is the end in itself, materialism is the human version of that but for power. Without a shared abstraction for morality, there is no basis of trust or responsibility to expose anything valuable to them. In this sense, belief in a supreme being is a much more rational position than its critics apprehend.
Masons require a belief in a supreme being and scripture, and various things online say they've explicitly forbidden atheists before. I take everything I read about Freemasonry with a grain of salt, but it still seems fairly hostile to atheists.
You're correct that Anglo-American Freemasonry requires a belief in a Supreme Being. However, the issue of scripture is a bit more nuanced. There's no requirement to believe in the veracity or to honor any scripture in particular. There is a Holy Bible on an altar in a lodge room but it's used as a symbol. During an initiation, a candidate usually has the option to use the holy book of his choice. If one is opposed to the idea that holy books should be honored at all, he might not be a good fit for the institution, but there's nothing technically preventing him from joining. There's also a few times when portions of the Hebrew scriptures are read aloud, though they're pretty unoffensive from a universalist perspective.
They seem to be somewhat welcoming towards most major religions, but atheists still seem frowned upon. One could argue that the universe itself is a supreme being, but any scripture put forth would likely raise some questions.
I'm sure an atheist could successfully become a member, but I doubt many are trying to as the original post joked.