RegionIntersection of 3D objects

Here is a simple example:

RegionIntersection[Polygon[{{0, 0, 0}, {1, 0, 0}, {1, 1, 0}, {0, 1, 0}}],Ball[]]

How can I get rid of a small notch in the arc?

Update

cvgmt showed useful methods, and I intend to apply them to another polygon.

pts= {{-0.857143, 0.571428, -0.0612242}, {-0.75, 0.571428, 0.107143}, {-0.75, 0.625, 0.0382656}}
reg=RegionIntersection[Polygon[pts],Ball[]];
DiscretizeRegion[reg, Method -> #] & /@ {Automatic, "MarchingCubes", "DualMarchingCubes", "Semialgebraic"}

In this case the "Semialgebraic" method is not adequate. It seems difficult to apply one method to many polygons at once.