Yeah, that’s stato-dynamic training. I use that a lot with athletes. The pause can be at various positions depending on the training effect you want.
Just for future reference, I understand that by saying a 90 degrees angle you probably (hopefully) mean when the thighs are parallel to the floor. In reality this is closer to 70 degrees. When we talk in degrees for squat, we refer to the angle of the knee joint. A 90 degrees knee angle is essentially a quarter squat.