An integrated circuit structure include a semiconductor substrate, a gate stack over the semiconductor substrate, and a recess extending into the semiconductor substrate, wherein the recess is adjacent to the gate stack. A silicon germanium region is disposed in the recess, wherein the silicon germanium region has a first p-type impurity concentration. A silicon cap substantially free from germanium is overlying the silicon germanium region. The silicon cap has a second p-type impurity concentration greater than the first p-type impurity concentration.