Weak antilocalization and electron-electron interaction effects are investigated in Sb 2 Te 3 layers. We accomplish smooth top and bottom surfaces for the layer using molecular-beam epitaxy, as revealed by the Kiessig oscillations in the x-ray reflectivity. The two helical surface states of the layer are found to contribute identically to the weak antilocalization effect. They are left intact in spite of low mobility and high concentration of unintentionally doped holes. The magnitude of the electron-electron interaction effect is consistent with the indication that both of the surface states survive in the layer. The robustness of the surface states demonstrates superiority of Sb 2 Te 3 over Bi 2 Se 3 and Bi 2 Te 3. We also show that the phase-change property of Sb 2 Te 3 provides controllability to switch the existence of the surface states.