a method , and corresponding apparatus , of imaging sub - surface features at a plurality of locations on a sample includes coupling an ultrasonic wave into a sample at a first lateral position . the method then measures the amplitude and phase of ultrasonic energy near the sample with a tip of an atomic force microscope . next , the method couples an ultrasonic wave into a sample at a second lateral position and the measuring step is repeated for the second lateral position . overall , the present system and methods achieve high resolution sub - surface mapping of a wide range of samples , including silicon wafers . it is notable that when imaging wafers , backside contamination is minimized .