content was measured using xps x ray photoelectron spectroscopy also the knoop hardness for each of the layers in the test samples was studied and it was found that in all cases the outermost aln film was softer than the inner ticn film layer using the cutting conditions shown in table 24 the cutting efficiency of the surface coated drills with outermost layers as shown in table 23 was observed for cutting conditions 3 the number of holes bored until the tool broke was studied for cutting conditions 4 the roundness of the holes was studied the results of the tests are shown in table 25 based on the results in the test samples 11 1 through 11 3 which have aluminum nitride layers with more than 0 and not more than 0 5 atomic percent of chlorine on the outermost layer as shown in table 25 and inner layers with films having predetermined compositions superior chip ejection properties were provided and damage to the cutting section was reduced allowing good cuts over an extended period of time this significantly increased the number of cuts that could be made until the tool broke this indicates that tool life was extended for the test samples 11 1 11 3 it was found that the roundness of the bored holes was superior and.