sputter target power and the flow rate of n 2 gas in this way six different kinds of tin x layer 1 respectively having values of 0 0 3 0 5 0 8 0 9 and 1 0 for x were formed so that each layer 1 had a thickness of about 30 mm and a tin layer 2 having a thickness of 200 nm was formed on each of the six tin x layers 1 subsequently an al layer 3 was formed on each tin layer 2 and the tin x film 1 the tin film 2 and the al film 3 of each assembly were etched in the same pattern using a known reactive ion etching technique to form a structure such as that shown in fig1 which was then subjected to a heat treatment thereafter the contact resistance in the contact region between the wiring layer and the si substrate and the leakage current in the above described impurity doped region were measured table 1 shows the measured values for the contact resistance in the contact region between the wiring and the substrate of each of the samples in which the contact area was circular and had a diameter of 1 2 u03bcm and the measured values for the leakage current obtained in the case where the contact area was in the shape of a square one side of which had a length of 200 u03bcm table 1__________________________________________________________________________impurity xitemsdoped region 0 0 0 3 0 5 0 8 0 9 1 0__________________________________________________________________________contactn sup layer 1 u00d7 10 sup 7 1 u00d7 10.