A buried layer used in a semiconductor device is formed by diffusing N+ impurities into a P-type substrate before growing an epitaxy layer. That is, the buried layer is formed inside the semiconductor device to provide a low resistance in a device current path. Antimony (Sb) or arsenic (As) is used as a dopant to form a typical buried layer.
In general, as shown in FIG. 1, prior to forming an epitaxy layer on a P-type substrate 10, a heavily-doped N-type buried layer 20 is formed below an active region on which a transistor will be formed. A function of the buried layer 20 is to secure a connection with the active region on which the transistor will be formed. Further, the buried layer 20 functions to provide junction insulation since the buried layer 20 is formed to have a conductivity type opposite to that of a substrate on which the epitaxy layer is formed. The buried layer 20 also causes the P-type substrate 10 to be suitably biased.
However, as shown in FIG. 2, after formation of the N-type buried layer 20, upon forming the epitaxy layer 30, a stepped portion 21 (FIG. 1) of the N-type buried layer 20 is partially positioned on the epitaxy layer 30. On the other hand, a stepped portion 31 formed at the epitaxy layer 30 is not formed at a position corresponding to the stepped portion 21 (FIG. 1) of the N-type buried layer 20, but is formed to be shifted by a distance 30a from the position corresponding to the stepped portion 21 (FIG. 1) thereof.
Accordingly, an N+ plug 33 must be formed by applying an offset 32 by the shifted distance in order to compensate for the shifting as shown in FIG. 3. In this case, in order to measure the shifting extent of the stepped portion 21 (FIG. 1) of the epitaxy layer 30, a section of a wafer 10 must be cut and measured. However, to periodically perform the measurement, a number of wafers are used every time increasing fabrication cost and causing loss of time taken to analyze the section of the wafer.