A well contact diffusion layer (a so-called “guard ring”) is frequently used in a semiconductor device to electrically connect semiconductor elements such as a transistor to a well diffusion layer. Contacts connecting wirings from a semiconductor device to a guard ring are often formed to be circular or elongated-circular in a planar shape.
In terms of reducing a chip size of a semiconductor device, contacts of a guard ring are desirably circular-hole contacts having a circular shape. However, if all the contacts of a guard ring are circular-hole contacts, contact resistances to wells are increased when some of the circular-hole contacts are not opened.
On the other hand, in terms of reducing contact resistances to wells, contacts of a guard ring are desirably elongated-hole contacts having an elongated shape. However, if all the contacts of a guard ring are elongated-hole contacts, the chip size may be increased. For example, the width of the guard ring needs to be increased to match the major axis of the elongated-hole contacts. Alternatively, distances between adjacent wirings need to be increased to match the major axis of the elongated-hole contacts.