Polysilicon formed on a field oxide layer may be used as a resistor element for use in the semiconductor integrated circuit. In such a case, a plurality of polysilicon members having the same shape and the same characteristics may be formed as a resistor element unit for the purpose of providing a desired resistance value. The number of polysilicon members connected in series or in parallel is then adjusted to adjust the resistance value. The size and shape of such polysilicon members are required to be highly precise. The polysilicon members may thus need to be manufactured under the same process conditions. Namely, the conditions of photolithography and etching performed during the wafer process may need to be maintained constant with respect to each polysilicon member.
When a plurality of polysilicon members having the same shape are arranged in matrix form at constant intervals, polysilicon members situated in the interior of the matrix are formed under the same process conditions because each of these polysilicon members has identical positional relationships with the surrounding adjacent polysilicon members. The polysilicon members situated at the periphery of the matrix, however, have adjacent polysilicon members only on one side thereof, and, thus, are subjected to different process conditions than the conditions applied to the interior polysilicon members which are surrounded by adjacent polysilicon members on the four sides thereof. Accordingly, the polysilicon members situated at the periphery are provided, as dummy members unused for actual circuit operations, only for the purpose of achieving constant process conditions for the interior polysilicon members.
FIG. 1 is a plan view illustrating an example of a related-art resistor-element unit. FIG. 2 is a cross sectional view of the resistor-element unit illustrated in FIG. 1 as taken along a line A-A′.
As illustrated in FIG. 1 and FIG. 2, a resistor-element unit 10 includes a P-type substrate 13, a field oxide layer 14 formed on the P-type substrate 13, and a plurality of polysilicon members 11 and 12 formed on the field oxide layer 14. The polysilicon members 11 and 12 are arranged in matrix form at constant intervals which are an interval “a” in the vertical direction and an interval “b” in the horizontal direction. The polysilicon members 12 are dummy polysilicon members situated at the periphery of the matrix, and the polysilicon members 11 are resistor-element polysilicon members situated in the interior of the matrix.
The resistor-element polysilicon members 11 situated in the interior of the matrix are formed under the same process conditions because each of these polysilicon members has identical positional relationships with the surrounding adjacent polysilicon members. Accordingly, the resistor-element polysilicon members 11 have the same resistor-element characteristics. A desired resistor value can thus be obtained by connecting a desired number of resistor-element polysilicon members 11 in series or in parallel.
The dummy polysilicon members 12 situated at the periphery of the matrix, however, have adjacent polysilicon members only on one side thereof, and, thus, are subjected to different process conditions than the conditions applied to the interior resistor-element polysilicon members 11 which are surrounded by adjacent polysilicon members on the four sides thereof. Accordingly, the dummy polysilicon members 12 situated at the periphery are formed, as dummy members unused for actual circuit operations, only for the purpose of achieving constant process conditions for the interior polysilicon members.
In the resistor-element unit 10 formed as described above, the dummy polysilicon members 12 situated at the periphery are not used as part of an actual operating circuit, which means that there are needless elements and areas provided in the semiconductor integrated circuit chip. This gives rise to problems such as an increase in chip size and a cost increase.