Semiconductor Device Having Resistor Structure

The present invention relates to a semiconductor device having a resistor structure provided on an insulating layer on a semiconductor substrate.

Conventionally, the resistor element made of a polycrystalline silicon film, etc. as well as wiring layers connected to the resistor element is provided on a thick field insulating layer having substantially uniform thickness, for reducing the parasitic capacitance between the resistor element and the silicon substrate and between the wiring layer and the silicon substrate. However, the heat produced in the resistor element cannot be effectively dispersed through the thick insulating layer into the silicon substrate. If the resistor element is designed to have a large area and provided on a thicker insulating layer, on the other hand, the high integrated circuit semiconductor device cannot be realized.

Accordingly, an object of the present invention is to provide a semiconductor device having a resistor structure including a resistor element and a wiring layer connected to the resistor element, in which the heat produced in the resistor element during the operation can be effectively dispersed into the semiconductor substrate.

According to a feature of the present invention, there is provided a semiconductor device comprising a semiconductor substrate having a major surface, an insulating layer provided on the major surface of the substrate, the insulating layer including a first portion and a thinner second portion, a resistor element provided on the second portion of the insulating layer, and a wiring layer provided on the first portion of the insulating layer and connected to the end part of the resistor element. Generally, the length of the wiring layer extending on the first portion is 200 .mu.m to 800 .mu.m. Favorably, the thickness of the first portion ranges from 1.3 .mu.m to 3.0 .mu.m, and that of the second portion ranges from 0.05 .mu.m to 0.8 .mu.m. The first portion of the insulating layer may be constituted by multi-layered insulating films, and the second portion of the insulating layer may be constituted by only one of them. Each insulating film may be made of silicon oxide, silicon nitride or silicate glass such as phosphosilicate glass and borosilicate glass. The resistor element may be made of lightly-doped polycrystalline silicon or thin metal film such as SiCr (silicon-chromium alloy), and the wiring layer may be made of metallic film such as aluminum film or highly doped polycrystalline silicon. The insulating layer on which the resistor structure is formed may be used as the field insulator. Therefore, the thickness of the first portion of the insulating is determined so that no parastic MOS transistor effect is produced between device elements formed in the substrate. The second portion on which the resistor element of the resistor structure is formed may be surrounded by the first portion in plan view.

FIG. 1 is a cross-sectional view showing a semiconductor device in the prior art;

FIG. 2A is a plan view showing an embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along line B--B' in FIG. 2A as viewed in the direction of arrows.

Referring to FIG. 1, on the silicon substrate 1 the field silicon oxide film 2 having the substantially uniform thickness of 1.5 .mu.m is provided by a thermal oxidation. The polycrystalline silicon resistor element 3 having the sheet resistivity of 180 .OMEGA./.quadrature. is provided on the field silicon oxide film 2. The aluminum wiring layers 7, 8 are connected to contact parts of the resistor element 3 at their one ends, respectively, through the openings 5, 6 in the intermediate insulating film 4 of silicon oxide having 0.2 .mu.m thickness and extend on the film 4 at a distance l.sub.3, l.sub.4 of about 400 .mu.m, respectively. The wiring layer 8 is connected to another wiring layer 10 provided on another intermediate insulating film 9 at its other end. Also, the wiring layer 7 may be connected to an upper wiring layer (not shown) or to an impurity region (not shown) in the substrate at its other end. The resistor element 3 has the width of 10 .mu.m, the effective length l.sub.1 of 25 .mu.m and the thickness of 0.25 .mu.m, and therefore the resistance of the resistor element becomes 450 .OMEGA.. In such a structure, when electrical current of 10 mA, 12 mA, 14 mA and 16 mA is flown, the increase of the temperature from the room temperature in the resistor element 3 becomes 25.degree. C., 30.degree. C., 45.degree. C. and 85.degree. C., respectively. On the other hand, the capacitance between the resistor element 3 and the substrate 1 can be estimated as 26.times.10.sup.-6 (pF/.mu.m.sup.2).times.10.times.39 (total length l.sub.2 of the resistor element) .apprxeq.10.times.10.sup.-3 pF. If the aluminum wiring layers has the width of 6 .mu.m, and extend 400 .mu.m, respectively, the capacitance between the wiring layers and the substrate can be estimated as 23.times.10.sup.-6 (pF/.mu.m.sup.2) .times.6.times.400.times.2.apprxeq.110.times.10.sup.-3 pF. Therefore, the total capacitance of the resistor structure including the resistor element and the wiring layers becomes about 120.times.10.sup.-3 pF.

Referring to FIGS. 2A and 2B, through a thermal oxidation process the thick silicon oxide film 12 having the thickness of 1.0 .mu.m is selectively formed and embedded in the silicon substrate 11 such that the surface portion 21 of the substrate and the upper surface of the silicon oxide layer 12 are substantially co-planar. The silicon oxide film 13 having the thickness of 0.5 .mu.m is provided on the thick silicon oxide film 12 and on the surface portion 21 by CVD process, for example. The polycrystalline silicon resistor element 23 having the sheet resistivity of 180 .OMEGA./.quadrature. is provided on the silicon oxide film 13 above the surface portion 21. The aluminum wiring layers 17, 18 are connected at contact parts of the resistor element 23 at their one ends through the contact holes 15, 16 provided in the intermediate silicon oxide film 14 having the thickness of 0.2 .mu.m and formed by CVD process. The wiring layers 17, 18 extend on the film 14 at a distance l.sub.3, l.sub.4 of about 400 .mu.m, respectively. The wiring layer 18 may be connected at its other end to the upper wiring layer 20 provided on the intermediate insulating film 19, and the wiring layer 17 also may be connected to an upper wiring layer (not shown) or to an impurity region (not shown) formed in the substrate at its other end. The resistor element 23 has the same shape as the resistor element 3 in FIG. 1. Namely, the effective length l.sub.1, the width W.sub.1 and the thickness t are 25 .mu.m, 10 .mu.m and 0.25 .mu.m, respectively. Therefore, the resistance thereof becomes 450 .OMEGA..

According to the present invention, when electrical current of 10 mA, 12 mA, 14 mA and 16 mA is made to flow through the resistor, the increase in the temperature from room temperature can be restrained to only 12.degree. C., 14.degree. C., 21.degree. C. and 40.degree. C., respectively. Namely, only about one half of temperature is raised in comparison with the prior art structure shown in FIG. 1. This is because, in the present invention, the silicon oxide film 13 which has a low thermal conductivity of 3.3.times.10.sup.-7 cal/(.mu.m.multidot.sec.multidot..degree. C.) has a thin thickness of 0.5 .mu.m and under the film 13 the silicon surface portion 21 of the silicon substrate 11 which has a high thermal conductivity of 3.58.times.10.sup.-5 cal/(.mu.m.multidot.sec.multidot..degree. C.) is provided.

On the other hand, the capacitance between the resistor element 23 and the substrate 11 can be estimated as 78.times.10.sup.-6 (pF/.mu.m.sup.2).times.10.times.39 (total length l.sub.2 of the resistor element) .apprxeq.30.times.10.sup.-3 pF. Total thickness of films 12, 13, 14 is 1.7 .mu.m which is the same value as the total thickness of films 2, 4 in FIG. 1, and the width W.sub.2 of the wiring layers is also 6 .mu.m. Therefore, the capacitance between the wiring layers 17, 18 and the silicon substrate 11 becomes about 110.times.10.sup.-3 pF, and the total capacitance of the resistor structure of the present invention becomes about 140.times.10.sup.-3 pF. Namely, the total capacitance of the present invention is increased only by less than 20% of that of the resistor structure in the prior art.

Accordingly, the resistor element in the resistor structure of the present invention can maintain its temperature at a low level during the operation and the increase of the capacitance can be restrained in a small value. Therefore, stable, reliable and high-speed operation of the semiconductor device can be expected.