Abstract:
To improve resistance to instantaneous surge power of semiconductor devices having resistor films. The semiconductor device includes: a semiconductor substrate; a first insulating film formed on the semiconductor substrate; a polysilicon resistor film formed on the first insulating film; a second insulating film formed on the resistor film; a high heat conductor film consisting of a highly heat-conducting material formed on the second insulating film; and a pair of terminal wirings and formed on the second insulating film and connected to the resistor film, in which a thickness T 3  of the second insulating film is thinner than a thickness T 2  of the resistor film.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a semiconductor device, and more particularly to a semiconductor device that comprises a resistor film consisting of polysilicon formed in an insulating film on a semiconductor substrate.  
           [0003]    2. Background Art  
           [0004]    [0004]FIG. 5 is a sectional view showing a schematic configuration of a conventional integrated circuit that comprises polysilicon resistors. In this drawing, reference numeral  1  is a silicon substrate, i.e. a semiconductor substrate;  2  is an insulating film consisting of a field oxide film or an interlayer insulating film formed on the silicon substrate  1 ,  3  is a resistor film consisting of polysilicon formed in the insulating film  2 ;  4 A and  4 B are terminal wirings of the resistor film  3  formed on the insulating film  2 , and connected to the resistor film  3  through connecting portions  5 A and  5 B.  
           [0005]    The integrated circuit comprising a conventional resistor film is constituted as described above, and heat generated in the resistor film  3  is dissipated into the silicon substrate  1  through the insulating film  2  underneath the resistor film  3 , but the heat is not sufficiently transferred because the insulating film  2  underneath the resistor film  3  is as thick as about 0.5 μm, thereby raising a problem of low resistance to instantaneous surge electric power.  
           [0006]    Specifically, as shown by curve a in FIG. 3 that indicates the result of simulation of the temperature rise of the resistor film  3  in the case where a step electric power of about 3 mW was consumed, a temperature rise per unit power consumption was as large as 2,200 deg./W, in 1 μs showing a large transient heat impedance.  
           [0007]    Also, as shown by curve a in FIG. 4 that indicates the result of ESD (electrostatic discharge) simulation of discharge from a 200 pF capacitor, temperature rose rapidly in 700 ns after starting power supply to over 2,000 K, leading to thermal breakdown.  
           [0008]    In recent years, since the resistor film  3  is becoming thinner accompanying the size reduction of transistors due to the advancement of micro machining technology, the resistance to surge power tends to further lower.  
         SUMMARY OF THE INVENTION  
         [0009]    Therefore, an object of the present invention is to cope with such a problem, and to provide a semiconductor device that can improve a resistance to a surge power of integrated circuits or the like having resistor films.  
           [0010]    According to one aspect of the present invention, a semiconductor device comprises a semiconductor substrate, a first insulating film formed on the semiconductor substrate, a polysilicon resistor film formed on the first insulating film, a second insulating film formed on the resistor film, a high heat conductor film consisting of a highly heat-conducting material formed on the second insulating film, and a pair of terminal wirings formed on the second insulating film and connected to the resistor film, wherein a thickness of the second insulating film is thinner than a thickness of the resistor film.  
           [0011]    According to another aspect of the present invention, a semiconductor device comprises a semiconductor substrate, a first insulating film formed on the semiconductor substrate, a polysilicon resistor film formed on the first insulating film, a second insulating film formed on the resistor film, a high heat conductor film consisting of a highly heat-conducting material formed on the second insulating film, and a pair of terminal wirings formed on the second insulating film and connected to the resistor film, wherein a thickness of the high heat conductor film is thicker than a thickness of the resistor film.  
           [0012]    According to the present invention, the resistance to instantaneous surge power of the semiconductor devices having resistor films can be improved.  
           [0013]    Other and further objects, features and advantages of the invention will appear more fully from the following description. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a sectional view showing a schematic constitution of Embodiment 1.  
         [0015]    [0015]FIG. 2 is a top view showing a schematic constitution of modification of Embodiment 1.  
         [0016]    [0016]FIG. 3 is a graph of characteristic curves showing the results of a temperature rise simulation obtained to clarify the constitution of Embodiment 1 as well as to confirm the effect  
         [0017]    [0017]FIG. 4 is a graph of characteristic curves showing the results of an ESD simulation obtained to clarify the constitution of Embodiment 1 as well as to confirm the effect  
         [0018]    [0018]FIG. 5 is a sectional view showing a schematic configuration of a conventional integrated circuit that comprises polysilicon resistors. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Embodiment 1  
       [0019]    Embodiment 1 of the present invention will be described below referring to the drawings.  
         [0020]    [0020]FIG. 1 is a sectional view showing a schematic constitution of Embodiment 1. In FIG. 1, reference numeral  1  is a silicon substrate, i.e. a semiconductor substrate;  2  is an insulating film consisting of a field oxide film or an interlayer insulating film formed on the silicon substrate  1 ;  3  is a resistor film consisting of polysilicon formed in the insulating film  2 ;  4 A and  4 B are terminal wirings of the resistor film  3  formed on the insulating film  2 , and connected to the resistor film  3  through connecting portions  5 A and  5 B.  
         [0021]    Reference numeral  6  denotes a high heat conductor film consisting of a high heat conductor material formed above the resistor film  3  through a thin insulating film  2 A, and is made of aluminum (Al) or an alloy thereof.  
         [0022]    T 1  is a thickness of the insulating film  2  (silicon oxide film) provided underneath the resistor film  3 , for example 0.5 μm. T 2  is the thickness of the resistor film  3 , for example 0.15 μm. T 3  is a thickness of the insulating film  2 A (silicon oxide film) between the resistor film  3  and the high heat conductor film  6 . T 4  is a thickness of the high heat conductor film  6 . Specific values of T 3  and T 4  will be described later.  
         [0023]    Embodiment 1 is constituted as described above. Thereby, since a heat path is produced from the resistor film  3  to the high heat conductor film  6  through the thin insulating film  2 A over the resistor film  3 , in addition to a path for dissipating heat into the silicon substrate  1  through the thin insulating film  2  underneath the resistor film  3 , a heat capacity of the high heat conductor film  6  can temporarily absorb the heat generated in the resistor film  3  due to surge power until the heat is accumulated in the high heat conductor film  6 , thus improving the resistance to the surge power.  
         [0024]    In this case, since the pulse width of the surge current is usually about 0.2 μs, the heat generated in the resistor film  3  passes through the insulating film  2 A in about the above-described time and reaches the high heat conductor film  6 . Furthermore, in order to maintain the heat absorption by the high heat conductor film  6  thereafter, a thickness T 3  of the insulating film  2 A becomes an important factor.  
         [0025]    Similarly as an interlayer film used in general IC processes, when the thickness T 3  of the insulating film  2 A is, for example, 0.5 μm, the time for heat to pass is about 1 μs. Therefore, the thickness is too thick for a pulse width of the above-described surge current to expect sufficient effect.  
         [0026]    Also, since the heat transferred to the high heat conductor film  6  scarcely diffuses to a lateral direction because of the narrow pulse width of a surge current, a heat absorption must be supplemented by increase in thickness.  
         [0027]    [0027]FIGS. 3 and 4 are graphs of characteristic curves showing the results of a temperature rise simulation and an ESD simulation obtained to clarify the constitution of Embodiment 1 as well as to confirm the effect, and show characteristics of each of T 3  and T 4  when the thicknesses of T 3  and T 4  is set to various values in the structure shown in FIG. 1, for example, T 1 =0.5 μm and T 2 =0.15 μm. That is, in these characteristic diagrams, a curve b shows when T 4 =1 μm and T 3 =0.2 μm, a curve c shows when T 4 =0.2 μm and T 3 =0.1 μm, a curve d shows when T 4 =0.45 μm and T 3 =0.1 μm, and a curve e shows when T 4 =1 μm and T 3 =0.1 μm.  
         [0028]    As seen in the curves c, d, and e of FIG. 4, when the thickness T 3  of the insulating film  2 A on an upper surface of the resistor film is T 3 =0.1 μm, thinner than the thickness T 2 =0.15 μm of the resistor film  3 , a peak temperature lowers to 1,400 K, then the permanent breakdown does not occur. However, as seen in the curve b, when the thickness T 3 =0.2 μm, thicker than the thickness of the resistor film  3 , a temperature rises rapidly causing permanent breakdown, and it is seen that a resistance to surge power is low.  
         [0029]    For the thickness T 4  of Al of the high heat conductor film  6 , when T 4 =0.2 μm or more, thicker than the thickness of the resistor film  3 , permanent breakdown does not occur, as seen in any of curve c (T 4 =0.2 μm), curve d (T 4 =0.45 μm), and curve e (T 4 =1 μm).  
         [0030]    When the curves c, d, and e are compared, the peak temperature of the curve d or curve e where the thickness T 4  of Al is twice the thickness T 2  of the resistor film  3  or more, 0.45 μm or 1 μm, respectively, is nearly 200 K lower than a peak temperature of the curve c, achieving larger effect. Furthermore, when transient heat impedance characteristics in the above-described cases are viewed from FIG. 3, an instantaneous temperature rise up to 0.4 μs is large in the curve b and the curve a (prior art) in FIG. 4, which lead to permanent breakdown, and it is seen that characteristics up to this time point are significantly related to the occurrence of ESD breakdown.  
         [0031]    From the above results, in Embodiment 1, it was concluded, to obtain the sufficient effect of absorbing surge power, that the thickness T 3  of the insulating film  2 A should be thinner than the thickness T 2  of the resistor film  3 , and the thickness T 4  of the high heat conductor layer  6  should be thicker than T 2 , preferably twice T 2  or more.  
         [0032]    Although the high heat conductor layer  6  is composed of Al or the alloys thereof, the materials are not limited to these, and the same effect can be expected from copper, poly-amorphous silicon, or the like. The same effect can also be expected from a multi-layer wiring structure in which a wiring layer is further provided on the high heat conductor layer  6  through an insulating film.  
         [0033]    Furthermore, heat capacity can further be increased by making the high heat conductor layer  6  wider than the resistor film  3 , not only to cover the resistor film  3 , as shown in FIG. 2.  
         [0034]    Also, when the high heat conductor layer  6  is used in common with terminal wirings  4 A and  4 B made of Al or the like, since the area of the high heat conductor layer  6  can be increased by using the high heat conductor layer  6  as a part of the ground/power wiring region or input/output pads, the resistance to surge power of not only an extremely short time such as ESD, but also a relatively long time of the millisecond order, can be improved.  
         [0035]    Since the semiconductor device according to the present invention is constituted as described above, the resistance to instantaneous surge power of the semiconductor devices having resistor films can be improved.  
         [0036]    The entire disclosure of a Japanese Patent Application No. 2000-377581, filed on Dec. 12, 2000 including specification, claims, drawings and summary, on which the Convention priority of the present application is based, are incorporated herein by reference in its entirety.