Semiconductor element

A semiconductor element is disclosed, with which it is possible to obtain an area sufficiently large for evacuating heat and to have a high thermal conductivity so as to have an extremely high heat evacuation efficiency by using cooling fins having a microchannel structure.

FIELD OF THE INVENTION 
The present invention relates to a semiconductor element, with which an 
ultra high speed and ultra high integration density electronic circuit can 
be realized, owing to the fact that heat produced in semiconductor is 
evacuated rapidly to the exterior through cooling fins having a 
microchannel structure. 
BACKGROUND OF THE INVENTION 
In semiconductor integrated circuits the integration density becomes high 
and higher, accompanied by demand for an ultra high speed and an ultra 
high integration density. Already at present, the integration density for 
integrated circuits consuming a large amount of electric power because of 
high speed drive is being limited by the limit of heat evacuation. 
However electric power consumption per chip is increased rapidly, 
accompanied by demand for increasing the performance and the speed of 
semiconductor circuits. Almost all consumed electric power is transformed 
into heat and produced heat raises the temperature of a whole chip, which 
causes deterioration in characteristics of elements and lowering in 
reliability. 
However, by the cooling technique using a present structure, heat 
evacuation is about 30W/cm.sup.2 by water cooling and a new technique for 
removing rapidly heat produced within a semiconductor chip to the exterior 
is required. In a prior art heat current circuit for heat evacuation, the 
part, at which heat conducting characteristics are the worst, is a heat 
conducting portion from a wall of solid to cooling medium (air, water). 
FIG. 15 represents a heat current circuit in an integrated circuit by the 
prior art technique, using heat resistance and heat capacity. The figure 
represents a heat current circuit in an integrated circuit having e.g. a 
chip thickness of about 500 .mu.m and a chip size of about 1 cm.sup.2 and 
the meaning of Rf, Rp, Cp, Rsi, Csi and Rb is as follows: 
Rf: heat resistance to heat conduction from the front side of the chip, 
Rp: heat resistance to heat conduction in a passivation film on the front 
side of the chip (thickness of about 5 .mu.m), 
Cp: heat capacity of the passivation film (negligible in a stationary 
state), 
Rsi: heat resistance to heat conduction in an Si substrate (thickness of 
about 494 .mu.m), 
Csi: heat capacitance of the Si substrate (negligible in a stationary 
state), and 
Rb: heat resistance to heat conduction from the front side of the chip. 
FIGS. 16A and 16B show a concrete example of an equivalent circuit of a 
heat current circuit in a stationary state, in the case where the 
passivation film used by the prior art technique is made of SiO.sub.2, 
FIG. 16A representing a case where the front surface is cooled by natural 
convection and the rear surface by forced air cooling, FIG. 16B 
representing a case where the front surface is cooled by natural 
convection and the rear surface by water cooling. In the stationary state 
heat capacity can be neglected. Representative experimental values of the 
prior art technique are used for boundary conditions and the heat 
resistances converted from heat conductivity by force air 
cooling=0.2W/cm.sup.2 .multidot.K, heat conductivity by water 
cooling=1W/cm.sup.2 .multidot.K and heat conductivity by natural 
convection=1.times.10.sup.-3 W/cm.sup.2 .multidot.K are indicated. 
As clearly seen from FIGS. 16A and 16B, by the prior art heat evacuating 
technique, although within the solid of the semiconductor chip the heat 
resistance is sufficiently low, order of 10.sup.-2 K/W, the heat 
resistance to the cooling medium is about 5K/W by forced air cooling and 
about 1K/W by water cooling, which are higher by almost 2 orders of 
magnitude than that obtained for the solid. 
Further e.g. D. B. Tuckerman and F. Pease (IEEE Electron Device Lett., Vol. 
EDL-2, No. 5, pp 126-129, May 1981, "High Performance Heat Sinking for 
VLSI") have indicated that it is possible to deal with an extremely high 
heat production density by forming microchannels of about 50 
.mu.m.times.300 .mu.m in a comb shape directly on the rear surface of the 
Si substrate, through which water is made flow. 
However, by this method, since the microchannels are formed by processing 
directly the Si substrate, there are a number of problems in the 
fabrication from the practical point of view. 
As described above, by the prior art heat evacuating technique, since the 
heat resistance from the cooling fins to the cooling medium is too high, 
the cooling fins cannot effect heat evacuation with a high efficiency. 
Further, by the method, by which the microchannels are formed in the 
silicon substrate, there is a problem in the fabrication in practice. 
OBJECT OF THE INVENTION 
The object of the present invention is to reduce remarkably the heat 
resistance to the cooling medium by disposing microchannel type fins, 
which can be easily fabricated in practice. 
SUMMARY OF THE INVENTION 
In order to achieve the above object, the present invention is 
characterized in that fins having a microchannel structure, in which a 
plurality of microchannel flow paths are formed, are bonded to a 
semiconductor chip. 
In order to increase the quantity of evacuated heat or to improve the 
cooling efficiency, it is necessary primarily to secure a sufficiently 
large surface area at the contact surface with cooling medium for heat 
evacuation or cooling and secondly to increase as far as possible the heat 
conductivity within the limit imposed by the state of use of cooling 
medium. 
Since the cooling fins according to the present invention have a 
microchannel structure, it has a high heat conductivity, a large surface 
area can be formed in a small size therewith, and it can be fabricated 
easily.

DETAILED DESCRIPTION 
Hereinbelow several preferred embodiments of the present invention will be 
explained, referring to the drawings. 
FIG. 1 shows an embodiment of fins having a microchannel structure 
according to the present invention. In the figure, reference numeral 1 is 
a semiconductor chip; 2 indicates fins having a microchannel structure; 
and 3 represents microchannel flow paths. Although the size and the number 
of stages of the flow paths in the fins having a microchannel structure 2 
are determined, depending on the object, a good result is obtained, when 
the size is small in a practically usable domain and the number of stages 
is great. FIG. 1 shows a structure, in which microchannels serving as flow 
paths for cooling medium are arranged in 4 stages in the vertical 
direction. The cross section of each of the flow paths 3 for cooling 
medium is about 50 .mu.m.times.250 .mu.m and the length thereof is about 1 
cm. The flow paths are sectioned by a wall 3' about 50 .mu.m thick. The 
fins having a microchannel structure 2 can be made of any material, if it 
has a high thermal conductivity. However, Al, Al alloys, Cu, Cu alloys, 
etc. among metals and AlN, BN, etc. among insulating materials are found 
suitable. Water, compressed air and fleon are suitable for the cooling 
medium and liquid nitrogen, liquid helium, etc. are suitable for the 
cryogenic drive. However it is found that water and compressed air, which 
can be used in a simple manner, are the most suitable. Although a better 
effect can be obtained with decreasing temperature of the cooling medium, 
from the point of view of the simplicity a temperature from about 
5.degree. C. to about 25.degree. C. is preferable in practice. 
In the present embodiment the semiconductor chip 1 and the fins having a 
microchannel structure 2 are bonded with each other by the direct bonding 
technique. 
TABLE 1 indicates the thermal conductivity of the flow in a tube having the 
cross section of about 50 .mu.m.times.250 .mu.m as described above and the 
pressure loss when the cooling medium flows through the tube about 1 cm 
long, in the case where the flow in the tube in the microchannels is water 
of 10.degree. C., water of 17.degree. C., air of 5.degree. C. and air of 
17.degree. C. 
TABLE 1 
______________________________________ 
Thermal conductivity of flow in tube and pressure loss 
______________________________________ 
(a) in the case where cooling medium is water 
Thermal Pressure 
Temperature 
Flow Speed Conductivity 
Loss 
(.degree.C.) 
(m/s) (W/cm.sup.2..degree.C.) 
(kgf/cm.sup.2) 
______________________________________ 
10 6 2.40 3.7 
10 15 3.69 9.6 
17 6 2.40 3.1 
17 15 3.74 8.3 
______________________________________ 
(b) in the case where cooling medium is air 
Flow Thermal Pressure 
Temperature 
Pressure Speed Conductivity 
Loss 
(.degree.C.) 
(kgf/cm.sup.2) 
(m/s) (W/cm.sup.2..degree.C.) 
(kgf/cm.sup.2) 
______________________________________ 
5 1.0 5 1.20 .times. 10.sup.-19 
0.04 
5 1.0 24 1.60 .times. 10.sup.-5 
0.20 
5 5.1 24 1.70 .times. 10.sup.-2 
0.20 
17 1.0 5 4.50 .times. 10.sup.-21 
0.04 
17 1.0 24 8.5 .times. 10.sup.-6 
0.20 
17 5.1 24 1.5 .times. 10.sup.-2 
0.20 
______________________________________ 
As clearly seen from TABLE 1, the thermal conductivity indicating the 
cooling capacity is very low for air in the neighborhood of the normal 
pressure (pressure of 1 kgf/cm.sup.2). Consequently, in the present 
embodiment, liquid or water, for which the pressure loss in tube is lower 
than about 10 kgf/cm.sup.2, or compressed gas or compressed air, for which 
the pressure loss in tube is lower than about 0.5 kgf/cm.sup.2, is used. A 
better result can be obtained with increasing flow speed of the cooling 
medium. However, in practice, the flow speed as high as possible, which 
can be obtained with a pressure loss in tube under the value described 
above, is found to be suitable. 
FIG. 2 indicates a case as a mode of realization of the present embodiment, 
where the cooling medium is water of about 17.degree. C.; the flow speed 
thereof is about 6 m/s; heat produced at the surface of the semiconductor 
chip is about 2 kW/cm.sup.2 ; and the fins having a microchannel structure 
are made of Al. Although a part of the semiconductor chip and the fins is 
indicated, it can be considered as a representative temperature 
distribution representing the whole. 
As described above, in spite of a heat production as great as about 2 
kW/cm.sup.2 at the surface of the semiconductor chip, the temperature of 
the semiconductor chip is kept at about 96.degree. C. Since semiconductor 
chip such as LSI are used usually at a junction temperature below 
125.degree. C., the value of about 96.degree. C. described above 
represents a temperature usable in practice. 
FIG. 3 indicates a case where Al is changed into Cu for the material for 
the fins having a microchannel structure as another mode of realization of 
the embodiment indicated in FIG. 1. The other conditions are identical to 
those used for the example indicated in FIG. 2. Although the flow speed of 
water of 17.degree. C. serving as the cooling medium is about 6 m/s, even 
for a heat production of about 2.5 kW/cm.sup.2 at the surface of the 
semiconductor chip, the temperature of the semiconductor chip is kept at 
about 96.degree. C. owing to the fact that the material is changed into 
Cu. 
In the modes of realization indicated in FIGS. 2 and 3, the semiconductor 
chip is a semiconductor single element or an integrated circuit of MOS 
transistors, bipolar type transistors, semiconductor lasers, light 
emitting diodes, etc. and the effect is obtained for all of them. 
FIG. 4 shows an embodiment in the case where compressed air is used for the 
cooling medium. Compressed air of about 17.degree. C. (pressure=about 5 
kgf/cm.sup.2) flows through the tube 3 of the microchannels with a flow 
speed of about 24 m/s and the fins having a microchannel structure are 
made of Al. When the heat production at the surface of the semiconductor 
chip is about 30W/cm.sup.2, the temperature at the surface of the 
semiconductor chip is kept at about 96.degree. C. Although the heat 
evacuation efficiency is fairly low with respect to that obtained by water 
cooling, it is remarkably higher than that obtained by usual forced air 
cooling. When Al is changed into Cu for the material for the fins having a 
microchannel structure, no great difference as found in the case of water 
cooling is observed. This is because the heat conduction rate from the 
cooling medium to air is small, i.e. the heat resistance is great, and the 
heat resistance to air is considerably greater than the heat resistance 
due to the heat conduction through the solid of the fins, so that the 
difference in the solid material of the fins does not influence thereon. 
Consequently the material of the fins is not limited to Al and Cu, but any 
material may be used, if it is a solid material. 
The semiconductor chip is a single element or an LSI of heat producing 
semiconductor elements, as described previously, and the effect can be 
obtained for all of them. 
TABLE 2 
______________________________________ 
Heat resistance and equivalent thermal 
conductivity of fins having microchannels 
(per 1 cm.sup.2 of area) 
Equivalent 
Temperature 
Flow Heat Thermal 
of Water Speed Material Resistance 
Conductivity 
(.degree.C.) 
(m/s) of Fins (.degree.C./W) 
(W/cm.sup.2..degree.C.) 
______________________________________ 
(a) Water cooling 
17 6 Al 0.039 25.6 
Cu 0.031 32.0 
15 Al 0.031 32.2 
Cu 0.024 41.0 
10 6 Al 0.039 25.3 
Cu 0.032 31.5 
15 Al 0.032 31.5 
Cu 0.025 40.5 
(b) Air cooling 
17 24 Al.Cu 2.63 0.38 
5 24 Al.Cu 2.37 0.42 
______________________________________ 
TABLE 2(a) indicates numerical values of the heat resistance (.degree. 
C./W) and the equivalent thermal conductivity (W/cm.sup.2 
.multidot..degree. C.) per 1 cm.sup.2 of area viewed from the surface of 
the semiconductor chip connected with the surface of the fins, when the 
temperature of water, the flow speed and the material of the fins are 
varied, in the case of water cooling in the different modes of realization 
described above. 
In this TABLE, e.g. a heat resistance of about 0.025.degree. C./W is 
obtained, when the cooling medium is viewed from the surface of the 
semiconductor chip, in the case where fins having a microchannel structure 
(4 stage type) made of Cu are used and water having a temperature of 
10.degree. C. is made flow with a flow speed of about 15 m/s. 
This means that, when the heat production at the surface of the 
semiconductor chip is 100 W/cm.sup.2, the temperature rise is kept at 
about 2.5.degree. C. from 10.degree. C. If the temperature rise of the 
semiconductor chip from 10.degree. C. should be maintained at about 
85.degree. C., a heat production of about 3400 W/cm.sup.2 at the surface 
of the semiconductor chip is allowable. Further, in this TABLE, e.g. a 
heat resistance of about 0.039.degree. C./W is obtained, when the cooling 
medium is viewed from the surface of the semiconductor chip, in the case 
where fins having a microchannel structure (4 stage type) made of Al are 
used and water having a temperature of 17.degree. C. is made flow with a 
flow speed of about 6 m/s. For example, when the heat production at the 
surface of the surface of the semiconductor chip is about 100 W/cm.sup.2, 
the temperature rise is kept at about 4.degree. C. If the temperature rise 
of the semiconductor chip should be maintained at about 85.degree. C., a 
heat production of about 2180 W/cm.sup.2 at the surface of the 
semiconductor chip is allowable. 
TABLE 2(b) indicates numerical values obtained for the heat resistance 
(.degree. C./W) and the quivalent thermal conductivity (W/cm.sup.2 
.multidot..degree. C.) per 1 cm.sup.2 of area, when the cooling medium is 
viewed from the surface of the semiconductor chip connected with the 
surface of the fins and the temperature of air, the flow speed and the 
material of the fins area varied, in the case of air cooling in the 
different modes of realization described above. 
In this TABLE, e.g. a heat resistance of about 2.63.degree. C./W is 
obtained, when the cooling medium is viewed from the surface of the 
semiconductor chip, in the case where fins having a microchannel structure 
(4 stage type) made of Al are used and compressed air (about 5 
kgf/cm.sup.2) having a temperature of 17.degree. C. is made flow with a 
flow speed of about 24 m/s. For example, when the heat production in the 
semiconductor chip is about 1W/cm.sup.2, the temperature rise from 
17.degree. C. is kept at 2.7.degree. C. Further, if the temperature rise 
of the semiconductor chip from 17.degree. C. should be maintained at about 
85.degree. C., a heat production of about 32W/cm.sup.2 at the surface of 
the semiconductor chip is allowable. In the case of the air cooling result 
obtained by using Cu for the material for the fins are almost identical to 
those obtained by using Al therefor. Further the effect can be obtained 
for any single element and LSI as a heat producing semiconductor element, 
as described previously. 
FIG. 5 shows an embodiment, in which a bonding layer 4 is used between the 
semiconductor chip 1 and the fins having microchannel structure 2. Stress 
due to the difference in the thermal expansion between the semiconductor 
chip and the fins having a microchannel structure can be better 
alleviated. Low temperature solder, In, Mo, Cu-W alloy, etc. are useful as 
a material for the bonding layer. Further it is useful also to use a 
thermally highly conductive and electrically insulating thin film such as 
AlN, BN, SiC, etc. together therewith. The construction of the fins having 
a microchannel structure 2 is identical to that used in the embodiment 
indicated in FIG. 1. 
FIG. 6 shows a result obtained by using the construction used in the 
embodiment indicated in FIG. 5, in which In (about 50 .mu.m thick) is used 
for the bonding layer. It indicates a case where the flow speed of water 
serving as the cooling medium, having a temperature of 17.degree. C. is 
about 6 m/s; the heat production at the surface of the semiconductor chip 
1 is about 2 kW/cm.sup.2 ; and the fins having a microchannel structure is 
made of Al. Although, in FIG. 6, the temperature distribution of only a 
part of area of the semiconductor chip and the fins of about 1 cm.sup.2 is 
indicated, it can be considered as a representative temperature 
distribution representing the whole. 
As described above in spite of a heat production as great as about 2 
kW/cm.sup.2 at the surface of the semiconductor chip, the temperature at 
the surface of the semiconductor chip is kept at about 109.degree. C. 
Although a great temperature gradient is found in the layer of In serving 
as the bonding layer 4, the magnitude thereof gives rise to no problem in 
practice. 
FIG. 7 indicates a mode of realization (temperature distribution in the 
cooling fins), in the case where it differs from the example indicated in 
FIG. 6 only in that Al is changed into Cu for the material for the fins 
having a microchannel structure and that the temperature of water serving 
as the cooling medium is about 10.degree. C., and the other conditions are 
identical to those used for the example indicated in FIG. 6. In this case, 
although the heat production at the surface of the semiconductor chip 1 is 
as great as about 2.5 kW/ cm.sup.2, the temperature at the surface of the 
semiconductor chip is kept at about 106.degree. C. Similarly to the 
preceding example, although a great temperature gradient is found in the 
layer of In serving as the bonding layer 4, the magnitude thereof gives 
rise to no problem in practice. 
FIG. 8 shows another mode of realization using compressed air for the 
cooling medium, in which the other conditions are identical to those used 
in the example indicated in FIG. 6. Compressed air having a temperature of 
about 17.degree. C. (pressure: about 5 kgf/cm.sup.2) flows through the 
tube of the microchannels with a flow speed of about 24 m/s and the fins 
having a microchannel structure is made of Al. When the heat production 
within the semiconductor chip 1 is about 30 W/cm.sup.2, the temperature at 
the surface of the semiconductor chip is kept at about 96.degree. C. No 
lowering in the cooling capacity due to the insertion of the bonding layer 
of In is found. This is because the heat resistance to the heat conduction 
in the bonding layer of In is small with respect to the heat resistance to 
the heat conduction to the cooling medium flowing through the tube. 
Consequently, in the case of air cooling, any bonding material may be 
used, if it has a heat resistance, which is smaller than the heat 
resistance due to the thermal conductivity to the cooling medium, and 
adhesive materials such as epoxy resin, polyimide resin, silicone grease, 
etc. can be used usefully therfor. 
Further not only Al and Cu but also any material may be used for the 
material for the fins, if it is a solid material, as indicated in FIG. 4. 
TABLE 3 
______________________________________ 
Heat resistance and equivalent thermal 
conductivity of fins having microchannels 
(per 1 cm.sup.2 of area) 
Equivalent 
Temperature Heat Thermal 
of Water Material Bonding Resistance 
Conductivity 
(.degree.C.) 
of Fins Layer (K/W) (W/cm.sup.2.K) 
______________________________________ 
(a) Water cooling (6 m/s) 
17 Al exist 0.045 22.1 
Cu exist 0.037 26.6 
10 Al exist 0.046 21.7 
Cu exist 0.038 26.3 
(b) Air cooling (24 m/s) 
17 Al.Cu exist 2.63 0.38 
______________________________________ 
TABLE 3(a) indicates numerical values of the heat resistance (.degree. 
C./W) and the quivalent thermal conductivity (W/cm.sup.2 
.multidot..degree. C.) for 1 cm.sup.2 of area viewed from the surface of 
the semiconductor chip obtained in the different modes of realization, 
when In (about 50 .mu.m thick) is used for the bonding layer 4 and the 
temperature of water and the material of the fins are varied for a flow 
speed of about 6 m/s in the case of water cooling. In this TABLE, e.g. in 
the case where an In bonding layer (about 50 .mu.m thick) and fins having 
a microchannel structure (4 stage type) made of Cu described above are 
used and water having a temperature of about 10.degree. C. is made flow 
with a flow speed of about 6 m/s, a heat resistance of about 0.038 
(.degree. C./W) is obtained, when the cooling medium is viewed from the 
surface of the semiconductor chip. At this time, e.g. when the heat 
production in the semiconductor chip is about 100 W/cm.sup.2, the 
temperature rise at the surface of the semiconductor chip from 10.degree. 
C. is kept at about 3.8.degree. C. If the temperature rise of the 
semiconductor chip from 10.degree. C. should be maintained at about 
85.degree. C., a heat production of about 2200 W/cm.sup.2 at the surface 
of the semiconductor chip is allowable. 
TABLE 3(b) indicates numerical values of the heat resistance (.degree. 
C./W) and the equivalent thermal conductivity (W/cm.sup.2 
.multidot..degree. C.) per 1 cm.sup.2 of area, when the cooling medium is 
viewed from the surface of the semiconductor chip obtained in the 
different modes of realization and the material of the fins is varied, in 
the case of air cooling (flow speed of about 24 m/s and compressed air of 
about 5 kgf/cm.sup.2). 
For Al and Cu, of which the fins are made, an almost identical heat 
resistance=about 2.63.degree. C./W is obtained. For example, when the heat 
production at the surface of the semiconductor chip is about 1 W/cm.sup.2, 
the temperature rise from 17.degree. C. is kept at about 2.7.degree. C. 
Further, if the temperature rise of the semiconductor chip from 17.degree. 
C. should be maintained at about 85.degree. C., a heat production of about 
32 W/cm.sup.2 in the semiconductor chip is allowable. 
The semiconductor chip indicated in FIGS. 5 to 8 and TABLE 3 may be any 
kind and the effect can be obtained for any single element and LSI as a 
heat producing semiconductor element, as described previously. 
In an embodiment indicated in FIG. 9, a heat diffusing layer 6 is added 
previously to the semiconductor chip jointed with the fins having a 
microchannel structure, so that transient thermal response is further 
improved in a part of an integrated circuit according to the present 
invention. In order to utilize the capacity of the fins having a 
microchannel structure as far as possible, it is efficient to dispose a 
heat current circuit diffusing rapidly heat produced locally within the 
semiconductor chip. 
Although, in FIG. 9, a bipolar transistor is illustrated as an example of 
the semiconductor chip, the semiconductor chip may be a single 
semiconductor element or LSI using various sorts of semiconductor 
substrates made of Si, GaAs, InP, etc. such as an MOS type transistor, a 
bipolar type transistor, a semiconductor laser, a light emitting diode, 
etc. producing heat transiently and the effect can be obtained for all of 
them. 
Taking an integrated bipolar type transistor as an example, heat is 
produced locally, in particular in the neighborhood of the region between 
the base 9 and the collector 10, within each of integrated transistor 
elements. 
In FIG. 9, reference numeral 5 is a semiconductor substrate (Si in this 
example); 6 is a thermally highly conductive and electrically insulating 
layer; 7 is wiring (Al); 8 is an emitter; 9 is a base; 10 is a collector; 
and 11 is a depletion layer between the base and the collector. 
Although any thermally highly conductive and electrically insulating layer 
6 may be used, if it has a thermal conductivity as high as metals and it 
is electrically an insulator, e.g. AlN and BN are found suitable. Further, 
although, in FIG. 9, an example is shown, in which this thermally highly 
conductive and electrically insulating layer 6 is used uniformly in all 
the interlayer insulating layers and the passivation films, it has been 
used heretofore in a part of them. The effect can be obtained, also when 
it is used together with an SiO.sub.2 film, an Si.sub.3 N.sub.4 film, an 
Al.sub.2 O.sub.3 film, etc. 
FIGS. 10A and 10B show a temperature distribution from the interior to the 
surface and a plan view of the device corresponding to the region, for 
which the temperature distribution is indicated, respectively, after about 
5 .mu.sec from a point of time, where current begins to flow, when one 
bipolar element consumes electric power of about 4 mW in the mode of 
realization indicated in FIG. 9, having the heat diffusing structure. 
As indicated above, it can be understood that heat produced locally in the 
neighborhood of the depletion layer between the base and the collector is 
spread widely on the surface in a period of time as short as about 5 
.mu.sec in the construction having a thermally highly conductive and 
electrically insulating layer 6 serving as a heat diffusing structure. 
Heat is not spread so rapidly, widely and uniformly by using only 
interlayer insulating films and passivation films such as usual SiO.sub.2 
films, Si.sub.3 N.sub.4 films, etc. having low thermal conductivities. 
FIG. 11 indicates variations in the temperature in the case where fins 
having a microchannel structure are jointed to the rear side of a 
semiconductor chip having the heat diffusing structure indicated in FIG. 
9. 
In the semiconductor chip, e.g. a number of bipolar transistors as 
indicated in FIG. 9 are integrated and the temperature is measured, e.g. 
when heat of about 1500 W/cm.sup.2 is produced in the interior as a whole. 
The fins having a microchannel structure are jointed to the rear side of 
the semiconductor chip by the direct bonding method under the conditions 
indicated in FIG. 2. A stationary temperature is achieved after a period 
of time of about 0.1 sec from the beginning of drive and the temperature 
is lower than about 120.degree. C., i.e. the temperature is maintained 
approximately at the limit in practice. 
Further, although it is not indicated in the figure, when the fins having a 
microchannel structure using a bonding layer under the conditions 
indicated in FIG. 6 are connected with the semiconductor chip indicated in 
FIG. 9 described above, if heat production in the semiconductor chip is 
about 1200W/cm.sup.2, a stationary temperature is achieved similarly after 
a period of time of about 0.1 sec from the beginning of drive and the 
temperature is about 120.degree. C., i.e. the temperature is maintained 
approximately at the limit in practice. 
FIG. 12 indicates variations in the temperature in the case where fins 
having a microchannel structure are bonded to the front side of a 
semiconductor chip having the heat diffusing structure indicated in FIG. 
9. 
In the semiconductor chip, e.g. a number of bipolar transistors as 
indicated in FIG. 9 are integrated and the temperature is measured, e.g. 
when heat of about 1500 W/cm.sup.2 is produced in the interior as a whole. 
The fins having a microchannel structure are jointed to the front side of 
the semiconductor chip by the direct bonding method under the conditions 
indicated in FIG. 2. A stationary temperature is achieved after a period 
of time of about 0.1 sec from the beginning of drive and the temperature 
is lower than about 65.degree. C. 
Further, although it is not indicated in the figure, when the fins having a 
microchannel structure using the bonding layer indicated in FIG. 6 are 
connected with the front surface of the semiconductor chip having the heat 
diffusing structure indicated in FIG. 9, if heat production in the 
semiconductor chip is about 1500 W/cm.sup.2, a stationary temperature is 
achieved similarly after a period of time shorter than about 0.01 sec from 
the beginning of drive and the temperature is lower than about 85.degree. 
C. Further, owing to the fact that the fins having a microchannel 
structure is bonded to the front surface side, as clearly seen from FIG. 
12, a uniform temperature distribution is kept from the front surface of 
the semiconductor chip to the interior and further to the rear surface and 
it is possible to reduce remarkably influences of thermal stress. 
FIG. 13 shows an embodiment of a whole I/O package, in which the fins 
having a microchannel structure 2 are mounted on the rear side of the 
semiconductor chip 1. There exist a number of working regions producing 
heat in the interior on the front side of the semiconductor chip 1 and 
there is disposed a thermally highly conductive and electrically 
insulating layer 6 for spreading rapidly heat produced locally and 
transiently, the effect thereof being indicated in FIG. 9. The fins having 
a microchannel structure are bonded to the rear side of the chip by an 
adhesive layer 4, as described in the embodiments indicated in FIGS. 5 to 
8 and TABLE 3. Or, although it is not indicated in the figure, the rear 
side surface of the semiconductor chip 1 and the fins having a 
microchannel structure 2 may be jointed by the direct bonding method, as 
indicated in FIGS. 1 to 4, TABLE 2 and FIG. 9. 
Although the size and the number of stages of the flow paths in the fins 
having a microchannel structure 2 can be determined, depending on the 
object, a more remarkable effect can be obtained by decreasing the size 
and increasing the number of stages in a region usable in practice. 
In a typical example, as indicated in FIGS. 1 and 5, e.g. the cross section 
of the flow path of each of the channels about 1 cm long is 50 
.mu.m.times.250 .mu.m and different channels are sectioned by a wall about 
50 .mu.m thick, the channels being arranged horizontally over about 1 cm 
in 4 stages. 
The size of about 1 cm described above is a size, which is matched 
approximately with the area of the semiconductor chip, and it may be 
varied, depending on the size of the chip. Consequently the thickness of 
the chip 1, a higher heat evacuation efficiency is obtained with 
decreasing thickness. Usually it is 350 .mu.m to 450 .mu.m, but it is 
desirable that it is smaller than about 50 .mu.m. 
As described above, by using a multistage structure of fine microchannel 
flow paths it is possible to realize a small construction having an 
extremely high heat evacuation efficiency and capable of being mounted on 
one chip. In addition it can be formed together with an I/O pin package in 
one body. 
For the I/O pin package described above the material for the package 
substrate may be either one of Al.sub.2 O.sub.3, AlN, BN, SiC, etc. 
However AlN and BN, which have high thermal conductivities, are the most 
suitable. I/O pins 15 are connected with I/O terminals of the 
semiconductor chip by a solder bump array 12 through a wiring layer 13. 
Further, although, in the present embodiment, a case where there is only 
one semiconductor chip 1, a plurality of chips may be assembled in one 
body, depending on the object. 
FIG. 14 shows an embodiment representing a whole I/O package, in which fins 
having a microchannel structure 2 and 2' are mounted on both the sides of 
the semiconductor chip 1. There exist a number of working regions 
producing heat in the interior on the front side of the semiconductor chip 
1 and there is disposed a thermally highly conductive and electrically 
insulating layer 6 for spreading rapidly heat produced locally and 
transiently, the effect thereof being indicated in FIG. 9. The fins having 
a microchannel structure are bonded to the front side of this insulating 
layer 6 by a bonding layer 4, as described in the embodiments indicated in 
FIGS. 5 to 8 and TABLE 3. 
Or, although it is not indicated in the figure, the semiconductor chip 1 
may be jointed by the direct bonding method, as indicated in FIGS. 1 to 4, 
TABLE 2 and FIG. 12. Further the fins having a microchannel structure 2' 
is jointed through a bonding layer 4' to the rear side of the 
semiconductor chip 1, as indicated in FIGS. 5 to 8 and TABLE 3. Or, 
although it is not indicated in the figure, the fins having a microchannel 
structure 2' may be jointed with the rear side of the semiconductor chip 1 
by direct bonding method, as indicated in FIGS. 1 to 4, TABLE 2 and FIG. 
11. 
The construction of the fins having a microchannel structure 2 and 2' is 
almost identical to that described, referring to FIGS. 1, 5 and 13. 
The material for the package substrate 14 for the I/O pin package is the 
same as described, referring to FIG. 13. 
The I/O pins 15 are connected through multilayered wiring layers 13 and 13' 
and wire-bonded with bonding pads 17 on the chip 1. After package 
assembling, the whole device is sealed finally with a package sealing cap 
16. 
Concerning the thickness of the chip 1, a higher heat evacuation efficiency 
is obtained with decreasing thickness. Usually it is 350 .mu.m to 450 
.mu.m, but it is desirable that it is smaller than about 50 .mu.m. As 
described above, it is possible to joint fins having a fine microchannel 
structure to both the sides of the chip and in addition they can be formed 
together with an I/O pin package in one body. 
By constructing the heat evacuating body by fins having a microchannel 
structure bonded to both the sides, a heat evacuation efficiency can be 
obtained, which is about two times as high as that obtained by the 
construction using the fins having a microchannel structure bonded only on 
the front side or the rear side. Further this structure has heat 
evacuating characteristics excellent in the transient thermal response. 
Furthermore, although, in the example indicated in FIG. 14, a case where 
there is only one semiconductor chip 1 is indicated, a plurality of chips 
may be assembled in one body, depending on the object. 
As clearly seen from the above explanation, according to the present 
invention, it is possible to obtain a heat evacuation efficiency, which is 
about 10 to 100 times as high as that obtained by using usual fins, and to 
realize the heat evacuating body formed together with an I/O pin package 
in one body by disposing fins having a microchannel structure including 
multistage fine microchannel flow path structure on a semiconductor 
element. Further a more remarkable effect can be obtained by using them 
together with a heat diffusing structure making local heat production 
within the semiconductor element uniform. Consequently it is possible to 
realize an electronic circuit capable of dealing with increase in the 
integration density, the electric power consumption and the drive speed 
and thus to improve significantly the performance of the semiconductor 
device.