Semiconductor device comprising at least one IGBT and a diode

Abstract: The present invention provides a semiconductor device comprising, at least a pair of an insulated gate bipolar transistor, and a diode, both of which are in a reverse parallel connection with each other, wherein the resistivity of the base layer of the lowest impurity concentration in the diode is lower than that of the base layer of the lowest impurity concentration in the insulated gate bipolar transistor, and wherein a breakdown voltage of said insulated gate bipolar transistor at the time of switching from conduction state to blocking state is lower than a breakdown voltage of said insulated gate bipolar transistor and said diode at the time of blocking state.

Description: This invention relates to a semiconductor device (hereinafter referred to as IGBT wherein an insulated gate bipolar transistor and a diode are in a reverse parallel connection or are connected in parallel with each other in the opposite direction. With development of power electronics, it is important to make an inverter apparatus with a high performance, low noise and a small size. The insulated gate bipolar transistor (hereinafter referred to as IGBT) is a voltage drive type element with a high speed of MOSFET and a high output characteristic of the bipolar transistor. The drive circuit of IGBT can be made smaller as compared with the drive circuit of the bipolar transistor that is an electric current drive type element. This IGBT is usually used in a form of the IGBT module. IGBT modules are semiconductor devices formed in such a manner that IGBT and the diode which are in a reverse parallel connection or are connected in the opposite direction in parallel with each other are incorporated in a package, and the electrode terminal is taken out to the outside. The IGBT modules are mainly used in the inverter circuits, etc.. In order to reduce the loss of the inverter circuit, it is necessary to reduce a loss of the IGBT module. Therefore in the recent years, the improvement has been is done in order to reduce the switching loss and the loss by the ON-state voltage of the IGBT. For example, it is known that tail electric current is the main factor of switching loss. The tail electric current is such an electric current that decreases as the tail is pulled gently, after the collector electric current decreases steeply by turn-off. Reduction of the tail current decreases the switching loss. It is known that many cells are integrated in the same area by making the unit cells minute, so that the channel width per the unit area is increased to reduce the ON-state voltage. As a loss reduction technique of IGBT like the above, it is known that the resistivity of the n base layer of the IGBT is increased as seen in Japanese patent Laid-open print No. 4-133355. As mentioned above, it is possible to reduce the loss of IGBT by reducing tail electric current and the ON-state voltage. But, when the improved IGBT as stated above is incorporated in IGBT modules, the voltage noise occurs. EP-A-0423721, EP-A-0368246 and an article entitled 'A High Power IGBT Module for Traction Motor Drive' by M. Mori et al, published in Proceedings of the International Symposium on Power Semiconductor Devices and ICS (ISPD) on 18 May 1993 by the IEEE Electron Devices Society each disclose a semiconductor device with an insulated gate bipolar transistor and a diode in reverse parallel connection. According to the present invention there is provided a semiconductor device comprising: at least a pair of an insulated gate bipolar transistor, and a diode, both of which are in a reverse parallel connection; wherein: the resistivity of the base layer of the lowest impurity concentration in said diode is lower than that of the base layer of the lowest impurity concentration in said insulated gate bipolar transistor, and wherein the breakdown voltage of said insulated gate bipolar transistor at the time of switching from conduction state to blocking state is lower than that of the breakdown voltage of said insulated gate bipolar transistor and said diode at the time of blocking state. This invention permits a semiconductor device to be provided with a reduced voltage noise and loss, as well as a higher destruction capability. As shown in Fig. 2, the structure of IGBT is formed as follows. The second area 12 is formed so as to adjoin the first area 11. In addition, the third area 13 (collector side base layer) is formed so as to adjoin the second area 12. The fourth area 14 is formed selectively on the surface part of the third area 13. In addition, the fifth area 15 is formed selectively on the surface part in this fourth area 14. The surface part of the fourth area 14 held by the third area 13 and the fifth area 15 is formed as the channel area, and insulation film 19 is provided at this upper part. In addition, insulation gate 20 is provided at the upper part. Second main electrode 21 that is commonly connected to the fourth area 14 and the fifth area 15 is provided. First main electrode 22 connected to the first area 11 is provided. On the other hand, the structure of the diode is formed as follows. The seventh area (base layer) 17 is formed so as to adjoin the sixth area 16. The eighth area 18 is formed on the surface part of the seventh area 17. Third main electrode 23 connected to the sixth area 16 is provided. Fourth main electrode 24 connected to the eighth area 18 is provided. Here, the resistivity of the seventh area (base layer) 17 is lower than that of the third area (collector side base layer) 13. Generally, the higher the resistivity is, the wider the depletion layer expands easily. Therefore, when turn-on of the IGBT, the diode with low resistivity recovers softly, by the residual carriers of the area to which the depletion layer does not extend, so that the leap voltage is reduced. When the dynamic breakdown voltage at the time of turn on of IGBT is lower than the static breakdown voltage of the state that IGBT and the diode are in the blocking state, an avalanche breakdown takes place in the operating area of the IGBT, so the leap voltage can be suppressed to a certain constant voltage thereby to protect the diode from breakdown. Thus the reliability of the semiconductor device and the breakdown capability can be improved. In the drawings: Fig. 1 is a perspective view of an IGBT module to which this invention applied. Fig. 2 is a sectional view of the IGBT and the diode in the IGBT module. Fig. 3 is a circuit diagram of an inverter using the IGBT modules. Fig. 4 shows switching waveforms of an IGBT module. Fig. 5 shows the change of the leap voltage when the resistivity of the n- layer is changed. Fig. 6 shows the change of the leap voltage when the power voltage is changed. Fig. 7 is a graph showing relationship between resistivity of n- layer of IGBT and fall time (Tf). Fig. 8 is a graph showing relationship between resistivity of n- layer 17 and electric current changing rate (di/dt). Fig. 9 is a graph showing relationship between resistivity of n- layer of IGBT and diode and a rated voltage. Fig. 10 is a graph showing relationship between resistivity of n- layer 17 and electric current changing rate (di/dt). Fig. 11 is a graph showing relationship between resistivity of n- layer 13 and fall time (Tf) in IGBT. Fig. 3 shows the inverter circuit using the IGBT modules. In Fig. 3, 100a to 100f are the IGBTs, 101a to 101f are the diodes, 110 is a motor, and 120 is a power source. There are some kinds of IGBT modules. (1) IGBT modules in which only a pair of IGBT and the diode are incorporated in a package. (2) IGBT modules in which an upper arm and a lower arm in the one phase share are incorporated. (3) IGBT modules in which the upper arm and the lower arm in the three phases share are incorporated. These are properly used case by case basis. In Fig. 3, when 100a and 100e of IGBT are turned on, the electric current flows via IGBT 100a - motor 110 - IGBT 100e from the power source 120. This time, IGBT 100b and 100d in the other arm and diodes 101b and 101d are in blocking state, and thus the diode and the IGBT need approximately the same breakdown voltage. When IGBT 100e is turned off, the electric current flowing through the motor flows back via IGBT 100a, motor 110 and diode 101b by the energy of the motor. Again, when IGBT 100e is turned on, the electric current flowing in diode 101b flows back to IGBT 100e. Fig. 4 shows the switching waveform in IGBT modules. (a) shows the waveforms of an anode electric current I11 of the diode 101b in the upper arm in the circuit diagram of Fig. 3 and of voltage VAK between the anode and the cathode. (b) shows the waveforms of a collector electric current I11 of IGBT 100e in the lower arm and of voltage VCE between the collector and the emitter. When the IGBT is in the ON state, the electric current that flows in the diode is cut off, and when the IGBT is in the OFF state, the electric current flows in the diode again. As shown in the switching waveforms of Fig. 4, IGBT generates the leap voltage at the time of the turn-off, to produce the noise. And, the diode generates the leap voltage likewise when turning on of the IGBT, and the noise also comes out. The cause of the leap voltage when turning off the IGBT is in the steep decrease of the collector electric current when turnoff. When tail electric current is decreased to improve switching loss, the collector electric current decreases more steeply by turnoff, thereby to increase an electric current changing rate di/dt. Because the wiring has inductance in the IGBT modules the leap voltage is generated by the electric current changing rate and the wiring inductance. The leap voltage also increases as the electric current changing rate increases, which causes voltage noise. On the other hand, the noise generated in recovery of the diode is caused by making the unit cell of the IGBT minute. When the unit cell is made minute, to lower the ON-state voltage much more electric currents can be flown in the same gate voltage. Mutual conductance gm at this time becomes large inevitably. When IGBT turns on during the inverter operation, and the collector electric current increases, di/dt is proportional to gm. The larger gm is, the larger di/dt becomes. When gm of IGBT becomes larger, di/dt at the time of the turn-on becomes larger, and the turn-on time becomes shorter, to reduce the turn-on loss. However, when di/dt of IGBT becomes large, di/dt when the diode of the pair arm recovers becomes also large. By the wiring inductance and increase of this di/dt, the leap voltage of the diode increases to generate the noise voltage. The occurrence of the voltage noise deteriorates the element. The voltage noise sometimes causes other arms or IGBT of other phases operate wrongly, to lower the reliability of IGBT modules and of the inverters etc.. An example of this invention is explained in detail by using the drawings. Fig. 1 shows a perspective view of an IGBT module to which this invention is applied. An insulating plate 4 is provided on a heat sink board 5 made of metal. A metal board 3 is provided on the insulating plate 4. The IGBT 1 and diode 2 are set on the metal board 3. The collector electrode of the IGBT and the cathode electrode of the diode are connected to a collector terminal 6 through electrode board 3. The emitter electrode of the IGBT and the anode electrode of the diode are connected together by a wiring 25 to an emitter terminal 7, and the gate electrode of the IGBT is connected to a gate terminal 26. The above structure is built in a plastic package 8, and each terminal is taken out to outside of the plastic package 8. Fig. 2 shows a cross sectional structure of the module and the connecting formation of both IGBT 1 and diode 2. First of all, the structure of the IGBT is described below. On a p+ silicon substrate 11 an n+ layer 12 whose impurity concentration is lower than the p+ substrate is formed, and then n- layer 13 whose impurity concentration is lower than the n+ layer 12 is formed on n+ layer. P+ layer 14 with higher impurity concentration is formed selectively on the surface of n- layer 13, and then n+ layer 15 whose impurity concentration is higher than p+ layer 14 is formed selectively on the surface of p+ layer 14 area. Counter portions of the surface parts of p+ layer 14 sandwiched by n- layer 13 and n+ layer 15 are formed as channel area. A gate insulation film 19 is formed on this channel area. In addition, a gate electrode 20 is formed on insulation film 19. In addition, emitter electrode 21 connected together to p+ layer 14 and n+ layer 15 and a collector electrode 22 connected to p+ silicon substrate 11 are formed. Then, structure of the diode is explained. n- layer 17 with low impurity concentration is formed on the n+ substrate 16, and p+ layer 18 with high impurity concentration is formed on the surface part of n- layer 17. Cathode electrode 23 is connected to the n+ substrate 16, and anode electrode 24 is connected to p+ layer 18. The resistivity of n- layer 17 of the diode is lower than that of n- layer 13 of IGBT. The collector electrode 22 of the IGBT is connected to the cathode electrode 23 of the diode, and the emitter electrode 21 of the IGBT is connected to the anode electrode 24 of the diode. So, the IGBT and the diode are connected in the opposite direction in parallel with each other. Turnoff of the IGBT and tail electric current are explained. When the IGBT is turned off, the reverse bias is applied between n- layer 13 and p+ layer 14. As a result, depletion layer is extended in n- layer 13 with low resistivity. The depletion layer supports the voltage applied to the device. This time, the higher the resistivity of the n- layer is, the more easily the depletion layer extends. When the depletion layer extends, holes accumulated in the n- layer 13 and n+ layer 12 recombines with an electrons and disappear. The electric current that flows until the holes disappear is tail electric current. Fig. 7 shows the relationship between resistivity and fall time (Tf) in n- layer 13 in the IGBT of which the rated voltage is 600V. When the resistivity of n- layer 13 is large, depletion layer extends easily upon turnoff and amount of holes accumulated in n- layer 13 is not large, almost no tail electric current flows. Therefore, in this case the fall time becomes shorter. When the resistivity of n- layer 13 is small, a plenty of holes are accumulated in n- layer 13, and depletion layer does not extend easily. Thus tail electric current flows. In this case, the fall time becomes longer, and loss of IGBT increases. Therefore, the loss at the time of turnoff is reduced as the resistivity of n- layer 13 of the IGBT is higher. According to the examination result by the inventors, when a rated voltage is nV, it is desirable to set the resistivity of n- layer 13 in the IGBT to be more than n/17Ω·cm. Fig. 11 shows the relationship between thickness of n-layer 13 and fall time (Tf) in the IGBT of which the rated voltage is 600v. When n- layer 13 in IGBT is thin, as the depletion layer fully extends throughout n- when turnoff, almost no tail electric current flows, and the value of fall time becomes almost constant. When the n- layer 13 in the IGBT is thick, as the depletion layer extends not enough tail electric current flows, and fall time becomes longer. With an increase in n- layer 13 thickness, loss of IGBT increases. In order to secure static breakdown voltage higher than the rated voltage, a certain thickness is necessary. Therefore in IGBT, the thickness of n- layer 13 should be in the range that is necessary to secure static breakdown voltage higher than the rated voltage, and the thickness should be such that loss due to tail current is reduced. According to the examined result of the inventors, when the rated voltage is set to nV, it is desirable that the thickness of n- layer 13 in the IGBT is in the range of (n/10.5) - (n/7.5) µm. Here, the dynamic break down voltage of the IGBT will be explained. Fig. 6 shows relationship between the power voltage and the leap voltage at the time of turnoff of the IGBT. The resistivity of n- layer 13 of the IGBT is 40Ω · cm. The inventors found that, when the power voltage is low, the leap voltage increases with the increase of the power voltage, but when the power voltage reaches over 300V, the increase of leap voltage almost stops. The reason why the above phenomenon occurs is that when the power voltage becomes high, avalanche breakdown occurs in the active area of the IGBT. Generally, avalanche breakdown occurs in the termination area in the blocking state, and occurrence of avalanche breakdown determines the breakdown voltage. This breakdown voltage is called static breakdown voltage. But, in the conductive state, the resistivity of n- layer 13 in the IGBT becomes lower, because of conductivity modulation. Therefore, at the time of turnoff, the depletion layer does not extend easily than at the time of the state blocking. The voltage that is applied to the depletion layer becomes larger, and therefore, in the blocking voltage of termination area that is the voltage lower than the static breakdown voltage, avalanche breakdown occurs in the active area so as to k. ep the leap voltage constant. The voltage is called dynamic breakdown voltage of which avalanche breakdown occurs at the time of turnoff. The inventors discovered that the dynamic breakdown voltage exceeded the static breakdown voltage, when the dynamic breakdown strength becomes higher with the increase of the resistivity in the n- layer 13, and resistivity in the n- layer 13 is enlarged to reduce tail electric current. When the dynamic breakdown voltage is lower than the static breakdown voltage of the diode or the IGBT, electric currents disperse in the whole active area of the IGBT, and its breakdown capability becomes higher. Thus IGBT modules are not damaged, even if avalanche breakdown occurs in the dynamic breakdown voltage of the IGBT. When the dynamic breakdown voltage of the IGBT is higher than the static breakdown voltage of the diode and the IGBT at the time of turnoff, a voltage that is higher than static breakdown voltage is applied to the IGBT or the diode through leap voltage. There is a fear that the IGBT, the diode or the IGBT modules may be destroyed by the over voltage. Therefore, the diode can be protected from the leap voltage at the time of turnoff by setting the dynamic breakdown voltage of the IGBT lower than the static breakdown voltage of the IGBT or the diode. According to the test result, when the rated voltage is set as nV, it is desirable that the resistivity of n-layer 13 of the IGBT should be (n/6)Ω·cm or less. As mentioned above, it is effective, to reduce the turn-off loss of the IGBT modules and improve the destruction capability by the following measures. (1) Resistivity of n- layer 13 in the IGBT is increased. (2) n- layer 13 is made thinner in the range that the rated voltage is secured. (3) The dynamic breakdown voltage of IGBT should be lower than the static breakdown voltage of IGBT or the diode. In IGBT modules, leap voltage and noise are generated by recovery of the diode at the time of turn-on. To reduce these, it is necessary to reduce the electric current changing rate when the diode is recovering. The tail electric current of the IGBT is the recombination current, but the recovery electric current of the diode is decided by diffusion current. In case of the diode, the electric current changing rate of the IGBT becomes smaller when the resistivity of n- layer is kept lower. This is, in the low resistivity of n- layer, the depletion layer hardly extends at the time of recovery of the diode, and therefore, sweeping out of the carriers becomes slowly. Fig. 8 shows the relationship between the resistivity of n- layer 17 and electric current changing rate (di/dt) when recovering the diode by turn-on where the rated voltage of the diode is 600V. When the resistivity of n-layer 17 of the diode is low, as the depletion layer does not extend enough, sweeping out of the carrier becomes slowly. As a result, the electric current changing rate is suppressed low. But, when the resistivity of n- layer 17 becomes high, sweeping out of the carriers becomes fast, and the electric current changing rate also increases with the increase of resistivity. Therefore, a lower resistivity of n- layer 17 in the diode is better. However, when the resistivity is lowered too much, the static breakdown voltage may also be reduced. Therefore, it is desirable that the resistivity of n- layer 17 in the diode should be set low, in the range that static breakdown voltage can be higher than the rated voltage. According to the examination result by the inventors, when the rated voltage is set to nV, it is desirable that the resistivity of n- layer 17 of the diode should be in the range of (n/25) - (n/10)Ω·cm. Fig. 10 shows the relationship between the thickness of n- layer 17 and the electric current changing rate (di/dt), when the diode recovers by turn-on the rated voltage of the diode being 600V. When n- layer 17 is thick, the effect is the same as the resistivity value is low. That is, because the depletion layer is extended not enough at the time of recovery the carriers are swept out slowly. Therefore, the electric current changing rate could be suppressed. When n- layer 17 is thin, the electric current changing rate becomes larger. Therefore, the thickness of n- layer 17 of the diode should be made large. Therefore, in order to reduce the leap voltage and the noise at the time of turn-on, the resistivity of n- layer 17 in the diode should be kept low, as long as the rated voltage is attained. The n- layer 17 should be made thicker. According to the test result from the inventors, when the rated voltage is set to be nV, it is desirable that the thickness of n- layer 17 of the diode is set to (n/10) µm. The inventors found that it is possible to reduce turn-on loss, to secure high breakdown voltage and to reduce turn-on noise by the following measures. (1) Resistivity of n- layer 17 in the diode is made lower than the resistivity of n- layer 13 in the IGBT. (2) Thickness of n- layer 13 of the IGBT is made thinner than the n- layer 17 of the diode. (3) Static breakdown voltage of the IGBT and the diode are made not higher than dynamic breakdown voltage in the IGBT. In the above the inventors explained about the IGBT and the diode having a rated voltage of 600V or 1200V. Generally, the way that the depletion layer extends is decided by the applied voltage and resistivity (impurity concentration). More in detail, the width of the depletion layer is proportional in the 1/2square of the applied voltage and the 1/2square of the inverse number of impurity concentration. Therefore, even in another case of the rated voltage, relationship among the extension of the depletion layer and resistivity is the same as that in case of 600V and 1200V rated voltage. Fig. 9 shows the relation between the resistivity and the voltage of the n- layer in the IGBT and the diode, when the rated voltage is nV. The resistivity of the n- layer in the diode is lower than the resistivity of the n- layer in the IGBT, so the resistivity is in the range when dynamic breakdown voltage becomes lower than the static breakdown voltage of the diode. The static breakdown voltage of the diode is in a range which is higher than the rated voltage. According to the results of the inventors experiments, when the rated voltage of IGBT module is set to nV, the ranges that fulfill the above relations are described as follows. (I) Resistivity of n- layer 13 of the IGBT: (n/17) - (n/6) Ω· cm. (II) Resistivity of n- layer 17 of the diode: (n/25) - (n/10) Ω·cm. (III) Thickness of n- layer 13 in the IGBT: (n/10.5) - (n/7.5) µm. (IV) Thickness of n- layer 17 in the diode: (n/10) µm or more. In the IGBT modules which comprise the IGBT and the diode having the resistivity and the thickness in the range mentioned above, the maximum leap voltage is suppressed, and it has been confirmed through the experiment that the occurrence of the noise was suppressed. A thickness of n- layer 17 in the diode which is 1.2 times or more than the n- layer 13 of IGBT is preferable. The resistivity of the base layer in the diode is set lower than the resistivity of the base layer on the collector side of the IGBT. The IGBT module having a circuit in a reverse parallel connection with low noise and small loss could be obtained by setting the dynamic breakdown voltage of the IGBT lower than the static breakdown voltage of the diode and the IGBT.

Claims: A semiconductor device comprising: at least a pair of an insulated gate bipolar transistor (11, 12, 13, 14, 15), and a diode (16,17,18), both of which are in a reverse parallel connection; characterised in that: the resistivity of the base layer (17) of the lowest impurity concentration in said diode is lower than that of the base layer (13) of the lowest impurity concentration in said insulated gate bipolar transistor, and wherein the breakdown voltage of said insulated gate bipolar transistor at the time of switching from conduction state to blocking state is lower than that of the breakdown voltage of said insulated gate bipolar transistor and said diode at the time of blocking state. A semiconductor device according to claim 1,wherin said base layer (17) of the lowest impurity concentration in said diode is thicker than said base layer (13) of the lowest impurity concentration in said insulated gate bipolar transistor. A semiconductor device according to claim 1, wherein said base layer (13) in said insulated gate bipolar transistor has such resistivity and thickness that a depletion layer is former at about (n/2) volts, but the base layer (17) of said diode has such resistivity and the thickness that the depletion layer is not formed at (n/2) volts where a rated voltage is nV. A semiconductor according to claim 1, wherein the resistivity of said base layer (13) in said insulated gate bipolar transistor is in the range of (n/17) to (n/6)Ω · cm and the resistivity of said base layer (17) of said diode is in the range of (n/25) to (n/17) Ω · cm, where a rated voltage is n volts. The semiconductor device according to claim 1, wherein a thickness of said base layer (13) of said insulated gate bipolar transistor is in the range from (n/10.5) to (n/7.5) µ m and a thickness of said base layer (17) of said diode is (n/10) µ m or more, where a rated voltage is n volts. A semiconductor device according to claim 1, wherein the resistivity of said base layer (13), of said insulated gate bipolar transistor is 1.5 times more than that of said base layer (17) of said diode. A semiconductor device according to claim1, wherein; (1) the insulated gate bipolar transistor comprises, a fist main surface and a second main surface, a first main area (11) of a first conductive type, exposed to said first main surface, a second area (12) of a second conductive type, adjacent to said first area (11), having an impurity concentration lower than that of said first area (11), a third area (13) of the second conductive type forming the base layer of the insulated gate bipolar transistor, being adjacent to said second area, having an impurity concentration lower than that of said second area (12) and being exposed to the second main surface, a fourth area (14) of the first conductive type, selectively formed in said second main surface having an impurity concentration higher than that of said third area (17), a fifth area (15) of the second conductive type, selectively formed in the second main surface, having an impurity concentration higher than that of said fourth area (14), the insulated gate bipolar transistor being formed by the third, fourth and fifth areas through an insulation film (19), a first main electrode (22) in low ohmic contact with the first area, and a second main electrode (21) which shorts said fourth (14) and fifth (15) areas on the second main surface; and the diode has one and other main surfaces , and comprises; a sixth area (16) of the second conductive type, exposed to the first main surface, a seventh area (17) of the second conductive type adjacent to said sixth area(16), forming the base layer of said diode, and having an impurity concentration lower than that of Said sixth area (16), an eighth area (18) of the first conductive type, adjacent to said seventh area (17), having an impurity concentration higher than that of said seventh area (17) and being exposed to said other main surface, a third electrode (23) in low ohmic contact with said sixth area (16), and a fourth electrode (24) in low ohmic contact with said eighth area (18), wherein said first electrode (22) and said third electrode (23) are connected to each other, and said second electrode (20) and said fourth electrode (24) are connected to each other, wherein the resistivity of the seventh area (17) in said diode is lower than that of the third area (130 of said insulated gate bipolar transistor. A semiconductor device as according to claim 7, wherein the thickness the seventh area (17) of said diode is larger than that of the third are (13) of said insulated gate bipolar transistor. A semiconductor device according to claim 7, wherein the third area (13) of said insulated gate bipolar transistor has a resistivity and thickness such that a depletion layer is formed at (n/2) volts, and the seventh area said diode has a resistivity an thickness such that a depletion layer is not formed at (n/2) volts, where the rated voltage is n volts. A semiconductor device according to claim 7, wherein the resistivity of the third area (13) said insulated gate bipolar transistor is in the range of n/17 to n/6Ω · cm, and the resistivity of the seventh area (17) of said diode is in the range from n/25 to n/17Ω · cm, where the rated voltage is n volts. A semiconductor device according to claim 7, wherein the thickness of the seventh area (13) of said insulated gate bipolar transistor is from n/10.5 to n/7.5µ m, and the thickness of the seventh area (17) of said diode is n/10µ m or more, where the rated voltage is n volts. A semiconductor device according to claim 7, wherein the resistivity rate of the third area (13) of said insulated gate bipolar transistor is at least 1.5 times than that of the seventh area (17) of said diode. A semiconductor device according to claim 1, wherein (1) the insulated gate bipolar transistor comprises, a first main surface and a second main surface, a first area (11) of a first conductive type, exposed to said first main surface, a second area (12) of a second conductive type, adjacent to said first area, having an impurity concentration lower than that of said first area (11), a third area (13) of the second conductive type, forming the base layer of the insulated gate bipolar transistor, being adjacent to said second area, (11) having an impurity concentration lower than that of said second area (12) and being exposed tot the second main surface, a fourth area (14) of the first conductive type, selectively formed in said second main surface having an impurity concentration higher than that of said third area (13), a fifth area (15) of the second conductive type, selectively formed in the second main surface, having an impurity concentration higher than that of said fourth area (14), the insulated gate bipolar transistor being formed by the third, fourth and fifth areas through an insulation film (19), a first main electrode (22) in low ohmic contact with the first area (11), and a second main electrode (23) which shorts said fourth (14) and fifth area (15) on the second main surface; and (2) the diode has one and other main surfaces and comprises; a sixth area (16) of the second conductive type, exposed to the first main surface, a seventh area (17) of the second conductive type adjacent to said sixth area (16) forming the base layer of said diode, and having an impurity concentration lower than that of said sixth area (16), an eighth area (18) of the first conductive type, adjacent to said seventh area (17), having an impurity concentration higher than that of said seventh area (17) and being exposed to said other main surface, a third electrode (23) in low ohmic contact with said sixth area (16) and a fourth electrode (24) in low ohmic contact with said eighth area (18), wherein the depletion layer if said insulated gate bipolar transistor reaches to said second area (12) and the depletion layer of said insulated gate bipolar transistor reaches to said second area (12) and the depletion layer of said diode does not reach to said sixth area (16) at the maximum application voltage. An inventor apparatus which uses a semiconductor device according to any one of claim 1 to 13.

Inventors: HANAOKA KOUMEI, MORI MUTSUHIRO, SAKURAI NAOKI, HANAOKA, KOUMEI, MORI, MUTSUHIRO, SAKURAI, NAOKI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1995
Main classification: H01L29
IPC codes: H01L25, H02J7, H01L29