Static induction thyristor

Abstract: A static induction device (SI device) at least shares a structure in which an SI thyristor, an IGT and a capacitor are merged onto the single monolithic chip. The SI thyristor has a cathode (23), an anode (21) and gate regions (31), and a channel (22). The IGT has a well (59) on a surface of the channel, a source (31) and drain (32) regions within the well, a gate insulating film on the well, and a gate electrode (25) on the gate insulating film. The capacitor comprises the gate region (31) of the SI thyristor, the gate insulating film on the gate region, and the gate electrode (25). The cathode and the drain region are connected to each other through a high-conductive electrode (231).

Description: The present invention relates to a novel structure of a static induction device such as a static induction thyristor (hereinafter referred to as an "SI thyristor") and, more particularly, to a structure of a MOS controlled SI thyristor capable of simplifying a gate drive circuit. In recent years, various MOS controlled power devices, or MOS gated power devices such as MCT (MOS-controlled Thyristor). EST (Emitter Switched Thyristor), DMT (Deletion Mode Thyristor) have been proposed. However, each of these MOS controlled power devices has, as a main device a conventional type thyristor such as GTO, and a MOS transistor is integrated on the same monolithic chip. Since the ON-voltage of these MOS controlled power devices is determined by a characteristic of the main device, they have the disadvantages that ON-voltage and conduction loss are high. It is difficult to bring these MOS controlled power device to a high frequency use. In view of the above, a MOS controlled SI thyristor (hereinafter referred to as a "MCSITH") which expects high efficiency and high-speed operation and whose main thyristor is an SI thyristor, a device essentially low in both ON-voltage and conduction loss and capable of being operated at a high speed or high frequency, has already been proposed in Japanese Patent Application No. HEI 2-95251 (Japanese Patent Laid-Open No. HEI 3-292770) by the same Applicant as the present invention. The MCSITH is one which has, as shown in Fig. 17 and Fig. 18 (which is a cross-sectional view taken along a line A - A in Fig. 17), a structure in which a MOS transistor is integrated between a gate and a cathode of a normally-off SI thyristor. Fig. 17 is a top plan view, while Fig. 18 is a cross-sectional view taken along a line A - A in Fig. 17. As shown in Figs. 17 and 18, an SI thyristor is arranged such that an n + region 23 is a cathode, a p + region 21 is an anode, each of a pair of floating p + region 31 is a gate, and an n - region 22 is a channel. Each of the p + region 31 serves also as a source of a pMOS transistor in which a corresponding p + region 32 is a drain, and a high conductivity layer 25 such as a polysilicon silicon layer or the like is a gate electrode. Turning-on of the MCSITH is realized by the application of a positive potential to a capacitor which comprises the p + gate region 31, the high conductivity layer 25 and an oxide film 26 that is an insulating film arranged on the p + gate region 31, reducing the height of a potential barrier formed within the n - channel 22 by means of capacitive coupling (static induction effects). Turning-off is achieved realized by short-circuiting the p + gate regions 31 and the n + cathode region 23 to each other with a PMOS transistor extracting a hole through the p + gate regions 31 to the cathode region 23. However, this MCSITH has the following disadvantages. That is, if impurity density of the n - channel 22 is approximately 10 13 cm -3 in order that the main thyristor has a normally-off characteristic, it is required that a spacing between the adjacent p + gate regions 31 and 31 is equal to or less than approximately 6 µm. Assuming that a diffusion width of the n + cathode stripe 23 is 2 µm, then it is required that a spacing between the n + cathode stripe 23 and the stripe of p + gate regions 31 is narrowed to 2 µm at one side. Accordingly, the gate length L of the pMOS transistor should have a value, which is equal to or less than 2 µm, for example, 1 µm or the like. Owing to the small impurity concentration of 10 13 cm -3 , punch-through current incapable of being controlled by the gate electrode 25 always flows between the p + source region 31 and the p + drain region 32, and the main thyristor cannot be turned on. Particularly, since the depth of the p + gate regions 31 of the SI thyristor are deep such as, normally, 5 ∼ 15 µm, the MCSITH has a disadvantage that the punch-through current is apt to flow as compared with a standard, discrete MOS transistor; the source and drain regions of the standard MOS transistor have a diffusion depth almost equal to or less than twice of a gate length. Then, the MCSITH has a disadvantage that the diffusion depth of the p + source region 31 is equal to or more than 3 ∼ 15 times the gate length of the pMOS transistor so that the punch-through current is very apt to flow. Further, the aforesaid Japanese Patent Laid-Open No. HEI 3-292770 has proposed a structure in which, as shown in Fig. 19 and Fig. 20 (which is a cross-sectional view taken along a line Y - Y in Fig. 19), a pMOS transistor, comprising a p + source region 31, a p + drain region 32 and a gate electrode 25, is formed along the longitudinal direction of a cathode stripe 23. In this case, Japanese Patent Laid-Open No. HE 3-292770 has an advantage that a gate length L of the pMOS transistor can be selected independently of spacing between the p + gate regions 31 and 31 of the main thyristor. However, the above-described structure has the following disadvantage. That is, if the gate length L is lengthened to suppress the punch-through current of the pMOS transistor, the ON-resistance of the pMOS transistor is raised and the main thyristor cannot be turned off. Lengthening of the gate width w of the pMOS transistor in the structure illustrated in Figs. 19 and 20 has a limit because of a restriction of a spacing between the p + gate regions 31 and 31 of the main thyristor. A condition under which the main thyristor is brought to a normally-off and a condition under which the ON-resistance of the pMOS transistor is reduced are under a trade-off relationship. Thus, it is difficult to simultaneously satisfy the both condition. Moreover, in the structures illustrated in Figs. 17 through 20, since each of the p + gate regions 31 is under the floating condition, it is impossible to bring a metal electrode into direct contact with an upper portion of the p + diffused gate region 31 like a normal surface-gate SI thyristor. As a result, a resistance value of the p + gate region 31 is determined by a resistance of the diffused region. Thus, it is difficult to reduce a gate resistance. The above-described structure has also the following disadvantage. That is, since the p + gate resistance is high, maximum anode current that can be turned off and maximum forward blocking voltage of the main thyristor are small, and turning-off time is late. Furthermore, the gate length of the MISFET is fluctuated by photolith misalignment of the gate region and the drain region so that the ON-voltage of the MISFET is fluctuated, and a turning-off characteristic varies. Sze, "Physics of Semiconductor Devices", 2nd Edition (J. Wiley & Sons, New York 1981), pages 456 to 488 discloses on page 488 a MOSFET structure presented under the acronym "HMOS" where a single ion-implantation or a double ion-imptantation is carried out in order to increase the punch-through voltage. A well is formed which has a higher doping concentration of p type conductivity than that of the substrate having also p type conductivity. Source and drain regions are formed within the well region. The object of the invention is to provide an electrostatic induction device comprising a normally off type static induction thyristor and a normally on type MISFET according to the preamble of claim 1, the device being reliably operable if the gate length is chosen to be small, whereby the MISFET provides a define ON-voltage and a substantially invariable turning-off characteristic. According to the invention, there is provided a static induction device comprising: a static induction thyristor at least having a cathode region of n type conductivity having high impurity concentration, an anode region and a pair of gate regions of p type conductivity having high impurity concentration, and a channel region of n type conductivity having low impurity concentration, having a gate spacing of normally off type; a p-channel MISFET at least having a channel region of n type conductivity, a gate insulating film formed on said channel region, a gate electrode formed on said insulating film, a drain region of p type conductivity, said drain region being formed overlapping said cathode region a capacitor comprising the gate region, the gate insulating film formed on the gate region, and the gate electrode, wherein said cathode and drain region are connected to each other through a cathode electrode wherein said static induction thyristor and said MISFET are merged onto a single monolithic chip, whereby said MISFET is a depletion type p-channel MISFET having a well of n type conductivity formed on a part of a surface of said channel region of the static induction thyristor between said cathode region and said gate region , said drain region having high impurity concentration being formed within said well, said gate insulating film formed over said well, said well having an impurity concentration higher than that of said channel region of the static induction thyristor and a source region of said depletion type p-channel MISFET having high impurity concentration formed within the well and electrically connected to said gate region, the source and drain regions being self-aligned with the gate electrode. With this device, the gate regions may be formed in bottoms of grooves, said gate electrode may be formed on the side wall of said grooves, and said well may be formed longitudinally sandwiched between said grooves on an upper portion of a convexly formed channel likewise sandwiched in between said grooves. The device may include an isolation region formed within a trench formed between said gate regions and said drain region on a region different to the channel region of said depletion type p-channel MISFET. The device may include a floating gate electrode which is in contact with said gate regions. The device may include a capacitor, consisting of the floating gate electrode which extends on a gate insulating film, which itself is formed on said gate electrode. The device may include an isolation region formed by an insulating film between said cathode region and said gate region for preventing a breakdown voltage between said cathode region and said gate region from being reduced, the insulating film being disposed opposite to the drain region with respect to the cathode region. The device may include a thin layer of p tyre conductivity having higher impurity concentration than said gate region, being arranged at a location where said insulated gate electrode is in contact with said gate region. The device may include a buried gate region within said channel region of the static induction thyristor formed as a deeper portion than said gate region, said buried gate region being in contact with said gate region. The static induction thyristor of a double-gate type may have a second gate region formed on a surface of the channel region of the static induction thyristor and a first gate region formed within said channel region of the static induction thyristor. The well may be formed at a location spaced from said cathode region, and arranged on the outside of an area through which said main current flows. The cathode region may be arranged at a center between the adjacent gate regions, said depletion type p-channel MISFETs are formed at both sides of said cathode region, and said well is so formed as to include said cathode region and said depletion type p-channel MISFET. The anode region may be divided into a plurality of sections, and a shorted region of n type conductivity having high impurity concentration may be formed between said plurality of divided sections. The device may include a buffer layer of n type conductivity, arranged adjacent to said anode region. With the above arrangement of the invention, since it is possible to select the impurity concentration of the channel of the SI thyristor and the IGT independently, it is possible to suppress the punch-through current between the source and drain of the IGT while the normally-off characteristic of the SI thyristor is maintained. Particularly, even if the depth of the p + gate region of the SI thyristor is deep such as 3 ∼ 15 times the gate length of the IGT, it is possible to suppress the bulk punch-through current. Moreover, with the arrangement of the invention, it is possible to bring the impurity doping concentration of the SI thyristor to a value equal to or less than 10 12 cm -3 while that of the well is maintained to a value sufficient to suppress the punch-through current. As a result, it is possible to widen the lateral spacing between the gate and gate regions of the SI thyristor to a value equal to or more than 10 µm. Thus, a lateral space for a lithography on the planar pattern increases. Furthermore, with the another arrangement of the invention, unnecessary areas for the operation of the IGT between the gate regions of the SI thyristor and the drain of the IGT can be separated from each other by the isolation region. Accordingly, even if the spacing between the gates of the SI thyristor is sufficiently narrowed in order to obtain a normally-off characteristic, it is possible to design lateral parameters in which the gate width of the IGT increases. Further, with the arrangement of the invention, the high-conductive floating gate electrode such as metal can be directly in contact with the gate diffusion layer of the SI thyristor. Accordingly, even if the gate is under the floating condition, it is possible to sufficiently reduce the gate resistance of the SI thyristor. Furthermore, it is possible to maintain the capacitance connected to the p + diffused gate region of the SI thyristor to a sufficiently large value. As described above, the SI device according to the invention has the following advantages. That is, the normally-off characteristic of the SI thyristor can be made excellent, and the bulk punch-through current between the source and drain of the IGT can be suppressed. Thus, the SI device can be turned on by the smaller gate voltage. The superior switching can be made possible with a high efficiency and with a high speed. Further, the SI device according to the invention has the following advantage. That is, even if the impurity concentration of the channel of the SI thyristor of the main device is made sufficiently low, it is possible to suppress the punch-through current of the IGT. Thus, the spacing between the gate regions of the SI thyristor can be made large. The lateral space and the margin for misalignment and dimensional variation increases so that the manufacturing is made easy and the yield can be improved. Furthermore, the SI device according to the invention has the following advantage. That is, the well behaved normally-off characteristic of the SI thyristor and the reduced ON-resistance of the IGT can be simultaneously obtained. Accordingly, the turning-off characteristic of the MCSITH can be improved. In addition, the SI device according to the invention has the following advantage. That is, the gate resistance of the SI thyristor can be reduced to 1/2 ∼ 1/100. Accordingly, the higher speed switching of the MCSITH is possible, and the forward blocking voltage and the current handling capability (turn-off anode current) can increase. Moreover, the SI device according to the invention has the following advantage. That is, since the capacitance of the capacitor connected to the gate of the SI thyristor can be brought to an optimum value at which both the turning-on and turning-off time are reduced, high-speed switching is made possible. Further, the SI device according to the invention has also the following advantage. That is, since the area occupied by the capacitor connected to the gate of the SI thyristor can be reduced, the area of the gate can be reduced, and relatively, the area of the channel through which the main current flows can increase as a whole. As a result, the current value per unit chip area increases, and the ON-resistance is reduced. Fig. 1 is a top plan view showing a specific structure in which a MCSITH according to a first embodiment of the invention is integrated ; Fig. 2 is a cross-sectional view taken along a line A - A in Fig. 1; Fig. 3 is a cross-sectional view of a second embodiment of the invention; Fig. 4 is a view showing effects of a floating gate electrode in each of the first and second embodiments; Fig. 5 is a top plan view showing a specific structure in which a MCSITH according to a third embodiment of the invention is integrated; Fig. 6 is a cross-sectional view taken along a line C - C in Fig. 5; Fig. 7 is a cross-sectional view of a fourth embodiment of the invention; Fig. 8 is a cross-sectional view taken along a line Z - Z in Fig. 7; Fig. 9 is a cross-sectional view showing a first step of a manufacturing method according to a fifth embodiment of the invention; Fig. 10 is a cross-sectional view showing a second step of the manufacturing method according to the fifth embodiment of the invention; Fig. 11 is a cross-sectional view showing a third step of the manufacturing method according to the fifth embodiment of the invention; Fig. 12 is a cross-sectional view showing a fourth step of the manufacturing method according to the fifth embodiment of the invention; Fig. 13 is a cross-sectional view showing a fifth step of the manufacturing method according to the fifth embodiment of the invention; Fig. 14 is a cross-sectional view showing a sixth step of the manufacturing method according to the fifth embodiment of the invention; Fig. 15 is a cross-sectional view showing a final step of the manufacturing method according to the fifth embodiment of the invention; Fig. 16 is a cross-sectional view of a sixth embodiment of the invention; Fig. 17 is a top plan view of the prior art; Fig. 18 is a cross-sectional view taken along a line A - A in Fig. 17; Fig. 19 is a top plan view of another prior art; and Fig. 20 is a cross-sectional view taken along a line Y - Y in Fig. 19. Various embodiments of the invention will hereunder be described with reference to the accompanying drawings. Fig. 1 is a top plan view showing a specific structure in which a MCSITH according to a first embodiment of the invention is integrated, while Fig. 2 is a cross-sectional view taken along a line A - A in Fig. 1. A p + source region 312 and a p + drain region 32 are formed within an n-well 59. Differing to the source consisting of the deep p + gate regions 31 shown in prior art, the present embodiment uses a shallow source region 312 whose diffusion depth is same as that of the drain region 32. A gate electrode 25 is provided only on an upper portion of a channel of the pMOS transistor, and has a structure entirely same as a standard pMOS transistor. Each of the p + regions 312 and 32, which are respectively the source and drain of the pMOS transistor has a diffusion depth which is 0.5 ∼ 1 µm. The n-well 59 has impurity concentration which is 5 x 10 15 cm -3 ∼ 1 x 10 16 cm -3 , and has a diffusion depth which is 2 ∼ 5 µm. The pMOS transistor has a gate length which may be 1 ∼ 2 µm. An n + cathode region 23 has impurity concentration of 4 x 10 19 cm -3 ∼ 1 x 10 21 cm -3 , and a diffusion depth of 1 ∼ 2 µm. Each of a pair of p + gate regions 31 has impurity concentration of 1 x 10 18 cm -3 ∼ 2 x 10 19 cm -3 , and a diffusion depth of 6 ∼ 15 µm. By the structure, a source and drain regions are formed in a self-alignment manner. Even if misalignment shifting occurs in a masking step, the gate length L of the pMOS transistor is determined by the dimension of the mask, and is not fluctuated. As a result, the structure can be manufactured with an excellent yield. On this point, prior art has a fear that the gate length of the pMOS transistor is fluctuated by photolith misalignment of the p + gate 31 and the p + drain regions 32 so that the ON-voltage of the pMOS transistor is fluctuated, and a turning-off characteristic varies. However, the present embodiment can ensure that the gate length can be controlled. In Fig. 2, the gate electrode 25 is formed by a polysilicon (doped polysilicon: DOPOS) to which impurity is added, refractory metals such as W, Ti, Mo or a silicide thereof. The reference numerals 311 denote floating gate electrodes made of a metal such as Al, which are directly in contact with the p + diffusion regions 31, respectively, to reduce the gate resistance of the SI thyristor, thereby improving both the turning-off characteristic and the forward blocking voltage. As shown in Fig. 1, the floating gate electrodes 311 are provided for reducing the gate resistance of the SI thyristor. Accordingly, the floating gate electrodes 311 are not connected to a bonding bad or the like, and cannot electrically be driven from the external circuit. If necessary, however, a structure in which bonding pads are attached respectively to the floating gate electrodes 311 is also possible. It is desirable that contacting window portions between the floating gate electrodes 311 and the p + gate region 31 are p + -rediffused to form regions having high doping concentration. Further, it is desirable that a silicide film is formed on each of the contacting window portions to reduce a contact resistance. The reference numerals 261 denote first gate insulating films such as a thermal insulating film, while the reference numerals 262 denote second gate insulating films consisting of an oxide film of DOPOS, an oxide film of a refractory metal or a silicide thereof, or CVDSiO 2 , or the like. As described above, it is necessary that the capacitance connected to the gate regions 31 of the SI thyristor is brought to an adequate value of approximately 10 ∼ 80 times the capacitance (C GK ) of the gate regions 31 per se of the SI thyristor. Because the first capacitor comprising the gate electrode 25, the first gate insulating film 261 and the p + gate region 31 is connected in parallel with the second capacitor comprising the floating gate electrode 311, the second gate insulating film 262 and the gate electrodes 25, the capacitance connected to the gate regions of the SI thyristor increases to an optimum value, while the resistance of the SI thyristor decreases simultaneously, it is possible to improve both the turning-on and turning-off characteristics. In prior art, there is a limit in an area occupied by the capacitor on the p + region. from the point of view of an area occupying efficiency, and the capacitance cannot be increased to obtain the optimum value. In the case when the first gate insulating films 261 and the second gate insulating films 262 are formed by oxide films, respectively, it is preferable that the thickness of each of the oxide films is equal to or less than 10 -7 m (1000 Å), desirably, a value of 100∼200·10 -10 m (100 ∼ 200 Å). In Fig. 2, the reference numeral 266 denotes an isolation region by insulating film, which prevents a breakdown voltage between the n + cathode region 23 and the p + gate region from being reduced, and which facilitates miniaturization of the gate spacing of the SI thyristor. The n - cathode region 23 is not arranged at a center of the channel, but is shifted toward one side. However, if the impurity concentration of an n - channel area 22 is brought to a sufficiently low value equal to or less than 10 12 cm -3 , the spacing between the p + gate regions 31 and 31 can be brought to equal to or more than 10 µm. In this case, the position of the n + cathode region 23 could be located at a center of the channel, and there may be no need for isolation region by insulating film 266. After all, in the case when the SI thyristor does not have a normally-off characteristic owing to the rather high impurity concentration of the n - channel 22 such as 1.5 x 10 13 cm -3 ∼ 2 x 10 13 cm -3 and the spacing between the p + gate 31 and 31 such as equal to or less than 4.5 µm, the n + cathode region 23 should be shifted toward one side as shown in Fig. 2. Fig. 3 is a cross-sectional view of a second embodiment of the invention, in which, similarly to the first embodiment, floating gate electrodes 311 made of a metal film having a high conductivity are formed on each p + gate region 31. Although not shown in Fig. 3, a contact resistance is reduced if a very thin p ++ rediffused region or the like is formed on a contact window portion between the floating gate electrodes 311 and the p + gate areas 31. Further, if a silicide film made of a refractory metal such as WSi 2 , MoSi 2 is formed between the p ++ area and the floating gate electrodes 311, a gate resistance of the SI thyristor is reduced to 1/4 ∼ 1/100. It is needless to say that the aforesaid thin p ++ area and the silicide film made of a refractory metal should preferably be formed on the entire surface of each of the p + gate regions 31, not only on the contact window portion between the floating gate electrodes 311 and the p + gate areas 31, in the first and second embodiments. In Fig. 3, the width between p + buried gate regions 319 and 319 is a narrowest in the channel, whereby the present embodiment proposes a structure in which a normally-off characteristic is easily realized. In Fig. 3. the p + regions, or extrinsic gate regions 31 rather play a role of interconnecting regions from the p + buried gate regions, or intrinsic gate region 319 to the floating gate electrodes 311. Operation of the main thyristor becomes approximately that of a buried gate SI thyristor. Fig. 4 shows effects of the floating gate electrodes 311 in each of the first and second embodiments, a relationship between maximum turn-off anode current of the MCSITH and an ON-resistance of the pMOS transistor. ▴ indicates the case of the conventional MCSITH, while ▪ indicates the case of the invention. According to Fig. 4, it will be apparent that maximum turn-off anode current of the present invention increases approximately twice that of the conventional example. Fig. 5 is a top plan view showing a specific structure in which a MCSITH according to a third embodiment of the invention is integrated, while Fig. 6 is a cross-sectional view taken along a line C - C in Fig. 5. The third embodiment is different from the first to second embodiments in that an n-well is not formed between an n + cathode 23 and the p + gate regions 31. Specifically, the n-well 59 is arranged on the outside of an area through which main current flows. between the cathode 23 and an anode region 21 of the SI thyristor that is a main device. A pMOS transistor is formed within the n-well 59. The reference numerals 32 and 312 denote a p + drain and source regions of the pMOS transistor, respectively. A plurality of gate electrodes 25 are formed only on the pMOS transistor. Since these drain, source and gate regions can be formed by a self-alignment process step which is used in a normal fabrication method of a pMOS transistor, it is possible to control variation of a gate length L to a sufficiently small value. An n + cathode 23 and the p + drain region 32 are electrically connected to each other through a cathode electrode 231. The reference numerals 263 denote field insulating films or the like which are formed by a well-known LOCOS process or the like. According to the structure illustrated in Figs. 5 and 6, it is possible to select design parameters of the pMOS transistor and the SI thyristor, independently. As a whole, the structures illustrated in Figs. 5 and 6 have advantages that degree of freedom of design for an integrated structure is large, and manufacturing is made easy. Particularly, even if the spacing between the p + gate regions 31 and 31 of the SI thyristor is reduced sufficiently, it is possible to flexibly select a gate length L and a gate width w of the pMOS transistor. Accordingly, it is possible to obtain simultaneously a normally-off characteristic of the SI thyristor and reduced ON-resistance of the pMOS transistor. Figs. 5 and 6 show a structure of a single unit where there is the simple single n + cathode region 23. It is needless to say, however, that a plurality of these units, or segments are arranged in parallel relation to each other so as to be brought to a multichannel structure, whereby a MCSITH for large current can be realized. In this case, if the n-well 59 is formed below a cathode electrode wiring layer at which respective cathode electrodes 231 are gathered together, the pMOS transistor does not occupy so much area with respect to a whole chip area. Accordingly, area occupying efficiency does not significantly change with respect to the first to second embodiments. The superior area occupying efficiency can be obtained by the arrangement in which the n-well 59 is formed within the p + gate regions 31. Fig. 7 is a cross-sectional view of a fourth embodiment of the invention, while Fig. 8 is a cross-sectional view taken along a line Z - Z in Fig. 7, showing a case of a recessed gate SI thyristor. A pair of p + gate regions 31 are formed in a bottom of a recessed groove or a trench, and an n-buffer layer 71 is formed adjacent to a pair of p + anode regions 21. If impurity concentration of an n-buffer layer 42 is brought to 1 x 10 15 ∼ 1 x 10 17 cm -3 , it is possible to bring impurity concentration of n - channel 22 to extremely low of 10 11 ∼ 10 13 cm -3 , whereby an electric field strength between the p + gate 31 and the p + anode regions 21 is uniformized, and a depletion layer from the gate regions 31 does not reach the p + anode regions 21. Accordingly, it is possible to increase maximum forward blocking voltage and a switching speed, reducing a forward voltage drop. In Fig. 7, an SI anode shorted structure (or SI anode-emitter-shorted structure) is used in which each of the p + anode regions 21 is divided into a plurality of sections, and an n + shorted region 24 is inserted into a location between the sections. Since electrons can be diverted into the n + shorted region 24 by a potential field between the p + anode regions 21 and the n + shorted region 24, turn-off tail current of the SI thyristor is reduced so that higher speed switching is made possible. As shown in Fig. 8, an n-well 59 is formed, in a longitudinal direction along the long side of cathode stripe, on an end portion of a convexed channel 22 sandwiched in between a groove and a groove, and a p + drain 32 and a p + source region 312 of the p-channel MOS transistor are formed within the n-well 59. The p + drain 32 and an n + cathode regions 23 are connected to each other by a cathode electrode 231. The p + diffusion regions 31 and a floating gate electrode 311 are in contact with each other at the bottom of the U-shaped groove, and the gate resistance of the SI thyristor is extremely small. The p + gate regions 31, a first gate insulating film 261 and a gate electrode 25 cooperate with each other to form a first capacitor, and the gate electrode 25, a second gate insulating film 262 and the floating gate electrode 311 cooperate with each other to form a second capacitor. Since a gate capacitance connected to a gate region of SI thyristor increases, turning-on time is shortened. The p + source region 312 is electrically connected to the p + gate regions 31 by the floating gate electrode 311. The invention should not be limited to the first to fourth embodiments described above, but may consist of a combination of some of the first to fourth embodiments. Furthermore, it is needless to say that the invention may be one in which a conductivity type is arranged wholly reversely. Further, the arrangement may be such that the main thyristor is formed by GaAs, and the gate insulating film is formed by AlGaAs. Figs. 9 to 15 are views showing a method of manufacturing a fifth embodiment having a structure substantially the same as that of the first embodiment. As will be clear from Fig. 15 showing a final structure of the process sequence, reduction in lateral dimension is easy by the present embodiment, in which a plurality of insulating films 26 are formed between cathode electrodes 231 and floating gate electrodes 311. The present embodiment is manufactured by the following manufacturing steps: (1) A p + anode area 21 of 1 x 10 19 cm -3 whose depth is 10 ∼ 30 µm is formed on a rear surface of a n-type Si substrate having impurity density of 1 x 10 13 cm -3 and a thickness of approximately 400 µm by a diffusion method or the like. Subsequently, silicon nitride films 29 are formed on a surface of the n-type Si substrate by a CVD method so as to have a thickness of 1300∼2000·10 -10 m (1300 ∼ 2000 Å). In this connection, it is preferable that a thin pad oxide film of approximately 500·10 -10 m (500 Å) is beforehand formed under the silicon nitride films 29. Subsequently, similarly to a LOCOS in a manufacturing step of a standard MOS transistor, a photo-lithography and a plasma etching are used to leave the silicon nitride films 29 on portions (device areas) on which the SI device according to the invention is formed. Other silicon nitride films 29 are removed. The surface of the n-type Si substrate is selectively thermally oxidized with the remaining silicon nitride films 29 serving as masks. Thus, a thick field oxide films 27 of 6000∼15000·10 -10 m (6000 ∼ 15000 Å) are formed (refer to Fig. 9). (2) Subsequently, the silicon nitride films 29 are removed. Ions of 11 B + are implanted with photoresist films 39 serving as masks (refer to Fig. 10). Subsequently, a substrate into which the ions are implanted is heat-treated (drive-in), to form p + gate region 31 of an SI thyristor having impurity concentration of 2 x 10 18 ∼ 3 x 10 19 cm -3 and a depth of 4 ∼ 15 µm. The arrangement may be such that, in place of photoresists 39, a thermal oxide film is formed, and the p + gate regions 31 are formed by thermal diffusion. Further, the arrangement may be such that, after formation of the p + gate region 31, the field oxide films 27 are formed by a LOCOS step. Subsequently, ions of 31 P + are similarly implanted with the photoresist films 39 serving as masks, and drive-in is performed, to form n-well 59 having impurity concentration of 5 x 10 15 ∼ 5 x 10 16 cm -3 and a depth of 2 ∼ 5 µm.In the case where the U-shaped grooves in the second embodiment are formed and are plugged by the oxide films 269, the process steps are slightly changed as follows; the gate regions 31 and the n-wells 59 of the SI thyristor are formed and, subsequently, a pad oxide film of 500∼700.10 -10 m (500 ∼ 700 Å) and a silicon nitride film of 1300∼2000·10 -10 m (1300 ∼ 2000 Å) are formed. The nitride film, the pad oxide film and the n-type Si substrate in portions which become the U-shaped grooves are etched in order to form U-shaped grooves with the photoresist films 39 serving as the mask. Further, ions of 31 P + are implanted only into the bottoms of the U-shaped grooves with the photoresist films 39 serving as masks, to form n + channel stopper. Subsequently, if thermal oxidation (second LOCOS) is executed, oxide films are formed also on the bottoms and side walls of the U-shaped grooves. In a case where the second LOCOS is executed, the nitride films are removed and, subsequently, ions of 31 P + or 75 As + are implanted with the photoresist films 39 serving as masks (refer to Fig. 11). Subsequently, drive-in is executed to form the n + cathode regions 23 whose impurity concentration are 4 x 10 19 ∼ 1 x 10 21 cm -3 and whose depth are 1 ∼ 2 µm are formed. (3) Subsequently, after the photoresist films 39 and the pad oxide films have been removed, the first gate oxide film 261 each having a thickness of 70 ∼ 1000·10 -10 m (70 ∼ 1000 Å) is formed. Ions of 11 B + are implanted with the photoresist serving as a mask, to execute channel dope of the pMOS transistor. Conditions of the channel dope in order to get a depletion pMOS transistor are that acceleration voltage V ac = 30 ∼ 50 keV, and a dose amount Φ = 5 x 10 12 ∼ 2 x 10 13 cm -2 in the case, for example, where the gate length L = 2 µm. Subsequently, the photoresist is removed, polysilicon having added thereto impurities having a thickness of 3500 ∼ 5000.10 -10 m (3500 ∼ 5000 Å) (doped polysilicon: DOPOS) is formed on the gate oxide film by a CVD method. A plurality of gate electrodes 25 of the pMOS transistor are formed by anisotropic plasma etching such as RIE with the photoresist serving as a mask (refer to Fig. 12). If the gate electrodes 25 are brought to composite films in which silicide films are formed thereon, the gate resistance of the PMOS transistor is further reduced.Subsequently, portions of the n + cathode regions 23 are again covered with the photoresist films 39. Ions of 11 B + or 49 BF 2 + are implanted (refer to Fig. 13). Source 312 and drain regions 32 of the pMOS transistor having impurity concentration of 3 x 10 19 ∼ 8 x 10 19 cm -3 and a depth of 0.3 ∼ 0.7 µm are formed by a self-alignment step similarly to a standard process of a normal MOS transistor. Subsequently, the gate electrodes 25 of the polysilicon (DOPOS) are thermal-oxidized, or an oxide film is deposited on the entire surface by a CVD method, whereby a second gate oxide film 262 having 500∼1000·10 -10 m 500 ∼ 1000 Å is formed (refer to Fig. 14). (4) Subsequently, contact windows are formed in an upper portion of each of the P + gate regions 31. Although not shown in Fig. 15, the contact windows could be opened both on p + gate regions 31 and p + source regions 312. A refractory metal such as Mo, Ta, Ti, W or a silicide film thereof is formed by a CVD method, sputtering or a vacuum-evaporation method. Thus, floating gate electrodes 311 are formed by plasma etching with the photoresist serving as a mask. Moreover, thereafter, the insulating films 26 such as PSG films, polyimide films are formed on the entire surfaces of the floating gate electrodes 311 and , thereafter, contact windows for taking out the cathode electrodes 231 are formed by plasma etching or the like. A metal film having high conductivity such as Al is vacuum-evaporated with a thickness of 3500 ∼ 4000·10 -10 m (3500 ∼ 4000 Å) on the entire surface. Subsequently, the cathode electrodes 231 are defined by the use of the plasma etching (refer to Fig. 15). Subsequently, sintering is executed within vacuum or within inert gas, whereby this device is completed. In the case where there is a room in lateral pattern dimension on the surface, the insulating films 26 may be omitted, and the floating gate electrodes 311 and the cathode electrodes 231 may be formed simultaneously by A1. Moreover, Fig. 16 is a cross-sectional view of a sixth embodiment of the invention. In this case, an n-well 59 is so formed as to include two pMOS transistors arranged respectively at both sides of an n + cathode region 23. As described above, the SI device according to the invention can extremely easily be manufactured by application of a manufacturing step of a standard MOS transistor.

Claims: A static induction device comprising: a static induction thyristor at least having a cathode region (23) of n type conductivity having high impurity concentration, an anode region (21) and a pair of gate regions (31) of p type conductivity having high impurity concentration, and a channel region (22) of n type conductivity having low impurity concentration, having a gate spacing of normally off type; a p-channel MISFET at least having a channel region of n type conductivity, a gate insulating film (26, 261) formed on said channel region, a gate electrode (25) formed on said insulating film (26, 261), a drain region (32) of p type conductivity, said drain region (32) being formed overlapping said cathode region (23), a capacitor comprising the gate region (31), the gate insulating film (26,261) formed on the gate region (31), and the gate electrode (25), wherein said cathode (23) and drain region (32) are connected to each other through a cathode electrode (231), wherein said static induction thyristor and said MISFET are merged onto a single monolithic chip, characterized in that said MISFET is a depletion type p-channel MISFET having a well (59) of n type conductivity formed on a part of a surface of said channel region (22) of the static induction thyristor between said cathode region (23) and said gate region (31), said drain region (32) having high impurity concentration being formed within said well (59), said gate insulating film (26, 261) formed over said well (59), said well (59) having an impurity concentration higher than that of said channel region (22) of the static induction thyristor and a source region (312) of said depletion type p-channel MISFET having high impurity concentration formed within the well (59) and electrically connected to said gate region (31), the source and the drain regions (312, 32) being self-aligned with the gate electrode (25). A device according to claim 1, wherein said gate regions (31) are formed in bottoms of grooves, said gate electrode (25) is formed on the side wall of said grooves, and said well (59) is formed longitudinally sandwiched between said grooves on an upper portion of a convexly formed channel (22) likewise sandwiched in between said grooves. A device according to claim 1, including an isolation region (269) formed within a trench formed between said gate regions (31) and said drain region (32) on a region different to the channel region of said depletion type p-channel MISFET. A device according to claims 1 to 3, whereby a floating gate electrode (311) is in contact with said gate regions (31). A device according to claim 4, including a further capacitor, consisting of the floating gate electrode (311) which extends on a gate insulating film (262), which itself is formed on said gate electrode (25). A device according to claim 5, including an isolation region formed by an insulating film (266) between said cathode region (23) and said gate region (31) for preventing a breakdown voltage between said cathode region (23) and said gate region (31) from being reduced, the insulating film (266) being disposed opposite to the drain region (32) with respect to the cathode region (23). A device according to claim 5 or 6, including a thin layer of p type conductivity having higher impurity concentration than said gate region (31), being arranged at a location where said insulated gate electrode (311) is in contact with said gate region (31). A device according to anyone of the claims 5 to 7, including a buried gate region (319) within said channel region (22) of the static induction thyristor formed as a deeper portion than said gate region (31), said buried gate region (319) being in contact with said gate region (31 ). A device according to anyone of the claims 1 to 8, wherein the static induction thyristor is of a double-gate type having a second gate region (42) formed on a surface of channel region (22) of the static induction thyristor and a first gate region (31) formed within said channel region (22) of the static induction thyristor. A device according to anyone of the claims 1 to 9, wherein said well (59) is formed at a location spaced from said cathode region (23), and arranged on the outside of an area through which said main current flows. A device according to claim 3, wherein said cathode region (23) is arranged at a center between the adjacent gate regions (31), said depletion type p-channel MISFETs are formed at both sides of said cathode region (23), and said well (59) is so formed as to include said cathode region (23) and said depletion type p-channel MISFET. A device according to anyone of the claims 1 to 11, wherein said anode region (21) is divided into a plurality of sections, and a shorted region (24) of n type conductivity having high impurity concentration is formed between said plurality of divided sections. A device according to anyone of the claims 1 to 11, including a buffer layer (71) of n type conductivity, arranged adjacent to said anode region (21).

Inventors: NISHIZAWA JUN-ICHI, NISHIZAWA, JUN-ICHI
Applicants: ZH HANDOTAI KENKYU SHINKOKAI, ZAIDAN HOJIN HANDOTAI KENKYU SHINKOKAI
Application year: 1993
Main classification: H01L29
IPC codes: H01L29, H01L27