WO2013180186A1 - 高電圧絶縁ゲート型電力用半導体装置およびその製造方法 - Google Patents
高電圧絶縁ゲート型電力用半導体装置およびその製造方法 Download PDFInfo
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
- H01L29/70—Bipolar devices
- H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
- H01L29/739—Transistor-type devices, i.e. able to continuously respond to applied control signals controlled by field-effect, e.g. bipolar static induction transistors [BSIT]
- H01L29/7393—Insulated gate bipolar mode transistors, i.e. IGBT; IGT; COMFET
- H01L29/7395—Vertical transistors, e.g. vertical IGBT
- H01L29/7396—Vertical transistors, e.g. vertical IGBT with a non planar surface, e.g. with a non planar gate or with a trench or recess or pillar in the surface of the emitter, base or collector region for improving current density or short circuiting the emitter and base regions
- H01L29/7397—Vertical transistors, e.g. vertical IGBT with a non planar surface, e.g. with a non planar gate or with a trench or recess or pillar in the surface of the emitter, base or collector region for improving current density or short circuiting the emitter and base regions and a gate structure lying on a slanted or vertical surface or formed in a groove, e.g. trench gate IGBT
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
- H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/26—Bombardment with radiation
- H01L21/263—Bombardment with radiation with high-energy radiation
- H01L21/265—Bombardment with radiation with high-energy radiation producing ion implantation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
- H01L29/08—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
- H01L29/0804—Emitter regions of bipolar transistors
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/40—Electrodes ; Multistep manufacturing processes therefor
- H01L29/41—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions
- H01L29/423—Electrodes ; Multistep manufacturing processes therefor characterised by their shape, relative sizes or dispositions not carrying the current to be rectified, amplified or switched
- H01L29/42312—Gate electrodes for field effect devices
- H01L29/42316—Gate electrodes for field effect devices for field-effect transistors
- H01L29/4232—Gate electrodes for field effect devices for field-effect transistors with insulated gate
- H01L29/42356—Disposition, e.g. buried gate electrode
- H01L29/4236—Disposition, e.g. buried gate electrode within a trench, e.g. trench gate electrode, groove gate electrode
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L29/00—Semiconductor devices adapted for rectifying, amplifying, oscillating or switching, or capacitors or resistors with at least one potential-jump barrier or surface barrier, e.g. PN junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
- H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
- H01L29/66007—Multistep manufacturing processes
- H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
- H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
- H01L29/66234—Bipolar junction transistors [BJT]
- H01L29/66325—Bipolar junction transistors [BJT] controlled by field-effect, e.g. insulated gate bipolar transistors [IGBT]
- H01L29/66333—Vertical insulated gate bipolar transistors
- H01L29/66348—Vertical insulated gate bipolar transistors with a recessed gate
Definitions
- the present invention relates to a power semiconductor device, and more particularly to a high-voltage insulated gate power semiconductor device with low conduction loss and a method for manufacturing the same.
- IGBTs Insulated Gate Bipolar Transistors
- FIG. 1 shows the structure of the IGBT.
- the structure of the IGBT is selectively formed on the surface side of the low-concentration N-type layer (N base layer 1), and trenches 2 and 3 having a wide space and a narrow space alternately, and a trench 2 , 3, gate insulating films 4 and 5 formed on the surface, gate electrodes (control electrodes) 6 and 7 made of polysilicon formed inside the gate insulating films 4 and 5, and adjacent trenches having a narrow interval P base layer (P well layer) 8 selectively formed therebetween, high-concentration N source layer 9 selectively formed on the surface of P base layer 8, P base layer 8 and N source layer 9 And a first main electrode (emitter electrode 10) connected to both of the first and second electrodes.
- a MOS transistor structure is formed on the surface of the N source layer 9, the P base layer 8, and the N base layer 1, and a P-type layer having a depth similar to that of a trench between adjacent trenches with a wide interval ( The P-type layer 11) whose potential is not fixed is formed in a state where it is not connected to the emitter electrode 10 or is connected to the emitter electrode 10 with a high resistance.
- the IGBT structure is uniformly formed on the back surface side of the N base layer 1, and has an N buffer layer 12 having a higher impurity concentration than the N base layer 1, and is uniformly formed on the surface of the N buffer layer 12.
- a high-concentration P-type layer (P emitter layer 13) and a second main electrode (collector electrode 14) uniformly formed on the surface of the P emitter layer 13 are provided.
- Patent Document 1 As for the IGBT having a trench structure, various proposals and studies have been made as shown in Patent Document 1 and Non-Patent Documents 1 to 9.
- the thickness of the trench gate structure and the impurity diffusion layer is about 5 ⁇ m, which is deeper than the normal LSI process. For this reason, there has been a problem that it takes time for a structure forming process, for example, an RIE (Reactive (Ion Etching) etching process in a trench gate and a thermal diffusion process in forming a diffusion layer. Further, as described above, if the trench structure is formed deeply in the wafer, the wafer is warped, and it is difficult to increase the diameter of the wafer, which is indispensable for improving the mass productivity.
- RIE reactive (Ion Etching)
- the wafer thickness has been reduced to about 100 ⁇ m for higher performance, and the trend toward thinner layers continues.
- the trench gate and the diffusion layer are formed deeply into the wafer, it is difficult to further reduce the thickness.
- FIGS. 10 (a-1) and 10 (a-2) a P-type in which the potential which is the surface structure of the IGBT is not fixed to the semiconductor substrate 20 to be the N base layer 1 of about 400 ⁇ m to 600 ⁇ m.
- the layer 11, the P base layer 8, the N source layer 9, the gate insulating films 4 and 5, and the emitter electrode 10 are produced.
- the P-type layer 11 is produced using boron
- the N source layer 9 is produced using phosphorus and arsenic.
- the gate insulating films 4 and 5 are formed using a thermal oxide film, a CVD oxide film, polyimide, or the like.
- the emitter electrode 10 is made of AlSi or Ti—Al.
- B As shown in FIGS. 10 (b-1) and 10 (b-2), the semiconductor substrate 20 is turned over, a protective tape 30 is applied to the back surface, and the semiconductor substrate 20 is ground to 100 ⁇ m to 150 ⁇ m by grinding with a grinder and wet etching. Thin to the extent.
- C As shown in FIGS. 10 (c-1) and 10 (c-2), the back surface structure of the IGBT is formed by an impurity ion implantation step and a subsequent short time annealing (several tens of milliseconds to several seconds). An N buffer layer 12 and a P emitter layer 13 are formed.
- the N buffer layer 12 is formed using phosphorus, and the P emitter layer 13 is formed using boron. Since only the back surface becomes high temperature (about 1000 ° C.) by annealing, there is no change in the structure of the front surface IGBT.
- a collector electrode 14 (for example, made of Ai-Ni-Au) is attached.
- the protective tape 30 is peeled off. Then, sintering is performed at about 400 ° C.
- the present invention provides a high-performance, high-mass-productive high-voltage insulated gate power semiconductor device (IGBT) that can shorten the time for forming a trench gate on a wafer, and can cope with the thinning and large diameter of the wafer. And it aims at providing the manufacturing method.
- IGBT insulated gate power semiconductor device
- the present invention A low concentration first conductivity type base layer; A plurality of trenches selectively formed on the surface side of the low-concentration first conductivity type base layer so as to alternately have wide intervals and narrow intervals; A gate insulating film formed on the surface of the trench; A gate electrode formed inside the gate insulating film; A second conductivity type base layer selectively formed between adjacent trenches at a narrow interval; A high-concentration first conductivity type source layer selectively formed on the surface of the second conductivity type base layer; A first main electrode connected to both the second conductivity type base layer and the first conductivity type source layer; A MOS transistor structure formed on a surface portion of the first conductivity type source layer, the second conductivity type base layer, and the low concentration first conductivity type base layer; Between the trenches adjacent to each other at a wide interval, the first main electrode is not connected, or even if connected to the first main electrode, it is connected through a high resistance and has a depth similar to that of the trench.
- a high voltage insulated gate power semiconductor device having a second main electrode formed on the surface of the second conductivity type emitter layer The width S of the mesa region, the trench depth D T , the gate insulating film thickness T ox , and the gate drive voltage V ge , which are structural parts including the gate insulating film of the trench and the part where the MOS transistor structure is formed,
- the reference structure varies depending on the manufacturer.
- the trench depth DT is 5 to 6 ⁇ m
- the distance between the centers of adjacent trenches is 3 to 4 ⁇ m
- the overall cell width 2W is 15 ⁇ m.
- the gate drive voltage V ge in the conductive state of the power semiconductor device having the reference structure of ⁇ 20 ⁇ m is 15V.
- Some manufacturers use a square structure instead of stripes for the trench structure, so consider the above numbers in terms of area ratio. That is, of the area sandwiched between the centers of the trenches, the area ratio between the portion where the emitter electrode and the contact are present and the portion where the contact is present even if there is no contact is 1: 4 to 1: 6. Degree.
- the scale ratio k is 3 or more, preferably 5 or more.
- the trench depth DT is 3 ⁇ m or less
- the average value of the mesa width 2S of the silicon portion sandwiched between two adjacent trenches is 2 ⁇ m or less
- the gate oxide film thickness T ox is 333 nm.
- the value obtained by dividing the average value of the impurity concentration gradient of the second conductivity type emitter layer by the total impurity amount of the second conductivity type emitter layer is the second conductivity type layer or the second conductivity type in which the potential is not fixed. It is characterized in that it is lower than the value obtained by dividing the average value of the impurity concentration gradient of the mold base layer by the total amount of impurities.
- the slope of the impurity concentration corresponds to the thermal history in which the impurities are diffused.
- the semiconductor structure on the back surface side is manufactured first, and then the IGBT structure on the front surface side is manufactured later. As a result, the slope value of the impurity concentration of the semiconductor device is on the back surface side than the front surface structure. The structure is lower.
- the thickness of the second conductivity type emitter layer formed on the back surface side of the low concentration first conductivity type base layer is 1 ⁇ m or less and 10 nm or more.
- Such thin first conductivity type buffer layer and second conductivity type emitter layer can be fabricated by short-time annealing.
- the method of manufacturing the high voltage insulated gate power semiconductor device of the present invention first, the first conductivity type buffer layer and the second conductivity type emitter layer on the back side of the low concentration first conductivity type base layer are formed, and then A surface structure including a trench on the surface side of the low-concentration first conductivity type base layer and a MOS transistor structure is formed.
- Such a manufacturing process makes it possible to manufacture a high-performance (low-loss) IGBT with a small number of steps and a high yield.
- the manufacturing method of the present invention makes it possible to manufacture a high performance (low loss) IGBT with a small number of steps and a high yield.
- FIG. 4 is a structural diagram showing a current flow in a trench gate type IGBT.
- FIG. 2 is a structural diagram showing a contrast between miniaturization of only a main part according to the present invention and simple miniaturization by a conventional method, in which (a) is a basic form, and (b) and (c) are miniaturization of a main part according to the present invention (B ′) and (c ′) show the case of simple miniaturization by the conventional method. It is a graph which shows the Jc-Vce characteristic by calculation when changing the scale ratio k of refinement
- FIG. 1 It is a graph which shows the change of the collector current with respect to the collector-emitter voltage at the time of current conduction, (a) shows the case of miniaturization of the main part according to the present invention, and (b) shows the case of simple miniaturization by the conventional method. is there. It is a graph which shows the accumulation
- FIG. 1 is a manufacturing process diagram showing a first embodiment of a manufacturing method of the present invention, wherein (a-1) and (b-1) are front perspective views, and (a-2) and (b-2) are enlarged sectional views.
- FIG. 5 is a manufacturing process diagram showing a second embodiment of the manufacturing method of the present invention, wherein (a-1) to (d-1) are front perspective views, and (a-2) to (d-2) are enlarged sectional views.
- FIG. 6 is a graph showing potential-collector current characteristics of a gate electrode with respect to a change in scale ratio k when P-type polysilicon is used.
- FIG. 7 is a manufacturing process diagram showing an example of a conventional IGBT manufacturing method, wherein (a-1) to (d-1) are front perspective views, and (a-2) to (d-2) are enlarged sectional views.
- the first conductivity type is N type and the second conductivity type is P type.
- the first conductivity type is P type and the second conductivity type is N type. It can also be a type.
- FIG. 2 modeling of the injection efficiency on the cathode side was performed based on the structure parameters of the trench gate type IGBT. In this model, an electron current flowing from a MOS (Metal Oxide Semiconductor) gate is divided into two paths in a mesa region between the p base layer 8 and the N base layer 1. That is, the current density is represented by J n mesa and J p mesa .
- MOS Metal Oxide Semiconductor
- J n mesa and J p mesa are modeled as follows. However, it is assumed that electrons and holes diffuse one-dimensionally. Conductivity modulation occurs due to conductivity modulation, and the density of electrons and holes is kept approximately the same. As a result, the following differential equation which is an ambipolar diffusion type is obtained.
- ⁇ p and ⁇ n are the hole mobility and the electron mobility
- k is the Boltzmann constant
- T is the absolute temperature
- dn / dx is the gradient of the electron and hole density.
- ⁇ acc is the mobility of electrons in the electron storage layer formed on the side surface of the trench gate when a gate voltage is applied
- Q acc is the charge density per unit area of the electron storage layer
- d ⁇ n / dx represents the inclination of the electron potential (electron pseudo-Fermi potential) in the direction along the electron storage layer.
- W is a cell width half pitch
- S is a P base layer (mesa width) half width
- Equation (5) is obtained from equations (1) to (4).
- q is the elementary charge
- ⁇ n is the electron injection efficiency
- D p is the depth of the P-type layer 11.
- Expression (5) is a basic expression of the scaling law.
- the scaling laws of the present invention are summarized in Table 1. This law is logically derived from equation (5). Equation (5) shows that the scaled device has the same injection efficiency under the following conditions.
- the dn / dx of the mesa portion increases in inverse proportion to the reduction of the P base layer half width S, and the depth (D T ⁇ D P ) of the trench extending from the P base layer 8 is S
- the carrier density under the trench does not change even if it is proportionally shallow.
- the density of carriers (electrons and holes) that conduct current reduces the main part of the IGBT (the part where the MOS channel is formed between two trenches), and the gate voltage is the square of k.
- the carrier density does not change under the condition that the electric field of the gate insulating film is reduced in inverse proportion to k as the electric field of the gate insulating film is reduced.
- E ox ′ E ox may be used here.
- the left side of is not a constant, but grows as it shrinks.
- FIG. 3 shows a comparison between miniaturization of only the main part according to the present invention and simple miniaturization by a conventional method.
- (a) shows the basic form
- (b) and (c) show the case of miniaturization of the main part according to the present invention
- (b ') and (c') show the case of simple miniaturization by the conventional method.
- ⁇ 0 is the dielectric constant of vacuum
- ⁇ Si is the relative permittivity of silicon
- C ox is the capacitance per unit area of the MOS structure of the gate
- N A is the P base layer (P commonly referred to in the MOS structure)
- ⁇ s is the surface potential.
- V th decreases. However, V th is not accurately scaled by k even if N A and ⁇ s are constant.
- FIG. 5 The J c -V ce characteristics in the case of a constant gate oxide film electric field are shown in FIG. 5 comparing the case of miniaturization of only the main part of the present invention (a) and the case of simple miniaturization by the conventional method (b). Show. As shown to (a), Vce (sat) becomes small by scale-down. On the other hand, in the case of (b), it can be seen that V ce (sat) increases as the scale down, and the loss increases.
- the carrier distribution in the N-Base in the on state is shown in FIG. 6 comparing the case (a) where only the main part of the present invention is miniaturized and the case (b) where simple miniaturization is performed by the conventional method.
- the carrier density of the cathode side is increasing by the scale-down. That is, high ⁇ n and low V ce (sat) are obtained by scaling down in a shallow trench.
- the accumulated carrier density decreases in the shallow trench due to the scale down.
- the carrier accumulation can be increased by the shallow trench gate and the shallow doping structure by the scaling law of the trench gate IGBT.
- the scale-down of the trench IGBT can be manufactured using a wafer having a large diameter (large diameter wafer) with improved device performance by reducing the trench depth, thermal history, doping depth, and oxide film thickness.
- the collector voltage drop is very small due to a scaling factor that does not increase the gate oxide field strength. Therefore, the scaling law of the present invention increases the possibility of application to mass production technology using a CMOS process.
- the scale ratio is 5 or less, the trench depth is reduced to about 1 ⁇ m and the thickness of the gate insulating film is reduced to about 20 nm, so that almost no thermal process is required during the manufacturing process, and defects in the wafer and carrier life are reduced. It is possible to provide an IGBT with less time loss and less conduction loss.
- the wafer does not warp, it is possible to manufacture the IGBT with a large-diameter wafer, and there is an advantage that the productivity is remarkably improved.
- the N buffer layer 12 and the P emitter layer 13 which are the back surface structure of the semiconductor substrate 20 having a thickness of about 100 ⁇ m to 150 ⁇ m are formed in a short time ( The film is formed by annealing. Thereafter, a collector electrode 14 as a back electrode is attached.
- the thickness of the P emitter layer 13 is set to 1 ⁇ m or less, which is about the depth that can be formed by short-time annealing.
- FS-IGBT field stop IGBT
- the back surface structure does not require a reduction in carrier lifetime, there is an advantage that a device can be manufactured with high-quality crystals.
- the formation of the back surface structure has a manufacturing problem. That is, while making the diffusion layer on the back surface very thin, the effect of suppressing the injection of holes from the P emitter is obtained, while the formation of the diffusion layer needs to be performed in a very low thermal process (low temperature, short time). It was necessary to carry out after the formation of the surface structure (diffusion layer up to 5-6 ⁇ m) of a high thermal process (high temperature, long time). For this reason, since the surface once formed is inserted into the manufacturing apparatus, various yield deterioration such as surface damage has been a problem.
- the diffusion layer, the gate insulating films 4 and 5, and the gate electrodes 6 and 7, which are surface structures, are produced.
- a P-type layer 11 whose potential is not fixed is made using boron, and an N source layer 9 is made using phosphorus and arsenic.
- the gate insulating films 4 and 5 are formed using a thermal oxide film, a CVD oxide film, polyimide, or the like.
- the gate electrodes 6 and 7 are made of AlSi or Ti—Al. Formation of the diffusion layer uses high acceleration ion implantation (several hundred keV) and short-time annealing (about 1000 ° C.).
- the emitter electrode 10 is formed by sintering at about 400 ° C.
- the thickness of the P-type layer 11 whose potential is not fixed is set to 1.5 ⁇ m or less because the depth of implantation by ion implantation is about 1 ⁇ m. Conventionally, this thickness is deeper than this, but this thinness is made possible by high acceleration ion implantation.
- the thermal process of the front surface process is lower than that of the back surface process, or the surface also uses a short time annealing or the like, so that the heat transfer to the back surface is limited and the surface process does not affect the back surface structure.
- the surface structure is about 1 ⁇ m or less, high acceleration ion implantation, or ion implantation into a portion where grooves are selectively formed by a shallow trench, and a very low thermal history when short-time annealing is used. I can do it. As a result, it is possible to construct a process with high manufacturing efficiency in which the back surface structure is manufactured first and the surface is formed later.
- FIG. (A) As shown in FIGS. 8 (a-1) and (a-2), the N buffer layer 12 and the P emitter layer 13 which are the back surface structure of the semiconductor substrate 20 of about 100 ⁇ m to 150 ⁇ m are formed in a short time (several tens of milliseconds). It is formed by annealing. Thereafter, a collector electrode 14 as a back electrode is attached.
- the thickness of the P emitter layer 13 is set to 1 ⁇ m or less, which is about the depth that can be formed by short-time annealing.
- the base substrate 40 is attached.
- a quartz wafer, a silicon wafer, ceramic, polysilicon, or the like can be considered.
- an oxide film, a resin, or the like can be used.
- the diffusion layer, the gate insulating films 4 and 5, and the gate electrodes 6 and 7, which are surface structures, are produced.
- a P-type layer 11 whose potential is not fixed is made using boron, and an N source layer 9 is made using phosphorus and arsenic.
- the gate insulating films 4 and 5 are formed using a thermal oxide film, a CVD oxide film, polyimide, or the like.
- the gate electrodes 6 and 7 are made of AlSi or Ti—Al. Formation of the diffusion layer uses high acceleration ion implantation (several hundred keV) and short-time annealing (about 1000 ° C.). In order to avoid high temperature and long time, it is desirable to use a CVD film as the oxide film.
- the emitter electrode 10 is formed by sintering at about 400 ° C. (D) As shown in FIGS. 8D-1 and 8D-2, the base substrate 40 is peeled off.
- the manufacturing method according to the second embodiment when a wafer (semiconductor substrate 20) is very thin or a large-diameter wafer, the wafer is cracked, warped, or the like, and the process is focused on photolithography.
- the base substrate 40 is pasted in the process, and the number of processes is increased as compared with the first embodiment, but the yield is improved.
- the case where a back surface side electrode (collector electrode 14) is attached last is also considered.
- the manufacturing process of the IGBT of the above embodiment is merely an example.
- the first and second embodiments Even when the final N base layer thickness is reduced to about 40-100 ⁇ m using the method described in detail, the effect of enabling high performance and mass production can be obtained.
- polysilicon is used as the material of the gate electrodes 6 and 7 in the trenches 2 and 3, but P-type polysilicon is used when the scale ratio k is 5 or more. desirable.
- N-type polysilicon is used to reduce the resistance of the electrode material.
- N-type polysilicon has a lower resistance than P-type polysilicon and is generally used for the gate electrode of an IGBT. As shown in FIG. 9, N-type polysilicon has a built-in positive built-in voltage, and the voltage is generally about 0.5 to 0.6V.
- the scale ratio k is increased, for example, when the thickness of the gate insulating film is 20 nm or less, even if 0 V is applied to the gate terminal due to an inherent built-in voltage, the gate electrode inside the element has a positive value corresponding to the built-in voltage. This voltage induces some electrons at the P base interface.
- the scale ratio k is 5 or more, and the increase in the collector current (leakage current) in the OFF state at the gate voltage 0 V is an increase in the scale ratio k. Appears with.
- N-type polysilicon is used for the gate electrode, the off state cannot be maintained by the leakage current unless the gate driving circuit applies a negative voltage to the gate terminal. This becomes a problem especially at high temperatures.
- the gate charge is reduced when the scale ratio k is increased.
- the increase in material resistance is not a problem.
- P-type polysilicon a leak current (a minute current due to electrons passing through the N emitter, the P base surface, and the N base) through the channel of the MOS structure can be reduced due to the negative built-in voltage.
- the leakage current when the gate-emitter voltage V GE is 0 V can be reduced. As a result, there is an effect that a negative bias is not required in gate driving, and the gate driving circuit is simplified.
- a gate drive circuit can be configured with an IC configured with CMOS, and a gate drive IC can be provided at low cost. It becomes possible.
- the gate insulating films 4 and 5 are made of oxides such as hafnium (Hf), zirconium (Zr), aluminum (Al), and titanium (Ti), or high dielectric constant gate insulating films such as silicate compounds thereof.
- the scale ratio k is 10 or more, the leakage current due to the tunnel current passing through the gate insulating film can be greatly reduced.
- the time for forming the trench gate on the wafer is short, and the high-voltage insulated gate type with high productivity that can cope with the thinning and large diameter of the wafer.
- a power semiconductor device can be provided.
- the manufacturing method of the present invention makes it possible to manufacture a high performance (low loss) IGBT with a small number of steps and a high yield.
- the surface of the IGBT is thinned so that the fine LSI process can be performed simultaneously with the IGBT process, and the IGBT control circuit is the same. It is also possible to configure on a chip.
- the present invention can be applied not only to a vertical IGBT but also to a horizontal IGBT used in a power IC.
- the present invention can be suitably used for IGBT and other semiconductor manufacturing technologies as a miniaturization technology that can cope with future wafer diameter increase and thinning.
Abstract
Description
(a)図10(a-1),(a-2)に示すように、400μmから600μm程度の、Nベース層1となる半導体基板20に、IGBTの表面構造である電位が固定されないP型層11、Pベース層8、Nソース層9、ゲート絶縁膜4,5、エミッタ電極10を作製する。P型層11はボロンを用いて作製し、Nソース層9はリン、ヒ素を用いて作製する。ゲート絶縁膜4,5は熱酸化膜、CVD酸化膜、ポリイミドなどを用いて作製する。エミッタ電極10はAlSiまたはTi-Alで形成する。
(b)図10(b-1),(b-2)に示すように、半導体基板20をひっくり返し、裏面に保護テープ30を貼り、グラインダーによる研削とウエットエッチングにより半導体基板20を100μmから150μm程度まで薄化する。
(c)図10(c-1),(c-2)に示すように、不純物イオンの注入(implantation)工程とその後の短時間(数10m秒~数秒程度)アニールによりIGBTの裏面構造であるNバッファ層12、Pエミッタ層13を形成する。Nバッファ層12はリンを用いて作成し、Pエミッタ層13はボロンを用いて作成する。アニールにより裏面のみ高温(1000℃程度)になるため、表面のIGBTの構造に変化は生じない。次いで、コレクタ電極14(例えばAi-Ni-Auなどからなる)を付ける。
(d)図10(d-1),(d-2)に示すように、保護テープ30を剥離する。その後、400℃程度でシンターをする。
裏面、表面の順に作製した場合の問題点
(i)裏面工程の自由度が損なわれるため、IGBTの高性能化、すなわち低損失化ができない。また、キャリアの高注入化に対してライフタイム制御をすると、工程が増える上に高温動作が難しくなる。
表面、裏面の順に作製した場合の問題点
(ii)工程数が増える上に、微細な表面構造がステージ、ローダーまたは保護テープに触れるため、キズ・割れ・汚染により歩留まりが低下する。
(iii)プロセス中のグラインダーによる研削で半導体基板20にダメージが入る可能性がある。
(iv)裏面平坦性が損なわれるので、面内で特性がばらつく。また裏面工程を深く形成できないため、波形振動が大きい。
(v)保護テープを貼った際に出来る凹凸のために裏面パターニングが難しい。
低濃度第1導電型ベース層と、
前記低濃度第1導電型ベース層の表面側に、広い間隔と狭い間隔を交互に有するように選択的に形成された複数のトレンチと、
前記トレンチの表面に形成されたゲート絶縁膜と、
前記ゲート絶縁膜の内側に形成されたゲート電極と、
前記狭い間隔で隣り合うトレンチ間に選択的に形成された第2導電型ベース層と、
前記第2導電型ベース層の表面に選択的に形成された高濃度の第1導電型ソース層と、
前記第2導電型ベース層と第1導電型ソース層の双方に接続する第一の主電極と、
前記第1導電型ソース層と、前記第2導電型ベース層と、前記低濃度第1導電型ベース層の表面部に形成されたMOSトランジスタ構造と、
前記広い間隔で隣り合うトレンチ間に、前記第一の主電極と接続しないように、あるいは前記第一の主電極と接続しても高抵抗を介して接続され、前記トレンチと同程度の深さを有する、電位が固定されない第2導電型層と、
前記低濃度第1導電型ベース層の裏面側に一様に形成され、該低濃度第1導電型ベース層よりも不純物濃度の高い第1導電型バッファ層と、
該第1導電型バッファ層の表面に一様に形成された高濃度の第2導電型エミッタ層と、
該第2導電型エミッタ層の表面に形成された第2の主電極と
を有する高電圧絶縁ゲート型電力用半導体装置において、
前記トレンチのゲート絶縁膜と前記MOSトランジスタ構造が形成される部分を含む構造部分であるメサ領域の幅S、トレンチ深さDT、ゲート絶縁膜厚Tox、ゲート駆動電圧Vgeが、基準となる構造に対する小型化のスケール比率kの逆数となる関係を有し、セル幅2Wは前記基準となる構造と同じである高電圧絶縁ゲート型電力用半導体装置である。
また、本発明の製造方法により、少ない工程と高い歩留まりで高性能(低損失)IGBTを作製することが可能になる。
図2に示すように、トレンチゲート型IGBTの構造パラメータによりカソード側での注入効率のモデル化を行った。このモデルでは、MOS(Metal Oxide Semiconductor)ゲートから流れる電子電流は、pベース層8とNベース層1の間のメサ領域で2つの経路に分けられる。すなわち、Jn mesaとJp mesaで示される電流密度の電流である。
Jn mesaとJp mesaは次のようにモデル化される。ただし、電子、ホールは一次元的に拡散すると仮定する。伝導度modulationによって導電変調が起こり、電子およびホールの密度はほぼ同じに保たれる。結果として、アンバイポーラ拡散式である次の微分方程式が得られる。
また、電子蓄積層(トレンチゲート側壁絶縁膜表面で、Nベース層1と接している面に形成される)における電子電流式は次式で表される。
本発明のスケーリング則を表1に集約している。この法則は(5)式から論理的に導かれる。(5)式は、縮小デバイス(scaled device)は以下の条件下で同じ注入効率になることを示す。
k=1とk=2はよく一致しているが、k=3~5は飽和電流が小さくなっている。これはスケーリングにより、下式に示すゲートの閾値電圧Vthが移動したためである。
(a)図7(a-1),(a-2)に示すように、100μmから150μm程度の厚みの半導体基板20の裏面構造であるNバッファ層12、Pエミッタ層13を、短時間(数10m秒~数秒程度)アニールにより形成する。その後、裏面電極であるコレクタ電極14を付ける。ここで、Pエミッタ層13の厚さは、短時間アニールで形成できる深さ程度の1μm以下とする。
このようなIGBT裏面構造は、すでに薄ウエハIGBTやフィールドストップIGBT(FS-IGBT)として、実用化されている。
本方法は従来に対し次のような利点がある。
従来、Nベース中のキャリアが多いことによるスイッチング特性の悪化を、高エネルギー電子、プロトン、ヘリウムなどを照射することによる、ウエハ内部のキャリアライフタイムの低減により、Nベース中での電子とホールの再結合を促進し、内部キャリアを少なくする方法により改善していた。しかし、このような照射プロセスはコストが高いだけではなく、不必要に半導体結晶欠陥を生成し、特性の悪化や信頼性の低下が起こっていた。とくにプロトン照射やヘリウム照射は、局所的にキャリアライフタイムを低減することで大きな効果を挙げたが、高温でのリーク電流の増加、信頼性の悪化、照射およびアニールによるプロセスコストの増加が問題であった。前記裏面構造は、キャリアライフタイムの低減が必要無いため、良質の結晶でデバイスを製造できるなど利点がある。一方で本裏面構造形成は製造面の課題があった。即ち、裏面の拡散層を非常に薄くすることでPエミッタからのホールの注入を抑える効果を得ている一方、拡散層の形成は非常に低い熱工程(低温、短時間)で行う必要があり、高い熱工程(高温、長時間)の表面構造(5-6μmまでの拡散層)の形成後に行う必要があった。このため一度形成した表面を下にして製造装置に挿入するために、表面ダメージなど様々な歩留まり悪化が問題となっていた。
この製造工程において、金属スパイクと汚染を避けるために、裏面側電極(コレクタ電極14)を最後に付けるケースも考えられる。また、裏面構造形成工程の際に、テープで表面側を保護することも考えられる。
(a)図8(a-1)(a-2)に示すように、100μmから150μm程度の半導体基板20の裏面構造であるNバッファ層12、Pエミッタ層13を、短時間(数10m秒~数秒程度)アニールにより形成する。その後、裏面電極であるコレクタ電極14を付ける。ここで、Pエミッタ層13の厚さは、短時間アニールで形成できる深さ程度の1μm以下とする。
(c)図8(c-1),(c-2)に示すように、表面構造である拡散層、ゲート絶縁膜4,5、ゲート電極6,7を作製する。拡散層は、ボロンを用いて電位が固定されないP型層11を作製し、リン、ヒ素を用いてNソース層9を作製する。なお、P型層11を付加することにより、阻止状態(オフ状態)での耐圧を改善することができる。ゲート絶縁膜4,5は熱酸化膜、CVD酸化膜、ポリイミドなどを用いて作製する。ゲート電極6,7はAlSiまたはTi-Alで形成する。拡散層の形成は高加速イオン注入(数100keV)と短時間アニール(約1000℃)を用いる。高温・長時間を避けるため、酸化膜はCVD膜を用いることが望ましい。エミッタ電極10の形成には、約400℃でのシンターも行う。
(d)図8(d-1),(d-2)に示すように、台基板40を剥がす。
なお、この製造工程において、金属スパイクと汚染を避けるために、裏面側電極(コレクタ電極14)を最後に付けるケースも考えられる。
以上の実施の形態のIGBTの製造プロセスについては一例であり、例えば厚い半導体基板を用いて作製し最終的なNベース層厚が500μmになるような場合でも、第1および第2の実施形態で詳述した方法を用いて最終的なNベース層厚が40-100μm程度に薄型化された場合でも、高性能化と量産化が可能になる効果が得られる。
N型のポリシリコンはP型のポリシリコンに比べて抵抗が低く、IGBTのゲート電極に一般的に用いられている。図9に示すように、N型のポリシリコンは正のビルトイン電圧を内在しており、電圧は約0.5~0.6V程度が一般的である。
ところがスケール比率kを大きくすると、たとえばゲート絶縁膜の厚さが20nm以下になると、内在するビルトイン電圧により、たとえゲート端子に0Vを印加しても、素子内部のゲート電極にはビルトイン電圧分の正の電圧が発生しており、この電圧により、Pベース界面に若干の電子が誘起される。図9に示すように破線の電圧(N型ポリシリコンのビルトイン電圧)ではスケール比率k=5以上で、ゲート電圧0Vでのオフ状態でのコレクタ電流(リーク電流)の増加がスケール比率kの増加とともに現れる。その結果、N型ポリシリコンをゲート電極に用いると、ゲート駆動回路がゲート端子に負の電圧を加えないと、オフ状態がリーク電流により維持できないことになる。これは特に高温の際に問題となる。
また、本発明の製造方法により、少ない工程と高い歩留まりで高性能(低損失)IGBTを作製することが可能になる。
第1の実施例、第2の実施例に共通するが、本発明ではIGBTの表面が薄くなることで微細LSIの工程をIGBTの工程と同時に行うことが可能であり、IGBTの制御回路を同一チップ上に構成することも可能である。
本発明は、縦型のIGBTのみならず、パワーICに用いられる横型のIGBTにも適用することができる。
2,3 トレンチ
4,5 ゲート絶縁膜
6,7 ゲート電極(制御電極)
8 Pベース層(Pウエル層)
9 Nソース層
10 エミッタ電極(第一の主電極)
11 電位が固定されないP型層
12 Nバッファ層
13 Pエミッタ層
14 コレクタ電極(第2の主電極)
20 半導体基板
30 保護テープ
40 台基板
Claims (14)
- 低濃度第1導電型ベース層と、
前記低濃度第1導電型ベース層の表面側に、広い間隔と狭い間隔を交互に有するように選択的に形成された複数のトレンチと、
前記トレンチの表面に形成されたゲート絶縁膜と、
前記ゲート絶縁膜の内側に形成されたゲート電極と、
前記狭い間隔で隣り合うトレンチ間に選択的に形成された第2導電型ベース層と、
前記第2導電型ベース層の表面に選択的に形成された高濃度の第1導電型ソース層と、
前記第2導電型ベース層と第1導電型ソース層の双方に接続する第一の主電極と、
前記第1導電型ソース層と、前記第2導電型ベース層と、前記低濃度第1導電型ベース層の表面部に形成されたMOSトランジスタ構造と、
前記低濃度第1導電型ベース層の裏面側に一様に形成され、該低濃度第1導電型ベース層よりも不純物濃度の高い第1導電型バッファ層と、
該第1導電型バッファ層の表面に一様に形成された高濃度の第2導電型エミッタ層と、
該第2導電型エミッタ層の表面に形成された第2の主電極と
を有する高電圧絶縁ゲート型電力用半導体装置において、
前記トレンチのゲート絶縁膜と前記MOSトランジスタ構造が形成される部分を含む構造部分であるメサ領域の幅S、トレンチ深さDTが、基準となる構造に対する小型化のスケール比率kの逆数となる関係を有し、
セル幅2Wは前記基準となる構造に対し、スケール比率kの逆数となる関係よりも大きく、前記基準となる構造が、トレンチ深さDTが5~6μm、全体のセル幅2Wが15~20μmであり、前記基準となる構造を有する前記電力用半導体装置の導通状態でのスケール比率kが3以上であることを特徴とする、高電圧絶縁ゲート型電力用半導体装置。 - 前記トレンチのゲート絶縁膜と前記MOSトランジスタ構造が形成される部分を含む構造部分であるメサ領域の幅S、トレンチ深さDT、ゲート絶縁膜厚Tox、ゲート駆動電圧Vgeが、基準となる構造に対する小型化のスケール比率kの逆数となる関係を有し、
セル幅2Wは前記基準となる構造に対し、スケール比率kの逆数となる関係よりも大きくかつ基準となる幅と同じか小さく、前記基準となる構造が、トレンチ深さDTが5~6μm、隣接するトレンチの中心間距離が3~4μmで、全体のセル幅2Wが15~20μmであり、前記基準となる構造を有する前記電力用半導体装置の導通状態でのゲート駆動電圧Vgeが15Vであるとするとき、スケール比率kが3以上であることを特徴とする、請求項1記載の高電圧絶縁ゲート型電力用半導体装置。 - 前記スケール比率kが3以上であり、第2導電型エミッタ層の不純物濃度の傾斜の平均値を第2導電型エミッタ層の不純物総量で割った値が、前記電位が固定されない第2導電型層や第2導電型ベース層の、不純物濃度の傾斜の平均値をそれぞれの不純物総量で割った値より低いことを特徴とする請求項1または2記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記スケール比率kが5以上であることを特徴とする、請求項1から3のいずれかの項に記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記第2導電型エミッタ層の厚みが1μm以下であり、前記第2導電型エミッタ層を形成する不純物イオンの注入工程が、前記第2導電型ベース層および前記電位が固定されない第2導電型層を形成する不純物イオンの注入工程より前にあることを特徴とする請求項1から4のいずれかの項に記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記低濃度第1導電型ベース層の裏面側に形成される前記第2導電型エミッタ層の厚みが、1μm以下10nm以上であることを特徴とする、請求項1から5のいずれかの項に記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記トレンチ内部のゲート電極がP型ポリシリコンであることを特徴とする請求項1記載の高電圧絶縁ゲート型電力用半導体装置。
- 請求項6記載の高電圧絶縁ゲート型電力用半導体装置を製造するに際し、最初に、低濃度第1導電型ベース層の裏面側の第1導電型バッファ層と第2導電型エミッタ層を形成し、その後、前記低濃度第1導電型ベース層の表面側のトレンチおよびMOSトランジスタ構造を含む表面構造を形成することを特徴とする高電圧絶縁ゲート型電力用半導体装置の製造方法。
- 低濃度第1導電型ベース層と、
前記低濃度第1導電型ベース層の表面側に、広い間隔と狭い間隔を交互に有するように選択的に形成された複数のトレンチと、
前記トレンチの表面に形成されたゲート絶縁膜と、
前記ゲート絶縁膜の内側に形成されたゲート電極と、
前記狭い間隔で隣り合うトレンチ間に選択的に形成された第2導電型ベース層と、
前記第2導電型ベース層の表面に選択的に形成された高濃度の第1導電型ソース層と、
前記第2導電型ベース層と第1導電型ソース層の双方に接続する第一の主電極と、
前記第1導電型ソース層と、前記第2導電型ベース層と、前記低濃度第1導電型ベース層の表面部に形成されたMOSトランジスタ構造と、
前記広い間隔で隣り合うトレンチ間に、前記第一の主電極と接続しないように、あるいは前記第一の主電極と接続しても高抵抗を介して接続され、前記トレンチと同程度の深さを有する、電位が固定されない第2導電型層と、
前記低濃度第1導電型ベース層の裏面側に一様に形成され、該低濃度第1導電型ベース層よりも不純物濃度の高い第1導電型バッファ層と、
該第1導電型バッファ層の表面に一様に形成された高濃度の第2導電型エミッタ層と、
該第2導電型エミッタ層の表面に形成された第2の主電極と
を有する高電圧絶縁ゲート型電力用半導体装置において、
前記トレンチのゲート絶縁膜と前記MOSトランジスタ構造が形成される部分を含む構造部分であるメサ領域の幅S、トレンチ深さDT、ゲート絶縁膜厚Tox、ゲート駆動電圧Vgeが、基準となる構造に対する小型化のスケール比率kの逆数となる関係を有し、セル幅2Wは前記基準となる構造と同じであり、前記基準となる構造が、トレンチの中心で挟まれた面積のうち、エミッタ電極およびコンタクトがある部分と、コンタクトがないかあっても高抵抗にコンタクトされている部分との面積比が、1:4~1:6程度であり、前記基準となる構造を有する前記電力用半導体装置の導通状態でのゲート駆動電圧Vgeが15Vであるとするとき、スケール比率kが3以上であることを特徴とする、高電圧絶縁ゲート型電力用半導体装置。 - 前記スケール比率kが3以上であり、第2導電型エミッタ層の不純物濃度の傾斜の平均値を第2導電型エミッタ層の不純物総量で割った値が、前記電位が固定されない第2導電型層や第2導電型ベース層の、不純物濃度の傾斜の平均値をそれぞれの不純物総量で割った値より低いことを特徴とする請求項9記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記スケール比率kが5以上であることを特徴とする、請求項9または10に記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記第2導電型エミッタ層の厚みが1μm以下であり、前記第2導電型エミッタ層を形成する不純物イオンの注入工程が、前記第2導電型ベース層および前記電位が固定されない第2導電型層を形成する不純物イオンの注入工程より前にあることを特徴とする請求項9から11のいずれかの項に記載の高電圧絶縁ゲート型電力用半導体装置。
- 前記低濃度第1導電型ベース層の裏面側に形成される前記第2導電型エミッタ層の厚みが、1μm以下10nm以上であることを特徴とする、請求項9から12のいずれかの項に記載の高電圧絶縁ゲート型電力用半導体装置。
- 請求項13記載の高電圧絶縁ゲート型電力用半導体装置を製造するに際し、最初に、低濃度第1導電型ベース層の裏面側の第1導電型バッファ層と第2導電型エミッタ層を形成し、その後、前記低濃度第1導電型ベース層の表面側のトレンチおよびMOSトランジスタ構造を含む表面構造を形成することを特徴とする高電圧絶縁ゲート型電力用半導体装置の製造方法。
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