JP3812379B2 - MOS type semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device having a high withstand voltage and a large current capacity that can be applied to MOSFET (insulated gate field effect transistor), IGBT (conductivity modulation transistor), bipolar transistor, diode and the like.
[0002]
[Prior art]
In general, semiconductor elements can be broadly classified into a horizontal structure having electrode portions on one side and a vertical structure having electrode portions on both sides. For example, FIG. 10 shows an SOI (Silicon on Insulator) -MOSFET having a lateral structure. This SOI-MOSFET structure is an n-channel MOSFET offset gate structure. A p-type channel diffusion layer 7 formed on the insulating film 6 on the semiconductor substrate 5 and a gate insulation on the channel diffusion layer 7. The gate electrode 11 with a field plate formed through the film 10 and the n formed on one end side of the gate electrode 11 in the channel diffusion layer 7⁺N formed in a position spaced from the other end of the source region 8 of the mold and the gate electrode 11⁺Type drain region 9, n-type low concentration drain region (drain / drift region) 90 extending between the drain and gate, and thick insulating film 12 formed on this low concentration drain region 90.
[0003]
The portion of the lightly doped drain region 90 functions as a drift region in which carriers are caused to flow by an electric field when the MOSFET is in an on state, and is depleted when the MOSFET is in an off state to relax the electric field strength and increase the breakdown voltage. Increasing the impurity concentration of the low-concentration drain region 90 and shortening the current path length of the region 90 have the effect of lowering the substantial on-resistance (drain-source resistance) of the MOSFET because the drift resistance decreases. Although connected, conversely, the drain-channel depletion layer proceeding from the pn junction Ja of the p-type channel diffusion layer 7 and the n-type low-concentration drain region 90 hardly spreads, and reaches the maximum (critical) electric field strength of silicon quickly. Therefore, the breakdown voltage (drain-source voltage) is lowered. That is, there is a trade-off relationship between on-resistance (current capacity) and breakdown voltage. This trade-off relationship is also known to hold in semiconductor devices such as IGBTs, bipolar transistors, and diodes.
[0004]
FIG. 11 shows another structure of a lateral structure MOSFET. FIG. 11A shows a p-channel MOSFET, p⁻N-type channel diffusion layer 3 formed on type semiconductor layer 4, gate electrode 11 with a field plate formed on channel diffusion layer 3 via gate insulating film 10, and gate electrode of channel diffusion layer 3 P formed on one end of 11⁺Type source region 18, p-type low-concentration drain region (drain / drift region) 14 in which the well end is located directly under the other end side of gate electrode 11, and a position separated from the other end of gate electrode 11. p⁺Type drain region 19 and p⁺N adjacent to the source region 18 of the mold⁺Type contact region 71 and thick insulating film 12 formed on p-type low concentration drain 14. Even in such a structure, the ON resistance and the breakdown voltage are determined in a trade-off relationship by the current path length and the impurity concentration of the well-shaped p-type low concentration drain region 14.
[0005]
FIG. 11B shows a double diffusion n-channel MOSFET, p⁻An n-type low concentration drain layer (drain / drift layer) 22 formed on the type semiconductor layer 4, a gate electrode 11 with a field plate formed on the low concentration drain layer 22 via the gate insulating film 10, A well-shaped p-type channel diffusion region 17 formed on one end side of the gate electrode 11 in the low-concentration drain layer 22, and an n-type formed in the p-type channel diffusion region 17 in a well shape⁺Type source region 8, gate electrode 11 and n spaced apart from it⁺A well-shaped p-type top layer 24 formed on the surface layer between the n-type drain region 9 and n⁺P adjacent to the source region 8 of the mold⁺And a thick insulating film 12 formed on the p-type top layer 24. Even in such a structure, the ON resistance and the breakdown voltage are determined in a trade-off relationship by the current path length of the n-type low concentration drain layer region 22 and the impurity concentration.
[0006]
However, in the structure of FIG. 11B, the n-type low concentration drain layer 22 has a lower p⁻Since the p-type top layer 24 is sandwiched between the p-type semiconductor layer 4 and the p-type top layer 24, the n-type low-concentration drain layer 22 is not only from the pn junction Ja with the p-type channel diffusion region 17 when the MOSFET is off. A depletion layer also spreads from the upper and lower pn junctions Jb and Jb. For this reason, since the low concentration drain layer 22 is depleted quickly, it has a high breakdown voltage structure. Accordingly, the impurity concentration of the low-concentration drain layer 22 can be increased, and the current capacity can be increased by reducing the on-resistance.
[0007]
On the other hand, for example, a trench gate type n-channel MOSFET shown in FIG. 12 is known as a vertical semiconductor device. In this structure, the back electrode (not shown) is in conductive contact.⁺N-type low-concentration drain layer 39 formed on type drain layer 29, and a trench gate electrode embedded in trench groove dug in the surface side of low-concentration drain layer 39 via gate insulating film 10 21, a p-type channel diffusion layer 27 formed on the surface layer of the lightly doped drain layer 39 as shallow as the depth of the trench gate electrode 21, and an n formed along the upper edge of the trench gate electrode 21⁺A type source region 18 and a thick insulating film 12 covering the gate electrode 21 are provided. In addition, single layer n⁺In place of the type drain layer 29, n⁺Mold upper layer and p⁺An n-type IGBT structure can be obtained when the two-layer structure is formed of a mold lower layer. Even in such a vertical structure, the portion of the low concentration drain layer 39 functions as a drift region that forms a drift current in the vertical direction when the MOSFET is in the on state, and is depleted and increases the breakdown voltage in the off state. Again, the on-resistance and breakdown voltage are governed by the thickness and impurity concentration of the low-concentration drain layer 39, and there is a trade-off relationship between the two.
[0008]
[Problems to be solved by the invention]
FIG. 13 is a graph showing the relationship between the ideal breakdown voltage and ideal on-resistance of a silicon n-channel MOSFET. It was assumed that the ideal breakdown voltage does not decrease the pn junction breakdown voltage due to the shape effect. It was assumed that the ideal on-resistance is so small that the resistance of the portion other than the low-concentration drain region can be ignored. (1) in FIG. 13 shows the relationship between the ideal breakdown voltage and the ideal on-resistance of the vertical n-channel MOSFET shown in FIG. In the vertical element, the direction in which the drift current flows when turned on is the same as the direction in which the depletion layer extends and spreads due to the reverse bias when turned off. Focusing only on the low-concentration drain layer 39 in FIG. 12, the ideal breakdown voltage BV at the OFF time is approximately obtained by the following equation.
BV = E_c ²ε₀ε_Siα (2-α) / 2qN_D          (1)
E_c: E_c(N_D), Impurity concentration N_DMaximum field strength of silicon at
ε₀: Dielectric constant of vacuum
ε_Si: Dielectric constant of silicon
q: Unit charge
N_D: Impurity concentration in low concentration drain region
α: coefficient (0 <α <1)
Also, the ideal on-resistance per unit area at the time of on is approximately obtained by the following equation.
R = αW / μqN_D
μ: μ (N_D), Impurity concentration N_DMobility of electrons
Where W = E_cε₀ε_Si/ QN_DSo R is
R = E_cε₀ε_Siα / μq²N_D ²                    (2)
It becomes. QN from equations (1) and (2)_DAnd using 2/3 as the optimal value of α,
R = BV²(27 / 8E_c ³ε₀ε_Siμ) (3)
Is obtained. Here, the on-resistance R appears to be proportional to the square of the breakdown voltage BV, but E_cAnd μ is N_DTherefore, (1) in FIG. 13 is actually proportional to about 2.4 to 2.6 of BV.
[0009]
(2) in FIG. 13 shows the relationship between the ideal breakdown voltage and the ideal on-resistance of a MOSFET in which the structure of the lateral MOSFET shown in FIG. In this n-channel MOSFET, the flow direction of the drift current at the time of on is lateral, whereas the direction of the depletion layer extending at the time of off is not the lateral direction from the well end but the vertical direction from the well bottom (upward direction). ) Is faster. In order to obtain a high breakdown voltage with a depletion layer extending in the vertical direction, depletion from the pn junction surface (well bottom) between the low concentration drain region 14 and the channel diffusion layer 3 to the surface of the low concentration drain layer 14 (well surface) must be performed. I must. Therefore, the maximum value of the net doping amount of the lightly doped drain region 14 is
S_D= E_cε₀ε_Si/ Q (4)
Limited to When the lateral length of the low-concentration drain region 14 is L, the ideal breakdown voltage BV is
BV = E_cLβ (5)
It becomes. However, β is an unknown coefficient (0 <β <1). The ideal on-resistance R per unit area is
R = L²/ ΜqS_D                                  (6)
Can be obtained approximately. Therefore, if L is deleted from the expressions (5) and (6) and the expression (4) is substituted,
R = BV²/ Β²E_c ³ε₀ε_Siμ (7)
[0010]
(3) in FIG. 13 shows the relationship between the ideal breakdown voltage and the ideal on-resistance of the structure of the lateral double diffusion n-channel MOSFET shown in FIG. In the structure of FIG. 11B, the p-type top layer 24 is provided in the structure of FIG. 11A, and the low concentration drain layer 22 is quickly depleted in a pinch manner by the depletion layers extending from the upper and lower sides. Net doping amount S of lightly doped drain region 22_DCan be increased up to about twice that of FIG.
S_D= 2E_cε₀ε_Si/ Q (8)
In this case, the relationship between the ideal on-resistance R and the ideal breakdown voltage BV is
R = BV²/ 2β²E_c ³ε₀ε_Siμ (9)
It becomes.
[0011]
Although (3) in FIG. 13 has a slightly improved trade-off relationship between on-resistance and withstand voltage compared to (2), it can only be set to twice as high as the current capacity and withstand voltage of the semiconductor element. The degree of design freedom is still low.
[0012]
In view of the above problems, the first problem of the present invention is to improve the structure of the drift region, thereby greatly reducing the trade-off relationship between the on-resistance and the withstand voltage, while maintaining a high withstand voltage. An object of the present invention is to provide a semiconductor device capable of increasing current capacity by reducing resistance. A second object of the present invention is to provide a manufacturing method capable of manufacturing the semiconductor device with high productivity.
[0013]
[Means for Solving the Problems]
In order to solve the above-described problem, the means taken by the present invention is to provide a drift region in a semiconductor device having a drift region that flows a drift current in an on state and depletes in an off state, such as a low concentration drain region of a MOSFET. As shown schematically in FIG. 1, a parallel split structure such as a layered structure, a fibrous structure, or a honeycomb structure is used, and is interposed between adjacent side surfaces (boundaries) of the first conductivity type split drift path region 1. Then, the second conductivity type partition region 2 for separating the pn junction is provided.
[0014]
That is, as shown in FIG. 1A, the drift region is a parallel layered structure having two or more plate-like first conductivity type (for example, n-type) divided drift path regions 1 connected in parallel to each other at least at the end portions. It has a drift path group (divided drift path aggregate) 100 and a plate-like second conductivity type (for example, p-type) partition area 2 that is interposed between the divided drift path areas 1 and 1 and separates a pn junction. . The plurality of second conductivity type partition regions 2 are connected in parallel to each other at least at the end portions.
[0015]
Further, the structure of the drift region shown in FIG. 1B is a fibrous structure, and the first conductive type (n-type) segmented drift path region 1 and the second conductive type (p-type) partition are formed. The region 2 is arranged in a checkered pattern in the cross section of the assembly.
[0016]
Furthermore, the 1st conductivity type (n-type) division | segmentation drift path | route area | region 1 shown in FIG.1 (c) has the connection part 1a in the four corners.
[0017]
As can be clearly seen in FIG. 1A, the second conductivity type that separates the pn junction along the outside of the first conductivity type split drift path region 1 at the outermost end (uppermost end or lowermost end) of the parallel drift path group 100. The side end region 2a may be provided.
[0018]
When the semiconductor device is in the on state, a drift current flows through the plurality of parallel-connected divided drift path regions 1 and 1. On the other hand, when the semiconductor device is in the off state, the first conductivity type divided drift path region 1 and the second conductivity Each depletion layer extends from the pn junction with the mold partition region 2 into the first conductivity type split drift path 1 and is depleted. Since the depletion ends spread laterally from both side surfaces of the single second conductivity type partition region 2, depletion is extremely accelerated. The second conductivity type partition region 2 is also depleted at the same time. For this reason, the semiconductor device has a high breakdown voltage, and the impurity concentration of the n-type divided drift path region 1 can be increased, so that the on-resistance can be reduced. In particular, in the present invention, the depletion ends enter both the adjacent first conductivity type divided drift path regions 1 and 1 from both side surfaces of the single second conductivity type partition region 2, and the depletion spreading to both sides is achieved. Since the end effectively acts on the divided drift path regions 1 and 1, the total occupied width of the second conductivity type partition region 2 for forming the depletion layer can be halved. The cross-sectional area of the region 1 can be increased, and the on-resistance is reduced as compared with the prior art. The occupied width of the second conductivity type partition region 2 is preferably small. The impurity concentration of the second conductivity type partition region 2 is preferably low. As the number (division number) per unit area of the first conductivity type divided drift path region 1 is increased, the trade-off relationship between the on-resistance and the withstand voltage can be greatly relaxed.
[0019]
In the present invention, the trade-off relational expression between the ideal on-resistance r and the ideal withstand voltage BV for the first conductivity type divided drift path region 1 is as follows: if the width of the second conductivity type partition region 2 is assumed to be infinitesimal, Since the ideal on-resistance r corresponds to N times the ideal on-resistance R in equation (9),
r = NR = BV²/ 2β²E_c ³ε₀ε_Siμ (10)
The relationship between the ideal on-resistance R and the ideal breakdown voltage BV of the entire parallel drift path group is
R = BV²/ 2Nβ²E_c ³ε₀ε_Siμ (11)
It becomes. Therefore, it can be seen that the larger the number of divisions N of the drift region, the more a semiconductor device with a reduced on-resistance can be realized.
[0020]
  That is, the present inventionA first conductivity type source region in the second conductivity type channel region;A drift region that flows laterally in the on state and depletes in the off stateMOS typeIn the semiconductor device, the drift region has a second conductivity interposed between a parallel drift path group having a plurality of first conductivity type divided drift path regions connected in parallel and adjacent first conductivity type divided drift path regions. The drift region is sandwiched between the insulating film on the semiconductor layer and the surface-side insulating film.The drift region and the channel region are in contactIt is characterized by being. With such a configuration, it is possible to reduce the on-resistance and increase the breakdown voltage.
[0021]
Here, it is desirable to form the insulating film on the semiconductor layer thicker than the surface-side insulating film. The drift region can be a superimposed parallel structure in which a layered first conductivity type divided drift path region and a layered second conductivity type partition region are alternately and repeatedly stacked, and this superimposed parallel structure is a semiconductor layer. It is sandwiched between the upper insulating film and the surface-side insulating film. The drift region may have a structure in which stripe-shaped first conductivity type divided drift path regions and stripe-shaped second conductivity type partition regions are alternately arranged along the surface of the insulating film on the semiconductor layer. it can.
[0022]
  Further, in the present invention, the second conductivity type side end region is formed outside the outermost first conductivity type divided drift path region of the parallel drift path group, and the length of the second conductivity type side end region is increased.SagaSecond conductivity type partition areaAnd first conductivity type split drift path areaLength ofWhenEqualIn addition, the widths of the second conductivity type partition region and the first conductivity type split drift path region are equal.It is characterized byThe ThisWith this configuration, it is possible to reduce the on-resistance and increase the breakdown voltage.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the accompanying drawings.
[0024]
Embodiment 1
2A is a plan view showing the SOI-MOSFET having a lateral structure according to the first embodiment of the present invention, and FIG. 2B is a cut showing a state cut along the line AA ′ in FIG. 2A. FIG. 2 and FIG. 2C are sectional views showing a state cut along the line BB 'in FIG.
[0025]
The structure of the SOI-MOSFET of this example is an offset gate structure of an n-channel MOSFET, similar to the structure shown in FIG. 10, and a p-type channel diffusion region formed on the insulating film 6 on the semiconductor substrate 5. 7, a gate electrode 11 with a field plate formed on the channel diffusion region 7 via the gate insulating film 10, and an n formed on one end side of the gate electrode 11 in the channel diffusion region 7⁺N formed in a position spaced from the other end of the source region 8 of the mold and the gate electrode 11⁺It has a drain region 9 of a type, a drain / drift region 190 extending between the drain and gate, and a thick insulating film 12 formed on the drain / drift region 190.
[0026]
The drain / drift region 190 in this example has a striped parallel structure in which strip-shaped n-type divided drift path regions 1 and strip-shaped p-type partition regions 2 are alternately and repeatedly arranged on a plane. One end of the plurality of n-type divided drift path regions 1 is pn-junction to the p-type channel diffusion region 7, and the other end thereof is n⁺Connected to the drain region 9 of the type, n⁺A drift path group 100 connected in parallel is formed by branching from the drain region 9 side of the mold. A stripe-shaped p-type side end region 2a is provided outside the split drift path region 1 at the outermost end of the parallel drift path group 100, and all the split drift path regions 1 are p-type semiconductor regions along the side surfaces. 2 (2a). One end of the plurality of p-type partition regions 2 is connected to the p-type channel diffusion region 7, and the other end thereof is n⁺The p-type drain region 9 is pn-junctioned and branched from the p-type channel diffusion region 7 side to be connected in parallel.
[0027]
When the MOSFET is in the on state, n is passed through the channel inversion layer 13 immediately below the gate insulating film 10.⁺Carriers (electrons) flow from the source region 8 into the plurality of n-type divided drift path regions 1, and a drift current flows due to an electric field generated by the drain-source voltage. On the other hand, in the off state, the channel inversion layer 13 immediately below the gate insulating film 10 disappears, and the pn junctions Ja, n between the n-type divided drift path region 1 and the p-type channel diffusion region 7 are caused by the drain-source voltage. A depletion layer extends from the pn junction Jb between the type division drift path region 1 and the p type partition region 2 into the n type division drift path region 1 and is depleted. The depletion end from the pn junction Ja extends in the path length direction in the n-type split drift path region 1, while the depletion end e from the pn junction Jb extends in the path width direction in the n-type split drift path region 1, and Since the depletion edge spreads from both sides, depletion becomes very fast. The p-type partition region 2 is also depleted at the same time. For this reason, the electric field strength is relaxed and the withstand voltage is increased, and accordingly, the impurity concentration of the n-type divided drift path region 1 can be increased, so that the on-resistance is reduced. In particular, in this example, since the depletion end e enters both the adjacent n-type divided drift path regions 1 and 1 from both side surfaces of the p-type partition region 2, the p-type for forming the depletion layer is formed. The total occupied width of the partition region 2 can be halved, and accordingly, the cross-sectional area of the n-type divided drift path region 1 can be increased, and the on-resistance is reduced as compared with the prior art. As the number (number of divisions) N per unit area of the n-type divided drift path region 1 is increased, the trade-off relationship between the on-resistance and the breakdown voltage can be greatly relaxed. Three or more are more prominent than two. Note that the occupied width of the p-type partition region 2 is preferably small.
[0028]
Here, assuming that the ideal breakdown voltage BV is, for example, 100 V, the impurity concentration N of the n-type divided drift path region 1_D= 3 × 10¹⁵(Cm^-3), Maximum electric field strength E of silicon_c= 3 × 10⁵(V / cm), electron mobility μ = 1000 (cm²/ V · sec), vacuum dielectric constant ε₀= 8.8 × 10^-12(C / V · m), relative dielectric constant ε of silicon_Si= 12, unit charge q = 1.6 x 10^-19(C). In the lightly doped drain region 90 shown in FIG. 10, when the length is 6.6 μm and the thickness is 1 μm, the ideal on-resistance R is 9.1 (m ohm · cm²). In contrast, in this example, when the ideal on-resistance R is calculated by setting the widths of the n-type divided drift path region 1 and the p-type partition region 2 to values of, for example, 10 μm, 1 μm, and 0.1 μm (β = 2/3, n The length of the mold-dividing drift path region 1 and the p-type partition region is assumed to be 5 μm),
When the width is 10 μm, 7.9 (m ohm · cm²)
When the width is 1 μm, 0.8 (m ohm · cm²)
When the width is 0.1 μm, 0.08 (m ohm · cm²)
Thus, when the width is 1 μm or less, a dramatic reduction in on-resistance is possible. If the width of the p-type partition region 2 is made smaller than the width of the n-type divided drift path region 1, the effect will be remarkable. The width of the n-type divided drift path region 1 and the p-type partition region is currently limited to about 0.5 μm by photolithography and ion implantation. However, with the steady progress of micromachining technology, the width dimension will be further increased in the future. Since downsizing is possible, the on-resistance can be significantly reduced.
[0029]
In particular, since the structure of the drift region in this example is a repetitive structure of striped pn on a plane, it can be formed by one photolithography, so that the cost of the device can be reduced by simplifying the manufacturing process. be able to.
[0030]
[Embodiment 2]
3A is a plan view showing a double diffusion n-channel MOSFET according to Embodiment 2 of the present invention, and FIG. 3B shows a state cut along the line AA ′ in FIG. 3A. FIG. 3C is a sectional view showing a state cut along the line BB ′ in FIG.
[0031]
The double-diffused n-channel MOSFET structure of this example is an improvement of the structure shown in FIG.⁻Type or n⁻A drain / drift region 122 formed on the type semiconductor layer 4, a gate electrode 11 with a field plate formed on the drain / drift region 122 via the gate insulating film 10, and the drain / drift region 122. A well-shaped p-type channel diffusion region 17 formed on one end of the gate electrode 11 and an n-type formed in the p-type channel diffusion region 17 in a well shape⁺Type source region 8 and n spaced apart from gate electrode 11⁺And a thick insulating film 12 formed on the drain / drift region 122.
[0032]
In the drain / drift region 122 in this example, similarly to the first embodiment shown in FIG. 2, strip-shaped n-type divided drift path regions 1 and strip-shaped p-type partition regions 2 are alternately arranged on a plane. Striped parallel structure. One end of the plurality of n-type divided drift path regions 1 is pn-junction to the p-type channel diffusion region 17, and the other end thereof is n⁺Connected to the drain region 9 of the type, n⁺A parallel drift path group 100 connected in parallel is formed by branching from the drain 9 side of the mold. A p-type side end region 2a is provided outside the split drift path region 1 at the outermost end of the parallel drift path group 100, and all the split drift path regions 1 are p-type along the side surface. It is sandwiched between regions 2 (2a). One end of the plurality of p-type partition regions 2 is connected to the p-type channel diffusion region 7, and the other end thereof is n⁺The p-type drain region 9 is pn-junctioned and branched from the p-type channel diffusion region 7 side to be connected in parallel.
[0033]
Also in this example, in the off state, the depletion end from the pn junction Jb spreads in the path width direction in the n-type split drift path region 1 and the depletion end spreads from both sides, so that depletion is very quick. At the same time, the p-type partition region 2 is also depleted. For this reason, as in the first embodiment, the withstand voltage is increased, and the impurity concentration in the n-type divided drift path region 1 can be increased, so that the on-resistance can be reduced.
[0034]
Here, comparing the conventional structure shown in FIG. 11B with an ideal breakdown voltage of 100 V, the conventional structure shown in FIG. 11B has an on-resistance of about 0.5 (mΩ · cm).²On the other hand, in the structure of this example, when the divided drift path region 1 and the p-type partition region 2 have a thickness of 1 μm and a width of 0.5 μm, the on-resistance is 0. 4 (m ohm · cm²). By further reducing the widths of the divided drift path region 1 and the p-type partition region 2, the on-resistance can be greatly reduced. In addition, by increasing the thickness of the divided drift path region 1 and the p-type partition region 2, the resistance cross-sectional area of the divided drift path 1 can be increased and the on-resistance can be reduced. For example, if it is 10 μm, the on-resistance can be reduced to 1/10, and if it is set to 100 μm, the on-resistance can be reduced to 1/100. In order to dope such a thick region, impurity ions may be implanted into the same portion with a plurality of (or continuously different) energies.
[0035]
[Embodiment 3]
4A is a plan view showing a lateral-structure SOI-MOSFET according to Embodiment 3 of the present invention, and FIG. 4B is a cross-sectional view taken along the line AA ′ in FIG. 4A. FIG. 4 and FIG. 4C are cut views showing a state cut along the line BB ′ in FIG.
[0036]
The SOI-MOSFET structure of this example is formed by a p-type channel diffusion layer 77 formed on the insulating film 6 on the semiconductor substrate 5 and a gate insulating film 10 on the side wall of the channel diffusion layer 77. Trench gate electrode 111 and n formed along the upper edge of trench gate electrode 111⁺N type source region 88 and n formed at a position separated from trench gate electrode 111⁺A drain region 99 of a type, a drain / drift region 290 extending between the drain and gate, and a thick insulating film 12 formed on the drain / drift region 290 are provided.
[0037]
Unlike the case of the first embodiment, the drain / drift region 290 in this example is a superposed parallel structure in which plate-shaped n-type divided drift path regions 1 and plate-shaped p-type partition regions 2 are alternately and repeatedly stacked. It has a structure. A p-type side end region 2a is formed immediately below the lowest n-type divided drift path region 1, and a p-type side end region 2a is also formed on the uppermost n-type divided drift route region 1. ing. The net doping amount of this p-type side end region 2a is 2 × 10.¹²/ Cm²The following. One ends of the plurality of n-type divided drift path regions 1 are pn-junction to the p-type channel diffusion layer 77, and the other ends thereof are n⁺Connected to the drain region 99 of the mold, n⁺A parallel drift path group 100 connected in parallel is formed by branching from the drain 99 side of the mold. One end of the plurality of p-type partition regions 2 is connected to the p-type channel diffusion layer 77, and the other end thereof is n⁺A pn junction is connected to the drain region 99 of the type, and is branched from the p-type channel diffusion layer 77 side and connected in parallel.
[0038]
Also in this layered structure, the ideal on-resistance is given by the above equation (11), and N is the number of stacked n-type divided drift path regions 1. When the ideal breakdown voltage is 100 V, in the conventional structure (N = 1), the ideal on-resistance R = 0.5 (m ohm · cm²In this example, when N = 10, R = 0.05 (m ohm · cm²), And the on-resistance drastically decreases in inverse proportion to the division number N.
[0039]
By the way, the key technology of the embodiment shown in FIGS. 2 and 3 is photolithography and ion implantation, whereas the key technology of this example shown in FIG. Crystal growth method for alternately and repeatedly laminating the p-type partition regions 2 in the form of a ring. As the number of stacked layers is increased, the total thickness increases and the time required for crystal growth increases, so that the disturbance of impurity distribution due to impurity diffusion cannot be ignored. Ideally, it is preferable that the n-type divided drift path region 1 and the p-type partition region 2 are formed as thin as possible and the crystal is grown at a low temperature at which the disturbance of the impurity distribution can be ignored. For this purpose, MOCVD (metal organic vapor phase decomposition crystal growth method) and MBE (molecular beam crystal growth method) used in compound semiconductors such as gallium-arsenic are more suitable than the epitaxial growth method frequently used in silicon technology. . According to this, the layer thickness of the layered n-type divided drift path region 1 and the layered p-type partition region 2 can be miniaturized, and the on-resistance can be greatly reduced.
[0040]
In the case of this example, if the n-type divided drift path region 1 and the p-type partition region 2 are formed thin and the impurity concentration is increased, the channel inversion layer 13 is difficult to form, and the channel resistance is difficult to lower, resulting in the on-state. Resistance is difficult to lower. In order to improve this, it is effective to make a portion of the n-type divided drift path region 1 and the p-type partition region 2 in contact with the gate insulating film 10 locally a low concentration region.
[0041]
[Embodiment 4]
FIG. 5A is a plan view showing a lateral MOSFET according to Embodiment 4 of the present invention, and FIG. 5B is a sectional view showing a state cut along the line AA ′ in FIG. 5A. FIG. 5C is a cross-sectional view showing a state cut along the line BB ′ in FIG.
[0042]
The MOSFET structure of this example is p⁻Type or n⁻P-type channel diffusion layer 77 formed on type semiconductor layer 4, trench gate electrode 111 formed on the side wall of channel diffusion layer 77 via gate insulating film 10, and upper edge of trench gate electrode 111 N formed along⁺N type source region 88 and n formed at a position separated from trench gate electrode 111⁺A drain region 99 of a type, a drain / drift region 290 extending between the drain and gate, and a thick insulating film 12 formed on the drain / drift region 290 are provided.
[0043]
The drain / drift region 290 in this example is the same as in the third embodiment, and has a parallel structure in which plate-shaped n-type divided drift path regions 1 and plate-shaped p-type partition regions 2 are alternately and repeatedly stacked. It has become. A p-type side end region 2a is formed immediately below the lowest n-type divided drift path region 1, and a p-type side end region 2a is also formed on the uppermost n-type divided drift route region 1. ing. The net doping amount of this p-type side end region 2a is 2 × 10.¹²/ Cm²The following. One end of the plurality of n-type divided drift path regions 1 is pn-junction to the p-type channel diffusion layer 77, and the other end thereof is n⁺Connected to the drain region 99 of the mold, n⁺A parallel drift path group 100 connected in parallel is formed by branching from the drain 99 side of the mold. One end of the plurality of p-type partition regions 2 is connected to the p-type channel diffusion layer 77, and the other end thereof is n⁺A pn junction is connected to the drain region 99 of the type, and is branched from the p-type channel diffusion layer 77 side and connected in parallel.
[0044]
In this example, the on-resistance can be reduced and the breakdown voltage can be increased as in the third embodiment. The relationship between this example and the third embodiment shown in FIG. 4 corresponds to the relationship between the second embodiment shown in FIG. 3 and the first embodiment shown in FIG. Similar to the embodiment of FIG. 3 with respect to the embodiment of FIG. 2, this example can reduce the cost because it is not SOI.
[0045]
[Embodiment 5]
FIG. 6A is a cross-sectional view showing a lateral p-channel MOSFET according to Embodiment 5 of the present invention, and corresponds to an improved example of FIG.
[0046]
The structure of this example is p⁻N-type channel diffusion layer 3 formed on type semiconductor layer 4, gate electrode 11 with a field plate formed on channel diffusion layer 3 via gate insulating film 10, and gate electrode of channel diffusion layer 3 P formed on one end of 11⁺Type source region 18, p-type drain / drift region 14 in which the well end is located directly under the other end of gate electrode 11, and n-type side end region 2 b formed in the surface layer of p-type drain / drift region 14 And p formed at a position separated from the other end of the gate electrode 11⁺Type drain region 19 and p⁺N adjacent to the source region 18 of the mold⁺Type contact region 71 and thick insulating film 12 formed on p-type drain drift 14.
[0047]
In the case of this example, the number of divisions of the drain region is 1, and the p-type drain / drift region 14 corresponds to a single divided drain path region 1 on the cross section. The thickness of the n-type side end region 2b on the p-type drain / drift region 14 is made thin in order to accelerate depletion. Compared with the structure of FIG. 11A, in this example, the n-type side end region 2b is formed, and the depletion layer from the channel diffusion layer 3 below the p-type drain / drift region 14 and the n-type side region on the upper side are formed. Depletion is promoted by the depletion layer from the side end region 2a. The net doping amount of the drain / drift region 14 in FIG.¹²/ Cm²On the other hand, in this example, about 2 × 10¹²/ Cm²Doubled with the degree. Accordingly, the impurity concentration of the drain / drift region 14 can be increased by the amount that can achieve a high breakdown voltage, and a low on-resistance can be achieved.
[0048]
[Embodiment 6]
FIG. 6B is a cross-sectional view showing an n-channel MOSFET having a lateral structure according to Embodiment 6 of the present invention, and corresponds to an improved example of FIG.
[0049]
This example is a double-diffused n-channel MOSFET, p⁻Drain / drift region 22 (first n-type split drift path region 1) formed on the p-type semiconductor layer 4 (p-type side end region 2a) and a gate with a field plate formed via the gate insulating film 10 The electrode 11, a well-shaped p-type channel diffusion region 17 formed on one end side of the gate electrode 11 in the drain / drift region 22, and an n-type formed in the p-type channel diffusion region 17 in a well shape⁺Type source region 8, gate electrode 11 and n spaced apart from it⁺A p-type top layer 24 (p-type partition region 2) formed in the surface layer between the p-type partition region 2 and a second n-type split drift path region 1 formed in the surface layer of the p-type partition region 2; , N⁺P adjacent to the source region 8 of the mold⁺And a thick insulating film 12 formed on the p-type partition region 2.
[0050]
The lower drain / drift region 22 and the upper divided drift path region 1 are connected in parallel with the p-type partition region 2 interposed therebetween. Compared with the structure of FIG. 11B, in this example, the divided drift path region 1 is arranged in parallel on the p-type partition region 2. As described above, since the depletion layer extends from the p-type partition region 2 to both the lower drain / drift region 22 and the upper divided drift path region 1, a high breakdown voltage can be achieved. Therefore, the on-resistance can be reduced. The net doping amount of the drift region 22 in FIG.¹²/ Cm²On the other hand, in this example, the doping amount of the lower drain / drift region 22 and the upper divided drift path region 1 is about 3 × 10¹²/ Cm²The degree can be 1.5 times. According to the structure of this example, the trade-off relationship between the ideal breakdown voltage and the ideal on-resistance indicated by (4) in FIG. 13 can be obtained. Obviously, it was found that the trade-off relationship between the ideal breakdown voltage and the ideal on-resistance can be relaxed compared to the conventional structure.
[0051]
As a manufacturing method for obtaining the structures of Embodiments 5 and 6, first, p⁻After n-type semiconductor layer 3 (22) is formed by phosphorus ion implantation and heat treatment (thermal diffusion) into type semiconductor layer 4, selective boron ion implantation into the surface of n-type semiconductor layer 3 (22) is performed. The p-type region 14 (24) is formed by heat treatment (thermal diffusion), and then subjected to thermal oxidation treatment to increase the concentration by segregation of phosphorus on the silicon surface and decrease the concentration by segregation of boron into the oxide film. Is used to form a thin n-type side end region 2b (n-type split drift path region 1) on the surface layer. Since the reverse conductivity type layer is not adjacent to the upper layer of the n-type side end region 2b or the n-type split drift path region 1, a thinner layer is better for easy depletion. Therefore, the advantage that the n-type side end region 2b (n-type split drift path 1) can be formed only by the thermal oxidation treatment process contributes to the reduction of the number of processes and enables mass production.
[0052]
In the fifth embodiment, the n-type side end region 2b is separated from the gate insulating film 10 and the drain / drift region 14, but since this uses the above manufacturing method, the n-type side is entirely formed on the silicon surface layer. This is because the end region 2b is formed. However, if the n-type side end region 2b is thin, there is no problem because the drain / drift region 14 is conducted by the channel inversion layer formed immediately below the gate 10.
[0053]
[Embodiment 7]
7A is a plan view showing a trench gate type n-channel MOSFET of a vertical structure according to Embodiment 7 of the present invention, and FIG. 7B is along the line AA ′ in FIG. 7A. FIG. 8A is a cross-sectional view showing a state cut along the line BB ′ in FIG. 7A, and FIG. 8B is a cross-sectional view in FIG. 7B. FIG. 9A is a sectional view showing a state cut along the line CC ′, FIG. 9A is a sectional view showing a state cut along the line DD ′ in FIG. 7A, and FIG. ) Is a cutaway view showing a state cut along the line EE ′ in FIG.
[0054]
The structure of this example is such that the back electrode (not shown) is in conductive contact.⁺Type drain layer 29, a drain / drift layer 139 formed thereon, and a trench gate electrode embedded through a gate insulating film 10 in a trench groove dug into the surface side of the drain / drift layer 139 21, a p-type channel layer 27 formed on the surface of the drain / drift layer 139 as shallow as the depth of the trench gate electrode 21, and n formed along the upper edge of the trench gate electrode 21⁺A type source region 18 and a thick insulating film 12 covering the gate electrode 21 are provided. In addition, single layer n⁺In place of the type drain layer 29, n⁺Mold upper layer and p⁺An n-type IGBT structure can be obtained by using a two-layer structure or a p-type layer composed of a mold lower layer.
[0055]
As shown in FIGS. 8B and 9, the drain / drift layer 139 in this example has alternating plate-shaped n-type divided drift path regions 1 in the vertical direction and plate-shaped p-type partition regions 2 in the vertical direction. It is a side-by-side parallel structure that is adjacent to each other repeatedly. The upper ends of the plurality of n-type divided drift path regions 1 are pn-junction to the p-type channel diffusion layer 27, and the lower ends thereof are n⁺Connected to the drain layer 29 of the type, n⁺A parallel drift path group 100 connected in parallel is branched from the drain layer 29 side of the mold. Although not illustrated, a p-type side end region is provided outside the split drift path region 1 at the outermost end of the parallel drift path group 100, and all the split drift path regions 1 are p-type along the side surface. It is sandwiched between the partition region 2 or the p-type side end region. The upper ends of the plurality of p-type partition regions 2 are connected to the p-type channel diffusion layer 27, and the lower ends thereof are n⁺The p-type drain layer 29 is pn-junctioned and branched in parallel from the p-type channel diffusion layer 27 side.
[0056]
In the off state, the channel inversion layer 13 immediately below the gate insulating film 10 disappears, and the pn junction Ja, n-type split between the n-type split drift path region 1 and the p-type channel diffusion layer 27 is caused by the drain-source voltage. A depletion layer extends from the pn junction Jb between the drift path region 1 and the p-type partition region 2 into the n-type split drift path region 1 and is depleted. The depletion end from the pn junction Ja extends in the path length direction in the n-type split drift path region 1, while the depletion end from the pn junction Jb extends in the path width direction in the n-type split drift path region 1 Since the depletion edge spreads from the surface, depletion becomes very fast. The p-type partition region 2 is also depleted at the same time. In particular, since the depletion ends enter both the adjacent n-type divided drift paths 1 and 1 from both side surfaces of the p-type partition region 2, the total occupation of the p-type partition region 2 for forming the depletion layer The width can be halved, and the cross-sectional area of the n-type divided drift path region 1 can be increased correspondingly, and the on-resistance is reduced as compared with the prior art. As the number of n-type divided drift paths 1 per unit area (number of divisions) is increased, the trade-off relationship between on-resistance and breakdown voltage can be greatly relaxed.
[0057]
Compared with the ideal on-resistance in the n-channel MOSFET having the ideal withstand voltage of 100 V (conventional structure shown in FIG. 12), in the conventional structure, the ideal on-resistance R = approximately 0.6 (mohm · cm²However, in this example, assuming that the depth (path length) of the n-type divided drift path region 1 and the p-type partition region 2 is about 5 μm and β = 2/3, When the thickness in the stacking direction of 1 and the p-type partition region 2 is calculated as, for example, 10 μm, 1 μm, and 0.1 μm,
When the thickness is 10 μm, 1.6 (m ohm · cm²)
When the thickness is 1 μm, 0.16 (m ohm · cm²)
When the thickness is 0.1 μm, 0.016 (m ohm · cm²)
Therefore, dramatic reduction in on-resistance is possible even in the order of μm. If the width of the p-type partition region 2 is made smaller than the width of the n-type divided drift path region 1, the effect will be remarkable. The width of the n-type divided drift path region 1 and the p-type partition region is currently limited to about 0.5 μm by photolithography and ion implantation. However, with the steady progress of micromachining technology, the width dimension will be further increased in the future. Since downsizing is possible, the on-resistance can be significantly reduced.
[0058]
As in this example, the repeating structure of the n-type divided drift path region 1 and the p-type partition region 2 arranged in the vertical direction is difficult in terms of manufacturing as compared with the case of a horizontal semiconductor structure. After the n-type layer is formed on the layer 29 by epitaxial growth, the n-type layer is removed by etching in a striped manner, the etching groove is filled by p-type epitaxial growth, and unnecessary portions are removed by polishing. can do. Another possible method is to selectively form deep reverse conductivity regions using selective implantation of neutron beams or high-energy particles having a large range and the resulting nuclear transmutation.
[0059]
The structure according to the present invention can be applied not only to the drain / drift region of a MOSFET, but also to a semiconductor region that becomes a drift region when turned on and becomes a depletion region when turned off, and is an IGBT, bipolar transistor, diode, JFET, thyristor, The present invention can be applied to almost all semiconductor elements such as MESFET and HEMT. Further, the conductivity type can be appropriately changed to a reverse conductivity type. Further, in FIG. 1, the parallel division drift group is shown in a layer shape, a fiber shape, a net shape, or a honeycomb shape, but is not limited thereto, and other repeated shapes can be adopted.
[0060]
【The invention's effect】
  As described above, the drift region in the present invention is between a parallel drift route group having a plurality of first conductivity type divided drift route regions connected in parallel and adjacent ones of the first conductivity type divided drift route regions. The drift region is sandwiched between the insulating film on the semiconductor layer and the surface-side insulating film.The drift region and the second conductivity type channel region are in contact with each other.It is characterized by being. With such a configuration, it is possible to reduce the on-resistance and increase the breakdown voltage.
[0061]
  Further, in the present invention, the second conductivity type side end region is formed outside the outermost first conductivity type divided drift path region of the parallel drift path group, and the length of the second conductivity type side end region is increased.SagaSecond conductivity type partition areaAnd first conductivity type split drift path areaLength ofWhenEqualIn addition, the widths of the second conductivity type partition region and the first conductivity type split drift path region are equal.It is characterized byThe ThisWith this configuration, it is possible to reduce the on-resistance and increase the breakdown voltage.
[Brief description of the drawings]
FIGS. 1A to 1C are schematic views showing structures of drift regions in a semiconductor device according to the present invention.
2A is a plan view showing an SOI-MOSFET having a lateral structure according to Embodiment 1 of the present invention, and FIG. 2B is a sectional view showing a state cut along the line AA ′ in FIG. (C) is a cutaway view showing a state cut along the line BB ′ in (a).
3A is a plan view showing a double-diffused n-channel MOSFET according to Embodiment 2 of the present invention, and FIG. 3B is a cut-away view showing a state cut along line AA ′ in FIG. (C) is a cutaway view showing a state cut along line BB ′ in (a).
4A is a plan view showing an SOI-MOSFET having a lateral structure according to Embodiment 3 of the present invention, and FIG. 4B is a sectional view showing a state cut along the line AA ′ in FIG. (C) is a cutaway view showing a state cut along the line BB ′ in (a).
5A is a plan view showing a lateral structure MOSFET according to Embodiment 4 of the present invention, FIG. 5B is a sectional view showing a state cut along the line AA ′ in FIG. (c) is a cutaway view showing a state cut along the line BB ′ in (a).
6A is a cross-sectional view showing a lateral p-channel MOSFET according to Embodiment 5 of the present invention, and FIG. 6B is a cross-sectional view showing a lateral n-channel MOSFET according to Embodiment 6 of the present invention. is there.
7A is a plan view showing a trench-gate n-channel MOSFET having a vertical structure according to Embodiment 7 of the present invention, and FIG. 7B is taken along line AA ′ in FIG. 7A. It is a cutaway figure which shows the state cut | disconnected.
8A is a cross-sectional view showing a state cut along line BB ′ in FIG. 7A, and FIG. 8B is taken along line CC ′ in FIG. 7B. It is a sectional view showing the state where it cut.
9A is a cross-sectional view showing a state cut along a line DD ′ in FIG. 7A, and FIG. 9B is a cross-sectional view taken along a line EE ′ in FIG. It is a sectional view showing the state where it cut.
10A is a plan view showing a conventional SOI-MOSFET having a lateral structure, and FIG. 10B is a cross-sectional view thereof.
11A is a cross-sectional view showing another structure of a conventional lateral structure MOSFET, and FIG. 11B is a cross-sectional view showing the structure of a conventional double-diffused n-channel MOSFET.
FIG. 12 is a cross-sectional view showing a conventional trench gate type n-channel MOSFET.
FIG. 13 is a graph showing a trade-off relationship between ideal breakdown voltage and ideal on-resistance of various silicon n-channel MOSFETs.
[Explanation of symbols]
1 ... n-type split drift path area
1a: Connection site
2 ... p-type partition region
2a ... p-type side edge region
3 ... n-type channel diffusion layer
4 ... p⁻Type semiconductor layer
5 ... Semiconductor substrate
6 ... Insulating film
7 ... p-type channel diffusion layer
8 ... n⁺Type source area
9 ... n⁺Type drain region
10 ... Gate insulating film
11 ... Gate electrode with field plate
12 ... Thick insulating film
13 ... Channel inversion layer
14 ... p-type low concentration region
17 ... p-type channel diffusion region
18, 28 ... p⁺Type source area
19 ... p⁺Type drain region
21 ... Trench gate electrode
22 ... n-type low concentration drain layer
24 ... p-type top layer
27 ... p-type channel layer
29 ... n⁺Type drain layer
39 ... n-type low concentration drain layer
71 ... n⁺Type contact area
72 ... p⁺Type contact area
77 ... p-type channel diffusion layer
88 ... n⁺Type source area
90 ... n-type low concentration drain region (drain / drift region)
99 ... p-type drain region
100: Parallel drift path group
111 ... Trench gate electrode
90, 122, 139, 290 ... Drain drift region
e ... depletion end
Ja, Jb ... pn junction.

Claims (5)

In a MOS type semiconductor device having a first conductivity type source region in a second conductivity type channel region and having a drift region in which a drift current flows in a lateral direction in an on state and is depleted in an off state, the drift region is connected in parallel A parallel drift path group having a plurality of first conductivity type split drift path areas and a second conductivity type partition area interposed between adjacent ones of the first conductivity type split drift path areas. Te, the drift region is sandwiched between the insulating film and the surface-side insulating film on the semiconductor layer, MOS-type semiconductor, wherein the drift region and the second conductivity type channel region is in contact apparatus. 2. The MOS semiconductor device according to claim 1, wherein the insulating film on the semiconductor layer is formed thicker than the surface-side insulating film. The drift region according to claim 1 or 2, wherein the drift region has a stacked parallel structure in which the layered first conductivity type divided drift path region and the layered second conductivity type partition region are alternately and repeatedly stacked. Te, the superimposed parallel structure MOS type semiconductor device characterized by being sandwiched between the insulating film and the surface-side insulating film on the semiconductor layer. 3. The drift region according to claim 1, wherein the drift region extends along the surface of the insulating film on the semiconductor layer between the stripe-shaped first conductivity type divided drift path region and the stripe-shaped second conductivity type partition region. A MOS type semiconductor device characterized in that the structure is alternately arranged. 5. The method according to claim 1, further comprising a second conductivity type side end region outside the first conductivity type split drift path region, which is the outermost side of the parallel drift path group. 2 long conductive type side end region Saga second conductivity type partition region and the first conductivity type drift regions rather equal to the length, the second conductivity type partition region and the first conductivity type drift regions of width MOS type semiconductor devices characterized by equality .

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