JP3001601B2 - Semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to a semiconductor device having an integrated circuit or the like formed on a substrate, and more particularly to a semiconductor device having a lateral bipolar transistor constituting the integrated circuit. It concerns the device.

[Prior Art] Conventionally, a lateral bipolar transistor (hereinafter referred to as a horizontal bipolar transistor) in which a current flows in a lateral direction, that is, along a substrate surface.
BPT) is known, but the horizontal BPT is a vertical type in which the current flows in the vertical direction, that is, the depth direction of the substrate.
It has the advantage that it can coexist easily with BPT (for example, if the conduction type array of horizontal BPT is pnp, it can be mounted as npn which is the conduction type arrangement of vertical BPT) Widely used from.

[Problems to be Solved by the Invention] However, the conventional horizontal BPT has a drawback that the current amplification factor (h _FE ) cannot be increased for the following reasons.

That is, in the horizontal BPT, since the emitter region and the collector region are symmetrical, the emitter-collector breakdown voltage is low, the base width is easily affected by the collector voltage, and the so-called Early effect (depletion layer spreading effect) occurs. Because the emitter current spreads widely inside, the recombination current in the base region becomes dominant, the base current becomes large, and the current amplification factor (h _FE ) decreases significantly. There is a problem.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems of the related art, and has as its object to provide a semiconductor device capable of easily increasing the current amplification factor of a lateral BPT.

[Means for Solving the Problems] A semiconductor device according to the present invention is a semiconductor device in which a first conductivity type emitter region and a collector region and a second conductivity type base region are formed in a semiconductor substrate in a horizontal structure. The base region has a barrier in the depth direction of the semiconductor substrate with respect to a small number of carriers of the base region in a narrow bandgap region on the front surface side and a region having a wider bandgap than that in contact with the base region. A thin film layer formed thereon and through which a tunnel current flows, and a polycrystalline layer formed on the thin film layer and having a band gap wider than the band gap of the material of the emitter region. In the structure of the first aspect, for example, a heterojunction between the mixed crystal layer and the single crystal layer is formed at the interface between the emitter and the base region, so that a small number of base regions can be formed in the depth direction of the emitter region. A potential barrier to the carrier is formed, so that the emitter current is not diffused into the substrate, the recombination current in the base region is not reduced, and the tunnel thin film and the polycrystalline layer are also formed on the emitter region. A heterojunction with the crystal layer is provided to prevent the diffusion of electrons from the base region injected into the emitter region, reduce the injected current component, and thereby increase the current amplification factor (h _FE ) of the lateral BPT.

According to the configuration of the second aspect, a barrier for preventing diffusion of holes in the depth direction of the emitter region can be easily formed.

According to the configuration of the third aspect, one of the components of the base current, that is, the hole recombination current is effectively reduced.

According to the configuration of the fourth aspect, the recombination current of holes can be drastically reduced.

In the configuration of the fifth aspect, the emitter current can be concentrated and flow near the substrate surface.

Embodiment FIG. 1 shows a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a P-type Si substrate, and the Si substrate 1 is a P-type Si substrate doped with a P-type impurity such as boron (B).

Reference numeral 2 denotes a buried region, and the buried region 2 has, for example, an impurity concentration of 10 ¹⁶ to 10 ²⁰ [cm ⁻³ ].

3 is an n-type region as part of the base region B _R, the n-type region 3 having a low impurity concentration formed by epitaxial technique or the like (for ^{example, 10 14 ~5 × 10 7 [} cm -3] Degree).

4 is an n-type region serving as an important component in the present invention, the n-type region 4 is formed by a narrow mixed crystal Si _1-x Ge _x having a band gap, constituting the base region B _R.

5,5 'are P ⁺ regions, the both P ⁺ regions 5 and 5' are formed in the n-type region 4, constituting the respective emitter region E _R and a collector area C _R.

6 is an n ⁺ region, said n ⁺ region 6 to reduce the base resistance of the horizontal BPT, is intended for connecting the base electrode 201 is the buried region 2 and the metal electrode.

Reference numerals 7 and 8 denote an n region serving as a channel stop, p
Area.

Reference numeral 20 denotes an ultra-thin tunnel oxide film (for example, a film thickness of 20 [Å] or less), and the oxide film 20 tunnels both electrons and holes.

30 and 31 are polycrystalline layers, and the polycrystalline layer 3031 has a high concentration of boron (B) in polycrystalline silicon (for example, 10 ¹⁸ to 10 ²⁰ [cm
^-3 ]).

Numeral 100 denotes an element isolation region, and 110 denotes an insulating region for separating electrodes.

Reference numerals 201 and 202 denote a base electrode and a collector electrode which are metal electrodes, respectively.

As shown in FIG. 2 (b), the potential along the line BB 'in FIG. 1 shows the same potential as the normal BPT, and the collector current I
_C is a concentration N _B of the base region B _R, so determined by the base width W _B can be easily calculated. However, the horizontal BPT
Emitter region and the collector region whereas very few parts are relative, since very often the portion extending along the surface of the substrate, injected from the emitter region E _R along the depth direction of the substrate to the base region B _R The current contributed by the generated holes and the diffusion current contributed by the electrons flowing from the base region to the emitter region become dominant, and the current amplification factor _hFE is restricted from increasing.

Therefore, to form a barrier △ phi _B by hetero-interface between the emitter region and the semiconductor layer from the emitter region to the depth of X _B in the present invention, the upper layer of the emitter region,
To prevent diffusion of electrons injected into the emitter region,
A polycrystalline layer 30 made of polycrystalline silicon having a wider band gap than the tunnel thin film and the emitter region is formed.

 Next, each current component of the horizontal BPT will be described.

(A) Collector current I _{C The} collector current I _C is approximately determined by the following equation (1) between the opposing emitter and collector. Incidentally, the emitter depth X _E, when the emitter length is L, the area of the emitter region which faces the collector region in the horizontal BPT can be expressed approximately by X _E · L.

Here, q is the elementary charge [C], and D _P is the hole diffusion coefficient [cm].
² / s], L _P is the hole diffusion length [cm] n _i is the intrinsic carrier density [cm ^-3], V _BE is emitter-base voltage applied, W _B is base width [cm], N _B is The base impurity density [cm ^-3 ], _XE is the emitter depth, L is the emitter length, R is the Boltzmann constant [J / K], and T is the absolute temperature [K].

(B) the base current I _B the base current I _B is less predominantly below (2) as ~
It consists of three current components as shown in equation (4).

(A). Recombination in the base region B _R by the positive holes flowing laterally from the emitter region E _R current I _B1 (B). Recombination current of holes flowing vertically from the emitter area E _R I _B2 However, W _EF is emitter width, X _B is the distance along the depth direction from the emitter region E _R.

(C). Diffusion from the base region B _R of electrons to emitter region E _R current I _B3 However, N _E is impurity concentration in the emitter region E _R, L _n is the electron diffusion length, the D _n is the diffusion coefficient of the electrons.

Those in the present invention should be noted in particular among the above formulas is a base current component I _B3 of (3) the base current with a component I _B2 of (4).

In the conventional horizontal type BPT, most of holes injected from the emitter region E _R whereas the base current by recombination flows vertically, in the present invention, the distance from the emitter region E _R X _B
Thus, a potential barrier Δφ _B is formed, and injected carriers are blocked by this barrier.

Then, the probability of exceeding the barrier △ phi _B is, exp - a (△ φ _B / RT).

The probability is △ φ _B = 0.1 [eV] at room temperature, which is about 1/54 as compared with the conventional horizontal BPT.

In the above equation (3), if X _B << L _P holds, then tanh (X _B / L _P ) ≒ X _B / L _P , so that the horizontal BPT of the present invention has I _B2 compared to the conventional horizontal BPT. Is significantly reduced.

Next, we describe the diffusion distance L _P of positive holes in the n-type region.

Incidentally, for the hole mobility mu _P, over a wide range of the n-type impurity concentration N _D, the following equation is established.

Thus, as can be understood from this equation (5), the impurity concentration N _D becomes smaller, the mobility mu _P is ^{500 [cm 2 / V · sec} ]
Approaching a certain value. Also, the impurity concentration
When it becomes 10 ¹⁷ [cm ⁻³ ] or more, the mobility μ _P becomes the impurity concentration N _D
Is a function of

On the other hand, the lifetime τ _{P of the} minority carrier depends on the impurity concentration of 10 ¹⁷
In the case of [cm ^-3 ] or more, it is expressed by the following equation.

When the impurity concentration becomes 10 ¹⁷ [cm ⁻³ ] or more, the mobility μ _P
Is a function of N _D.

On the other hand, the lifetime τ _P [sec] of the minority carrier is expressed by the following equation when the impurity concentration is 10 ¹⁷ [cm ⁻³ ] or more.

From the mobility μ _P and lifetime τ _P , the hole diffusion distance L
_P is generally represented by the following equation.

FIG. 3 shows a calculation of the mobility μ _P , the lifetime τ _P , and the diffusion distance L _P of the holes, which are minority carriers, in n-type Si based on the above equations (5), (6), and (7). N _D as a value of 10
^It shows the range of ¹⁷ to 10 ¹⁹ [cm ^-3 ].

As is apparent from FIG. 3, the hole diffusion distance L _P is extremely long, and reaches L _P = 120 [μm] when N _D = 10 ¹⁷ [cm ⁻³ ].

Even concentration N _D is 10 ¹⁸ [cm ^-3], a L _P ≒ 30 [μm].

Normally, pn formed on the same substrate as npn type vertical BPT
In the case of p-type horizontal BPT, the impurity concentration in the base region is
Since the impurity concentration becomes the same as that of the collector region of the npn type vertical BPT, it becomes small, for example, 10 ^{14 to} 5 × 10
^{It is} about ¹⁷ [cm ^-3 ]. Therefore, although the relationship X _B "L _P can be easily established, preferably it is about X _B ≦ L _P / 10.

Since the recombination current I _B2 is drastically reduced in such conditions, the base current I _B of the horizontal BPT becomes dominant I _B1, I _B3, it is possible to approximate the current amplification factor h _FE that of vertical BPT.

When the recombination current I _B2 is decreased, the component of base current I _B is the base in the recombination current I _B1, but the diffusion current I _B3 is in the main, a conventional normal horizontal in BPT diffusion current I _B3 is dominant Met.

Therefore, in the present invention, as shown in FIG. 2A, a polycrystalline layer 30 made of polycrystalline Si having a wider bandgap than the bandgap of the emitter region is further laminated on the upper part of the emitter region. Blocks the diffusion of electrons.

Since the conventional horizontal BPT has an electrode made of metal just above the emitter region 5, the diffusion current _IB3 is considerably large.

As can be understood from the above equation (4), when electrons are injected from the base region into the emitter region, the diffusion current _IB3 is proportional to W _E / L _n ² under the condition of W _E << L _N. Suruga, becomes proportional to the conventional horizontal type BPT in 1 / W _E. That is,
I _B3 in horizontal BPT of the present invention as compared with the conventional horizontal BPT W _E ² / L
_n ² only smaller.

Next, the diffusion distance of electrons in the P ⁺ type region 5 will be described.

Mobility mu _n electrons The following equation is established over a wide range of P-type impurity concentration Na.

Therefore, at a place where the impurity concentration Na is low, the mobility μ _n is 14
It approaches 12 [cm ² / V · sec]. Further, the impurity concentration Na is infinite, the mobility mu _n becomes ^{232 [cm 2 / V · sec} ].

On the other hand, the minority carrier lifetime τ _n is
Above ¹⁷ [cm ^-3 ], it is expressed by the following equation.

Based on the mobility μ _P and the lifetime τ _n , the diffusion distance L _n is
It is generally expressed by the following equation.

FIG. 4 shows the electron mobility μ _n lifetime τ _n and the diffusion distance L _n obtained from the equations (8), (9) and (10) in P-type Si.
Is calculated when the impurity concentration Na is in the range of 10 ¹⁷ to 10 ²⁰ [cm ⁻³ ].

The following can be understood from FIG. That is, since the P-type emitter region of the horizontal BPT usually uses the base region of the vertical BPT, the impurity concentration of the base region is 10 ¹⁸ [cm ⁻³ ].
Although less, the diffusion length L _n at this time is reached on the degree 15 to 70 [[mu] m]. Therefore, emitter width W _E is equal to or less than about L _n / 5, it is possible to sufficiently reduce the diffusion current I _B3 in the emitter region.

The Si _1-x Ge _x constituting the n-type region 4 can have a low carrier mobility due to the alloy effect. However, if the impurity concentration is as high as 10 ¹⁸ [cm ⁻³ ] or more, for example, the carrier effect due to the impurity will occur. Is dominant, and exhibits characteristics similar to Si.

As mentioned above, according to the structure of the present invention, the base current component approaches the value of the recombination current I _B1, the current amplification factor h _FE is as matches that of the heterojunction bipolar transistor of vertical BPT. The current amplification factor h _{FE at} that time is W
_B << If L _P holds, It is represented by

As described above, in the present invention, holes injected from the P ⁺ region 5 as the emitter region are blocked by the hetero interface between the n-type region 3 and the n-type region 4 made of a mixed crystal, and The aim is to prevent holes from being diffused and to prevent electrons injected into the emitter region from being diffused by a potential barrier formed at a hetero interface between a mixed crystal of Si—Ge and a single crystal of silicon.

Next, the manufacturing process of the first embodiment shown in FIG. 1 will be described.

Group V elements As and S are deposited on a P-type conduction type Si substrate 1.
b, P etc. are ion-implanted (impurity diffusion or the like may be performed) to obtain n ⁺ having an impurity concentration of, for example, 10 ¹⁵ to 10 ¹⁹ [cm ⁻³ ].
The buried region 2 is formed.

The impurity concentration is 10
An n-type region 3 of ¹⁴ to 10 ¹⁷ [cm ⁻³ ] is formed.

Forming an n ⁺ region 6 for reducing the base resistance (and the impurity concentration of, for example, ^{10 17 ~10 20 [cm -3]} ).

An insulating film 100 for element isolation is formed by a selective oxidation method, a CVD method, or the like, and a channel / stop region 7 is formed below the insulating film 100.

Ge ions are selectively implanted into the Si substrate 1 (1 × 10 ¹⁶ to 1 ×
10 ¹⁷ [cm ⁻² ]) and heat treatment to form an n-type region 4 of Si _1-x Ge _x .

P ⁺ regions 5 and 5 ′ serving as emitter and collector regions are formed by ion-implanting B ⁺ at a concentration of 1 × 10 ¹⁵ [cm ⁻² ] and then performing a heat treatment.

For example, an oxide film 20 made of an ultra-thin film of 20 [Å] or less is formed by low-temperature oxidation of, for example, about 500 to 650 [° C.].

After depositing the polycrystalline silicon layers 30 and 31, for example, 4000 [Å],
Boron is implanted, for example, by ion implantation at a concentration of 1 × 10 ¹⁶ [cm ⁻² ], and after a heat treatment of, for example, about 800 to 900 [° C.], patterning is performed. In the case of a single crystal, for example, 800
Epitaxial growth near [° C.].

After an insulating film 110 is deposited and annealed, an opening for a contact is made.

Al-Si (1%) to be the electrodes 200, 201, and 202 is sputtered, and thereafter, patterning of Al-Si is performed.

After alloying the Al-Si electrode at, for example, 450 ° C. for 30 minutes, a passivation film is formed.

FIG. 5 shows the change in the band gap of the mixed crystal of Si _1-x Ge _x .

In FIG. 5, the abscissa represents the Ge mixed crystal ratio (the amount of contaminant X is expressed in percentage), and the ordinate represents the band and band as compared with the Si single crystal.
The gap reduction amount-ΔE is shown. In the figure, a curve H _O shows a state without distortion, and a curve H _U shows a distortion state, respectively, which are taken in a semiconductor device in a distortion state.

According to the figure, the band gap reduction amount − △ E ₁ ≒ 0.1 [e
V] corresponds to the case where the mixing amount X is about 0.12, and at this time, a barrier 0.1 [eV] is formed.

When Ge ions are implanted under the conditions of a concentration of 1 × 10 ¹⁶ [cm ⁻² ] and an accelerating voltage of 150 [keV], the peak concentration is about 1 × 10 ²⁰
[Cm ^-3 ]. Therefore, the mixing amount of Ge is about 2% since the density of single crystal Si is 5 × 10 ²² [cm ⁻³ ]. X = 0.
12 can be achieved, for example, when the Ge concentration is about 6 × 10 ¹⁶ [cm ⁻³ ].

[Other Embodiment] FIG. 6 shows a second embodiment.

In this embodiment, after growing the n-type layer 4 of Si ₁ -xGex _by an epitaxial method instead of an ion implantation method, a P ⁺ region 5 of an emitter / collector portion is formed therein. In this case, the contact portion of the base region is also a mixed crystal of Si-Ge.

In the first embodiment as well, in order to reduce the contact resistance, the extraction portion of the base region may be formed of a Si-Ge mixed crystal.

Further, in the above description, a pnp type horizontal BPT has been described, but it is apparent that the present invention may be applied to an npn type horizontal BPT. Further, a heterojunction of a mixed crystal of another material may be used. For example, GaAs and GaAlAs, InP and InGa
Si and Si-Ge may be substituted by compound semiconductors such as PAs, respectively.

The other configuration and operation are the same as those of the first embodiment, and thus the description is omitted.

 FIG. 7 shows a third embodiment.

In the present embodiment, the n-type region 4 of Si _1-x Ge _x is formed in a shallower region than in the first embodiment. That is,
Emitter depth X _B is a negative value, the depth of the mixed crystal region of Si _1-x Ge _x has shallower than the emitter-collector region.

The pn junction between the n-type region 4 and the P ⁺ region 5 is in Si—Ge, and the other is formed in Si. As shown in FIG. 5, when the band gap is Si-Ge, the band gap is smaller than that of Si. Therefore, at the same applied voltage, the Si-Ge pn junction is exp (△ E / RT) times as large as the Sipn junction. Become big. Therefore, if ΔE = 0.1 eV at room temperature, it is about 55.

In the case of the present embodiment, the horizontal BPT that allows the current to flow in the horizontal direction is effectively operated by mainly flowing the emitter current near the surface.

The operation of the other components is the same as that of the first embodiment, and the description is omitted.

[Effects of the Invention] According to the present invention, a horizontal BPT can be easily formed with a simple configuration.
Can be increased.

In addition, since the conventional integrated circuit mass production technology can be used,
Can be provided at low cost. Further, since other MOS transistors and the like can be integrated at the same time, the range of application as a semiconductor device is wide.

According to the configuration of claim 2, one of the components of the base current,
That is, the recombination current of holes can be effectively reduced, and the current amplification factor is further increased.

According to the configuration of the third aspect, the recombination current of holes can be further drastically reduced, which greatly contributes to an increase in current amplification factor.

According to the configuration of the fourth aspect, the emitter current can be concentrated and flown in the vicinity of the substrate surface.
Suitable for BPT.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a first embodiment of the present invention, FIG. 2 (a) is a schematic view showing a potential in a cross section taken along line AA 'of FIG. 1, and FIG. 2 (b). Is B- in FIG.
FIG. 3 is a schematic diagram showing a change in potential, lifetime, and diffusion distance of holes with respect to the n-type impurity concentration, and FIG. 4 is a graph showing changes in electron mobility with respect to the P-type impurity concentration. time, lifetime, graph showing changes in diffusion distance, FIG. 5 is a graph showing the change in the band gap of the mixed crystal of Si _1-x -Ge _x, FIG. 6 is a sectional view showing a second embodiment, the FIG. 7 is a sectional view showing the third embodiment. 4... N-type region, 5... P ⁺ -type region (emitter region), 20
…… Tunnel oxide film (thin film layer), 30 …… Polycrystalline layer, E _R …
... Emitter region, B _R ... Base region, C _R ... Collector region, Δφ _B.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/68-29/737

Claims (4)

(57) [Claims] 1. A semiconductor device having a lateral structure of a first conductivity type emitter region and a collector region and a second conductivity type base region in a semiconductor substrate, wherein the base region has a forbidden band width on a surface side. A thin film layer formed on the emitter region and having a tunnel in which a tunnel current flows, having a barrier in the depth direction of the semiconductor substrate with respect to a small number of carriers in the base region in a narrow region and a region having a wider band gap than the narrow region And a polycrystalline layer formed on the thin film layer and having a wider bandgap than a bandgap of a material of the emitter region. 2. The semiconductor device according to claim 1, wherein a depth of said emitter region is set to be shorter than at least a diffusion length of a minority carrier injected from said base region into said emitter. 3. The semiconductor device according to claim 1, wherein the emitter region and the collector region are provided in a narrow band gap region forming a barrier of the base region, and a distance from an interface forming the barrier to an interface of the emitter region is at least. 3. The semiconductor device according to claim 1, wherein the diffusion length is set to be shorter than a diffusion length of the minority carrier injected from the emitter region. 4. The method according to claim 1, wherein the depth of the interface at which the region is joined is set to be shallower than the depth of either the emitter region or the collector region. 13. The semiconductor device according to claim 1.