JP2002158232A - Hetero bipolar transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hetero bipolar transistor having characteristics such as high current amplification factor or the like by suppressing the recombination current of the emitter and base while lowering the drive voltage utilizing an SiGeC layer. SOLUTION: An Si-collector buried layer 11, a first base region 12 mode of the SiGeC layer having a high C content, a second base region 13 made of the SiGeC layer or an SiGe layer having a low C content, and an Si-cap layer 14 having an emitter region 14a, are laminated on an Si substrate 10. The C content of at least an emitter region side end of the region 13 is less than 0.8%. Thus, in a depletion layer of an emitter-base junction, formation of the recombination center of the C is suppressed. An improvement in electrical characteristic such as a current amplification factor or the like due to a reduction in the recombination current is realized while maintaining low voltage drive properties.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hetero-bipolar transistor using a semiconductor layer containing silicon, and more particularly, to a countermeasure for reducing a driving voltage.

[0002]

2. Description of the Related Art Conventionally, by changing the composition of the emitter region and the base region so that the band gap of the emitter region is larger than that of the base region, the injection efficiency of the emitter is greatly improved and the characteristics of the transistor are improved. Hetero bipolar transistor (hereinafter, HBT)
Has attracted attention as a high-performance device. This H
BT is being used as a device in a microwave / millimeter wave band because of its particularly excellent high frequency characteristics.
HBT has conventionally been made of GaAs, which is a III-V group compound semiconductor.
s and AlGaAs, etc., but in recent years, a SiGeHBT utilizing the fact that the band gap of a base layer made of a SiGe layer is smaller than Si.
R & D is being actively pursued.

[0003] SiGeHBT utilizes the fact that the band gap of Ge (0.66 eV at room temperature) is smaller than that of Si (1.12 eV at room temperature), and the band gap of SiGe mixed crystal is smaller than that of Si. Then, a Si layer is used as an emitter region and a Si layer is used as a base region.
By using a Ge layer and making the band gap of the base layer smaller than that of the emitter layer, it becomes possible to drive the transistor at a voltage lower than the driving voltage (about 0.7 V) of the homo-Si bipolar transistor. Here, the driving voltage indicates a state where the voltage between the base and the emitter becomes equal to the diffusion potential between the base and the emitter in the active region of the bipolar transistor. That is, in the NPN bipolar transistor, the energy difference at the valence band edge between the emitter layer and the base layer is increased to some extent to suppress the injection of holes from the base layer to the emitter layer, and to reduce the energy difference between the emitter layer and the base layer. Since the energy difference at the conduction band edge can be reduced, the driving voltage can be reduced.

In the HBT, the band gap of the base region is gradually reduced in the direction from the emitter region to the collector region by gradually increasing the Ge content of the base region in the direction from the emitter region to the collector region. It is possible to configure a gradient composition. The carrier injected into the base layer is accelerated by the electric field generated by the gradient composition and drifts. The drift electric field enables the carrier speed to be higher than the carrier speed due to diffusion, so that the base transit time can be reduced and the cutoff frequency (f _T ) can be improved.

However, since the lattice constant of Ge (5.65 °) is different from the lattice constant of Si (5.43 °), when the content of Ge is increased, dislocations due to distortion due to the difference in lattice constants occur, and electrical The characteristics deteriorate. That is, in order to promote lower voltage driving, it is necessary to increase the Ge content in the SiGe layer.
If the content of Ge in the e layer is increased, the difference in lattice constant from the Si layer becomes larger, so the content of Ge has an upper limit. Therefore, paying attention to the fact that the lattice constant of the C crystal is smaller than the lattice constant of the Si crystal, it is possible to reduce the strain in the SiGeC mixed crystal containing C in the SiGe layer (LD Lanzerotti, A. St. . Amour, CW Liu,
JC Strum, JK Watanabe and ND Theodore, I
EEE Electron Device Letters, Vol.17 No.7 334 (199
6)). An HBT utilizing a heterojunction between the Si layer and the SiGeC layer is conceivable. In this HBT, the impurities contained in the base region diffuse into the collector region during heat treatment, so that the base-collector gap is reduced. Have a problem of forming a so-called paraistic barrier (JW Slotboom, G. Streutker, A. Pruijmboom
and DJ Gravesteijn, IEEE Electron Device Letter
s 12 pp 486 (1991)). The formation of the parasitic barrier causes a decrease in the current multiplication factor (β) and a deterioration in the early voltage Va and the cutoff frequency f _T. To solve this, there is a method of interposing an undoped spacer layer between the base and collector (EJ Prin
z, PM Garone, PV Schwartz, X. Xiano and J.
C. Strum, IEDM Technology Digitalp.p.853 (199
1)). C has the effect of suppressing impurity diffusion (LD L
anzerotti, J. C. Strum, E. Stach, R. Hull, T. Buy
uklimanli and C. Magee, AppliedPhysics Letters 70
(23) 3125 (1997)). By this effect, the profile of boron which is a p-type impurity in the base region is maintained,
Early properties such as voltage Va and the cutoff frequency f _T are expected to be improved.

[0006]

However, a conventional SiGeC-H utilizing a SiGeC / Si heterojunction.
BT has the following problems.

[0007] In order to further improve the current multiplication factor, SiGeC, which is a base region of SiGeC-HBT, is used.
To reduce the bandgap of the layer, the Ge content must be higher. At this time, as described above, in order to reduce lattice distortion accompanying an increase in the Ge content, the C content may be increased. However, according to experiments performed by the present inventors, for example, in an HBT using a SiGeC layer having a C content of 0.8% or more as a base region, the n value of the base current becomes about 2, for example. It has been found that when the content of C is increased, the high-frequency characteristics of the HBT deteriorate. Hereinafter, the results of experiments performed by the present inventors will be described.

FIGS. 8A and 8B respectively show S
IgE _0.268 HBT, a diagram illustrating a Gummel plot of SiGe _{0.26 8} C _0.0091 HBT. FIGS. 9A and 9B
_Are SiGe _0.268 HBT and SiGe
It is a diagram illustrating a _0.268 C _0.0091 HBT current multiplication factor of the (beta). However, in this specification, “SiGe _0.268 HB
T "," SiGe _0.268 C _0.0091 HBT ", etc., the composition ratio of Si is from 1 to other materials (Ge, C
Etc.) are subtracted.

It can be seen by comparing FIGS. 8A and 8B.
Yeah, SiGe_0.268 C_0.0091HBT base current Ib
Is the n value (slope) of SiGe_0.268 Compared to n value of HBT
Has deteriorated significantly. 9A and 9B are compared.
As you can see from the comparison, SiGe_0.268 C_0.0091HBT
Has a maximum value of only 50 at the maximum value,
_0.268 The maximum value of the current multiplication factor β of the HBT is 400
Has deteriorated compared to. This is because SiGeC-HB
When the C content approaches 1% at T, the recombination current becomes
The n value deteriorates due to the increase, and the deterioration of the n value
Therefore, it is considered that the current multiplication factor β decreases.

FIG. 10 shows SiGe _0.268 HBT, SiG
e _0.268 C _0.0091 A diagram for examining the fitting between the measurement result of the forward current-voltage characteristic of the diode characteristic between the emitter and base of the HBT and the measurement result of the sum of the electron recombination current and the diffusion current. is there. In the figure,
The calculated value of the sum of the electron recombination current and diffusion current of the diode is calculated as the recombination lifetime (τr
) Is used as a parameter to fit the measurement result. As can be seen from the results of the diode characteristics,
SiGeC layer containing 0% of C (that is, SiGe layer)
, The recombination lifetime is about 100 nsec, whereas the recombination lifetime is about 400 psec in the SiGeC layer having a C content of 0.91%. in this way,
It is considered that as the C content approaches 1%, the recombination lifetime becomes extremely short and the recombination current becomes very large, resulting in deterioration of characteristics.

FIGS. 11A and 11B show, respectively,
SiGe _0.268 containing Ge uniformly in the base region
The recombination lifetime in the base region of the HBT is 1 × 10 ⁻⁵ s
It is a figure which shows the result which simulated the Gummel plot and the current multiplication factor by changing from ec to 1 * 10 <^-9> sec. As can be seen from FIG. 11 (a), when the recombination lifetime is reduced, the collector current is not significantly affected, but the n-value is degraded due to a very large recombination current of the base current. . FIG.
As can be seen from (b), when the recombination lifetime becomes shorter,
As described above, when the recombination current of the base current increases, the current multiplication factor β greatly decreases. As described above, when the recombination lifetime is reduced, the characteristics of the transistor may be deteriorated.

In SiGeC-HBTs having a high C content, one of the causes of a reduction in the recombination lifetime is that in the case of a SiGeC crystal having a high C content, the amount of C existing at interstitial positions in the crystal is low. Increase. It is considered that C existing at this interstitial position constitutes a recombination level and increases recombination current.

An object of the present invention is to provide a hetero-bipolar transistor which can realize a reduction in the recombination current between the emitter and the base, a low voltage drive, and an improvement in high frequency characteristics.

[0014]

A first hetero-bipolar transistor of the present invention is provided on a substrate, and is provided on a collector region of a first conductivity type made of a semiconductor material containing Si, and provided on the collector region. , S with non-uniform C content
a second conductivity type base region composed of an i _1-xy Ge _x C _y layer (0 <x <1, 0 ≦ y <1) and a hetero region between the base region and the base region; A first conductivity type emitter region made of a semiconductor material containing Si for forming a junction, and a portion having a maximum C content in the base region is separated from a region adjacent to the emitter region.

As a result, the region adjacent to the emitter region in the base region has a relatively low C content, so that the depletion layer formed at the emitter-base junction has fewer regions with a high C content, and depletion occurs. The number of recombination centers in the layer can be reduced. Therefore, the recombination current caused by the recombination center existing in the depletion layer can be suppressed. That is, by using a heterojunction using a base region made of a SiGeC layer, it is possible to improve the electric characteristics such as the current multiplication factor and the high-frequency characteristics while reducing the driving voltage.

It is preferable that a C content in a region of the base region adjacent to the emitter region is less than 0.8%.

When the C content of the base region adjacent to the emitter region is 0.01% or more, the band structure in the base region can be finely adjusted.

Since the depletion layer formed at the emitter-base junction is located in the region of the base region that is in contact with the emitter region, the recombination current can be more effectively suppressed. .

Since the Ge content of the region of the base region that is in contact with the emitter region is constant, even if the depth position of the diffusion layer varies, the diffusion potential of the emitter-base junction is substantially constant. It can be kept almost constant.

At least a central portion of a region of the base layer other than a region adjacent to the emitter region has a uniform Ge.
By having the content, the epitaxial growth of the base region in the manufacturing process can be facilitated.

The thickness of a region of the base layer adjacent to the emitter region is preferably 5 nm or more, more preferably 10 nm or more.

A region of the base region other than a region adjacent to the emitter region is configured such that a band gap is reduced in a direction from the emitter region to the collector region. Acceleration of traveling can improve high frequency characteristics.

The region of the base region other than the region adjacent to the emitter region has a composition in which the C content increases in the direction from the emitter region to the collector region, so that the C content is high and recombination occurs. Keep the centered area as far away from the emitter-base junction as possible,
There is an advantage that the driving voltage can be reduced while suppressing the recombination current.

The base region is divided into a first base region including a region adjacent to the collector region and a second base region including a region adjacent to the emitter region. Since the band gap at the end portion on the side of the second base region is equal to or smaller than the band gap of the second base region, a particularly low driving voltage can be significantly reduced.

In this case, the G at least at the end of the first base region on the side of the second base region and the second base region.
Assuming that the difference in the e content is Δx and the difference in the C content between at least the end portion of the first base region on the side of the second base region and the second base region is Δy, there is a relationship of Δx ≧ 4.288Δy. Is preferred.

The second base region of the first base region
In the region excluding the base region side end portion, the band gap is reduced in the direction from the second base region to the collector region in the first base region. , The high-frequency characteristics can be improved.

In this case, the G at least at the end of the first base region on the side of the second base region and the second base region.
Assuming that the difference in the e content is Δx and the difference in the C content between at least the end portion of the first base region on the side of the second base region and the second base region is Δy, there is a relationship of Δx ≧ 4.288Δy. Is preferred.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing each embodiment, a ternary mixed crystal semiconductor containing Si, Ge and C is used.
A basic advantage of the hetero bipolar transistor in which the base layer of the hetero bipolar transistor is formed by the GeC layer will be described.

FIG. 1 is a state diagram showing the relationship between the contents of Ge and C, the band gap, and the lattice distortion in a ternary mixed crystal semiconductor of SiGeC. In the figure, the abscissa represents the Ge content and the ordinate represents the C content, and the straight line represents the composition conditions under which the strain amount (including the compressive strain and the tensile strain) and the band gap are constant. . FIG.
The middle and dot-hatched areas represent Si on the Si layer.
This is a region where the amount of lattice distortion in the GeC layer is within 1.0% and the band gap can be made smaller than the band gap of conventional practical SiGe (Ge content is about 10%). In SiGeC, which is expressed as Si _1-xy G _x C _y , this region is represented by the following four straight lines, where x is the Ge content and y is the C content: y = 0.122x-0. 032 straight line: y = 0.1245x + 0.028 straight line: y = 0.332x−0.0233 (Ge content is 22% or less) straight line: y = 0.0622x + 0.0127 (Ge content is 22% or less) Area. In the figure, a SiGeC layer having a composition on a straight line with a lattice strain of 0% is:
It is lattice-matched with the underlying Si layer.

Therefore, in the hetero bipolar transistor including the emitter layer, the base layer, and the collector layer, the base layer is formed of SiGeC having the composition of the region shown by the dot hatching in FIG. , A narrow band gap base can be realized.

In other words, SiGeC is used as a material having a small band gap and a small lattice strain in the base layer.
By selecting a ternary mixed crystal semiconductor material, a highly reliable heterobipolar transistor capable of low-voltage operation and high-speed operation can be realized.

FIG. 1 shows that the underlying layer of the SiGeC layer is S
FIG. 3 is a phase diagram in the case of having an i-single composition.
Even if i contains some Ge or C, the lattice distortion of the SiGeC layer is 1.0% or less, and the SiGeC layer
As long as a large difference between the C layer and the band gap can be ensured, the same effect can be exerted.

FIG. 2 is a sectional view of a hetero bipolar transistor (HBT) common to the embodiments of the present invention. As shown in the figure, the HBT of this embodiment includes a Si substrate 10 containing a p-type impurity, a Si collector buried layer 11 formed by introducing an n-type impurity (for example, phosphorus) into the Si substrate 10, A first base region 12 made of a SiGeC layer having a high C content provided on the collector burying layer 11, and a first base region 12 made of a SiGeC layer or a SiGe layer having a low C content provided on the first base region 12. The semiconductor device includes a second base region 13, a Si cap layer 14 provided on the second base region 13, and an emitter electrode 15 made of a polysilicon film provided on the Si cap layer 14.

Next, a method of manufacturing the HBT will be described.
I do. First, ion implantation or the like is performed on the surface of the Si substrate 10.
Is used to reduce the concentration of phosphorus (p), which is an n-type impurity, to about 2 ×
10 ¹⁷/ Cm^Three And the collector buried layer 11 is
Form. Then, on the collector buried layer 11, U
SiGe with a high C content by HV-CVD etc.
A first base region 12 made of a C layer and a first base region 1
SiGeC layer or SiGe layer having a lower C content than 2
And the second base region 13 composed of
Let it grow. Here, at least the second base region 13
At the emitter region side end (Si cap layer side end)
Makes the C content less than 0.8%. At this time, Epita
As a source for the axial growth, silane and
Using disilane, using germane as a raw material for Ge,
As a raw material, methylsilane, methylgermane, or the like is used.
The first and second base regions 12 and 13 have, for example, p-type impurities.
About 4 × 10 of boron (B)¹⁸/ Cm^Three At a concentration of
Doping, the thickness of the first base region 12 is about 35 nm.
And the film thickness of the second base region 13 is about 25 nm (total).
(Total thickness is about 60 nm). Then, the second base area
An Si cap layer 14 made of a Si layer is
Growing kishal. Impurities are added to the Si cap layer 14.
Without doping, the thickness of the Si cap layer 14 is about 10 n
m. Further, on the Si cap layer 14,
A silicon oxide film 16 having only a portion opened is formed.
Arsenic (As) or the like is formed on the opening and the silicon oxide film 16.
N containing n-type impurities such as phosphorus (P)⁺ Type polysilicon
An emitter electrode 15 made of a film is formed. This emitter
Arsenic (or phosphorus) is approximately 1 × 10²⁰/ Cm
^Three Doped at a high concentration as described above,
The n-type impurity is diffused into the i
An emitter region 14a is formed in the cap layer 14.

That is, the second C region having a low C content is located between the first base region 12 having a high C content and the emitter layer 14a.
With the base region 13 interposed and the second base region 13
By setting the C content at least at the emitter region side end to less than 0.8%, the recombination center generated due to the high C content in the first base region 12 is reduced between the emitter and base. It is configured to be outside the depletion layer. With such a configuration, the n value of the base current can be improved and the leak current can be reduced, and the problems shown in FIGS. 8B and 9B can be suppressed. . On the other hand, by providing the first base region 12 having a high C content, similarly to the conventional HBT using the Si / SiGeC heterojunction, low voltage driving can be achieved while suppressing generation of lattice distortion. . This is,
This is a basic effect of the present invention.

In FIG. 2, the first base region 1 is shown for convenience.
2 and the second base region 13,
The present invention can also be applied to those which cannot be divided into the first base region and the second base region. For example, the case where the component ratio of Si _1-xy G _x C _y constituting the base layer continuously changes throughout the base layer may be adopted. That is, the C content in the region of the base layer adjacent to the emitter layer is higher than the C content in the region of the base layer adjacent to the collector layer.
If the content is smaller than the content, the basic effects of the present invention can be exhibited.

(First Embodiment) FIGS. 3A and 3B
FIG. 5 is a diagram showing the C and Ge contents of the first base region and the second base region and the concentration of boron (B) as an impurity in the first embodiment, and shows an emitter region-base region-collector when a voltage is applied. It is an energy band figure of a field. In FIG. 3A, the illustration of the concentration of the n-type impurity is omitted.

As shown in FIG. 3A, in this embodiment, the Ge content is constant (for example, 26.8%) over the first base region 12 and the second base region 13. On the other hand, the C content is 0.91% in the first base region 12 and 0.3% in the second base region 13.
Assume that it is 5%. That is, the first base region 12 is made of Si
Consists Ge _0.268 C _0.0091 layer, the second base region 13 is made of SiGe _0.268 C _0.0035 layer.

[0039] At this time, the band gap of the SiGe _0.268 C _0.0091 layer is about 0.95eV, Ge _0.268 C
The band gap of the _0.0035 layer is about 0.92 eV. As described above, when two SiGeC layers having the same Ge content are stacked, the band gap having the higher C content becomes larger, so that as shown in FIG. A SiGeC layer having a low C content (a second base region 1) is provided between the first base region 12 having a high content and the first base region 12 having a high content.
By interposing (3), a barrier is hardly generated at the emitter-base junction. Therefore, the presence of the second base region 13 having a low C content does not adversely affect the driving voltage of the HBT. On the other hand, as described above, C
The second base region 13 having a low content is the emitter region 14a.
By being interposed between the first base region 12 and the first base region 12, the recombination current in the depletion layer between the emitter and base (region Rdp shown in FIG. 3B) can be reduced. In other words, HBT
In this case, it is possible to further lower the voltage while suppressing the deterioration of the n value and the reduction of the current multiplication factor due to the increase in the recombination current.

When there is no boundary between the first base region 12 and the second base region 13 and the base layer cannot be divided into two layers, or when the base layer can be divided into three or more layers, for example, Si _1-xy Ge _x C _y constituting the layer
Depletion formed in the emitter-base junction if the C content in the portion of the base layer adjacent to the emitter layer is sufficiently small even if the component ratio of The effect of suppressing the recombination current in the layer can be exhibited.

-Experimental Data on First Embodiment- FIG. 12 is a table showing parameters of samples used in an experiment for confirming the effect of the present invention. In FIG. 12, the thickness of the Si cap layer 14 is indicated as S, the thickness of the first base layer 12 is indicated as D1, and the thickness of the second base layer 1 is indicated as D1.
The thickness of the first base layer 12 is denoted by D2.
e The content rate, C content rate, and boron concentration are respectively N _G1 ,
N _C1 and N _B1 are indicated, and the Ge content, the C content, and the boron concentration in the second base layer 13 are N _G2 , N _C2 , and N, respectively.
_It is displayed as _B2 .

FIG. 13 is a diagram showing data of bias voltage-current characteristics measured for the sample shown in FIG. As shown in the figure, in the sample (No. 1) in which the layer having the low C content (the second base region) is not provided, the slope of the voltage-current characteristics is gentle, so that the recombination current is large. Understand. Further, in the sample (No. 2) in which the thickness of the second base region 13 having a low C concentration is 10 nm, the slope of the voltage-current characteristic rises slightly as compared with the sample (No. 1), and the effect of slightly reducing the recombination current is small. Although effective, the effect is small. In the sample (No. 3) in which the thickness of the second base region 13 with a low C concentration is 20 nm (No. 3), the gradient of the current is slightly steep, and the effect of reducing the recombination current clearly appears. Further, in the sample (No. 4) in which the thickness of the second base layer 13 is 30 nm, the slope of the voltage-current characteristics is steep, and the effect of reducing the recombination current is very large.

In the samples used in this experiment,
Are impurities in the first and second base regions 12 and 13
(Boron) concentration 2 × 10¹⁸cm^-3And standard
In the base region of the hetero bipolar transistor,
Pure substance concentration 1 × 10¹⁹cm^-3It is much lower than. That
The depletion layer at the emitter-base junction
It is thought that it is. That is, in the base area
Impurity concentration of 1 × 10 ¹⁹cm^-3If you do
Emitter-base junction than the sample used in this experiment
Of the depletion layer in the second base region 1
If the thickness of 3 is about 5 nm or more, reduction of recombination current
The effect is obtained.

(Second Embodiment) FIGS. 4A and 4B
FIG. 4 is a diagram showing the C and Ge contents of the first base region and the second base region and the concentration of boron (B) as an impurity in the second embodiment, and shows an emitter region-base region-collector when a voltage is applied. It is an energy band figure of a field. In FIG. 4A, the illustration of the concentration of the n-type impurity is omitted.

In this embodiment, the first base region 1
The feature is that the Ge and C contents of the two regions 12 and 13 are adjusted so that the band gap between the second region 12 and the second base region 13 becomes equal. For this purpose, the Ge content in the first base region 12 may be made higher than that in the second base region 13 without setting the Ge content to the same value in the first and second base regions. The composition of the SiGeC layer is represented by the general formula Si _1-xy Ge _x C _y , and the difference in the C content between the first base region 12 and the second base region 13 is Δ
When y is set, the difference Δx in the Ge content between the first base region 12 and the second base region 13 is determined based on the following equation (1) Δx = 4.288 Δy (1). Note that both the first base region 12 and the second base region 13 have a composition that undergoes compressive strain with respect to the Si layer.

As shown in FIG. 4A, in this embodiment, the Ge content of the first base region 12 is set to a relatively high constant value (for example, 31.3%), and the G content of the second base region 13 is increased.
The e content is set to a low constant value (for example, 26.8%). On the other hand, the content of C in the first base region 12 is 1.
4%, and 0.35% in the second base region 13. That is, the first base region 12 is made of SiGe
_0.313 C _0.014 layer, the second base region 13 is Si
It _{consists of 0.0035} layers of Ge _0.268 C.

At this time, the band gap of the SiGe _0.313 C _0.014 layer is about 0.92 eV, and the Ge _0.268 C _0.014
The band gap of the _0.0035 layer is also about 0.92 eV,
As shown in FIG. 4B, the two base regions 12, 13
Is flat at the conduction band edge. As described above, when two SiGeC layers having the same band gap are stacked, further lower voltage driving can be achieved. As described above, since the second base region 13 having a low C content is interposed between the emitter region 14a and the first base region 12, the depletion layer between the emitter and the base (FIG. 4B) ) Can reduce the recombination current in the region Rdp). That is, in the HBT, a particularly remarkable low-voltage driving can be promoted while suppressing the deterioration of the n value and the reduction of the current multiplication factor due to the increase of the recombination current.

Since the conduction band edges of the two base regions 12 and 13 are flat, there is no hetero barrier which hinders the traveling of carriers, so that the operation speed of the hetero bipolar transistor can be increased. it can.

(Third Embodiment) FIGS. 5A and 5B
FIG. 4 is a diagram showing the C and Ge contents of the first base region and the second base region and the concentration of boron (B) as an impurity in the third embodiment, and shows an emitter region-base region-collector when a voltage is applied. It is an energy band figure of a field. In FIG. 5A, the illustration of the concentration of the n-type impurity is omitted.

In the present embodiment, the first base region 1
The band gaps of the two at the boundary between the second base region 13 and the second base region 13 are made equal so that the band gap of the first base region 12 changes in the direction of accelerating the base traveling electrons.
The feature is that the Ge and C contents of the first and second base regions 12 and 13 are adjusted. Therefore, it represents a composition of the SiGeC layer in the general formula _{Si 1-xy Ge x C y} , the second base region side end portion of the first base region 12 and the difference in C content in the second base region 13. and Δy When you do
The difference Δx in the Ge content between the end of the first base region 12 on the side of the second base region and the second base region 13 is determined based on the above equation (1). Then, the first base region 12
In the direction from the second base region side end toward the collector buried layer 11.

As shown in FIG. 5A, in this embodiment, the Ge content at the end of the first base region 12 on the side of the second base region is set to a higher value (for example, 20.0%). The Ge content at the end of the first base region 12 on the side of the collector buried layer is set to a higher value (for example, 30%), and the Ge content of the second base region 13 is set to a low constant value (for example, 15.2%). On the other hand, the C content is a relatively high constant value (for example, 1.4) in the first base region 12.
%) In the second base region 13 is a lower constant value (for example, 0.3%). That is, the end of the first base region 12 on the second base region side is SiGe _0.20 C
_The end of the first base region 12 on the side of the collector buried layer is composed of _0.014 layer of SiGe _0.30 C.
The base region 13 is composed of a SiGe _0.152 C _0.003 layer.

At this time, the band gap of the Ge _0.20 C _0.014 layer is about 1.02 eV, and the SiGe _0.152 C
The band gap of the _0.003 layer is also about 1.02 eV,
As shown in FIG. 5B, the two base regions 12, 13
Have the same band gap at the boundary. Meanwhile, the first
The band gap at the end of the base region 12 on the side of the collector buried layer is about 0.93 eV. Therefore, in the first base region 12, the band gap changes so as to gradually decrease in the direction from the end of the second base region to the collector buried layer 11, so that the electrons in the first base region 12 have a drift electric field. And the transit time of electrons is shortened, and the high-frequency characteristics of the hetero bipolar transistor are improved. Further, when two SiGeC layers having the same band gap are stacked at the boundary portion, further lower voltage driving can be achieved as in the second embodiment. As described above, since the second base region 13 having a low C content is interposed between the emitter region 14a and the first base region 12, the depletion layer between the emitter and base (FIG. 5B ) Can reduce the recombination current in the region Rdp).

That is, in this embodiment, in addition to the same effects as in the second embodiment, the high-frequency characteristics of the hetero bipolar transistor can be improved.

(Fourth Embodiment) FIGS. 6A and 6B
FIG. 9 is a diagram showing the C and Ge contents of the first base region and the second base region and the concentration of boron (B) as an impurity in the fourth embodiment, and shows an emitter region-base region-collector when a voltage is applied. It is an energy band figure of a field. In FIG. 6A, the illustration of the concentration of the n-type impurity is omitted.

In this embodiment, the first base region 1
In order that the band gaps of the second base region 13 and the second base region 13 are equal to each other and that the lattice distortion at the boundary between the first and second base regions 12 and 13 is as small as possible.
The feature is that the Ge and C contents of the first and second base regions 12 and 13 are adjusted. Therefore, the Ge and C contents at the end of the first base region 12 on the side of the second base region are the same as those of the second base region 13, and the Ge and C contents of the first base region 12 are set to the second. It is increased in the direction from the base region side end toward the collector buried layer 11. At this time, the composition of the SiGeC layer is represented by the general formula Si _1-xy G _x C _y , and the region of the first base region 12 excluding the first base region side end and the second base region 13
The difference Δx in the Ge content between the region excluding the first base region-side end of the first base region 12 and the second base region 13 is represented by the above equation (1), where Δy is the difference in the C content between Determined based on

As shown in FIG. 6A, in this embodiment, the Ge content in the second base region 13 and the end of the first base region 12 on the side of the second base region is set to a common value (for example, 26). 0.8%), and the Ge content at the end of the first base region 12 on the side of the collector buried layer is set to a higher value (for example, 31.3%). On the other hand, the C content is a common value (for example, 0.35%) in the second base region 13 and the end of the first base region 12 on the second base region side.
It is assumed that the value is higher (for example, 1.4%) at the end of the first base region 12 on the side of the collector buried layer. That is, the second base region 13 and the first base region 12
And the second base region end of the consist SiGe _0.268 C _{0. 0035} layers, collector buried layer side end portion of the first base region 12 is made of SiGe _{0. 313} C _0.014 layer.

At this time, the band gap of the SiGe _0.268 C _0.0035 layer is about 0.93 eV and the SiGe _0.313 C
The band gap of the C _0.014 layer is about 0.93 eV, and as shown in FIG.
The band gaps at 13 are equal. And the first,
Since the contents of Ge and C at the boundary between the second base regions 12 and 13 are equal to each other, there is no sharp change in the lattice constant at the boundary, so that the lattice distortion of the entire base region can be minimized. Therefore, generation of defects such as dislocations due to lattice distortion can be suppressed, and the electrical characteristics of the hetero bipolar transistor can be improved.

On the other hand, two SiGs having the same band gap
When the eC layers are stacked, further lower voltage driving can be achieved as in the second embodiment. As described above, since the second base region 13 having a low C content is interposed between the emitter region 14a and the first base region 12, a depletion layer between the emitter and base (FIG. 6B ) Can reduce the recombination current in the region Rdp).

That is, in this embodiment, in addition to the same effects as those of the second embodiment, the electrical characteristics of the hetero bipolar transistor can be improved by suppressing the occurrence of defects.

(Fifth Embodiment) FIGS. 7A and 7B
FIG. 14 is a diagram showing the C and Ge contents of the first base region and the second base region and the concentration of boron (B) as an impurity in the fifth embodiment, and shows an emitter region-base region-collector when a voltage is applied. It is an energy band figure of a field. In FIG. 7A, the illustration of the concentration of the n-type impurity is omitted.

In this embodiment, the first base region 1
The band gap at the boundary between the second base region 13 and the second base region 13 is made equal to change the band gap of the first base region 12 in the direction in which the base traveling electrons are accelerated. The feature is that the Ge and C contents of the first and second base regions 12 and 13 are adjusted so that the lattice distortion at the boundary portion of is as small as possible. Therefore, the second base region 12
The Ge and C contents at the base region side end are the same as those of the second base region 13, and the C and Ge contents in the first base region 12 are changed from the second base region side end to the collector buried layer 11. Increase in the direction to go.

As shown in FIG. 7A, in this embodiment, the Ge content in the second base region 13 and the end of the first base region 12 on the second base region side is set to a common value (for example, 15%). .2%), and the Ge content at the end of the first base region 12 on the side of the collector buried layer is set to a higher value (for example, 30%). On the other hand, the C content is a common value (for example, 0.3%) between the second base region 13 and the end portion of the first base region 12 on the side of the second base region, and the first content is 1%.
It is assumed that the value is higher (for example, 1.4%) at the end of the base region 12 on the side of the collector buried layer. In other words, the second base region 13 and the second base region end portion of the first base region 12 made of SiGe _0.152 C _0.003 layer, the collector buried layer side end portion of the first base region 12 is SiGe _0.30 C _{0. 014} Consists of layers.

At this time, the band gap of the SiGe _0.152 C _0.003 layer is about 1.02 eV, and the SiGe _0.30 C
_{The 0.014} layer band gap is about 0.93 eV. Therefore, in the first base region 12, the band gap changes so as to gradually decrease in the direction from the end of the second base region to the collector buried layer 11, so that the electrons in the first base region 12 have a drift electric field. And the transit time of electrons is shortened, and the high-frequency characteristics of the hetero bipolar transistor are improved. Since the contents of Ge and C at the boundary between the first and second base regions 12 and 13 are the same, there is no sharp change in the lattice constant at the boundary, so that the lattice distortion of the entire base region is minimized. can do. Therefore, generation of defects such as dislocations due to lattice distortion can be suppressed, and the electrical characteristics of the hetero bipolar transistor can be improved.

When two SiGeC layers having the same band gap are laminated at the boundary, the second
Similarly to the embodiment, further lower voltage driving can be achieved. As described above, since the second base region 13 having a low C content is interposed between the emitter region 14a and the first base region 12, the depletion layer between the emitter and base (FIG. 7B ) Can reduce the recombination current in the region Rdp).

That is, in this embodiment, the effects of the third embodiment and the fourth embodiment can be exhibited together.

(Other Embodiments) In each of the above embodiments, only the case where the second base region 13 is a SiGeC layer has been described. However, in each of the above embodiments, the second base region 13 is made of a SiGe layer. The present invention can also be applied to a configuration.

[0067]

According to the hetero bipolar transistor of the present invention, the C content of the region adjacent to the emitter region in the base region made of the SiGeC layer is made smaller than the C content of the region adjacent to the collector region. By suppressing the recombination current, it is possible to improve the electric characteristics such as the current multiplication factor and the high-frequency characteristics while reducing the driving voltage.

[Brief description of the drawings]

FIG. 1 Ge and C in a SiGeC ternary mixed crystal semiconductor
FIG. 4 is a state diagram showing the relationship between the content ratio of, band gap and lattice distortion.

FIG. 2 is a cross-sectional view of a hetero bipolar transistor (HBT) common to the embodiments of the present invention.

FIGS. 3 (a) and 3 (b) show H in the first embodiment.
It is a figure which shows the C and Ge content of BT, and boron density | concentration, and an energy band figure at the time of voltage application.

FIGS. 4A and 4B show H in the second embodiment; FIGS.
It is a figure which shows the C and Ge content of BT, and boron density | concentration, and an energy band figure at the time of voltage application.

FIGS. 5A and 5B show H in the third embodiment; FIGS.
It is a figure which shows the C and Ge content of BT, and boron density | concentration, and an energy band figure at the time of voltage application.

FIGS. 6A and 6B show H in the fourth embodiment; FIGS.
It is a figure which shows the C and Ge content of BT, and boron density | concentration, and an energy band figure at the time of voltage application.

FIGS. 7A and 7B show H in the fifth embodiment; FIGS.
It is a figure which shows the C and Ge content of BT, and boron density | concentration, and an energy band figure at the time of voltage application.

FIGS. 8A and 8B respectively show SiGe in order.
_0.268 HBT, SiGe_0.268 C _0.0091HBT gunme
FIG.

FIGS. 9 (a) and (b) respectively show SiGe
_0.268 HBT, a diagram illustrating a SiGe _0.268 C _{0. 0091} HBT current multiplication factor of the (beta).

FIG. 10: SiGe _0.268 HBT, SiGe _0.268 C
Measurement results of the forward current-voltage characteristics of the diode characteristic between the emitter and base of _0.0091 HBT, a view for examining fitting between the measurement results of the calculated value of the sum of electron recombination and diffusion current.

FIGS. 11 (a) and 11 (b) are diagrams respectively simulating a Gummel plot and a current multiplication factor by _sequentially changing the recombination lifetime in the base region of SiGe _0.268 HBT containing Ge uniformly in the base region. FIG. 9 is a diagram showing the result of the session.

FIG. 12 is a table showing parameters of samples used in an experiment for confirming the effect of the present invention.

13 is a diagram showing data of bias voltage-current characteristics measured for the sample shown in FIG.

[Explanation of symbols]

 Reference Signs List 10 Si substrate 11 Collector buried layer 12 First base region 13 Second base region 14 Si cap layer 14a Emitter region 15 Emitter electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tsuyoshi Takagi 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Teruhito Onishi 1006 Odakadoma Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (72) Minoru Kubo 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. 5F003 AP00 BA92 BB01 BB04 BC04 BC08 BE04 BF06 BG06 BM01 BP32

Claims (14)

[Claims] 1. A collector region of a first conductivity type provided on a substrate and made of a semiconductor material containing Si; and a Si _1-xy Ge _x provided on the collector region and having a nonuniform C content. C _y layer (0 <x <1, 0 ≦ y <
1) a second conductivity type base region, and a first conductivity type emitter region provided on the base region and formed of a semiconductor material containing Si and forming a heterojunction with the base region. A hetero-bipolar transistor, wherein a portion having the highest C content in the base region is separated from a region adjacent to the emitter region. 2. The heterobipolar transistor according to claim 1, wherein a C content in a region of said base region adjacent to said emitter region is less than 0.8%. 3. The hetero bipolar transistor according to claim 1, wherein a C content in a region of said base region adjacent to said emitter region is 0.01% or more. 4. The hetero bipolar transistor according to claim 1, wherein a depletion layer formed at an emitter-base junction is located in a region of said base region that is in contact with said emitter region. A hetero-bipolar transistor, which is housed therein. 5. The hetero-bipolar transistor according to claim 1, wherein a Ge content of a region of said base region that is in contact with said emitter region is constant. Transistor. 6. The hetero bipolar transistor according to claim 1, wherein at least a central portion of a region of the base layer other than a region adjacent to the emitter region has a uniform Ge content. A hetero-bipolar transistor comprising: 7. The hetero bipolar transistor according to claim 1, wherein a region of the base layer adjacent to the emitter region has a thickness of 5 nm or more. Bipolar transistor. 8. The heterobipolar transistor according to claim 7, wherein a region of said base layer adjacent to said emitter region has a thickness of 10 nm or more. 9. The hetero bipolar transistor according to claim 1, wherein a remaining region of the base region excluding a region adjacent to the emitter region is from the emitter region to the collector region. Characterized in that the band gap is reduced in the direction toward. 10. The hetero bipolar transistor according to claim 1, wherein a region of the base region other than a region adjacent to the emitter region is from the emitter region to the collector region. A hetero bipolar transistor having a composition in which the C content increases in the direction. 11. The hetero bipolar transistor according to claim 1, wherein the base region is adjacent to a first base region including a region adjacent to the collector region, and is adjacent to the emitter region. And a second base region including a second base region, wherein a band gap of at least an end of the first base region on the side of the second base region is equal to or smaller than a band gap of the second base region. Transistor. 12. The hetero-bipolar transistor according to claim 11, wherein a difference in Ge content between at least an end of the first base region on the side of the second base region and the second base region is Δx, A heterojunction bipolar transistor characterized in that, when a difference in C content between at least the end portion on the side of the second base region and the second base region is Δy, there is a relationship of Δx ≧ 4.288Δy. 13. The hetero-bipolar transistor according to claim 12, wherein, in the first base region except for an end on the side of the second base region, the first base region goes from the second base region to the collector region. A hetero bipolar transistor characterized in that the band gap is reduced in the direction. 14. The hetero bipolar transistor according to claim 13, wherein a difference in Ge content between at least an end of the first base region on the side of the second base region and the second base region is Δx, A heterojunction bipolar transistor characterized in that, when a difference in C content between at least the end portion on the side of the second base region and the second base region is Δy, there is a relationship of Δx ≧ 4.288Δy.