CN1057404C - Ge-Si heterojunction diode with low forward voltage drop and high velocity - Google Patents

Abstract

The present invention gives an SiGe heterostructure VF high-speed diode with a new structure, which is characterized in that the present invention uses SiGe polycrystals, SiGe pseudocrystals and a Si monocrystal multilayer structure, and the VF of a PN junction is greatly decreased. When Ge components in the SiGe polycrystal are much enough, the present invention becomes a multi-molecule device. The present invention has the advantages of low VF, high switching speed, high working frequencies, simple processes of devices, good repeatability, etc., also gives selecting principles of the Ge components in the SiGe polycrystals and design principles of layers in the diode of the present invention, is suitable for industrial mass production, and is a new-type high-speed diode with good performance and strong practicability.

Description

Ge-Si heterojunction diode with low forward voltage drop and high velocity

The invention belongs to technical field of semiconductor device.

As everyone knows, the forward voltage drop V of silicon PN junction diode _FBe about 0.7～0.8V, because there is few sub-storage effect in the bipolar operation pattern, make device that shortcomings such as switching speed is slow, operating frequency is low be arranged, people had invented Schottky barrier diode (SBD) afterwards, and PN junction potential barrier control Schottky diode (JBS), their V _F=0.55V, and be how sub-device, the switching speed of device and operating frequency are improved, but the former exist reverse leakage current big, and the shortcoming that further increases with anti-the increase partially, and the latter all has very high requirement (requiring the following hachure of 0.5 μ m) to technology and equipment; On the other hand, germanium (Ge) PN junction diode has low V _F(about 0.25v), but there is reverse breakdown voltage V in it _BRLow shortcoming, and similar with SiPN knot be the bipolar operation pattern, switching speed is slow; In recent years, someone has proposed germanium silicon (SiGe)/silicon (Si) heterojunction diode, it is on the epitaxy Si sheet, be provided with a layer thickness less than critical thickness, high concentration SiGe pseudomorphic layer that its conduction type is opposite with epitaxy Si, directly form and draw metal electrode then thereon, make the SiGe/Si heterojunction diode, since the restriction of device architecture, the self-built electromotive force V of this PN heterojunction _BiCan not be effectively reduced, make the forward characteristic of SiGe/Si heterojunction diode more little than the improvement of Si diode.

The objective of the invention is to propose a kind of germanium and silicon heterogeneous junction diode of new construction, make it both have low V _F, high switching speed and operating frequency, the V identical with the Si device _BR, have simple, the good reproducibility of technology again, be easy to characteristics such as industrialized production.

According to the invention task, the low V of the SiGe heterojunction that the present invention proposes _FHigh speed diode is characterized in that adopting the p of high-dopant concentration ⁺SiGe polycrystalline (or n ⁺The SiGe polycrystalline) as the positive pole (or negative pole) of diode.Its concrete structure: as shown in Figure 1, promptly the surface of Si substrate low doping concentration epitaxial loayer 2 is provided with conduction type SiGe pseudomorphic layer 3 identical with it and SiGe polycrystal layer 4, on described 4 layers, also be provided with the conduction type high-dopant concentration SiGe polycrystal layer 5 opposite with it, form metal electrodes and draw positive pole (or negative pole) from described 5 layers, 1 forms metal electrode and draws negative pole (or anodal) from Si substrate high-dopant concentration district.It corresponds to energy band diagram such as Fig. 2 of Fig. 1.

With p ⁺The SiGe/nSi diode is an example, as can be seen from Figure 2, SiGe/Si heterojunction boundary place valence band fracture Δ Ev, it will stop the hole to be injected into the Si district from the SiGe district, promptly stop the injection of minority carrier, thereby when the Ge component is enough big, when promptly Δ Ev is enough big, can regard device of the present invention as more than one sub-device, so it has high-speed and high operating frequency.

As everyone knows, the self-built electromotive force V of diode _BiClosely related with the energy gap Eg of material.The Eg=0.67ev of Ge material, the V of Ge PN junction _BiBe about 0.25v; And the Eg=1.18ev of Si material, the V of Si PN junction _BiBe about 0.7v.From Fig. 1, Fig. 2 as can be seen, heterojunction diode of the present invention can be regarded as by p in fact when positively biased ⁺The pn knot that SiGe/nSiGe forms, its V _BiObviously be V between Ge and SiGeP-N knot _BiBetween, the V that can realize _BiScope is: 0.25v≤V _Bi≤ 0.5v is than the V of Si material _BiReduce its V greatly _BiChange to some extent with the variation of Ge component in the SiGe material, when the Ge component was 100%, the SiGe material became the Ge material, then V _Bi=0.25v.When the Si1 layer, when 2 layers upward pressure drop can be ignored, its V _F=V _Bi=0.25v, this characteristic is that the described SiGe diode of prior art institute is irrealizable; And when anti-inclined to one side, the PN junction depletion region is mainly to n ^-The expansion of Si district, i.e. n ^-The Si district is the device withstand voltage district.In other words, this device has the withstand voltage V of Si diode _BR

As everyone knows, because of the Eg of Si is bigger, under identical doping content condition, the Si device has the V more much higher than Ge device _BRTherefore, SiGe diode of the present invention has Ge or SiGe device advantage when positively biased, and has Si device advantage when anti-inclined to one side.

Ge component X can regulate Ge component content from 1%～100% variation in the SiGe material in the present invention, and promptly the size of scalable Δ Ev just can be traded off according to actual needs and be regulated V _FAnd the contradiction between the operating frequency.When the needs operating frequency is high, increase the Ge component, can stop the hole to enter n ^-The Si district; As needs V _FWhen low, can reduce the Ge component, allow a small amount of hole enter n ^-Play electricity and lead modulating action in the district, makes V _FReduce.Concretely, to reverse breakdown voltage V _BRThe low-voltage device of≤50v, V _FMain self-built electromotive force V by heterojunction _BiDecision, i.e. V _F≈ V _Bi, the Eg little then V of healing _BiLittler, V _FLittler, so should choose bigger Ge component X, generally should get 0.3≤X≤1; To reverse breakdown voltage V _BRThe high tension apparatus of 〉=100v, its V _FBy V _BiAnd n ^-Pressure drop Vn on the Withstand voltage layer ^-Decision, i.e. V _E=V _Bi+ Vn ^-, work as Vn ^-＞＞V _BiThe time, under the requirement of satisfying frequency of utilization, should suitably reduce Ge component X, at this moment, the value of X is generally 0.01≤X＜1.

Provide design principle of the present invention below:

In the present invention, with the effect of the SiGe pseudomorphic layer 3 of Si substrate identical conduction type be the mismatch that reduces or eliminate SiGe/Si heterojunction boundary lattice, thereby reduce or eliminate the reverse current that consequent interfacial state and defective cause, the thickness of this pseudomorphic layer is Δ _SiGe, generally should be less than the critical thickness that forms pseudo-crystal, for example when Ge component X is 0.4 in the SiGe material, Δ _SiGeShould be less than 100 .

Thickness with the SiGe polycrystal layer 4 of Si substrate identical conduction type among the present invention is W ₁, its W ₁Selection principle be: to single side abrupt junction, depletion width X under the zero-bias _DoCan be expressed as: $X_{\mathrm{do}}=\sqrt{(2{\mathrm{\ϵ}}_o{\mathrm{\ϵ}}_3/q{N}_D)\·V_{\mathrm{bi}}}$ In the formula: N ₀Doping content for the n-SiGe layer

ε _oDielectric constant for vacuum

ε _sRelative dielectric constant for SiGe

To reverse breakdown voltage V _BRThe low-voltage device of≤50v: should get W ₁=X _Do, can make V among the present invention like this _Bi≈ V _F, and 0.25v≤V _Bi≤ 0.5v;

To reverse breakdown voltage V _BRThe high tension apparatus of 〉=100v: generally get 0＜W ₁＜X _Do, W ₁Reduce help improving Δ Ev blocking hole and enter n ^-The ability in Si district, thus help improving device speed.

Thickness with the high-dopant concentration SiGe polycrystal layer 5 of Si substrate transoid among the present invention is W ₂W ₂Should be able to satisfy with its on metal electrode form good Ohmic contact.

SiGe layer among the present invention can adopt the method growth of chemical vapor deposition (CVD), carries out phosphorus, arsenic or boron autodoping then and forms, and its technology is simple, good process repeatability, be fit to industrialized production.

In SiGe3,4,5 layers, the distribution of Ge component can be uniformly, and also distribution gradient 5 increases with metal electrode from SiGe layer 3/Si layer 2 interface to the SiGe layer at the interface gradually such as the Ge component, becomes Gradient distribution.During as Gradient distribution, can form the accelerating field to non-equilibrium few son, in turn-offing transient state, this electric field plays the effect of extracting non-equilibrium few son out, thereby can improve device speed.

Germanium silicon of the present invention (SiGe) heterojunction hangs down V _FHigh speed diode has low V _F(0.25v≤V _Bi≤ 0.5v), reverse leakage current is little and irrelevant with anti-increase partially, fast and the operating frequency advantages of higher of switching speed, compare with Schottky barrier diode and also to have advantages such as the little and equivalent capacity of parasitic series resistance is little, it is simple to add preparation technology, good process repeatability is suitable for industrialized production, is the good practical low V of a kind of performance _FHigh speed diode.

Fig. 1 structural representation of the present invention

Fig. 2 with respect to the heterojunction energy band diagram of Fig. 1 (with p ⁺SiGe-n Si diode is an example)

Among the figure: 1-high-dopant concentration Si substrate; The 2-Si epitaxial loayer; The SiGe pseudomorphic layer of 3-and Si substrate 1 homotype; The SiGe polycrystal layer of 4-and Si substrate 1 homotype; The SiGe polycrystal layer of 5-and Si substrate 1 transoid.

Provide embodiments of the invention in conjunction with Fig. 1:

Select＜100〉crystal orientation n/n+Si epitaxial wafer its epitaxial loayer p=0.5 Ω cm, d=6 μ m for use; On its n-Si face, use CVD method extension one deck n-SiGe pseudomorphic layer, its p=0.5 Ω cm, Δ _SiGe=100 , Ge component X=0.35 in the SiGe material; Use CVD method deposit one deck n-Ge polycrystal layer (being the X=1 of Ge in the SiGe material) on pseudomorphic layer then, its p=0.5 Ω cm, W ₁=2000 ; On nGe, use its N of CVD method deposit one deck p+Ge polycrystal layer (being Ge X=1 in the SiGe material) again _A=10 ²⁰Cm ^-3, W ₂=5000 ; Steam Al then thereon, alloy, the positive pole of formation diode; With the thinning back side of Si epitaxial wafer with carry out conventional multilevel metallization, form the negative pole of diode, thereby make the low V of SiGe heterojunction _FHigh speed diode.

SiGe diode parameters of the present invention with have identical Si substrate, the Si diode of identical layout size compares parameter testing and the results are shown in Table 1:

The conventional Si diode of test parameter SiGe diode of the present invention

V _F(v) 0.35 0.75

t _s(ns) 0 450

t _off(ns) 20 550

V _BR(V) 35 35

Claims (5)

1, the low V of SiGe heterojunction _FHigh speed diode, comprise a negative pole and a positive pole, it is characterized in that it comprises: the surface in the low doping concentration district (2) of epitaxy Si substrate is provided with conduction type SiGe pseudomorphic layer (3) identical with it and SiGe polycrystal layer (4), on described (4) layer, also be provided with the conduction type high-dopant concentration SiGe polycrystal layer (5) opposite with it, form metal electrode and draw positive pole (negative pole) from described (5) layer, from high-dopant concentration district (1) the formation metal electrode of epitaxy Si substrate and draw negative pole (positive pole).

2, the low V of SiGe heterojunction according to claim 1 _FHigh speed diode is characterized in that: described SiGe polycrystal layer Ge component X can change in 0.01≤X≤1.

3, the low V of SiGe heterojunction according to claim 1 _FHigh speed diode is characterized in that: the thickness deltat of the SiGe pseudomorphic layer (3) of described and Si substrate homotype _SiGeShould be less than the critical thickness that forms pseudo-crystal.

4, the low V of SiGe heterojunction according to claim 1 _FHigh speed diode is characterized in that: the thickness W of the SiGe polycrystal layer (4) of described and Si substrate homotype ₁Choose:

(1) to V _BRThe low-voltage device W of≤50v ₁=X _Do(X _DoDepletion width under the zero-bias);

(2) to V _BRHigh tension apparatus 0＜W of 〉=100v ₁＜X _Do(X _DoDepletion width under the zero-bias).

5, the low V of SiGe heterojunction according to claim 1 _FHigh speed diode is characterized in that: the Ge component in the SiGe material of described (3), (4), (5) layer:

(1) is evenly distributed;

(2) layer and metal electrode interface from SiGe (3)/Si (2) PN junction interface to (5), the Ge component is the Gradient distribution that increases gradually.

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