JPH05129635A - Field effect transistor and production thereof - Google Patents

Abstract

PURPOSE:To provide a high-gain n-type field effect transistor which uses Ge as a channel with improved channel electronic mobility and production thereof. CONSTITUTION:An n-type field effect transistor shown by the figure 1 is provided with a distortion modified Ge/Sn buffer layer 2 and an Si1-xGex layer 3 on a Ge (110) or Ge (111) substrate 1. The transistor is provided with a Ge channel layer 4 and a modulating dope n-Si1-xGex layer 5, which are lattice- aligned with the buffer layer and to which tensile strain is applied, and an Si layer 6. Then, an Si oxide film 7, source and drain areas 8 and 9, a gate electrode 11 and source and drain electrodes 10 and 12 are formed. Thus, the mobility is improved compared with the bulk by permitting the <1-10> direction of Ge to which tensile strain is applied in a direction parallel to the (110) plane to be the channel direction or by permitting Ge to which tensile strain is applied in a direction parallel to the (111) plane to be the channel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field effect transistor having Ge as a channel, and provides a high gain n-type field effect transistor and a method of manufacturing the same.

[0002]

2. Description of the Related Art As a structure for increasing the gain of an n-type field effect transistor (FET) having a channel of Ge, n-
A modulation-doped field effect transistor (MODFET) having a SiGe / Ge heterostructure is known (R. People .:
Phys. Rev. B34 , 2508 (1986)). This transistor will be described with reference to FIG.

A conventional MODFET schematically shown in FIG.
Is an n-type modulation doped S formed on the Ge (001) substrate 13.
i _0.15 Ge _0.85 layer 14, source and drain electrodes 15,
17 and a gate electrode 16. In this structure, electrons are supplied from the n-SiGe layer and the Ge at the n-SiGe / Ge interface
Since the side serves as a channel through which electrons travel, the electrons can travel two-dimensionally with high mobility without being subjected to impurity scattering.

[0004]

In the above-mentioned MODFET using Ge (001) as a channel, the ideal maximum electron mobility is about 3900 cm ² / Vs, which is the same as that of the bulk, and increasing it further is physical. Was impossible.

An object of the present invention is to provide a high-gain field-effect transistor which can obtain a mobility higher than that of a bulk by changing the electronic structure of Ge serving as a channel and thus has a large transconductance (g _m ). To get.
Moreover, it is providing the manufacturing method further.

[0006]

[Means for Solving the Problems] The above-mentioned object is to make the channel direction be the <1-10> direction of Ge that has been subjected to tensile strain in the direction parallel to the (110) plane in the modulation-doped structure, or This is achieved by using Ge strained in the direction parallel to the (111) plane as a channel.

As a method of manufacturing the same, a single crystal buffer layer having a lattice constant larger than that of Ge is formed in order to receive tensile strain parallel to the surface direction of the Ge channel, and the Ge layer is lattice-matched to the buffer layer. Grow strain. Here, the buffer layer was formed on the Ge substrate.
A superlattice layer consisting of Ge and Sn is used.

[0008]

First, FIG. 2 shows an energy diagram in the vicinity of the bottom of the conduction band of the strained Ge (110) layer which is subjected to tensile strain in the direction parallel to the (110) plane. As shown in Fig. 2, due to tensile strain, the 8-fold degeneracy at the bottom of the conduction band is released, and the electrons are <01-1>, <0-11>,
Four valleys in <10-1> and <-101> directions (hatched areas in the figure)
Localized to. Here, <-hkl> indicates the opposite direction to <hkl>. These electrons, <1-10> in the channel direction, the effective mass of bulk _{m e (≒ 0.12m 0: m} 0 is electron mass in vacuum) have a lighter effective mass m _t (≒ 0.082m ₀₎ than is doing. When the electron mobility is determined only by phonon scattering without impurity scattering as in the modulation-doped structure, the mobility is proportional to the effective mass of the electron to the (-5/2) th power. Therefore, in a MODFET using strained Ge (110) as a channel, the maximum electron mobility is 10000c.
It is possible to increase up to m ² / Vs.

Similarly, FIG. 3 shows an energy diagram in the vicinity of the bottom of the conduction band of the strained Ge (111) layer subjected to tensile strain in the direction parallel to the (111) plane. As shown in Fig. 3, due to tensile strain, the 8-fold degeneracy at the bottom of the conduction band is released, and the electrons are divided into two valleys in the <111> and <-1-1-1> directions (hatched areas in the figure). Localize. The electrons of these valleys have an effective mass m _t in the direction parallel to the (111) plane, so that the mobility can be increased similarly to the (110) plane.

Due to the action as described above, the strain Ge
In the (110) channel or strained Ge (111) channel,
It is possible to reduce the effective mass and realize a field effect transistor having high mobility, that is, high gain.

[0011]

EXAMPLE A MOS type MODFET will be described below with reference to FIG.
An example of manufacturing the will be described.

In order to receive tensile strain parallel to the surface direction of the Ge channel, a single crystal buffer layer having a lattice constant larger than that of Ge is formed, and lattice-matched with the buffer layer to grow Ge strained. Here, an example in which a superlattice layer made of Ge and Sn formed on a Ge substrate is used as the buffer layer will be described.

First, after chemically treating the 10 Ω · cm p-Ge (110) substrate 1, molecular beam epitaxy (MB) is performed.
E) It is introduced into the apparatus and the substrate surface is cleaned. Next, a strain-relaxed Ge / Sn superlattice is formed by the following procedure. After setting the substrate temperature to 95 ° C., the substrate is irradiated with a Sn molecular beam to form one Sn atomic layer at a deposition rate of about 0.01 nm / s. In order to suppress the surface segregation of Sn, the substrate temperature was lowered to 50 ° C and eight Ge atomic layers were formed at a deposition rate of about 0.01 nm / s. Then, the substrate temperature was raised to 230 ° C to improve the crystallinity. 12 layers of Ge atomic layers are formed. The above procedure is repeated to form the buffer layer 2 consisting of a Ge ₂₀ / Sn ₁ superlattice layer of about 0.5 μm. Here, when the Ge ₂₀ / Sn ₁ superlattice layer is formed as thick as 0.5 μm, the strain due to the difference in lattice constant between the Ge substrate and the buffer layer is relaxed, and the lattice constant of the buffer layer is almost the same as that of the Ge ₂₀ layer and the Sn 1 layer. It becomes a lattice constant, which is about 0.8% larger than that of Ge. Therefore, when the Ge layer is strain-grown by lattice matching with this buffer layer, 0.8% tensile strain is applied.

Here, in this embodiment, as the buffer layer, Ge / Sn having a band gap smaller than that of the channel Ge is used.
Since a superlattice layer is used, a large bandgap thickness of 10 nm is used as a barrier layer for electron confinement on the buffer layer.
A Si _1-x Ge _x layer 3 with x = 0.85 was formed. A 10 nm-thickness Ge layer 4 serving as a channel was formed thereon. Furthermore, as an electron supply layer, 1 × 10 ¹² (1 / cm ² )
Atomic layer doped x = 0.85 with 20 nm thickness of modulation-doped Si
Were sequentially formed under the conditions of strain grown at a growth temperature 400 ° C. The _1-x Ge _x layer 5. Further, a 1 nm Si layer 6 was formed. The heterostructure thus produced is taken out from the MBE apparatus, and a Si oxide film 7 having a film thickness of 12 nm is formed by chemical vapor deposition.
Using the known method, with the <1-10> direction as the channel direction, the source / drain regions 8 and 9 and the gate electrode 11,
The source and drain electrodes 10 and 12 were formed, and a field effect transistor was produced.

In the MODFET manufactured as described above, the mobility was 8000 cm ² / Vs, and the transconductance of the device having the effective channel length of 0.5 μm was 400 mS / mm, which was a good value.

Further, in the MODFET formed on the Ge (111) substrate by the same method, the mobility is 7500 cm ² / Vs,
The transconductance showed a good value of 350 mS / mm.

[0017]

According to the present invention, the _{n-Si 1-x Ge x} / Ge modulation doped structure, channel <1-10> direction of Ge that received a tensile strain in a direction parallel to (110) plane Direction, or G that has undergone tensile strain in the direction parallel to the (111) plane
By using e as a channel, the mobility can be increased more than that of the bulk, and a high gain n-type field effect transistor can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining a first embodiment.

Figure 2: Energy diagram near the bottom of the conduction band of strained Ge (110) layer

[Fig. 3] Energy diagram near the bottom of the conduction band of the strained Ge (111) layer

FIG. 4 is a cross-sectional view for explaining a conventional technique.

[Explanation of symbols]

1 ... Ge (110) or Ge (111) substrate 2 ... Ge / Sn buffer layer 3 ... Si _1-x Ge _x layer 4 ... strained Ge channel layer _{5 ... n-Si 1-x} Ge x modulation doped layer 6 ... Si Layer 7 ... Si oxide film 8, 9 ... Source / drain region 10, 12 ... Source / drain electrode 11 ... Gate electrode 13 ... Ge (001) substrate 14 ... n-Si _1-x Ge _x modulation doped layer 15, 17 ... Source / drain electrode 16 ... Gate electrode

Claims (6)

[Claims] 1. A field-effect transistor having a channel on the Ge side of a modulation-doped n-Si _1-x Ge _x / Ge interface, wherein (110)
<1-10> of the above Ge that has undergone tensile strain in the direction parallel to the plane
A field effect transistor, wherein the direction is a channel direction, or the Ge strained in the direction parallel to the (111) plane is used as a channel. 2. The field effect transistor according to claim 1, wherein the channel is formed on a buffer layer made of Ge and Sn. 3. A method for manufacturing a field effect transistor having a channel on the Ge side of a modulation-doped n-Si _1-x Ge _x / Ge interface, wherein a single crystal layer having a lattice constant larger than Ge of the channel is formed. A second step of strain-growing the Ge by lattice matching with the single crystal layer after the first step, and the strain-grown Ge after the second step. Is used as the channel, a source and a drain are formed, and a gate electrode is formed on the channel. 4. The main surface of a p-Ge (110) substrate is irradiated with a Sn molecular beam to form a Sn atomic layer, and the Ge atomic layer is formed thereon at least twice. A first step of forming a superlattice layer of Sn and Sn, a second step of forming a Ge atomic layer to be the channel above the superlattice layer after the first step, and the second step of After the process, the source and drain regions are formed so that the direction of the channel becomes the (1-10) direction of the Ge atomic layer that becomes the channel, and a gate electrode is formed on the Ge atomic layer that becomes the channel. And a third step of forming the field effect transistor. 5. The method of manufacturing a field effect transistor according to claim 4, wherein the Ge atomic layer serving as the channel and the superlattice layer is sandwiched between the second step and the third step. As described above, a method for manufacturing a field effect transistor, comprising forming a SiGe layer made of Si and Ge having a band gap larger than that of the superlattice layer. 6. The method of manufacturing a field effect transistor according to claim 4, further comprising an electron supply layer which is made of Si and Ge and which is atomically doped with Sb at a central portion in a film thickness direction. A method for manufacturing a field effect transistor, which is formed in contact with the Ge atomic layer to be the channel and below the gate electrode.