Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2000-09-08
2001-12-04
Wojciechowicz, Edward (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S018000, C257S019000, C257S055000, C257S616000, C257S617000
Reexamination Certificate
active
06326667
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a semiconductor device having a strained Si layer and a method of producing a semiconductor device having a strained Si layer.
BACKGROUND ART
Various semiconductor devices employing silicon crystals are used widely. To enhance mobility of an electron that runs through a silicon crystal make performance of such a semiconductor device enhance effectively.
However, since the upper limit of the mobility of an electron that runs through a silicon crystal depends on the physical characteristic of a silicon crystal, any change in the structure of a semiconductor device can't change the proper mobility that the silicon crystal has own. Nevertheless, it is reported that the mobility of an electron can be enhanced in a strained silicon crystal that is obtained by straining a usual silicon crystal.
Generally the strained Si layer is produced by growing a thin silicon crystal layer, whose thickness is thinner than the thickness that the crystal is lattice relaxed, on a crystal having a lattice constant that is slightly different from the lattice constant of the silicon crystal. Typically, a SiGe alloy crystal layer whose Ge content is about 20% (where the lattice constant of the SiGe crystal is larger by about 0.8% than the lattice constant of the silicon crystal) is provided as an underlying layer, and then the thin silicon layer having thickness of 100 nm or less on the SiGe layer.
However, because it is difficult to obtain an SiGe crystal substrate which is produced at an industrial large scale and which is not expensive but of a high quality, a silicon wafer is usually employed as a substrate and an SiGe layer is grown by a vapor phase growth on the silicon wafer to a thickness lattice-relaxed (critical film thickness). So, it can obtain a lattice-relaxed SiGe underlying layer.
Nevertheless, Since in this method the SiGe crystal layer whose Ge content is about 20% grows on the Si substrate directly, a lot of defects such as the dislocation that is yielded when the SiGe crystal layer is lattice-relaxed become nucleuses that make the dislocation penetrate to a strained silicon layer growing thereon.
In an attempt to prevent the defects in a SiGe layer upon the lattice relaxation, a buffer layer is formed between a silicon substrate and a lattice-relaxed SiGe layer. Such buffer layer is generally a sufficiently thick SiGe layer having the composition similar to the lattice-relaxed SiGe layer (similar lattice constant) or a gradient SiGe layer having the composition Ge to gradually increase to the lattice-relaxed SiGe layer.
However, since total thickness of the buffer layer and the lattice-relaxed SiGe layer is extremely thick layer, it may make following process difficult. For example, in a case where the devices are integrated, fine devices should be separated from each other, but a SiGe layer having a thickness of 1 &mgr;m or more is too thick to separate the devices from each other. Also in an SOI (silicon-on-insulator) technology expected to be capable of reducing the junction capacity, since a SiGe layer (combined with the buffer layer) having a thickness of 1 &mgr;m or more is too thick, it makes junction capacity of a device increase.
Thus, it is difficult to obtain a satisfactory strained Si layer unless a thick lattice-relaxed SiGe layer is formed in combination with a buffer layer, so it is difficult to separate devices and to decrease the junction capacity of a device.
SUMMARY OF THE INVENTION
An object of the invention is to provide a semiconductor device and a method of producing a semiconductor device capable of forming a thin lattice-relaxed SiGe layer on an oxide layer and also capable of forming on this lattice-relaxed SiGe layer a satisfactory strained Si layer.
Another object of the invention is to provide a method of producing a semiconductor device capable of re-growing a satisfactory strained Si layer on a lattice-relaxed SiGe layer.
Accordingly, the first aspect of the invention provides a method of producing a semiconductor device comprising the steps of:
forming a strained SiGe layer on a substrate;
introducing oxygen into said strained SiGe layer;
forming an oxide layer by a heat treatment at the position where the oxygen is introduced, so as to make a lattice-relaxed SiGe layer located over said oxide layer; and
growing a strained Si layer over said lattice-relaxed SiGe layer.
In this aspect, it is preferable further comprising a step of forming a Si cap layer over said strained SiGe layer, wherein the surface of said strained SiGe layer is protected during said heat treatment.
Also preferred is that a step of growing an SiGe growing layer over said lattice-relaxed SiGe layer is further comprised, and then growing said strained Si layer over said SiGe growing layer.
Also preferred is that a step of etching the surface of said lattice-relaxed SiGe layer is further comprised, and then growing said strained Si layer.
Also preferred is that said oxide layer divides said strained SiGe layer into a SiGe upper layer that formed over said oxide layer and a SiGe lower layer that formed under said oxide layer.
Also preferred is that said introducing oxygen by an oxygen ion implantation under a condition that the oxygen ion is in said strained SiGe layer.
Also preferred is that a step of a HF treatment for terminating the surface of said lattice-relaxed SiGe layer by hydrogen is further comprised, and then growing said strained Si layer.
Also preferred is that said hydrogen on the surface of said lattice-relaxed SiGe layer is removed by a heat treatment, and then growing said strained Si layer.
Also preferred is that the steps of forming an oxide layer on the surface of said lattice-relaxed SiGe layer and removing said oxide layer by a heat treatment under vacuum are further comprised, and then growing said strained Si layer.
Also preferred is that a step of forming a SiGe buffer layer on said substrate is further comprised, and then forming said strained SiGe layer on said SiGe buffer layer.
Also preferred is that said substrate is a Si substrate.
Also preferred is that said substrate is a silicon-on-insulator substrate.
According to the first aspect of the invention, oxygen atoms are introduced into the strained SiGe layer and then the oxide layer is formed in the strained SiGe layer by heat treatment. The oxide layer divides the strained SiGe layer into a lattice-relaxed SiGe upper layer and a lattice-relaxed SiGe lower layer. A layer thickness of the lattice-relaxed SiGe upper layer becomes thicker by controlling the projection range of the oxygen ion implantation. Since the strain of the strained SiGe layer is relaxed into the oxide layer during the heat treatment, a defect such as a dislocation does not occur upon the lattice relaxation of the SiGe layer.
A second aspect of the invention provides a method of producing a semiconductor device comprising the steps of:
forming a lattice-relaxed SiGe layer on an insulating layer;
a HF treatment for terminating the surface of said lattice-relaxed SiGe layer by hydrogen; and
growing a strained Si layer on the surface of said lattice-relaxed SiGe layer.
In this aspect, it is preferred further comprising a step of removing a part of the surface of said lattice-relaxed SiGe layer, and then terminating said hydrogen on the surface of said lattice-relaxed SiGe layer.
Also preferred is that a step of removing said hydrogen on the surface of said lattice-relaxed SiGe layer by a heat treatment is further comprised, and then growing said strained Si layer.
Also preferred is that a step of growing a SiGe growing layer on said lattice-relaxed SiGe layer is further comprised, and then growing said strained Si layer on said SiGe growing layer.
According to the second aspect of the invention, since terminating the hydrogen protects the surface of the lattice-relaxed SiGe layer and then the strained Si layer grows on the surface of the lattice-relaxed SiGe after removing the hydrogen, the strained Si layer can grow in the better condition.
The third aspect of the invention pr
Kurobe Atsushi
Mizuno Tomohisa
Sugiyama Naoharu
Takagi Shin-ichi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
Wojciechowicz Edward
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