JP2737152B2 - SOI forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an S-port for manufacturing a TFT or a three-dimensional IC.
The present invention relates to a method for forming an OI.

[Conventional technology]

Conventional SOI formation methods include the International Electron Device Meeting (IEDM) 1987, p.
36, T. Maekawa et al. In this conventional technique, a silicon single crystal layer is formed on a SiO ₂ insulating film on the surface of a silicon substrate, and as a procedure, a polycrystalline silicon layer is formed on the SiO ₂ insulating film by a low-pressure CVD method, and then a silicon ion layer is formed. To form an amorphous island by a photolithographic method, and then recrystallized by a solid phase growth method, and thereafter, a silicon single crystal layer is epitaxially grown.

[Problems to be solved by the invention]

However, according to the above-mentioned prior art, the SOI forming method has some problems as listed below.

(1) Although the ion implantation method of silicon is used to amorphize the deposited polycrystalline silicon, the ion implantation method has a low throughput and an expensive apparatus, so that the manufacturing cost increases. Further, there is a problem that the implanted ions cause a large damage to the underlying substrate, which adversely affects devices formed on the underlying substrate.

(2) The amorphous silicon layer is formed in an island shape by a photo process. However, the number of processes is increased, and the amorphous layer left by the photo process is contaminated, and the quality of the island crystal is reduced. There is a problem that it decreases.

(3) Since the thickness of the island-shaped amorphous layer is large and the number of silicon atoms contained in one island is large, annealing for a long time is required for crystallization.

(4) Since an ion implantation step and a photolithography step are required, it is difficult to use a large substrate such as a glass substrate.

The problems listed here are important issues related to the crystallinity and manufacturing cost of SOI. Therefore, the present invention is intended to solve these problems, and an object of the present invention is to provide a method for forming an SOI that has good crystallinity of the SOI and that can be uniformly manufactured over a large area at a low manufacturing cost. To provide.

[Means for solving the problem]

The SOI forming method of the present invention includes a step of forming trenches at a predetermined pitch in an insulating substrate, a step of depositing amorphous silicon in the trenches, and a step of annealing the amorphous silicon to form a single piece in the trenches. The method is characterized by including a step of forming a crystalline silicon seed and a step of forming an epitaxial layer by crystal-growing the single-crystal silicon seed.

The SOI forming method of the present invention is characterized in that the surface migration length of the atoms of the amorphous silicon is larger than the pitch between the trenches.

〔Example〕

 The present invention will be described in more detail based on examples.

(Reference Example) FIGS. 1 (a) to 1 (d) are for explaining a reference example of the present invention, and a method of forming an SOI of Si by forming a single crystal Si layer on a SiO ₂ layer on the surface of a Si substrate. 3 is a schematic cross-sectional view of the substrate in the middle of each step of FIG. FIG. 1 (a) shows the Si in the preparation.
FIG. 3 is a schematic sectional view of a substrate. The entire surface of a Si substrate 101 is provided with an SiO ₂ layer 102 as an insulator to constitute an insulating substrate. The SiO ₂ layer 102 is formed by thermally oxidizing a Si substrate, and has a thickness of about 5000 °. The SiO ₂ layer may be formed using a CVD method, a sputtering method, or the like in addition to the thermal oxidation method. Fig. 1 (b)
FIG. 3 is a schematic cross-sectional view of the Si substrate after an amorphous Si film is deposited, and an amorphous Si film 103 is formed on the surface of the SiO ₂ layer 102.
The amorphous Si film 103 is deposited by subjecting a monosilane (SiH ₄ ) gas to plasma decomposition while the Si substrate is heated to 250 ° C. The surface of the amorphous Si film 103 has irregularities, and the average thickness is 120 °. Further, the thickness of the amorphous semiconductor layer may be 200 ° or less. As a method of forming an amorphous Si film, there are a thermal CVD method and a sputtering method other than the plasma CVD method. Fig. 1 (c)
FIG. 4 is a schematic cross-sectional view after an amorphous Si single crystallization step performed following the above-described amorphous Si film deposition step. The single crystallization process is a process in which a substrate is placed in an inert atmosphere and heated to a high temperature, and the energy is applied to amorphous Si to promote migration, interatomic bonding or aggregation. In this embodiment, the substrate is heated to 600 ° C. in an N ₂ atmosphere.
By keeping the above conditions and performing annealing for 5 hours or more, single-crystal Si seeds 104 were formed on the surface of the SiO ₂ layer 102 as shown in FIG. 1C. The single-crystal Si seeds were partially aggregated and formed, and the average distance between the single-crystal Si seeds was about 2 μm.
As a result of X-ray diffraction, each single-crystal Si seed was a single crystal preferentially oriented in the (111) direction. In this single crystallization process, Si
The energy given to the atoms may be, for example, light energy or particle energy that promotes the above-mentioned recrystallization, in addition to heat energy. That is, a step of irradiating the amorphous Si film with ultraviolet light such as an excimer laser may be adopted as the single crystallization step. FIG. 1 (d) is a schematic cross-sectional view after a single crystal Si epitaxial growth step performed subsequent to the above-described amorphous Si single crystal step. The epitaxial growth of single crystal Si is performed by a thermal decomposition CVD method by heating the substrate shown in FIG. 1 (c) to a growth temperature of 1100 ° C., introducing dichlorosilane (SiH ₂ Cl ₂ ) gas. When the pressure in the reaction tube was set to 30 Torr and epitaxial growth was performed for 20 minutes, the Si epitaxial layer 1 was formed over the entire surface of the SiO ₂ layer 102 as shown in FIG.
05 was formed. The thickness of this Si epitaxial layer is about 3
μm and the lateral grain size was about 2 μm. As a result of X-ray diffraction, the epitaxial layer is oriented in the (111) direction. A thin film transistor (TFT) was manufactured using this epitaxial layer, and the electric field mobility was measured. As a result, the electron mobility was 190 cm ² / V · S at room temperature. This value is one or more orders of magnitude better than that of a TFT using a polycrystalline Si layer.

(Embodiment) FIGS. 2 (a) to 2 (d) are for explaining an embodiment of the present invention, in which a selective SOI formation for forming a single crystal Si layer in a trench formed on the surface of a quartz substrate. FIG. 2 is a schematic cross-sectional view of a quartz substrate in each step of the method. Fig. 2 (a)
1 is a schematic cross-sectional view of a quartz substrate used for forming an SOI.
A trench 202 is formed on the surface of a quartz substrate 201. The pitch between the trenches is set to be shorter than the migration length of the Si atoms. In this embodiment, the pitch is set to 5 μm. The size of the trench was 2 μm square and the depth was 1 μm. As a method for forming the trench, there is a dry etching method such as a wet etching method and a reactive gas phase etching. FIG. 2 (b) is a schematic cross-sectional view of the quartz substrate after the amorphous Si is deposited.
Amorphous S by the plasma CVD method as described in Example-1
An i film 203 was formed on the surface of the quartz substrate 201 and the trench 202.
The thickness of the amorphous Si film is 80 ° on average. FIG. 2 (c) is a schematic cross-sectional view of the quartz substrate after a single crystallization step performed after the above-described amorphous Si film forming step. The single crystallization process is intended to aggregate all the amorphous Si deposited on the surface of the quartz substrate in the trench to form a single crystal Si seed inside the trench, and the condition is that the Si atom is used. The temperature of the quartz substrate was set to 800 ° C. so that the surface migration length of the substrate was larger than the pitch between the trenches of 5 μm. When annealing is performed for 3 hours or more in an N ₂ atmosphere, as shown in FIG.
204 was formed. This single crystal Si seed was a single crystal oriented (111) with respect to the surface of the quartz substrate. FIG. 2 (d) is a schematic cross-sectional view after an epitaxial growth step performed subsequent to the above-described single crystallization step. The pressure inside the reaction tube is reduced, the temperature is kept high, and the single-crystal S
Epitaxial growth is performed using the i species as growth nuclei. In this embodiment, the pressure inside the reaction tube is 10 Torr, the substrate temperature is 1100 ° C.,
Monosilane (SiH ₄ ) was used as a source gas. As shown in FIG. 2D, the cross section of the quartz substrate after the epitaxial growth has a Si epitaxial layer 205 formed in the trench. This Si epitaxial layer is a single crystal having a (111) orientation, and is epitaxially grown on the single crystal Si layer 204.

In the reference examples and the examples, each step of the SOI formation method uses a separate semiconductor device.
It is easy to continuously form SOI with a single apparatus that can perform deposition, single crystallization, and epitaxial growth of an amorphous semiconductor layer. In the embodiments, as a semiconductor material
Although the present invention is directed to Si, the present invention is not limited to this material, and a mixed crystal such as Ge or Si-Ge; a III-V compound semiconductor such as GaAs; a II-VI compound semiconductor such as ZnSe; And a semiconductor material composed of these mixed crystals. As the epitaxial growth technique, a vapor phase method such as an MBE method and a MOCVD method can be applied in addition to the thermal decomposition CVD method.

According to the above embodiment, the following effects can be obtained.

(1) Since a single crystal seed is formed by utilizing the aggregation effect of an amorphous semiconductor layer on an insulating substrate, a semiconductor substrate having a seed crystal is unnecessary, and patterning is also unnecessary. Inexpensive, large-area substrates can be used, and manufacturing costs are reduced.

(2) Since the steps from the deposition of the amorphous semiconductor layer to the epitaxial growth can be continuously performed with the same apparatus, a high-quality SOI structure with good reproducibility without contamination by impurities and the like can be obtained. Further, since the number of apparatuses and the number of steps can be reduced, the manufacturing cost is reduced.

(3) SOI at any place even if the insulating substrate has irregularities
Can be formed.

(4) There is no damage to the substrate, and there is no need to process the substrate with high precision as in graphoepie.

(5) Since the annealing time from amorphous to single crystallization can be short, the throughput is large.

〔The invention's effect〕

The invention of the present application can provide the following remarkable effects by satisfying the above constitutional requirements.

(A) A trench is formed at a predetermined pitch in an insulating substrate, a crystal seed is formed therein, and the crystal seed is epitaxially grown. Therefore, epitaxial layers can be formed at predetermined intervals.

(B) Even if the insulating substrate has irregularities, SO
I can form.

[Brief description of the drawings]

FIGS. 1A to 1D are views for explaining a first embodiment of the present invention, and are schematic cross-sectional views of a substrate in the middle of each step of a method of forming an SOI of Si. 101 ... Si substrate 102 ... SiO ₂ layer 103 ... Amorphous Si film 104 ... Single crystal Si seed 105 ... Si epitaxial layer FIGS. 2 (a) to 2 (d) show a second embodiment of the present invention. It is for explaining an example and shows a schematic cross-sectional view of a quartz substrate in each step of a selective SOI forming method. 201 ... Quartz substrate 202 ... Trench 203 ... Amorphous Si film 204 ... Single crystal Si seed 205 ... Si epitaxial layer

Claims (2)

(57) [Claims] A step of forming trenches at a predetermined pitch in an insulating substrate; a step of depositing amorphous silicon in the trenches; and annealing the amorphous silicon to form a single-crystal silicon seed in the trenches. Forming an epitaxial layer by crystal-growing the single-crystal silicon seed. 2. The SOI forming method according to claim 1, wherein a surface migration length of the amorphous silicon atoms is larger than a pitch between trenches.