JP3266185B2 - Method for manufacturing polycrystalline semiconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a polycrystalline semiconductor thin film, and more particularly, to a method for manufacturing a polycrystalline semiconductor thin film such as polysilicon (poly-Si) formed at a low temperature.

[0002]

2. Description of the Related Art Transistors are used mainly for improving the performance and definition of amorphous silicon TFTs, which have been developed and put into practical use as switching elements of liquid crystal display devices (LCDs), and for realizing circuits on glass substrates. Polycrystalline silicon thin film field effect transistor using polycrystalline silicon for the active layer (hereinafter referred to as poly-Si TFT)
Is being developed.

Since polycrystalline silicon is a crystalline material, it has an advantage that its mobility is about 100 times higher than that of amorphous silicon which is an amorphous material.

[0004] A general process for manufacturing a poly-Si TFT is as follows. First, an SiO ₂ film is formed on glass as a substrate, and then an amorphous silicon layer is formed by LPCVD. Next, in order to crystallize the amorphous silicon layer, annealing is performed with an excimer laser to form a polycrystalline silicon layer.

Next, after separating each TFT element by etching and forming a gate SiO ₂ layer and a gate electrode in this order, source and drain regions are formed by ion implantation or ion doping. Finally, wiring is formed to complete the TFT.

As described above, a TFT is formed through a number of steps, and its characteristics, mainly the field effect mobility, are determined by the crystallinity of the polycrystalline silicon layer forming the active layer. The crystallinity in this case means, of course, how close the arrangement of silicon atoms of each crystal constituting the polycrystalline semiconductor thin film is to that of single crystal silicon, but also the grain size and surface flatness. Including the contents.

As this kind of technology, Japanese Patent Application Laid-Open No. 5-315
No. 269 (hereinafter referred to as Conventional Example 1) discloses that Si _n H
_{Using 2n + 2} (n = 1 to 3) and GeF ₄ , polycrystalline silicon germanium (poly-SiG
e) A method for forming a thin film is disclosed.

In the method disclosed in Conventional Example 1, the substrate temperature = 3
The selection of the condition of 00 to 450 ° C. suppresses the incorporation of Si or the formation of an alloy to grow a Ge epitaxial thin film.

Japanese Patent Application Laid-Open No. 62-73624 (hereinafter referred to as Conventional Example 2) discloses that the raw material gases Si ₂ H ₆ , Ge
Method of forming the amorphous silicon germanium are disclosed by the F ₄ plasma chemical deposition method.

Japanese Patent Application Laid-Open No. 7-235490 (hereinafter referred to as Conventional Example 3) discloses that excimer laser annealing is performed after forming amorphous silicon of 30 nm to 50 nm on a substrate and annealing at 350 to 500 ° C. A method for forming a polycrystalline silicon thin film by irradiation is disclosed.

Japanese Patent Application Laid-Open No. 5-182923 (hereinafter referred to as Conventional Example 4) discloses that amorphous silicon is formed on a substrate and a large number of dangling bonds are formed in the amorphous silicon. Heat annealing at a temperature lower than the crystallization temperature of amorphous silicon, and then irradiating with excimer laser annealing, polycrystalline silicon with high crystallinity, small dependence on laser energy density, and excellent uniformity A method for forming a thin film is disclosed.

[0012]

However, in the conventional example 1, a poly-Si (Ge) thin film is formed. However, with respect to the formed poly-Si (Ge) thin film, the plane orientation and the particle size As for controlling the
Not disclosed at all.

Further, in the conventional example 2, the amorphous silicon germanium is deposited by using the plasma chemical vapor deposition method, and as described above, an additional annealing step is required to obtain a polycrystalline semiconductor thin film. It has.

Similarly, also in the conventional example 3, since the amorphous thin film is formed on the substrate and then the laser annealing is performed, it is necessary to heat the substrate before the laser annealing step. And the number of steps is increased.

Further, in the third conventional example, there is no mention of controlling the plane orientation and the crystal grain size of the polycrystalline semiconductor thin film to a large extent.

Further, also in Conventional Example 4, a process of performing laser annealing after forming an amorphous thin film on a substrate is used. To obtain a polycrystalline semiconductor thin film,
It has the drawbacks that it takes a long time to perform steps such as laser annealing and the number of steps of heating the substrate.

Further, in the conventional example 4, there is no mention of controlling the plane orientation of the crystalline thin film or controlling the crystal grain size largely.

In short, when amorphous silicon formed by conventional LPCVD is annealed by an excimer laser, a very good crystallinity in terms of how close the arrangement of silicon atoms is to that of single crystal silicon is obtained. Can be.

Therefore, in order to realize a TFT with higher mobility, a polycrystalline semiconductor thin film having a relatively large particle size of 5,000 to 10,000 angstroms (hereinafter referred to as A) and excellent surface flatness is realized. For this purpose, tens to hundreds of laser scans were required. This is unsuitable for mass production technology because the processing capacity is low.

[0020]

[0021] Accordingly, one technical object of the present invention is to provide a method for producing a polycrystalline semiconductor thin film capable of controlling the plane orientation and crystal grain size of the polycrystalline semiconductor thin film.

[0022]

According to Means for Solving the Problems] The present invention, having a thin film forming step of directly forming a polycrystalline semiconductor film on a substrate surface
A method for producing a polycrystalline semiconductor thin film, comprising:
The process is a Si ₂ H ₆ -GeF ₄ based reactive thermal CVD process.
A scan method of the polycrystalline semiconductor thin film reaction pressure and this <br/> and features a 0.5~0.8Torr is obtained.

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, the present invention will be described more specifically.

According to the present invention, in a manufacturing process of a thin film field effect transistor (TFT) which is a semiconductor device using a glass substrate or the like, a polycrystalline semiconductor thin film realizing high performance device characteristics, that is, a TFT having high mobility is realized. In this method, a polycrystalline semiconductor thin film is formed on a substrate in advance, and the thin film is annealed with an excimer laser to obtain a high-quality polycrystalline semiconductor thin film by a small number of laser annealings.

More specifically, the following steps are used as a method of forming a polycrystalline semiconductor thin film before laser annealing.

First, by utilizing the oxidation-reduction reaction between Si ₂ H ₆ and GeF ₄ and the etching property of GeF ₄ , He
Is used as a carrier gas to grow a polycrystalline semiconductor thin film at a relatively low temperature of 450 ° C. At this time, Si ₂ H ₆ and Ge
In the embodiment, the flow ratio of F ₄ and He is set to 2.
5: 0.1: 500 was used, but as a preferable range, these flow ratios are (2.0-2.5) :( 0.0
8 to 0.13): (450 to 500).

The process of growing a thin film is divided into two stages: a stage in which crystal nuclei are generated in the initial stage of film formation and a stage in which the generated crystal nuclei are selectively grown to form a continuous film. Is formed, and the polycrystalline semiconductor thin film is formed in which the particle size itself is controlled to an arbitrary size.

The film forming pressure in this nucleation stage is set to 0.45 To
By setting it to be equal to or less than rr, the plane orientation of the crystal nucleus becomes the (111) preferential orientation, and the plane orientation of the final polycrystalline semiconductor thin film also becomes the (111) preferential orientation. Is formed.

When laser annealing is performed using this polycrystalline semiconductor thin film, a film having a relatively flat surface is used from the beginning, so that the film after laser annealing also has a flat surface.
Also, the (111) plane is preferentially oriented to the plane where the secondary crystal growth of adjacent crystals is most likely to occur,
Since each particle size is relatively large, such as 1000 to 1500 A, a large particle size after laser annealing can be obtained.

Next, an embodiment of the present invention will be described.

(First Embodiment) In a first embodiment of the present invention, a polycrystalline semiconductor thin film is formed by reactive thermal CVD of a Si ₂ H ₆ -GeF 4 system capable of forming a crystalline thin film as-depo. After the formation, annealing is performed with an excimer laser. In forming this polycrystalline semiconductor thin film, a two-step process of generating crystal nuclei and controlling density → nucleus growth is used. In a polycrystalline silicon thin film field effect transistor (hereinafter, referred to as a poly-Si TFT), the active layer is formed of polycrystalline silicon (hereinafter, referred to as poly-Si).

The method for manufacturing a polycrystalline semiconductor thin film according to the first embodiment of the present invention will be described in detail with reference to the drawings along with a general operation procedure.

FIG. 1 is a cross-sectional view of a substrate on which SiO ₂ film formation has been completed. FIG. 2 is a view showing a SiO ₂ / Si substrate. FIGS. 3 to 6 are scans showing the particle structure of the polycrystalline semiconductor thin film when formed on the SiO ₂ / Si substrate shown in FIG. 2 at each reaction pressure between 0.4 Torr and 1.0 Torr. It is a scanning electron microscope photograph. FIG. 7 is a diagram showing a state of forming a germanium-containing polycrystalline silicon (hereinafter, referred to as poly-Si (Ge)) thin film due to a difference in reaction pressure. FIG. 8 is a diagram showing the relationship between the reaction pressure and the nucleus density in the nucleation stage in FIG. 7 and the particle size when each nucleus grows as it is. FIG. 9 is a view showing an X-ray diffraction profile of the thin film shown in FIGS. FIG. 10 is a cross-sectional scanning electron micrograph showing the particle structure of a poly-Si (Ge) thin film formed under the selective growth conditions shown in FIG.

Referring to FIG. 1, an SiO ₂ film 10 having a thickness of about 5000 A is formed on a glass substrate 11, and this SiO ₂ 10 is formed by LPCVD using Si ₂ H ₆ and O ₂ as source gases. Have been. Specifically, first, a reactive thermal CVD using Si ₂ H ₆ and GeF ₄ as source gases (hereinafter, referred to as a Si ₂ H ₆ -GeF ₄ system reactive thermal CVD) is performed at a substrate temperature of 450 ° C. to form SiO 2. A poly-Si (Ge) thin film having a Si composition ratio of 95% or more is formed on ₂ .
In this case, He is used as the carrier gas, and the flow ratio of each source gas and the carrier gas is Si ₂ H ₆ : GeF ₄ : H
e = 2.2: 0.1: 500.

The thermal S grown on the single-crystal Si substrate shown in FIG.
By patterning the iO ₂ layer, the SiO ₂ / Si substrate having a portion 21 where the Si surface is exposed on the surface of the substrate and a portion of the thermal SiO ₂ layer 20 which is covered with the SiO ₂ surface is formed.
Poly-Si (Ge) thin film is formed, and 0.4 Torr ~
The particle structure of the film at each reaction pressure between 1.0 Torr is shown in FIGS.

As shown in FIG. 7, from the state where the film formation pressure is low, gradually growing at about 0.48 Torr and about 0.9 Torr as boundaries, selective growth → nucleation → non-selective growth.
Changes to a staged growth process.

As shown in FIG. 8, since the nucleus density varies between 1E + 9 and 1E + 11 (cm ⁻² ) depending on the reaction pressure, it is possible to control the nucleus density by controlling the nucleation pressure. , This is 200 ~
It means that the particle size can be controlled between 2000A. For example, the core density of a particle size of 1500 A is 5E + 10 (cm ^-2 ), and in order to obtain such a thin film, it is necessary to form a film at a reaction pressure of 0.55 (Torr).

As shown in FIG. 9, the plane orientation of the crystal nuclei changes from (220) preferential orientation to (11) depending on the reaction pressure.
1) The orientation changes between the preferred orientations, and when the film is formed at the reaction pressure of 0.55 (Torr) as described above, the orientation becomes the (111) preferred orientation. Referring to a cross-sectional transmission electron microscope (TEM) photograph showing the particle structure of the poly-Si (Ge) thin film in FIG. 10, after the generation of crystal nuclei in the description using FIG. 9, the selection shown in FIG. When the film is formed under the growth condition, the particle size is 1000 to 1500 A, which is almost the same as the particle size calculated from the core density.

The poly-Si film thus formed
When a (Ge) thin film is annealed with an excimer laser, poly-Si having a very large particle size and a flat surface is obtained.
(Ge) A thin film is obtained. This is because the poly-Si (Ge) film before laser annealing is a (111) preferentially oriented film having a flat surface and most likely to cause secondary crystal growth, and has a relatively small grain size of 1000 to 1500 A. This is due to the large size.

As described above, in the first embodiment of the present invention, as a material before laser annealing, the particle size is about 1500 A and the structure is (11).
1) By forming a poly-Si (Ge) thin film controlled at a preferred orientation at a deposition temperature of 450 ° C., a thin film having a large grain size and a flat surface is formed on an inexpensive glass substrate after laser annealing. can do.

(Second Embodiment) In a second embodiment of the present invention, a polycrystalline semiconductor thin film is formed by reactive thermal CVD of a Si ₂ H ₆ -GeF ₄ system capable of forming a crystalline thin film as-depo. Is formed and then annealed with an excimer laser. When forming this polycrystalline semiconductor thin film, a two-stage process of generating crystal nuclei and controlling the density → nucleus growth is used, and the angle between the substrate surface and the gas flow direction during the nucleus growth is 90 to 0 degrees. Fixed at any angle.

A method for manufacturing a polycrystalline semiconductor thin film according to the second embodiment of the present invention will be specifically described with reference to the drawings.

FIGS. 11 (a), 11 (b) and 11 (c) show the angle between the substrate surface and the direction of gas flow during nucleus growth between 90 and 0 degrees (90, 45 and 0 degrees, respectively). 7) is a diagram which is provided for describing a method of fixing by changing in FIG. Also, FIG.
2 (a), (b) and (c) correspond to FIGS.
It is a figure which shows schematically the process of nucleation and each growth in the case of using the method of (b) and (c). Furthermore, FIG.
FIG. 3 is a diagram showing a relationship between gas and substrate surface angle and aspect ratio (a / b).

When forming a poly-Si (Ge) thin film on a glass substrate, the flow ratio of the source gas and the carrier gas is set to Si ₂ H ₆ : GeF ₄ : He = 2.2: 0.1: 50.
Nucleation is performed under the conditions of a substrate temperature of 450 ° C. and a reaction pressure of 0.5 to 0.8 Torr at a ratio of 0 to 600.

Next, FIGS. 11 (a), (b) and (c)
As shown in, the raw material gas from the gas nozzle 82 Si ₂ H
₆ and GeF ₄ and the supply direction of the carrier gas are fixed within a range of 0 to 90 degrees from the substrate surface 81 as indicated by an arrow 83 to perform nucleus growth. In this case, the film forming temperature, the flow ratio of the source gas and the carrier gas are the same as the conditions at the time of nucleation, and the film forming pressure is 1 Torr or less.

In the second embodiment of the present invention, when a film is formed on a substrate having a nucleus already present on the surface, FIG.
As shown in (a), (b), (c) and FIG. 13, as the angle between the substrate surface 92 and the flowing direction of the source gas becomes smaller, the growth amount in the horizontal direction with respect to the growth amount in the vertical direction is reduced. The percentage increases. That is, the growth mode of the crystal nuclei 91 changes from an isotropic mode to a preferential mode in the lateral direction. If a film is formed in this laterally preferential growth mode, it becomes possible to grow a thin film which is impossible in an isotropic growth mode in which a thin film having a very small thickness and a large grain size is grown.

As shown in FIG. 12, when growing a thin film having a crystal grain size of 2000 A in the isotropic growth mode, the film thickness needs to be 1000 A or more, but preferentially in the lateral direction. When the film is formed in the growth mode, it is possible to grow a thin film having a particle size of 2000 A with a thin film of about 500 A.

The poly-Si film thus formed
When a (Ge) thin film is annealed with an excimer laser, a poly-Si (Ge) thin film having a very thin film thickness, a very large particle size and a flat surface is obtained. A TFT formed using this thin film can operate at a higher speed than before by thinning the active layer.

As described above, in the second embodiment of the present invention, the poly-S
At the stage of selective growth in i (Ge) film formation, the flow direction of the source gas and the carrier gas is set to 0 with respect to the substrate surface.
By fixing in the range of up to 90 degrees, a thin film having a large particle size of 2000 A or more can be formed with a thin film of about 500 A. Laser annealing is performed using this film and TF
When T is made, the capacitance decreases due to the thinning of the active layer,
Higher speed operation than before becomes possible.

[0063]

As described above, according to the present invention ,
Controlling plane orientation and crystal grain size of polycrystalline semiconductor thin film
A method for manufacturing a polycrystalline semiconductor thin film that can be provided can be provided.

[0064]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a substrate on which deposition of SiO ₂ has been completed.

FIG. 2 is a view showing a SiO ₂ / Si substrate.

FIG. 3 shows a 0.4 T film on the SiO ₂ / Si substrate shown in FIG.
3 is a scanning electron micrograph showing the particle structure of a polycrystalline semiconductor thin film when formed at a reaction pressure of orr.

FIG. 4 shows a 0.6T film on a SiO ₂ / Si substrate shown in FIG.
3 is a scanning electron micrograph showing the particle structure of a polycrystalline semiconductor thin film when formed at a reaction pressure of orr.

FIG. 5 is a diagram showing a method of forming 0.8T on the SiO ₂ / Si substrate
3 is a scanning electron micrograph showing the particle structure of a polycrystalline semiconductor thin film when formed at a reaction pressure of orr.

In [6] SiO ₂ / Si substrate shown in FIG. 2, 1.0 T
3 is a scanning electron micrograph showing the particle structure of a polycrystalline semiconductor thin film when formed at a reaction pressure of orr.

FIG. 7: Poly-Si (Ge) due to difference in reaction pressure
It is a figure showing about the state of film formation of a thin film.

8 is a diagram showing a relationship between a reaction pressure and a nucleus density in a nucleus generation stage in FIG. 7 and a particle size when each nucleus grows as it is.

FIG. 9 is an X-ray diffraction profile showing a change in preferred orientation due to a difference in reaction pressure of a thin film.

FIG. 10 shows a pol film formed under the selective growth conditions shown in FIG.
It is a cross-sectional scanning electron microscope photograph which shows the particle structure of a y-Si (Ge) film.

FIG. 11 (a) is a view used to explain a method in which the angle between the gas flow direction and the substrate surface is fixed to 90 degrees during nucleus growth. FIG. 4B is a diagram which is used for describing a method in which the angle between the substrate surface and the gas flowing direction is fixed to 45 degrees during nucleus growth. (C) is a diagram provided for explaining a method in which the angle between the substrate surface and the flowing direction of the gas is fixed to 0 degree during nucleus growth.

FIG. 12 (a) is a view schematically showing a process of nucleation and growth of FIG. 11 (a). (B) is FIG.
It is a figure which shows schematically the process of nucleation and nucleus growth of (b). (C) is a figure which shows roughly the process of the nucleation and nucleus growth of FIG.11 (c).

FIG. 13 shows gas to substrate surface angle and aspect ratio (a /
It is a figure which shows the relationship with b).

[Explanation of symbols]

10 SiO ₂ 11 glass substrate 20 thermal SiO ₂ layer 21 Si surface 81 substrate surface 82 flows gas nozzle 83 gas direction 91 crystal nuclei 92 substrate surface 93 crystals

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-8319 (JP, A) JP-A-2-14831 (JP, A) JP-A-3-159116 (JP, A) JP-A 8- 264440 (JP, A) Autumn 58th Annual Meeting of the Japan Society of Applied Physics Proceedings (1997) 4p-YD-2 Autumn 58th Annual Meeting of the Japan Society of Applied Physics Abstracts (1997) 4p-YD-3 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/20

Claims (1)

(57) [Claims] 1. A method for manufacturing a polycrystalline semiconductor thin film having a thin film forming step of directly forming a polycrystalline semiconductor film on a substrate surface.
In addition, the thin film forming step is performed based on a Si ₂ H ₆ -GeF ₄ system.
It is a reactive thermal CVD process and the reaction pressure is 0.5 to
A method for producing a polycrystalline semiconductor thin film, wherein the pressure is 0.8 Torr .