JP2002151408A - Method of manufacturing semiconductor thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a semiconductor film of face direction [111] preferentially directed in mobility and uniformity with a good controllability. SOLUTION: An amorphous semiconductor film 12 is formed on substrates 10 and 11, a mask layer 15 having a plurality of openings 16 of a very small diameter is formed on the amorphous semiconductor film 12 as positioned nearly in the center of a honeycomb shape, crystalline nuclei are formed by light irradiation from the side of the mask layer in zones of the amorphous semiconductor film 12 corresponding to the openings 16, and the crystalline nuclei are grown by irradiation of an energy beam to thereby form a semiconductor thin film preferentially oriented to face direction [111] with a good controllability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor thin film by crystallizing the semiconductor thin film from energy by light irradiation.

[0002]

2. Description of the Related Art Development of devices that can be driven on an arbitrary substrate such as thin film transistors (TFTs) is underway. Thin film transistors are sometimes used as control elements in a liquid crystal portion of a liquid crystal display device. It is also used as such. As a demand for the thin film transistor, there is a demand for higher performance of electrical characteristics such as carrier mobility, conductivity, subthreshold characteristics, and on / off current ratio. In order to improve the electrical characteristics of such a semiconductor thin film, the SPC technology (So
Lid Phase Crystallization (solid phase crystallization from amorphous silicon) and ELA technology (melt crystallization using Excimer Laser Anneal, excimer laser) are being studied.

Meanwhile, as one of the semiconductor materials satisfying such requirements of the electrical characteristics, the present inventors have previously devised a technique for a so-called quasi-single-crystal structure, and disclosed in Japanese Patent Application Laid-Open No. H11-145056. Discloses a semiconductor thin film substantially composed of a single crystal and a manufacturing method therefor. This so-called quasi-single crystal has a crystal structure similar to that of a single crystal, and is composed of a plurality of substantially single crystal grains made of a semiconductor, and the crystal grains are preferentially oriented in one plane direction. Are characterized by being substantially lattice-matched to each other at least at a part of the grain boundary.

[0004]

The so-called quasi-single crystal described in the above publication is characterized in that its plane orientation is preferentially oriented in one direction. However, when crystal growth is actually performed, there arises a problem that it is not easy to control a desired plane orientation. That is, in the case of manufacturing a thin film device such as a thin film transistor, in particular, it is easier to use a crystal having a {111} plane orientation so that grain boundaries can be more easily aligned. Therefore, a thin film device can be formed at an arbitrary position. Even when formed in various places, the advantage that the element characteristics are uniform can be obtained. However {111}
Until how to form crystal grains preferentially oriented in the plane direction, no effective manufacturing method has been established, and this has been a problem to be solved in manufacturing a high-performance thin-film semiconductor device.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of manufacturing a semiconductor thin film for obtaining a so-called quasi-single crystal, in particular, a method for obtaining a crystal having a {111} plane orientation with good controllability.

[0006]

In order to solve the above-mentioned problems, the present inventors have made intensive studies and found that when the nucleation region is relatively large, for example, about 1.2 μm, and the polycrystal grain size is large, the polycrystal is large. Grains (micropolysilicon) are generated and dendritic and disk-shaped grains grow on the outside,
Conversely, it has been found that when the nucleation region is relatively small, for example, about 0.5 μm, the region where polycrystalline grains (micropolysilicon) is generated is small. Based on this result, it is advantageous to form a small opening for nucleation for the crystal nucleus of the {111} plane orientation, which is superior in crystallinity, and also for the crystal growth from the crystal nucleus. It has been found that the combination of this crystal nucleus control and irradiation with an energy beam such as an excimer laser is extremely effective.

That is, a method of manufacturing a semiconductor thin film according to the present invention comprises the steps of: forming an amorphous semiconductor film on a substrate; Forming a mask layer having an opening;
Forming a crystal nucleus in a region of the amorphous semiconductor film corresponding to the opening by irradiating light from the mask layer side; and forming a semiconductor thin film by growing the crystal nucleus by irradiation of an energy beam. And a process.

In the above-described manufacturing method, the crystal nucleus of the {111} plane orientation, which is superior in crystallinity, has a regular hexagonal shape crystallographically, and actually has some thermal non-uniformity. In some cases, the closest-packed structure in a plane is a honeycomb shape. Therefore, by arranging a plurality of small-diameter openings substantially at the center of each honeycomb-shaped cell, it becomes optimal for crystal growth in the {111} plane orientation. Although the growth of the crystal from the crystal nucleus can be shortened by the irradiation of the energy beam, the crystal orientation of the crystal grains can be easily adjusted at the grain boundary portion by the irradiation of the energy beam.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. The present embodiment is a method for forming a quasi-single-crystal semiconductor film that generates and grows crystal grains having a {111} plane orientation using silicon as a semiconductor.

First, as shown in FIG.
Forming a silicon oxide layer 11 on a single crystal substrate 10
SOI structure. The substrate itself is silicon bonded as shown in Fig. 1.
Having a silicon oxide layer 11 formed on a crystalline substrate 10
Or an insulating substrate such as a glass substrate.
May be. An amorphous semiconductor film on the silicon oxide layer 11;
And the amorphous silicon layer 12 is formed by a low pressure CVD method or the like.
Is done. The thickness of the amorphous silicon layer 12 is about 10 nm
In the range of about 100 nm, and in this embodiment, amorphous
The thickness of the silicon layer 12 is about 40 nm, and the formation temperature is
It is about 610 ° C. Next, the amorphous silicon layer 12
In order to increase the incubation time of nucleation, Si ⁺Ion implantation
Is applied. As an example of the conditions for this ion implantation, implantation energy
Energy 20keV, dose 1.5x10^Fifteencm^-2In
You.

Next, as shown in FIG. 1B, a CVD SiO ₂ film 14 is formed as an antireflection film, and a polycrystalline silicon layer 15 serving as a mask layer is formed thereon with a thickness of about 100 nm.
It is formed so that An opening 16 is formed in the polycrystalline silicon layer 15 using a photolithography technique. Wherein the opening size is fine diameter, size or diameter d ₁ to a diameter d ₁ is 1μm or less 1
It can be μm or submicron, preferably in the range of 0.01 μm to 0.7 μm, more preferably in the range of 0.02 μm to 0.5 μm. The horizontal plane shape of the opening 16 when the main surface of the substrate is supported horizontally is a circle, an ellipse, a square, a rectangle, a hexagon, or another polygonal shape, and includes a shape with rounded corners. The vertical plane shape of the opening 16 is a rectangular cross section with a vertical side wall because it is formed using photolithography technology, but is not particularly limited thereto, and may have a taper or the like.

The opening 16 is arranged so as to be located substantially at the center of each cell of the honeycomb shape. FIG. 3 is a diagram showing a honeycomb shape which is a pattern of grain boundaries formed by crystal growth. In FIG. 3, a portion indicated by an x mark is the position of the opening 16, and the opening 16 is arranged substantially at the center of each honeycomb-shaped cell which is a pattern of a grain boundary formed by crystal growth. $ 11 when manufacturing semiconductor devices
By growing a crystal nucleus having a 1-plane orientation and obtaining a crystal having a {111} -plane orientation, an element having excellent uniformity is formed. The crystal of the {111} plane orientation is a regular hexagonal crystallographically, and in reality, may be substantially disc-shaped due to some thermal non-uniformity. The closest-packed structure has a honeycomb shape. Therefore, by arranging the positions of the openings 16 in advance in an optimal shape for the honeycomb shape, the in-plane crystal structure can be quasi-single-crystallized as described later.

Since the openings 16 are located substantially at the centers of the honeycomb-shaped cells, the positions of the openings 1 are shifted from the positions of the openings of the adjacent rows and columns by a half pitch.
6 may be formed. The adjacent openings 16 are located at positions separated by the same distance in the six directions in FIG.
The distance D ₀ between the openings is the distance between the crystal nuclei and 0.2
μm to 5 μm, preferably 0.5 μm to 3 μm
m.

After such openings 16 are formed in the polycrystalline silicon layer 15 serving as a mask layer, a laser beam 17 of an excimer laser is irradiated so that crystal nuclei having {111} plane orientations correspond to the openings 16 respectively. Is formed on the amorphous silicon layer 12 in the region 13 thus formed. At this time, since the size of the opening 16 is a submicron diameter, this corresponds to the case where the nucleation region is relatively small as described above, and the region where the polycrystalline grains (micropolysilicon) is generated is Less. On the surface of the amorphous silicon layer 12 located at the bottom of the opening 16, the crystal nucleus of the {111} plane orientation, which is one of the most stable states controlled by the surface energy, is preferentially placed. An extremely small crystal nucleus of about 0.05 μm is formed.

The laser beam 17 of the excimer laser is irradiated using, for example, a laser beam of a XeCl excimer laser having a wavelength of 308 nm, a pulse width of 44 nanoseconds, and an energy density of 270 mJ · cm ⁻² or less. This irradiation may be performed by a single laser beam irradiation or a plurality of laser beam irradiations. The energy density of this irradiation may be, for example, 500 mJ · cm ⁻² or less.
It is preferably 50 mJ · cm ⁻² , and more preferably 40 mJ · cm ^−2.
It is preferably 0 mJ · cm ⁻² . At the stage of this laser light 17 irradiation, C
Although the VDSiO ₂ film 14 is formed, the surface of the silicon nitride film or the amorphous silicon layer 12 may be exposed.

FIG. 2 shows an example of an ELA (Excimer Laser Anneal) system for irradiating a laser beam of an excimer laser. In this embodiment, it can be used for irradiating a laser beam 17. In the ELA system shown in FIG. 2, pulsed laser light is derived from the XeCl excimer laser device 21, and the beam reflected by the mirror 31 enters the homogenizer 23 via the attenuator 22, mirrors 32 and 33. In the homogenizer 23, control for performing uniform irradiation is performed, and the semiconductor wafer 24 on the table 25 is irradiated with laser light from the XeCl excimer laser device 21. When the laser beam is irradiated by the ELA system, the laser beam is scanned, but the table side can be moved, or both the laser beam and the table can be moved.

The fact that the crystal nucleus having the {111} plane orientation is formed as described above is apparent from an experiment conducted by the present inventor. FIG. 4 is a photograph substituted for a drawing, in which a substantially disk-shaped crystal nucleus having a {111} plane orientation is formed on the surface of the amorphous silicon layer 12. The images in these photographs are based on experiments performed by the present inventors, and have a wavelength of 308 nm.
Energy of excimer laser of 17
Irradiation was performed at 8 mJ · cm ⁻² and the size of the opening 16 was 0.8 μm. In FIG. 4, (a) is an electron beam diffraction image, and (b) is an image obtained by TEM analysis (transmission electron microscope analysis). For this experiment, Proceedings
A similar statement is found on page 200 of the Sony Research Forum (1992). Noguchi and Ikeda: 1992 Autumn Applied Physics Conference Proceedings No.2 p666 17p-2T-11.

Next, as shown in FIG. 1C, the polycrystalline silicon layer 15 as a mask layer is removed, and the {111} plane crystal nuclei formed on the surface of the amorphous silicon layer 12 are formed. Irradiation of an excimer laser with a low energy enough not to melt the crystal grains 41 is performed to grow crystal grains 41 having honeycomb-shaped grain boundaries 42 shown in FIG. FIG. 1C corresponds to a cross-sectional view in a state where crystal grains 41 having honeycomb-shaped grain boundaries 42 are grown. When removing the polycrystalline silicon layer 15, the CVD formed as an anti-reflection film was performed.
The surface of the amorphous silicon layer 12 may be exposed by removing the SiO ₂ film 14.

The light irradiation of the excimer laser is performed by irradiating light in the ultraviolet wavelength range. However, in order to make the crystal grains larger, it is desirable to perform the irradiation multiple times (multi-shot). It is also possible to irradiate linear rays to grow crystals, but it is also possible to irradiate planar rays and proceed heat treatment collectively in the plane. The latter is more effective in obtaining uniformity. It is. For excimer laser light irradiation, for example, a laser beam of a XeCl excimer laser having a wavelength of 308 nm is used, and the energy density is 300 mJ · c.
m ⁻² or less, more preferably 200 mJ · cm ⁻² or less. The laser light of the excimer laser may have another wavelength, for example, a wavelength of 248 nm. Excimer laser light irradiation conditions are conditions for growing crystal nuclei in the {111} plane orientation, and the temperature in the amorphous silicon layer 12 is set at most to the melting temperature of the amorphous silicon layer. The condition is valid. Depending on the irradiation with an ultraviolet pulse laser such as a general excimer laser, the temperature is higher near the surface and tends to decrease toward the bottom of the film. Therefore, quasi-single crystallization does not necessarily have to be completed over the entire depth of the amorphous silicon layer.

[0020] By irradiation with light from an excimer laser,
Crystal grains 18 gradually grow around crystal nuclei of the 11 ° plane. In the process of growing the crystal grains 18, substantially hexagonal crystal grains increase in size, but in the final stage, the grain boundaries of the adjacent crystal grains 18 collide with each other. At this time, when the directions of the crystal planes of the grain boundaries are aligned, there is no problem. The plane orientation can be adjusted. Since the crystal grains 18 of the {111} plane orientation are based on regular hexagons,
The crystal grains 18 having the {111} plane orientation are rotationally symmetric and six-fold rotationally symmetric. Therefore, the angle between adjacent crystal grains differs at most by only 30 degrees. In other words, if a rotation of at most 30 degrees is obtained during melting, the directions of the crystal planes of the grain boundaries are aligned and aligned. Become. This maximum angle of 30 degrees is a lower value than the maximum angle of 45 degrees when the {100} plane orientation of the 4-fold rotationally symmetric body is preferentially oriented,
This is effective for forming a quasi-single crystal structure.

The grain boundaries of the adjacent crystal grains 18 collide with each other, and the directions of the crystal planes of the grain boundaries are aligned, so that a honeycomb shape as shown in FIG. 3 is obtained. At this stage, the semiconductor layer on the silicon oxide layer 11 is composed of a plurality of substantially single crystal grains 18 made of silicon, and the crystal grains 18 are preferentially oriented in a substantially {111} plane orientation. The crystal grains 18 adjacent to each other among the crystal grains 18 are substantially lattice-matched to each other at least at a part of the grain boundaries 19, and exhibit a quasi-single crystal structure or a crystal structure having a low grain boundary barrier height close to a single crystal.

By using a semiconductor layer having good crystallinity as the active region in this manner, a semiconductor element having excellent electrical characteristics such as excellent uniformity as well as mobility and S value can be formed. It is possible to improve the performance of a thin film semiconductor device on an arbitrary substrate such as a TFT by using the present embodiment. For example, a large area active matrix flat panel display including a peripheral switch TFT is also used in the present embodiment. A portion requiring a high-speed operation, such as a horizontal scanning circuit or a vertical scanning circuit, can be provided together with another polycrystalline silicon thin film transistor.
Further, a vertical bipolar transistor can be formed on an arbitrary substrate.

It should be noted that the numerical values, materials, structures, processes, and the like described in the above embodiments are merely examples, and different numerical values, materials, structures, processes, and the like can be used as necessary. . Further, the semiconductor is not limited to silicon, and a semiconductor made of any one of Si, Ge, and C or a combination thereof can be selected.

[0024]

As described above, according to the method for manufacturing a semiconductor thin film of the present invention, it is advantageous in terms of mobility and uniformity.
It becomes possible to form a semiconductor film having an 11 ° plane orientation with good controllability by laser irradiation. Therefore, by applying the method for manufacturing a semiconductor thin film of the present invention to form a semiconductor element or a semiconductor thin film, a device having excellent high-speed operation and stability can be obtained by taking advantage of the semiconductor film having excellent electrical characteristics. Can be provided.

[Brief description of the drawings]

FIG. 1 is a process sectional view showing one embodiment of a method for manufacturing a semiconductor thin film of the present invention, wherein (a) is a process for forming an amorphous silicon layer, (b) is a process for irradiating an excimer laser, and (c).
FIG. 3 is a process sectional view up to the step of forming crystal grains.

FIG. 2 is a block diagram showing a structure of an annealing system using an excimer laser used in an embodiment of the method for producing a semiconductor thin film of the present invention.

FIG. 3 is a plan view showing a honeycomb shape of crystal grains formed in an embodiment of the method for manufacturing a semiconductor thin film of the present invention and positions of openings of a mask layer.

FIG. 4 is a drawing substitute photograph of a crystal nucleus portion after annealing by an excimer laser based on the method for producing a semiconductor thin film of the present invention (Noguchi, Ikeda: Proceedings of the 1992 Autumn Society of Applied Physics No.
2p666 17p-2T-11, source from Photo 18), (a) is an electron diffraction image, and (b) is an image by TEM analysis (transmission electron microscope analysis).

[Explanation of symbols]

Reference Signs List 10 silicon single crystal substrate 11 silicon oxide layer 12 amorphous silicon layer 14 CVD SiO ₂ film 15 polycrystalline silicon layer 16 opening 17 laser beam 18 crystal grain 19 grain boundary 21 XeCl excimer laser 22 attenuator 23 homogenizer 24 semiconductor wafer 25 table 31, 32, 33 mirror 41 crystal grain 42 grain boundary

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5F052 AA02 BB07 DA02 DB02 EA03 EA05 EA06 FA01 FA19 HA06 JA01 5F110 AA30 BB01 DD02 DD05 DD13 GG01 GG02 GG03 GG13 GG16 GG17 GG25 GG47 PP03 PP04 PP11 PP33

Claims (16)

[Claims] A step of forming an amorphous semiconductor film on a substrate; and a step of forming a mask layer having a plurality of small-diameter openings located substantially at the center of each honeycomb-shaped cell on the amorphous semiconductor film. Forming a crystal nucleus in a region of the amorphous semiconductor film corresponding to the opening by irradiating light from the mask layer side; and growing the crystal nucleus by irradiation of an energy beam. Forming a semiconductor thin film. 2. The semiconductor thin film includes a plurality of substantially single crystal grains made of a semiconductor, and the crystal grains have a size of about # 11.
2. The semiconductor thin film according to claim 1, wherein the semiconductor thin film is preferentially oriented in a 1｝ plane direction, and adjacent ones of the crystal grains are substantially lattice-matched to each other at least at a part of the grain boundary. Manufacturing method. 3. The method according to claim 1, wherein a distance between the crystal nuclei is in a range of 0.2 μm to 5 μm. 4. The method according to claim 1, wherein a distance between the crystal nuclei ranges from 0.5 μm to 3 μm. 5. The method according to claim 1, wherein the minute diameter of the opening of the mask layer is submicron. 6. A minute diameter of an opening of the mask layer is 0.0.
6. The method according to claim 5, wherein the thickness is in a range of 1 μm to 0.7 μm. 7. The minute diameter of an opening of the mask layer is 0.0
6. The method according to claim 5, wherein the thickness is in a range of 2 μm to 0.5 μm. 8. The method according to claim 1, wherein the light irradiation is performed by irradiating light from an excimer laser. 9. The method according to claim 8, wherein the light of the excimer laser is irradiated once or plural times. 10. The light of the excimer laser is 450 m
The method for producing a semiconductor thin film according to claim 8, wherein the value is set to J · cm ⁻² or less. 11. The method according to claim 1, wherein the energy beam is a beam in an ultraviolet wavelength range. 12. The method according to claim 1, wherein the substrate has a structure in which an insulating layer is formed on an insulating substrate or a semiconductor substrate. 13. The semiconductor constituting the semiconductor thin film is S
2. The method according to claim 1, wherein the method comprises one of i, Ge, and C or a combination thereof. 14. The semiconductor thin film according to claim 1, wherein a thickness of the semiconductor thin film ranges from about 10 μm to about 100 μm.
The method for producing a semiconductor thin film according to the above. 15. After forming an amorphous semiconductor film on a substrate, and forming a mask layer having a plurality of small-diameter openings located substantially at the center of the honeycomb shape on the amorphous semiconductor film,
A crystal nucleus having a substantially {111} plane orientation is formed in a region of the amorphous semiconductor film corresponding to the opening by light irradiation from the mask layer side, and then the crystal nucleus is grown by irradiation with an energy beam. Semiconductor thin film characterized by the above-mentioned. 16. After forming an amorphous semiconductor film on a substrate and forming a mask layer having a plurality of small-diameter openings located substantially at the center of the honeycomb shape on the amorphous semiconductor film,
A crystal nucleus having a substantially {111} plane orientation is formed in a region of the amorphous semiconductor film corresponding to the opening by light irradiation from the mask layer side, and then the crystal nucleus is grown by irradiation with an energy beam. Semiconductor thin-film device having a semiconductor thin film as an active region.