JP2000260707A - Formation of polycrystalline silicon film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a high quality polysilicon film having a large silicon grain diameter on an insulating substrate by crystallizing an amorphous silicon film by casting the excimer laser on it to form a polycrystalline silicon film having a grain diameter of at least a specified size. SOLUTION: The silicon ion beam is cast on a glass substrate 1 to form a crystal nucleus 2 made of crystalline silicon. The silicon ion beam is cast repeatedly to form a plurality of nuclei 2, for example, at specified intervals (d). Then, an amorphous silicon film 5 is so formed as to cover the nuclei 2 on the glass substrate 1 by plasma CVD using silane gas diluted with hydrogen. Next, annealing is conducted to eliminate hydrogen from the amorphous silicon film 5. Then, the amorphous silicon film 5 is annealed. A part of the amorphous silicon which is cast with the excimer laser is melted once and then is solidified and recrystallized to be turned into a polysilicon film 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a polycrystalline silicon film on a glass substrate, and more particularly to a method for forming a high-quality polycrystalline silicon film having a large grain size.

[0002]

2. Description of the Related Art Liquid crystal display devices (Liquid Crystal Displa)
(y: LCD) is a display device in which liquid crystal is sealed between two opposing glass substrates. With the increase in the definition of LCDs, there is a demand for so-called system-on-glass in which various electrodes for driving liquid crystals and circuits for controlling the electrodes are formed on a glass substrate. For this purpose, a technique for forming a high-quality silicon thin film on a glass substrate at a low temperature is indispensable.

[0003] Even if the glass is a so-called heat-resistant glass obtained by adding alumina to silicon oxide, 640 ° C to 670 ° C.
Softens to a degree. Therefore, each step of forming electrodes and circuits on the glass substrate must be performed at least at a temperature lower than the softening point.

FIG. 7 is a sectional view showing a step of forming a conventional polycrystalline silicon film. Step 1: As shown in FIG. 7 (a), plasma CVD (Chemical Vapor Deposi) using a gas obtained by diluting higher-order silane such as silane (SiH ₄ ) or disilane (Si ₂ H ₆ ) with hydrogen.
), an amorphous silicon film 102 is formed on the glass substrate 101 to a thickness of about 500.
Next, annealing is performed at 400 ° C. to 500 ° C. to release hydrogen contained in the amorphous silicon film 102.
This is because, when hydrogen is contained in the film, the film quality is prevented from being deteriorated due to rapid desorption of hydrogen when recrystallization is performed by excimer laser irradiation in a later step. Step 2: As shown in FIG. 7B, annealing is performed by irradiating the amorphous silicon film 102 with an excimer laser 103 such as ArF, KrF, or XeCl. The amorphous silicon in the region irradiated with the excimer laser 103 is once melted, re-solidified and crystallized, and becomes a polycrystalline (poly) silicon film 104. Step 3: Scanning the entire surface with the excimer laser 103,
As shown in FIG. 7C, the entire surface is formed as a polysilicon film 104. Step 4: As shown in FIG. 7D, silane and nitrogen oxide N ₂
A gate oxide film 105 is formed on the surface of the polysilicon film 104 by plasma CVD using an O mixed gas. Step 5: Next, a conductive film made of a metal or a doped silicon film is formed on the entire surface, and this is etched using a mask formed by photolithography to form a gate electrode 10.
6 is formed. Next, as shown in FIG. 7E, using a gate electrode 106 as a mask, impurities such as phosphorus, arsenic, and boron are implanted into the polysilicon film 104 by self-alignment to form a source 107 and a drain 108, thereby forming a transistor. Form.

In steps 1 and 2, an amorphous silicon film is formed and excimer laser annealing is performed.
The polysilicon film may be formed directly by thermal CVD at 0 ° C. to 650 ° C.

[0006]

According to the above-described steps, the following problems occur.

First, when a polysilicon film is formed by thermal CVD, it is necessary to set the temperature of the polysilicon film to a high temperature close to the softening point of the glass substrate. Therefore, in order to perform the thermal CVD, it is necessary to use a glass having a softening point as high as possible for the glass substrate 1. However, since a glass having a high softening point is generally expensive, the manufacturing cost of the LCD increases. Further, since thermal CVD is a heat treatment step, the production energy consumption is large, and a more energy-saving production method is required.

Further, in the initial stage of film formation by thermal CVD or in the initial stage of recrystallization by excimer laser annealing, silicon crystal nuclei 109 are formed randomly and innumerably as shown in FIG. At this time, the interval between the generated crystal nuclei 109 is at most about several tens nm at most.
When film formation or recrystallization proceeds, this crystal nucleus 109
The crystal grows with the nucleus as a nucleus. Crystal growth is the crystal nucleus 10
It progresses isotropically around 9. However, crystal nucleus 1
Since the distance between the cells 09 is small, the crystals collide with each other and the lateral growth is suppressed, and the crystal grows mainly in a direction perpendicular to the glass substrate. Therefore, the grain size r of the polysilicon film 104 is about several tens nm at most.

[0009] Between the grains are discontinuous faces of crystals, so-called grain boundaries. The grain boundary becomes a barrier potential when, for example, current is to flow. If the particle size is small, one device contains many grain boundaries, so that the barrier potential increases and the silicon / silicon oxide interface characteristics and the silicon film quality characteristics decrease. For example, in a transistor formed using such a film, device characteristics such as an increase in leakage current and a decrease in on-current are caused.

The crystal orientations of the crystal nuclei 109 are different from each other, and the crystal growth proceeds so as to be equal to the crystal orientation of the crystal nuclei 109. Therefore, the crystal orientation of each grain is random. Silicon, depending on the crystal orientation,
Since characteristics such as electric mobility are different, when a circuit element is formed over a plurality of grains, a problem such as a difference in characteristics depending on an element portion occurs.

Accordingly, an object of the present invention is to provide a lower-temperature manufacturing process for forming a high-quality polysilicon film having a large silicon crystal grain size on an insulating substrate.

[0012]

Means for Solving the Problems The present invention has been made to achieve the above object, and a plurality of silicon crystal nuclei are formed on an insulating substrate at predetermined intervals, for example, at intervals of 100 nm or more. An amorphous silicon film is formed over the entire surface by using plasma CVD, and the amorphous silicon film is recrystallized by excimer laser irradiation to form a polycrystalline silicon film having a grain of a predetermined size, for example, a grain size of 100 nm. This is a method for forming a silicon film.

The excimer laser is ArF or K
100m with rF or XeCl excimer laser
It has an energy of J / cm2 to 600 mJ / cm2.

The method for forming a silicon crystal nucleus is to irradiate a focused silicon ion beam to a position where the crystal nucleus of the insulating substrate is to be formed in a vacuum, or to form the silicon substrate in an atmosphere of a silane-based gas. A laser is irradiated to the position where a crystal nucleus is formed, or a polysilicon film is formed on the entire surface and left in a region to be a crystal nucleus to remove, or a silicon nitride film is formed on an insulating substrate to form a crystal nucleus. An opening is formed in a region where the insulating film is formed, and the insulating substrate is exposed to selectively form a silicon crystal in the opening.

[0015]

1 and 2 are cross-sectional views sequentially showing manufacturing steps of a first embodiment of the present invention. Step 1: As shown in FIG. 1, a silicon substrate is irradiated with a silicon ion beam in a vacuum reduced to a pressure of 10 ⁻² Torr or less to form a crystal nucleus 2 made of single crystal silicon. The irradiation area of the silicon ion beam is narrowed to about 1 μm by using a converging lens 4 using a slit electrode 3. Step 2: As shown in FIG. 2A, the irradiation of the silicon ion beam is repeated, and a plurality of crystal nuclei 2 are
It is formed at a predetermined interval d of nm or more. Step 3: As shown in FIG. 2B, amorphous silicon covering the crystal nuclei 2 on the glass substrate 1 by plasma CVD at a temperature of 100 ° C. to 300 ° C. using a gas obtained by diluting a silane-based gas with hydrogen. The film 5 has a thickness of 200 to 500 mm.
Degree formed. Next, annealing is performed at 400 ° C. to 500 ° C. for about 2 hours to release hydrogen contained in the amorphous silicon film 5. Step 3: As shown in FIG. 2C, an excimer laser such as ArF, KrF, or XeCl is applied to the amorphous silicon film 5 at 100 mJ / cm2 to 600 mJ / cm2, preferably 300 mJ / cm2.
Irradiation corresponding to 3 to 10 shots is performed at an energy of mJ / cm2, and this is scanned to perform annealing. Excimer laser 10
The amorphous silicon in the region irradiated with 3 is once melted, re-solidified and crystallized to form a polysilicon film 7.

According to this step, the crystal grains 6 having the particle diameter R are obtained.
Is formed. Since the crystal nuclei 2 are spaced apart by a distance d, the epitaxial growth in the lateral direction proceeds without being suppressed, so that the grain size R is almost equal to the distance d, and in this case is 100 nm or more. When the distance d between the crystal nuclei 2 is reduced, the particle size R also decreases, and when the distance d increases, the particle size R increases. Since the lateral growth of the crystal proceeds radially around the crystal nucleus 2, the crystal grains 6 are formed around the position of the crystal nucleus 2. Step 4: As shown in FIG. 2C, a gate oxide film 8 is formed on the surface of the polysilicon film 7 and a gate electrode 9 is formed in the same manner as in the steps 4 and 5 of the prior art, and this is used as a mask. A transistor is formed by forming the source 10a and the drain 10b. The gate electrode 9 may be made of any conductive material such as metal or doped polysilicon.

In the step 2, the crystal nuclei 2 are formed in a lattice shape as shown in FIG. 3A so that the polysilicon film 7 of uniform quality can be formed over the entire surface. Further, as shown in FIG. 3B, the formation position of the crystal nucleus 2 may be limited only to a region where a device requiring a particularly high-quality polysilicon film is formed. By omitting the formation of the crystal nuclei 2 in a region where high quality is not required, the manufacturing time can be reduced, and further energy saving can be achieved.

Next, a second embodiment of the present invention will be described. Step 1: As shown in FIG. 4, a laser is irradiated onto the glass substrate 1 in an atmosphere of a silane-based gas. Some hydrogen is dissociated from the silane molecules by the energy of the laser to form radicals, and crystal nuclei 2 made of single-crystal silicon are formed in the irradiation region. As the laser, for example, an ArF excimer laser or the like is used at 100 to 300 mJ / cm ² . The laser diameter is reduced to 1 μm or less. As in the first embodiment, the silane-based gas is preferably higher order silane.

After step 2, as shown in FIG. 2, a plurality of crystal nuclei 2 are formed, an amorphous silicon film is formed, and recrystallization is performed to form a device. Since it is the same as the first embodiment, a detailed description is omitted.

Next, a third embodiment of the present invention will be described. Step 1: As shown in FIG. 5A, for example, a glass substrate 1
The amorphous silicon film 11 formed thereon by using plasma CVD is subjected to excimer laser annealing and recrystallized, so that the polysilicon film 12 has a thickness of 100 .ANG.
It is formed to about 500 °. Step 2: A photoresist is applied to the entire surface to a thickness of about 1 μm, exposed and developed to form a photomask 13 in a region where the crystal nuclei 2 are to be formed, as shown in FIG. The size of the photomask 13 is a minimum size of the processing limit. Step 3: As shown in FIG. 5C, the polysilicon film 12 is etched using the photomask 13 as a mask to form crystal nuclei 2. If the etching is isotropic etching, since the etching is also performed in the lateral direction, that is, under the end of the photomask 13, the crystal nucleus 2 can be made smaller than the processing limit of the photomask 13. The size of the crystal nucleus 2 can be controlled by the etching time.

After the step 4, as shown in FIG. 2, a plurality of crystal nuclei 2 are formed, an amorphous silicon film is formed, and recrystallization is performed to form a device. Step 3 of the first embodiment
Since it is the same as the following, detailed description is omitted.

Next, a fourth embodiment of the present invention will be described. Step 1: As shown in FIG. 6A, a silicon nitride film 21 having a thickness of 100 is formed on the glass substrate 1 by plasma CVD.
The thickness is about {1000}. Step 2: As shown in FIG. 6B, the silicon nitride film 21
Is etched using a mask formed by photolithography to form an opening 21a.
To expose. Step 3: whole surface or opening 2 in a silane-based gas atmosphere
When 1a is irradiated with ultraviolet light from, for example, a high-pressure mercury lamp, the silane-based gas is converted into radicals by the ultraviolet light,
As shown in FIG. 6C, crystal nuclei 2 are selectively formed in the openings. This is because the adhesion rate of radicals differs between the glass substrate 1 made of silicon oxide and the silicon nitride film 21, and silicon selectively grows in the opening 21 a where the glass substrate 1 having a higher adhesion rate is exposed. Things. Step 4: As shown in FIG. 6D, a polysilicon film 6 is formed by epitaxial growth in substantially the same manner as in Step 3 of the first embodiment. After the step 5, a device is formed as shown in FIG. Since it is almost the same as the first embodiment, a detailed description is omitted.

In any of the first to fourth embodiments,
It is common that the crystal nuclei 2 are epitaxially grown to obtain a polysilicon film having a large grain size. It is desirable that the size of the crystal nuclei 2 be as small as possible. This is because when the crystal nucleus 2 is large, the probability that the crystal nucleus 2 has a plurality of crystal orientations therein increases. When crystal nuclei 2 having a plurality of crystal orientations are epitaxially grown therein, a plurality of grains will result.

In any of the first to fourth embodiments, the distance d between the crystal nuclei 2 is 100 nm or more. Therefore, the grain size of the formed polysilicon film 6 becomes larger than 100 nm. For example, a polysilicon film 6 having a grain size of 1 μm is formed with an interval between crystal nuclei 2 of 1 μm and a gate length of 1 μm
If a transistor of a certain degree is formed immediately above this, the active region of the transistor (region between the source 9 and the drain 10)
Has one or several grains. Therefore, the number of crystal grain boundaries is extremely small as compared with the polysilicon film formed by the conventional manufacturing method. Therefore, the transistor formed using the polysilicon film 6 has significantly improved device characteristics such as a small leak current.

Further, according to the manufacturing method of the present invention, it is not necessary to use thermal CVD requiring a relatively high temperature, and a more energy-saving manufacturing process is realized. Further, since the manufacturing temperature can be lowered, a less expensive glass substrate having low heat resistance can be used.

In the present invention, the glass substrate 1 has been described, but other insulating substrates, for example, ceramics or acrylics may be used as the substrate.

[0027]

As described above, according to the present invention, a plurality of silicon crystal nuclei are formed at intervals of at least 100 nm and the polycrystal silicon film is formed by epitaxially growing the crystal nuclei. The film size is large and high quality.

Further, since a higher-order silane gas is used as the silane-based gas, it can be decomposed or formed into radicals at a lower temperature, and the production energy can be saved more effectively in the present invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a manufacturing method according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating the manufacturing method of the present invention.

FIG. 3 is a perspective view illustrating a manufacturing method of the present invention.

FIG. 4 is a sectional view illustrating a manufacturing method according to a second embodiment of the present invention.

FIG. 5 is a cross-sectional view illustrating a manufacturing method according to a third embodiment of the present invention.

FIG. 6 is a sectional view illustrating a manufacturing method according to a fourth embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a conventional manufacturing method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Insulating substrate, 2 Crystal nucleus, 5 grains, 6 Polysilicon film 13 Photoresist, 21 Silicon nitride film

Continued on front page (72) Inventor Keiichi Sano 2-5-1-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Kiyoshi Yoneda 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka No. Sanyo Electric Co., Ltd. F term (reference) 5F045 AA08 AB03 AB04 AB33 AC01 AD05 AD06 AD07 AF07 AF14 BB07 DB02 HA16 HA18 5F052 AA02 BB07 CA04 DA02 DB03 EA15 FA01 FA21 GA01 HA01 HA03 JA01

Claims (8)

[Claims] A plurality of silicon crystal nuclei are formed on an insulating substrate at predetermined intervals or more, an amorphous silicon film is formed on the entire surface to cover the crystal nuclei, and the amorphous silicon film is irradiated with an excimer laser. And forming a polycrystalline silicon film having grains with a grain size of a predetermined size or more. 2. The method according to claim 1, wherein the predetermined distance between the silicon crystal nuclei is 10 or more.
0 nm, and the predetermined size of the grain size is 10
2. The method according to claim 1, wherein the thickness is 0 nm. 3. The excimer laser is ArF or K.
an rF or XeCl excimer laser, wherein the excimer laser is 100 mJ / cm2 to 600 mJ / c.
2. Irradiation with energy of m2.
Alternatively, the method of forming a polycrystalline silicon film according to claim 2. 4. The method for forming a silicon crystal nucleus according to claim 1, wherein a focused silicon ion beam is applied to a position on the insulating substrate where the crystal nucleus is formed in a vacuum. The method for forming a polycrystalline silicon film according to claim 3. 5. The method for forming a silicon crystal nucleus according to claim 1, wherein a laser is applied to the insulating substrate at a position where the crystal nucleus is formed in a silane-based gas atmosphere. 4. The method for forming a polycrystalline silicon film according to 3. 6. The method for forming a crystal nucleus of silicon includes forming a polycrystalline silicon film over the entire surface, leaving the polycrystalline silicon film in a region where the crystal nucleus is used, and removing a region other than the crystal nucleus. The method for forming a polycrystalline silicon film according to claim 1, wherein: 7. The polycrystalline silicon film according to claim 6, wherein in the method of forming a polycrystalline silicon film on the entire surface, amorphous silicon is formed on the entire surface and crystallized by irradiating a laser beam. Formation method. 8. The method for forming a crystal nucleus of silicon includes forming a silicon nitride film on the insulating substrate and providing an opening in a region of the silicon nitride film where the crystal nucleus is formed. 4. The method for forming a polycrystalline silicon film according to claim 1, wherein the substrate is exposed, and a silicon crystal is selectively formed in the opening.