JP2003218028A - Method of manufacturing polycrystalline silicon semiconductor thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which the protruding part of polycrystalline silicon can be selectively removed and, in addition, the surface of a polycrystalline silicon film can be planarized without giving plasma damages to the surface. <P>SOLUTION: This method of manufacturing thin polycrystalline silicon semiconductor film includes a step of irradiating single argon, helium, neon, and nitrogen gas cluster beams and their mixed gas cluster beam onto a thin polycrystalline silicon film. This method also includes a step of projecting an oxygen gas cluster beam and a step of removing oxides formed on the surface of the thin polycrystalline silicon film. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for planarizing a polycrystalline silicon thin film. More specifically, the present invention relates to a method for planarizing a polycrystalline silicon thin film that can easily and reliably remove protrusions on the surface of a polycrystalline silicon thin film used in thin film transistors and auxiliary capacitors of liquid crystal display devices and EL display devices.

[0002]

2. Description of the Related Art Polycrystalline silicon thin films are used in a wide range of fields including various semiconductor devices and liquid crystal display devices. In particular, as a technique for realizing high performance, light weight and small size, and low cost of a liquid crystal display device, a polycrystalline silicon thin film transistor (T) formed on a quartz or glass substrate is used.
A thin film transistor (TFT) is drawing attention. When using a polycrystalline silicon TFT,
In addition to the pixel switching element, high-speed operation is possible, so that there is an advantage that it can be used in a drive circuit to form a drive circuit integrally. In particular, cost can be reduced by forming a high-quality polycrystalline silicon film on a glass substrate.

However, in a polycrystalline silicon thin film, abnormal growth is likely to occur in the process of crystallization, and large crystal grains or projections that are abnormally grown are often formed. Such abnormally grown crystals and protrusions worsen the step coverage of the insulating film formed on them and contribute to interlayer short-circuiting and interlayer current leakage, which is a major problem that deteriorates the manufacturing yield and product reliability. ing.

In order to flatten such abnormally grown protrusions and crystal grains, a method has been proposed in which the abnormal crystal grains and a part of the surface are simultaneously oxidized and the oxide layer is selectively removed by a chemical solution. ing. As a document disclosing this method, JP-A-2-163935 can be cited. That is, according to the document, the shape of abnormally grown crystal grains is usually needle-like and has a height which is several times the film thickness of the polycrystalline semiconductor layer, but its width is a fraction of the film thickness. It is a degree. Therefore, it is possible to oxidize all the abnormal crystal grains only by oxidizing the surface layer of the polycrystalline semiconductor layer, and the oxidized polycrystalline grains and the surface layer of the polycrystalline semiconductor layer are selectively removed by a chemical solution. As a result, it is said that the surface of the polycrystalline semiconductor layer can be flattened.

On the other hand, in Japanese Unexamined Patent Publication No. 2001-23962, a bias voltage is applied to a polycrystalline silicon thin film and then exposed to plasma of a gas containing carbon (C), fluorine (F) and hydrogen (H). Therefore, a method of selectively removing the protrusions formed on the surface of the polycrystalline silicon has been proposed. According to this method, as shown in FIG.
On a polycrystalline silicon surface 102 formed on a glass substrate, preferably an insulating substrate 101 having a silicon nitride or silicon oxide film formed on the glass substrate, a protrusion P is formed at a grain boundary. This polycrystalline silicon surface 102 is shown in FIG.
By exposing to the plasma of a mixed gas of CF4 and H2 as shown in (b), etching of silicon by a chemical reaction between these activated gas atoms and silicon and fluorocarbon deposition simultaneously proceed, and the flat portion is While the protrusion P is less likely to be covered with the fluorocarbon while being relatively easily covered with the fluorocarbon to suppress the etching, the etching progresses preferentially, and the polycrystalline silicon surface 102 is covered by the surface of FIG. Is reported to be flattened.

[0006]

However, some problems still remain in the above-mentioned conventional techniques. That is, among the polycrystalline silicon thin films, particularly when used in a liquid crystal display device, usually, an amorphous silicon thin film deposited on an insulating glass substrate is polycrystallized by excimer laser annealing or the like. It is formed by converting. In the thus obtained polycrystalline body, the grain boundary, particularly the grain boundary triple point, is the final solidification portion, and the protrusion is generated by the volume expansion due to the difference in density. The thickness of the protrusion is smaller than the particle size, but the height is often at least about twice the film thickness. Here, the film thickness of amorphous silicon before polycrystal is usually 50 n.
It is often about m.

In such a case, it is very difficult to selectively oxidize only the surface of the polycrystalline thin film. For example,
When wet oxidation is performed at 950 ° C. as in the embodiment described in JP-A-2-163935, not only the surface but also the entire polycrystalline silicon layer is oxidized. Then, if this is etched with hydrofluoric acid, the entire silicon layer is lost.

On the other hand, a method of performing etching by exposing to plasma of a gas containing carbon (C), fluorine (F) and hydrogen (H) as in Japanese Patent Laid-Open No. 2001-23962 is described in the embodiment. As described above, in order to reduce the height of the protrusion, the film thickness is reduced by etching even in the flat portion, and the film thickness is reduced to nearly half of the original film thickness. When crystallized by excimer laser annealing, crystals usually grow from the bottom (bottom surface) to the top (surface) of the silicon film, and the crystallinity improves as the crystal grows. The part has the highest mobility. In this method, the polycrystalline silicon film surface is flattened by deeply etching the surface portion with good crystallinity and high mobility, so the portion left unetched has low mobility and the surface is damaged by plasma damage. Since the crystal is destroyed, the transistor using the polycrystalline silicon film planarized by this method cannot exhibit sufficient performance.

The present invention has been made in order to solve such a problem, and its object is to remove the protrusions of polycrystalline silicon very selectively and to prevent the surface from being plasma-damaged. It is to provide a method for planarizing a surface.

[0010]

In order to achieve the above object, the method of flattening a polycrystalline silicon thin film according to the present invention is characterized by including a step of irradiating the polycrystalline silicon thin film with a gas cluster beam.

Here, the gas cluster beam is a gas cluster beam in which argon, helium, and nitrogen gases are clustered.

The gas cluster beam is a gas cluster beam in which oxygen gas is clustered, and comprises a flattening step using an oxygen gas cluster beam and a step of wet etching the surface of the polycrystalline silicon film with hydrofluoric acid. And

The polycrystalline silicon thin film is formed by a step of irradiating an energy beam such as a laser on the amorphous silicon film to melt the amorphous silicon film and recrystallize it. And

Further, the polycrystalline silicon thin film is formed by a process of melting and recrystallizing the amorphous silicon film by using a second harmonic pulse laser of YAG laser, so-called YAG2ω laser, on the amorphous silicon film. It is characterized by being done.

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. Embodiment 1 of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic process diagram showing the first embodiment of the present invention. That is, this figure shows a method for manufacturing a semiconductor thin film.

First, as shown in FIG. 1A, a polycrystalline silicon thin film 102 is formed on a glass substrate, preferably an insulating substrate 101 having a silicon nitride or silicon oxide film formed on the glass substrate. . This silicon thin film 102
Can be formed by depositing a non-single-crystal silicon thin film such as amorphous or polycrystalline on the insulating substrate 101 and melting and crystallizing it by excimer laser annealing. The polycrystallized silicon thin film 102 thus formed usually exhibits a surface morphology in which large protrusions P are formed at the grain boundary triple points.

Next, as shown in FIG. 1B, the surface of the polycrystalline silicon thin film 102 is irradiated with a gas cluster beam and etched. In the figure, a state where a cluster beam of argon gas is irradiated is illustrated. In addition to this, for example, noble gases such as helium and neon, nitrogen,
A cluster beam such as oxygen gas may be irradiated.

Conventionally, these gas cluster beams have been used for processing gold or diamond film, and have not been used by those skilled in the art for processing silicon. This is because the etching rate for silicon is very low. The gas cluster beam that is usually used for processing silicon is used to increase the etching rate.
It uses sulfur hexafluoride, which promotes the etching action by the chemical reaction of fluorine and silicon, and increases the etching rate by chemical etching.

On the other hand, the inventors of the present invention preferentially etch the projections of the polycrystalline silicon thin film 102 by irradiating these gases, which have not been conventionally used for etching silicon, with the cluster beam, Figure 1 (c)
As shown in FIG. 5, a unique phenomenon was found that the surface of the polycrystalline silicon thin film 102 was flattened.

FIG. 2 is a conceptual diagram showing a process of producing a gas cluster beam. Here, the case of argon gas is shown as an example. The argon gas 11 adiabatically expands into a vacuum through the nozzle 12 to form a gas cluster 13 in which thousands of argon atoms are collected. The gas clusters 13 are charged by the ionizer 14, accelerated by the electric field of the electrode 15, and then driven into the process chamber 16 to irradiate the surface of the polycrystalline silicon 102 to flatten the surface of the polycrystalline silicon 102. To be done. After that, a gate insulating film, a gate electrode, an interlayer insulating film and source / drain electrodes (not shown) are formed to form a polycrystalline silicon semiconductor.

FIG. 3 is a conceptual diagram for explaining the phenomenon that the surface of polycrystalline silicon is processed. When the argon gas clusters bombarded in the process chamber collide with the polycrystalline silicon surface, the impact etches the silicon due to the interaction between the gas clusters and the silicon. This interaction only physically destroys the silicon surface and does not cause chemical interaction. For this reason,
The flat portion of the polycrystalline silicon is hardly broken, and only the portion where the stress is concentrated, such as the protrusion P, is broken.

On the other hand, when a gas cluster such as sulfur hexafluoride that chemically etches silicon is used, not only the above-mentioned physical interaction but also the chemical interaction between silicon and fluorine. Since the silicon is etched by the method described above, the etching rate of silicon is extremely high. The surface part is also removed by etching.

FIG. 4 shows a comparison of electrical characteristics of a transistor using a polycrystalline silicon film planarized by a planarization process using an argon gas cluster beam and a sulfur hexafluoride gas cluster beam. The polycrystalline silicon film used has an average film thickness of about 50 nm and a protrusion height of about 100 nm, and the conditions of the irradiated gas cluster beam are acceleration voltage: 20 kV, beam current: ² μA / cm ² cluster atom: about 2000. It was an individual. When sulfur hexafluoride gas clusters are used, the etching rate is extremely high and silicon is etched in a short time, so the withstand voltage of the insulating film formed on the polycrystalline silicon film can be reduced by a flattening process in a short time. improves. On the other hand, since the flat portion of the polycrystalline silicon film is also etched at the same time, the surface portion having good crystallinity disappears, and the electron mobility of the polycrystalline silicon film is extremely lowered. Therefore, the performance as a transistor was very low. When flattening using an argon gas cluster, the time required for flattening to improve the withstand voltage is relatively long. Therefore, it was not used for the processing of silicon, but in this planarization process, the electron mobility of the transistor is only slightly lowered even if it is planarized until the withstand voltage is sufficiently improved, and the electron mobility is relatively high. It has been found that it is possible to achieve both of the performances that are essential for a withstand voltage transistor.

Further, when a gas cluster beam was generated by a similar method using helium gas, neon gas, or nitrogen gas instead of argon gas, and the polycrystalline silicon film was irradiated, the argon gas was optimized by accelerating voltage and beam current. It was confirmed that the withstand voltage of the insulating film was improved without lowering the mobility, which is the same as the planarization treatment by the cluster beam.

Embodiment 2. FIG. 5 is a schematic process diagram showing the second embodiment of the present invention. That is, this figure shows a method of manufacturing a semiconductor thin film according to the second embodiment.

A step of flattening the polycrystalline silicon film when oxygen gas is used as the gas cluster beam will be described. In this case, the polycrystalline silicon film 102 having the protrusions as shown in FIG. 5A was irradiated with the oxygen gas cluster beam as shown in FIG. 5B. At this time, due to the physical interaction between the oxygen gas cluster and silicon, the polycrystalline silicon film was flattened as shown in FIG. 5C, but at the same time, the very surface layer of the polycrystalline silicon film 102 reacted with oxygen. As a result, a silicon oxide film 151 was formed. The silicon oxide film 151 can be easily removed by wet etching with hydrofluoric acid as shown in FIG. 5D, and the surface of the polycrystalline silicon film 102 exposed by removing the silicon oxide film is FTIR (Fo
By urier Transfer Infrared) measurement, it was found that there was no physical damage due to collision of gas clusters.

Embodiment 3. 6A to 6C are schematic process diagrams showing a third embodiment of the present invention.

In FIG. 6, a polycrystalline silicon thin film 112 is formed on a glass substrate, preferably an insulating substrate 101 having a silicon nitride or silicon oxide film formed on the glass substrate. Substrate 1
In FIG. 6, a non-single-crystal silicon thin film 111 such as amorphous or polycrystal is deposited on 01.
As shown in (a), this non-single crystal silicon thin film 111 was irradiated with a YAG2ω pulse laser beam to be melted and crystallized. Thereafter, the polycrystalline silicon film 112 formed by the YAG 2ω pulse laser annealing is subjected to a flattening treatment by an argon gas cluster beam as shown in FIGS. 6B to 6D, and the polycrystalline silicon thin film 1 having high flatness is obtained.
It was set to 12.

FIG. 7 shows the electrical characteristics of a transistor formed by flattening the polycrystalline silicon film 112 formed by YAG2ω pulse laser annealing with an argon gas cluster beam, and comparing the polycrystalline silicon film 102 formed by excimer laser annealing with argon. It is shown in comparison with a transistor formed after being flattened by a gas cluster beam. When the polycrystalline silicon film 102 formed by the excimer laser annealing is used, the electron mobility of the transistor is slightly lowered, but when the polycrystalline silicon film 112 formed by the YAG2ω pulse laser annealing is used, the electron transfer is reduced. It was found that no decrease in the degree was observed, and the withstand voltage exhibited the same performance as in the case of using the polycrystalline silicon film 102 formed by the excimer laser annealing.

Here, excimer laser annealing and YAG
The formation mechanism of a polycrystalline silicon film in 2ω laser annealing is compared. FIG. 8 shows the absorptance of amorphous silicon for each laser wavelength. The absorption coefficient of amorphous silicon for excimer laser is very high,
The excimer laser light with which the amorphous silicon film is irradiated is almost absorbed by the surface layer of about 20 nm, and the temperature of the amorphous silicon surface layer portion first rises. Therefore, the deeper layer is melted through the heat conduction while melting from the surface layer of the amorphous silicon sequentially. Therefore, the surface is high in the silicon film,
A thermal gradient of low bottom occurs. At the time of recrystallization, solidification starts from the low temperature portion, so the crystal grows from the bottom surface toward the surface. On the other hand, in the case of the YAG2ω laser, the absorption coefficient of the amorphous silicon for the YAG2ω laser light is small, the amorphous silicon is absorbed by the entire amorphous silicon having a thickness of about 50 nm, and the temperature becomes uniform in the depth direction.
Therefore, the entire surface from the silicon surface to the bottom surface melts almost at the same time, and recrystallization does not occur in the surface direction from the bottom surface. Rather, the laser irradiation energy at the end of the laser beam is low, and the temperature is relatively low. It is considered that crystal growth occurs in the direction parallel to the so-called lateral direction. That is, a polycrystalline silicon film in which the crystal properties do not change in the depth direction is formed.

As described above, the polycrystalline silicon film 11 formed in the step of crystallizing by the YAG2ω laser annealing.
In No. 2, when the projections of the polycrystalline silicon film 112 are removed by the flattening process using an argon gas cluster beam, even if the polycrystalline silicon film 112 in the flat portion is slightly removed, the electron mobility of the transistor is reduced. It became clear for the first time that it did not deteriorate.

For the polycrystalline silicon film 112 formed by YAG2ω laser annealing, helium,
It goes without saying that even if the flattening step using the neon gas and nitrogen gas cluster beams is performed, the same result as the flattening step using the argon gas cluster beam can be obtained.

Further, the polycrystalline silicon film 112 formed by YAG2ω laser annealing is flattened by an oxygen gas cluster beam, and the polycrystalline silicon film 11 is formed.
By performing the process including the removal of the oxide film formed on the second surface, a polycrystalline silicon film that is not physically damaged by the gas cluster beam can be obtained.

In the third embodiment, YAG2ω laser annealing with a wavelength of 532 nm is used as the energy beam, but it is absorbed by almost the entire amorphous silicon film.
And the absorption rate is relatively high, wavelength 400nm to 600n
If the energy beam is m, the same effect can be obtained.

[0035]

As described above, according to the present invention, the polycrystalline silicon thin film can be irradiated with a gas cluster beam to selectively remove the protrusions on the surface of the polycrystalline silicon film, thereby flattening the surface. It is possible to realize a high-performance transistor having a high withstand voltage and a small decrease in mobility.

Further, since the projections of the polycrystalline silicon thin film are selectively removed by the oxygen gas cluster beam and then the oxide film on the surface of the polycrystalline silicon film is removed, a high-performance transistor having higher mobility is realized. can do.

Further, a polycrystalline silicon thin film is irradiated on the amorphous silicon film with a second harmonic pulse laser of a YAG laser to form a uniform crystal in the film thickness direction, and a gas cluster is formed on the polycrystalline silicon film. Irradiate the beam,
Since the projections on the surface of the polycrystalline silicon film are selectively removed to flatten the surface, a high-performance transistor with high mobility and high withstand voltage can be realized because the crystallinity is good even when flattened. .

Further, according to the present invention, the projections of the polycrystalline silicon thin film can be easily and surely removed and flattened, and various applied products such as high-performance liquid crystal display devices and EL display devices are subjected to dielectric breakdown. This is a great industrial advantage in that stable manufacturing is possible by suppressing point defects and the like.

[Brief description of drawings]

FIG. 1 is a schematic process diagram showing a method for manufacturing a polycrystalline silicon semiconductor according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a process of generating a gas cluster beam used in the method for manufacturing a polycrystalline silicon semiconductor according to the first embodiment of the present invention.

FIG. 3 is a conceptual diagram illustrating a processing phenomenon of a polycrystalline silicon surface in the method for manufacturing a polycrystalline silicon semiconductor according to the first embodiment of the present invention.

FIG. 4 is an electrical characteristic diagram of a transistor formed by the method for manufacturing a polycrystalline silicon semiconductor according to the first embodiment of the present invention.

FIG. 5 is a schematic process diagram showing a method for manufacturing a polycrystalline silicon semiconductor according to a second embodiment of the present invention.

FIG. 6 is a schematic process diagram showing a method for manufacturing a polycrystalline silicon semiconductor according to a third embodiment of the present invention.

FIG. 7 is an electrical characteristic diagram of a transistor formed by the method for manufacturing a polycrystalline silicon semiconductor according to the third embodiment of the present invention.

FIG. 8 is a characteristic diagram showing absorptance for each laser wavelength of amorphous silicon according to the method for producing a polycrystalline silicon semiconductor of the present invention.

FIG. 9 is a schematic process diagram showing a conventional method for manufacturing a polycrystalline silicon semiconductor.

[Explanation of symbols]

13 Argon gas cluster, 102 polycrystalline silicon film, 111 amorphous silicon thin film, 112 YA
Polycrystalline silicon film crystallized by G2ω laser, 1
51 Oxide film.

Continued front page    (72) Inventor Tetsuya Ogawa             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 5F052 AA02 BB02 BB03 BB07 CA08                       DA01 DA02 EA15 EA16 JA01                 5F110 AA18 DD02 DD13 DD14 GG02                       GG13 GG25 PP03 PP04 PP38                       QQ19

Claims (4)

[Claims] 1. A method for producing a polycrystalline silicon semiconductor thin film, which comprises a step of irradiating a polycrystalline silicon thin film with a single gas of argon, helium, neon, and nitrogen, and a gas cluster beam which is a mixture thereof. 2. A polycrystalline silicon semiconductor thin film, comprising: a step of irradiating the polycrystalline silicon thin film with an oxygen gas cluster beam; and a step of removing an oxide formed on the surface of the polycrystalline silicon thin film. Manufacturing method. 3. The method for producing a polycrystalline silicon semiconductor thin film according to claim 1, wherein the polycrystalline silicon thin film is formed by irradiating an amorphous silicon thin film with an energy beam. 4. The method for manufacturing a polycrystalline silicon semiconductor thin film according to claim 3, wherein the energy beam is a second harmonic of a YAG laser.