JPH11121752A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to constitute a MIS field-effect transistor, which is actuated on a low-cost insulating board in a low voltage and at a high speed, is highly reliable and consists of a polycrystalline silicon thin film, by a method wherein an excimer laser having a prescribed wavelength irradiates the surface of the polycrystalline silicon thin film to form a gate insulating film. SOLUTION: An excimer laser irradiates an amorphous silicon thin film layer 1 deposited on an insulative substrate 10, which consists of glass, by a CVD method, whereby the thin film layer 1 is crystallized to form a polycrystalline silicon thin film layer 9 on the substrate 10. Subsequently, the excimer laser irradiates the surface of the thin film layer 9 in an oxygen atmosphere and a gate insulating film 17 consisting of an SiO2 film is formed on the layer 9. Here, when a laser beam of an ultraviolet-range wavelength (shorter than 400 nm) irradiates the layer 9 being put in the oxygen atmosphere, the surface of the layer 9 not only can be locally heated but also a reaction in the interface between the layer 9 and the film 17 can be accelerated. Moreover, an oxide film is a linearity proportional region until its thickenss is a thickness of 100 nm and the thickness of the oxide film is increased in proportion to the number of times of laser irradiation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a MIS field-effect transistor formed on a polycrystalline silicon thin film on an insulating substrate, and more particularly to a semiconductor device having a high-quality gate insulating film and a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventional MIS using a polycrystalline silicon thin film
A thermal silicon oxide film formed by thermally oxidizing a polycrystalline silicon thin film in a high-temperature furnace at 900 ° C. or higher has been used as a gate insulating film of a field effect transistor (Japanese Patent Laid-Open No. Sho 62-62).
No. 117371). On the other hand, low-pressure chemical vapor deposition (CVD) or ECRCVD, which can be formed at low temperature, can be used as a gate insulating film in order to construct a MIS field-effect transistor of polycrystalline silicon thin film on an inexpensive insulating substrate such as glass. (IEDM95 Dige
st, 837 (1995)) is SiO ₂ deposited film formed in the like has been used.

[0003]

The above-described conventional thermal oxide silicon film requires a heat treatment process at a high temperature of 900 ° C. or higher, so that an inexpensive insulating substrate such as glass cannot be used. Further, in the thermal oxidation process, oxidation does not proceed uniformly over the entire film due to the fact that oxygen easily diffuses into the grain boundaries of the polycrystalline silicon film and the crystal grains have different plane orientations. For this reason, problems such as the inability to form a gate insulating film having a uniform thickness and an increase in unevenness on the surface of the polycrystalline silicon film occur. This causes a decrease in gate breakdown voltage of transistor characteristics or a decrease in mobility due to carrier surface scattering. In the related art, it is difficult to reduce the thickness of a gate insulating film effective for improving device performance for the above reasons, and it is difficult to reduce the voltage, increase the speed, and improve the reliability of the transistor.

On the other hand, the SiO ₂ deposited film contains impurities in the film, and thus causes a flat band voltage shift and an increase in interface state density. For this reason, there has been a problem in reducing the threshold voltage of the transistor, improving controllability, and improving sub-threshold characteristics. Further, problems such as a decrease in gate breakdown voltage and a change in transistor characteristics occur. Therefore, it has been difficult to reduce the voltage, increase the speed, and improve the reliability of the transistor.

Further, according to the prior art, it has been difficult to arbitrarily change the thickness of the gate insulating film of the transistor on the same substrate. For this reason, the transistor characteristics cannot be controlled according to the performance of the circuit or the system.

A first object of the present invention is to solve the above-mentioned problems of the prior art and provide a highly reliable polycrystalline silicon thin film which operates at low voltage and high speed on an inexpensive insulating substrate such as glass.
An object of the present invention is to provide a semiconductor device capable of forming an MIS field-effect transistor and a method of manufacturing the same.

A second object of the present invention is to provide a semiconductor device in which the thickness of a gate insulating film of a transistor on the same substrate is arbitrarily changed, and a method of manufacturing the same.

[0008]

The first object is achieved by irradiating the gate insulating film with an excimer laser having a wavelength of 600 nm or less. Furthermore, by using a gate insulating film composed of two layers, an oxide film formed by irradiating the surface of the polycrystalline silicon thin film with an excimer laser and an oxide film deposited by a chemical vapor deposition (CVD) method, The purpose can be achieved. Further, the second object can be achieved by controlling the thickness of the gate insulating film by changing the irradiation energy and the number of times of the laser.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION

(Embodiment 1) FIG. 1 shows a method of manufacturing a semiconductor device according to a first embodiment of the present invention. Insulating substrate 10 made of glass
On top, a thickness of 5 deposited by chemical vapor deposition (CVD)
The 0 nm amorphous silicon thin film layer 1 is crystallized by excimer laser irradiation to form a polycrystalline silicon thin film layer 9 (FIGS. 1 (a) and 1 (b)). Followed by irradiating the excimer laser to the polycrystalline silicon thin film layer 9 surface in an oxygen atmosphere, SiO ₂
A 20-nm-thick gate insulating film 17 made of
(C)). Here, polycrystalline silicon having a thickness of 200 nm having conductivity is deposited on the entire surface by a CVD method, and then a gate electrode 18 is formed by anisotropic etching (FIG. 1D). Subsequently, high-concentration n-type impurities are introduced in a self-aligned manner using the gate electrode 18 as a mask to form source and drain regions 20 and 19 (FIG. 1E). As described above, a polycrystalline silicon thin film MIS type field effect transistor was obtained.

In this embodiment, the crystallization of the amorphous silicon thin film and the laser irradiation for forming the gate insulating film were performed independently. As a result, the quality of the gate insulating film and the state of the interface are improved, and the accuracy of controlling the film thickness is also improved.

The oxidation process by excimer laser irradiation will be described in detail. When a polycrystalline silicon thin film in an oxygen atmosphere is irradiated with a laser having an ultraviolet region wavelength (400 nm or less), not only can the thin film surface be locally heated, but also the reaction at the interface can be promoted. As shown in FIG.
This is because the light absorption coefficient of Si significantly increases when the wavelength is 400 nm or less.

FIG. 2B shows the dependence of the oxide film thickness in 1 atmO ₂ on the number of laser irradiations and the irradiation energy. The region up to an oxide film thickness of 100 nm is a linearity proportional region, and the oxide film thickness increases in proportion to the number of laser irradiations. For this reason, 1 nm
The thickness of the oxide film can be accurately controlled with the precision described above, and the linearity proportionality constant at that time shows a value that is 100 times or more larger than that in the case of thermal oxidation in 1000 ° C. and 1 atmO ₂ . This is an effect that oxygen molecules are excited by the laser beam, and diffusion of the oxidized species to the silicon surface through the already formed oxide film is promoted. Therefore, the oxidation rate can be greatly increased in the reaction rate controlling process. Further, there is an effect that the interface state density of the polycrystalline silicon thin film / gate insulating film is reduced.

As can be seen from FIG. 2, the oxide film thickness increases with an increase in laser irradiation energy. On the other hand, since the laser irradiation time in one pulse is as short as 10 ns or less, the distance over which oxygen diffuses into the grain boundaries can be suppressed to several nm or less. Therefore, a gate insulating film having a uniform thickness can be formed, and at the same time, irregularities on the surface of the polycrystalline silicon film can be suppressed. Therefore, the gate breakdown voltage of the transistor characteristics can be improved, and the mobility can be improved.

As described above, according to this embodiment, the thickness of a thin gate insulating film can be uniformly and accurately controlled on an inexpensive insulating substrate such as a thin film glass, so that low voltage and high speed can be achieved. Operates and is highly reliable
An MIS type field effect transistor can be obtained.

In this embodiment, a silicon oxide film is formed as a gate insulating film. However, after forming the silicon oxide film, a highly reliable oxynitride film is obtained by irradiating an excimer laser in a nitriding gas atmosphere. Can be. Also,
By irradiating an excimer laser in a fluorine-based gas atmosphere after the formation of the gate insulating film, the reliability of the gate insulating film can be further improved.

Embodiment 2 FIG. 4 shows a method of manufacturing a semiconductor device according to a second embodiment of the present invention. A 50 nm thick amorphous silicon thin film layer 1 deposited on a glass insulating substrate 10 by applying a chemical vapor deposition (CVD) method is crystallized by irradiating an excimer laser to a polycrystalline silicon thin film. The layer 9 is formed (FIGS. 2A and 2B). Subsequently, an oxygen ion introduction region 16 having a depth of 20 nm corresponding to the required thickness of the gate insulating film is formed in the depth direction from the polycrystalline silicon thin film layer 9 by ion implantation or ion doping (FIG. 1 (c)). )).

Next, the surface of the polycrystalline silicon thin film layer 9 is irradiated with an excimer laser in a vacuum to react with oxygen introduced on the surface of the polycrystalline silicon thin film, thereby forming a 20-nm thick gate insulating film 17 made of SiO _2. (FIG. 1 (d)). Hereinafter, although not shown, a 200-nm-thick conductive polycrystalline silicon film is further deposited on the entire surface by a CVD method, and then a gate electrode is formed by anisotropic etching. Source and drain regions were formed by introducing n-type high-concentration impurities, and an MIS field-effect transistor of a polycrystalline silicon thin film was obtained.

According to this method, the thickness of the gate insulating film can be controlled by the oxygen ion implantation energy as shown in FIG. Further, since the laser irradiation time in one pulse is as short as 10 ns or less, the distance over which oxygen diffuses into the grain boundary can be suppressed to several nm or less. Therefore, a gate insulating film having a uniform thickness can be formed, and at the same time, irregularities on the surface of the polycrystalline silicon film can be suppressed. Therefore, the gate breakdown voltage of the transistor characteristics can be improved, and the mobility can be improved.

As described above, according to the present embodiment, the thickness of a thin gate insulating film can be uniformly and accurately controlled on an inexpensive insulating substrate such as glass.
High-speed, highly reliable polycrystalline silicon thin film MIS
Type field effect transistor can be obtained.

In this embodiment, the crystallization of the amorphous silicon thin film and the laser irradiation for forming the gate insulating film are performed independently, but the crystallization and the formation of the gate insulating film may be performed simultaneously in an oxygen atmosphere. Similar effects can be obtained.

(Embodiment 3) FIG. 5 shows a cross-sectional structure of a polycrystalline silicon thin film MIS type field effect transistor according to a third embodiment of the present invention. The gate insulating film has two layers: a gate insulating film 17 formed by irradiating an excimer laser according to the first or second embodiment of the present invention and a gate insulating film 14 deposited by a chemical vapor deposition (CVD) method. Consists of That is, on the surface of the polycrystalline silicon thin film 9 on which the channel is formed, a gate insulating film 17 having a low impurity content and a low interface state density is adopted, and a gate insulating film 14 having an excellent covering property is formed thereon. Are laminated. According to the present embodiment, it is possible to obtain a highly reliable polycrystalline silicon thin film MIS field effect transistor that operates at a low voltage and at a high speed.

Example 4 A thin film transistor formed on a glass substrate of the present invention was used as an image display element, and peripheral circuits such as a drive circuit 102, a memory 104, a CPU 103, and an interface 105 were integrated with the glass substrate. FIG. 6 shows an image display device. Since it is configured integrally, special mounting is not required, and there are effects that signals can be transmitted at high speed and cost can be reduced.

It is important that the MIS type thin film field effect transistor constituting the peripheral circuit be driven at high speed and at low voltage. For this reason, the gate insulating film needs to be thinned to 50 nm or less.
On the other hand, it is important for the MIS type thin film field effect transistor that drives the image display section to have high breakdown voltage and improved reliability. For this reason, the gate insulating film cannot be made as thin as 20 nm or less. Therefore, it is important to locally change the thickness of the gate insulating film of the transistor on the same substrate depending on the application.

The fourth embodiment of the present invention is a manufacturing method for changing the number of irradiations or the irradiation energy of an excimer laser having a wavelength of 400 nm or less for forming a gate insulating film. That is, the image display unit can control the thickness of the gate insulating film with high precision by increasing the number of laser irradiations or increasing the laser irradiation energy compared with the peripheral circuit unit.

[0025]

According to the present invention, it is possible to obtain a highly reliable polycrystalline silicon thin film MIS type field effect transistor which operates at a low voltage and at a high speed with a high quality gate insulating film.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a graph showing a light absorption characteristic of Si (a) and a relationship (b) between laser energy and a formed SiO ₂ film thickness.

FIG. 3 is a graph showing a relationship between oxygen ion implantation energy and formed SiO ₂ film thickness.

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

FIG. 5 is a cross-sectional structure of a semiconductor device according to a third embodiment of the present invention.

FIG. 6 is a perspective view showing a semiconductor device and a method of manufacturing the same according to a fourth embodiment of the present invention.

[Explanation of symbols]

9 ... polycrystalline silicon thin film layer, 10 ... insulating substrate, 1 ... amorphous silicon thin film layer, 14 ... gate insulating film, 17 ... gate insulating film, 18 ... gate electrode, 19 ... drain region, 20 ... source region, 16 ... Oxygen ion introduction region, 100 ... Glass substrate, 101
... image display unit, 102 ... drive circuit, 103 ... CPU, 104 ... memory, 105 ... interface.

Claims (11)

[Claims] An MIS having a gate electrode provided on a semiconductor layer made of an amorphous silicon or polycrystalline silicon thin film on an insulating substrate via a gate insulating film, and a source / drain region provided in the semiconductor layer In the field-effect transistor, the gate insulating film is formed by irradiating an excimer laser having a wavelength of 400 nm or less, and the thickness of the gate insulating film is controlled by irradiation energy and the number of times. Manufacturing method. 2. The method of manufacturing a semiconductor device according to claim 1, further comprising an oxidation step of irradiating the surface of the amorphous silicon or polycrystalline silicon thin film with an excimer laser in an oxygen atmosphere. 3. The method according to claim 1, wherein oxygen ions are implanted into the surface of the amorphous silicon or polycrystalline silicon thin film by ion implantation or ion doping.
Irradiating an excimer laser to the surface of the polycrystalline silicon into which the oxygen ions have been introduced. 4. The method according to claim 1, further comprising an oxidizing step of irradiating the surface of the amorphous silicon or polycrystalline silicon thin film with an excimer laser in an oxygen atmosphere, and a nitriding step of irradiating the excimer laser in a nitriding gas atmosphere. A method for manufacturing a semiconductor device, comprising: 5. The method according to claim 1, further comprising an oxidation step of irradiating the surface of the amorphous silicon or polycrystalline silicon thin film with an excimer laser in an oxygen atmosphere, and a step of irradiating the excimer laser in a fluorine-based atmosphere. Manufacturing method of a semiconductor device. 6. An oxide film formed by irradiating the surface of an amorphous silicon or polycrystalline silicon thin film on an insulating substrate with an excimer laser having a wavelength of 400 nm or less, and a gate insulating film formed by chemical vapor deposition (CVD). A semiconductor device comprising two layers: an oxide film deposited by a method). 7. A semiconductor device according to claim 6, wherein the thickness of the oxide film formed by irradiating the excimer laser is 20 nm or less. 8. The gate insulating film according to claim 6, wherein the oxide film is formed by an oxidation step of irradiating the surface of the amorphous silicon or polycrystalline silicon thin film with an excimer laser in an oxygen atmosphere, and a chemical vapor deposition (CVD) method. A method for manufacturing a semiconductor device, comprising: a step of depositing; and a step of irradiating an excimer laser in a nitrogen or oxygen atmosphere. 9. An image display device having an image display unit and a peripheral circuit on an insulating substrate, wherein the image display unit is driven.
A semiconductor device, wherein the first gate insulating film of the MIS type thin film field effect transistor is thicker than the second gate insulating film of the MIS type thin film field effect transistor forming the peripheral circuit. 10. An image display device having an image display section and a peripheral circuit on an insulating substrate, wherein the first gate insulating film of the MIS type thin film field effect transistor for driving the image display section is formed. A method of manufacturing a semiconductor device, wherein irradiation energy of an excimer laser having a wavelength of 400 nm or less is larger than irradiation energy for forming a second gate insulating film of an MIS type thin film field effect transistor constituting the peripheral circuit. 11. An image display device having an image display portion and a peripheral circuit on an insulating substrate, wherein the first gate insulating film of an MIS type thin film field effect transistor for driving the image display portion is formed. A method for manufacturing a semiconductor device, wherein the number of times of irradiation with an excimer laser having a wavelength of 400 nm or less is larger than the number of times of irradiation for forming a second gate insulating film of an MIS type thin film field effect transistor constituting the peripheral circuit. .