JPH02297923A - Recrystallizing method for polycrystalline silicon - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for recrystallizing a thin film of polycrystalline silicon, which is a basic element constituting a driving transistor of a flat panel display device.

[Conventional technology]

In recent years, as the capacity of display devices such as ELDSLCDs has increased, active matrix drive systems in which each cell is driven by TFTs have been studied. This method requires a driver to drive the X1Y electrode lines in addition to the TPT provided for each cell, but it is preferable to integrate these onto the glass substrate together with the TPT in order to reduce costs. desirable for. The faster the transistors constituting this driver operate, the better the performance of the display device and the larger the capacity.

The mobility of polycrystalline silicon deposited by the commonly used low-pressure CVD method is extremely low, on the order of several c+f/Vsec, which is two orders of magnitude smaller than that of single-crystal silicon. low pressure CV
The reason why the mobility of polycrystalline silicon deposited by the D method is two orders of magnitude lower than that of single-crystal silicon is that there are many dangling bonds, and the crystal grain boundaries have many trap ranks, so this electrical It is thought that this is because carriers are captured by actively active traps, deplete the surrounding region, and form a potential barrier. In order to solve these problems, a hydrogen plasma treatment method in which the potential barrier is eliminated by terminating dangling bonds with hydrogen ions has been studied, but this method has only resulted in a mobility of about 10 cd/VsθC at most. On the other hand, a method of melting and recrystallizing a polycrystalline silicon thin film by irradiating it with an electron beam or a laser beam to obtain a single crystal film with large crystal grain size or almost no grain boundaries is also being considered.

Next, an example of a conventional method for recrystallizing polycrystalline silicon will be explained using FIG.

Polycrystalline silicon layer 2 provided in an island shape on a glass substrate 201
05 is covered with a cap layer 206 made of an insulating film such as silicon dioxide or silicon nitride, and a beam on a spot is scanned and irradiated with a CwAr laser or a pulse mode YAG laser from above. In this case, the cap layer 206 is provided to prevent evaporation of molten silicon.

When irradiated with a high-energy beam, the polycrystalline silicon melts, so that the temperature near the interface with the glass substrate 201 becomes close to the melting point of silicon (~1400° C.). Therefore, the glass substrate 201 is limited to high melting point glasses such as quartz glass. Furthermore, since silica glass has low thermal conductivity, there is an inappropriate heat distribution for the growth of crystal grains in the polycrystalline silicon layer 205 (temperature is higher at the center than at the edges), making it difficult to form a film with good crystallinity. .

FIG. 3 is a diagram for explaining a second example of the conventional polycrystalline silicon recrystallization method.

This second example is a simpler method than the first example, and uses a method in which the polycrystalline silicon layer 305 on the quartz substrate 301 is directly irradiated with a beam of laser light 307 to melt and recrystallize it. . In this case as well, since the temperature near the interface of the glass substrate 301 reaches a high temperature as in the first example, the glass substrate 301 is limited to quartz glass.

FIG. 4 is a diagram for explaining a third example of the conventional polycrystalline silicon recrystallization method.

This third example of the published patent publication (A) 1986-. 18141
9, and is characterized by increasing the crystal grain size of the polycrystalline silicon layer formed by low pressure CVD. In this third example of the polycrystalline silicon recrystallization method, an insulating film 402 and a high thermal conductive layer film 403 are laminated on a glass substrate.
Furthermore, a cap layer consisting of an insulating film 404, a polycrystalline silicon layer 405, and an insulating layer 406 covering the polycrystalline silicon layer is continuously stacked on the high thermal conductivity layer in an island shape, and a high-energy beam is emitted from above the cap layer. laser light 40
7 is being irradiated.

[Problem to be solved by the invention]

Although the method of the third example obtains a polycrystalline layer film with a larger crystal grain size than a polycrystalline layer formed by low-pressure CVD, the heat sink material 403 is formed over a wider area than the polycrystalline silicon layer 405, so Island-shaped polycrystalline silicon layer 40 generated when irradiated with energy beam
Heat at the periphery and center of the heat sink 5 is uniformly conducted to the heat sink material 403 through the high heat conductive insulating film 404. For this reason, the edge heat sink effect, in which the center of the polycrystalline silicon layer is lowered, is not performed efficiently, making it difficult to easily obtain single-crystalline silicon with almost no grain boundaries for driving TFTs in high-definition, high-gradation flat panel display devices. It was difficult.

The present invention eliminates such drawbacks by providing a heat sink layer that conducts heat from the silicon layer through a high thermal conductivity layer and efficiently dissipates heat from the silicon layer, thereby recrystallizing polycrystalline silicon with less thermal influence on the substrate. The aim is to provide a method for promoting

By the way, a driver formed on a quartz glass substrate is
When integrated with a display device such as an LD or LCD, the price of the display device increases. Furthermore, as the displayed price increases, the price of the board plays a larger role. In the conventional method, it was impossible to use inexpensive glass (for example, Corning 7059) due to thermal distortion caused by high-temperature processing, so the display device had to be expensive. Furthermore, since the temperature distribution when recrystallizing the polycrystalline silicon provided in an island shape is inappropriate for the growth of crystal grains (high temperature in the center), it is difficult to easily form a film with good crystallinity.

Furthermore, the prior art, Japanese Patent Publication No. 181419/1986
Although polycrystalline silicon with a larger crystal grain size can be obtained by the method of 1, high-speed drive TPT
It has been difficult to obtain single-crystal silicon with almost no grain boundaries, which is necessary for this purpose.

The purpose of the present invention is to eliminate such conventional drawbacks, provide an insulating film with low thermal conductivity and a patterned heat sink layer with high thermal conductivity, and efficiently produce single crystal silicon with almost no grain boundaries without thermal influence on the substrate. The objective is to provide a method for good recrystallization.

[Means to solve the problem]

In the polycrystalline silicon recrystallization method of the present invention, a first insulating film is formed on a glass substrate, a highly thermally conductive layer is further formed on the first insulating layer, the highly thermally conductive layer is patterned, and the highly thermally conductive layer is patterned. A cap layer consisting of a second insulating film and a third insulating film covering the polycrystalline silicon layer is successively stacked on the conductive layer, and a high-energy beam is irradiated from above the cap layer.
, I, and the polycrystalline silicon layer is made into a single crystal.

[For production]

It is desired that an insulating film such as silicon dioxide of an appropriate thickness and a high heat conductive layer made of a high melting point metal such as tungsten be formed on a glass substrate, and that the high heat conductive layer be able to efficiently conduct heat and dissipate heat. patterned in the shape of and further AIN
A highly thermally conductive insulating film such as is formed on the highly thermally conductive layer.

Furthermore, a polycrystalline silicon layer is formed into an island shape. Further, a cap layer made of an insulating film such as silicon nitride covers these highly thermally conductive insulating films and the polycrystalline silicon layer. From above, cw
When a beam is irradiated using an Ar laser or a pulse mode YAG laser, the polycrystalline silicon is melted and recrystallized, and the polycrystal on the high heat transfer insulating film is turned into a single crystal.

In this case, since an insulating film with high thermal conductivity and a high melting point metal are provided under the polycrystalline silicon layer, heat is conducted to the metal film through this high thermal conductive insulating film, and the heat is transferred to the metal film, which has extremely low thermal conductivity. Most of the heat is blocked by the silicon film and dissipated to the outside from the high melting point metal film that extends outside the area of the island-shaped polycrystalline silicon layer. Therefore, when the polycrystalline silicon layer is irradiated with a high-energy beam, the temperature of the polycrystalline silicon layer is close to its melting point, but the temperature of the glass substrate under the silicon dioxide film is that of the silicon dioxide film, and the thermal strain point is approximately 600℃ (for example, Corning 7
059) Glass can now be used as a substrate. Furthermore, by providing the highly thermally conductive film not on the entire surface of the substrate but in the center, which is narrower than the island-shaped polycrystalline layer,
When irradiated with a laser beam, the temperature of the center of the polycrystalline silicon film becomes lower than that of the periphery, and single crystal silicon grows.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram for explaining polycrystallization of polycrystalline silicon, which is one embodiment of the present invention.

First, a first insulating film 102 having low thermal conductivity such as silicon dioxide and W or M are formed on a glass substrate 101.

A high heat conductive layer 103 made of a high melting point metal such as is formed. The high thermal conductivity layer 103 is not necessarily limited to high melting point metals, but may also be a film such as polycrystalline silicon into which other impurities having high thermal conductivity are introduced.

This high heat transfer layer 103 is patterned into a band shape as shown in FIG. Further, the band-shaped high thermal conductive layer 103 and the insulating film 10
1, an insulator 11 having high thermal conductivity such as aluminum nitride!
Form II 04. Furthermore, polycrystalline silicon 105 is formed in an island shape on the insulating film 104. Note that the insulating film 104
is provided to prevent impurities from being mixed into the high thermal conductivity layer 103 and the polycrystalline silicon layer when the polycrystalline silicon 105 is heated, thereby preventing partial deterioration of the film quality. The insulating film 104 may be a thin silicon dioxide film that conducts heat well.

Next, the island-shaped polycrystalline silicon layer 105 is covered with a cap layer 106 made of a silicon dioxide film, a silicon nitride film, or a multilayer film of silicon dioxide and silicon nitride, and then a cwAr laser or a pulsed mode YAG laser beam is applied onto the cap layer 106. Laser light 107 is irradiated. F1 polycrystalline silicon layer 10
5 is melted, and the applied thermal energy first passes through the insulating film 104 and then through the high heat conductive layer 103. Since the high thermal conductivity layer 103 is located at the center of the island-shaped silicon layer, the heat of the silicon in the center is dissipated first than in the periphery, so the temperature of the center is lower than that of the periphery of the polycrystalline silicon layer. A high-quality single-crystalline film can be obtained by efficiently generating the tinging effect.

On the other hand, the thermal conductivity of the insulating film 102 provided under the high thermal conductivity layer 103 as a heat sink material is, for example, in the case of silicon dioxide, which is more than three orders of magnitude lower than that of silicon. Heat conduction is largely prevented. Therefore, if the thickness of the insulating film 102 that blocks heat conduction is appropriately selected, an inexpensive glass (for example, 7059 manufactured by Corning Inc.) can be used as the glass substrate 101 instead of a high-strength quartz substrate.

〔Effect of the invention〕

As explained above, according to the present invention, a high thermal conductivity layer for a heat sink is provided under the polycrystalline silicon layer so that heat is effectively conducted from the center of the polycrystalline silicon layer to the periphery and dissipated to the outside. Because it is patterned, the edge heating effect works better than conventional techniques.
A single crystal silicon film with almost no grain boundaries can be obtained.

In addition, since the heat generation effect on the substrate can be reduced, a single crystal silicon film can be formed even on a glass substrate that has a lower strain point than quartz (for example, Corning 7059), which can drive flat display devices. Since there is no need to form a TPT for use on expensive glass such as quartz, the cost of a flat display device in which driving transistors are formed on the same substrate becomes cheaper.

Furthermore, since the high-speed driving TPT is formed of single-crystal silicon with almost no grain boundaries, a flat display device with high definition and high gradation display can be obtained.

[Brief explanation of the drawing]

FIG. 1(a) and FIG. 1(b) are respectively the first embodiment of the present invention.
2, 3, and 4 are diagrams for explaining the conventional recrystallization method of polycrystalline silicon. 101.201.301.401 Glass substrate 102.402 Insulating film 103.403 High temperature conductive layer 1'04.404 Φ Insulating film 105.205.305.405 Multi Crystalline silicon layer 106.206.406 Cap layer and above Applicant Seiko Epson Co., Ltd. Agent Patent attorney Kizobe Suzuki (and 1 other person) RO7 Ray jet Figure 1 (a) Figure 2 No. 07 Rayi bill - Figure 3 o7 Laser also Figure 4

Claims (1)

[Claims] (1) Form a first insulating film on a glass substrate, and then
A highly thermally conductive layer is formed on the insulating film, the highly thermally conductive layer is patterned, and a cap layer consisting of a second insulating film and a third insulating film covering the polycrystalline silicon layer is continuously formed on the highly thermally conductive layer. A polycrystalline silicon recrystallization method characterized in that the polycrystalline silicon layer is stacked, and a high-energy beam is irradiated from above the cap layer to single-crystallize the polycrystalline silicon layer.