KR100659095B1 - Method of crystallizing semiconductor and polycrystalline semiconductor tft - Google Patents

Abstract

A method for crystallizing a semiconductor and a polycrystalline semiconductor TFT are provided to crystallize amorphous silicon as polycrystalline silicon by using an energy absorbing layer. An energy absorbing layer(30) is formed on an upper surface of a metal substrate(10). An amorphous semiconductor layer is formed on an upper surface of the energy absorbing layer. The amorphous semiconductor layer is crystallized as a polycrystalline semiconductor layer by using laser beams. The energy absorbing layer is used for absorbing laser energy. The laser beam method is an excimer laser annealing method or a sequential lateral solidification method.

Description

Polycrystalline semiconductor crystallization method and polycrystalline semiconductor thin film transistor TECHNICAL FIELD

1 is a cross-sectional view briefly showing the movement of the energy incident from the laser into the silicon layer during the conventional laser heat treatment.

2A and 2B are cross-sectional views briefly illustrating movement of energy incident from a laser into a silicon layer during laser heat treatment according to embodiments of the present invention.

3A to 3C are cross-sectional views schematically illustrating a crystallization process of a polycrystalline silicon layer according to an embodiment of the present invention.

4A to 4B are cross-sectional views showing in detail a cross section of a polycrystalline semiconductor thin film transistor employing the method of FIGS. 3A to 3C according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline semiconductor crystallization method and a polycrystalline semiconductor thin film transistor employing the method. In particular, when crystallizing polycrystalline silicon, that is, polysilicon into amorphous silicon by a laser heat treatment method, an energy absorbing layer under the silicon layer is used. Adopting a polycrystalline silicon crystallization method and method that can prevent the energy diffuse reflection from the metal substrate by blocking the energy transfer to the metal substrate to improve the grain growth of the silicon and the uniformity of the grain shape The present invention relates to a polycrystalline semiconductor thin film transistor.

Generally, among the elements constituting a thin film transistor (TFT), a semiconductor active layer is formed of amorphous silicon containing hydrogen having no periodicity of lattice depending on its crystal state. Or polycrystalline silicon, which is a polycrystalline solid, is used.

Amorphous silicon can be deposited at a low temperature to form a thin film, and is mainly used for switching elements of liquid crystal panes using glass having a low melting point as a substrate.

In this case, when the semiconductor active layer of amorphous silicon including hydrogen is used as a switching device, especially when exposed to light, photocurrent is generated by photoelectric conversion, which acts as an off-state leakage current that is fatal to the operation of the switching device. Done.

In addition, even if the semiconductor active layer is not exposed to light, many defects such as dangling bonds, which are characteristic of amorphous silicon, are formed, and the operation characteristics of the device are not smooth due to the flow of electrons. This is not good.

Accordingly, the amorphous silicon thin film has problems of deterioration of electrical characteristics and reliability of the liquid crystal panel driving device and difficulty of large display area.

In general, the commercialization of large area, high-definition and panel image driving circuits, integrated laptop computers, and wall-mounted LCDs has excellent electrical characteristics, such as high field effect mobility and high frequency operation characteristics. Low leakage current pixel driving elements are required.

When the polysilicon layer is used as a semiconductor active layer, fewer defects are generated on the surface, and the operation speed of the thin film transistor is about 100 to 200 times faster than that of the semiconductor active layer of amorphous silicon. Therefore, the thin film transistor using the polysilicon layer as a semiconductor active layer has extremely fast operation characteristics and can operate in conjunction with an external high speed driving integrated circuit, thereby displaying real-time image information such as a large area liquid crystal display device. It becomes a switching element suitable for the apparatus.

The method of manufacturing polysilicon can be divided into low temperature process and high temperature process according to the process temperature. Among the high temperature process, the process temperature is about 1000 ° C, and the temperature condition is higher than the deformation temperature of the insulating substrate, and instead of the glass substrate having low heat resistance It is necessary to use an expensive quartz substrate with high heat resistance, and the polycrystalline silicon thin film by this high temperature process has high surface roughness and low crystallinity such as fine grains during film formation. Since there is a disadvantage in that device application characteristics are poor, a technology for forming a polycrystalline silicon by crystallizing it using amorphous silicon capable of low temperature deposition has been researched and developed.

The low temperature process may be classified into laser annealing, metal induced crystallization, and the like.

Among them, the laser heat treatment process uses a method of irradiating a pulsed laser beam onto a substrate, which repeats melting and solidification by a pulsed laser beam in units of 10 to 10 ² nanoseconds. In order to minimize the damage to the lower insulating substrate, it is most attention in the low temperature crystallization process.

However, even in the case of the metal substrate, as shown in FIG. 1, a part of the energy incident on the amorphous silicon layer 40a from the laser beam (solid arrows in FIG. 1) as shown in FIG. Arrows) are transferred to the metal substrate 10 through the buffer layer 20 and the energy is reflected back by the metal substrate 10, resulting in non-uniformity of the surface of the metal substrate, that is, surface roughness and defect. ) And the energy is transferred to the silicon layer 40a again.

As a result, as shown in FIG. 1, an imbalance occurs between the energy transferred back to the silicon layer 40a by diffuse reflection, and so on, resulting in a decrease in silicon grain growth and a non-uniformity of grain form, resulting in an electric field mobility. ), There is a problem of lowering the characteristics. Further, although the case of the metal substrate is taken as an example, the same problem may still occur in the case of a substrate having high energy reflectivity.

The present invention was devised to solve the problems of the prior art, an object of the present invention, by forming an energy absorbing layer capable of absorbing energy under the amorphous silicon layer to block its movement, amorphous silicon by a laser heat treatment method When crystallization to polycrystalline silicon, the energy incident from the laser beam is prevented from moving to the metal substrate, thereby preventing the energy diffuse reflection from the metal substrate described above to improve the grain growth of the silicon and maintain the grain shape uniformity. There is provided a polycrystalline semiconductor crystallization method that can be used and a polycrystalline semiconductor TFT having excellent characteristics employing the method.

In order to achieve the above object, the present invention provides a first step of forming an energy absorbing layer on a metal substrate, a second step of forming an amorphous semiconductor layer on the energy absorbing layer and the amorphous semiconductor layer using a polycrystalline semiconductor. And a third step of crystallizing the layer, wherein the energy absorbing layer is provided to absorb laser energy in the third step.

In order to achieve the above object, the present invention also provides a metal substrate, an energy absorbing layer formed on the metal substrate, a polycrystalline semiconductor active layer formed on the energy absorbing layer and having a source, a drain and a channel region, and formed on the polycrystalline semiconductor active layer. And a first electrode and a second electrode insulated from the gate electrode and the gate electrode insulated from the polycrystalline semiconductor active layer, and in contact with a source and a drain region of the polycrystalline semiconductor active layer, wherein the energy absorbing layer is formed of the polycrystalline semiconductor active layer. It provides a polycrystalline semiconductor thin film transistor, characterized in that provided to absorb laser energy for.

As the energy absorbing layer, it is preferable to use a material capable of effectively absorbing the wavelength of the laser beam used in the laser heat treatment, and the use of an energy insulating film capable of appropriately blocking the energy can be obtained in some cases. In the meantime, the semiconductor mainly refers to a silicon semiconductor, and will be described below with a silicon semiconductor.

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

FIG. 2A is a cross-sectional view schematically showing the movement of energy incident from the laser beam into the silicon layer during the laser annealing process according to the first embodiment in terms of the vertical structure, and the silicon is formed by the laser beam (solid arrows in FIG. 2A). A portion of the energy incident to the layer 40a (dashed arrows in FIG. 2A) is absorbed by the energy absorbing layer 30 formed between the buffer layers 20a and 20b, unlike in FIG. 1, to the metal substrate 10. It is shown that it is not transmitted, and as a result, no energy reflection occurs in the metal substrate 10. On the other hand, even if a portion of the energy is passed through the energy absorbing layer to the metal substrate and reflected back, the energy absorbing layer is absorbed again, so that uneven energy reflected from the metal substrate is blocked from being transferred directly to the silicon layer 40a. It will act to block the energy transfer.

The material used as the energy absorbing layer should be an effective material for energy absorption in consideration of the energy of the laser wavelength used in the laser heat treatment. In other words, as an annealing method, an excimer laser annealing (ELA) method or a sequential lateral solidification (SLS) method is used, wherein the wavelength of the laser beam used and the amorphous silicon layer are amorphous. Considering the energy to be crystallized by breaking the metal and the energy transferred by the heat conduction, the typical materials include silicon (Si), gallium arsenide (GaAs), germanium (Ge), and indium having an energy band gap of 0.5 to 1.5 eV. Phosphorus (InP) and other compound semiconductors may be used.

FIG. 2B is a cross-sectional view schematically showing the movement of energy in the laser heat treatment process according to the second embodiment. Unlike FIG. 2A, the energy absorbing layer 30 is formed on the metal substrate 10 without the buffer layers. It has been shown that the absorber layer 30 can also perform the function of the buffer layer. Therefore, the energy absorbing layer 30 must have characteristics as a buffer layer, and the thickness of the energy absorbing layer or the selection of a material having an appropriate energy band gap, etc., can be used to have the same energy absorbing and blocking effect as the buffer layer of FIG. 2A exists. Should be considered

On the other hand, the energy absorption rate of the energy absorbing layer is also assumed to be somewhat uniform, because if the energy absorbing layer is formed directly in the amorphous silicon layer, the energy absorbing layer immediately absorbs energy during crystallization and there is a nonuniformity in the absorption rate of the energy absorbing layer. This results in non-uniformity of crystallization.

As the material of the energy absorbing layer, as described above, an appropriate material may be used in consideration of the wavelength of the laser beam used for laser heat treatment and the energy absorption of the amorphous silicon layer.

3A to 3C are cross-sectional views schematically illustrating a polycrystalline silicon crystallization process by the laser heat treatment method according to the first embodiment.

3A schematically illustrates the step of forming the energy absorbing layer 30 on the buffer layer 20a after forming the buffer layer 20a on the metal substrate 10. Although an energy absorbing layer is formed on the buffer layer in this figure, it is a matter of course that the energy absorbing layer simultaneously having the characteristics of the buffer can be formed directly on the metal substrate as in the second embodiment.

3B is a step of forming a buffer layer 20b on the formed energy absorbing layer 30 again, and then forming an amorphous silicon layer 40a thereon, using pure amorphous silicon on the buffer layer 20b. The amorphous silicon is deposited by plasma enhanced chemical vapor deposition (PECVD) or low pressure CVD (LPCVD).

When the amorphous silicon is deposited using the chemical vapor deposition (CVD) method or the like, it contains a lot of hydrogen. Since hydrogen has a characteristic of being separated from the silicon by heat, the amorphous silicon is first heat treated to undergo a dehydrogenation process. It is necessary. This is because, if hydrogen is not removed in advance, the surface of the crystal becomes very rough during crystallization, resulting in poor electrical characteristics. Although only the CVD method is mentioned above, this is only one example, and other vapor deposition methods apparent to those skilled in the art may be used.

Meanwhile, in FIG. 3B, the buffer layer 20b is formed on the energy absorbing layer 30 and the amorphous silicon layer is formed thereon. However, when the energy absorbing layer can serve as a buffer layer, the amorphous silicon is immediately added to the energy absorbing layer without the buffer layer 20b. It is of course possible to form a layer. However, when the buffer layer is formed without the buffer layer as described above, the energy band gap of the absorber material and the uniformity of the energy absorption rate should be considered.

3C schematically illustrates a step of crystallizing the polycrystalline silicon layer 40b through laser annealing after the amorphous silicon layer 40a is formed. As shown in FIG. 3C, a laser beam by the laser device 200 is illustrated. (The hatched rectangular portion below the laser device) is irradiated moving from the left side to the right side of the amorphous silicon layer (arrow direction), whereby the already irradiated portion shows that the polycrystalline silicon layer 40b is being formed.

As the crystallization method using the laser heat treatment, an ELA method or an sequential lateral solidification (SLS) method using an excimer laser, which is generally a high output pulse laser, is used.

In particular, the short wavelength of the excimer laser utilizes the energy concentration of the laser light, so that it is possible to perform precise heat treatment in a short time and locally, and the size of crystal grains of the polycrystalline silicon layer to be produced is generated by the thickness of the amorphous silicon film and the laser. It is possible to precisely control the temperature by varying the density of ultraviolet radiation and the temperature of the lower substrate.

The SLS method takes advantage of the fact that the grain of silicon grows in the direction perpendicular to the interface at the interface between the liquid and solid silicon, and properly controls the size of the laser energy and the shift of the irradiation range of the laser beam. By growing the grains of silicon by a predetermined length, the amorphous silicon layer is crystallized.

As described above, the crystallization method using the laser has a problem of causing grain growth and morphology of silicon due to energy transfer to the lower metal substrate and diffuse reflection in the metal substrate, as shown in FIG. 3C. By forming an energy absorbing layer in the lower portion in advance to absorb and block energy during laser heat treatment, it is possible to solve the above problems, thereby forming a polycrystalline silicon layer having excellent characteristics with improved grain growth and uniform grain shape. It becomes possible.

The polycrystalline silicon layer formed by the above method is then used as a semiconductor active layer of the TFT through various processes such as patterning and activation, thereby producing an excellent polycrystalline semiconductor TFT having high channel mobility.

Fig. 4A shows in detail the cross section of the polycrystalline semiconductor TFT fabricated using the polycrystalline silicon layer formed by the first embodiment.

The polycrystalline semiconductor TFT (hereinafter referred to as 'first TFT') using the polycrystalline silicon layer according to the first embodiment is formed on the metal substrate 10. In addition to the metal substrate, a substrate made of another material having high energy reflectance is used. Of course, the present invention can be applied to.

The lower buffer layer 20a is formed on the metal substrate 10 to prevent diffusion of impurity ions, and to act as a buffer for preventing distortion, which may occur due to non-uniform contact between the substrate and the upper layer. This buffer layer may be optional depending on the material of the substrate or the characteristics of the top layer. On the other hand, although not shown in Figure 4a, a barrier layer may be formed to prevent the penetration of moisture or outside air.

An energy absorbing layer 30 that absorbs energy is formed on the lower buffer layer 20a to block energy transfer from the silicon layer to the metal substrate 10. This energy absorbing layer 30 blocks the transfer of energy from the silicon layer to the metal substrate as well as from the metal substrate when crystallizing the subsequently formed amorphous silicon layer into the polycrystalline silicon layer as described above in the description of FIG. 2A. By also blocking the reflected energy, the grain growth of the silicon layer due to energy diffuse reflection from the metal substrate and the grain shape irregularities are prevented.

As the material of the energy absorbing layer 30 in consideration of the wavelength of the laser beam used for laser heat treatment and the energy absorption of the amorphous silicon layer, and the like, it is as described above.

The upper buffer layer 20b is formed on the energy absorbing layer 30 again, and acts as a buffer between the energy absorbing layer 30 and the upper layer similarly to the lower buffer layer.

The first TFT includes a semiconductor active layer 40, a gate electrode 70 insulated from the semiconductor active layer 40, and first and second electrodes 80 in contact with the semiconductor active layer.

The semiconductor active layer 40 is formed on the upper buffer layer 20b. As described above in the first embodiment, the amorphous silicon layer is laser heat treated to crystallize into a polycrystalline silicon layer, and then patterned and activated by implantation of impurity ions. It is formed by. The semiconductor active layer is divided into a source and a drain region, which are portions in which impurity ions are implanted, and a channel region in which impurity ions are not implanted.

A gate insulating film 50 is formed on the semiconductor active layer 40 so as to cover the gate insulating film 50. A gate electrode 70 is formed on the gate insulating film 50 at a portion corresponding to the channel region of the semiconductor active layer, and the gate insulating film 50 is formed thereon. An interlayer insulating film 60 is formed to cover 70. Contact holes 50a are formed in the gate insulating film 50 and the interlayer insulating film 60, and source and drain electrodes, which are the first and second electrodes 80, are formed on the interlayer insulating film 60.

The source and drain electrodes 80 are in contact with the source and drain regions of the semiconductor active layer through contact holes, as shown in FIG. 3A.

The structure of such a TFT is not necessarily limited thereto, and of course, TFTs having various structures can be applied to the present invention.

FIG. 4B is a detailed cross-sectional view of a polycrystalline semiconductor TFT (second TFT) using the polycrystalline silicon layer according to the second embodiment, and unlike FIG. 4A, there are no buffer layers 20a and 20b. That is, the step of the process can be reduced by using the energy absorbing layer 30 together as a buffer layer. The energy absorbing layer 30, as well as the effect of energy absorption and blocking should be provided with the characteristics as a buffer, as described above, the uniformity of a certain energy absorption rate and the selection of a material having an appropriate energy band value, etc. Is required. Other parts of FIG. 4B are the same as in FIG. 4A, and thus, further descriptions thereof will be omitted.

The TFTs of Figs. 4A or 4B have a high channel mobility and excellent operating characteristics by using a polycrystalline semiconductor layer having improved grain growth and uniform shape as the semiconductor active layer 30 formed according to the first or second embodiment. It may be usefully used for a flat panel display for realizing an area video.

So far, the present invention has been described with reference to the embodiments shown in the drawings, which are merely exemplary and will be understood by those skilled in the art that various modifications and equivalent other embodiments are possible. . Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

As described in detail above, the present invention, in the process of crystallizing amorphous silicon into polycrystalline silicon by the laser heat treatment method, by absorbing and blocking the energy incident on the silicon layer using the energy absorbing layer to block the energy diffuse reflection from the metal substrate It is possible to fabricate a polycrystalline silicon layer having excellent characteristics with improved grain growth and morphology of silicon.

In addition, by using such a polycrystalline silicon layer as a semiconductor active layer of a TFT, it is possible to fabricate an excellent polycrystalline semiconductor TFT having high channel mobility and operating characteristics, and enabling such a large-area moving image of a flat panel display device by using such TFT. Can be.

On the other hand, when using the energy absorbing layer as a buffer layer as in the second embodiment, it is possible to reduce the process step of forming a separate buffer layer, there is an advantage that can be produced a polycrystalline semiconductor TFT in a simpler process.

Claims (13)

Forming a energy absorbing layer on the metal substrate; A second step of forming an amorphous semiconductor layer on the energy absorbing layer; And A third step of crystallizing the amorphous semiconductor layer into a polycrystalline semiconductor layer using a laser, The energy absorbing layer is a polycrystalline semiconductor crystallization method, characterized in that provided in the step 3 to absorb the laser energy. According to claim 1, The method using the laser of the third step is an excimer laser crystallization (ELA) method or a sequential lateral solidification (SLS) method, characterized in that the polycrystalline semiconductor crystallization method. According to claim 1, The energy absorbing layer is a polycrystalline semiconductor crystallization method, characterized in that using a material having an energy band gap of 0.5 ~ 1.5 eV. The method of claim 3, wherein The energy absorbing layer is formed of silicon (Si), gallium arsenide (GaAs), germanium (Ge), indium phosphorus (InP) or other compound semiconductor crystallization method, characterized in that. According to claim 1, And said metal substrate further comprises a buffer layer. According to claim 1, And a buffer layer interposed between the energy absorbing layer and the amorphous semiconductor layer. The method according to any one of claims 1 to 6, And said polycrystalline semiconductor is polysilicon. Metal substrates; An energy absorbing layer formed on the metal substrate; A polycrystalline semiconductor active layer formed on the energy absorbing layer and having a source, a drain, and a channel region; A gate electrode formed on the polycrystalline semiconductor active layer and insulated from the polycrystalline semiconductor active layer; And First and second electrodes insulated from the gate electrode and in contact with source and drain regions of the polycrystalline semiconductor active layer, The energy absorbing layer is a polycrystalline semiconductor thin film transistor, characterized in that provided to absorb the laser energy for the formation of the polycrystalline semiconductor active layer. The method of claim 8, The energy absorbing layer is a polycrystalline semiconductor thin film transistor, characterized in that using a material having an energy band gap of 0.5 ~ 1.5 eV. The method of claim 9, And the energy absorbing layer is formed of silicon (Si), gallium arsenide (GaAs), germanium (Ge), indium phosphide (InP), or other compound semiconductors. The method of claim 8, The metal substrate further comprises a buffer layer. The method of claim 8, And a buffer layer interposed between the energy absorbing layer and the polycrystalline semiconductor active layer. The method according to any one of claims 8 to 12, And said polycrystalline semiconductor active layer is polysilicon.

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