KR100579176B1 - Semiconductor device and method fabricating thereof - Google Patents

Abstract

In the present invention, when the conventional amorphous silicon layer is crystallized by the ELA method, protrusions generated on the surface of the polycrystalline silicon layer subsequently cause non-uniform interface characteristics between the semiconductor layer and the gate insulating layer, thereby lowering the reliability of the thin film transistor. In order to solve such a problem, the present invention provides a semiconductor device in which a crystal is turned on by ELA and irradiates a laser beam by flipping the substrate, or irradiates a laser beam from the bottom of the substrate so that the protrusions are formed at the interface between the polycrystalline silicon layer and the buffer layer. It is related with the formation method.

A semiconductor device of the present invention and a method for forming the same include an insulating substrate; And a buffer layer, a polycrystalline silicon layer, and an insulating film layer formed on the insulating substrate, and are not formed at the interface between the insulating film layer and the polycrystalline silicon layer, and are formed at the interface between the polycrystalline silicon layer and the buffer layer, and formed in the buffer layer direction. There is a technical feature to a semiconductor device and a method of forming the same.

Accordingly, the semiconductor device of the present invention and the method of forming the same by irradiating a laser beam by inverting the substrate during crystallization by ELA method, or by irradiating a laser beam from the bottom of the substrate so that the projections are formed at the interface between the polycrystalline silicon layer and the buffer layer. The interfacial characteristics between the semiconductor layer and the gate insulating film of the thin film transistor formed of the polycrystalline silicon layer are excellent and the uniformity is increased, thereby improving the characteristics of the thin film transistor.

ELA method, crystallization, protrusion

Description

Semiconductor device and method for forming the same             

1A and 1B are cross-sectional views of a crystallization process by the ELA method of the prior art.

Figure 2 is a photograph of the projections formed on the surface of the polycrystalline silicon crystallized by the ELA method of the prior art.

3A to 3C are cross-sectional views of a process of crystallizing an amorphous silicon layer by the ELA method according to the present invention.

4 is a cross-sectional view of a thin film transistor formed using a semiconductor layer crystallized by the ELA method of the present invention.

5A-5C are cross-sectional views showing three mechanisms of the crystallization process.

 <Description of Symbols for Main Parts of Drawings>

102 buffer layer 103 amorphous silicon layer

104: insulating film layer 105: laser beam

106 polycrystalline silicon layer 108 projection

The present invention relates to a semiconductor device and a method of forming the same, and more particularly, to sequentially form a buffer layer, an amorphous silicon layer, and an insulating film layer on an insulating substrate, turn the substrate over, irradiate a laser beam from the top, or The present invention relates to a semiconductor device and a method of forming the same, wherein the projections are formed in the buffer layer direction at the interface between the polycrystalline silicon layer and the buffer layer by crystallizing by an ELA method irradiating a laser beam from the bottom.

Flat Plane Displays, such as organic electroluminescent display devices or liquid crystal display devices, may be used as switching elements or driving elements, and may be thin film transistors. Transistor) is used.

In this case, the thin film transistor is formed of a semiconductor layer including a source / drain region, a gate insulating layer, a gate electrode, an interlayer insulating layer, and a source / drain electrode. Among the devices constituting the thin film transistor, the semiconductor layer is the device having the greatest influence on the movement of electrons or holes. When the semiconductor layer is formed of an amorphous silicon layer, it is difficult to increase the size of the flat panel display device due to low mobility of electrons or holes, and to increase the size of the thin film transistor, thereby reducing the aperture ratio of the display device. Generate. Therefore, many researchers or inventors have conducted a lot of research on the method of forming the amorphous silicon layer as a polycrystalline silicon layer.

Crystallization of the amorphous silicon layer into a polycrystalline silicon layer can be classified into three types as follows.

The first method, laser annealing, is a method of growing a polycrystalline silicon layer by applying a laser to a substrate on which an amorphous silicon thin film is deposited.

The second method, solid phase crystallization, is a method of forming a polycrystalline silicon layer by heat-treating amorphous silicon at a high temperature for a long time.

A third method, metal induced crystallization, is a method of forming a polycrystalline silicon layer by depositing a metal on amorphous silicon.

The first method, laser heat treatment, is a method of forming a polycrystalline silicon layer, which is currently widely studied, which supplies laser energy to a substrate on which an amorphous silicon layer is deposited to make the amorphous silicon layer in a molten state, and then forms a polycrystalline silicon layer by cooling. Way.

The second method, solid crystallization, forms a buffer layer with a predetermined thickness to prevent diffusion of impurities on a quartz substrate that can withstand high temperatures of 600 degrees or more, and deposits an amorphous silicon layer on the buffer layer. A method of obtaining a polycrystalline silicon layer by heat treatment at a high temperature for a long time in a furnace. As described above, since the solid crystallization is performed at a high temperature for a long time, a desired polycrystalline silicon phase cannot be obtained, and the crystal growth direction is irregular, so that a thin film transistor can be obtained. In the application of the furnace, the gate insulating film to be connected to the polycrystalline silicon layer is grown irregularly, the breakdown voltage of the device is lowered, and the grain size of the polycrystalline silicon is very uneven, which not only lowers the electrical characteristics of the device. However, there is a problem of using an expensive quartz substrate.

The third method, metal-induced crystallization, can form a polycrystalline silicon layer using a low-cost, large-area glass substrate, but the film quality is reliable because there is a high possibility that metal residues exist in the network inside the polycrystalline silicon layer. There is a problem that it is difficult to guarantee.

1A and 1B are cross-sectional views of a crystallization process by the ELA method of the prior art.

First, FIG. 1A is a sectional view of a crystallization process by the ELA method of the prior art. As shown in the figure, a buffer layer 12 and an amorphous silicon layer 13 formed of a silicon oxide film or a silicon nitride film are sequentially formed on a transparent insulating substrate 11 such as plastic or glass. In this case, the buffer layer and the amorphous silicon layer are formed by a deposition apparatus such as plasma enhanced chemical vapor deposition (PECVD).

1B is a cross-sectional view of the step of crystallizing the ELA method on the substrate on which the amorphous silicon layer is formed. As shown in the figure, the laser beam 14 is irradiated on the amorphous silicon layer on the substrate on which the amorphous silicon layer is formed to crystallize. At this time, the laser beam proceeds while moving in a constant direction 15, wherein the amorphous silicon layer irradiated with the laser beam is crystallized by the polycrystalline silicon layer 16, and the laser beam is continuously crystallized. 17).

However, when the amorphous silicon layer is crystallized to the polycrystalline silicon layer by the conventional ELA method, protrusions 18 are generated on the surface of the polycrystalline silicon as shown in FIG. 2, which is a laser beam. When the irradiated amorphous silicon layer melts in a liquid phase and causes phase transition to a solid phase, it occurs at grain boundaries. The protrusions are then present at the interface between the polycrystalline silicon layer and the gate insulating film, causing nonuniformity of the characteristics, and using a compensation circuit or a compensation thin film transistor to compensate for the nonuniformity of the characteristics.

Accordingly, the present invention is to solve the above-mentioned disadvantages and problems of the prior art, when crystallizing the amorphous silicon layer formed on the substrate by the ELA method, flip the substrate to irradiate the laser beam, or the laser beam from the bottom of the substrate It is an object of the present invention to provide a semiconductor device and a method of forming the projections so that the projections are formed at the interface between the polycrystalline silicon layer and the buffer layer, and the projections are formed in the buffer layer direction.

The object of the present invention is an insulating substrate; And a buffer layer, a polycrystalline silicon layer, and an insulating film layer formed on the insulating substrate, and are not formed on the interface between the insulating film layer and the polycrystalline silicon layer, and are formed at an interface between the polycrystalline silicon layer and the buffer layer, and are formed in the buffer layer direction. It is achieved by a semiconductor element consisting of projections.

In addition, the above object of the present invention comprises the steps of preparing an insulating substrate; Forming a buffer layer and an amorphous silicon layer on one surface of the substrate; Degassing the substrate on which the buffer layer and the amorphous silicon layer are formed; Forming an insulating film layer on the degassed substrate; Irradiating a laser beam on top of the other surface of the substrate; And crystallizing the amorphous silicon layer on the interface between the amorphous silicon layer and the buffer layer by the irradiated laser beam and crystallizing the polycrystalline silicon layer having protrusions formed in the buffer layer direction. Is achieved.

Details of the above object and technical configuration of the present invention and the effects thereof according to the present invention will be more clearly understood by the following detailed description with reference to the drawings showing preferred embodiments of the present invention.

3A to 3C are cross-sectional views of a process of crystallizing an amorphous silicon layer by the ELA method according to the present invention.

First, FIG. 3A is a cross-sectional view of a process of forming a buffer layer, an amorphous silicon layer, and an insulating film layer on an insulating substrate. As shown in the figure, a buffer layer 102, an amorphous silicon layer 103 and an insulating film layer 104 are sequentially formed on a transparent insulating substrate 101 such as plastic or glass.

The buffer layer is formed of an insulating film such as an oxide film or a nitride film. It is also desirable for the transparency of the laser beam to pass through without loss.

Subsequently, sputtering and chemical vapor deposition apparatus such as PECVD, Low Pressure Chemical Vapor Deposition (LPCVD), Atmospheric Pressure Chemical Vapor Deposition (APCVD) or Electro Cyclotron Resonance Chemical Vapor Deposition (ECR-CVD) are performed on the buffer layer. Amorphous silicon layer is formed by using a physical vapor deposition apparatus such as. In this case, it is generally preferable to form amorphous silicon using the chemical vapor deposition apparatus.

The amorphous silicon layer formed by the chemical vapor deposition apparatus contains 10 to 20% of hydrogen, and in the case of the amorphous silicon layer formed by the physical vapor deposition apparatus, a source generating plasma such as argon (Ar) or helium (He) gas, etc. Gas is contained. Gases contained in the amorphous silicon layer such as hydrogen, argon or helium gas not only adversely affect the surface roughness, grain size or quality of polycrystalline silicon when the amorphous silicon layer is crystallized by ELA method, but in severe cases The crystallized polycrystalline silicon layer may be peeled off in some cases. Therefore, the deposited amorphous silicon layer is subjected to dehydrogenation or degassing. The dehydrogenation is performed continuously after forming the amorphous silicon layer in the chemical vapor deposition apparatus, or the substrate on which the amorphous silicon layer is formed. It may also proceed after moving to a dehydrogenation apparatus. At this time, the dehydrogenation is preferably carried out for 30 to 120 minutes at a relatively low temperature of 200 to 500 ℃.

Subsequently, an insulating film layer is formed on the insulating substrate on which the amorphous silicon layer is formed. The insulating film layer is formed of a silicon oxide film or a silicon nitride film. In addition, the insulating layer serves as a seed layer in the subsequent crystallization by the ELA method. That is, the amorphous silicon layer melted by the laser beam solidifies again and crystallizes. The crystal silicon starts to crystallize in the seed layer, which is the seed layer.

Next, FIG. 3B is a cross-sectional view of the process of irradiating a laser beam on the upper surface of the other side of the substrate. As shown in the figure, the laser beam 105 of the ELA method is irradiated on the upper surface of the other side of the insulating substrate opposite to the one surface of the insulating substrate on which the buffer layer, the amorphous silicon layer and the insulating film layer are formed.

The method of irradiating the laser beam is a method of irradiating a laser beam from the upper portion of the insulating substrate after flipping the insulating substrate on which the buffer layer, the amorphous silicon layer and the insulating film layer are formed as shown in FIG. In FIG. 3A, after forming the buffer layer, the amorphous silicon layer, and the insulating layer, there is a method of irradiating a laser beam from the lower part of the substrate, which method may be used.

In this case, the laser beam of the ELA method is "on" the laser beam for 30 to 200 nanoseconds to instantaneously melt and crystallize the amorphous silicon layer, thereby crystallizing the polycrystalline silicon layer 106. Let's go. In addition, the laser beam moves in a constant direction 107 to crystallize the entire amorphous silicon layer.

At this time, the crystallization by the ELA method can be largely divided into three mechanisms (mechanism).

The first mechanism is that after the laser beam 203a is irradiated to the amorphous silicon layer 202a formed on the substrate 201a as shown in Fig. 5a (a in Fig. 5a), the temperature of the amorphous silicon layer is instantaneously Although elevated to a high temperature, crystallization proceeds in the solid state 204 in which the amorphous silicon layer is not melted (b in FIG. 5A), thereby forming a polycrystalline silicon layer 205 having a fine grain size (c in FIG. 5A). ).

The second mechanism is that after the laser beam 203b is irradiated to the amorphous silicon layer 202b formed on the substrate 201b as shown in FIG. 5B (a of FIG. 5B), the lower portion of the amorphous silicon layer is not melted. In the solid state 206, the upper part is melted and the crystallization proceeds in a partially molten state in the liquid state 207 (b of FIG. 5B), and when crystallized in the lower solid state, very crystallized as in the first mechanism. This very fine polycrystalline silicon layer 208 is formed, and on the upper side, the lower fine polycrystalline silicon layer acts as a seed layer to form a polycrystalline silicon layer 209 having a small grain size (c in FIG. 5B).

The third mechanism is formed on the substrate 201c as shown in FIG. 5C. After the laser beam 203c is irradiated to the amorphous silicon layer 202c (a in FIG. 5C), the amorphous silicon layer is completely melted to form amorphous silicon. The entire layer is crystallized in the liquid state 210 (b in FIG. 5C), thereby forming a polycrystalline silicon layer 211 having a large grain size (c in FIG. 5C). At this time, when crystallization proceeds in the liquid state, nuclei (212a, 213b, 213c), which are starting points of crystal growth, exist on the surface of the substrate, and silicon atoms are arranged 213 around the nucleus to form crystals. Will grow. At this time, the nucleus is formed on the surface of the solid state substrate (not shown in the figure, but there is a seed layer between the substrate and the amorphous silicon layer, where the nucleus is generated). A polycrystalline silicon layer can be obtained. That is, when only one nucleus is present on the substrate, the amorphous silicon layer can crystallize into a single crystal silicon layer.

The grains 214a, 214b, and 214c grown in the nucleus grow in each nucleus 212a, 212b, and 212c, and become grain boundaries 215a and 215b in regions where the grains contact each other. That is, the first nucleus 212a at the left side in b of FIG. 5c forms the first grains 214a at the left side in c of FIG. 5c due to crystal growth, and the second nucleus 212b at b in FIG. 5c. In FIG. 5C, the boundary region where the second grains meet each other becomes the first grain boundary 215a, and the boundary region between the second grain 214b and the third grain 214c becomes the second grain boundary 215b.

By using the three crystal mechanisms described above, the ELA method crystallizes the amorphous silicon layer into a polycrystalline silicon layer, and the crystallization mechanism is most preferably a third mechanism capable of increasing the size of crystal grains.

At this time, the ELA method has a laser beam size of 0.4 mu m in width and 270 mm in length, and the energy density is preferably irradiated at an energy density of 250 to 1000 mJ / cm 3.

3C is a cross-sectional view after crystallizing an amorphous silicon layer into a polycrystalline silicon layer by the ELA method of the present invention. As shown in the figure, a polycrystalline silicon layer having protrusions 108 formed in the buffer layer direction is formed on the interface between the polycrystalline silicon layer 106 crystallized by the ELA method and the buffer layer.

The protrusions are formed when the amorphous silicon layer is crystallized by the mechanism described in FIGS. 5A to 5C by the ELA method. Particularly, the grains are formed in the nuclei on the insulating layer as the seed layer as described in the third mechanism of FIG. 5C. (The growth direction of the grains is the interface direction of the polycrystalline silicon layer and the buffer layer at the interface between the insulating film layer and the polycrystalline silicon layer), and the crystal grains formed when the molten amorphous silicon layer is completely crystallized, and the grains meet each other. Are formed. At this time, the grain boundary is a region where the molten, amorphous silicon layer in the liquid state is solidified at the latest and becomes a polycrystalline silicon layer in the solid state. Therefore, as the grain boundary is solidified at the latest, some of the silicon atoms are pushed up to the surface of the polycrystalline silicon layer as the silicon atoms are irregularly or differently oriented grains come into contact with each other, and the pushed up silicon is the polycrystalline silicon layer and the buffer layer. At the interface of the protrusions are formed in the buffer layer direction.

When the crystallization process is performed by the conventional ELA method, the protrusions are formed on the surface of the polycrystalline silicon layer as shown in FIG. 2, and then the polycrystalline layer is patterned to form a semiconductor layer, and a gate insulating film, a gate electrode, an interlayer insulating film, and the like. When the source / drain electrodes are formed to form a thin film transistor, the protrusions exist between the semiconductor layer and the gate insulating layer formed by patterning the polycrystalline silicon layer, and the protrusions adversely affect the interface characteristics between the semiconductor layer and the gate insulating layer. . However, in the crystallization process of the ELA method according to the present invention, since the projections are formed at the interface between the polycrystalline silicon layer and the buffer layer, after the thin film transistor is formed, no projections exist at the interface between the semiconductor layer and the gate insulating film. Existing problems can be prevented at the source.

4 is a cross-sectional view of a thin film transistor formed using a semiconductor layer crystallized by the ELA method of the present invention. As shown in the figure, after the buffer layer 152 is formed on the transparent insulating substrate 151 such as plastic or glass, and the amorphous silicon layer and the insulating film layer are formed on the buffer layer, the pattern described above with reference to FIGS. 3A to 3C. The amorphous silicon layer is crystallized by the ELA method of the present invention to form a polycrystalline silicon layer, and the polycrystalline silicon layer is patterned to form a semiconductor layer 153. In this case, the insulating layer may be removed by etching after crystallization, or may be removed by etching after the patterning process.

In this case, protrusions 154 are formed in the semiconductor layer due to crystallization by the ELA method, and the protrusions are formed in the buffer layer direction at the interface between the semiconductor layer and the buffer layer.

Subsequently, a gate insulating layer 155 is formed on the substrate on which the semiconductor layer is formed, a gate electrode forming material is deposited on the gate insulating layer, and then patterned to form a gate electrode 156. In this case, impurity implantation may be performed in a predetermined region of the semiconductor layer using the gate electrode as a mask to define a source / drain region.

As other methods of forming the semiconductor layer and the gate insulating film, an amorphous silicon layer is formed on a substrate on which the puffer layer is formed, the amorphous silicon layer is patterned, an insulating film layer is formed, and the ELA method of the present invention. The patterned amorphous silicon layer is crystallized to form a semiconductor layer formed of a polycrystalline silicon layer, and the insulating layer is not etched and removed, and the insulating layer is not etched and removed after the crystallization process and the method used as a gate insulating layer. There may be a method of simultaneously forming the gate insulating film and the semiconductor layer by simultaneously patterning the insulating film layer and the polycrystalline silicon layer.

Subsequently, an interlayer insulating layer 157 is formed on the entire surface of the substrate on which the gate electrode is formed, and a portion of the interlayer insulating layer and the gate insulating layer are etched to form contact holes for exposing source / drain regions of the semiconductor layer. A drain electrode forming material is formed on a substrate and patterned to form a source / drain electrode 158 to form a thin film transistor.

The thin film transistor formed by the above-described method is formed by the projection formed in the direction of the buffer layer at the interface between the semiconductor layer and the buffer layer, the adverse effect of the projections present at the interface between the semiconductor layer and the gate insulating film crystallized by the conventional ELA method, By not present at the interface between the semiconductor layer and the gate insulating film, adverse effects caused by the projections can be eliminated at the source.

The present invention has been shown and described with reference to the preferred embodiments as described above, but is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

Accordingly, the semiconductor device of the present invention and the method of forming the same by irradiating a laser beam by inverting the substrate during crystallization by ELA method, or by irradiating a laser beam from the bottom of the substrate so that the projections are formed at the interface between the polycrystalline silicon layer and the buffer layer. The interfacial characteristics between the semiconductor layer and the gate insulating film of the thin film transistor formed of the polycrystalline silicon layer are excellent and the uniformity is increased, thereby improving the characteristics of the thin film transistor.

Claims (10)

Insulating substrate; And A buffer layer, a polycrystalline silicon layer and an insulating film layer formed on the insulating substrate, The polycrystalline silicon layer is not formed at the interface between the insulating film layer and the polycrystalline silicon layer, but is formed at the interface between the polycrystalline silicon layer and the buffer layer and is formed in the buffer layer direction. A semiconductor device comprising a. The method of claim 1, The insulating layer is a semiconductor device, characterized in that the silicon oxide film or silicon nitride film. The method of claim 1, The insulating layer is a semiconductor device, characterized in that the gate insulating film of the thin film transistor. The method of claim 1, And the insulating layer is a seed layer which causes the amorphous silicon layer to crystallize into a polycrystalline silicon layer. The method of claim 1, The polycrystalline silicon layer is a semiconductor device, characterized in that the amorphous silicon layer is crystallized by the ELA method. The method of claim 1, Wherein the protrusion is formed when the amorphous silicon layer is crystallized by ELA. Preparing an insulating substrate; Forming a buffer layer and an amorphous silicon layer on one surface of the substrate; Degassing the substrate on which the buffer layer and the amorphous silicon layer are formed; Forming an insulating film layer on the degassed substrate; Irradiating a laser beam on top of the other surface of the substrate; And Crystallizing the amorphous silicon layer on the interface between the amorphous silicon layer and the buffer layer by the irradiated laser beam, and crystallizing the polycrystalline silicon layer having protrusions formed in the buffer layer direction. Method of forming a semiconductor device comprising a. The method of claim 7, wherein And crystallizing by irradiating the laser beam comprises crystallizing by an ELA method. The method of claim 7, wherein Irradiating a laser beam on an upper surface of the other surface of the substrate, inverting a substrate on which the buffer layer, an amorphous silicon layer, and an insulating film layer are formed, and then irradiating a laser beam on the upper surface of the substrate. The method of claim 7, wherein Irradiating a laser beam on an upper portion of the other surface of the substrate, irradiating a laser beam on a lower portion of the substrate on which the buffer layer, the amorphous silicon layer, and the insulating layer are formed.

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