KR100543016B1 - Method for fabricating Thin Film Transitor - Google Patents

Abstract

Provided is a method of manufacturing a thin film transistor. The method includes forming a photoresist pattern on an insulating substrate on which a semiconductor layer is formed, patterning the semiconductor layer using the photoresist pattern, and ozone water for 10 to 20 seconds on the entire surface of the substrate on which the semiconductor layer pattern is formed. Carry out the first wash used and the second wash with hydrofluoric acid solution for 26-30 seconds, then perform the third wash with ozone water for 10-20 seconds and the fourth wash with hydrofluoric acid solution for 66-70 seconds. It includes the step of performing. Performing the cleaning in this manner provides the advantage that a curable photoresist residue can be removed, resulting in elimination of humps, resulting in a thin film transistor with good properties.

Hump, Undercut

Description

Method for manufacturing thin film transistor {Method for fabricating Thin Film Transitor}             

1A to 1C are photographs of a thin film transistor in which bursting occurs;

1D is a cross-sectional photograph of a thin film transistor in which rupture occurs;

Figure 2a is a graph showing the s-factor (s-factor) in the conventional process conditions,

Figure 2b is a graph showing the S factor in the process conditions of the present invention.

<Explanation of symbols for the main parts of the drawings>

10a, 30a: NMOS S factor 10b, 30b: PMOS S factor

20: Hump

The present invention relates to a method of manufacturing a thin film transistor, and more particularly, to a method of manufacturing a thin film transistor including the step of repeatedly cleaning the surface of polysilicon using ozone water and hydrofluoric acid solution.

 In the manufacture of thin film transistors, many residues or contaminants remain on the surface after each process, so the importance of the cleaning process for removing them is increasing. Contaminants generated during the thin film transistor manufacturing process must be removed because they significantly affect the performance, reliability, and yield of the device by reducing distortion of the structural shape and electrical characteristics of the device. Many pollutants generated during the manufacturing process or contaminated from various pollutants can be classified into organic pollutants, particles, metal impurities, and natural oxide films. Also, the surface roughness, which is not contaminant but must be controlled through the cleaning process, is included in the pollutant to remove it. .

The method of removing the contaminants includes a wet cleaning method and a dry cleaning method. In particular, the wet cleaning method can be easily rinsed with DI water, there are very few residues after drying, and it is suitable according to the contaminants to be removed. Many types of chemical solutions can be used, which is widely used.

In the step of forming the silicon layer during the manufacturing process of the thin film transistor, the silicon layer is formed and a natural oxide film is also formed. If there is a natural oxide film, the performance of the silicon layer is degraded and the contact resistance may be increased when forming a contact. As the natural oxide film is grown, inorganic contaminants such as some metal impurities may be included therein. If the natural oxide film is not completely removed, it may be a source of contamination of the metal impurities. In addition, these metal impurities may diffuse into the silicon layer, and the metal impurities diffused during subsequent heat treatment may cause device defects. Since the natural oxide film is an object to be removed, a wet cleaning method is generally used as a wet cleaning method to remove it. HF cleaning etches the natural oxide or chemical oxide and removes the impurities contained in the oxide. Usually, a dilute HF cleaning (DHF) cleaning method using a dilute solution of HF and H ₂ O is used. The HF cleaning solution can effectively remove metal contaminants contained in the oxide film, but it is difficult to remove metals such as Cu and Au. Therefore, a cleaning solution in which hydrogen peroxide as an oxidizing agent is added to HF may be used.

In addition, after the semiconductor layer pattern is formed, a process of removing the photoresist on the semiconductor layer pattern, that is, a strip process is performed. The strip process may be performed by dry etching. When the dry etching is performed, most of the photoresist is removed, but residues may remain. If the residue is not removed and is cured, the characteristics of the thin film transistor may be degraded. HF cleaning is usually performed to remove this photoresist residue.

 As the HF washing method, a method of washing ozone water and HF alternately is used. Conventionally, ozone water was applied for 20 seconds to form an oxide film followed by shaving for 160 seconds with HF to remove photoresist residue. However, in this case, there is a problem that an undercut occurs under the semiconductor layer pattern and the thin film transistor is bursted. The undercut means that the lower part of the membrane is excessively etched and recessed.

1A to 1C are photographs of a thin film transistor in which bursting occurs.

Referring to FIGS. 1A to 1C, the thin film transistors are microscopically photographed, and it can be seen that the gate insulating film is thinned in the region where the gate electrode and the drain electrode meet, respectively, so that the rupture occurs. FIG. 1C is a SEM photograph of the thin film transistor shown in FIG. 1A.

1D is a cross-sectional photograph of a thin film transistor in which rupture occurs.

Referring to FIG. 1D, it is a SEM photograph showing the cross-sectional structure of the thin film transistor shown in FIG. 1A, and it can be seen that an undercut occurs in the lower portion of the semiconductor layer, resulting in thinning of the lower buffer layer and the gate insulating layer.

In addition, when the photoresist residue is cured without being removed, the characteristics of the thin film transistor may be degraded. In particular, a hump may occur in the s-factor. The humfraham refers to the bending of the S-factor curve due to photoresist residues and other contaminants on the surface of the film. The generation of the hump means that the device characteristics of the thin film transistor are deteriorated, and thus are to be removed.

The technical problem to be achieved by the present invention is to solve the problems of the prior art described above, to provide a method of manufacturing a thin film transistor having a good characteristic by removing the hump (Hump) phenomenon by removing other contaminants, including the curable photoresist residue. Its purpose is.

In order to achieve the above technical problem, the present invention provides a method of manufacturing a thin film transistor. The method includes forming an amorphous silicon layer on an insulating substrate, crystallizing and patterning the amorphous silicon layer to form a semiconductor layer pattern, and using the ozone water for 10 to 20 seconds on the entire surface of the substrate on which the semiconductor layer pattern is formed. Perform a first wash, perform a second wash with hydrofluoric acid for 26 to 30 seconds, then perform a third wash with ozone water for 10 to 20 seconds, and perform a fourth wash with hydrofluoric acid for 66 to 70 seconds. Performing the steps.

It is preferable that the total execution time of the washing using the hydrofluoric acid solution is 90 to 100 seconds.

It is preferable to flow the ozone water at 3 to 3.5 l / min, and to flow the hydrofluoric acid solution at 9 to 10 l / min.

The cleaning using the hydrofluoric acid solution may use a dilute HF cleaning (DHF) cleaning method. The hydrofluoric acid solution may be a hydrofluoric acid and water ratio of 1: 200. That is, a hydrofluoric acid solution diluted to a concentration of 0.5 percent can be used.

Furthermore, the method may further include performing ultrasonic cleaning using deionized water after performing the fourth cleaning. Ultrasonic cleaning using deionized water may be added to remove contaminants such as particles generated by HF cleaning.

Furthermore, the method may further comprise the step of cleaning the amorphous silicon layer with a hydrofluoric acid solution after the step of forming the amorphous silicon layer. HF cleaning may be added to remove contaminants such as a natural oxide film or the like that may be formed together with the amorphous silicon layer.

The method may further include forming a buffer layer between the insulating substrate and the amorphous silicon layer.

The thin film transistor manufactured by the above method may be used in a liquid crystal display device or an organic electroluminescent device.

Hereinafter, with reference to the accompanying drawings in accordance with the present invention to describe the present invention in more detail.

Looking at the overall process of the thin film transistor, first, an amorphous silicon layer is formed on an insulating substrate. The amorphous silicon layer is crystallized to form a polycrystalline silicon layer. A photoresist pattern is formed on the polycrystalline silicon layer. The semiconductor layer pattern is formed by patterning the polycrystalline silicon layer using the photoresist pattern. After removing the photoresist, a gate insulating film is formed on the semiconductor layer pattern. Subsequently, a metal layer and a photoresist layer are sequentially stacked on the gate insulating film. The gate electrode is formed by patterning the photoresist layer and etching the metal layer using the patterned photoresist layer as a mask. Subsequently, an ion implantation process is performed using the gate electrode as a mask to define source / drain regions at both ends of the semiconductor layer pattern. An interlayer insulating layer is formed on the gate electrode, and a contact hole reaching the source / drain regions is formed in the interlayer insulating layer. A metal layer is deposited on the resultant and patterned to form a source electrode and a drain electrode to complete a thin film transistor.

As described above, several processes are required to manufacture the thin film transistor, and after each process, residues or contaminants remain on each resultant, and thus, a cleaning process is performed to remove the thin film transistors. In particular, the present invention further includes a cleaning method for solving the problem caused by the residue of the photoresist remaining without being removed after the formation of the semiconductor layer pattern.

The cleaning method in the present invention provides a cleaning method for removing humps that may occur when the above-described problems, namely, HF cleaning, are performed.

In detail, the first surface of the substrate is washed with ozone water for 10 to 20 seconds to remove the residue of the photoresist pattern. Through the cleaning, the entire surface of the substrate is covered with an oxide film. In general, in the case of washing with ozone water, it is difficult to generate an oxide film when the saturation point is 20 seconds or more. Therefore, it is preferable to wash with ozone water for 10 to 20 seconds.

Subsequently, a second wash with hydrofluoric acid solution is performed for 26 to 30 seconds. The HF serves to shave the oxide film formed by the ozone water. That is, the photoresist residue is removed together with the oxide film by HF cleaning. In general, since HF (0.5 percent concentration) serves to etch about 100 kPa per minute, it is possible to clean the HF for 26 to 30 seconds to remove the oxide film formed by the ozone water.

Subsequently, a third washing with ozone water is performed for 10 to 20 seconds to form an oxide film on the entire surface of the substrate. Subsequently, a fourth cleaning using a hydrofluoric acid solution is performed for 66 to 70 seconds to remove the oxide film formed on the entire surface of the substrate. As a result, any remaining photoresist residue is once again removed along with the oxide film. In the second cleaning using hydrofluoric acid solution, the oxide film and contaminants must be completely removed, and a cleaning time of at least 60 seconds is required to maintain the angle of the semiconductor layer pattern more than 60 degrees. In addition, by maintaining the total execution time of the cleaning using the hydrofluoric acid solution for 90 to 100 seconds, preferably 100 seconds, the undercut of the lower layer of the semiconductor layer, in particular the buffer layer is prevented from occurring, resulting in the tearing of the thin film transistor ( To prevent bursting). Therefore, in the present invention, the cleaning time of the second hydrofluoric acid solution was set to 60 to 70 seconds.

On the other hand, when the total execution time of the cleaning using the hydrofluoric acid solution is performed for 100 seconds or more, excessive etching may be caused to the lower layer of the semiconductor layer, thereby degrading device characteristics.

In addition, it is preferable to flow the ozone water at 3 to 3.5 l / min, and to send the hydrofluoric acid solution at 9 to 10 l / min. In the case of ozone water, the surface of the semiconductor layer pattern is kept hydrophilic, so that a water film can be formed even at a low flow rate (3 to 3.5 l / min), but in the case of hydrofluoric acid solution, the surface is changed to hydrophobic. Because of this difficulty, it is preferable to flow the hydrofluoric acid solution at 9 to 10 l / min.

In the present invention, as described above, by repeatedly washing the entire surface of the substrate with ozone water and hydrofluoric acid solution to remove contaminants such as natural oxide film, and also to remove the cured photoresist residue to confirm the effect of eliminating the hump generation.

2A is a graph showing an s-factor under conventional process conditions.

Referring to FIG. 2A, the S factor 10a of the NMOS and the S factor 10b of the PMOS are shown. It can be seen that the S factor 10a of the NMOS is more sensitive to contaminants than the S factor 10b of the PMOS. It can be seen that in the conventional cleaning process conditions, the residue of the photoresist is not removed, and thus, a hump (Hump) 20 is generated in the S factor 10a of the NMOS. As described above, the generation of the hump means that there are a lot of contaminants including residues at the interface of the semiconductor layer, thereby degrading device characteristics of the thin film transistor. In addition, the slope of the S factor is low, it can be seen that a high voltage is required when driving the device.

Figure 2b is a graph showing the S factor in the process conditions of the present invention.

Referring to FIG. 2B, the S-factor 30b of the PMOS is almost unchanged from the conventional one, but in the case of the N-factor S-factor 30a of the NMOS, the hump that has occurred in the past has disappeared. This means that contaminants, including photoresist residues, were removed at the semiconductor layer interface. In addition, the slope of the S-factor is also higher, so that the device can be driven even at a lower driving voltage, thereby improving the characteristics of the switching thin film transistor.

As described above, according to the present invention, the entire surface of the insulating substrate on which the semiconductor layer pattern is formed is subjected to primary cleaning using ozone water for 10 to 20 seconds and secondary cleaning using hydrofluoric acid solution for 26 to 30 seconds, and then By performing the third cleaning using ozone water for 20 to 20 seconds and the fourth cleaning using hydrofluoric acid solution for 66 to 70 seconds, the curable photoresist residue is removed, thereby eliminating the generation of humps, thereby producing a thin film transistor having good characteristics. It offers the advantage that it can.

While the foregoing has been described with reference to preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. Could be.

Claims (10)

Forming an amorphous silicon layer on the insulating substrate; Crystallizing and patterning the amorphous silicon layer to form a semiconductor layer pattern; And After performing the first cleaning using ozone water for 10 to 20 seconds and performing the second cleaning using hydrofluoric acid solution for 26 to 30 seconds on the entire surface of the substrate on which the semiconductor layer pattern is formed, and then performing the third cleaning using ozone water for 10 to 20 seconds. A method of manufacturing a thin film transistor comprising performing a cleaning and performing a fourth cleaning using a hydrofluoric acid solution for 66 to 70 seconds. The method of claim 1, Method of manufacturing a thin film transistor, characterized in that the total execution time of the cleaning using the hydrofluoric acid solution is 90 to 100 seconds. The method of claim 1, The method of manufacturing a thin film transistor, characterized in that to send the ozone water to 3 to 3.5l / min.  The method of claim 1, The method of manufacturing a thin film transistor, characterized in that for flowing the hydrofluoric acid solution at 9 to 10l / min. The method of claim 1, The cleaning using the hydrofluoric acid solution is a method of manufacturing a thin film transistor, characterized in that using a dilute HF cleaning (DHF) cleaning method. The method of claim 5, The hydrofluoric acid solution is a method of manufacturing a thin film transistor, characterized in that the ratio of hydrofluoric acid and water 1: 200. The method of claim 1, And performing ultrasonic cleaning using deionized water after the fourth cleaning. The method of claim 1, And after the step of forming the amorphous silicon layer, further cleaning the amorphous silicon layer with a hydrofluoric acid solution. The method of claim 1, The method of claim 1, further comprising forming a buffer layer between the insulating substrate and the amorphous silicon layer. The method of claim 1, The thin film transistor manufactured by the above method is used for a liquid crystal display device or an organic electroluminescent device.

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