KR100270908B1 - Process of vacuum lithography and thin film as resist - Google Patents

Abstract

PURPOSE: A vacuum lithography process is provided to clean a substrate by a plasma treatment, to form and develop a resist layer by plasma polymerization and plasma etching respectively, and to form a pattern by an electron beam, in a single vacuum chamber. CONSTITUTION: A substrate is cleaned by using a plasma treatment. A resist layer is formed by using plasma polymerization. An electron beam is exposed. The resist layer is developed by using a plasma etching process. The resist layer is stripped. The aforementioned processes are performed in a single chamber.

Description

Process of vacuum lithography and thin film as resist

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vacuum lithography process and a resist film prepared during the process, and more particularly, to a substrate cleaning process using plasma treatment, a plasma polymerization process. Vacuum process consisting of a process for producing a resist film using an electron beam, an exposure process using an electron-beam, a development process of a resist film using plasma etching, and a stripping process of a resist film. It relates to a lithography process and a resist film produced by plasma polymerization in the process.

Lithography is the process of transferring a geometric pattern on a mask to a resist covering the surface of a semiconductor wafer, which pattern includes several areas in the integrated circuit: buried layers, isolation regions, transistor bases, resistors, emitters, contact windows, and metal electrodes. And the like.

A general lithography process is a wet process in which processes such as substrate cleaning, preparation of a resist film, development of a resist film, and removal of a resist film as shown in FIG . 1 are separated, and a source irradiated to a resist film to form a pattern (source ) Employs an optical lithography process using light. FIG. 2 also shows a conventional general lithography process for forming a pattern in a resist fabricated on a silicon wafer.

The problem of the conventional optical lithography process is that even though the substrate is cleaned well, the substrate is easily contaminated by dust in the air during the movement of the wafer, and the spin coating is mainly used as a method of forming a resist on the wafer. It is difficult to form a uniform resist film due to the increase in size of the film. In addition, although a wet method using a strong solvent is used for developing the resist film, a strong solvent penetrates into the resist film, and thus, it is difficult to implement a clean fine pattern. Moreover, in the conventional optical lithography process, light is used as a source for forming a pattern, but it is difficult to form a nanometer pattern due to diffraction of light as it enters the Giga DRAM era.

Accordingly, the present inventors have been trying to overcome the problems of the above optical lithography, unlike the conventional method, if the cleaning of the substrate is performed by using a plasma treatment, the entire vacuum lithography process is completely dry in a single chamber It was found that the present invention was completed, and thus the present invention was completed.

It is an object of the present invention to provide a vacuum lithography process in which a substrate is cleaned as a plasma treatment in a single vacuum chamber, plasma polymerization and plasma etching are used for fabrication and development of a resist film, respectively, and an electron beam is used as a source for forming a pattern. It is.

It is a further object of the present invention to provide a resist film suitable for nanometer pattern realization produced during the vacuum lithography process.

1 is a flow chart of a conventional wet lithography process,

2 is a conventional lithography process diagram,

3 is a flow chart of a vacuum lithography process of the present invention,

FT-IR: Fourier Transform Infrared

Fourier Transform Infrared Spectroscopy

SEM: Scanning Electron Microscope

Figure 4a shows the polymerization rate of the PPMST thin film according to the change in the discharge power,

Figure 4b shows the polymerization rate of the PPMST thin film with the change in pressure,

Figure 5a shows the etching rate of the PPMST thin film according to the change in the discharge power,

■; Polymerization at 50 [W] ●; Polymerization at 100 [W]

▲; Polymerization at 150 [W] ▼ Polymerization at 200 [W]

Figure 5b shows the etching rate of the PPMST thin film with the change in pressure,

■; Polymerization at 50 [W] ●; Polymerization at 100 [W]

▲; Polymerization at 150 [W] ▼ Polymerization at 200 [W]

6 shows a sensitivity characteristic diagram of a PPMST thin film,

7A is an electron micrograph of a pattern formed on a PPMST thin film,

7B is an electron micrograph of a pattern formed on the PPMST thin film.

In order to achieve the above object, the present invention comprises a substrate washing step using a plasma treatment, a manufacturing step of a resist film using plasma polymerization, an irradiation step using an electron beam, a developing step of a resist film using plasma etching, and a removing step of a resist film. Provide a vacuum lithography process.

Hereinafter, the present invention will be described in detail.

The vacuum lithography process of the present invention is characterized by cleaning the substrate by using a plasma treatment, unlike in the conventional lithography process. The use of plasma treatment to clean the substrate allows the entire lithography process to be carried out completely dry in a single chamber, thus solving the problems encountered in conventional lithography processes.

Substrate cleaning (wafer cleaning) in a vacuum lithography process is a process of cleaning a substrate by inserting a substrate (silicon wafer) into a reaction tube in which vacuum is evacuated and inducing plasma to clean the substrate, unlike a conventional wet substrate cleaning process. Ions, electrons, and radicals excited by plasma collide with the substrate to remove dust or pollutants. In the conventional wet process using a solvent, it takes a long time to dry the substrate after cleaning the substrate and exposes the substrate to the air again. Therefore, the wet process has a disadvantage in that it is contaminated by the pollutant in the air until the resist film is formed. In addition, the substrate is not only cleaned by plasma but also exposed to a pollutant in the air since only a monomer is injected into the same vacuum chamber after the substrate cleaning process to form a resist film. Therefore, it is possible to prevent the yield degradation caused by the contamination of dust and other existing substrates. The substrate cleaning process is carried out at a discharge power of 100 [W] and a carrier gas flow rate of 30 [ml / min] with the reaction tube pressure exhausted to 10 ⁻³ [torr].

After the substrate is cleaned, a resist film is prepared by using plasma polymerization. The plasma polymerization method is a method of plasmalizing an organic monomer in a glow discharge and manufacturing an organic thin film on the substrate therefrom. This plasma polymerization method can produce a polymer film from almost all organic monomers. In addition, the polymer thin film manufactured by plasma polymerization is amorphous, has almost no pinhole, and is composed of complex crosslinking than the conventional thin film by chemical polymerization method, which is excellent in heat resistance, abrasion resistance, and chemical resistance. It is utilized for the application development of the protective film of a semiconductor element, the thin film for sensors, and the optical thin film.

Irradiation with an electron beam is performed after the manufacture of the resist film, which can solve the problem of difficult to realize a fine pattern due to diffraction of light in conventional lithography.

After the above process, the resist film is developed using plasma etching. When wet etching using a conventional strong solvent, it is difficult to realize precise line width due to the shortcoming of undercutting, and there is a concern that it is adversely affecting the environment because the solvent is a strong acid, especially due to diffraction of light. Since it is difficult to form a fine pattern of units, it may contribute to the drying of the process by performing development using plasma etching.

The vacuum lithography process of the present invention made up of the above processes can prevent various problems arising in a general lithography process, in particular, swelling of the resist film due to a strong solvent, lowering the yield of the wafer caused by dust in the gas phase, and the like. In addition, since the irradiation is performed by the electron beam as described above, it is possible to solve the difficulty of implementing a fine pattern due to the diffraction phenomenon of light. And most of all, the post-baking process, which is required in the general lithography process, is not necessary due to the strong crosslinking properties of the plasma polymerized film, and the time required for the process by performing the process in a single vacuum chamber. It can be shortened.

In addition, the present invention provides a resist film which is a plasma polymerization thin film produced by the plasma polymerization method in the vacuum lithography process. At this time, the plasma polymerized thin film is composed of PPMST (Plasma Polymerized Methyl methacrylate-Styrene-Tetramethyltin), PPT (Plasma Polymerized Tetramethyltin), PPH (Plasma Polymerized Hexamethyl disiloxane), PPPI (Plasma Polymerized Phenyl Isothiocyanate), PPPrI (Plasma Polymerized Propyl), Isothiocyanate It may be selected from the group consisting of Plasma Polymerized Methyl Isothiocyanate (PPMI).

The plasma polymerized thin film was fabricated on an oxide film (SiO ₂ ) prepared by a thermal oxidation method with a thickness of 5000 [Å] using an electrostatically coupled plasma polymerization apparatus, and discharged from 20 to 200 [W], with a reaction tube pressure of 0.1. The polymerization was carried out by constantly introducing a monomer under polymerization conditions of -0.7 [torr] and an argon gas flow rate of 10-30 [ml / min]. After the polymerization of the appropriate time, the inflow of the monomer is stopped, the power is cut off to stop the plasma, and the plasma polymerization thin film is stabilized in the state where argon gas is introduced. Investigate the characteristics of

The plasma polymerized thin film has no pinhole, has a very dense surface, has a relatively regular structure, and has a uniform and uniform thickness.

In addition, the plasma polymerization thin film of the present invention can change the polymerization rate and the etching rate by changing the discharge power and pressure, and is excellent in sensitivity and contrast, and is suitable for nanometer pattern realization. .

By the following examples will be described in detail the manufacturing process of the resist film of the present invention and the properties of the resist film produced. However, the following examples are only for illustrating the present invention and the present invention is not limited by the examples.

Example 1 Preparation of PPMST Polymer Thin Film

The silicon wafer was fixed to the substrate and held for several minutes while evacuating the reaction tube pressure to 10 ⁻³ [torr]. Next, while argon gas was introduced into the reaction tube, power was applied to cause discharge and maintained for 5 minutes. After the plasma is stabilized, the valve is adjusted to introduce the monomers, methylmethacrylate (MMA), styrene and tetramethyltin, into the reactor for polymerization. The plasma was stopped by stopping the influx of monomer and shutting off the power. After argon gas was introduced, the plasma polymerized film PPMST was stabilized, and then the silicon wafer on which the PPMST thin film was formed was taken out.

The plasma polymerized thin film was fabricated on an oxide film (SiO ₂ ) prepared by a thermal oxidation method to a thickness of 5000 [Å] using an electrostatically coupled plasma polymerization apparatus, and the argon gas flow rate was 10 [ml / min], The discharge power and the reaction tube pressure were prepared while varying in the range of 20 to 70 [W] and 0.1 to 0.7 [torr], respectively.

Example 2 Polymerization Rate of PPMST Thin Film

4A and 4B show polymerization rates according to changes in discharge power and pressure of the PPMST thin film prepared in Example 1 above. As the discharge power was increased, the polymerization rate of the thin film increased and saturated (see FIG. 4A ). This may be because the discharge power was increased and the electrons, ions or radicals in the plasma were excited and reached their limit. . In addition, the polymerization rate was remarkably decreased when the pressure was increased (see FIG. 4B ), which seems to be due to the fact that as the pressure increases, the electrons are not sufficiently accelerated and energy is lost by collision with other particles.

As can be seen from the above, since the polymerization rate is changed by polymerization power or pressure during plasma polymerization, the thickness of the thin film can be controlled by changing the discharge conditions.

As can be seen in FIG. 4A , the polymerization rate was 230 to 600 [dl / min] when the polymerization power was changed to 20 to 120 [W] at a reaction tube pressure of 0.5 [torr] and a carrier gas flow rate of 10 [ml / min]. . As shown in Fig. 4B , the polymerization rate was 200 to 60 [dl / min] when the system pressure was changed to 0.1 to 0.7 [torr] at a discharge power of 30 [W] and a carrier gas flow rate of 10 [ml / min].

Example 3 Etching Characteristics of PPMST Thin Film

The etching characteristics of the PPMST thin film according to the change of discharge power and pressure are shown in FIGS . 5A and 5B . Among the evaluations of lithographic processes for fabricating super integrated circuits, the etch rate of the resist occupies a significant place because of the selectivity of the oxide film (SiO ₂ ) and the resist after resist development.

FIG. 5A shows the etching rate when the thin film was manufactured according to each discharge power, the system pressure was 0.2 [torr], the carrier gas flow rate 10 [ml / min], and the discharge power was changed to 50 to 200 [W]. As the discharge power increases, the etching rate increases because the number of electrons or ions increases as the discharge power increases, thus increasing the probability that they can cleave the polymer ring. The etching rate was 875 to 3520 [dl / min] for the discharge power of 50 to 200 [W].

FIG. 5B shows the etching rate when the thin film was manufactured according to each discharge power, and the discharge power was changed to 100 [W], carrier gas flow rate 10 [ml / min] and system pressure 0.2 to 0.7 [torr]. The etching rate was 2870 to 360 [dl / min] for the system pressure of 0.2 to 0.7 [torr], but it can be seen that the etching rate decreases as the pressure increases. This is because the increase in the pressure in the reaction chamber increases the number of particles in the reaction tube, which decreases the average free path of the electrons and does not have enough energy to cut the polymer ring. In addition, under the film forming conditions, the thinner the discharge power, the higher the etching rate, because the radicals in the plasma do not obtain sufficient energy when forming the film.

Example 4 Vacuum Lithography Characteristics of PPMST Thin Film

Sensitivity and contrast, which are the most important criteria for evaluating the performance of the lithography process, are obtained by measuring the film thickness remaining after development on the irradiated portion of the irradiated dose at the required linewidth.

6 shows the sensitivity and contrast of the PPMST thin film. It can be seen that the sensitivity and contrast show excellent properties as 5 [μC / cm ² ] and 4.5, respectively. The developing conditions at this time were 100 [W], a pressure of 0.2 [torr], and a carrier gas flow rate of 10 [ml / min].

7A and 7B are Scanning Electron Microscope (hereinafter referred to as "SEM") photographs of a nanometer (20 nm) unit pattern formed on a resist film by a vacuum lithography process. As can be seen in FIGS . 7A and 7B , if the polymerization conditions, electron beam irradiation conditions, and etching conditions are properly adjusted, the resolution of the resist can be increased.

The present invention replaces the conventional wet lithography process with a dry vacuum lithography process that can be performed in a single vacuum chamber by performing substrate cleaning using a plasma treatment to improve the reliability of the lithography pre-process, thereby improving wafer yield. In addition, the present invention provides a vacuum lithography process that is easy to implement a nanometer pattern by using plasma polymerization and plasma etching, and at the same time, a resist film suitable for the vacuum lithography process is provided.

Claims (2)

Substrate cleaning using plasma treatment, Resistor film manufacturing using plasma polymerization, Expose process using electron-beam, Plasma etching A vacuum lithography process, wherein a development process of a resist film and a stripping process of a resist film are carried out in a single chamber. The plasma polymerized thin film of claim 1, wherein the plasma polymerized film is formed of PPMST (Plasma Polymerized Methyl methacrylate-Styrene-Tetramethyltin), PPT (Plasma Polymerized Tetramethyl-tin), PPH (Plasma Polymerized Hexamethyldisiloxane), and PPPI. (Plasma Polymerized Phenyl Isothiocyanate), PPPrI (Plasma Polymerized Propyl Isothiocyanate) and PPMI (Plasma Polymerized Methyl Isothiocyanate).