KR20070071072A - Method for patterning thin film using by-product of plasma - Google Patents

Abstract

A method for patterning a thin film using a reaction byproduct of plasma is provided to reduce a line space between floating gates by attaching the reaction byproduct of plasma onto a photoresist pattern. A thin film(120) to be etched is formed on a substrate(100). An anti-reflective layer(130) is formed on the thin film. A photoresist pattern(140) is formed on the anti-reflective layer. The anti-reflective layer is etched by using the photoresist pattern as an etch mask. The photoresist pattern is plasma-treated using Ar gas and C5F8 gas. The amount of flowing of Ar:C5F8 is controlled to 5:1 below so that reaction byproducts are attached onto an outer wall of the photoresist pattern. The photoresist pattern on which the reaction byproducts are attached is used as an etch mask to pattern the thin film.

Description

Patterning Method of Thin Film Using Plasma Reaction By-Products {METHOD FOR PATTERNING THIN FILM USING BY-PRODUCT OF PLASMA}

1A to 1D are diagrams illustrating a conventional floating gate patterning method using a hard mask to form a floating gate array of a flash memory device.

2A to 2D illustrate a method of patterning a thin film using a plasma reaction by-product according to the present invention.

3A is an image of a scanning electron microscope showing a state in which reaction by-products are formed on an etching target in the process of attaching the plasma reaction by-products to the photoresist pattern, and FIG. 3B is a state in which reaction by-products are selectively formed only on the photoresist pattern in the method according to the present invention. An image of a scanning electron microscope showing.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a manufacturing technique of a semiconductor device, and more particularly, to a method of patterning a thin film formed on a semiconductor substrate.

The semiconductor device is formed on a substrate by repeatedly performing a thin film process (eg, chemical vapor deposition, physical vapor deposition, oxidation, etc.), a photographic process, an etching process, and the like. In particular, photolithography refers to a technique for implementing a pattern designed on a mask on a wafer in accordance with process control specifications. To this end, light having a specific wavelength is exposed on the substrate on which the photosensitive agent is applied through a mask on which a pattern is formed, causing a photochemical reaction to the photosensitive agent, and by a chemical reaction in a subsequent developing process. A photosensitive film pattern is formed. The lower layer is etched through the formed photoresist pattern to transfer the mask pattern to the lower layer.

Recently, as the degree of integration of semiconductor devices has increased greatly, the pattern specifications of integrated circuit devices have greatly decreased. In particular, in the case of flash memory devices, the design specifications are decreasing to 130 nm or less, and thus process technologies for finer patterns are being developed.

On the other hand, flash memory refers to a kind of PROM (programmable ROM) capable of electrical data rewriting, which combines the advantages of EPROM (Erasable PROM) and EEPROM (Electrically Erasable PROM). The device is made to perform the erase method. The flash memory is called nonvolatile memory because the memory information does not disappear even when the power is turned off. In this regard, the flash memory is different from DRAM (Dynamic RAM) and SRAM (Static RAM).

In addition, according to a cell array scheme, a flash memory may be divided into a NOR-type structure in which cells are disposed in parallel between a bit line and ground, and a NAND-type structure in series. NOR flash memory, which is a parallel structure, is widely used for booting a mobile phone because high-speed random access is possible when performing a read operation.NAND flash memory, which is a serial structure, is usually used for data storage because of a slow reading speed but a fast writing speed. It has a merit that it is suitable for the and suitable for miniaturization. In addition, the flash memory may be classified into a stack gate type and a split gate type according to the unit cell structure, and may be divided into a floating gate device and a silicon-oxide-nitride-oxide-silicon (SONOS) device according to the shape of the charge storage layer. Can be distinguished.

Among them, the performance of the floating gate device is greatly influenced by the area of the floating gate. In particular, the spacing between the floating gate lines is gradually becoming smaller, and recently, it is required to be formed to 100 nm or less. In order to form the gap between the gate lines to 100 nm or less by using a conventional photographic process, it is necessary to use a light source having a small wavelength, such as an ArF excimer laser having a wavelength of 193 nm. However, because ArF excimer laser equipment is very expensive, the manufacturing cost of semiconductor devices is greatly increased.

Instead of using expensive exposure equipment, a method of reducing the gap between floating gates using a hard mask has recently been developed. 1A to 1D illustrate a process of forming a floating gate electrode using a hard mask.

First, as shown in FIG. 1A, a polycrystalline silicon layer 14 for forming a floating gate is formed on a semiconductor substrate 10 on which a tunnel oxide film 12 is formed. Thereafter, the hard mask layer 16 is formed on the polycrystalline silicon layer 14, and then the photoresist pattern 18 is formed through a photolithography process. Then, the hard mask layer 16 is partially etched using the photoresist pattern 18 as an etching mask, thereby forming a hard mask pattern 16a as shown in FIG. 1B.

The spacer formation film 17 is formed on the thus formed hard mask pattern 16a and on the surface of the polycrystalline silicon layer 14 exposed by removing a part of the hard mask layer 16. After that, when the spacer formation film 17 is blank etched, as shown in FIG. 1C, the spacer 17a is formed on the sidewall of the hard mask pattern 16a.

Finally, using the hard mask pattern 16a and the spacer 17a as an etch mask and patterning the lower polycrystalline silicon layer 14, the plurality of floating gate electrodes constituting the unit cell as shown in FIG. 14a) is formed.

In the above method, since the spacing D2 between the floating gate electrodes 14a can be formed smaller than the spacing D1 between the photoresist patterns 18 used to form the initial hard mask pattern, the critical dimension It is used by the method which is advantageous for manufacture of the device whose (Critical Dimension) is 100 nm or less. However, the above method requires a complicated process to manufacture the hard mask and the spacer, thereby lowering the overall product productivity.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method of significantly reducing the line spacing between floating gates of a flash memory device without using expensive exposure equipment by attaching a plasma reaction byproduct to a photoresist pattern.

Another object of the present invention is to provide a method for effectively preventing the formation of a bridge between reaction by-products attached to neighboring photoresist patterns when the reaction by-products are attached to the photoresist pattern.

The method for patterning a thin film using a plasma reaction by-product according to the present invention includes the steps of (a) forming a thin film as an etching target on a substrate, (b) forming an antireflection film on the thin film, and (c) the anti-reflection film Forming a photoresist pattern thereon; (d) etching the antireflective coating using the photoresist pattern as an etch mask; and (e) plasma treating the photoresist pattern using Ar and C ₅ F ₈ gas. Adjusting a flow rate of Ar: C ₅ F ₈ to 5 or less to attach the reaction byproduct to the outer wall of the photoresist pattern, and (f) using the photoresist pattern to which the reaction byproduct is attached as an etch mask. Patterning the;

Here, steps (d), (e), and (f) may be performed using a capacitively coupled plasma (CCP) plasma apparatus. In addition, step (d) may be performed using a pressure of 30 to 100 mTorr, RF power of 300 to 1500 W, CF ₄ of 30 to 200 sccm, Ar of 50 to 300 sccm, and O ₂ of 5 to 30 sccm as process conditions. In addition, step (e) may be performed using a pressure of 10 to 50 mTorr, C ₅ F ₈ of 5 to 30 sccm, Ar of 30 to 200 sccm, and RF power of 300 to 1500 W as process conditions.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the method for patterning a thin film using the plasma reaction by-product according to the present invention.

First, as shown in FIG. 2A, the thin film 120 as an etching target is formed on the substrate 100. The thin film may be a polycrystalline silicon layer constituting a floating gate of a flash memory device. In addition, there may be various kinds of films to be patterned at fine intervals, and the material of the thin film is not limited. Further, the thin film may be formed by a method such as physical vapor deposition, chemical vapor deposition, atomic layer deposition, or the like depending on the properties of the material.

In addition, when developing the photoresist in a subsequent photographic process, unpredictable horizontal and vertical bending due to diffuse reflection and high reflection of the substrate may occur on the sidewalls of the photoresist, which may affect subsequent processes. Therefore, an antireflective coating 130 is formed on the thin film 120 before the photoresist pattern is formed.

Thereafter, the photoresist pattern 140 is formed on the thin film 120 through a general photographic process. The interval between the photoresist patterns 140 may be greater than the line interval of the thin film pattern to be finally formed. If the line spacing of the final thin film pattern is set to 100 nm, the spacing between the photoresist pattern 140 may be formed to be 100 nm or more. As will be described later, the spacing between the photoresist patterns 140 may be narrowed to a desired line spacing (100 nm or less) by the plasma reaction by-products.

Next, as shown in FIG. 2B, the antireflection film pattern 130a is formed by etching the antireflection film 130 using the photoresist pattern 140 as an etching mask. The etching process of the anti-reflection film 130 may use a Capacitively Coupled Plasma (CCP) plasma apparatus. Preferably, CF ₄ and O ₂ gases are used as process gases. In particular, when the flow rate ratio of CF ₄ : O ₂ gas is adjusted to 8: 1 or more, the thin film 120 may be effectively prevented from being etched during the etching process of the anti-reflection film 130. Specific process conditions are carried out for about 5 to 25 seconds at 30 to 100 mTorr pressure, 300 to 1500 W RF power, 30 to 200 sccm CF ₄ , 50 to 300 sccm Ar, and 5 to 30 sccm O ₂ as process conditions. More preferably.

Then, as shown in FIG. 2C, before the etching process of the thin film 120, the reaction by-product generated by plasma treatment of the photoresist pattern 140 is attached to the outer wall of the photoresist pattern 140. It is preferable to use C ₅ F ₈ plasma for this plasma treatment. Reaction of the photoresist with C ₅ F ₈ plasma may produce CxFy-based reaction by-products. Reaction by-products generally have high energy and are therefore very unstable. Because of this, reaction by-products tend to lose their energy and return to a stable state, which is discharged out of the process chamber in most processes. However, in the present invention, the reaction by-products generated by appropriately adjusting the process conditions are attached to the outer wall of the photoresist pattern 140 with an appropriate thickness.

On the other hand, the reaction by-products may be attached to the top of the thin film 120 as well as the outer wall of the photosensitive film pattern 140. If reaction by-products are attached to the surface of the thin film 120, the etching of the thin film may not be performed properly in the subsequent etching process. In FIG. 3A, the reaction by-product 150 is formed not only on the photoresist pattern but also on the thin film 120, so that the bridge 150a is formed between the reaction by-products formed between the neighboring photoresist patterns 140. Indicated.

In order not to generate the bridge 150a of the reaction byproduct, it is preferable to appropriately adjust the amount of ions having linearity with the process gas for forming the reaction byproduct so that the reaction byproduct is not formed on the thin film 120. To this end, argon (Ar) and fluorocarbon gas are used for plasma treatment of the photoresist film, but the flow rate of Ar is controlled to be 5 times or less than the flow rate of fluorocarbon gas. In FIG. 3B, a scanning electron photographing a state in which the reaction by-product 150 is attached to the photoresist pattern 140 using a CCP (Capacitively Coupled Plasma) type plasma apparatus (TEL's Dipole Ring Magnetron (DRM)) The image of the microscope is shown. Here, plasma processing conditions include a process chamber pressure of 10 to 50 mTorr, RF power of 300 to 1500 W, C ₅ F ₈ of 5 to 30 sccm, CH ₂ F ₂ of 1 to 20 sccm, Ar of 30 to 200 sccm, and 0 to 10 sccm O ₂ was carried out for about 10 to 60 seconds under the process conditions. In particular, the flow rate ratio of Ar: C ₅ F ₈ was set to 5: 1 or less.

Comparing FIGS. 3A and 3B, in FIG. 3A, the reaction by-product bridge 150a is formed on the thin film 120 to about 1200 GPa or more. In FIG. 3B, the bridge 150a is not formed and the photoresist pattern ( It can be seen that the reaction byproduct 150 is selectively attached only to the outer wall of the 140.

Next, as illustrated in FIG. 2D, the thin film 120 is etched using the photoresist pattern 140 having the reaction byproduct 150 as an etching mask, thereby forming the thin film patterns 120a spaced at predetermined intervals. . The line spacing of the thin film pattern 120a patterned by the above method may be smaller than the line spacing of the photosensitive film pattern 140.

According to the present invention, when forming a floating gate at a line interval of 100 nm or less in a semiconductor device, especially a flash memory device, the floating gate may be formed at a desired line interval without using expensive exposure equipment. In particular, in the present invention, the plasma by-products are attached to the photoresist pattern and used as an etch mask, so that the reaction by-products are not formed on the thin film, which is an object to be etched, and may be selectively formed only on the outer wall of the photoresist pattern.

Although a preferred embodiment of the present invention has been described so far, those skilled in the art will be able to implement in a modified form without departing from the essential characteristics of the present invention. Therefore, the embodiments of the present invention described herein are to be considered in descriptive sense only and not for purposes of limitation. Should be interpreted as being included in.

Claims (4)

(a) forming a thin film to be etched on the substrate; (b) forming an anti-reflection film on the thin film; (c) forming a photoresist pattern on the anti-reflection film; (d) etching the anti-reflection film using the photoresist pattern as an etching mask; (e) plasma treatment of the photoresist pattern using Ar and C ₅ F ₈ gas, but adjusting the flow rate of Ar: C ₅ F ₈ to 5 or less to attach the reaction byproduct to the outer wall of the photoresist pattern; (f) patterning the thin film using the photoresist pattern on which the reaction byproduct is attached as an etching mask. In claim 1, Step (d), (e) and (f) is a method of patterning a thin film using a plasma reaction by-product, characterized in that performed using a CCP-type plasma apparatus. In claim 1, The step (d) is carried out using a pressure of 30 ~ 100mTorr, RF power of 300 ~ 1500W, CF ₄ of 30 ~ 200sccm, Ar of 50 ~ 300sccm and O ₂ of 5 ~ 30sccm under the process conditions Patterning method of thin film using reaction by-products. In claim 1, The thin film using the plasma reaction by-product is characterized in that step (e) is performed under a process condition using a pressure of 10 to 50 mTorr, C ₅ F ₈ of 5 to 30 sccm, Ar of 30 to 200 sccm, and RF power of 300 to 1500 W. Patterning method.

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