KR100780404B1 - Dry Etching Method for Phase Change Materials - Google Patents

Abstract

The present invention relates to a dry etching method for a phase change material (Ge _x Sb _y Te _z ), and more particularly, using the chlorine gas or bromine gas as an etching gas, the etching gas is plasma A dry etching method for a phase change material including etching a Ge _x Sb _y Te _z alloy by ions and radicals, wherein the phase change material according to the dry etching of the present invention is wet etching using a conventional chemical solution. As a result, it shows excellent etching characteristics such as very fast etching rate and clean anisotropic etching profile without redeposition.

Phase Change Materials, Dry Etching, Plasma Etching

Description

Dry Etching Method for Phase Change Materials

1 is an X-ray diffractogram of a GST thin film deposited according to an embodiment of the present invention;

2 is a graph illustrating etching rate change of a GST thin film for a Cl ₂ / Ar etching gas according to an embodiment of the present invention;

3 is a scanning electron microscope (SEM) photograph showing the change in the etching profile of the GST thin film with respect to the change in the concentration of Cl ₂ / Ar etching gas according to an embodiment of the present invention;

4A to 4C are graphs showing changes in etching speed of a GST thin film with respect to changes in etching process parameters according to an embodiment of the present invention;

5 is a graph showing an etching profile of a GST thin film according to a change in coil high frequency power according to an embodiment of the present invention;

6 is a graph showing an etching profile of a GST thin film according to a dc-bias voltage change according to an embodiment of the present invention;

7 is a graph showing an etching profile of a GST thin film according to a change in gas pressure according to an embodiment of the present invention.

FIG. 8 is a graph illustrating a change in composition of the surface of a GST thin film with an etch time according to an embodiment of the present invention using an X-ray photoelectron spectrometer (XPS) spectrum; And

9A to 9B are graphs showing XPS spectra of GST films according to specific etching times in one embodiment of the present invention.

The present invention relates to a dry etching method for a phase change material (Ge _x Sb _y Te _z ), and more particularly, using the chlorine gas or bromine gas as an etching gas, the etching gas is plasma It relates to a dry etching method for a phase change material comprising etching the Ge _x Sb _y Te _z alloy by ions and radicals.

With the spread of portable devices, the demand for nonvolatile memory devices is increasing rapidly. In addition to flash memory which is widely used as a nonvolatile memory device, ferroelectric memory, magnetic memory, and phase change memory are attracting attention as a next generation nonvolatile memory. In particular, phase change memory is being researched and developed as a new memory device that can solve the disadvantages of flash memory, such as slow access speed, limit on the number of times of use (10 ⁵ to 10 ⁶ times) and high voltage required during operation. .

Phase change memory is a memory device using a chalcogenide-based phase change material, Ge-Sb-Te alloy, in particular Ge ₂ Sb ₂ Te ₅ (GST) is used. The phase change material is a material having a reversible phase change characteristic between crystalline and amorphous states, and has a property of increasing resistivity when amorphous, and decreasing resistivity when crystalline. By using the resistivity change during the phase change, digital data can be stored in a CD-RW, a DVR and a DVD-RAM.

Recently, research on phase-change random access memory (PRAM) using such phase change characteristics has been extensively performed. The advantages of the PRAM are that it is a nonvolatile memory device, and it has high read / write speed, low voltage operation, and high density. PRAM devices, along with ferroelectric memory (FeRAM) and magnetic memory (MRAM), are attracting attention as next-generation new memory devices.

The principle of PRAM is based on the resistance difference according to the phase change between crystalline and amorphous states by heat treatment. Among the stoichiometric configurations of such ternary systems, Ge ₂ Sb ₂ Te ₅ (GST) thin films as described above are known to be one of the most suitable materials for the application of the present technology.

Although wet etching technology using a chemical solution has been used for the deposition of GST thin films, it has disadvantages such as being easily affected by impurities such as residues and etching isotropically.

In order to overcome this problem, various GST thin film depositions and their characteristics have been extensively studied, but the pattern transfer technique by dry etching is not known until now.

Accordingly, the present inventors have been studying the reactive ion etching technology of the GST thin film having a photoresist mask on a high density plasma of Cl ₂ / Ar gas mixture, and can obtain excellent etching characteristics such as very fast etching rate and excellent etching profile. Optimum dry etching process parameters were found and the present invention was completed.

Accordingly, an object of the present invention is to provide a dry etching method for a phase change material exhibiting a clean anisotropic profile without very fast etching rate and redeposition.

In order to achieve the above technical problem, the present invention uses a chlorine-based gas or bromine-based gas as an etching gas, and plasmas the etching gas to form a Ge _x Sb _y Te _z alloy by ions and radicals in the plasma. , x, y, and z are integers), and provides a dry etching method for a phase change material.

Hereinafter, the present invention will be described in detail.

The present invention includes a method of dry etching a Ge _x Sb _y Te _z alloy, wherein x, y and z are integers.

In the present invention, the etching gas is to cause the etching by the chemical reaction with the etching material may be preferably used a chlorine-based gas, specific examples thereof include Cl ₂ , BCl ₃ , SiCl ₄ and the like. have.

At this time, in the case of using Cl ₂ as the chlorine-based etching gas, the concentration is preferably 40 to 100% by volume, and the balance is 100% by volume with an inert gas selected from He, Ne, Ar, and N ₂ gases. Can be made and used.

In addition, a bromine-based gas may be used as the etching gas, and specific examples thereof may include Br ₂ and HBr.

In the present invention, there is no particular limitation on a method of activating the etching gas to a plasma state by causing a chemical reaction with a phase change material to be etched so as to perform etching, but preferably an inductively coupled plasma reactive ion etching. Selected from high density plasma reactive ion etching (ICPRIE), magnetically enhanced reactive ion etching (MERIE) and reactive ion etching (RIE) The etching process may be performed using a high density plasma etching method.

In the high-density plasma etching method, the main process parameters showing a clean anisotropy profile without redeposition include etch gas, coil high frequency power, and dc-bias voltage applied to the substrate. ), Gas pressure and the like. At this time, the range of the most preferable etching process parameters for obtaining an excellent etching profile in the present invention is a coil high frequency power of 200 ~ 400 W, dc bias voltage of 100 ~ 200 V, and gas pressure of 1 ~ 10 mTorr.

The phase change material manufactured as described above can be applied not only to the production of phase change (optical) disks and phase change storage devices, but also to the production of phase change semiconductor memory devices that are being actively studied as next generation semiconductor memories.

Hereinafter, the present invention will be described in more detail with reference to Examples and the accompanying drawings. However, the following examples and drawings are provided to aid the understanding of the present invention, and the contents of the present invention are not limited or limited by the embodiments of the following drawings.

< Example  1> Phase change  Manufacture of substances

A GST thin film was deposited by rf magnetron sputtering on a Pt / Ti coated SiO ₂ / Si substrate. The ceramic target composition was made such that Ge: Sb: Te was 14.1: 23.7: 62.2 (% by weight). The substrate was placed at a distance of 70 mm from the target central axis. The substrate was left at room temperature for uniform film deposition and spun at a rate of 12 revolutions / minute. The deposited GST thin film was heat-treated in a temperature range of 150 to 400 ° C. under N ₂ gas atmosphere in a high temperature furnace. Phase change with temperature change was confirmed by X-ray diffraction (XRD) analysis. A 400 nm thick GST film was deposited on a Pt / Ti / SiO ₂ / Si substrate, followed by photoresist masking directly on the GST film. The etching equipment used was an inductively coupled plasma reactive ion etch system (ICPRIE).

1 is an X-ray diffractogram of a GST thin film deposited according to an embodiment of the present invention.

Referring to FIG. 1 , a Ge _x Sb _y Te _z (GST) thin film according to an embodiment of the present invention was deposited using sputtering, which is one of vacuum thin film deposition methods. A Ge ₂ Sb ₂ Te ₅ thin film was deposited using a GST target and an Ar gas, and the phase change characteristics of the GST thin film were confirmed by X-ray diffraction. As a result, it was observed that the GST thin film caused a phase change with temperature change between 150 degrees and 200 degrees, 300 degrees and 35 degrees.

FIG. 2 is a graph illustrating etching rate variation of a GST thin film with respect to a Cl ₂ / Ar etching gas according to an embodiment of the present invention. FIG.

Referring to FIG. 2 , after forming a mask pattern by a lithography process using a photoresist on a deposited GST thin film as shown in FIG. 1 , a Cl ₂ gas, which is a representative chlorine-based etching gas, is used. Using inductively coupled plasma reactive ion etching (ICPRIE) equipment at coil rf power, 200 V dc-bias voltage, and 5 mTorr process pressure The result obtained by etching the GST thin film.

When pure Ar gas was used, an etching rate of about 340 nm / min was obtained, and the etch rate of the GST thin film gradually increased as chlorine was added, and an etching gas of 60% Cl ₂ /40% Ar was used. The etching rate was very fast at 500 nm / min. In particular, increasing the etching rate of the GST thin film with increasing Cl ₂ gas means that the reactive ion etching is maximized under the well-selected etching gas and etching conditions, and the etching rate is continuously increased. .

3 is a scanning electron microscope (SEM) photograph showing a change in etching profile of a GST thin film with respect to a change in concentration of Cl ₂ / Ar etching gas according to an embodiment of the present invention.

Referring to FIG. 3 , the etching profile of the GST thin film etched at each Cl ₂ concentration based on the etching rate result obtained in FIG. 2 is observed using a scanning electron microscope. GST thin films etched using pure Ar gas were observed to have trace amounts of redeposited materials or etch residues on the side of the etched thin films. However, the etching results of GST thin films using 20% Cl ₂ to 80% Cl ₂ gas showed a clean etching profile with no redeposition or etch residue on the etched side. In particular, as the concentration of Cl ₂ gas was increased, the etch gradient of the GST thin film was gradually improved, showing the best vertical anisotrophy etching profile with 80% Cl ₂ gas.

In inductively coupled reactive ion etching (ICPRIE), one of the high density plasma etching methods, the main process parameters of etching are etch gas, coil rf power and dc bias voltage applied to the substrate (dc-bias). voltage, gas pressure, and the like.

From the etching results obtained in FIG. 3 , the concentration of the etching gas was fixed at 60% Cl ₂ /40% Ar, and each process was fixed at 400 W coil high frequency power, 200 V dc-bias voltage, and 5 mTorr gas pressure at standard etching conditions. Variables were varied to investigate the etch rate and etch profile of the GST thin film.

4A to 4C are graphs showing changes in etching speed of a GST thin film with respect to changes in etching process parameters according to an embodiment of the present invention.

4A is a graph illustrating a change in etching speed of a GST thin film with respect to a change in coil high frequency power. Referring to FIG. 4A , as the coil high frequency power is changed from 200 W to 600 W, the etching rate of the GST thin film is increased from approximately 330 to 600 nm / min. This is the result of increasing the plasma density and the etching rate as the coil power increases.

4B is a graph showing a change in etching rate of a GST thin film with a change in a dc-bias voltage. Referring to FIG. 4B , as the dc-bias voltage was increased from 100 V to 300 V, the etching rate of the GST thin film increased from approximately 330 to 640 nm / min. This is because as the dc-bias applied to the substrate increases, the cations in the plasma are attracted to the GST thin film with greater energy.

4C is a graph showing a change in etching rate of a GST thin film with a change in gas pressure. Referring to FIG. 4C , as the gas pressure in the reactor increased from 1 mTorr to 10 mTorr, the etching rate of the GST thin film increased from approximately 420 to 600 nm / min. It is interpreted that the reactive ion etching mechanism prevails, generating more radicals at high pressure, thereby increasing the etching rate of the GST thin film.

5 is a graph illustrating an etching profile of a GST thin film according to a change in coil high frequency power according to an embodiment of the present invention.

Referring to FIG. 5 , as shown in FIG . 4 , the GST thin film was etched and the etch profile was observed by changing coil high frequency power, which is one of the main process variables, to 200, 400, and 600 W in the high density plasma reactive ion etching method. In all three conditions, the etched sides showed clean and no redeposition and showed an etch slope of approximately 80 to 85 degrees. In particular, the etch profile of the GST thin film etched at 200W coil high frequency power, which is lower than 400, 600W, showed the best anisotropy etch profile of more than 85 degrees.

FIG. 6 is a graph illustrating an etching profile of a GST thin film according to a dc-bias voltage change according to an embodiment of the present invention.

Referring to FIG. 6 , the etching profile of the GST thin film was observed after etching by changing the dc-bias voltage applied to the substrate to 100, 200, and 300 V. Referring to FIG. The etching slope of the GST thin film was in the range of 75 to 90 degrees under three conditions, and showed a very good etching profile of 90 degrees at 100 V, the lowest dc-bias voltage.

7 is a graph showing an etching profile of a GST thin film according to a change in gas pressure according to an embodiment of the present invention.

Referring to FIG. 7 , the GST thin film was etched while the gas pressure in the reactor was changed to 1, 5, and 10 mTorr, and the etching profile was observed. The etching slopes of the GST thin films were similar under the three conditions, and were approximately 80 to 85 degrees.

Since the GST film is composed of three components, that is, Ge, Sb, and Te, it is meaningful to understand the etching mechanism by comparing the relative composition of each component by etching.

FIG. 8 is a graph illustrating a change in composition of the surface of a GST thin film with an etch time according to an embodiment of the present invention using an X-ray photoelectron spectrometer (XPS) spectrum.

Referring to FIG. 8 , 60% Cl ₂ , a coil high frequency power of 400 W, a dc-bias voltage of 200 V, and a gas pressure of 5 mTorr were used as etching conditions. Since the Cl ₂ / Ar gas mixture was used as the etching gas, this etching result was expected to be a chlorine compound. As the etching process proceeded, the relative atomic concentration of Ge gradually decreased, but the atomic concentration of Te increased. In the case of Sb, the relative atomic concentration initially decreased but remained constant over time. This is because Ge rather than Sb and Te reacted easily with the Cl radical to form a GeCl _x compound.

9 is a graph showing the XPS spectrum of a GST film according to a specific etching time according to an embodiment of the present invention, (a) shows the Ge 2p peak change of the GST etching surface according to the etching time; (b) shows the change of the Sb 3d and Te 3d peaks of the GST etching surface according to the etching time. Etching conditions were 60% Cl ₂ , a coil high frequency power of 400 W, a dc-bias voltage of 200 V and a gas pressure of 5 mTorr.

Referring to FIG. 9A , it can be seen that the germanium compound (ie GeClx) was formed at 2 and 3 minutes. On the other hand, referring to Figure 9b , it can be seen that no chlorine compound was formed.

As a result of comparing the relative atomic concentrations of Ge, Sb and Te, which are the GST etching surface components, it was found that the etching speed of Ge was the fastest and that of Te was the lowest. Accordingly, it was found that Te etching in the GST film was a rate limiting step in the etching process of the present invention.

The phase change material prepared according to the dry etching process of the present invention exhibits excellent etching characteristics as compared to wet etching using a conventional chemical solution, and thus exhibits excellent etching characteristics such as a very fast etching rate and a clean anisotropic etching profile without redeposition. It provides a useful effect that can be used for change disks and storage devices as well as phase change memory which is being actively studied recently.

Claims (7)

60 to 100 vol% Cl _2/40 ~ using 0 vol% Ar as an etching gas, in the etching gas to plasma and Ge _x Sb _y Te _z alloy by ions and radicals in the plasma (wherein, x, y And z is an integer) at a coil high frequency power of 200 to 400 W, a dc-bias voltage of 100 to 200 V, and a gas pressure of 1 to 10 mTorr. delete delete delete The method of claim 1, wherein the plasma of the etching gas is performed by a method selected from high density plasma reactive ion etching, self-enhanced reactive ion etching, and reactive ion etching including inductively coupled plasma reactive ion etching. Dry etching method for phase change material. delete A phase change material comprising a Ge _x Sb _y Te _z alloy, wherein x, y and z are integers, prepared according to claim 1.

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