KR100805844B1 - Dry etching method for phase change materials - Google Patents

Abstract

A dry etching method for a phase change material is provided to obtain a clear anisotropic etching profile by using a bromine-based gas and etching an alloy using an ion and a radical in the plasma. A GexSbyTez alloy is etched by using a mixture gas of HBr or Br2 and H2 as a main etching gas and generating plasma in the etching gas. The HBr gas has concentration of 40 volume%, and a remainder is an inert gas selected from the group consisting of He gas, Ne gas, Ar gas and N2 gas. The etching process is performed under conditions comprising a coil high-frequency power of 700W to 1000W, a DC-bias voltage of 200V to 300V, and a gas pressure of 5 to 10mTorr.

Description

Dry etching method for phase change material {Dry Etching Method for Phase Change Materials}

Figure 1 is a graph of etch rate changes for the GST thin HBr / Ar etching gas, according to one embodiment of the present invention;

2 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 the HBr / Ar etching gas according to an embodiment of the present invention;

3 is a graph illustrating etching rate variation of a GST thin film with respect to a change in coil high frequency power according to an embodiment of the present invention;

4 is a graph illustrating etching rate variation of a GST thin film with respect to a dc-bias voltage change according to an embodiment of the present invention;

5 is a graph illustrating etching rate change of a GST thin film with respect to a change in gas pressure according to an embodiment of the present invention;

6 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the coil high frequency power change according to an embodiment of the present invention;

7 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the dc-bias voltage change according to an embodiment of the present invention;

8 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the gas pressure change in accordance with an embodiment of the present invention;

9 is a graph showing a surface analysis result of a GST thin film for a change in etching time under a constant etching condition according to an embodiment of the present invention; And

FIG. 10 is a graph illustrating changes in surface components of a GST thin film with respect to a change in etching time under a constant etching condition according to an embodiment of the present invention. FIG.

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

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 a low resistance 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, together 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 difference in resistance according to the phase change between crystalline and amorphous states by heat treatment. Among such stoichiometric configurations of the three-component system, the Ge ₂ Sb ₂ Te ₅ (GST) thin film as described above is known to be one of the most suitable materials for the application of the present technology.

Conventionally, a wet etching technique using a chemical solution has been used to etch a GST thin film, but this is easily affected by impurities such as residues, isotropic etching and difficulty in forming a fine pattern. There are disadvantages.

In order to overcome this problem, various GST thin film depositions and their characteristics have been extensively studied, but until now, only the case of using chlorine-based gas as a pattern transfer technique by dry etching is known.

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

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

Hereinafter, the present invention will be described in detail.

The present invention includes a method of dry etching a phase change material.

In detail, the present invention uses a bromine-based gas as an etching gas, and converts the etching gas into plasma to etch by the ions and radicals in the plasma. Ge _x Sb _y Te _z Dry etching methods for alloys, wherein x, y and z are integers.

The etching gas is to be etched by the physical reaction and chemical reaction with the etching material, preferably bromine-based gas, and specific examples thereof may be HBr or Br ₂ / H ₂ Etc. can be mentioned.

In this case, when the HBr / Ar mixed gas is used as the bromine-based etching gas, the concentration of the HBr is preferably 40% by volume to 100% by volume, and thus may exhibit an excellent anisotropic etching profile in the above range. , Remaining volume can be used to make up to 100% by volume supplemented with one or more inert gas selected from He, Ne, Ar and N ₂ gas.

In the present invention, the method of activating the etching gas in a plasma state to cause the chemical reaction with the phase change material to be etched to perform the etching is not particularly limited, but preferably inductively coupled plasma reactive ion etching. Choose from high density plasma reactive ion etching including inductively coupled plasma reactive ion etching (ICPFIE), magnetically enhanced reactive ion etching (MERIE) and reactive ion etching (RIE) In particular, it is more preferable to perform the etching process using a high density plasma etching method.

In the high density plasma etching method, the main process parameters showing a clean anisotropic profile without redeposition include etching gas, coil high frequency power, dc-bias voltage and gas pressure applied to the substrate. Etc.

In this case, the most preferable etching process parameters for obtaining an excellent etching profile in the present invention are coil high frequency power of about 700 W to 1000 W, dc-bias voltage of about 100 V to 300 V, and gas pressure of about 1 mTorr. To 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

The GST thin film used in the experiments for the present invention was deposited on a Pt / Ti coated SiO ₂ / Si substrate using rf-magnetron sputtering. 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. A 400-600 nm thick GST thin film was deposited on a Pt / Ti / SiO ₂ / Si substrate, and then photoresist masked by lithography on the GST thin film. The etching equipment used was an inductively coupled plasma reactive ion etch system (ICPRIE).

1 is a graph illustrating etching rate change of a GST thin film for an HBr / Ar etching gas according to an embodiment of the present invention. Referring to FIG. 1 , after forming a mask pattern by a lithography process using a photoresist on a deposited GST thin film, a high frequency power of 700 W using HBr gas, which is a typical bromine-based etching gas, The result is obtained by etching GST thin film using inductively coupled plasma reactive ion etching (ICPRIE) at a dc-bias voltage of 300 V and a process pressure of 5 mTorr.

When pure Ar gas was used, an etching rate of about 320 nm / min was obtained, whereas as HBr gas was added at 20% HBr concentration, the etching rate of the GST thin film rapidly increased to a maximum etching rate of about 430 nm / min. As the HBr gas increased by more than 20%, the velocity of the GST thin film tended to decrease slightly. Finally, the etching rate was about 360 nm / min at 100% HBr gas concentration. In particular, the increase in the etching rate of the GST thin film with respect to the increase in the HBr gas means that the etching reaction proceeded by the reactive ion etching mechanism under the well-selected etching gas and etching conditions. However, due to the addition of excessive HBr gas, a protective layer containing hydrogen is generated on the side and surface of the thin film, rather it is interpreted to inhibit the etching reaction.

FIG. 2 is a scanning electron microscope (SEM) photograph showing a change in an etching profile of a GST thin film with respect to a change in concentration of an HBr / Ar etching gas according to an embodiment of the present invention. Referring to FIG. 2 , an etching profile of the GST thin film etched at each HBr concentration based on the etching rate result obtained in FIG. 1 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 formed on the side of the etched thin films. The redeposition of and the residue of etching was observed. Less redeposition or etch residues were observed with 20% HBr etch gas than with pure Ar. However, the etching results of the GST thin film using 40% HBr to 100% HBr gas showed a clean etching profile without redeposition or etching residue on the etched side. In particular, as the concentration of HBr gas increased, the etch slope of the GST thin film was gradually improved to show the best vertical anisotrophy etching profile when using 80% to 100% HBr gas.

From the etching results obtained in FIGS. 1 and 2 , the concentration of the etching gas was fixed at 60% HBr / 40% Ar, and the 700 W coil high frequency power, 300 V dc-bias voltage, and 5 mTorr gas pressure were fixed at standard etching conditions, respectively. The etch rate and etch profile of GST thin films were investigated by varying the process parameters of.

3 is a graph illustrating a change in etching speed of a GST thin film with respect to a change in coil high frequency power according to an embodiment of the present invention. Referring to FIG. 3 , the result of etching the GST thin film by varying the coil high frequency power using an etching gas of 60% HBr gas at a dc-bias voltage of 300 V and a process pressure of 5 mTorr.

As the coil high frequency power varied from 300 W to 700 W, the etching rate of the GST thin film increased to approximately 170 to 400 nm / min. This is the result of increasing the plasma power as the coil power increases, that is, the amount of ions or radicals in the plasma increases, thereby increasing the etching rate.

4 is a graph illustrating a change in etching rate of a GST thin film with respect to a change in a dc-bias voltage according to an embodiment of the present invention. Referring to FIG. 4 , a result obtained by etching a GST thin film by using a 60% HBr gas, which is an etching gas, and changing a dc-bias voltage at a coil high frequency power of 700 W and a process pressure of 5 mTorr.

As the dc-bias voltage increased from 200 V to 400 V, the etching rate of the GST thin film increased to approximately 340 to 520 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.

5 is a graph showing a change in etching rate of a GST thin film with a change in gas pressure according to an embodiment of the present invention. Referring to FIG. 5 , a result obtained by using 60% HBr gas, which is an etching gas, by varying the gas pressure at 700 W coil high frequency power and 300 V dc-bias voltage, and etching the GST thin film.

As the gas pressure in the reactor increased from 2 mTorr to 10 mTorr, the etch rate of the GST thin film remained constant at approximately 400 nm / min. This is because the reactive ion etching mechanism is predominantly causing more radicals at high pressure to increase the etch rate of the GST thin film, and the portion that reduces the etch rate by decreasing the average free path of ions or radicals with increasing pressure. It is interpreted as the offset result.

6 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the coil high frequency power change according to an embodiment of the present invention. Referring to FIG. 6 , the GST thin film is etched by varying the coil high frequency power using a 60% HBr gas, which is an etching gas, at a dc-bias voltage of 300 V, and a process pressure of 5 mTorr.

As shown in FIG . 3 , the GST thin film was etched and the etching profile was observed by changing the coil high frequency power, which is one of the main process variables, to 300 W, 500 W, and 700 W in the high density plasma reactive ion etching method. In all three conditions, the etched side showed a clean and no redeposition etch profile, but as the coil high frequency power increased, the side slope (etch slope) of the etched pattern increased. In particular, the etch profile of the GST thin film etched at 700 W coil high frequency power showed the best anisotropy etch profile of nearly 85 degrees.

7 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the dc-bias voltage change according to an embodiment of the present invention. Referring to FIG. 7 , a result obtained by etching a GST thin film by using a 60% HBr gas, which is an etching gas, and changing a dc-bias voltage at a coil high frequency power of 700 W and a process pressure of 5 mTorr.

After etching by varying the dc-bias voltage applied to the substrate to 200 V, 300 V and 400 V, the etching profile of the GST thin film was observed. Under these three conditions, the etch gradient of the GST thin film was in the range of 80 to 90 degrees, and showed a very good etching profile of 90 degrees at 200 V, the lowest dc-bias voltage. Because of the low energy of ions at low dc-bias voltages, it was etched without undue removal of the side passivation, resulting in an etch slope of 90 degrees. At low dc-bias voltages, however, the etch rate of the thin films decreased.

8 is a scanning electron micrograph showing a change in the etching profile of the GST thin film with respect to the gas pressure change according to an embodiment of the present invention. Referring to FIG. 8 , the GST thin film is etched using 60% HBr gas, which is an etching gas, by varying the process pressure at a coil high frequency power of 700 W, and a dc-bias voltage of 300 V. FIG.

The etching profile was observed by etching the GST thin film while varying the gas pressure in the reactor to 1, 5 and 10 mTorr. The etching slope of the GST thin film was similar under these three conditions, but showed an etching slope of 90 degrees at high pressure. In other words, it is interpreted that the reduced ion energy plays a larger role as compared to the increased amount of ions at high pressure.

9 is a graph showing surface analysis of a GST thin film with respect to a change in etching time according to an embodiment of the present invention. Referring to Figure 9 , after etching by varying the etching time to 15 seconds, 30 seconds and 45 seconds at 60% HBr / 40% Ar gas concentration, 700 W coil high frequency power, 300 V dc-bias voltage and 5 mTorr process pressure The surface of the etched GST thin film was examined by XPS analysis. As a result of analyzing the components of the etched surface, it can be seen that the Te component rapidly decreases as the etching proceeds.

10 is a graph showing a relative ratio of surface components of a GST thin film to a change in etching time according to an embodiment of the present invention. Referring to FIG. 10 , a surface component of a GST thin film etched according to a change in etching time is obtained from FIG . 9 . As etching progressed, Ge and Sb components gradually increased and Te components decreased. This shows that the Te component reacts with the GST thin film at 60% HBr gas concentration and the etching conditions selected above, resulting in a relatively fast etching rate. Therefore, the etching rate of the Te component has the fastest etching characteristics among the components of the GST thin film.

As described above, in a preferred embodiment of the present invention, the GST thin film was etched by using inductively coupled plasma reactive ion etching to generate a high density plasma. In the etching process according to the exemplary embodiment of the present invention, a general photoresist mask was used instead of a hard mask which is costly and time consuming by an additional process. As an etching gas, a mixture of bromine-based HBr and Ar, which has not been studied and reported to date, was used and the etching conditions such as the concentration of the etching gas, the coil high frequency power, the dc-bias voltage and the process pressure were changed. Etched. As described above, it was confirmed that the GST having a clean and excellent etching profile could be manufactured by examining the etching rate, etching profile, and etching surface of the GST thin film etched according to the optimal etching process.

Phase change material (Ge _x Sb _y Te _z ) prepared according to the dry etching process of the present invention is faster than the wet etching using a conventional chemical solution and dry etching using a plasma containing a chlorine-based gas as a result of the faster etching rate It shows excellent etching characteristics such as clean anisotropic etching profile without redeposition and redeposition, thus providing useful effects that can be used for phase change disks and storage devices as well as phase change memory which is being actively studied recently.

Claims (6)

As a bromine-based gas, HBr or a mixed gas of Br ₂ and H ₂ is used as a main etching gas, and the etching gas is plasma to form a Ge _x Sb _y Te _z alloy (wherein x, y and z is an integer). delete The dry etching method of claim 1, wherein the concentration of the HBr gas is 40 vol% or more, and the balance is an inert gas selected from at least one of He, Ne, Ar, and N ₂ gases. . 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. The phase change material of claim 1, wherein the etching process is performed at a coil high frequency power of 700 W to 1000 W, a dc-bias voltage of 200 V to 300 V, and a gas pressure in a range of 5 mTorr to 10 mTorr. For dry etching method. delete

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