KR20060085840A - Process for preparing nickel oxide thin film by atomic layer deposition using nickel aminoalkoxide precursor - Google Patents

Abstract

The present invention relates to a method for preparing a nickel oxide thin film by atomic layer deposition (ALD) using a nickel aminoalkoxide precursor of Formula 1 as a raw material compound of nickel, according to the existing method. A better quality nickel oxide thin film can be obtained under milder process conditions than the atomic layer deposition method of.

<Formula 1>

Wherein m is an integer ranging from 1 to 3, R ¹ , R ² , R ³ and R ⁴ are each independently a C ₁ -C ₄ linear or branched alkyl group.

Description

PROCESS FOR PREPARING NICKEL OXIDE THIN FILM BY ATOMIC LAYER DEPOSITION USING NICKEL (II) AMINOALKOXIDE}             

1 is a process drawing illustrating a method for manufacturing a nickel oxide thin film according to the present invention;

2 is a graph showing growth rate of a nickel oxide thin film against a supply time of a nickel source according to Example 1 of the present invention;

3 is a growth rate graph of the nickel oxide thin film with respect to the temperature change of the substrate according to Example 2 of the present invention,

4 is an X-ray photoelectron spectroscopic spectrum of the nickel oxide thin film prepared in Example 2 of the present invention,

5 is a graph showing a thickness change of a thin film with respect to the number of ALD cycles according to Example 3 of the present invention;

6 is an atomic force microscopy photograph of a nickel oxide thin film prepared according to Example 4 of the present invention.

7 is a graph showing growth rates of nickel oxide thin films with respect to a supply time of a nickel source according to Example 5 of the present invention.

The present invention relates to a method for producing a nickel oxide thin film, and more particularly, by using an atomic layer deposition method (ALD) using nickel aminoalkoxide as a nickel source and oxygen, ozone or water as a source of oxygen. The present invention relates to a method for producing a nickel oxide thin film having excellent properties on a substrate.

Nickel oxide (NiO) has excellent electrical, magnetic, and optical properties, and is currently used for p-type transparent conductive thin films, chemical sensors, electrochromic displays, antiferromagnetic layers of spin-valve thin films, and resistance random access memory (RRAM). Its applications include a variety of intermediate oxide layers, and high-k materials by doping lithium and aluminum (H. Sato et al., "Transparent conducting p-type NiO thin films prepared by magnetron sputtering," Thin Solid Films , 1993 236, 27-31; I. Hotov, et al., "Preparation and characterization of NiO thin films for gas sensor applications," Vacuum , 2000 , 58, 300-307; [SA Makhlouf et al., "Humidity sensing properties of NiO / Al ₂ O ₃ nanocomposite materials, " Solid State Ionic , 2003 , 164, 97-106]; JS Svensson et al.," Electrochromic hydrated nickel oxide coatings for energy efficient windows: Optical properties and coloration mechanism, " Appl. Phys. Lett. , 1986 , 49, 1566-1568; S. Yamada et al., "Electrochr omic properties of sputtered nickel-oxide films " J. Appl. Phys. , 1988 , 63, 2116-2119]; [H. Yamane et al.," Differential type giant magnetoresistive memory using spin-valve film with a NiO pinning layer, " J Appl. Phys. , 1998 , 83, 4862-4868; SS Lee et al., "Field sensitivity in spin-valve sandwiches with antiferromagnetic NiO films," IEEE Tran. Magn. , 1996 , 32, 3416-3418; [S. Seo et al., "Reproducible resistance switching in polycrystalline NiO films," Appl. Phys. Lett. , 2004 , 85, 5655-5657; And [Y. Lin et al., "High permittivity Li and Al doped NiO ceramics," Appl. Phys. Lett. , 2004 , 85, 5664-5666).

Therefore, researches on the production of nickel oxide thin films have been actively conducted for many years. Methods of forming a nickel oxide thin film on a substrate may be classified into physical vapor deposition methods such as sputtering, chemical vapor deposition such as metal organic chemical vapor deposition (MOCVD), ALD method.

The chemical vapor deposition method is easy to grow a thin film having a low surface roughness and relatively uniform to a large area substrate as compared with the physical vapor deposition method. The ALD method is to alternately supply a nickel source and an oxygen source to deposit, and it is possible to process at a lower temperature than MOCVD, so that a thin film having excellent quality can be deposited on a substrate that is weak to heat such as glass. The thickness can be adjusted very easily and the surface roughness of the thin film is very low.

In order to grow high quality thin film by ALD method, the selection of a suitable compound that induces a surface reaction under appropriate process conditions is one of the most important factors. Therefore, excellent raw material compound synthesis for the chemical vapor deposition of nickel oxide and the appropriate thin film manufacturing process is of great interest.

Research on nickel compounds and processes applied to ALD methods for the deposition of nickel oxide has only been reported so far (M. Utriainen et al., "Studies of NiO thin film formation by atomic layer epitaxy, " Mater. Sci. Eng. B , 1998 , 54, 98-103"; and M. Utriainen et al., "Studies of metallic thin film growth in an atomic layer epitaxy reactor using M (acac) ₂ (M = Ni, Cu , Pt) precursors, " Appl. Surf. Sci. , 2000 , 157, 151-158).

Nickel compounds applied to ALD include nickel chloride (NiCl ₂ ), Ni (acac) ₂ (acac = acetylacetonato), Ni (tmhd) ₂ (tmhd = 2,2,6,6-tetramethyl-3,5 Β-diketo such as -heptanedionate), Ni (dmg) ₂ (dmg = dimethylglyoxymeto), Ni (apo) ₂ (apo = 2-amino-pent-2-ene-4-oneato) Several nate and β-ketoiminoate compounds have been introduced (M. Utriainen et al., “Studies of NiO thin film formation by atomic layer epitaxy,” Mater. Sci. Eng. B , 1998 , 54, 98 -103].

Among these, nickel chloride is in a solid state at room temperature, and is inconvenient to handle, and hydrogen chloride (HCl) is generated in the thin film manufacturing process, causing problems such as corrosion of the device and pollution of the environment. Crazy

In addition, nickel compounds such as β-diketonate and β-ketoiminoate have high ALD process temperatures and low reactivity with oxygen sources such as H ₂ O or O ₂ , which requires ozone as an oxygen source (M [M] Utriainen et al., See "Studies of NiO thin film formation by atomic layer epitaxy," Mater. Sci. Eng. B , 1998 , 54, 98-103). As a result, the oxidation of the substrate occurs simultaneously.

Therefore, in order to alleviate the above-mentioned disadvantages, there is a need to develop a nickel source that is highly reactive to an oxygen source such as water and that can be deposited at a low temperature.

Accordingly, the present invention is to develop a nickel source suitable for the ALD process to provide a nickel oxide thin film with a good surface uniformity, good coverage, high quality without contamination of carbon.

In order to achieve the above technical problem, the present invention provides a method for producing a nickel oxide thin film by the ALD method using a nickel aminoalkoxide represented by the following formula (1) with an oxygen source as a nickel precursor.

Where

m is an integer ranging from 1 to 3, preferably 1 or 2,

R ¹ , R ² , R ³ and R ⁴ are each independently C ₁ -C ₄ linear or branched alkyl.

Nickel aminoalkoxide compounds used as precursors in the present invention are more reactive than compounds such as β-diketonate or β-ketoiminoate that are too stable and can be easily applied to ALD processes even at low temperatures.

The nickel oxide thin film manufacturing process according to the present invention specifically includes the following steps:

1) supplying nickel aminoalkoxide to the ALD reactor as a nickel source to adsorb nickel species on the substrate,

2) a first purification step of removing unreacted nickel source and reaction by-products from the reactor,

3) supplying an oxygen source to the reactor to adsorb oxygen species on the substrate adsorbed by the nickel species to cause an oxidation reaction, and

4) A second purge step of removing unreacted oxygen sources and reaction byproducts from the reactor.

The present invention is explained in more detail below.

In the method for forming a nickel oxide thin film according to the atomic layer deposition method, a nickel source and an oxygen source are alternately supplied to the substrate for adsorption while maintaining a constant temperature of the substrate, and the reactor is evacuated between these steps or an inert gas such as argon is introduced into the reactor. Thin film is deposited by removing unreacted residues and by-products.

1 is a manufacturing process chart of the nickel oxide thin film according to the present invention. In FIG. 1, the process of forming the nickel oxide thin film according to the present invention comprises a adsorption step of a nickel source, a first purification step, an adsorption step of an oxygen source, and a second purification step, and the above four steps constitute one cycle. . In order to obtain the nickel oxide thin film with the desired thickness, the above four steps may be repeated in one cycle until the target thickness is reached.

In the method of the present invention, a substrate may be a silicon (Si) wafer, a germanium (Ge) wafer, a silicon carbide (SiC) wafer, glass, or a metal.

The precursor of nickel oxide used in the present invention is represented by Ni [OCR ¹ R ² (CH ₂ ) _m NR ³ R ⁴ ] ₂ , which is represented by Scheme 1 below with nickel hexaammine dichloride [Ni (NH ₃ ) ₆ Cl ₂ ] MOCR ¹ R ² (CH ₂ ) _m NR ³ R ^{4 in the} form of a compound and two equivalents of an alkali metal salt (Where M is Li or Na) can be obtained by refluxing in toluene to induce a ligand substitution reaction (see Korean Patent Application No. 2003-0069585).

[Ni (NH ₃ ) ₆ Cl ₂ ] + 2 Na [OCR ¹ R ² (CH ₂ ) _m NR ³ R ⁴ ] →

Ni [OCR ¹ R ² (CH ₂ ) _m NR ³ R ⁴ ] ₂ + 2 NaCl + 6 NH ₃

The synthesis is carried out in an inert argon or nitrogen atmosphere using a glove box or Schlenk line and the structure and physical properties of the reaction product obtained in the synthesis are characterized by ¹ H nuclear magnetic resonance (NMR), Confirmed using carbon atom nuclear magnetic resonance ( ¹³ C NMR), elemental analysis (EA), mass spectrometry, thermogravimetric / differential thermal analysis (TG / DTA) Can be.

In the ALD process of manufacturing a nickel oxide thin film using the precursor, the temperature of the nickel source is preferably used by changing the temperature from room temperature to 120 ° C., and the nickel source is supplied to the surface of the substrate for at least 4 seconds per cycle. desirable. If the feeding time is less than 4 seconds, it is difficult to sufficiently adsorb nickel species. The reaction time of one cycle may be controlled by controlling the amount of nickel or oxygen source fed into the reactor per unit time.

After performing the primary adsorption step of the nickel species, the unreacted nickel source and reaction by-products are removed by exhausting the unreacted nickel source and reaction by-products through an exhaust pump by sending an inert gas such as argon gas to the reactor or vacuum purifying (step 2: first Purification step).

Upon completion of the first purification step, an oxygen source is fed into the reactor to allow oxygen species to adsorb to the surface of the substrate on which the nickel species is adsorbed (step 3). The oxygen source is preferably water, oxygen gas or ozone. When oxygen gas is used, the plasma state helps to react with the nickel-containing species. Oxygen source is preferably supplied at least 0.1 second per cycle, because if the supply time is less than 0.1 seconds, it is difficult to sufficiently adsorb oxygen species. In the adsorption step of the oxygen source, one of simply supplying an oxygen source and generating a plasma together with the supply of the oxygen source may be selected.

Then, when the adsorption step of oxygen species is complete, they are evacuated through an exhaust pump by sending an inert gas to the reactor or vacuum purifying to remove unreacted oxygen sources and reaction byproducts (step 4: second purification step). .

According to the present invention, the temperature of the substrate can be maintained at 80 to 400 ° C, more preferably 90 to 170 ° C to form a nickel oxide thin film having excellent properties.

The present invention will be described in more detail with reference to the following Examples. However, the following examples are merely examples of the present invention, and the claims of the present invention are not limited thereto.

Formation of Nickel Oxide Thin Films by Atomic Layer Deposition

<Example 1>

The silicon substrate to be deposited on the nickel oxide thin film was washed sequentially with acetone, ethanol and deionized water, and then mounted in an atomic layer deposition reactor, and the reactor was evacuated with an exhaust pump. Therefore, there are several tens of native oxide layers on the surface of the silicon substrate. Bis (dimethylamino-2-methyl-2-propoxy) nickel (II) [Ni (dmamp) prepared according to the method described in Korean Patent Application No. 2003-69585 with a nickel source at a temperature of 120 캜. ) ₂ ] the temperature of the vessel containing was raised to 100 ℃. Under these conditions, the steam pressure can be kept constant by opening the valve of the nickel source supply pipe set at 110 ° C. Water was used as the oxygen source.

The temperature of the reactor, the nickel source supply pipe, and the nickel source container was kept constant and the deposition reaction was carried out in the order shown in FIG. 1. At this time, the flow rate of argon, a purge gas, was adjusted to 200 sccm, the purge time was 40 seconds, the water supply time was 1 second, and the working pressure of the reactor was adjusted to 1 Torr.

In FIG. 2, the thickness of the thin films obtained by maintaining the temperature of the substrate at 120 ° C. and increasing the feeding time of Ni (dmamp) ₂ was measured by ellipsometry, and the growth rate thereof was shown with respect to the feeding time. The ALD cycle was fixed at 100 times. As shown in FIG. 2, as the supply time of Ni (dmamp) ₂ exceeds 4 seconds, the surface reaction is saturated and the growth rate is almost constant, which is the most characteristic property of atomic layer deposition. This result confirms that Ni (dmamp) ₂ reacts well with water unlike other β-diketonate compounds to show atomic layer deposition characteristics.

<Example 2>

Under the same conditions as in Example 1, atomic layer deposition was performed at various temperatures while increasing the temperature of the substrate with a supply time of 5 seconds for Ni (dmamp) ₂ . The ALD cycle was fixed at 100 times. Figure 3 shows the change in growth rate of the nickel oxide thin film according to the temperature of the substrate, the growth rate is almost constant in the substrate temperature 90 ~ 160 ℃ interval, this temperature interval is an atomic layer using Ni (dmamp) ₂ It can be seen that it is an area suitable for deposition. This temperature range is significantly lower than the deposition region (250 to 350 ° C.) obtained using other β-diketonate compounds and ozone, and the precursor according to the present invention is suitably applied to substrates such as glass, polymer and the like which are weak to heat. Prove that you can.

4 is a clean surface with argon ion sputtering for 5 minutes in Example 2, Ni (dmamp) for the thin film thickness is formed by 5 seconds, the _second supply time of ~ 660 Å in order to remove carbon contamination on the surface X-ray photoelectron spectroscopy spectrum measured after. In this spectrum, only the characteristic optoelectronic peaks of nickel and oxygen can be observed. The ratio of nickel to oxygen was measured at about 1: 1, and the shape and binding energy values of the Ni 2p internal level spectrum indicate that the film is a typical nickel oxide (NiO). In particular, near 284 eV, there are few C 1s peaks indicating carbon contamination. The contamination of carbon adversely affects the properties of the nickel oxide thin film. From this, it was confirmed that the nickel oxide thin film having almost no carbon contamination was produced due to almost complete surface reaction under the conditions of Example 2.

<Example 3>

Under the same conditions as in Example 2, the thickness of the thin film obtained by increasing the cycle of the ALD process 50, 100, 300, 1000 circuits was measured and shown in FIG. Since the thickness of the thin film is primarily dependent on the ALD period, it can be clearly seen from FIG. 5 that the thin film manufacturing process using Ni (dmamp) ₂ exhibits true ALD characteristics.

<Example 4>

The surface roughness of the thin film obtained by performing 1000 cycles of the ALD process under the same conditions as in Example 2 was measured by atomic force microscopy (Atomic Force Microscopy, AFM), and is shown in FIG. 6. In FIG. 6, the surface roughness of the thin film having a thickness of 81 nm was measured to be about 0.391 nm. From this result, it can be seen that an excellent film having a very low surface roughness, which is a characteristic of the ALD method, was formed.

Example 5

Bis (dimethylamino-2-methyl-2-butoxy) nickel (II) [Ni (dmamb) ₂ ] prepared according to the method described in Korean Patent Application No. 2003-69585 with nickel source under the same conditions as in Example 1. Nickel oxide thin film was prepared using the above. The temperature of the vessel containing the nickel source was raised to 80 ° C. Under this condition, opening the valve of the nickel source supply pipe set to 100 degreeC can maintain a constant vapor pressure. Water was used as the oxygen source. At this time, the temperature of the substrate was maintained at 130 ℃.

In FIG. 7, the thicknesses of the thin films obtained by maintaining the temperature of the substrate at 130 ° C. and increasing the supply time of Ni (dmamb) ₂ were measured by elliptical polarization, and their growth rates were shown with respect to the supply time. The ALD cycle was fixed at 200 times. As shown in FIG. 7, as the supply time of Ni (dmamb) ₂ exceeds 4 seconds, the surface reaction is saturated, and the growth rate is almost constant. This is the most characteristic property of atomic layer deposition. This result confirms that Ni (dmamb) ₂ also reacts well with water in the same manner as Ni (dmamp) ₂ , showing atomic layer deposition characteristics.

In Examples 1, 2, 3, 4, and 5, a silicon wafer with a natural oxide film was used as the substrate, but growth rates were slightly different and the general tendency was the same even when a metal such as glass or platinum was used.

As mentioned above, the method for producing ALD of the nickel oxide thin film using the nickel aminoalkoxide according to the present invention uses nickel, which is difficult to handle, using a solid precursor material NiCl ₂ or nickel having high deposition temperature and low reactivity to oxygen sources such as water. It is more advantageous than an ALD process using a β-diketonate compound and the like, and has excellent physical properties of the thin film. In addition, in the ALD process using the nickel aminoalkoxide according to the present invention, unlike the process using other precursors, true ALD properties are exhibited even when water is used as an oxidizing agent, and a good quality nickel oxide thin film with very low carbon contamination can be produced. Can be.

Claims (9)

In the method for producing a nickel oxide thin film on a substrate by atomic layer deposition (ALD) using a nickel source and an oxygen source as precursors, a nickel oxide comprising nickel aminoalkoxide represented by the following formula (1) as a nickel source Manufacturing method of thin film: Formula 1

Wherein m is an integer ranging from 1 to 3, R ¹ , R ² , R ³ and R ⁴ are each independently a C ₁ -C ₄ linear or branched alkyl group. In claim 1, Wherein m is 1 or 2 in formula (1). In claim 1, Using water, oxygen, or ozone as an oxygen source. In claim 3, Using water as the source of oxygen. In claim 1, A method of changing the temperature of a nickel source from room temperature to 120 ° C. and using the same. In claim 1, And varying the temperature of the substrate from 80 deg. C to 400 deg. In claim 6, Changing the temperature of the substrate from 90 ° C to 170 ° C. In claim 1, A method comprising using a silicon (Si) wafer, a germanium (Ge) wafer, a silicon carbide (SiC) wafer, glass, or a metal as a substrate. In claim 1, 1) supplying nickel aminoalkoxide to the ALD reactor as a nickel source to adsorb nickel species on the substrate, 2) a first purification step of removing unreacted nickel source and reaction by-products from the reactor, 3) supplying an oxygen source to the reactor to adsorb the oxygen species on the substrate adsorbed by the nickel species to cause an oxidation reaction, and 4) a second purge step of removing unreacted oxygen sources and reaction byproducts from the reactor.

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