KR100621914B1 - Process for preparing hafnium oxide thin films by atomic layer deposition - Google Patents

Abstract

The present invention uses hafnium precursor Hf (mp) ₄ [tetrakis (3-methyl-3-pentoxy) hafnium (IV), tetrakis (3-methyl-3-pentoxy) hafnium (IV)] A method for producing a hafnium oxide thin film by atomic layer deposition (ALD) using as a raw material of hafnium, comprising: 1) hafnium containing on a substrate by feeding Hf (mp) ₄ as a hafnium source to an ALD reactor; Adsorbing chemical species, 2) first purifying step of removing unreacted hafnium source and reaction by-products from the reactor, and 3) supplying an oxygen source to the reactor to adsorb oxygen species on the substrate adsorbed by the hafnium-containing chemical species. And a second purifying step of removing the unreacted oxygen source and the reaction by-product from the reactor, in accordance with the present invention. This quality can get a good hafnium oxide film from.

Description

PROCESS FOR PREPARING HAFNIUM OXIDE THIN FILMS BY ATOMIC LAYER DEPOSITION}             

1 is a thermogravimetric analysis (TGA) graph of Hf (mp) ₄ compared to the existing precursor Hf (O ^t Bu) ₄ ,

FIG. 2 is a graph of vapor pressure versus temperature of Hf (mp) ₄ compared to the existing precursor Hf (O ^t Bu) ₄ ,

3 is a process diagram illustrating a method of manufacturing a hafnium oxide thin film according to the present invention;

Figure 4 is a graph of the growth rate of the hafnium oxide thin film with respect to the supply time of the hafnium source in the production of hafnium oxide thin film according to the present invention,

5 is a graph of growth rate of a hafnium oxide thin film with respect to a temperature change of a substrate,

6 is an X-ray photoelectron spectral spectrum of a hafnium oxide thin film prepared in Example 2,

7 is a graph showing a thickness change of a thin film with respect to the number of ALD cycles.

8 is a graph showing a growth rate of a hafnium oxide thin film with respect to a supply time of a hafnium source when using an oxygen plasma in the manufacture of a hafnium oxide thin film according to the present invention;

9 is a graph of growth rate of hafnium oxide thin film against temperature change of a substrate when using oxygen plasma,

10 is a graph of the thickness change of the thin film with respect to the number of ALD cycles when using the oxygen plasma.

The present invention relates to a method for producing a hafnium oxide thin film, and more specifically, tetrakis (3-methyl-3-pentoxy) hafnium (IV) [Hf (mp) ₄ ] as a hafnium source and oxygen as a source of oxygen. The present invention relates to a method for producing a high quality hafnium oxide thin film on a substrate using atomic layer deposition (ALD) using ozone or water.

Until now, SiO ₂ has been used as the gate dielectric material of silicon transistors, but as the design rules of semiconductor devices become smaller and smaller, tunneling current leakage and corresponding power dissipation at a thickness of less than 1.5 nm ) And the generation of heat have reached a serious problem. Therefore, there is a need to replace the SiO ₂ dielectric with another material having a high dielectric constant. Decades ago, many studies have been conducted to use Ta ₂ O ₅ instead of SiO ₂ , but ultimately HfO is due to several problems with Ta ₂ O ₅ , including the small band offset value that affects leakage current. _The opinion that ₂ should be used is dominant.

Hafnium oxide thin film is a high- k material and is an important material to be used as a gate dielectric of next-generation semiconductor devices. Hafnium dioxide (HfO ₂ ) has a bulk dielectric constant of 40, which is quite high and does not react with silicon to form silicides (KJ Hubbard et al . , J. Mater. Res. , 1996, 11 , 2757) . The gap is 5.68 eV, which is effective for the suppression of tunneling phenomenon and thermal ion radiation and is very stable compound. Therefore, research on the production of hafnium oxide thin films has been actively conducted for many years, and the synthesis of raw material compounds of hafnium oxide and the manufacturing process of thin films are of great interest. Hafnium oxide thin films can be manufactured by metal organic chemical vapor deposition (MOCVD), but in the semiconductor field, most of the hafnium oxide thin films are manufactured by an ALD method that can accurately control the thickness of thin films.

Hafnium tetrachloride, an early and still popular hafnium compound (M. Ritala et al., Thin Solid Films , 1994, 250 , 72) is a solid at room temperature and inconvenient to handle, and also because of the presence of hydrogen chloride (HCl) in the thin film manufacturing process. Chlorine remains in the thin film and adversely affects the device properties (K. Kukli et al., Thin Solid Films , 2002, 416 , 72; S. Ferrari et al. , J. Appl. Phys. ., 2002, 92, 7675). Hafnium compounds of other halogen elements, such as iodine, are also inconvenient to use and cause additional problems (J. Aarik et al., Thin Solid Films , 2002, 418 , 69). Hafnium iodide is a solid at room temperature and must be heated to a high temperature of 200 ° C. to vaporize it.

Tetrakis (dimethylamido) hafnium (IV) [Hf (NMe ₂ ) ₄ , tetrakis (dimethylamido) hafnium, TDMAH], tetrakis (ethylmethylamido) hafnium, TEMAH], Amido compounds of the form Hf (NR ¹ R ² ) ₄ , such as tetrakis (diethylamido) hafnium (IV) [Hf (NEt ₂ ) ₄ , tetrakis (diethylamido) hafnium, TDEAH], are available from (RG Gordon et al., J. .. Cryst Growth, 2001, 13 , 2463; Y. Ohshita , such as, J. Cryst Growth, 2001, 233 , 292;. DM Hausmann , etc., Chem Mater 2002, 14, 4350 ;.. , such as A. Ogura, Thin Solid Films , 2003, 441 , 161) The decomposition temperatures are very low, 90 ° C, 140 ° C and 150 ° C, respectively. Thus, these compounds exhibit ALD process characteristics at low temperatures, but chemical vapor deposition at higher substrate temperatures (K. Kukli et al. , Chem. Vap. Deposition , 2002, 8 , 199).

Many researchers have used hafnium t-butoxide [Hf (O ^t Bu) ₄ ] as a hafnium source among hafnium alkoxide compounds, but few have successfully used hafnium t-butoxide in ALD processes. HS Chang et al . , Electrochem.Solid-State Lett. 2004, 7 , F42). Hafnium t-butoxide has high reactivity, making it difficult to handle in thin film manufacturing processes and therefore unstable to the extent that white decomposition products form at the edge of the container even when the compound is stored in a glove box. The use of this material in chemical vapor deposition (MOCVD) or ALD processes is a significant inconvenience. The most serious problem is clogging with hafnium t-butoxide, which breaks down the supply pipe of the precursor. In addition, since Hf (O ^t Bu) ₄ generates 30% of residues in the thermal weight analysis (see FIG. 1), carbon contamination may occur when HfO ₂ thin films are prepared from this precursor. Another problem (O ^t Bu) Hf ₄ is because even trace amounts of water cause a catalytic hydrolysis (catalytic hydrolytic decomposition) reaction is that the shelf life is short (PA Williams, etc., Chem. Vap. Deposition, 2002 , 8 , 163). In the ALD process using water as a source of oxygen, hafnium t-butoxide reacts with water, which remains in the gas phase, so that true atomic layer deposition does not occur and atomic layer chemical vapor deposition occurs. , ALCVD).

To address these drawbacks of hafnium t-butoxide, several compounds containing more complex alkoxides that are more coordinated to the central metal, hafnium, have been proposed. These are tetrakis (1-methoxy-2-methyl-2- Propoxy) hafnium (IV) [Hf (OCMe ₂ CH ₂ OMe) ₄ , Hf (mmp) ₄ ; PA Williams et al. , Chem. Vap. Deposition , 2002, 8 , 163], hafnium oxone neopentoxide [Hf ₃ (μ ₃ —O) (μ ₃ -ONep) (μ-ONep) ₃ (ONep) ₆ ; A. Abrutis et al., J. Cryst. Growth , 2004, 267 , 529], tetrakis (dimethylaminoethoxy) hafnium (IV) [Hf (OCH ₂ CH ₂ NMe ₂ ) ₄ , Hf (dmae) ₄ ; M.-K. Song, et al., Thin Solid Films , 2004, 450 , 272]. The large ligands make them difficult to handle, making them difficult to use directly in ALD processes. In the example in which Hf (mmp) ₄ was applied to the ALD process, increasing the hafnium source supply time did not result in a true ALD reaction because the growth rate of the film continued to increase (K. Kukli et al. , Chem. Mater). ., 2003, 15, 1722).

In Hf (mp) ₄ used as a precursor in the present invention, the effect of reducing intermolecular interaction is because the central hafnium atom is first surrounded by a 3-methyl-3-pentoxy group larger than the t-butyl group of Hf (O ^t Bu) ₄ . Appears. Hf (mp) ₄ is therefore much more stable than Hf (O ^t Bu) ₄ . At the same time, Hf (mp) ₄ is more reactive because the mp ligand is simpler than the above compounds, which are more overly stable due to the complex ligands that make up the hafnium coordination sites. In the present invention, by selecting a ligand having a suitable size, the precursor Hf (mp) ₄ which can be easily applied to the ALD process without causing a clogging of the precursor supply pipe is used.

Accordingly, the present invention is to provide a hafnium oxide thin film having a good surface uniformity, good coverage, good carbon contamination and good quality by selecting a hafnium source suitable for the ALD process.

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

Formula 1

Wherein Et represents -CH ₂ CH ₃ and Me represents -CH ₃ .

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

1) adsorbing hafnium species on a substrate by feeding Hf (mp) ₄ into the ALD reactor as a hafnium source;

2) a first purification step of removing unreacted hafnium 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 hafnium species to cause a 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 of forming the hafnium oxide thin film according to the atomic layer deposition method, the hafnium source and the oxygen source are alternately supplied to the substrate to be adsorbed while maintaining the temperature of the substrate to be constant, 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.

3 is a manufacturing process chart of a hafnium oxide thin film according to the present invention. In FIG. 3, the process of forming a hafnium oxide thin film according to the present invention includes an adsorption step of a hafnium source, a first purifying step, an adsorption step of an oxygen source, and a second purifying step, and the above four steps constitute one cycle. . In order to obtain a hafnium oxide thin film with a desired thickness, the above four steps may be repeated in one cycle until the target thickness is reached. In the adsorption step of the oxygen source, it is possible to simply select the method of supplying the oxygen source and the method of generating the plasma with the supply of the oxygen source. For example, the use of oxygen plasma can improve the electrical properties of hafnium oxide thin films by reducing carbon contamination on the surface of growing thin films.

The precursor Hf (mp) ₄ of the hafnium oxide used in the present invention is a hafnium amide complex represented by the following formula (2) and an alcohol represented by the formula (3) in a nonpolar solvent or represented by the following formula (4) as a starting material. It can be prepared by reacting hafnium chloride with the alkali metal salt of the alcohol represented by the formula (5).

Hf (NR ' ₂ ) ₄

HOCMeEt ₂

HfCl ₄

M'OCMeEt ₂

Wherein R 'is methyl or ethyl and M' is Li, Na or K.

The synthesis experiment 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), Can be identified using carbon nuclear magnetic resonance ( ¹³ C NMR), elemental analysis (EA), mass spectroscopy, thermogravimetric / differential thermal analysis (TG / DTA) have.

In the ALD process of manufacturing a hafnium oxide thin film using the precursor, it is preferable to supply a hafnium source to the surface of the substrate for 5 seconds or more per cycle. The reason is that if the supply time is less than 5 seconds, adsorption of hafnium species is difficult to be achieved sufficiently. However, one cycle reaction time can be controlled by controlling the amount of hafnium or oxygen sources fed into the reactor per unit time.

After carrying out the primary adsorption step of the hafnium species, an unreacted hafnium source and reaction byproducts are removed by exhausting the unreacted hafnium source and reaction by-products through an exhaust pump by sending an inert gas such as argon gas to the reactor or vacuum purifying (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 hafnium species are adsorbed. 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.

Upon completion of the adsorption step of the oxygen species, they are evacuated through an exhaust pump by sending an inert gas to the reactor or vacuum purging to remove unreacted oxygen sources and reaction byproducts (second purification step).

The oxygen source is preferably water, oxygen gas or ozone, and when using oxygen gas, putting it in a plasma state helps to reduce carbon contamination.

According to the present invention, the hafnium oxide thin film having excellent properties can be formed by maintaining the temperature of the substrate at 100 to 400 ° C, more preferably at 140 to 350 ° C.

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

Tetrakis (3-methyl-3-pentoxy) hafnium (IV) [Hf (mp) ₄ Synthesis

<Example 1>

Tetrakisdiethylamidohafnium (IV) (5.00 g, 10.7 mmol) was dissolved in a flame dried 125 mL Schlenk flask containing hexane (50 mL). The solution was slowly added to hexane (30 mL) in which mpH (3-methyl-3-propanol, 3-methyl-3-propanol) (4.37 g, 47.1 mmol) was dissolved and stirred for 12 hours. The solvent was removed under reduced pressure and distillation under reduced pressure (130 ° C./10 ⁻² Torr) gave 6.13 g of the title compound as a yellow liquid (yield: 98.2%).

¹ H NMR (C ₆ D ₆ , 300.13 MHz): δ 1.03 (t, 24H, J = 7.5 Hz, CCH ₂ C H ₃ ), 1.22 (s, 12H, CC H ₃ ), 1.54 (q, 16H, J = 7.5 Hz, CC H ₂ CH ₃ ).

¹³ C { ¹ H} NMR (C ₆ D ₆ , 75.03 MHz): δ 79.9 (O C CH ₃ ), 35.6 (C ( C H ₂ CH ₃ ) ₂ ), 27.5 (C C H ₃ ), 8.80 (C (CH ₂ C H ₃ ) ₂ ).

Elemental Analysis C ₂₄ H ₅₂ O ₄ Hf {calculated (calculated)}: C, 49.43 (49.87); H, 8.99 (9.20).

<Test Example 1>

Thermogravimetric analysis (TGA) was performed to compare the thermal properties of Hf (mp) ₄ with Hf (O ^t Bu) ₄ .

Figure 1 is a two inde TGA graph of the precursor material, close to the 30% residue in the ₄ (O ^t Bu) Hf in the graph, but Hf (mp) Hf (mp) residues in less than 10% at ₄₄ The thermal properties of are much better than Hf (O ^t Bu) ₄ .

<Test Example 2>

In order to compare the vapor pressure of Hf (mp) ₄ with Hf (O ^t Bu) ₄ , their vapor pressures were measured with temperature.

2 is a graph showing the natural logarithm of the vapor pressure in mmHg for 1000 / T by measuring the vapor pressures of Hf (O ^t Bu) ₄ and Hf (mp) ₄ . From this graph, it can be seen that the vapor pressure of Hf (mp) ₄ is higher than that of Hf (O ^t Bu) ₄ in the entire temperature range of 25-60 ° C.

Atomic Layer Deposition of Hafnium Oxide

<Example 2>

The silicon substrate to be deposited on the hafnium 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. The temperature of the substrate was adjusted to 250 ° C. and the temperature of the vessel containing hafnium circle Hf (mp) ₄ was raised to 100 ° C. Under these conditions, the steam pressure can be kept constant by opening the valve of the hafnium source supply pipe set at 110 ° C. Water was used as the oxygen source. The temperature of the reactor, the hafnium source feed pipe, and the hafnium source container was kept constant and the deposition reaction was carried out in the order shown in FIG. 3. 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. 4, the thickness of the thin films obtained while maintaining the temperature of the substrate at 250 ° C. and increasing the feeding time of Hf (mp) ₄ was measured by ellipsometry, and the growth rate thereof was plotted against the feeding time. The ALD cycle was fixed at 50 times. As shown in FIG. 4, as the supply time of Hf (mp) ₄ exceeds 5 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 Hf (mp) ₄ exhibits atomic layer deposition characteristics unlike Hf (O ^t Bu) ₄ .

<Example 3>

Under the same conditions as in Example 2, atomic layer deposition was performed at various temperatures while increasing the temperature of the substrate with a supply time of Hf (mp) ₄ of 5 seconds. The ALD cycle was fixed at 100 times. 5 shows the change in growth rate of the hafnium oxide thin film according to the temperature of the substrate. This figure shows the appropriate temperature range for the deposition using hafnium source, which has a constant growth rate in the substrate temperature range of 100 to 400 ° C, and thus the temperature range is used for atomic layer deposition using Hf (mp) ₄ . Tell the appropriate area.

FIG. 6 shows that for thin films having a thickness of ˜660 한 formed by supplying Hf (mp) ₄ at 5 seconds in Example 2, the surface was cleaned by argon ion sputtering for 5 minutes to remove carbon contamination on the surface. X-ray photoelectron spectroscopy spectrum measured after. Only the characteristic photoelectron peaks of hafnium and oxygen can be observed in this spectrum. In particular, near 284 eV, there are no C 1s peaks, indicating carbon contamination. Contamination of carbon has a great adverse effect on the electrical properties of the hafnium oxide thin film, it was confirmed that the surface reaction under almost the conditions of Example 2 to produce a hafnium oxide thin film with almost no carbon contamination.

<Example 4>

Under the same conditions as in Example 3, this time, the thickness of the thin film obtained by increasing the cycle of the ALD process 50, 75, 100, 300, 500 circuits was measured and shown in FIG. From this graph, it can be seen that the thin film manufacturing process using Hf (mp) ₄ shows true ALD characteristics since the thickness of the thin film is primarily dependent on the ALD period.

In Examples 2, 3, and 4, a silicon oxide with a natural oxide film was used as the substrate, but even when using a silicon wafer adsorbed by hydrogen by surface treatment with HF solution, the growth rate was slightly different and the general tendency was the same.

Example 5

ALD experiments were performed using oxygen plasma as the oxygen source.

First, the silicon wafer was immersed in a piranha solution (H ₂ SO ₄ : H ₂ O ₂ = 4: 1) for 10 minutes, then taken out, and diluted in dilute aqueous HF solution (hydrofluoric acid: deionized water = 1: 100). A hafnium oxide thin film was prepared by remote plasma ALD after immersion for minutes to form an H-terminated silicon surface. At this time, the temperature of the substrate was adjusted to 250 ° C., the temperature of the precursor Hf (mp) ₄ was 95 ° C., the temperature of the precursor supply pipe was 110 ° C., and the process pressure was 0.1 Torr. The flow rate of argon carrier gas to the bubbler containing Hf (mp) ₄ was 50 sccm, the supply time of Hf (mp) ₄ was 5 seconds, the flow rate of oxygen-causing oxygen gas was 60 sccm, and the oxygen supply time was 10 Adjusted to seconds. Argon, a purge gas, was sent for 30 seconds after supplying Hf (mp) ₄ and 20 seconds after supplying oxygen gas. During the oxygen supply, oxygen plasma was generated to carry out the remote plasma ALD process.

8 shows the growth rate of the thin films obtained by varying the feeding time of Hf (mp) ₄ from 1 second to 10 seconds to confirm the ALD characteristics of the Hf (mp) ₄ -O ₂ plasma process. This is the graph shown for. The ALD cycle was fixed at 50 times. In this figure, as in Example 2 (FIG. 4), when the supply time of Hf (mp) ₄ exceeds 5 seconds, it can be seen that the ALD characteristics appear.

<Example 6>

A thin film was prepared by adjusting the feeding time of Hf (mp) ₄ to 5 seconds and changing the temperature of the substrate from 150 ° C to 400 ° C under the same conditions as in Example 5. The ALD cycle was fixed at 50 times. Looking at the change in growth rate according to the temperature of the substrate in Figure 9 it can be seen that the growth rate is a constant section from 225 ℃ to 300 ℃. Therefore, it was confirmed that the 225-300 ℃ section is the ALD temperature window. This temperature range is included in the temperature range of Example 3 but the range is narrower.

<Example 7>

Under the same conditions as in Example 6, the thickness of the thin film obtained by maintaining the temperature of the substrate at 250 ° C. and increasing the ALD process cycle to 50, 75, 100, 125, 150, and 200 cycles was measured to measure the thickness of the film against the number of ALD cycles. 10 is shown. In this figure, as in Example 4 (FIG. 7), since the thickness of the thin film is primarily dependent on the ALD cycle, the thin film manufacturing process using Hf (mp) ₄ and oxygen plasma as the oxygen source shows true ALD characteristics. Able to know.

Carbon contamination of the thin films obtained from the remote plasma ALD process was measured by Auger Depth Analysis, and the concentration was within 3 at% (atomic%), indicating that the ALD process using Hf (mp) _{4 produced} 2-3 at% carbon contamination. It is evident that there is no inferiority to the ALD process using visible Hf (NEt ₂ ) ₄ .

As presented above, the ^{Hf (mp) (O t Bu} ) ALD method of manufacturing a hafnium oxide thin film using a ₄ recalcitrant solids write or precursor HfCl ₄ or HfI _4, is too strong reactivity Hf according to the present invention ₄ It is more advantageous than ALD processes that use Hf (NR ¹ R ² ) _4, which has a relatively low decomposition temperature, or Hf (mmp) ₄ , Hf (dmae) ₄ , which are complex in structure, and Hf (mp) _4. The precursor material has excellent physical properties and is very convenient to handle. And most of all, the ALD process using Hf (mp) ₄ shows true ALD characteristics unlike other precursor materials, and uses water or oxygen plasma as an oxygen source to produce high quality hafnium oxide thin films with very low carbon contamination. I can make it.

Claims (6)

A method for preparing a hafnium oxide film on a substrate using a hafnium compound Hf (mp) ₄ represented by Chemical Formula 1 below as a precursor to an ALD process with an oxygen source: <Formula 1>

Wherein Et represents -CH ₂ CH ₃ and Me represents -CH ₃ . The method of claim 1, wherein water, oxygen plasma, or ozone is used as the oxygen source. The method of claim _{1 wherein} the temperature of Hf (mp) ₄ is varied from room temperature to 120 ° C. and used. The method of claim 1 wherein the temperature of the substrate is varied from 100 ° C. to 400 ° C. and used. 2. The method of claim 1, wherein a silicon (Si) wafer, a germanium (Ge) wafer, a silicon carbide (SiC) wafer are used as the substrate. In claim 1, 1) supplying a hafnium compound Hf (mp) ₄ of Formula 1 to the ALD reactor as a hafnium source to adsorb the hafnium species on the substrate, 2) a first purge step of removing from the reactor hafnium sources and reaction byproducts not reacted in step 1) by introducing an inert gas into the reactor or vacuum purifying the reactor; 3) supplying an oxygen source to the first purified reactor to adsorb the oxygen species on the substrate to which the hafnium species are adsorbed, and 4) a second purge step of removing from the reactor oxygen sources and reaction byproducts not reacted in step 3) by introducing an inert gas into the reactor or vacuum purifying the reactor.

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