KR100409040B1 - Preparation of organic polymer-like thin films from thiopene derivatives using plasma enhanced chemical vapor deposition - Google Patents

Abstract

The present invention provides a high dielectric film thin film of thiophene (C ₄ H ₄ S) as a high-speed deposition by plasma assisted chemical vapor deposition method has a low dielectric constant and low leakage current characteristics for the interlayer wiring material applied to semiconductor integrated devices It is about developing an insulating material.

Description

Process for the preparation of organic polymer thin film by plasma assisted chemical vapor deposition of thiophene derivatives

The present invention relates to a method for preparing an organic polymer thin film from thiophene or a derivative thereof by plasma assisted chemical vapor deposition, and to an organic polymer thin film having low dielectric constant and low current density characteristics.

In general, in the wiring of a semiconductor device, Al is used as a metal wire and SiO ₂ is used as an insulating material between metals.

In recent years, due to the trend of miniaturization, high speed, and high integration of semiconductor integrated devices, the integration level of unit devices has already reached the giga level, and even in the wiring connecting the devices, the ultra fine line width and multilayer structure of 0.25 micrometers and 0.13 micrometers are passed. Is asking. This deepening of integration leads to an increase in relative capacitance in narrow and long wirings, resulting in signal delay and cross-talk of electrical signals.

Therefore, the limit of dielectric constant of insulating material between wiring materials has emerged as a new obstacle to device integration. To overcome this, new materials and wiring process technologies with low dielectric constant and high thermal stability and low leakage current This is urgently needed.

As such, in order to solve the RC delay problem in the wiring according to the increase in the degree of integration of semiconductor devices, in the case of metal wires, Al (2.7 μm ) having a high resistivity is replaced with Cu (1.67 μm ) having a low specific resistance. In addition, as an insulating material between metals, it is necessary to introduce a low-k material having a lower dielectric constant than conventional SiO ₂ .

Although Cu wiring process technology is well known and researched to a considerable level, research on a new low dielectric interlayer insulating film has only begun relatively recently.

Currently, many low-k materials have been proposed and developed such as SiO ₂ aerogels, methyl sisesquoxane (MSQ), hydrogen silsesquoxane (HSQ), parylene, and divinyl siloxane bis-benzocyclobutene (DVS-BSB) polymers.

However, in the case of SiO ₂ airgel, which is an inorganic insulating film, it exhibits excellent characteristics in dielectric constant but exhibits problems in thin film formation and mechanical strength, and thus, organic films are difficult to form a reliable film and have low thermal stability. Research is being carried out to

In addition, when the organic thin films made of a material having a low dielectric constant were in contact with Cu, the diffusion of Cu into the thin films during the heat treatment was observed. In order to prevent this, a diffusion barrier was formed between the low dielectric constant material film and the Cu. However, these diffusion barriers place many constraints on reducing the RC delay.

In the case of Ta, TaN, and TiN, which are conductive diffusion barriers, the overall resistance becomes large due to the large resistance of the diffusion barrier, and in the case of SiN, which is an insulating diffusion barrier, the overall dielectric constant is higher because the diffusion barrier has a higher dielectric constant than the low dielectric constant material. Becomes high.

In addition, when the diffusion barrier is used, a complicated process such as depositing the diffusion barrier into a hole having a large aspect ratio required in the wiring process is required. For these reasons, diffusion barriers are only recognized as an intermediate solution, and ultimately, there is a strong demand for a wiring process without diffusion barriers and a low dielectric interlayer insulating material that can be used in such wiring processes.

The inventors have found that organic polymer thin films produced by plasma assisted chemical vapor deposition using low cost thiophene have a dielectric constant lower than 3.0, high thermal stability even above 400 ° C, and low lower than 10 ^-8 A / cm2. In addition to having a leakage current characteristic, it has been found that such an organic polymer thin film can be formed at a high speed, and the thiophene-derived polymer thin film thus prepared can be used as a thin film made of a low dielectric constant material that does not require a diffusion barrier. This invention was completed.

FIG. 1 is a diagram illustrating deposition rates of polymer thin films using Ar and H ₂ gases in a 2: 1 ratio according to RF power change.

Figure 2a is a diagram showing the change in dielectric constant of the polymer thin film formed on the Pt substrate using Ar and H ₂ gas in a 1: 1 and 2: 1 ratio according to the RF power change, Figure 2b is a process temperature room temperature and It is a figure which shows the change of the dielectric constant of the polymer thin films formed on the semiconductor substrate at 100 degreeC according to the RF power change.

3 is a graph showing leakage current characteristic curves of polymer thin films obtained at various RF powers using Ar and H ₂ gases in a 2: 1 ratio.

Figure 4 is a view showing the XRD pattern of the plasma organic polymer thin film prepared at RF 70W, 100W, 200W and 300W, respectively, according to the method of the present invention.

5 and 6 are obtained from the thin films grown in the deposition conditions of 100 ℃, RF power 50 W ~ 100 W, gas flow rate Ar: H ₂ = 2: 1 and 1: 1, respectively, according to the method of the present invention Each of the SEM photographs is shown.

Accordingly, an object of the present invention is to provide a method for preparing an organic polymer thin film by plasma assisted chemical vapor deposition and a organic polymer thin film prepared by thiophene (C ₄ H ₄ S) or derivatives thereof. More specifically, an object of the present invention is to prepare an organic polymer thin film, characterized in that the plasma assisted chemical vapor deposition of thiophene or derivatives thereof on a substrate while supplying a gas having a mixture ratio of argon and hydrogen of 1: 1 to 2: 1. It is to provide a method and an organic polymer thin film produced thereby.

The organic polymer thin film prepared according to the present invention has low dielectric constant and low current density characteristics.

Representative methods of thin film formation technology include chemical vapor deposition (CVD) and physical vapor deposition (PVD), and thin film formation by chemical vapor deposition (CVD) contributes to high-speed particles compared to physical vapor deposition (PVD). There is less advantage of less damage to the substrate surface. In addition, the chemical vapor deposition method has the advantages that can be processed at the first low temperature, second can synthesize a high purity material, third, mass production, and fourth has a good step coverage (Step coverage).

Chemical vapor deposition includes plasma CVD and laser CVD, and plasma enhanced chemical vapor deposition (PECVD) used in the present invention is a kind of such chemical vapor deposition, and theoretical studies have been widely conducted in the art, and process conditions thereof. Etc. are well known [M. Ohring, " The Material Science of Thin Film ", Academic Press (1992); S. Morita et al., J. Appl. Phys. , 51 (1980) 3938; S. Roualdes et al., Journal of Non-Crystalline Solids , 248 (1999) 235; YC Quan et al., Jpn. J. Appl. Phys. , 38 (1999) 1356; S. Takeishi et al., J. Electrochem. Soc. 144 (1997) 1797; T. Fujii et al., Thin Solid Films 343-344 (1999) 457; O. Baehr et al., Mat. Sci. and Eng. , B46 (1997) 101]

In the present invention, a process of forming a thin film is described, for example, after liquid phase pretreatment of a substrate (Si single crystal or wafer, glass, SUS, aluminum, SKD 11, ITO glass, etc.), and then placed in a chamber and before deposition. Argon plasma pretreatment for about 5 minutes, and the raw material in the raw material container maintained at room temperature at a pressure of 2 x 10 ^-2 Torr or less is a gaseous raw material (thiophene) and hydrogen (1-10 sccm) and argon (2-20). sccm) into the reactor, at which the optimum process pressure is approximately 3 × 10 ⁻¹ Torr and at the same time supplying RF power (30 to 300 W) with a frequency of about 13.56 MHz to the stage on which the substrate is placed, thereby Is produced and a thin film is formed.

As a raw material, thiophene or a derivative thereof containing a sulfur atom in a molecule is used, and examples of the derivative may mention an alkyl derivative thereof. Sulfur atoms are generally known to react easily with many metals and can also react with inert metals such as gold, silver and copper. In general, the organic thin film is pointed out that the weak adhesion to the metal, but the organic thin film prepared from the thiophene or derivatives thereof by the method according to the present invention has excellent adhesion to copper and the like due to the sulfur atoms contained in the thiophene. .

In a general chemical vapor deposition method, since raw materials such as organic monomers are introduced together at the time of bubbling hydrogen, its exact supply amount is difficult to measure, and in general, the supply amount is controlled by the bubbling rate of hydrogen. Also in this invention, the quantity of the organic monomer supplied, ie, thiophene, was not specifically measured, It is used by the quantity well known by the general chemical vapor deposition method.

The deposition temperature can be set from room temperature to high temperature according to the characteristics of the thin film required. The heating method used a hot wall method of winding and heating a heating wire in the reactor. The deposition time is not particularly limited and may be about 5 to 40 minutes.

According to the method of the present invention, a thin film using a plasma assisted chemical vapor deposition process and having a low dielectric constant (k <3), high thermal stability and low leakage current characteristics (<10 ^-8 A / cm ² ) even with a short deposition time Can be obtained at high speed (up to 110 nm / min) (see FIG. 1).

In the present invention, plasma assisted chemical vapor deposition may use a plasma chemical vapor deposition apparatus commonly used in the art.

Referring to the plasma chemical vapor deposition apparatus that can be used in the present invention as an example. The PECVD apparatus which consists of a cylindrical vacuum chamber using SUS 304L, a gas supply system, a vacuum exhaust system, a power supply system, a heating system, a cooling system, etc. can be used. The vacuum chamber is made of cylindrical shape using SUS 304L, and the inside of the vacuum chamber is capable of supplying heat to the Kantal resistance heating element of the hot wall heating method. It can prevent overheating. In addition, a shielding plate can be manufactured to compensate for the problem of dielectric breakdown during deposition.

As the reaction gas, an inert gas such as Group 8 element on the periodic table of elements, for example, Ar, and a precursor gas of H ₂ can be used, and each of them uses an MFC (Mass Flow Controller) to control the flow rate into the vacuum chamber. It is possible to fine tune. The carrier gas, H ₂ , may be mixed with Ar through a preheated line through a bubbler containing precursor thiophene and enter the vacuum chamber. Inside the chamber, it is evenly spread throughout the chamber through a gas shower. An RF (Radio Frequency: 13.56 MHz) power supply with a capacity of 1000 kW can be used to power the specimen stand located in the vacuum chamber.

For example, Edwards rotary pumps can be used to provide a vacuum exhaust system and the initial vacuum can be lowered to 2 × 10 ⁻² Torr. In order to remove harmful components and secure stability, a cold trap may be installed at the exhaust portion to absorb exhaust gas, thereby reducing emissions.

The composition, crystallinity, and surface properties of the formed organic polymer thin film were evaluated by known methods such as XPS, XRD, TEM, TED, SEM, AFM, contact angle, FT-IR analysis, and the like. The optical properties of the thin films were evaluated by UV-Vis and PL spectra analysis, and the leakage current and dielectric constants were measured by I-V measurement and C-V measurement.

In the present invention, various process conditions are not particularly limited in most cases, and generally, process conditions commonly used in plasma chemical vapor deposition can be used. Those skilled in the art will be able to select most of these process conditions as needed.

In the present invention, as the process conditions, for example, the deposition temperature may be a room temperature ~ 500 ℃, the process pressure is 1 × 10 ^-1 to 5 × 10 ^-1 Torr, the deposition time may be 5 to 40 minutes.

The gas used may be supplied separately or a mixture of hydrogen gas and inert gas under plasma chemical vapor deposition conditions. These mixing ratios are used in ratios well known for plasma chemical vapor deposition, and are generally about 3: 1 to 1: 3, preferably about 3: 1 to 1: 2, specifically about 2: 1 or about 1: 1 The ratio may be, but is not particularly limited thereto.

In the present invention, RF power may be a typical value for plasma chemical vapor deposition, for example 30 to 300 W.

Hereinafter, the present invention will be described in more detail based on examples.

Example

In organic polymer thin film deposition using thiophene, as shown in Table 1, the organic polymer thin film was formed while varying the process conditions.

Deposition Conditions for Thiophene Thin Films Item fixing variable Board Si (100) (2 cm x 2 cm), or cover glass Precursor Thiophene (liquid): C ₄ H ₄ S Deposition temperature Room temperature ~ 400 ℃ Base pressure 2 × 10 ^-2 Torr Deposition pressure 3x10 ^-1 to 4x10 ^-1 Torr Deposition time 5 to 20 minutes Carrier and Bubbler Gas Ar and H ₂ (1: 1, 2: 1) RF power 30-300 W

The experimental procedure is as follows.

(1) Si (100) wafer and cover glass were used as substrates, and in order to remove contaminants of various components and oxide films formed on the surface, Si oxide wafers were fluorinated on the surface After removal of the alkali, ultrasonic cleaning with acetone after alkaline cleaning, and finally with washing with distilled water, the specimen was placed in the chamber after drying.

(2) The specimen was placed in the chamber, and the chamber was heated by a hot-wall method to evaporate moisture on the surface that can be evaporated and exhausted. In addition, plasma pre-treatment with 100 W RF power under argon gas atmosphere sputters the surface by Ar-ion bombardment in the plasma to clean the surface again, increase the surface reactivity for thin film growth, and deposit the thin film. Entered the process. When the temperature was suitable for deposition, precursors and hydrogen were introduced into the reactor, and the process was performed by changing conditions such as gas flow rate, RF power, and temperature.

(3) After the deposition was completed, the specimens were removed after sufficient cooling to room temperature. At this time, if the cooling speed is high, care should be taken because thermal stresses may cause crystal defects in the specimen, cracks in the membrane, and poor adhesion. After all of these deposition processes, the specimens were taken out and analyzed.

The composition, crystallinity, and surface properties of the organic polymer thin films thus formed were evaluated by known methods such as XPS, XRD, TEM, TED, SEM, AFM, contact angle, and FT-IR analysis. The optical properties of the thin films were evaluated by UV-Vis and PL spectra analysis, and the leakage current and dielectric constants were measured by I-V measurement and C-V measurement.

Test Example 1

The XRD pattern of the plasma organic polymer thin film deposited on the Si (100) and the cover glass substrate according to the change in the ratio of power, carrier gas and bubbler gas at the deposition temperature of 100 ° C. and the deposition time of 20 minutes was examined. It describes in.

In the plasma organic polymer thin film, the structure of the thin film is generally amorphous due to the plasma effect. However, as shown in FIG. 4, peaks of two peaks appearing in a broad form at a low 2θ value are shown. This suggests that the thin film is entirely amorphous but has a certain degree of orientation. In the case of polythiophenes, several peaks appearing between 2θ = 5 to 25 ° have been described by several authors in HS Nalwa, "Handbook of Low and High Dielectric Constant Materials and Their Applications", Academic Press Inc, volume 1 (1999). ) pp. 63-65; A. J. Lovinger, D. D. Davis, A. Dodabalapur, and H. E. Katz, Chem. Mater., 8 (1996) 2836; And in Y. Kanemitsu, K. Suzuk, N. Shimizu, Y. Shiraishi and M. Kuroda, Jpn. J. Appl. Phys., 35 (1996) 1097, which is well known from Phys., 35 (1996) 1097, can be important evidence that these peaks are amorphous polymers with some orientation. Referring to FIG. 4, a broad peak near 2θ = 8 ° is maintained as the RF power increases overall, but the broad peak at about 17 ° increases in intensity gradually as the power increases from 70 W to 200 W. It can be seen that when the 300 W rather decreases. Accordingly, it was found that the thin film was grown in two directions as a whole, and a polycrystalline thin film having a relatively high crystallinity was obtained when the RF power was 200 W.

In other words, X-ray diffraction (XRD) analysis showed that the grown plasma organic thin film was amorphous in general, but had highly oriented amorphous properties with some degree of directivity in two directions.

Test Example 2

SEM images were obtained from thin films grown under the conditions of deposition conditions of 100 ° C., RF power of 50 W to 100 W, gas flow rates Ar: H ₂ = 2: 1 and 1: 1, respectively, and FIG. 5 (Ar: H ₂ = 2: 1) and FIG. 6 (Ar: H ₂ = 1: 1), respectively.

Ar: H ₂ = _2: 1 day, when RF power is increased as in accordance with the surface form of the more rough thin film is produced on the other hand Ar is: H ₂ = 1: 1 when the rather a smooth surface according to the RF power increase obtained seen that Could. This is because, when Ar: H ₂ = 2: 1, a relatively rough surface would be obtained because the reaction of pre-sorption of the atoms or molecules that had already been adsorbed by the more Ar ⁺ ion bombardment effect in the plasma would predominate. I think.

Therefore, the optimum condition for obtaining a smooth surface in the present invention is when maintaining a ratio of Ar: H ₂ = 1: 1, but the overall roughness showed a very low surface roughness value (1.109-2.284 nm) as in the AFM analysis. .

In addition, when the surface morphology and the cross-section were compared in the SEM photographs of the organic polymer thin films obtained under Ar: H ₂ = 2: 1 and 1: 1 conditions, a smoother surface was obtained when Ar: H ₂ = 1: 1 condition. In addition to being obtained, it was found that the interface between the plasma polymer and the silicon wafer was very sharp and crack-free.

The most optimal condition was 20 minutes, RF 200 W, 0.3 Torr, 100 ° C., and a film having a thickness of about 3 μm was obtained, but the present invention is not limited to these. Therefore, the main characteristics of the plasma organic thin films obtained in this study show that there is an advantage that a uniform thin film in the depth direction of the substrate can be obtained by the sharp interlayer interface and excellent adhesion, and thus the stress reduction. .

Test Example 3

The composition, crystallinity, and surface properties of the formed organic polymer thin film similar to those used in Test Examples 1 and 2 were further evaluated by known methods, such as XPS, TEM, TED, AFM, contact angle, FT-IR analysis, and the like. . The optical properties of the thin films were evaluated by UV-Vis and PL spectra analysis, and the leakage current and dielectric constants were measured by I-V measurement and C-V measurement. The result is as follows.

The FT-IR analysis confirmed that some heterocycles were retained and some were broken up by particle bombardment and ion bombardment effects in the plasma generated by RF power, resulting in a new form.

UV-Vis analysis showed excellent crosslinking density and optical transmission characteristics of the plasma polymerized thin film according to the deposition conditions.

Photoluminescence spectra analysis using UV-Vis data confirmed the possibility of applying the thin film as a polymer light-emitting diode.

X-ray photoelectron spectroscopy (XPS) showed that the oxygen on the surface of the thin film is due to exposure to air, but not inside the thin film, thus forming a very dense thin film.

As a result of analyzing the composition ratio of the thin film components, it could be predicted that not only the hetero ring but also the ring was broken and thin films having different compositions exist together to form a polymer.

In the experiment up to 100 W, the deposition rate increased with increasing RF power, and the deposition rate decreased with the temperature change above 100 ℃.

Also, in order to see the temperature dependence of the deposition rate, the Arennius plot shows that a thin film is formed on the surface as the reaction rate predominantly occurs in the temperature region below 100 ° C, and the activation energy of the thin film deposition in this region is 1.3 kJ / On the other hand, the activation energy of the thin film deposition was calculated as -6.9 kJ / mol in the temperature range above 100 ℃, and the diffusion rate governing reaction in the thin film deposition was predominant, so it was desorbed from the surface to the gas phase. This could be expected to happen.

The analysis of leakage current characteristics at Ar: H ₂ = 1: 1 and 2: 1 showed the opposite result depending on the gas flow rate. For example, Ar: H ₂ = 2: 1, RF power 100 Excellent insulation properties were given at W, and the current density value was about 10 ⁻¹¹ A / cm ² , showing excellent insulation properties [see FIG. 3].

According to the C-V (Capacitance-Voltage) analysis, the width of the hysteresis showed that the insulator-semiconductor interface characteristics were excellent.

Dielectric constants for the two structures (MIM, MIS) were calculated using the capacitance of the carrier and the thickness of the thin film at 1 MHz, measured using an impedance analyzer, from about 1.6 to 4 Low values of At this time, although the dielectric constant value of the MIM structure is larger than that of the MIS structure, both structures have shown applicability to interlayer insulators and passivation layer materials. [Reference, FIGS. 2A and 2B]

As a result of analyzing the change of chemical properties of the plasma polymerized film surface by measuring the contact angle, it was confirmed that the surface properties were changed according to the deposition temperature and the RF power change, and the surface energy was calculated by comparing the surface properties under each condition. The value of -48.86 dyne / cm was obtained.

According to the method of the present invention, firstly, the economic benefit can be obtained by using inexpensive liquid thiophene (C ₄ H ₄ S), and second, using a plasma assisted chemical vapor deposition process and low dielectric constant even with short deposition time. Thin films having a constant (k <3) and high thermal stability and low leakage current characteristics (<10 ⁻⁸ A / cm ² ) can be obtained at high speed (up to 110 nm / min). Therefore, when applied to an insulating material applied to a semiconductor device, it is possible to more economically produce a low-k dielectric material having better physical properties than other materials currently used, and to shorten the process time, thereby achieving a great economic effect. .

Claims (8)

A method for producing an organic polymer thin film, comprising: plasma assisted chemical vapor deposition of thiophene or a derivative thereof on a substrate while supplying a gas having a mixing ratio of argon and hydrogen of 1: 1 to 2: 1. The method of claim 1, wherein the plasma assisted chemical vapor deposition is performed by supplying a radio frequency (RF) power (30 to 300 W) having a frequency of 13.56 MHz to the stage on which the substrate is placed. Manufacturing method. The method of claim 1, wherein the plasma assisted chemical vapor deposition is performed at an RF power of 30 to 300 W at a temperature of room temperature to 500 ° C. 2. The method for producing an organic polymer thin film according to claim 1, wherein Si single crystal or wafer, glass, SUS substrate, aluminum, SKD 11, ITO glass, or the like is used as the substrate. The method of claim 1, wherein the plasma assisted chemical vapor deposition is performed by supplying argon and hydrogen at 1: 1 to 2: 1 at a process pressure of 1x10 ^-1 to 5x10 ^-1 Torr. Method for producing an organic polymer thin film. The method of claim 1, wherein the plasma assisted chemical vapor deposition is performed using a hot-wall heating method. The method of claim 1, wherein the substrate is pretreated with argon plasma to increase the adhesion between the substrate and the organic polymer film. An organic polymer thin film formed by plasma assisted chemical vapor deposition from thiophene or a derivative thereof according to the method according to any one of claims 1 to 7.