CN104008997A - Ultra-low dielectric constant insulating film and manufacturing method thereof - Google Patents

Abstract

The invention discloses an ultra-low dielectric constant insulating film and a preparation method thereof. The method comprises: Step 1. Depositing a film by using plasma-enhanced chemical vapor deposition technology: MTES and LIMO are used as reaction sources, and helium is introduced as a carrier gas Into the chemical vapor deposition reaction chamber, deposit and form an insulating layer of 50-100nm, the flow ratio of MTES and LIMO=1:1~1:2.5; Step 2. Use Ar plasma to treat the surface of the insulating layer in situ to form a dense Step 3. Repeat the above steps 1 and 2 to obtain an insulating film with a target thickness; Step 4. Perform high-temperature annealing on the insulating film to form an ultra-low dielectric constant insulating film. The invention innovatively adopts the method of alternating plasma enhanced chemical vapor deposition insulating film and post-plasma treatment, the process is simple, the deposition rate is fast, the formed film has good moisture absorption resistance, is compatible with the integration process, and the film forming quality Well, it can fully meet the requirements of advanced integrated circuits for the electrical properties, mechanical properties and insulation properties of low dielectric constant materials.

Description

A kind of ultra-low dielectric constant insulating film and preparation method thereof

technical field

The invention belongs to the technical field of ultra-large-scale integrated circuit (ULSI) interconnection, in particular to a preparation method for filling a low dielectric constant insulating film between interconnection metal layers. the

Background technique

As device dimensions continue to shrink into the deep sub-micron, multilayer interconnect structures are required to minimize delays due to parasitic resistance (R) and capacitance (C). Due to the increased RC delay, the gain in device speed obtained at the gate is offset by the propagation delay between the metal interconnect lines; see Liu Ming, Liu Yuling, Liu Bo et al. "Low-k Dielectric and Copper Interconnect Integrated Process ".[J]. "Micro-Nano Electronics Technology", 2006, 10(6): 464-469. In order to reduce the RC constant in ULSI circuits, the interconnection material is required to have low resistivity and low capacitance between film layers. As we all know, ,in is the dielectric constant, A is the area, d is the thickness of the dielectric film, and the dielectric length Equal to the product of k and ε ₀ , ε ₀ is the permittivity of vacuum, and k is the relative permittivity. Considering the low capacitance case, it is not easy to reduce the parasitic capacitance by increasing the film thickness of the dielectric layer (causing more difficult gap filling) or reducing the thickness and area of the wire (causing increased resistance). Therefore, this requires the material to have a lower dielectric constant, thus creating a demand for low dielectric constant materials.

The continuous development of ultra-large-scale integrated circuits requires the use of materials with lower dielectric constants, that is, dielectric films with k<2.6. However, the dielectric constant of materials is mainly related to the total polarizability of materials and the density of materials. At present, ultra-low dielectric constants have been obtained. The constant material is mainly realized by introducing pores (dielectric constant is approximately equal to 1) in the dielectric matrix, mainly because the introduction of pores can effectively reduce the density of the material itself. According to domestic and foreign literature (for example, Miller R.D. Miller R.D. etc. In search of low-k dielectrics. Research on low-k dielectric constant [J]. "Science Science", 1999, 286 (5439): 421-423) And Chinese patents (Ding Shijin et al., "A porous ultra-low dielectric constant material film and its preparation method", publication number CN 101789418 A) report that the pores in the porous film material are usually added with a template in the precursor, and then pass The heat treatment method removes the templating agent, thereby obtaining a porous film material. For example, Shen et al. used tetraethyl orthosilicate (TEOS) as the silicon source, cetyltrimethylammonium bromide (CTAB) as the template agent, and prepared porous films by sol-gel method under acidic conditions. Materials with a pore size of 4nm and a dielectric constant of 2.5 (reference J. Shen, A. Luo, L. F. Yao, et al. Low dielectric constant silica films with ordered nanoporous structure [J]. Materials science and Engineering, 2007 , 27(5-8):1145-1148). However, the preparation method of the low dielectric constant film mentioned in the above-mentioned patent "a porous ultra-low dielectric constant material film and its preparation method" is spin-coating (spin-coating) film formation, and the films prepared by the spin-coating method mostly exist The quality of the film is poor, the thickness is not uniform, etc. Therefore, the modern large-scale integrated circuit technology basically does not use the spin coating method to prepare the film, but uses the plasma enhanced chemical vapor deposition (plasma enhanced chemical vapor deposition) mentioned in the present invention. PECVD) method. Compared with the spin coating method, the use of PECVD technology to prepare low dielectric constant films has good uniformity and repeatability, and can form large-area films with excellent step coverage. In addition, the composition and thickness of the film are easy to control, and have a wide application range, simple equipment, easy industrialization, high efficiency and low cost. the

Since Grill et al first reported in 2001 that PECVD technology prepared porous thin film materials with low dielectric constant, related literature reports have appeared in the world, as shown in Table 1:

Table 1. Preparation of low dielectric constant porous thin film materials by PECVD method

 

Reference 5: R. Navamathavan, C. K. Choi. Plasma enhanced chemical vapor deposition of low dielectric constant SiOC(-H) films using MTES/O ₂ precursor [J], Thin Solid Films, 2007, 515(12): 5040-5044 .

Reference 6: Grill Alfred. Plasma enhanced chemical vapor deposited SiCOH dielectrics: from low-k to extreme low-k interconnect materials [J], Journal of Applied Physics, 2003, 93(3): 1785-1790.

Reference 7: S.-K. Kwak, K.-H. Jeong, S.-W. Rhee et al., Nanocomposite Low-k SiCOH Films by Direct PECVD Using Vinyltrimethylsilane [J]. Journal of the Electrochemical Society, 2004 , 151(2): F11-F16.

As shown in Table 1, literatures 5 and 7 reported using MTES+O ₂ and VTMS+O ₂ as precursors, and deposited films by PECVD at different temperatures. The final annealing temperatures were 500°C and 450°C, respectively. However, Such a high annealing temperature condition cannot meet the thermal stability requirements (≤420°C) for low dielectric constant materials in the usual integrated circuit back-end process. Document 6 uses heat treatment to remove the porogen to obtain a thin film material with a dielectric constant of 2.05, but the mechanical properties are not ideal, and it is difficult to meet the requirements of the technology industry for thin film materials. The present invention utilizes the novel mixed precursor of MTES and LIMO, innovatively adopts the method of alternating PECVD insulating film and post-plasma treatment, that is, the step of insulating layer deposition and the step of dense layer formation are carried out alternately, and the formed film has anti-moisture absorption Strong resistance, good mechanical properties, low film annealing temperature, and compatibility with integrated processes.

Contents of the invention

The purpose of the present invention is to provide a method for preparing an ultra-low dielectric constant insulating film. The insulating film prepared by the method has ideal electrical and mechanical properties and can be used in the technical field of very large scale integrated circuit interconnection. the

In order to achieve the above object, the invention provides a kind of preparation method of ultra-low dielectric constant insulating film, and this method comprises following concrete steps:

Step 1, using plasma-enhanced chemical vapor deposition technology to deposit thin films: methyltriethoxysilane and limonene are used as reaction sources, and both methyltriethoxysilane and limonene are introduced into the chemical vapor phase with helium as the carrier gas In the deposition reaction chamber, an insulating layer of 50-100 nm is deposited and formed, wherein the flow ratio of methyltriethoxysilane to limonene is 1:1~1:2.5, and the flow rate is measured in grams/minute;

Step 2, use Ar or He plasma in the above cavity to treat the surface of the insulating layer in situ for 1-5 minutes to form a dense modified layer, which is used to prevent water molecules from top to bottom in the entire insulating layer. Diffusion under the environment, thereby reducing the adsorption of water to the pores in the above insulating layer, and curbing the increase in the dielectric constant caused by water absorption;

Step 3, repeating the above steps 1 and 2 until the target thickness of the insulating film is reached to obtain the insulating film;

Step 4, in an inert atmosphere, perform high-temperature annealing on the insulating film obtained in step 3 to remove the hydrocarbon groups (the hydrocarbon groups include the hydrocarbon groups in the precursor and the hydrocarbon groups in limonene) , thus forming an ultra-low dielectric constant insulating film with a porous structure.

The above method, wherein the radio frequency frequency used in the deposition process in step 1 is 13.56 MHz, the initial vacuum in the reaction chamber is 0.018-0.02 Torr, the substrate temperature when depositing the insulating layer is 100-400 ° C, and the power is 200 -600 watts, the working pressure is 2-5 Torr (1 Torr = 133.322Pa), the MTES flow into the reaction chamber is 1.0-2.0 g/min, the LIMO flow is 1.0-3.5 g/min, and the He carrier gas flow is 500 - 5000 sccm. the

The above method, wherein, in step 2, the power of Ar or He plasma surface treatment is 300-600 watts, the treatment time is 1-5 minutes, and the air pressure is 2-8 Torr. the

The above method, wherein, in step 4, the annealing temperature is 200-420° C., the pressure in the annealing furnace is 0.2-0.3 Torr, the annealing time is 2-6 hours, and the annealing atmosphere is argon or nitrogen. Preferably, in the above annealing process, the annealing temperature is raised from room temperature to the annealing temperature within 5-30 minutes. the

The above method, wherein the vaporization temperatures of the methyltriethoxysilane and limonene before being introduced into the reaction chamber are 50-60°C and 60-100°C, respectively. the

The present invention also provides an ultra-low dielectric constant insulating film prepared by the above-mentioned method, wherein the insulating film comprises: several insulating layers; each insulating layer is provided with a modification layer, and inside the insulating layer is a Several pores; the dielectric constant of the ultra-low dielectric constant insulating film is 2.2-2.4, and the leakage current density at 1MV/cm is 10 ^-9 -10 ^-8 A/cm ² ; Young's modulus is 4.2-17GPa, The hardness is 0.5-1.3GPa.

The preparation method of the ultra-low dielectric constant insulating film provided by the present invention is to use MTES and LIMO as the reaction source respectively, introduce the reaction chamber under the carrier gas of He, adopt the plasma enhanced chemical vapor deposition technology to deposit and form the insulating layer, and then Use argon (Ar) or helium (He) plasma to in-situ treat the surface of the insulating layer to form a dense modified layer, repeat the above process until the film with the required thickness is reached, and finally place the film at high temperature for annealing. Hydrocarbon groups are removed to form ultra-low dielectric constant porous insulating films. the

The film provided by the present invention adopts novel reaction sources MTES and LIMO, which are simple and easy to obtain, safe to use, and the by-products do not pollute the environment. It also has excellent mechanical properties. In addition, the film also has excellent insulating properties, and the leakage current density can reach 10 ^-9 -10 ^-8 A/cm ² under an external electric field of 1MV/cm. Therefore, the ultra-low dielectric constant insulating film prepared by the invention can fully meet the requirements of advanced integrated circuits on the electrical properties, mechanical properties and insulating properties of low dielectric constant materials.

In addition, the thin film preparation method provided by the present invention innovatively adopts alternate plasma enhanced chemical vapor deposition, and the formed thin film has good moisture absorption resistance, good mechanical properties, and is compatible with the integration process. Not only the process is simple, but the deposition rate Fast, and good film quality. the

Description of drawings

1a-1d are schematic diagrams of the preparation process of the ultra-low dielectric constant insulating film of the present invention. the

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. In the figure, for convenience of description, the sizes of different layers and regions are enlarged or reduced, and the sizes shown do not represent actual sizes, nor do they reflect the proportional relationship of the sizes. the

The invention adopts plasma-enhanced chemical vapor deposition technology to prepare an ultra-low dielectric constant insulating film, and uses helium (He) as a carrier gas to separate the precursor methyltriethoxysilane (C ₇ H ₁₈ O ₃ Si, MTES for short) and porogen limonene (C ₁₀ H ₁₆ , LIMO for short) are brought into the plasma-enhanced chemical vapor deposition reaction chamber to deposit and form an insulating layer. The radio frequency frequency used in the plasma-enhanced chemical vapor deposition process is 13.56MHz. The initial vacuum in the reaction chamber is 0.018-0.02 torr, the substrate temperature is 100-400°C, the deposition power is 200-600 watts, the working pressure is 2-5 torr, and the He carrier gas flow rate is 500-5000 sccm (standard-state cubic centimeter per minute). The vaporization temperatures of MTES and LIMO before being introduced into the reaction chamber are 50~60°C and 60~100°C respectively, the flow rate of MTES is 1.0-2.0g/min, the flow rate of LIMO is 1.0-3.5g/min, the ratio is 1:1 -1:2.5, the deposition thickness is 50-100 nm, forming an insulating layer 10 as shown in FIG.

In the above cavity, Ar or He plasma is used to in-situ treat the surface of the insulating layer to form a dense modified layer 20 (as shown in Figure 1b), the power is 300-600 watts, the treatment time is 1-5 minutes, and the air pressure For 2-8 Torr. The function of the modification layer 20 is to seal the outer surface of the insulating layer 10 and prevent the pores formed by annealing in the insulating layer 10 from absorbing water. the

The above two steps are repeated to achieve the target thickness of the insulating film. As shown in FIG. 1 c , an insulating film 30 in which insulating layers and modified layers are alternately arranged three times is formed. the

Place the above-mentioned target insulating film 30 in an annealing furnace under Ar or _N2 atmosphere, the pressure of the annealing furnace is 0.2-0.3 Torr, rise from room temperature to the annealing temperature within 5-30 minutes, and anneal at 200-420°C for 2-6 hours, remove the hydrocarbon groups, and form some irregular pores 13 inside the insulating layer of the insulating film (the pores 13 include some worm-like holes and some irregular circular holes), and finally obtain ultra-low dielectric constant with a porous structure. insulating film, as shown in Figure 1d.

Thin film performance measurement: In order to measure the electrical properties of the above-mentioned thin film, the present invention uses a low-resistance silicon wafer (with a resistivity of 0.001-0.02Ω·cm) as the substrate, and forms a film with a diameter of 400-420 microns on the thin film with aluminum evaporated by electron beams. The circular metal electrodes are used to form capacitors, so as to obtain a metal-insulator-semiconductor (MIS for short) capacitor structure. Capacitance is measured based on the capacitance-voltage characteristics of the above-mentioned capacitors at room temperature, and a reliable average capacitance value is obtained by multi-point testing, while considering the area of the electrode and the film thickness to determine the dielectric constant. In addition, the leakage characteristics of the film were obtained through the measurement of current-voltage. The hardness and Young's modulus of the films were obtained by nanoindentation. the

In embodiment 1-6, by changing the relative flow rate of methyltriethoxysilane and limonene, prepared 7 kinds of different thin film samples (that is, the sample numbered 1-6), table 2 has listed in different The electrical properties, mechanical properties and leakage current of the samples prepared under the condition of flow ratio. As the relative flow rate increases gradually, the dielectric constant and its mechanical properties show a trend of first decreasing and then increasing. It can be seen from Table 2 that the minimum dielectric constant of the obtained film is 2.2, and the refractive index is 1.309. In terms of mechanical properties, the hardness is 0.55GPa, and the Young's modulus is 4.23GPa, reaching the mechanical properties of porous low dielectric constant films reported in the literature. In addition, other samples also showed excellent mechanical properties. At the same time, the leakage current density is also small, showing better insulation performance. Therefore, the requirements of the next-generation integrated circuit technology for low dielectric constant thin film materials can be met. the

Attached Table 2. The deposition rate, electrical properties, mechanical properties and leakage current of the samples

Although the content of the present invention has been described in detail through the above preferred embodiments, it should be understood that the above description should not be considered as limiting the present invention. Various modifications and alterations to the present invention will become apparent to those skilled in the art upon reading the above disclosure. Therefore, the protection scope of the present invention should be defined by the appended claims.

Claims (7)

1. a preparation method of ultra-low dielectric constant insulating film, is characterized in that, the method comprises following concrete steps: Step 1, using plasma-enhanced chemical vapor deposition technology to deposit thin films: Methyltriethoxysilane (MTES) and limonene (LIMO) are used as reaction sources, and both methyltriethoxysilane and limonene are carried by helium The gas is introduced into the chemical vapor deposition reaction chamber to form an insulating layer with a thickness of 50-100nm, wherein the flow ratio of methyltriethoxysilane to limonene is 1:1~1:2.5, and the flow rate is measured in grams per minute ; Step 2, using Ar or He plasma in the above cavity to in-situ treat the surface of the insulating layer to form a dense modified layer, and the plasma treatment time is 1-5 minutes; Step 3, repeating the above steps 1 and 2 until the target thickness of the insulating film is reached to obtain the insulating film; Step 4, performing high-temperature annealing on the insulating film obtained in step 3 in an inert atmosphere to remove hydrocarbon groups therein, thereby forming an ultra-low dielectric constant insulating film with a porous structure. 2. The method according to claim 1, wherein the radio frequency used in the deposition process in step 1 is 13.56 MHz, the initial vacuum in the reaction chamber is 0.018-0.02 Torr, and the substrate temperature when depositing the insulating layer The temperature is 100-400℃, the power is 200-600W, the working pressure is 2-5 Torr, the flow rate of MTES into the reaction chamber is 1.0-2.0 g/min, the flow rate of LIMO is 1.0-3.5 g/min, and the flow rate of He carrier gas is 500 - 5000sccm. 3. The method according to claim 1, characterized in that, in step 2, the power of Ar or He plasma surface treatment is 300-600 watts, the treatment time is 1-5 minutes, and the air pressure is 2-8 Torr. 4. The method according to claim 1, wherein in step 4, the annealing process is as follows: the annealing temperature is 200-420°C, the pressure in the annealing furnace is 0.2-0.3 Torr, and the annealing time is 2-6 hours , the annealing atmosphere is argon or nitrogen. 5. The method according to claim 4, characterized in that, in the above-mentioned annealing process, the temperature is raised from room temperature to the annealing temperature within 5-30 minutes. 6. The method according to claim 1, wherein the vaporization temperatures of the methyltriethoxysilane and limonene before being introduced into the reaction chamber are 50-60°C and 60-100°C respectively. 7. An ultra-low dielectric constant insulating film prepared by the method of claim 1, characterized in that the insulating film comprises: several insulating layers (10); each insulating layer (10) is provided with There is a modified layer (20), and there are several pores (13) inside the insulating layer (10); the dielectric constant of the ultra-low dielectric constant insulating film is 2.2-2.4, and the leakage current density at 1MV/cm is 10 ^-9 -10 ^-8 A/cm ² ; Young's modulus is 4.2-17GPa, hardness is 0.5-1.3GPa.