CN1386043A - Deposition method of copper interconnection seed layer for integrated circuit - Google Patents

Abstract

A method for depositing a copper interconnect seed layer of an integrated circuit is disclosed, which comprises depositing a thin metal layer in a trench or a hole by displacement plating, and performing an electroplating or electroless plating process through a solution containing an additive to deposit a conductor therein, thereby forming a metal wire structure of an interconnect or an external circuit. Overcomes the defects of higher cost of the traditional physical or chemical deposition and the effect of wiring with submicron-sized circuits in the integrated circuit chip.

Description

Deposition method of copper interconnection seed layer for integrated circuit

The invention relates to a deposition method of a wiring seed layer in an integrated circuit copper. That is to say, through the catalysis of the replacement solution, the replacement plating is directly performed on the barrier layer to deposit a metal layer to replace the original copper seed layer. Copper electroplating is performed after displacement plating to manufacture sub-micron copper interconnect structures.

In order to cooperate with integrated circuits with smaller volume and higher performance, the fabrication of interconnection lines must be able to meet the requirements of sub-micron depth. However, due to properties such as resistance and electromigration resistance, the aluminum metal used in the traditional manufacturing process no longer has absolute advantages. In contrast, copper metal has the advantages of low resistance, high melting point, and better electromigration resistance. The shortcomings of the original dry etching process and the problem of diffusion to the oxide layer have also been overcome by the development of damascene technology and It can be said that it has been regarded as the best material for the next generation of IC interconnection.

At present, the copper metal deposition process is a very important process in the integrated circuit or printed circuit board industry, especially on fine lines with high aspect ratio. Nowadays, in the research on the technology of using copper as interconnection in integrated circuits, the following methods are roughly used to deposit copper metal: sputtering, physical vapor deposition, chemical vapor deposition or electrochemical deposition.

Among them, physical vapor deposition has reached a difficult point on the problem of opening encapsulation. Chemical vapor deposition produces non-volatile CuCl ₂ solids in the copper process, which cannot form vapor under the production temperature environment, which has become an urgent problem to be overcome. The replacement of aluminum lines by highly conductive copper lines must therefore be performed in other ways.

The copper layer is deposited by electroplating. US Pat. No. 5,256,274 discloses that the plating solution contains copper sulfate pentahydrate at 12 oz/gallon of water, 10% concentrated sulfuric acid, 50 ppm of chloride ions and 0.4% of additives. After more than ten years of research and development, IBM also officially announced at the end of 1997 that it had successfully completed copper circuits below 0.25 μm on IC chips by electrochemical deposition. So far, the advantages of copper metal plating have been recognized by the semiconductor industry.

Before depositing the copper layer by electroplating, a diffusion barrier layer and a copper seed layer film must be deposited on the silicon wafer by sputtering or chemical vapor deposition. Currently, the material of the diffusion barrier layer is mostly titanium nitride (TiN) or tantalum nitride (TaN), the purpose of which is mainly to prevent the diffusion between the copper metal and the dielectric layer silicon dioxide. The copper seed layer is used for conducting electricity during electroplating.

In the academic research on the replacement reaction, in 1997 Yosi Shacham-Diamand et al. (THEELECTROCHEMCIAL SOCIETY 144 P.898-908, 1997) proposed a formula for wet activation of the titanium nitride surface with a solution to produce a Cu layer as an electroplating Or an electroless seed layer, so that expensive PVD or CVD methods can be used to prepare the seed layer. In terms of industrial research, American International Business Machines Corporation proposed a method of activating the surface of titanium nitride with a solution containing hydrofluoric acid and copper sulfate, so that it can be replaced and plated with a copper seed layer. This method is described in detail in Chinese Patent Application No. 86119270.

Utilizing the method of displacement plating to deposit a layer of metal layer on the surface of the barrier layer material, US Patent No. 4574095 discloses that the catalytic reaction is catalyzed by light irradiation, and palladium metal is deposited on the silicon substrate, and then the subsequent The electroless plating process deposits copper metal.

Wong also disclosed in U.S. Patent No. 5,358,907 that by means of displacement plating, metals of various groups such as IB, IIB, IIIA, IVB, VB, VIB, VIIB, or VIIIB can be deposited on silicon substrates or silicon-containing compounds. above, its replacement fluid formula contains hydrofluoric acid (HF).

Valery M.Dubin et al. disclosed in U.S. Patent No. 5891513 that the method of displacement plating can be used on integrated circuits. The solution of ions and 0.01-10 mg/l surfactant can deposit a copper seed layer on the titanium nitride substrate, and then apply electroless plating to increase the thickness of the copper layer.

As we all know, electroplating is a kind of electrochemical deposition method. Its principle is to apply an external voltage to form a cathode and an anode, and generate individual electrochemical half-reactions. Among them, the oxidation reaction occurs at the anode, while the reduction reaction occurs at the cathode, that is, the ions in the solution are reduced to atomic state and plated on the surface of the plate. The current method is to apply this principle to make copper interconnects to connect the components of various parts of the integrated circuit. The traditional electroplating manufacturing procedure is shown in Figure 1-Figure 7.

In FIG. 1 , 1 is the initial substrate, that is, the silicon wafer itself. 2 and 4 are silicon nitride layers, that is, silicon nitride (SiN), and 3 is a dielectric layer produced after a heat treatment process, that is, silicon oxide, that is, silicon dioxide.

8 in FIG. 2 is a photomask designed to meet the needs of the layout of the entire integrated circuit, and the photoresist coated on the surface of the substrate.

FIG. 3 is the pattern obtained after the lithographic etching process. It can be found that part of the dielectric layer and the nitride layer are removed, and finally the photoresist 8 is removed.

In Fig. 4, a layer of diffusion barrier layer material 5 is deposited on the dielectric layer 4, such as titanium nitride (TiN), tantalum nitride (TaN) or tantalum (Ta), its function is to prevent the copper layer from Diffusion into the dielectric layer 4 during the heat treatment process affects the transmission of the interconnection.

In FIG. 5 , a copper seed layer 6 is plated by physical vapor deposition (PVD) or chemical vapor deposition (CVD), as a conductive layer required for subsequent electroplating.

In FIG. 6 , the deposited copper seed layer is used to conduct electricity, and the copper layer is filled in the trench or hole by electroplating, and 7 is the copper metal layer plated by this method.

FIG. 7 shows that the base material undergoes the final planarization and chemical mechanical polishing procedures, and the material protruding from the surface layer is polished flat.

By repeating the above-mentioned steps in FIGS. 1-7 , a multi-layer copper interconnection structure can be manufactured. The main disadvantages of the above method are:

Since the copper seed layer is deposited by physical or chemical vapor deposition for electrical conduction, expensive vacuum equipment must be spent, the procedure is relatively complicated, and the manufacturing cost is relatively high.

The main purpose of the present invention is to provide a method for depositing a seed layer of an integrated circuit copper interconnection, by depositing a thin metal layer in a groove or hole that has undergone a lithography process by means of displacement plating, through a solution containing additives. Electroplating or electroless plating process, to deposit conductors in it, form the metal wire structure of internal wiring or external wiring, overcome the disadvantages of the existing technology, and achieve low-cost manufacturing and sub-micron-sized wiring in integrated circuit chips Purpose.

The second object of the present invention is to provide a method for depositing a copper interconnection seed layer of an integrated circuit, through the method of manufacturing an interconnection structure on an integrated circuit, including depositing and forming an insulating dielectric layer on a silicon wafer substrate , and define and form lines or through holes by lithography, and after depositing the barrier layer material, the substrate is immersed in the activation solution for displacement plating to deposit a thin metal layer on the surface of the barrier layer, which contains a surfactant The solution is electrochemically deposited with conductors therein to form interconnection lines, and finally planarization or chemical mechanical polishing processes can be used to form interconnected metal wire structures.

The third object of the present invention is to provide a method for depositing a copper interconnect seed layer of an integrated circuit, by activating the substrate through a solution and depositing a layer of metal layer by displacement plating, as required for subsequent electroplating procedures The conductive layer does not need to be deposited by physical or chemical vapor deposition as a copper seed layer for conductive purposes, so as to achieve the purpose of reducing the manufacturing cost of integrated circuits and saving expensive expenses on vacuum equipment.

The fourth object of the present invention is to provide a method for depositing a copper interconnection seed layer of an integrated circuit. By uniformly filling the copper layer of the sub-micron circuit, the aspect ratio of the hole is greater than 1, and the width of the hole or circuit is less than 1. Purposes as small as 0.2 μm or less.

The object of the present invention is achieved like this: a kind of deposition method of the copper interconnection seed layer of integrated circuit, the seed layer on this deposition is as the conductive layer needed when filling the microhole with electroplating, it is characterized in that: it Including the following steps:

(1) First equip the device to change the plating solution, which includes palladium ion compound 0.2-20g/l, halogen ion compound 0.6-60g/l, inorganic acid 0.09-9g/l and/or surfactant 10-1000ppm;

(2) Dip the substrate on which the barrier layer material has been deposited into a displacement bath for 1-20 minutes, the pH of the displacement bath is between 1-7.0, and the temperature is between 20-70°C.

The palladium ion compound is palladium halide, palladium nitrate, palladium sulfate, palladium perchlorate or palladium acetate. The palladium halide is palladium chloride, palladium bromide or palladium iodide. The halide ion compound is a compound containing fluoride ion, chloride ion, bromide ion or iodide ion, which is derived from hydrogen halide or its ionic compound combined with a group IA or IIA metal ion. The inorganic acid is nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid or hydroiodic acid or perchloric acid. The surfactant is a copolymer of polyethylene glycol, polypropylene glycol or ethylene glycol/propylene glycol. The barrier layer is tantalum nitride or titanium nitride.

A method for depositing an integrated circuit copper interconnecting seed layer, the deposited seed layer is used as a conductive layer required for electroplating to fill micropores, and it is characterized in that: it comprises the following steps:

(1) first equip the device to change the plating solution, which includes silver ion compound 0.2-20g/l, halogen ion compound 0.6-60g/l, inorganic acid 0.09-9g/l and surfactant 10-1000ppm;

(2) Dip the substrate on which the barrier layer material has been deposited into a displacement bath for 1-20 minutes, the pH of the displacement bath is between 1-7.0, and the temperature is between 20-70°C.

The silver ion compound is silver nitrate or silver perchlorate.

Further description will be given below in conjunction with preferred embodiments and accompanying drawings.

FIG. 1 is a schematic diagram of oxide and dielectric layers deposited on a conventional silicon wafer.

FIG. 2 is a schematic diagram of the conventional structure after photoresisting.

FIG. 3 is a schematic diagram of a conventional structure after a lithography process.

FIG. 4 is a schematic diagram of a wafer structure after conventionally depositing an upper barrier layer.

FIG. 5 is a schematic diagram of the structure after conventional deposition of a copper seed layer.

FIG. 6 is a schematic diagram of conventional holes filled with copper metal on the wafer surface.

FIG. 7 is a schematic diagram of a conventional planarized structure.

FIG. 8 is a schematic diagram of depositing a palladium metal layer to replace a copper seed layer in the present invention.

Fig. 9 is an electron microscope image of a layer of palladium metal deposited on a planar tantalum nitride substrate according to the present invention.

Fig. 10 is an electron microscope image of a layer of palladium metal deposited on a planar titanium nitride substrate according to the present invention.

FIG. 11 is an electron microscope image of silver metal deposited on the surface of titanium nitride according to the present invention.

FIG. 12 is an electron microscope image of the direct deposition of copper layer on the surface of palladium/tantalum nitride/silicon substrate according to the present invention.

Fig. 13 is an electron microscope image of micropores refilled by adding a surfactant in the present invention.

Referring to FIG. 8-FIG. 13, FIG. 8 is a step proposed in the present invention to replace the step of depositing the upper seed layer with vacuum equipment in FIG. 5. The present invention proposes a wet activation formula for activating the barrier layer material 5 deposited on FIG. 4 tantalum nitride or titanium nitride, and make it undergo substitution reaction with metal ions in the solution. The composition of the formula is palladium ion compound 0.2-20g/l, halogen ion compound 0.6-60g/l, inorganic acid 0.9-9g/l and surfactant 10-1000ppm, for example: palladium chloride is 1.77g/l, hydrogen fluoride Ammonium (NH ₄ F·HF) was 5.7 g/l and nitric acid was 0.63 g/l. The method is to immerse the substrate on which the barrier layer material has been deposited in a displacement bath for 5 minutes. The pH of the displacement bath is about 4.5 and the temperature is 40°C. Palladium chloride in the formula is used to provide the ion source of palladium metal, while ammonium bifluoride is the key to drive this reaction. In fact, ammonium bifluoride itself is a buffer solution of hydrogen fluoride. In addition, since the solubility of palladium chloride in aqueous solution is not high, nitric acid can be used to increase the solubility of palladium chloride and adjust the pH value of the solution.

In the invention, the displacement plating can be performed not only on silicon substrates, various silicides or titanium nitride substrates, but also on tantalum nitride substrates. As for the barrier layer material of copper wire, the reliability and chemical stability of tantalum nitride are better than that of columnar structure titanium nitride. This point contributes to the industrial applicability of the present invention.

FIG. 9 shows that a layer of dense palladium metal is deposited on the surface of a planar tantalum nitride substrate by means of displacement plating of palladium ions.

In the present invention, in the composition of the displacement plating solution, copper ions are not the only ones that can react with the titanium nitride substrate. For example, palladium metal and silver metal can be deposited on the surface of the titanium nitride substrate through displacement plating, and As a conductive layer required for the subsequent electroplating process.

Figure 11 shows that silver metal is deposited on the surface of a flat titanium nitride substrate through displacement plating. The composition of the formula is: silver ion compound 0.2-20g/l, halogen ion compound 0.6-60g/l, inorganic acid 0.9-9g /l and surfactant 10-1000ppm.

Furthermore, in the present invention, in the solution composition of displacement plating, it is not necessary to use hydrofluoric acid with strong toxicity, but ammonium bifluoride, i.e. a buffer solution of hydrofluoric acid can be used instead; even other halogen ions can be used To replace hydrofluoric acid to drive the displacement reaction between metal ions and the substrate.

FIG. 10 shows that palladium metal is catalyzed by potassium iodide to cause a displacement reaction and deposit on the surface of the titanium nitride substrate.

The inventor thinks that the barrier layer material can react with metal ions in the solution, mainly due to the participation of halogen ions in the reaction, and its total reaction can be generally divided into two half reactions, wherein the oxidation reaction is the barrier layer material (such as nitriding Tantalum or titanium nitride) and halogen ions generate a complex (complex) and release electrons. The possible form of the complex is the complex ion of titanium hexahalide (TiX ₆ ^-2 or tantalum hexahalide (TaX ₆ ^-2 ) In addition, the released electrons are received by the metal ions in the solution, so that the metal ions are reduced to metal atoms and deposited on the substrate. These metal ions include copper ions, silver ions and palladium ions, all of which are Elements with high reduction potential, that is, such metal ions are extremely prone to redox reactions and are reduced to atomic states. This can explain why tantalum nitride and titanium nitride with high chemical stability can be replaced by displacement plating. , depositing metal ions.

After the displacement plating is applied on the barrier layer material, the copper plating layer can be deposited and thickened by electrochemical means, such as electroplating or electroless plating. Here, the inventor chooses an electroplating method commonly used in industry to fill holes. The basic formula of the electroplating solution is: 75g/l anhydrous copper sulfate, 92g/l sulfuric acid and 200ppm chloride ions.

FIG. 12 shows that after the displacement plating process, the copper plating layer is directly deposited on the surface of the palladium/tantalum nitride/silicon substrate by the electroplating process.

However, the wettability of the plating solution is also very important because the pore size to be filled is extremely small, only about 1.0 micron or less. Therefore, surfactants must be added to the replacement plating solution and electroplating solution.

In terms of additives, US Patent No. 4110176 discloses a polyalkanol quaternary ammonium salt formed from a reaction product, which can deposit a bright, low-stress and ductile copper layer from an acidic copper plating solution. And U.S. Patent No. 4,975,159 organizes and lists many kinds of additives. It includes three categories such as lactams through alkyl oxidation, sulfides with water-solubilizing groups and organic compounds. The present invention selects polyvinyl alcohol as the additive in the displacement plating and electroplating solution, and its effect is completely different from that of the traditional technology.

Figure 13 is a schematic cross-sectional view of the micropores filled by electroplating after adding surfactant polyvinyl alcohol (PEG 5000) to the displacement plating solution.

In terms of the electroplating system, the present invention takes the device of R.J.Contolinii as a reference, and the electroplating system is divided into three parts: electroplating main tank, circulation filter system and automatic control system. Among them, the electroplating main tank is designed in a cylindrical shape. The tank body is divided into inner, middle and outer layers. The inner layer is the area where the solution is electroplated. The tank body is a hollow with a diameter of 10 cm and a height of 7.5 cm without a cover. The cylinder has a wall thickness of about 5 mm. The bottom of the tank has a vertical tank bottom, an opening of 1 cm, and a fixed glass tube with a height of 5 mm connected to the external pipeline, pump body and flowmeter. Entering the entrance of the inner tank, the plating solution directly flushes the cathode in this way, which is a jet flow design to enhance the mass transfer effect of metal ions. The middle tank body is mainly the overflow area and the filter channel, the bottom of the tank is an extension of the bottom of the inner tank, and the height of the tank wall is 11 cm. The outer tank is a closed design with a volume of about 1.8 liters, covering the inner and middle tanks. There are two openings on the tank wall, the lower one and the higher one, both with a diameter of 8 mm, which are the input and output ports of the water flow in the constant temperature tank respectively. Through the circulation of the constant temperature water flow, the constant temperature of the plating solution can be maintained, so that the electroplating work can be operated at a constant temperature.

The design of the entire electroplating tank provides cathode and anode electroplating devices, and various sensors such as reference electrodes, thermometers, pH meters, etc. can be added, and the temperature is controlled through a constant temperature bath, plus jet stirring that can control the flow rate Design, so that most of the work can be carried out in the electroplating tank without having to have an auxiliary tank. The volume of the plating solution in the plating tank is about 1 liter. The cylindrical tank design and the upper and lower cathode and anode arrangements roughly resemble A symmetrical geometric shape aims to make the distribution of the electric field and the flow field in the plating tank relatively symmetrical, and the operating conditions of the experiment are relatively simple.

Before the plating solution enters the plating tank, it is first treated with activated carbon to remove organic impurities, and then filtered with 10μ, 5μ, and 1μ filters respectively. There is a circulating filtration system in the electroplating process, which is mainly composed of a pump body and two filters. The filter cores can filter 1μ and 0.2μ respectively, and the filtration rate is 1.5L/min to remove tiny particles in the plating solution. The automatic control system consists of a potentiostat and a host computer with Autolab software. The 362-type potentiostat produced by EG&G can supply a stable current to the plating tank, and it can be monitored and read by the automatic experiment (Autolab) software at any time.

Through experiment, the formula composition of displacement plating of the present invention comprises following preferred formula:

1. Palladium chloride 10g/l, sodium chloride 30g/l, nitric acid 4.5g/l and polyethylene glycol 400ppm.

2. Silver nitrate 12g/l, sodium chloride 35g/l, nitric acid 5.0g/l and polyethylene glycol 500ppm.

3. Silver nitrate 15g/l, sodium chloride 40g/l, nitric acid 6.0g/l and polyethylene glycol/propylene glycol 600ppm.

Claims (12)

1, a kind of deposition process of IC copper inner conductive wire inculating crystal layer, the crystal seed layer on this deposition is as conductive layer required when electroplate filling micropore, and it is characterized in that: it comprises the steps:

(1) equipped earlier displacement plating bath, it comprises palladium ion compound 0.2-20g/l, halide ion compound 0.6-60g/l, inorganic acid 0.09-9g/l and/or interfacial agent 10-1000ppm;

(2) base material that will deposit barrier layer materials soaks and placed among the displacement plating bath 1-20 minute, and pH value of this displacement plating bath is between 1-7.0, and temperature is between 20-70 ℃.

2, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 1 is characterized in that: this palladium ion compound is halogenation palladium, palladium nitrate, palladium sulfate, crosses chloric acid palladium or palladium.

3, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 2 is characterized in that: this halogenation palladium is palladium bichloride, palladium bromide or palladium iodide.

4, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 1, it is characterized in that: this halide ion compound is the compound that contains fluorine ion, chloride ion, bromide ion or iodide ion, and it derives from hydrogen halides or its ionic compound that combines with IA or IIA family metal ion.

5, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 1 is characterized in that: this inorganic acid is nitric acid, sulfuric acid, hydrofluoric acid, hydrochloric acid, hydrobromic acid or hydroiodic acid or crosses chloric acid.

6, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 1 is characterized in that: this interfacial agent is the copolymer of polyethylene glycol, polypropylene glycol or ethylene glycol/propylene glycol.

7, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 1 is characterized in that: this barrier layer is tantalum nitride or titanium nitride.

8, a kind of deposition process of IC copper inner conductive wire inculating crystal layer, the crystal seed layer on this deposition is as conductive layer required when electroplate filling micropore, and it is characterized in that: it comprises the steps:

(1) equipped earlier displacement plating bath, it comprises silver iron compound 0.2-20g/l, halide ion compound 0.6-60g/l, inorganic acid 0.09-9g/l and interfacial agent 10-1000ppm;

(2) base material that will deposit barrier layer materials soaks and placed among the displacement plating bath 1-20 minute, and pH value of this displacement plating bath is between 1-7.0, and temperature is between 20-70 ℃.

9, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 8 is characterized in that: this silver iron compound is silver nitrate or crosses silver chlorate.

10, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 8, it is characterized in that: this halide ion compound is the compound that contains fluorine ion, chloride ion, bromide ion or iodide ion, and it derives from hydrogen halides or its ionic compound that combines with IA or IIA family metal ion.

11, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 8 is characterized in that: this inorganic acid is nitric acid or crosses chloric acid.

12, the deposition process of IC copper inner conductive wire inculating crystal layer as claimed in claim 8 is characterized in that: this interfacial agent is the copolymer of polyethylene glycol, polypropylene glycol or ethylene glycol/propylene glycol.

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