CN1610066A - Metallization method for preparing integrated circuit copper interconnection lines by separated double-electrode acidic electroless plating - Google Patents

Abstract

The present invention relates to separated double electrode acid chemical plating process of preparing copper interconnection in integrated circuit, and belongs to the field of chemical plating application. The process adopts one silicon substrate as cathode, and one silicon substrate with coated refractory metal or its nitride on one side and the other parts coated with silver glue or organic glue to prevent corrosion in the chemical plating as anode, and the separated cathode and anode are set in acid solution to produce oxidation-reduction reaction, so as to plate one layer of copper film directly on the silicon substrate with refractory metal or its nitride. Thus produced copper film has homogeneous and fine particles, powerful combination with substrate, preferable (1, 1, 1) crystal particle orientation, and no cuprous oxide. The process may be used to replace alkaline and single electrode acid chemical copper plating process.

Description

Metallization method for preparing integrated circuit copper interconnection lines by separated double-electrode acidic electroless plating

technical field

The invention belongs to the application field of electroless plating, and in particular relates to a novel separated double-electrode acidic electroless plating method, which is mainly applied to the interconnection wire metallization process of integrated circuits.

Background technique

In an integrated circuit, it is necessary to deposit a metal thin film on the silicon substrate of the integrated circuit, and form a metal wire by photolithography technology, and connect the isolated components into the required circuit according to certain requirements. This metal wire is called an integrated circuit interconnection. connection. The process of depositing a metal thin film on an integrated circuit silicon substrate is called a metallization process.

With the emergence of ultra-large-scale integrated circuits, aluminum and aluminum alloys have high resistivity and weak anti-electromigration ability. Depositing aluminum and aluminum alloy thin films on integrated circuit silicon substrates no longer meets the requirements of ultra-large-scale integrated circuits. Because copper has the advantages of low resistivity, high resistance to electromigration and stress failure, and high thermal conductivity, it replaces aluminum as a new generation of interconnect material. However, since copper is easily diffused in the silicon substrate, the performance of the silicon substrate is invalid. Therefore, a layer of refractory metals such as Ta, Ti, W or their nitrides are introduced between the copper metal film and the silicon substrate in the copper metallization process as a barrier. Barrier layer for copper diffusion into silicon substrate. Therefore, in the metallization process of copper interconnection, the copper film is plated on the barrier layer composed of Ta, Ti, W and other refractory metals or their nitrides.

Copper metal thin films can be prepared by physical vapor deposition, chemical vapor deposition and electrochemical deposition. Electroless plating is a kind of electrochemical deposition. Because of its simple preparation, excellent film properties, good step coverage and low cost, it is a promising copper interconnection preparation technology.

Traditional electroless copper plating uses the redox reaction of the solution to reduce copper ions on the deposition surface under alkaline conditions. The copper salt in the solution provides copper ions, formaldehyde is a reducing agent, tetramethylammonium hydroxide is a pH regulator, and EDTA forms a complex with copper ions to improve the stability of the solution. At the same time, surfactants and leveling agents are added to the solution to improve the quality of the copper-plated film. However, since the barrier layer of refractory metals such as Ta, Ti, W or their nitrides has no catalytic activity to copper ions, copper ions cannot be directly deposited on the surface, so the deposition surface needs to be catalytically sensitized before electroless plating. Today's main catalytic sensitization process is the use of Pd atom catalysis: Pd ions are reduced to Pd atoms in an acidic solution, and at the same time, the acidic solution is used to etch the refractory metal to pin the Pd atomic group on the deposition surface. The Pd atomic group is Backrest for the deposition of copper ions. This alkaline electroless plating method has many process steps, and the difficulty of process control is large. At the same time, because Pd is a precious metal, the production cost is increased.

Now in Taiwan, Japan and other countries, research on direct electroless copper plating on the barrier layer has been carried out. Among them, the acidic electroless copper plating method designed in Taiwan has become a relatively successful example. Since the oxidation reaction of the cathode and the reduction reaction of the anode are carried out on one substrate in this acidic copper plating method, it is called a single-electrode acidic electroless plating method.

The method is as follows: a silicon substrate coated with a layer of refractory metal nitride barrier layer is put into an acidic solution composed of copper chloride and hydrofluoric acid to react, and the hydrofluoric acid oxidizes the exposed silicon surface of the silicon substrate , the reaction formula is as follows:

The released electrons are transported by fluoride ions and chloride ions to the surface of the barrier layer, accepted by copper ions and reduced to copper, deposited on the surface of the barrier layer, and direct electroless plating is realized. The reaction formula is as follows:

Although this acidic electroless plating method realizes direct electroless copper plating on the barrier layer, the silicon surface of the silicon substrate exposed to the solution is corroded while the copper film is deposited on the surface of the barrier layer, and the substrate is damaged and cannot be used. This method is not suitable for industrial applications.

Contents of the invention

The purpose of the present invention is to propose a metallization method for preparing integrated circuit copper interconnection lines by acidic electroless plating of separated double electrodes. Realize direct electroless copper plating on the refractory metal or its nitride barrier layer, and at the same time solve the corrosion problem of the silicon substrate in the acidic solution of the single-electrode acidic electroless plating method. The copper film prepared by this method has fine and uniform grains, It is a powerful alternative to alkaline electroless plating and single-electrode acidic electroless plating methods due to its strong combination with the barrier layer.

The present invention proposes a metallization method for preparing integrated circuit copper interconnection wires by separating double-electrode acidic electroless plating. The exposed silicon surface of the anode substrate is coated with a protective layer of silver glue or organic glue to prevent its corrosion during the electroless plating process; the cathode and anode are separated and placed in an acidic solution, and the cathode and anode The oxidation-reduction reaction is carried out in an acidic solution, and a layer of copper film is electrolessly plated directly on the silicon substrate of refractory metal and nitride.

Features and effects of the present invention:

The electroless plating method of the present invention is characterized in that the negative and positive electrodes are separated under an open circuit. The fluoride ions in the solution oxidize the cathode of the silicon substrate under acidic conditions, and the electrons released by oxidation combine with the fluoride ions to form complex ions, which diffuse and transport to the anode in the solution; the anode substrate removes refractory metal or its nitrogen The silicon surface outside the barrier layer made of compound is protected by silver glue or organic glue, which ensures that the silicon substrate will not fail due to corrosion. Copper ions receive electrons transported by fluorine ions on the surface of the barrier layer of the anode and deposit directly on the surface of the barrier layer.

The fluoride ions and nitrate ions contained in the acidic electroless plating solution adopted by the present invention have the effect of cleaning and etching refractory metals and their nitrides. On the one hand, the oxide layer on the precipitation surface has been removed, and the effect of catalytic sensitization has been played. The direct electroless plating of copper ions creates a premise; on the other hand, the etching effect of fluoride ions on the precipitation substrate increases the backrest of copper ion deposition and improves the bonding force between the copper film and the precipitation substrate.

And because the two electrodes are placed separately, the distance between the two electrodes can be changed with the configuration of the solution and the reaction temperature. When the distance between the cathode and the anode varies between 0 and 5 mm, the size and shape of the deposited copper film particles, the covering ability of the copper film, and the bonding force between the copper film and the barrier layer will all change accordingly. The cathode can also be placed against the surface of the barrier layer, and the prepared copper film is also related to the distance between the two electrodes, and the copper film prepared when the cathode and the barrier layer are placed opposite to each other has different particle size, shape, coverage and binding force. There are also differences.

The copper film plated by this separated double-electrode acidic electroless plating method not only has fine and uniform crystal particles, but also has better bonding force with the substrate, and because the oxidation-reduction reaction needs to introduce solid silicon electrodes, the stability of the solution is stronger than that of the alkaline solution. Good, there will be no disproportionation reaction to make the solution useless. At the same time, the copper film plated by this method has a (111) preferred orientation, which can meet the crystal grain orientation requirement of the copper metal layer of the integrated circuit. And since the redox reaction takes place on two separate electrodes, the formation of cuprous oxide is suppressed. X-ray analysis method was used to analyze the copper film prepared by the separation double-electrode acidic electroless plating method, and no cuprous oxide was found on the copper film. In alkaline electroless plating, due to the disproportionation reaction, cuprous oxide is easily formed on the surface of the plated copper film, which increases the resistivity of the copper film. The copper film prepared by the present invention can successfully solve this problem. Therefore, the method of preparing integrated circuit copper interconnection wires by separated double-electrode acidic electroplating has realized direct electroless plating on refractory metals and their nitrides. The prepared copper film has fine and uniform particles, good bonding force, and has (111) The preferred orientation of crystal grains is preferred, and the formation of cuprous oxide is effectively inhibited; the solution composition and preparation process are simple and easy, and the cost is low.

The electroless plating method of the present invention can be directly applied to the copper interconnection wire in the deep submicron integrated circuit of the preparation integrated circuit, and can also be used in the preliminary catalytic sensitization step of the alkaline chemical plating, or to prepare the copper seed crystal layer for electroplating.

Detailed ways

The metallization method for preparing integrated circuit copper interconnection wires by acidic electroless plating with separated double electrodes of the present invention uses a silicon substrate as a cathode, and a silicon substrate coated with a refractory metal or its nitride on one side as an anode, and the anode substrate is exposed to the outside The silicon surface is coated with a layer of silver glue or organic glue protective layer to prevent its corrosion in the chemical plating process; the cathode and anode are separated and placed in an acidic solution, and the cathode and anode are oxidized and reduced in the acidic solution Reaction, a layer of copper film is directly electroless plated on the silicon substrate of refractory metal and nitride.

The electroless plating solution used in the present invention can be at least one of copper salt of 0.1～1mol/l, 0～16g/l ammonium fluoride and 0～20wt% hydrofluoric acid, and acid and deionized water are added dropwise to adjust the pH of the solution The value is 0.1-5.

When the silicon substrate cathode is placed on the surface of the anode barrier layer, the distance between the two can be between 0 and 5mm; when the silicon substrate cathode is placed on the back of the anode barrier layer, the distance between the two can be 0 ~5mm.

Embodiments of the present invention are as follows:

Embodiment one:

The acidic solution is 1mol/l copper sulfate, 20wt% hydrofluoric acid, nitric acid and deionized water are added dropwise to adjust the pH of the solution to 0.2. The cathode of the silicon substrate is placed on the surface of the barrier layer facing the anode with a distance of 5mm, and the temperature of the acid solution during electroless plating is 50°C.

Embodiment two:

The acidic solution is 0.45mol/l copper nitrate, 10wt% hydrofluoric acid, adding deionized water to adjust the pH of the solution to 5, the silicon substrate cathode is placed on the surface of the barrier layer facing away from the anode, the distance is 0mm, the temperature of the acidic solution during electroless plating is 70°C.

Embodiment three:

The acid solution is 0.45mol/l copper sulfate, 8wt% hydrofluoric acid, adding deionized water to adjust the pH value of the solution to 3, the silicon substrate cathode is placed on the surface of the barrier layer of the anode, and the distance is 1mm. During electroless plating, the acid solution The temperature is 50°C.

Embodiment four:

The acidic solution is 0.45mol/l copper nitrate, 8wt% hydrogen fluoride, adding deionized water to adjust the pH of the solution to 1, the silicon substrate cathode is facing the surface of the barrier layer of the anode, the distance is 0.5mm, and the temperature of the acidic solution during electroless plating is 50 ℃.

Embodiment five:

The acid solution is 0.30mol/l copper chloride, 16g/l ammonium fluoride, hydrochloric acid and deionized water are added dropwise to adjust the pH value of the solution to 0.1, and the silicon substrate cathode is placed on the surface of the barrier layer facing away from the anode, with a distance of 5mm. The temperature of the acidic solution during plating was 80°C.

Embodiment six:

The acidic solution is 0.1mol/l copper nitrate, 4wt% hydrogen fluoride, 2g/l ammonium fluoride, nitric acid and deionized water are added dropwise to adjust the pH value of the solution to 2, and the cathode of the silicon substrate is placed on the surface of the barrier layer facing the anode, with a distance of 2mm, the temperature of the acidic solution during electroless plating is 40°C.

Embodiment seven:

The acidic solution is 0.1mol/l copper sulfate, 5wt% hydrogen fluoride, add sulfuric acid and deionized water dropwise to adjust the pH value of the solution to about 1, place the silicon substrate cathode against the surface of the barrier layer of the anode, and the distance is 0mm, acidic during electroless plating The temperature of the solution was 60°C.

Embodiment eight:

The acidic solution is 0.5mol/l copper sulfate, 10wt% hydrogen fluoride, 6g/l ammonium fluoride, nitric acid and deionized water are added dropwise to adjust the pH value of the solution to 1, and the silicon substrate cathode is placed on the surface of the barrier layer facing away from the anode, with a distance of 2mm, the temperature of the acidic solution during electroless plating is 65°C.

Embodiment nine:

The acidic solution is 0.45mol/l copper chloride, 4wt% hydrogen fluoride, 10g/l ammonium fluoride, nitric acid and deionized water are added dropwise to adjust the pH value of the solution to 2, and the cathode of the silicon substrate is placed on the surface of the barrier layer facing the anode. 2mm, the temperature of the acid solution during electroless plating is 55°C.

Embodiment ten:

The acidic solution is 0.40mol/l copper sulfate, 8wt% hydrogen fluoride, 3g/l ammonium fluoride, nitric acid and deionized water are added dropwise to adjust the pH value of the solution to 1, and the silicon substrate cathode is placed on the surface of the barrier layer facing the anode, with a distance of 1mm, the temperature of the acidic solution during electroless plating is 60°C.

Claims (5)

1, a kind of metallization method that separates double-electrode acidic electroless plating to prepare integrated circuit copper interconnection line, it is characterized in that, use silicon substrate as negative electrode, one side is plated with the silicon substrate of refractory metal or its nitride as anode, to all The exposed silicon surface of the anode substrate is coated with a protective layer of silver glue or organic glue; the cathode and anode are separated and placed in an acidic solution, and the cathode and anode undergo oxidation-reduction reactions in the acidic solution. A layer of copper film is directly chemically plated on the silicon substrate of metal and nitride. 2. The method according to claim 1, characterized in that the acidic solution is composed of at least one of 0.1-1mol/l copper salt, 0-16g/l ammonium fluoride and 0-20wt% hydrofluoric acid species, and drop acid and deionized water to adjust the pH of the solution to 0.1-5. 3. The method according to claim 1, wherein the copper salt is selected from one of copper sulfate, copper nitrate and copper chloride, and the acid used to adjust the pH value of the solution is selected from nitric acid, sulfuric acid and hydrochloric acid one of a kind. 4. The method according to claim 1, characterized in that the distance between the cathode and the anode is kept at 0-5 mm. 5. The method according to claim 1, wherein the silicon substrate cathode and anode barrier layer surfaces are placed opposite to each other, or the silicon substrate cathode and anode barrier layer surfaces are placed opposite to each other.