JP2001023985A - Interconnection structure and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an interconnection structure and a method of preparing the same, capable of easily protecting interconnections made of a metal, such as copper which are formed on a substrate. SOLUTION: This method comprises the steps of embedding a conductive metallic material into fine recesses formed in a substrate, such as a semiconductor wafer (step 1), polishing the surface of the metallic material by a mechanical and chemical operation using a working solution (including a polishing solution, a chemical solution and a cleaning solution) from the outermost layer of the buried metal (step 2), whereby an interconnection structure is prepared. During or after the polishing step 2, a chemical conversion treatment is conducted through a contact with an electrolytic solution, either with the surface of the substrate in contact as is with the working solution or immediately after the working solution is removed, whereby the surface of the embedded metallic material is provided with a protective chemical conversion coating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring structure suitable for use as a multilayer buried wiring in a substrate and a method of manufacturing the same.

[0002]

2. Description of the Related Art There is a remarkable tendency to use copper as a material for low electric resistance multilayer wiring which is an essential condition for realizing a highly integrated semiconductor.

[0003] By using copper as a conductive material, it is possible in principle to suppress signal delay due to low electric resistance and to greatly improve electromigration resistance (longer life by one digit or more than Al wiring).

On the other hand, in order to actually form a multilayer wiring structure having a large current capacity by using copper (Cu) having a low electric resistance as a wiring material as a wiring material, it is necessary to form a wiring connection (via).
There is a great need to remove harmful oxide films that tend to form on the parts and the flattened surface layer. This is because it is recognized that it is an essential proposition to make the electrical resistance of the connection portion as low as that of the bulk and to prevent oxidation from progressing into the inside of the wiring conductor.

[Low resistance process of aluminum wiring] Here, when returning to the case of the conventional Al wiring, the via forming process is as shown in FIG.

As apparent from FIG. 3, after a via hole is formed by etching in step (1), aluminum (A) under the via is formed in a mask removing step in step (2).
1) As a result of exposing the wiring surface to oxygen plasma, an oxide is generated, which forms a high-resistance interface layer, thereby increasing the via resistance.

Therefore, a measure is taken to remove the aluminum (Al) oxide layer present on the wiring surface by irradiating argon (Ar) ions by the cleaning step (3).

On the other hand, when copper is used for wiring, it is much easier to oxidize than aluminum, and the degree of oxidation progressing to the inside of the bulk is severe, so the former process (2)
When oxygen plasma or wet etching is performed as described above, the conductivity of the copper wiring is greatly impaired.

Further, the copper ions repelled by the sputtering are re-adhered to the surrounding insulating film and the like, and this diffuses inside the SiO ₂ layer during the post-process, thereby significantly deteriorating the device characteristics. It is clear.

As described above, the mask removal treatment by oxygen plasma or wet etching as shown in the step (2) in FIG. 3 is harmful due to the two points of remarkable oxidizing property and easy diffusion property of copper. It is necessary to avoid this.

[Removal of oxide film in the case of copper wiring] As a means for obtaining a clean copper via interface without generating oxides by oxygen plasma or reattaching metal atoms by sputtering, the above-described aluminum wiring process is replaced. The following two methods have been proposed.

That is, after a series of treatments, the final removal of cuprous oxide (Cu ₂ O) remaining on the copper surface is achieved by exposing to H (hfac) gas to reduce Cu ₂ O. It has been claimed that vapor phase cleaning (CVC) or sputter cleaning with hydrogen plasma makes this possible.

CVC of hexafluoroacetyl ace
Tongas [H (hfac)] and Cu _TwoO is given by the following equation (1)
Therefore, as a result of the reaction, it is possible to remove cuprous oxide.
We are using. Cu_TwoO + 2H (hfac) → Cu + Cu (hfac)_Two+ H_TwoO · · (1)

It has been found that the cleaning effect according to the above equation (1) becomes significant at a temperature of 150 ° C. or higher.

FIG. 4 shows a flow of a part of a continuous process for forming a copper wiring. In FIG. 4, naturally, unlike the case of the aluminum wiring, it may be considered that the dual damascene method, which is an advantage unique to the copper wiring, is included. Considering that the wiring burying is performed by, for example, CVD in the process [2] of FIG.
Since the C cleaning can be easily performed by inserting only the gas in the same apparatus environment as the CVD by inserting the C cleaning between the steps [1] and [2], the step [2] is performed by the CVD.
It is particularly convenient to perform the above.

On the other hand, in the case of the aforementioned hydrogen plasma,
Using the same equipment as argon sputter etching, hydrogen plasma is generated by an inductively coupled plasma device, and copper oxide is reduced by the chemical action of the hydrogen plasma.
Since the physical action by the sputtering here is insignificant, it is considered that a low-resistance via can be formed as a result. In the same manner as described above, when the wiring embedding in the step [2] is performed by the CVD method, it can be performed as a part of the continuous processing operation without interrupting the operation of moving the cluster tool between the chambers. That is, it has been proposed to form a recess in an etching chamber, switch gases in the same chamber, generate hydrogen plasma, and reduce and remove unnecessary copper oxide.

[Problems of the Conventional Method] In the case of forming a copper wiring, it is possible to remove the oxide film at the via interface by the above method. On the other hand, after the surface of the semiconductor substrate is polished for wide area planarization in the step [3] of FIG. 4, a new oxide film is newly formed by exposing the buried copper wiring to the atmosphere. Remains.

Cuprous oxide (Cu ₂ O) which is a copper oxide film
When the film of the metal is present on the surface of the copper wiring conductor, this gradually grows into the inside of the copper bulk, and there is a serious problem that the metal copper portion is substantially depleted. Therefore, not only the via interface described above, but also the cuprous oxide generated on the buried copper wiring surface is extremely harmful in securing the function of the semiconductor,
In particular, when a further upper layer wiring is to be stacked on the wiring surface, it is necessary to remove and place all of the wiring.

Therefore, a method of forming a thin silver (Ag) film on the exposed surface of the copper wiring which has been subjected to the surface polishing in the step [3] by so-called displacement plating to protect the inside of the bulk may be considered. Although this method is excellent in that a protective film can be selectively formed only on a copper surface quickly and easily, the following problem may occur in some cases.

That is, the maximum thickness of the film formed by silver plating is extremely thin, at most about 10 nm. Since silver is a pure metal, it is easily eroded when exposed to a severely corrosive or damaging atmosphere. During later steps,
Require careful consideration of the surrounding environment.

In particular, in the high-temperature CVD gas atmosphere, the etching, or the resist removing step in forming the next layer wiring, the silver film surface is exposed to severe erosion factors such as oxygen plasma, acid solution, fluorine and chlorine radical. Considerable care must be taken to avoid damage due to damage.

[0022]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a wiring structure and a wiring structure capable of easily protecting a metal wiring such as copper formed on a base material. It is to provide a manufacturing method.

[0023]

As a means for solving the above-mentioned problems, the present invention provides a method for polishing a wiring surface with a working liquid during or after a substrate surface polishing step by chemical mechanical polishing (CMP). Utilizing that it is wet, while wet,
A method for forming a film having the property of protecting the metal on the surface of the wiring metal to suppress damage to the metal and a wiring structure manufactured by the method have been proposed.

In the present invention, a film formed by a chemical conversion treatment is used as a film for covering and protecting the exposed surface of the wiring metal.

That is, according to the present invention, a conductive metal material is embedded in fine recesses provided in a base material, and then the surface of the metal material is worked from the outermost layer side of the embedded metal with a working liquid (including a polishing liquid, a chemical liquid, and a cleaning liquid. In the method for manufacturing a wiring structure, wherein the wiring structure is manufactured by polishing by a mechanical / chemical action using the method, the substrate surface is kept in contact with the working liquid during or after the polishing step. Alternatively, a chemical conversion treatment was performed by contacting the electrolyte immediately after removing the working liquid to form a protective chemical conversion film on the surface of the embedded metal material.

In the present invention, the base material is a semiconductor substrate, the conductive metal material is copper (Cu), and the protective chemical conversion film is cupric oxide (CuO).

The present invention also provides a wiring structure in which a conductive metal material is buried in fine recesses provided in a base material and the outermost layer of the buried metal is polished. To form a protective chemical conversion film.

Here, the chemical conversion treatment means that a chemical reaction between the solution and the metal is caused by bringing an electrolyte solution suitable for the target metal into contact with the metal, and a protective film (chemical conversion film = This is a method for forming a chemical conversion coating, and is conventionally used for the purpose of realizing a rust-preventive film, a base for painting, and a base for plastic working.

Here, the outline of the chemical conversion treatment will be described in more detail. When the metal surface is observed microscopically, an extremely fine electrochemically minute anode portion and cathode portion are innumerably mixed. Now, if this metal is brought into contact with a certain electrolytic solution, a dissolution reaction of the metal occurs in the above-mentioned anode portion, and metal ions are dissolved in the liquid. At this time, the electrons emitted from the metal increase the PH of the component by reducing hydrogen ions near the cathode of the metal, etc., thereby causing precipitation and deposition / deposition reaction of the film components in the solution, and the metal surface A film is deposited on the surface. A film formed by such a formation mechanism is a chemical conversion film. Therefore, it can be said that the corrosion reaction itself of the metal in the electrolytic solution gives a driving force for causing a chemical reaction. FIG. 5 shows a reaction formula of a chemical conversion treatment with iron phosphate as an example of the chemical conversion treatment reaction.

Unlike the anodic oxidation and plating, the chemical conversion treatment does not require the use of a chemical plating solution containing an electric energy and a troublesome handling reducing agent and having an unstable composition. Providing proven means as a low cost process.

According to the present invention, a film formed by a chemical conversion treatment is formed as a surface film on a metal wiring formed on a substrate such as a semiconductor substrate. The specific procedure for forming the surface film depends on the target metal material. Different and different are conceivable.

For example, when copper is used as an embedded metal for wiring and the surface of the copper wiring is covered with a stable and dense cupric oxide (CuO) film by a chemical conversion treatment, the metal copper itself is protected and furthermore Corrosion, deterioration and damage can be avoided. At this time, the electrolytic solution used for chemical conversion treatment is 5%
Amount may be obtained by holding the NaOH-K ₂ S ₂ O ₈ solution boiling state.

[0033]

Embodiments of the present invention will be described below in detail with reference to the drawings. Specifically, a case where copper is buried in a fine wiring recess provided in a semiconductor substrate to manufacture a wiring will be described.

FIG. 1 is a schematic process flow chart of a method of manufacturing a wiring structure for forming a copper wiring on a semiconductor substrate by using the present invention. That is, copper is first buried in a fine recess provided in the semiconductor substrate W (step 1).

FIG. 2A is a diagram showing an example of the structure of the semiconductor substrate W at that time. In FIG.
Are wirings made of copper, each of which is a lower wiring, a via portion,
This is the upper layer wiring. 30, 40, 50 are SiO ₂ , 35,
45 is SiN, 55 is a barrier layer TaN (tantalum nitrite). In this step 1, the upper wiring 20 is formed by burying copper in a concave portion provided in a portion to be the upper wiring 20 in the uppermost layer.

Next, the surface of the semiconductor substrate W is polished by CMP to flatten the entire surface over a wide area (step 2). At the time of polishing by CMP, a polishing slurry is applied to the surface of the semiconductor substrate W and polished in a wet state.

At any time during the progress of polishing by CMP or at the completion of polishing, the surface of the semiconductor substrate W is kept in contact with the polishing slurry (that is, in a wet state) and the electrolytic solution (5% NaOH-K ₂ S) is used. _{When the 2} O ₈ solution is kept in a boiling state) and brought into contact with the entire surface of the semiconductor substrate W, a chemical reaction occurs immediately, and the copper surface is covered with a chemical conversion film (step 3). The state at this time is shown in FIG. 25 is CMP
Is a chemical conversion film formed on the exposed surface of the upper wiring 20 polished by the above method. In FIG. 2B, the thickness of the chemical conversion film 25 is described as being large for convenience of explanation. However, the chemical conversion film 25 is actually formed only on the exposed surface of the upper wiring 20 and is extremely thin.

Here, since the copper surface has a remarkable oxidizing property, it is preferable to avoid keeping the wet state from the wet state to the dry state (contact with the atmosphere) for a certain period of time, since undesirable copper oxide is generated. Once the chemical conversion coating 25 is formed, the copper metal surface is shielded from the atmosphere thereafter, so that undesired copper oxide (including cuprous oxide Cu ₂ O) formation, surface deterioration, deterioration,
The worry of damage can be eliminated.

As a matter of course, it is essential that the surface of the upper wiring 20 be cleaned immediately before the chemical conversion treatment. However, in the planarization step by the CMP, the surface of the upper wiring 20 is not mixed with the slurry containing abrasive grains. Copper upper layer wiring 2 by friction
Since 0 is subject to abrasion, a fresh copper surface is always exposed. There is almost no possibility that impurities or foreign substances are present on the fresh surface, and the surface has a high reactivity. Therefore, immediately after contact with the electrolyte solution, a chemical reaction starts easily, and a copper base is formed. A stable and dense protective film 25 having excellent consistency and adhesion to the surface can be formed.

When the surface of the upper wiring 20 is brought into contact with the electrolytic solution, the surface of the semiconductor wafer W is not in contact with the polishing slurry, as described above, and the cleaning liquid (pure water, chemical solution, etc.) other than the polishing slurry is in contact with the surface. Even when you are. In short, CMP
May be in contact with various working liquids (including a polishing slurry) used during or after the polishing process, or may be brought into contact with the electrolytic solution immediately after removing the working liquid.

In the chemical conversion treatment, care must be taken to quickly replace the liquid contact so as not to promote surface oxidation by contact with the atmosphere. As a method of bringing the electrolytic solution for chemical conversion treatment into contact with the surface of the semiconductor substrate W, there are two methods, [1] dipping in the electrolytic solution, and [2] spraying the electrolytic solution onto the semiconductor substrate W by spraying. In general, it is considered that the method of spraying [2] is convenient for performing the chemical conversion treatment immediately after the CMP.

Originally, the surface of copper is gradually oxidized in the air or in fresh water, and the surface thereof becomes cuprous oxide (= cuprous oxide: Cu).
₂ O) Strongly covered with a film. Further C
u ₂ O generally tends to grow on thick scales,
The crystal grains also tend to be coarse.

On the other hand, cupric oxide (CuO) constituting the chemical conversion film 25 formed by the method of the present invention has a fine polycrystalline structure and has a chemically stable and dense structure. Rich in protecting copper metal.

Accordingly, there is no possibility that the inside of the copper wiring will be damaged by oxidation thereafter. In addition, since the chemical conversion film 25 formed here is as thin as about several nm at most,
The effect on the current capacity of the upper layer wiring 20 by itself is sufficiently small, and the risk of deteriorating device characteristics can be ignored.

After washing and drying (steps 4 and 5),
The wiring structure of the semiconductor substrate W is completed.

By the way, the chemical conversion film 25 made of CuO is used.
In order to remove this, the relevant portion may be brought into contact with diluted hydrofluoric acid. Therefore, the chemical conversion film 25 can be easily removed immediately before the step of stacking and forming the next layer wiring on the upper layer wiring 20 is started, so that a sufficiently low wiring interlayer connection resistance is secured without disturbing a series of steps. It is possible to do.

The type of the chemical conversion film 25 that can be formed on the copper surface by the chemical conversion treatment is as described in the above [1].
In addition to the copper oxide (cupric oxide) film, there are [2] zinc phosphate film and [3] chromate film.

In the above embodiment, a semiconductor substrate is used as a base material. However, the present invention may be used when a wiring structure is formed on other various base materials.

In the above embodiment, copper is used as the metal material to be embedded in the fine recesses of the substrate, but other metal materials may be used.

[0050]

As described above in detail, according to the present invention, there is an excellent effect that the metal wiring formed on the base material can be easily protected.

[Brief description of the drawings]

FIG. 1 is a schematic process flow chart of a method for manufacturing a wiring structure for forming a copper wiring on a semiconductor substrate W using the present invention.

FIG. 2 is a diagram showing a structural example of a semiconductor substrate W manufactured by the method shown in FIG.

FIG. 3 is a schematic process flow diagram showing a conventional process for forming a via of an Al wiring.

FIG. 4 is a schematic process flow chart showing a flow of a part of a continuous process for forming a copper wiring.

FIG. 5 is a diagram showing a reaction formula of a chemical conversion treatment with iron phosphate.

[Explanation of symbols]

10 the lower layer wiring 15 via portion 20 upper wiring 30,40,50 SiO ₂ 35,45 SiN 55 TaN

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference)

Claims (4)

[Claims] 1. A wiring structure in which a conductive metal material is buried in fine recesses provided in a base material and an outermost layer of the buried metal is polished. A wiring structure characterized by being formed. 2. The wiring according to claim 1, wherein the substrate is a semiconductor substrate, the conductive metal material is copper (Cu), and the chemical conversion film is cupric oxide (CuO). Construction. 3. A conductive metal material is buried in fine recesses provided in a base material, and then the surface of the metal material is polished from the outermost layer side of the buried metal by a mechanical / chemical action using a working liquid. In the method of manufacturing a wiring structure by manufacturing a wiring structure, during or after completion of the polishing step, the base material surface is kept in contact with the working liquid, or by contacting the electrolyte immediately after removing the working liquid A method of manufacturing a wiring structure, comprising forming a chemical conversion film on a surface of a buried metal material by performing a chemical conversion treatment. 4. The wiring according to claim 3, wherein the substrate is a semiconductor substrate, the conductive metal material is copper (Cu), and the chemical conversion film is cupric oxide (CuO). The method of manufacturing the structure.