JP3255095B2 - Polishing liquid and polishing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a wiring of a semiconductor device, and more particularly to a method of polishing a wiring material and a polishing liquid used therein. The present invention relates to a polishing method and a polishing liquid when wiring is formed by embedding a polishing liquid.

[0002]

2. Description of the Related Art Along with miniaturization of transistors, miniaturization of metal wiring such as aluminum is required. However, in conventional wiring formation using dry etching of a metal film, metal corrosion (metal corrosion) by an etching gas is required. ) Causes a problem of deterioration of wiring reliability. Therefore, a wiring groove or a via hole to the underlying wiring is formed in the interlayer insulating film in advance, and a metal film is grown on the entire surface of the interlayer insulating film while filling the wiring groove or the via hole by a high-temperature sputtering method or a CVD method. Chemical mechanical polishing (CM) of metal film on film
Attention has been paid to a method of forming a metal wiring buried in a wiring groove or a via hole by removing by selective polishing such as P). The metal-embedded wiring formed by the above process is called a damascene wiring.

For the damascene wiring, it is possible to apply a material that is difficult to process by dry etching, and to form a wiring / via integrated structure in which wiring metal is embedded in a via hole formed in a self-aligned manner with respect to a wiring groove. There is an advantage. On the other hand, when polishing soft metals such as aluminum,
There is a concern about processing irregularities on the metal surface after polishing. The properties of the metal surface after such polishing include polishing pressure, polishing pad rotation speed, polishing pad hardness, and polishing liquid (slurry) used for polishing.
Are affected by polishing factors that are intricately entangled.

FIG. 5 shows an example of a conventional CMP apparatus.
2. Description of the Related Art A conventional CMP apparatus includes a polishing head for adsorbing a substrate, a polishing platen, a rotational torque measuring unit for the polishing head, and a polishing liquid supply unit. The driving of the polishing head is controlled by a torque signal from the rotation torque measuring unit, and the polishing liquid supply unit supplies alkaline (pH> 7), neutral (pH = 7) and acidic (pH <7) polishing liquids. Can be supplied.

FIG. 6 shows an example of a damascene wiring forming process using a CMP apparatus. Hereinafter, the process will be briefly described in order of steps with reference to FIG.

A lower wiring 62 and an interlayer insulating film 63 are formed on a substrate 61 in advance, and a via hole 64 for embedding a via plug is opened. After that, a metal film 65 (for example, aluminum) is formed on the entire surface of the interlayer insulating film 63 (FIG. 6A). As a technique for forming the metal film 65, a chemical vapor deposition (CVD) method, a sputtering method, or the like can be used. There is.

Next, the metal film 65 is polished using a polishing liquid for metal polishing (FIG. 6B). As the polishing liquid for metal polishing, for example, an acidic (pH = about 3) alumina slurry or the like is used. Such an acidic polishing slurry is generally characterized in that the polishing rate of a metal film is higher than that of an interlayer insulating film. The end point detection of the metal film polishing in this step is performed by monitoring the rotation torque output signal from the drive control unit in the polishing apparatus of FIG. This utilizes the fact that when polishing is performed with a constant rotation speed in polishing with an acidic polishing slurry, when the interlayer insulating film 63 appears on the polishing surface, the rotational torque of the polishing head sharply increases. That is, as shown in FIG. 7, when the rotational torque increases with the progress of polishing and exceeds a preset torque signal output level, the metal polishing process is terminated.
At this point, as shown in FIG.
A part of the metal film 65 remains on the upper part.

Subsequently, the metal film 65 and the interlayer insulating film 63 are further polished using a neutral silica slurry in which silica particles are dispersed (FIG. 6C). This neutral silica slurry has a feature that the interlayer insulating film is polished simultaneously with the metal film. As a result, the metal film 65 remaining on the interlayer insulating film and the interlayer insulating film 63 are simultaneously flattened.

Finally, the polishing liquid is switched from the neutral silica slurry to an alkaline silica slurry to which potassium hydroxide or the like is added, and polishing is further continued. Since the alkaline silica polishing liquid has a feature that the polishing rate of the interlayer insulating film is higher than that of the metal film, the plug of the metal film 65 can be projected from the interlayer insulating film 63 by continuing the polishing. Thereafter, by forming and patterning the upper layer wiring metal, a multilayer wiring structure is formed.

The above-described prior art is disclosed in, for example,
No. 124886.

[0011]

The conventional polishing method described above has the following problems.

First, in conventional metal polishing using a polishing liquid, there is a problem that an altered layer remains on the metal surface after polishing. As a conventional polishing slurry for metal polishing, for example, an acidic slurry in which alumina particles are dispersed is used, and this slurry usually contains an oxidizing agent such as hydrogen peroxide solution, and a metal hydroxide or metal hydroxide on the metal surface. Form an oxide. That is, as the metal polishing proceeds, a metal hydroxide (or oxide) altered layer is formed on the metal surface by a reaction between the oxidizing agent in the polishing slurry and the metal, and the altered layer on the surface is formed by the polishing pad and the abrasive particles ( Here, it is performed by shaving off with alumina particles). Inevitably for this,
The metal surface after polishing will also be covered with the metal hydroxide or oxide. Since the deteriorated layer on the metal surface is insulative in many cases, there is a problem that the connection resistance increases when the upper metal wiring is formed on the polished metal. In addition, in some cases, the hydroxide (or oxide) formed on the metal surface is partially peeled off, causing a problem that the polished surface is not smooth. If a local concave portion exists on the surface of the metal wiring due to such peeling, the wiring may be disconnected from that region, causing a significant reduction in wiring reliability.

Further, in the conventional metal polishing using a polishing liquid, there has been a problem that polishing characteristics such as a polishing rate change with the progress of polishing. The polishing characteristics of the metal film largely depend on the state of aggregation of the polishing particles in the polishing liquid. Since the agglomerated state of the abrasive particles changes depending on the electrolyte concentration and pH in the polishing liquid, the components in the polishing liquid react with the metal as the metal film polishing progresses, or the metal dissolves in the polishing liquid. When the physical properties of the liquid change, the polishing characteristics change between the initial and final stages of polishing. In the conventional polishing liquid, since an acidic metal polishing slurry containing an oxidizing agent was used, the dissolution of a metal film or a hydroxide thereof in the polishing liquid was remarkable, and the metal ion concentration in the slurry was reduced by polishing. It had a tendency to increase with progress. Generally, when the electrolyte concentration in the slurry increases, the thickness of the electric double layer existing around the abrasive particles decreases, and the aggregation of the abrasive particles tends to occur. As a result, there is a problem that the viscosity of the polishing slurry increases with the progress of polishing.

The above problems cannot be avoided merely by making the polishing slurry for metal polishing neutral. This makes it possible to suppress the dissolution of the metal film being polished in the polishing slurry by making the polishing slurry neutral, but on the other hand, the polishing rate of the underlying interlayer insulating film increases, and This is because there is a problem that the selective polishing property of the film cannot be sufficiently obtained. In this case, it is very difficult to control the polishing process.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and improves the stability of polishing characteristics in metal polishing and the selectivity to a base insulating film, and at the same time reduces the occurrence of scratches on the metal surface. It is an object of the present invention to improve the reliability of a semiconductor device manufactured by using a polishing process.

[0016]

According to a first aspect of the present invention, in a method for polishing a metal film, abrasive particles are dispersed in water to form a metal film to be polished. A neutral polishing liquid to which an electrolyte salt containing a metal element to be added is added, and a polishing method using the polishing liquid.

According to a second aspect of the present invention, there is provided a neutral polishing solution in which abrasive particles are dispersed in water and further a water-soluble organic polymer is added, and a polishing method using the polishing solution. . As the water-soluble organic polymer in the polishing liquid, for example, cellulose can be used, and its concentration is 1 wt%.
It is desirable that:

The abrasive particles used in the first and second inventions are desirably monodisperse spherical fine particles.

The present invention also provides a method for polishing a metal film embedded and formed on an insulating film having a wiring groove,
First, a polishing method is disclosed in which an outline of a metal film is polished and removed using the polishing liquid according to the first invention, and further, the insulating film is exposed and the metal film is mirror-polished using the polishing liquid according to the second invention. After that, the method may include a step of cleaning the composite surface composed of the exposed insulating film and the metal film embedded in the wiring groove.

(Function) In the present invention, polishing is carried out by dissolving an electrolyte salt containing a metal to be polished or an organic polymer in a neutral polishing liquid. Since the basic neutral polishing liquid is typically one in which abrasive particles (silica or the like) are typically dispersed in pure water, the surface of the metal to be polished is altered such as an oxide or a hydroxide. No layer is formed.
In this case, polishing proceeds by direct contact between the metal and the abrasive particles. Strictly speaking, neutral means pH = 7, but the neutral polishing liquid in the present invention is a polishing liquid having a pH of about 6 to 8, and a conventional acidic polishing liquid having a pH of about 3 or pH
= 9 to 11 to distinguish the alkaline polishing liquid.

In the first invention, when polishing a metal film on a semiconductor substrate, a polishing solution to which an oxidizing agent is not added is used to form a metal hydroxide film or a metal oxide as an insulator on the metal surface. It becomes possible to polish without performing. In addition, by preliminarily dissolving the electrolyte salt such as nitrate, sulfate or chloride of the metal to be polished in the polishing liquid, it is possible to suppress a change in the metal ion concentration in the polishing liquid due to the progress of metal polishing. It becomes possible. Thereby, the aggregation state of the abrasive particles in the polishing liquid is less likely to change, and the speed stability of metal polishing is increased.

Further, in the second invention, the rate stability of metal polishing is increased by dissolving a water-soluble organic polymer in a polishing liquid to which an oxidizing agent is not added and preaggregating the polishing particles. Becomes possible. Further, since the water-soluble organic polymer is selectively adsorbed to the interlayer insulating film below the metal film to form a surface protective film of the organic film, it has an effect of improving the polishing selectivity of the metal film with respect to the interlayer insulating film. The amount of the water-soluble organic polymer to be added only needs to form an extremely thin organic film on the surface of the interlayer insulating film, so that even a small amount of about 1 wt% or less has its function sufficiently.

When the polishing liquids according to the first and second aspects of the invention are used, a metal oxide film or a metal hydroxide film is not formed on the metal polishing surface, and polishing is performed by direct contact between the abrasive particles and the metal. Progresses. In such a case, in order to prevent the generation of scratches on the metal surface, it is extremely effective to use monodispersed spherical particles having no solidification of the particles as abrasive particles.

In a method of forming a damascene wiring in which a metal film on a wiring groove formed in an interlayer insulating film is polished and a metal film is buried, an electrolyte salt of a metal film having high polishing stability is used as a first polishing step. The main portion of the metal film is planarized and polished using the added polishing liquid, and then, as a second polishing step, the interlayer insulating film is added using a polishing liquid added with a water-soluble organic polymer having a high selectivity to the interlayer insulating film. A polishing method for removing a metal film remaining on the film is effective. Further, as a third step, the cleaning substrate surface may be cleaned by dropping a neutral cleaning solution containing no abrasive.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention, an electrolytic salt such as a nitrate or a sulfate of the same metal as the metal film to be polished is previously added to the polishing liquid used for metal polishing. Polishing is performed using the added polishing liquid. Further, in the conventional metal polishing, it has been usual to add an oxidizing agent such as a hydrogen peroxide solution to oxidize or hydroxylate the metal surface and remove this surface reaction layer by polishing.
In the polishing liquid of the present invention, without adding an oxidizing agent to the polishing liquid,
The metal film is directly polished with an abrasive in a neutral polishing liquid. The apparatus configuration used for polishing may be a conventional one.

By dissolving the electrolyte salt in the polishing liquid,
The abrasive particles can be agglomerated to some extent in advance. This suppresses the dissolution of the metal film in the polishing liquid during polishing, thereby avoiding an increase in the viscosity of the polishing liquid due to an increase in the metal ion concentration and a change in polishing characteristics such as a polishing rate caused by the increase. At the same time, the selectivity of polishing the metal film with respect to the interlayer insulating film is obtained by the aggregation of the polishing particles. As the electrolyte salt, for example, when the metal film to be polished is aluminum, aluminum nitrate, aluminum sulfate, aluminum chloride, aluminum acetate, aluminum phosphate, or the like is used. When the metal film is copper, copper nitrate, copper sulfate,
Copper chloride, copper acetate, copper phosphate and the like. In other words, it is important that ions of the metal film to be polished are previously dissolved in the polishing liquid.

When the metal film to be polished is an alloy, it is most preferable to dissolve all metal ions of the elements constituting the alloy in the polishing liquid. For example, Al-
When polishing a Cu alloy, for example, both aluminum nitrate and copper nitrate are dissolved in a neutral polishing solution in advance. However, when the metal to be polished is an alloy in which a trace amount of another metal is added to the metal as the main component, ions of the main component metal may be simply dissolved in the neutral polishing liquid.
Generally, when the composition ratio of the main component metal is 95% or more, it is only necessary to dissolve the main component metal ions in the polishing liquid. For example, when polishing an Al—Cu alloy in which the composition ratio of copper frequently used for wiring of a semiconductor device is about 1% or less, only an electrolyte salt containing aluminum should be dissolved in the polishing solution. It is good.

As abrasive particles, for example, fine spherical silica particles having a particle size of 10 to 300 nm obtained by a liquid layer deposition method (wet method) by hydrolysis of tetraethyl silicate (TEOS) are used. It is desirable to use no monodisperse spherical particles. In the present invention, since an oxidizing agent is not added to the polishing liquid, an altered layer such as a hydroxide is not formed on the metal surface, and the abrasive particles directly contact the metal. At this time, the use of monodispersed spherical abrasive particles as the abrasive particles can greatly reduce the occurrence of scratches on the metal film surface. In addition to the fine spherical silica particles, oxide particles such as alumina particles, titanium oxide particles, and zirconia oxide obtained by hydrolyzing alkoxides of aluminum, titanium, and zirconium (each having a particle diameter of about 10 nm to 100 nm) may be used. Similar effects can be obtained. It is possible to use silica particles (generally referred to as fumed silica) obtained by gas phase pyrolysis of silicon chloride as an abrasive, but it is particularly effective in preventing scratches when polishing a soft metal film such as aluminum or copper. From the viewpoint of the above, it is desirable to polish using the monodispersed spherical particles by the above-mentioned wet method.

In the embodiment of the second invention, as another method of preaggregating abrasive particles to some extent,
A water-soluble organic polymer such as cellulose is added to the abrasive. Organic polymers such as cellulose are adsorbed on the surface of silica particles, which are abrasive particles, and have the effect of causing chains of silica particles by entanglement of the cellulose molecules. As a result, the viscosity of the polishing liquid increases. In this case, the silica particles are not directly aggregated but indirectly aggregated by entanglement of polymer chains such as cellulose.

An organic polymer such as cellulose is selectively adsorbed on an interlayer insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film on a substrate to be polished, while being adsorbed on a metal film surface. do not do. Therefore, the surface of the interlayer insulating film is covered with the organic polymer film, and the polishing of the metal film can be advanced while the polishing of the interlayer insulating film is suppressed. Therefore, in the polishing using this polishing liquid, it is possible to directly polish the metal film without causing any damage on the surface of the metal film and to have a high selectivity to the underlying interlayer insulating film. The polishing liquid to which the water-soluble organic polymer is added is effective when used at the final polishing stage where the underlying interlayer insulating film appears. Also,
Such an effect is effective when polishing not only a metal film such as aluminum, copper, tungsten and titanium, but also a conductive nitride film such as titanium nitride and tungsten nitride, and a metal silicide film such as tungsten silicide and titanium silicide.

As the above-mentioned water-soluble organic polymer, glycerin, acrylate or the like can be used in addition to cellulose. For the abrasive particles used in the embodiment of the second invention, monodisperse spherical particles such as fine spherical silica particles by a wet method may be used for exactly the same reason as in the first invention. desirable.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0033]

[Embodiment 1] A wiring groove was previously formed in an interlayer insulating film, and then Al was formed by high-temperature sputtering at a substrate temperature of 450 ° C.
Embedded film of Cu 0.5% (thickness 800 nm),
A substrate to be polished was formed. Ar was used as a sputtering gas in the Al-Cu film formation, and the pressure was 4 mTorr. Hereinafter, a description will be given of an embodiment in which the high-temperature sputtered Al-Cu film formed by the above process is polished by using the polishing liquid of the present invention to form an embedded wiring in which Al-Cu is embedded in a wiring groove.

First, the polishing liquid used in this embodiment will be described. In preparing the polishing solution, first, tetraethylorthosilicate (TEO) is used as polishing particles in pure water.
A neutral silica polishing liquid was prepared by dispersing spherical silica particles having a particle size of 10 to 40 nm by a wet method obtained by hydrolyzing S) in pure water. The concentration of silica particles used as abrasive particles is 1
0 wt%. The viscosity of this neutral silica polishing liquid is 1.0
It was 7 cP (1.07 × 10 ⁻³ Pa · s). A polishing solution to be actually used was prepared by adding an electrolyte salt or an organic polymer to the neutral silica polishing solution.

As a first polishing liquid, aluminum nitrate was added to the above-mentioned neutral silica polishing liquid to prepare an electrolyte-added neutral silica polishing liquid. Aluminum nitrate concentration of 10- ³ to
It is within the range of 1 wt%, typically 0.5 wt%. Polishing liquid viscosity is 5.09c by adding aluminum nitrate
P (5.09 × 10 ⁻³ Pa · s). That is, by adding aluminum nitrate to the neutral silica polishing liquid, the silica particles are aggregated in advance to increase the polishing liquid viscosity to 4.5.
About twice as large.

As a second polishing liquid, cellulose was added to the above-mentioned neutral silica polishing liquid to prepare a polymer-added neutral silica polishing liquid. Cellulose concentration is 10 ^-6 to 10 ^-1 w
t%, typically 4.7 × 10 ⁻³ wt%. The viscosity of the polishing liquid is 5.4 cP by adding this cellulose.
(5.40 × 10 ⁻³ Pa · s). That is,
By adding cellulose to the neutral silica polishing liquid, the silica particles were aggregated in advance to increase the polishing liquid viscosity about five times.

Using the above first and second polishing liquids,
A substrate to be polished having an Al-Cu film on its surface was polished. The polishing apparatus used was a conventional one, and the polishing pad was a foamed polyurethane (Rodel Nitta: I.
C-1000 laminated pad). The rotation speed of the polishing head and the polishing platen was 35 rpm, and the supply speed of the polishing liquid was 60 ml / min.

FIG. 1 is a diagram showing the effect of the polishing pressure on the polishing rate. The polishing rate increased with increasing polishing pressure, but almost no dependence on the type of additive was observed. FIG. 2 is a diagram showing the dependence of the polishing rate on the cellulose concentration when polishing is performed using a second polishing liquid at a polishing pressure of 0.4 kg / cm ² . In the experimental range where the cellulose concentration is 10 ⁻⁶ to 10 ⁻¹ wt%, the polishing rate is constant at 0.2 μm / min, and the polishing rate does not depend on the cellulose concentration. This also applies in the first polishing liquid, aluminum nitrate concentration of 10 ^-3 to
Within the experimental range of 1 wt%, the polishing rate did not depend on the amount of aluminum nitrate added. From the above,
It was confirmed that an aluminum film can be polished by adding an electrolyte salt or an organic polymer to a neutral silica polishing liquid in advance and agglomerating abrasive particles in advance. In addition, the stability of the polishing characteristics with respect to the progress of polishing, for example, the stability of the polishing rate, was significantly improved in both the first and second polishing liquids of the present invention as compared with the conventional polishing liquid. The first polishing liquid, in which metal ions were previously dissolved in the polishing liquid by adding, was more excellent in stability.

In addition to the above-described polishing of the aluminum film, an experiment for polishing a silicon oxide film using the first and second polishing liquids of the present invention was conducted. As a result, the polishing rate of the silicon oxide film when the first polishing liquid with the addition of aluminum nitrate is used is about 1/10 of that of the aluminum film, and about 20 times with the second polishing liquid with the addition of cellulose. It was about one-third. That is, by using the first and second polishing liquids according to the present invention, the selectivity of aluminum polishing to the underlying interlayer insulating film (here, silicon oxide film) is ensured despite the neutral polishing liquid. It was confirmed that it was done. However, it was also confirmed that the degree of selectivity was better for the second polishing liquid with the addition of cellulose.

FIG. 3 shows the results obtained by using the first polishing liquid (adding aluminum nitrate, concentration 0.5 wt%) and the second polishing liquid (adding cellulose, concentration 4.7 × 10 ^-2 wt%) according to the present invention. Reflectivity when the Al-Cu alloy film is polished by
FIG. 3 is a diagram comparing with before polishing (immediately after film formation). Note that the measurement of the reflectance in FIG. 3 was performed at the stage when the polishing of the metal film had progressed halfway (that is, at the time when the interlayer insulating film was not exposed). FIG. 3 shows that, when using any of the polishing liquids, the maximum was 7% compared to the Al—Cu film surface immediately after high-temperature sputtering film formation.
Large reflectivity. This is because the surface flatness of the Al—Cu film was improved by the polishing. Comparing the addition of aluminum nitrate and the addition of cellulose, at around 300 nm, the reflectance of the aluminum surface using the cellulose-added neutral silica polishing liquid is higher than that of the aluminum nitrate-added neutral polishing liquid by 10% or more. It was found that the aluminum surface had better smoothness. Note that even when the cellulose concentration was changed, the reflectance of the polished surface did not change within the experimental range of 10 ^-6 to 10 ^-1 wt%.

As described above, the neutralizing silica polishing liquid containing aluminum nitrate and the neutralizing silica polishing liquid containing cellulose do not contain an oxidizing agent such as a hydrogen peroxide solution which has been added to the conventional polishing liquid. Also, no metal oxide film or metal hydroxide film is formed on the metal surface during polishing. Further, since the polishing liquid is neutral, the metal film does not dissolve in the polishing liquid. Further, the use of fine spherical abrasive particles suppresses the occurrence of scratches on the surface of the metal film.

In connection with the first invention, the metal to be polished in the present embodiment was not pure aluminum but an Al-Cu alloy containing 0.5% copper, but was added to the first polishing liquid. As the electrolyte salt to be used, only aluminum nitrate was used. The reason why sufficient stability of the polishing characteristics was obtained even in this case is because the content of copper in the alloy is very small. Generally, the content of added metal other than the main component in the alloy is 5%
In the case of exceeding the above, it is desirable to add an electrolyte salt containing the added metal to prepare a polishing liquid. Needless to say, even when the content of the additive metal in the alloy is as small as 5% or less, the polishing salt may be prepared by adding the electrolyte salt.

In a buried wiring structure which is to be polished in this embodiment, a barrier metal layer (for example, having a thickness of several nm to several tens of nanometers) is provided between the interlayer insulating film and the metal wiring.
m of titanium or the like is often inserted. However, the thickness of such a barrier metal layer is usually very small, and the barrier metal layer is polished at the final polishing stage immediately before the interlayer insulating film is exposed. Fluctuations are usually not a problem.

[0044]

[Embodiment 2] In Embodiment 1 described above, the polishing of a stable metal film and the polishing of a metal film with respect to an interlayer insulating film can be performed by using either the electrolyte salt-added polishing liquid or the organic polymer-added polishing liquid of the present invention. It has been clarified that selective polishing is possible, and generation of scratches on the surface after polishing can be suppressed. However, there is also a difference in the polishing characteristics between the two polishing solutions, and the stability of the polishing characteristics with respect to the progress of polishing is superior to the electrolyte-added polishing solution. It was also found that the organic polymer-added polishing liquid was excellent in selectivity. In consideration of the above, the electrolyte-added polishing liquid is suitable for use in the flattening polishing step from the initial stage of polishing. This step is a step of flattening irregularities on the surface of the metal film and removing a large part of the metal film on the interlayer insulating film, and the most stable polishing characteristics are required. Further, the organic polymer-added abrasive is suitable for use in a mirror polishing step of removing the residual metal and exposing the interlayer insulating film. In this step, a high selectivity in polishing and suppression of generation of scratches on the metal surface are strongly required.

Therefore, in the second embodiment, as the first step, flattening polishing using an electrolyte-added polishing liquid is performed, then, as a second step, mirror polishing using an organic polymer-added polishing liquid is performed, and then the third polishing is performed. An example in which a cleaning step is performed as a step and an embedded metal wiring is formed by the above series of steps will be described.

FIG. 4 schematically shows the polishing apparatus used in this embodiment.
Shown in The polishing process in the present embodiment has three steps as described above. The polishing apparatus of this embodiment has three polishing stages corresponding to these steps. The first polishing stage 10 performs a flattening polishing step of roughly removing a metal film, and the second polishing stage 20 performs an interlayer polishing process. In the third polishing stage 30, a substrate cleaning step can be performed in a highly selective mirror polishing step of finishing the surface of the metal film while exposing the insulating film. Each of the polishing stages has basically the same configuration. Each of the polishing stages has polishing pads 11, 21, and 31, and polishing heads 12, 22, and 3 have a polishing pad on the upper surface.
2, load applying mechanism 13, 23, 33, polishing liquid supply mechanism 1
4, 24, 34. The polishing platen and the polishing head can each be rotated at an arbitrary speed by a rotating mechanism, and at this time, an arbitrary load can be applied to the polishing head by a load applying mechanism. The substrates 15, 25, and 35 to be polished are held by the polishing head with the surface facing downward, and polishing liquids 16, 26, and 3 are supplied from a polishing liquid supply mechanism.
By supplying 6, the substrate is polished or cleaned.
Although the main purpose of the process in the third polishing stage is to clean the substrate, the expression of a polishing liquid is used here.

In the polishing apparatus used in this embodiment,
The above-described first to third polishing stages are arranged on one support table 1 and have an integrated configuration. The substrate before polishing is first placed on the loader 2 and then sequentially transferred to the first to third polishing stages by an automatic transfer mechanism (not shown) to perform a three-stage polishing process. It is stored in the loader 3. Hereinafter, the substrates at the polishing positions on each stage are distinguished as substrates 15, 25, and 35, respectively.

The substrate to be polished is almost the same as the substrate used in the first embodiment. That is, a wiring groove having a depth of 500 nm is formed in the interlayer insulating film in advance, and then Al-Cu 0.5
% (Thickness: 700 nm).
The film forming conditions of the Al-Cu alloy are the same as those in the first embodiment.
Above the Al-Cu alloy film, there is a surface irregularity of about 300 nm reflecting the step of the underlying wiring groove.

Hereinafter, the polishing steps in the first, second, and third polishing stages in FIG. 4 will be described.

The polishing step in the first polishing stage includes A
This is a flattening polishing step for removing surface irregularities on the surface of the l-Cu alloy film. The polishing liquid 16 used here was prepared by dispersing spherical silica fine particles having a particle size of 40 to 80 nm by a wet method as pure abrasive particles in pure water, and further adding 0.5 wt% of aluminum nitrate.
% Of the electrolyte-added polishing liquid. The concentration of the silica particles was 10 to 20 wt%. The polishing pad has a hardness of 90.
A hard polishing pad of about 100 to 100 (JIS-A standard, the same applies hereinafter), and 0.3 to 0.4
A high polishing pressure of kg / cm ² was applied. The number of revolutions of the polishing platen 11 and the polishing head 12 was 30 to 90 rpm. This step is a step of polishing and removing a large amount of the Al-Cu alloy film, and high-speed polishing is very important. For this purpose, polishing particles and a hard pad having a somewhat large particle size are used as described above, and polishing is performed under conditions of high pressure application and high speed rotation. With the above configuration, the remaining aluminum film is 100
It was polished to nm.

The polishing step in the second polishing stage is a highly selective mirror polishing step of selectively polishing the aluminum film while minimizing the polishing of the underlying interlayer insulating film. As the polishing liquid 26 in this step, an organic polymer-added polishing liquid in which 0.1% by weight of cellulose is added to pure water in which 10 to 40% by weight of spherical silica fine particles of 10 to 40 nm are dispersed,
The Al-Cu alloy was mirror-polished with a polishing pad of a soft pad (hardness 60 to 90) until an underlying interlayer insulating film appeared. At this time, the pressure applied by the load applying mechanism 23 is 0.3
kg / cm ² or less, and the polishing platen 21
The number of rotations of the polishing head 22 was 10 to 40 rpm, respectively. Here, the use of small particles and soft pads having a small particle diameter, and polishing under conditions of low pressure and low speed rotation, in order to improve the smoothness of the polished surface of the polished Al-Cu alloy film, and This is for further improving the polishing selectivity. By this step, a buried aluminum wiring (damascene aluminum wiring) without surface irregularities is obtained.

The polishing step in the third stage is a step of cleaning the composite surface formed by the polishing steps up to the second stage and comprising the Al-Cu film and the interlayer insulating film.
Pure water was used as the polishing liquid 36 used in this step.
A soft pad having a hardness of 60 or less is used as the polishing pad, and the pressure applied by the load applying mechanism 33 is 0.3 kg.
/ Cm ² or less, polishing platen 31, rotating speed of polishing head 4
Polishing was performed under the condition of 0 rpm or less. The polishing liquid 36 used in this step may be a polishing liquid obtained by adding 0.1 wt% or less of an organic polymer (surfactant) such as cellulose to pure water.

By the above series of polishing steps, a damascene wiring in which an Al-Cu alloy having a thickness of 500 nm was embedded in the interlayer insulating film was formed. The surface roughness of the Al-Cu wiring is 10
nm or less, and was confirmed to be excellent in smoothness.

In this embodiment, as shown in FIG. 4, first to third polishing stages were connected, and a polishing apparatus capable of automatically transporting the substrate between the stages was used. However, a plurality of individual polishing apparatuses are prepared, and the first, second,
Even when the third polishing step is performed, the effect of the present invention is exactly the same. In addition, out of the above three steps, essentially important steps are the first and second polishing steps, and the third cleaning step may be performed by another cleaning means.

[0055]

In the conventional metal polishing, a polishing liquid in which a pH adjuster or an oxidizing agent is added to a dispersion of fine abrasive particles is used, so that a surface insulating film is formed on the metal surface or the metal is polished by polishing. There have been technical problems such as the occurrence of irregularities on the surface and the change in polishing characteristics as polishing proceeds.

However, according to the present invention, the use of a polishing liquid in which a trace amount of an organic salt such as an electrolyte salt containing a metal element constituting a metal film to be polished or an organic polymer such as cellulose is added to a neutral polishing liquid. I was able to solve the problem. In other words, by polishing the metal surface directly with the abrasive particles that have been agglomerated in advance, metal polishing with excellent smoothness is achieved, and stable polishing characteristics are obtained by preventing a change in the characteristics of the polishing liquid accompanying polishing. Was.

In the formation of the buried metal wiring, flattening polishing using an electrolyte salt-added abrasive is performed as a first polishing step, and highly selective polishing using an organic polymer-added polishing liquid is performed as a second polishing step. By performing the mirror polishing step, it became possible to form an embedded wiring having no surface irregularities.

As a result, a stable damascene wiring can be formed, and a remarkable effect that wiring reliability is remarkably improved is obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a relationship between a polishing rate and a polishing pressure of an Al—Cu alloy film by a polishing liquid of the present invention.

FIG. 2 is a graph showing the relationship between the concentration of organic polymer in the second polishing liquid of the present invention and A.
FIG. 4 is a diagram showing a relationship between polishing rates of an l-Cu alloy film.

FIG. 3 is a diagram showing the reflectance of an Al—Cu alloy polished with a polishing liquid according to the present invention.

FIG. 4 is a process sectional view showing a buried wiring formation polishing method according to the present invention.

FIG. 5 is a view showing a conventional polishing apparatus.

FIG. 6 is a process sectional view showing a conventional embedded wiring forming process.

FIG. 7 is a diagram showing the time dependence of a polishing head torque in a conventional polishing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support stand 2 Loader 3 Unloader 10 1st polishing stage 20 2nd polishing stage 30 3rd polishing stage 11,21,31 Polishing surface plate 12,22,32 Polishing head 13,23,33 Load application mechanism 14,24, 34 polishing liquid supply mechanism 15, 25, 35 substrate 16, 26, 36 polishing liquid 61 substrate 62 lower wiring 63 interlayer insulating film 64 via hole 65 metal film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/304 B24B 37/00 C09K 3/14

Claims (7)

(57) [Claims] 1. A polishing liquid for metal polishing, wherein abrasive particles are dispersed in a neutral solvent, and an electrolyte salt containing at least a main component element in the metal to be polished is added. 2. The polishing liquid according to claim 1, wherein the electrolyte salt is a nitrate, a sulfate, a chloride, an acetate, or a phosphate of a main element in the metal to be polished. 3. The polishing liquid according to claim 1, wherein the neutral solvent is water, and the abrasive particles are monodisperse spherical fine particles. 4. A method for polishing a metal film formed on a semiconductor substrate via an insulating film, wherein the polishing liquid according to claim 1 is used. 5. A method for polishing a metal film formed by embedding in a wiring groove on an insulating film in which a wiring groove is formed in advance, wherein the polishing liquid according to claim 1 is used. Polishing the metal film above the insulating film to expose a composite surface composed of the insulating film and the metal film embedded in the wiring groove. 6. A method of polishing a metal film formed by embedding in a wiring groove on an insulating film in which a wiring groove is formed in advance, wherein the polishing liquid according to claim 1 is used. A first polishing step of polishing an outline of the metal film above the insulating film, and then dispersing the abrasive particles in water.
And further cellulose, glycerin or acrylate
A second polishing step of polishing a metal film above the insulating film using a polishing liquid to which a tellurium is added to expose a composite surface composed of the insulating film and the metal film embedded in the wiring groove. A polishing method comprising: 7. The polishing method according to claim 6 , further comprising a third step of cleaning said composite surface following said second polishing step.