JPH07193034A - Polishing method - Google Patents

Abstract

PURPOSE:To suppress the occurrence of flaws and dishing on the surface by forming a film to be polished comprising metal so as to fill a recess part on a substrate having the recess part on the surface and polishing the film to be polished by using a polishing material so that the film to be polished is made to remain selectively in the recess part. CONSTITUTION:An SiO2 film 32 is formed on. a silicon substrate 31. Then, a carbon film 34 having the thickness of 50nm is formed on the entire surface on the SiO2 film 32. Thereafter, a groove for wiring is formed. Then, an Al film 33 is formed on the entire surface by a DC magnetron sputtering method. At this time, the thickness of the Al film 33 is set at the thickness larger than the step of the SiO2 film 32. Then, polishing is performed for the Al film 33, and the Al film 33 is mode to remain only in the groove. The polishing is performed under the state, wherein the diameter of the polishing particles is 100nm or less and the pH of the polishing liquid is 7.5 or more. When the diameter of the polishing particle is larger than 100nm and the pH of the polishing liquid is higher than 7.5, the chemical action in polishing becomes large, and clishing occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method which is one of semiconductor manufacturing techniques, and more particularly to a method for polishing a conductor film.

[0002]

2. Description of the Related Art In recent years, large-scale integrated circuits (LSIs) formed by integrating a large number of transistors, resistors and the like on one chip have been widely used in main parts of computers and communication devices. Therefore, the performance of these devices as a whole is
It is greatly affected by the performance of I itself. With the high integration of LSI, various fine processing techniques have been developed. The minimum feature size of the pattern has been decreasing year by year, and it is already on the order of submicrons. C is one of the technologies that have been developed to meet such strict miniaturization requirements.
There is MP (Chemical Mechanical Polishing) technology.
This technique is indispensable for flattening an interlayer insulating film, forming a plug, forming a buried metal wiring, and separating a buried element in a semiconductor device manufacturing process.

FIGS. 19A to 19G are process cross-sectional views showing an example of embedded metal wiring formation using a conventional polishing technique. In the figure, only the metal wiring portion is shown, and other structures such as elements below the insulating film 2 are omitted. First, as shown in FIG. 19A, an insulating film 2 is formed on a semiconductor substrate 1 such as a silicon substrate.
Are formed to flatten the surface of the insulating film 2. Then, FIG.
As shown in FIG. 9B, a groove for wiring or an opening for connecting wiring is formed in the insulating film 2 by the usual photolithography method and etching method. Then, in FIG.
As shown in (C), the wiring metal film 3 having a thickness exceeding the depth of the groove formed in the insulating film 2 is formed. In this case, a barrier metal film may be formed between the insulating film 2 and the wiring metal film 3 in order to prevent mutual diffusion or reaction between them.

Then, in order to leave the wiring metal film 3 only in the groove or opening, the wiring metal film 3 is subjected to polishing treatment using alumina particles or the like as abrasive particles. In this case, a film made of a material having a large polishing rate selection ratio with respect to the wiring metal film 3 may be formed on or below the wiring metal film 3 as a polishing resistant film.

Next, the method of Wada et al. (Japanese Patent Application No. 4-065).
781 specification, 4-212380 specification, 4-2.
69202 specification and 5-67410 specification), a polycrystalline Al film is used as a metal film for wiring.
As shown in FIG. 19 (D), annealing is continuously performed in a vacuum from the state shown in FIG. 9 (C) to monocrystallize Al in the groove portion, and the Al film is changed to a convex portion of the insulating film 2 ( 19 (E), the remaining Al film is removed by polishing as shown in FIG. 19 (E).

The ideal shape after the polishing process is, as shown in FIG. 19E, the wiring metal film 3 only in the groove.
Remains, and metal wiring (connection wiring) is formed on the surface without any scratches or impurities, the wiring metal film 3 does not exist at all in the convex portion, and the surface of the insulating film 2 and the wiring metal film 3 are not formed. The surfaces are coplanar.

However, in the actual polishing step, the metal film for wiring is mechanically operated between the surface to be polished of the wiring metal film 3 and the polishing particles or between the surface to be polished and the pad holding the polishing agent. The surface may be scratched and roughened, or the abrasive particles may be embedded or left in the wiring metal film 3. In addition, as shown in FIG. 19F, the wiring metal film 4 embedded in the groove and the opening,
Particularly in a wide area, a phenomenon called dishing occurs in which the thickness of the central portion becomes thin. Become When this dishing phenomenon occurs, abrasive particles tend to remain there. For example, when a metal having low hardness and ductility, such as Al or Cu, is used as the material of the wiring metal film 3, those tendencies are remarkable. Occurrence of scratches or dishing on the surface of the metal film for wiring, residual polishing particles, etc. increase resistance of the obtained wiring or cause disconnection, resulting in lower reliability and lower product yield.

As a polishing treatment capable of suppressing the generation of scratches or dishing on the surface of the wiring metal film, for example, when the film to be polished is an Al film, a slurry in which alumina particles are dispersed in an acidic aqueous solution of pH 3 or less is used. Treatment can be mentioned (Beyer et al, USP No. 4944836). However, in this polishing process, Si for Al
The polishing selectivity ratio of O ₂ (SiO ₂ / Al) cannot be sufficiently obtained. Therefore, if this polishing treatment is applied when forming the buried wiring, the SiO ₂ is simultaneously polished at the same time as the polishing of the Al film (wiring metal film 3).
The film (insulating film 2) is also polished, and SiO ₂
There is a problem that the depth of the groove formed in the film becomes small and the size of the wiring becomes small. Further, in this polishing process, since an acidic aqueous solution is used, there is a problem that the polishing apparatus is corroded.

On the other hand, a method of forming an aluminum plug by polishing treatment using a mixed solution of amine and hydrogen peroxide solution without using abrasive particles has been reported (IEDM 1992 p.976 Y. Hayashi. et al). In this method, since polishing particles are not used, polishing progresses almost chemically, and scratches and roughness hardly occur on aluminum. However, since the ratio of the polishing rate of aluminum to the dissolution rate of aluminum in the mixed solution (polishing rate / dissolution rate) is small, the occurrence of dishing becomes remarkable, and for example, the sample in the state shown in FIG. When the polishing process is performed,
As shown in FIG. 9 (G), there is a problem that the Al film in the groove to be the wiring disappears before the Al film (wiring metal film 3) remaining on the convex portion is removed.

[0010]

As described above, in the formation of the buried wiring using the conventional polishing method, scratches (roughness) and dishing which occur on the wiring surface cannot be prevented, and the reliability is high. Difficult to get wiring.

The present invention has been made in consideration of the above circumstances, and provides a polishing method capable of suppressing scratches (roughness) and dishing generated on a wiring surface to the extent that there is no practical problem and polishing. The purpose is to provide.

[0012]

Means for Solving the Problems The present inventors have paid attention to the relationship between the average particle size of abrasive particles and the pH of a polishing liquid, and the scratches and dishing that occur on the object to be polished. It was also found that by regulating the pH of the polishing liquid within a desired range, polishing can be performed without causing scratches and dishing on the object to be polished.

That is, according to the present invention, a step of forming a film to be polished made of a metal so as to fill at least the concave portion on a substrate having a concave portion on the surface thereof, and an abrasive having a pH of 7.5 or more containing abrasive particles and a solvent. Is used to polish the film to be polished so as to selectively leave the film to be polished in the recesses.

In this polishing method, the film to be polished is preferably a film containing aluminum as a main component, the polishing particles preferably contain polishing particles made of silica, and the particle size of the polishing particles is 100 nm or less. Is preferred.

Further, according to the present invention, a step of forming a film to be polished on a substrate having a concave portion on its surface so as to fill at least the concave portion, a solution for etching the film to be polished, and corrosion inhibition of the film to be polished. And a polishing agent containing a polishing particle to polish the film to be polished so as to selectively leave the film to be polished in the recesses.

In this polishing method, it is preferable that the corrosion inhibitor is a silicate and / or a chromate, and that it is generated by the reaction between the solution and the polishing particles. Further, it is preferable that the abrasive particles include silica particles, and the corrosion inhibitor is silicate ions and negatively charged silica.

Here, the particle size of the abrasive particles means the average particle size,
In particular, it means the average particle diameter of the primary particle diameter. 100 nm particle size
The following is preferable because the particle size is 100 nm.
This is because the number of scratches increases if the value exceeds. The film to be polished is an object to be polished in polishing, and examples of the material thereof include Al, Al alloy, Cu, Cu alloy, Ag, and Ag alloy.

In the present invention, the temperature below room temperature for supplying the abrasive means the temperature when the temperature of the slurry-like abrasive maintained at room temperature is lowered by a cooling mechanism.
It is preferable to supply the abrasive at 5 ° C. or lower, particularly 15 ° C. or lower, and most preferably 5 ° C. or lower.

[0019]

According to the polishing method of the present invention, a film to be polished is formed on a substrate having concave portions on its surface so as to fill at least the concave portions, and a pH of 7. containing polishing particles having a particle diameter of 100 nm or less.
It is characterized in that the film-to-be-polished is polished with 5 or more abrasives to selectively leave the film-to-be-polished in the recesses.

The reasons for selecting the particle size of the polishing particles and the pH of the polishing liquid in the present invention are as follows. That is, under the conditions outside the scope of the present invention, when the particle size of the abrasive particles is 100 nm or less and the pH of the polishing liquid is less than 7.5, and when the particle size of the abrasive particles is greater than 100 nm, There are practical problems.

First, when the particle size of the polishing particles is 100 nm or less and the pH of the polishing liquid is less than 7.5, the mechanical action in polishing becomes large, which is a practical obstacle to the film to be polished. To some extent (maximum surface roughness of 20 nm or more),
Furthermore, in this range, the polishing liquid becomes a gel, which makes handling difficult.

As is clear from FIGS. 3 and 4, the particle size of the polishing particles is 5 nm and the pH of the polishing liquid is 7.
In the case of 0, R _max is 20 nm, and the particle size of the abrasive particles is 1
When the polishing liquid has a pH of 00 nm and the polishing liquid has a pH of 7.5, R _max is 20 nm. Therefore, the pH of the polishing liquid is 7.0 to 7.
In the case of the range of 5, the maximum surface roughness can be 20 nm or less by appropriately reducing the particle size of the abrasive particles. That is, in FIG. 3, the particle size of the polishing particles is 5 nm and the pH of the polishing liquid is 7.0, and the particle size of the polishing particles is 10 nm and the pH of the polishing liquid is 7.5. It is preferable to employ a condition in which the particle size of the polishing particles and the pH of the polishing liquid are combined, which is indicated by the line connecting smoothly and the region on the particle size side lower than this line. However, considering the above-mentioned problems, the particle size of the abrasive particles is 10
Most preferably, it is 0 nm or less and the pH of the polishing liquid is less than 7.5.

On the other hand, when the particle size of the polishing particles is larger than 100 nm and the pH of the polishing liquid is higher than 7.5, the chemical action becomes large in the polishing, and the electromigration resistance is lowered and the reliability is lowered. The film to be polished in the recess is polished to the extent that problems occur, and dishing occurs.

Based on such knowledge, in the present invention, as the polishing conditions for the film to be polished, the grain size of the polishing particles is 100 nm or less and the pH of the polishing liquid is 7.5 or more, and the surface roughness and dishing are prevented. It is suppressed to the extent that there is no problem in practical use.

Further, in the polishing method of the present invention, a film to be polished is formed on a substrate having concave portions on its surface so as to fill at least the concave portions, and the pH is 7.5 or more including polishing particles having a particle diameter of 100 nm or less. It is characterized in that the polishing target film is selectively left in the recesses by supplying the polishing agent at a temperature below room temperature to polish the polishing target film. In this way, by supplying a polishing agent at a low temperature of room temperature or lower, polishing can be performed without causing scratches and dishing on the film to be polished.

[0026]

Embodiments of the present invention will be specifically described below with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic view showing an example of a polishing apparatus used in the polishing method of the present invention. This polishing apparatus includes a rotatable polishing plate 14, a polishing pad 13 affixed on the polishing plate 14, a polishing plate 14, and a rotatable sample holder 11.
And a polishing liquid supply pipe 15 connected to the polishing liquid tank and having a discharge portion extending to the vicinity of the polishing pad 13. The object to be polished 12 is vacuum-chucked to the sample holder 11 so that the surface to be polished faces the polishing pad 13. Further, the polishing agent 16 is supplied onto the polishing pad 13 by the polishing solution supply pipe 15, and the supply amount thereof can be arbitrarily controlled.

Here, in selecting the material of the polishing pad 13, the hardness (Shore hardness of 66 to 88) is selected.
And materials (foam polyurethane, foam polyurethane subjected to suede processing, non-woven fabric, resin-impregnated non-woven fabric)
The polishing pad (Al
The film) was subjected to polishing treatment, and the occurrence of scratches on the object to be polished was examined in each case. As a result, when a foamed polyurethane material having a suede finish was used as the material, scratches having a depth of 5 nm or more did not occur on the surface of the object to be polished regardless of hardness. Therefore, it was found that as the material for the polishing pad, foamed polyurethane with suede processing was most preferable. Therefore,
In this embodiment, this material is used for the polishing pad 13.

Further, as a polishing agent, SiO _{2 in} a dilute aqueous solution of piperazine [C ₄ H ₁₀ N ₂ ] which is a secondary amine is used.
A colloidal solution in which particles are dispersed was used. Various polishing liquids obtained by changing the average particle diameter of SiO ₂ particles by changing the proportion of SiO ₂ particles as polishing particles in the polishing liquid within the range of 50% by weight or less were used. The pH of the polishing liquid was adjusted by adjusting the amine concentration.

FIG. 2 is a sectional view showing an object to be polished used in this embodiment. In the figure, 21 indicates a silicon substrate. A SiO ₂ film 22 is formed on the silicon substrate 21.
The SiO ₂ film 22 has a width of 0.4 to 10 μm and a depth of 0.4.
A groove for wiring of about μm is formed. S with groove
A carbon film 23 having a thickness of 50 nm is formed as a polishing resistant film on the entire surface of the iO ₂ film 22 by a DC magnetron sputtering method. A polycrystalline Al film 24 is formed on the carbon film 23 by the DC magnetron sputtering method. The polycrystalline Al film 24 is formed without being heated in a vacuum and then continuously subjected to a heat treatment in a vacuum, whereby polycrystalline aluminum is aggregated and embedded in the groove to be a single crystal. At this time, part of the polycrystalline Al film 24
Even if a is aggregated, it is not embedded in the groove but single crystallized and remains in a wide region other than the groove.

The Al film 24 remaining in the regions other than the grooves by subjecting such an object to be polished to a polishing process (CMP)
a was removed. FIG. 3 is a graph showing the relationship between the particle size of abrasive particles and the maximum surface roughness R _max of the Al film 24 in the polishing process. In FIG. 3, the particle diameter on the horizontal axis means the maximum diameter of the abrasive particles contained in the abrasive. Further, FIG. 4 is a graph showing the relationship between the pH of the polishing liquid and the maximum surface roughness R _max . The results shown in FIGS. 3 and 4 are obtained by performing the polishing process under the polishing conditions of the polishing pressure of 300 gf / cm ² , and the rotation speed of the sample holder 11 and the polishing plate 14 of 100 rpm.

In FIG. 3, the particle size of the abrasive particles is 100 nm.
The maximum surface roughness R _max is 20 nm when the pH of the polishing liquid is 7.5 and the particle size of the polishing particles is 150 nm and the pH of the polishing liquid is 14. Further, as can be seen from FIG. 3, when the particle size of the abrasive particles is reduced, the maximum surface roughness R _max is also reduced. The reason for this is that scratches on the aluminum surface are formed by the mechanical action of aluminum and abrasive particles. Further, as can be seen from FIG. 3, the inclination of the graph becomes gentler as the particle size of the abrasive particles becomes smaller. Particularly, when the pH of the polishing liquid is 7.5 or more, the maximum surface roughness R _max is almost constant when the particle diameter of the polishing particles is around 10 nm. It is considered that this is because when the particle size of the abrasive particles becomes smaller, the abrasive particles tend to aggregate. That is, it is considered that even if the particle diameters of the individual polishing particles are small, those having a large particle diameter formed by aggregating the polishing particles having these small particle diameters are involved in the actual polishing.

On the other hand, as can be seen from FIG.
If H is increased, the maximum surface roughness R _max also decreases.
In particular, when the pH of the polishing liquid is between 7 and 7.5, the maximum surface roughness R
_max decreases rapidly. The reason for this is considered as follows. Generally, aluminum has the property of forming a passivation film such as an oxide film on its surface in an aqueous solution. This passivation film is stable in the pH range of 4 to 7.5 and works well as a barrier for protecting aluminum. However, in a solution having a pH of more than 7.5, the ability of the passivation film as a barrier is suddenly weakened, so that aluminum is dissolved. Therefore,
From such characteristics of aluminum, it is considered that the reason why the maximum surface roughness R _max rapidly changes in the vicinity of pH 7.5 is that the chemical action on aluminum rapidly increases in the vicinity of pH 7.5.

Regarding the polishing pressure, the value is 30.
It was found that, when it was 0 gf / cm ² or more, the maximum surface roughness R _max also increased substantially in proportion to the increase of the polishing pressure.
On the other hand, when the polishing pressure is less than 300 gf / cm ² , the maximum surface roughness R _max is almost saturated, and for example, the polishing pressure is 30
The value of the maximum surface roughness R _max in gf / cm ^2, the polishing pressure was about 90% to 100% of the value at 300 gf / cm ^2.
Regarding the rotation speeds of the sample holder 11 and the polishing plate 14, there was no particular change in the maximum surface roughness R _max in the range of 50 to 500 rpm.

Thus, from FIGS. 3 and 4, at least the particle size of the polishing particles is 100 nm or less, and the polishing liquid p
By polishing the Al film 24 under the condition that H is 7.5 or more, the maximum surface roughness R _max can be set to 20 nm or less, which is a value at which there is no practical problem. Even if the above conditions are not satisfied, the surface roughness R _max can be 20 nm or less if the pH of the polishing liquid is 7.5 or more.

Here, the fact that the maximum surface roughness R _max is 20 nm or less has a great significance in forming an actual LSI wiring. In FIG. 6, the wiring width is 0.2,
The relationship between the maximum surface roughness R _max and the specific resistance ρ for three cases of 0.4 and 1.0 μm is shown. The specific resistance here is different from a constant determined by a substance and its structure as generally defined. Hereinafter, the definition of the specific resistance will be described with reference to FIG. As shown in FIG. 5, the Al wiring 25 (solid line) having scratches on the polished surface
When obtaining the value of Al, the cross-sectional area is Al with no scratches
It is calculated by assuming the cross-sectional area of the wiring 25a (dotted line). In general, the specific resistance ρ is represented by ρ = R · S / L, where L is a wiring length, S is a cross-sectional area, and R is a resistance value. Therefore, the graph shown in FIG. 6 is drawn based on the measured value of the resistance value R with respect to the maximum surface roughness R _max with S and L fixed for each wiring width. As can be seen from FIG. 6, the specific resistance ρ of the wiring width on the order of submicron is the maximum surface roughness R _max.
It increases sharply at the boundary of 20 nm. The rate of increase increases as the wiring width decreases. Also,
As a realistic LSI wiring, for example, wiring width 0.2 μm
When a wiring of 2 is attempted to be manufactured, a scratch having a depth of 20 nm or more greatly increases the specific resistance, and the device performance and reliability are significantly reduced. In this way, suppressing the maximum surface roughness R _max to 20 nm or less is very important in forming a practical LSI wiring.

FIG. 7 shows the state of the surface of the object to be polished when the object to be polished shown in FIG. 2 is polished by fixing the particle size of the polishing particles to 100 nm and changing the pH of the polishing liquid in the range of 7 to 13. It is a figure. Specifically, the surface of the object to be polished polished under the above conditions is observed by an optical microscope and an electron microscope (SEM). The polishing pressure, rotation speed and polishing time were constant at all pH values. When the pH of the polishing liquid was 7, as shown in FIG. 7A, many scratches were observed on the surface of the Al film 24. It is considered that this is because the chemical action hardly works. Further, when the pH of the polishing liquid is 10, as shown in FIG.
There was no scratch on the surface of the film 24, and no decrease in film thickness was observed. Further, even when the pH of the polishing liquid was 13, as shown in FIG. 7C, there was no scratch on the surface of the Al film 24. However, in this case, dishing was large and the film thickness was considerably reduced. Regarding dishing, it becomes more remarkable when the pH of the polishing liquid is increased to increase the chemical action.

As described above, in order to suppress the dishing which appears remarkably when the pH of the polishing liquid is increased, the ratio (V _P / V _E ) of the polishing rate V _P of aluminum to the dissolution rate V _E of aluminum by the polishing agent is set. It needs to be large. Generally, on the aluminum surface during the polishing process, the convex portion of the surface is easily subjected to the mechanical action of the abrasive particles held by the polishing pad stuck on the polishing plate 14, and the new surface is always exposed to the abrasive. Therefore, it is easily affected by chemical action. That is, the convex portion receives both mechanical and chemical actions. On the other hand, the concave portion is less susceptible to mechanical action and is only isotropically etched by the chemical component of the abrasive. That is, it is considered that the recesses are only subjected to a chemical action. Therefore, in order to suppress the dishing, it is most desirable that the dissolution rate V _E of aluminum by the abrasive in the recess is 0 nm / min.

FIG. 8 is a graph showing the relationship between the pH of the polishing liquid and the dissolution rate. In the figure, the solid line shows the polishing liquid of the amine aqueous solution containing no polishing particles (SiO ₂ ), and the broken line shows the polishing liquid in which the polishing particles are dispersed in the amine aqueous solution. FIG. 9 is a graph showing the relationship between the pH of the polishing liquid and the polishing rate V _P. As can be seen from FIG. 8, the dissolution rate V _E
Is sharply reduced by dispersing abrasive particles in an aqueous amine solution. In particular, when the particle diameter φ of the abrasive particles is 100 nm or less, it is stable at 2 nm / min or less. Further, as can be seen from FIG. 9, the polishing rate V _P increases in proportion to the particle diameter φ and pH. However, when the particle diameter φ is larger than 100 nm, the polishing speed V increases with the increase of the particle diameter φ.
The increase in _P is small.

By the way, when polishing the object to be polished shown in FIG. 2, the value of V _P / V _E needs to be 90 or more from the practical point of view. This is the convex part A
The height of the I film 24a is generally in the range of 1 to 1.8 μm, while the dishing amount allowed for the Al film 24 as a wiring prevents an increase in resistance and a decrease in reliability (electromigration resistance etc.). Therefore, it is necessary to make the thickness 20 nm or less. In consideration of this point, the range of the particle size of the polishing particles and the pH of the polishing liquid at which the maximum surface roughness R _max is 20 nm or less and V _P / V _E is 90 or more are as follows.

As can be seen from FIG. 8, when the particle size of the polishing particles is 100 nm and the pH of the polishing liquid is 7.5 to 14, the dissolution rate V _E is 2 (pH 7.5) to 2.4. (PH 1
4). Further, as can be seen from FIG. 9, when the particle size of the polishing particles is 100 nm and the pH of the polishing liquid is 7.5 to 14, the polishing rate V _P is 180 (pH 7.
5) to 220 (pH 14). That is, the particle size is 1
00 nm and pH of 7.5-14, V _P /
V _E is 90 or more. Here, the increase rate of the dissolution rate V _E with respect to the particle size is always larger than the increase rate of the polishing rate V _P in the range of pH 7.5 to 14 (ΔV _E > Δ).
_VP ) is known. That is, the particle size is 100 nm
When it becomes larger, V in the range of pH 7.5 to 14
_P / V _E is less than 90, which makes proper polishing impossible. Therefore, in order to set the maximum surface roughness R _max to 20 nm or less and the V _P / V _E to 90 or more, the particle size of the polishing particles must be 100 nm or less and the pH of the polishing liquid must be 7.5 or more. . In addition, among the abrasives currently on the market, the most accurate particle size is, for example, a particle size of 1
There is an error of ± 5% at 00 nm. Therefore, the particle size is 1
Although it is specified to be 00 nm or less, it is necessary to consider the error (95 to 105 nm) as the true value. Also, FIG.
And FIG. 9 shows the case where the weight ratio of the abrasive particles to the whole abrasive is 5%, and when the weight ratio is higher than 5%,
For example, 10 to 3 used in normal polishing processing
When it is about 0%, the number of abrasive particles per unit area increases, and thus dishing is naturally suppressed.

In the object to be polished shown in FIG. 2, the carbon film 23
When the same polishing as above was carried out using the object to be polished which was omitted only as the object to be polished, the following was found. That is, since the carbon film 23 does not exist, the underlying S
Polishing has proceeded to the iO ₂ film 22 slightly, but there is no problem. However, in this case, Si is better than a polishing resistant film such as a carbon film.
Due to the high polishing speed of the O ₂ film, Al and SiO ₂
Both polishing amounts must be controlled to appropriate values. This can be done even if the object to be polished does not have a polishing resistant film, but the polishing conditions must be rigorously defined. In fact, when comparing the polishing rates of Al, carbon, and SiO ₂ at pH 11, as shown in FIG. 10, carbon is superior to SiO ₂ as a material for the polishing resistant film. However, in the case of a polishing liquid using KOH or NaOH for pH adjustment, SiO
The polishing speed of ₂ is 100 nm / min or more, and Al
Since the selection ratio between SiO ₂ and SiO ₂ becomes smaller, a polishing resistant film such as the carbon film 23 is required. The carbon film 23
Instead of TiN, ZrN, HfN, TaN, VN,
A film made of NbN, TiW or the like may be used as a polishing resistant film against aluminum polishing. (Embodiment 2) FIGS. 11A and 11B are process sectional views for explaining another example of the polishing method of the present invention.
First, as shown in FIG. 11A, a SiO ₂ film 32 was formed on a silicon substrate 31. Next, a carbon film 34 having a thickness of 50 nm was formed on the entire surface of the SiO ₂ film 32 by a DC magnetron sputtering method, and then a wiring groove was formed through a normal photolithography process.
Then, the Al film 33 was formed on the entire surface by the DC magnetron sputtering method. At this time, the thickness of the Al film 33 is 450 nm, and the thickness is equal to or larger than the step difference of the SiO ₂ film 32. Then, as shown in FIG.
l film 33 is subjected to a polishing treatment to form Al only in the groove.
Membrane 33 remained. In this polishing treatment, the particle size of the polishing particles is 100 nm or less as described above, and the polishing liquid p
H was set to 7.5 or more. Further, the polishing liquid and the polishing apparatus used are those described above.

Observation of the polished surface after the polishing treatment with an optical microscope and SEM revealed that Al
The film 33 was completely removed, and no scratches or roughness due to polishing were observed on the surface of the Al film 33 inside the groove. Further, it was found from the cross-sectional observation by SEM that the film thickness of the Al film 33 inside the groove was hardly reduced and that dishing did not occur. In the above-described examples, the case where colloidal silica prepared by dispersing SiO ₂ particles as abrasive particles in an aqueous solution of piperazine is used as the polishing liquid has been described.
A that occurs when abrasive particles are added to an alkaline aqueous solution
It has been found that the drastic decrease in the dissolution rate is particularly remarkable in the case of silica particles. Further, it has been found that other particles such as cerium oxide, titanium oxide, and alumina have a lower dissolution rate, but do not show a sharp change as compared with silica particles and can be used.

These mechanisms are believed to be as follows. When silica particles are dispersed in an alkaline aqueous solution as in this example, the surface of the silica particles is negatively charged, so that the electric double layer is formed by adsorption on the local anode on the aluminum surface, resulting in dissolution of aluminum. Suppress. That is, the silica particles play a role of a so-called corrosion inhibitor (inhibitor) with respect to aluminum. As a result, the alkaline silica dispersion solution of the present invention can be treated with Al without causing scratches or dishing.
Can be polished. For example, when Al is polished with a polishing agent in which alumina particles (particle diameter 50 nm) are dispersed in a piperazine aqueous solution (pH 11), R _max is within 20 nm, but dishing is large and it is difficult to form Al-embedded wiring.

By the way, when particles other than silica, such as cerium oxide, titanium oxide, and alumina, are dispersed in an alkaline aqueous solution, the decrease in Al dissolution rate is not as remarkable as that of silica particles as described above. For example,
By adding a certain amount of silica particles, the ratio of the dissolution rate to the Al polishing rate becomes sufficiently small. At this time, the effect of the present invention is exhibited by dispersing the cerium oxide, titanium oxide, or alumina particles in an aqueous solution having a particle size of 100 nm or less and having a pH of more than 7.5, and further adding silica particles having a particle size of 100 nm or less. .

Here, an example is shown in which alumina particles and silica particles are mixed to polish Al. The polishing liquid has a pH of 11.
Alumina particles with a particle size of 50 nm were added to 0 of the piperazine aqueous solution.
0.0 wt%, 1.0 wt% silica particles with a particle size of 50 nm
Each was dispersed and produced. As the polishing apparatus and the object to be polished, those shown in FIG. 1 and FIG. 11 (A) were used. As a result of polishing, no scratches or dishing were observed on the Al surface, and a cross-sectional shape as shown in FIG. 11 (B) was obtained, as in the above example. R _max of Al surface at this time
Was 9-10 nm. In addition, instead of the above-mentioned alumina particles, the same experiment was conducted using titanium oxide particles and cerium oxide particles having a particle diameter of 50 nm, but the same effects as above could be confirmed. In addition, it was confirmed that diamond, silicon carbide, zirconium oxide, and the like are effective in addition to the above-mentioned alumina, titanium oxide, and cerium oxide particles when they are used by mixing with silica particles.

Further, as the substance for adjusting the pH, amines such as triethylamine, choline, TMAH, ammonia, etc. may be used in addition to the above-mentioned piperazine. Also, by adding a substance generally known as an Al corrosion inhibitor, the Al dissolution rate can be extremely reduced even when particles other than silica are used. A
As the corrosion inhibitor of 1), silicates, chromates, amines, glucose, tragacanth rubber, agar and the like are known, although different ones are used depending on whether the solution is acidic or alkaline. As a result of examination by the present inventors,
It was confirmed that when the polishing liquid is alkaline, at least silica particles, silicates, glucose, agar and the like show good characteristics as a corrosion inhibitor, that is, a tendency of decreasing the Al dissolution rate. In addition, alumina particles (particle size 50n
m) was dispersed in an aqueous solution of piperazine (pH 11), each corrosion inhibitor was added, and Al was polished using this. It was confirmed that R _max was within 20 nm and dishing was also suppressed low. Was done.

Further, in the above embodiment, the material to be polished is A
Although the case where the 1 film is used has been described, an Al alloy film containing Al as a main component and a small amount of Cu or Si may be used as the object to be polished. Furthermore, if abrasive particles, a corrosion inhibitor that suppresses elution of metals, and a mixture of chemical components that dissolve metals are used in the abrasive, a film made of Cu, Cu alloy, Ag, Ag alloy, or the like is used as an object to be polished. You can also Further, in the present invention, the recess may have a different width depending on the location. In addition, various modifications can be made without departing from the scope of the present invention. (Embodiment 3) FIG. 12 is a schematic view showing another example of the polishing apparatus used in the polishing method of the present invention. In the figure, 41 indicates a sample boulder. The sample holder 41 is connected to a drive mechanism (not shown), and is vertically movable and rotatable by the drive mechanism. An object 42 to be polished is held on the sample boulder 41 by a vacuum chuck. A polishing plate 44 is arranged below the sample holder 41, and a polishing pad 43 is attached to the upper surface of the polishing plate 44. The polishing plate 44 and the polishing pad 43 form a polishing platen. This polishing platen is rotatable by a drive mechanism (not shown).

A pipe 45 is arranged in the polishing plate 44, and the pipe 45 is connected to a platen temperature adjusting device 46. A medium such as water is circulated in the pipe 45.
The platen temperature adjustment device 46 is provided with a refrigerator and a heater (not shown) inside and adjusts the temperature of the medium circulating in the pipe 45. Thereby, the temperature of the polishing platen is adjusted.

Above the polishing platen, a 50-liter polishing agent storage tank 47 containing the polishing agent is installed. In the abrasive storage tank 47, a propeller 48 for stirring the abrasive is attached. A polishing agent supply pipe 49 is attached to a side portion of the polishing agent storage tank 47, and the polishing agent temperature adjusting device 5 is attached to the polishing agent supply pipe 49.
2 is attached. This polishing agent temperature control device 52
Is equipped with a refrigerator (not shown). Abrasive 51
As the abrasive passes through the abrasive supply pipe 49,
Is temperature controlled prior to being applied to the polishing pad 43. A pipe 53 is wound around the abrasive storage tank 47, and the pipe 53 is connected to a tank temperature adjusting device 54. A medium such as water is circulated in the pipe 53.
The tank temperature adjustment device 54 is provided with a refrigerator and a heater (not shown) inside and adjusts the temperature of the medium circulating in the pipe 53. As a result, the temperature of the abrasive storage tank 47 is adjusted. The polishing agent temperature adjusting device 52 and the tank temperature adjusting device 54 may be controlled separately, or may be collectively controlled. Thus, the polishing apparatus according to the present invention is constructed.

In the polishing apparatus having the above structure, when actually polishing an object to be polished, the drive mechanism rotates the sample holder 41 and the polishing platen, and the sample holder 41 is lowered to remove the object 42 to be polished. It is pressed against the polishing pad 43 with a constant load. In this state, polishing is performed by supplying the polishing agent 51 onto the polishing pad 43 from the discharge portion 50 of the polishing agent supply pipe 49.

First, a SiO ₂ film 60 is formed on a silicon substrate. Then, a carbon film 61 having a thickness of 50 nm is formed on the entire surface of the SiO ₂ film 60 by a DC magnetron sputtering method, and then a wiring groove (widths 1 μm, 3 μm, 5 μm, and 10 μm) is formed through a normal photolithography process. To form. After that, the Al film 62 is formed on the entire surface by the DC magnetron sputtering method. At this time, the film thickness of the Al film 62 was set to 450 nm so as to be higher than the groove step. Thus, the object 42 to be polished as shown in FIG. 13 was produced.

The object 42 to be polished was placed on the sample holder 41, and the object 42 to be polished was subjected to CMP. As the polishing pad 43, one having a total thickness of 1.5 mm and a Shore hardness of 66 to 88 formed by sticking a foamed polyurethane layer on a non-woven fabric was used. The reason for selecting this polishing pad is that the polishing pressure is 30 to 600 gf / cm ² and only pure water is used for Al,
This is because when CMP was performed on a soft metal such as Cu, no scratches having a depth of 100 nm or more were generated on the polished surface regardless of hardness and polishing pressure. Further, as the abrasive 51, silica particles having an average particle diameter of 30 nm dispersed in an alkaline amine aqueous solution at 10% by weight were used. The polishing conditions were set as shown below. The polishing platen temperature was kept constant by the platen temperature controller 46.

Polishing pressure: 300 gf / cm ² Polishing plate temperature: 25 ° C. (room temperature) Polishing plate: 100 rpm rotation speed Sample holder: 100 rpm rotation speed Under the above polishing conditions, the temperature of the polishing agent supplied was as follows. Changed. That is, the polishing agent 51 is put into the polishing agent storage tank 47 at 25 ° C. (room temperature), and the polishing agent storage tank 47 is adjusted to 25 ° C. by the tank temperature adjusting device 54. At this time, the polishing agent 5 in the polishing agent storage tank 47
Stir 1 with propeller 48. When the polishing agent 51 is supplied onto the polishing pad 43 through the polishing agent supply pipe 49, the temperature of the polishing agent 51 is changed by the polishing agent temperature adjusting device 52 to −1 to 80 ° C.

A graph showing the relationship between the dishing amount of the Al wiring and the polishing agent temperature when the object to be polished shown in FIG. 13 was polished under these conditions, and the maximum surface roughness Rmax of the Al surface.
Graphs showing the relationship between the temperature and the polishing agent temperature are shown in FIGS. 14 and 15, respectively.

As is clear from FIG. 14, the dishing amount tends to decrease as the temperature of the polishing agent decreases.
Therefore, the dishing of the object to be polished can be reduced by lowering the temperature of the polishing agent. This effect was effective when an abrasive having a colloidal property was used. A fluid having such a colloidal property generally does not follow Newton's viscosity law, and exhibits a property called dilatancy, in which the apparent viscosity increases as the displacement stress increases. Due to this property, it is considered that the abrasive particles retained in the apparently gelled liquid mechanically remove the object to be polished in minute units. Therefore, the biggest cause of the effect of suppressing dishing by lowering the temperature of the polishing agent as in this example is that the above-described polishing mechanism has temperature dependency and dilatancy is emphasized more at low temperature. it is conceivable that.

In general, from the viewpoint of RC delay in LSI wiring, the reduction of the wiring cross-sectional area due to dishing is
It is required to be suppressed to about 10%. For this reason,
The suitable temperature range of the abrasive varies depending on the intended thickness and shape of the wiring. For example, when an embedded wiring having a thickness of 0.4 μm and a width of 0.4 to 10 μm is formed using a polishing resistant film having a thickness of 50 nm, the dishing amount is about 130.
Since it must be less than or equal to nm, it is necessary to keep the temperature of the polishing agent below 15 ° C. as shown in FIG. Further, more desirably, as is clear from FIG. 14, the dishing can be further suppressed by setting the temperature of the polishing agent near the freezing point, that is, -1 to 5 ° C.

Further, as is apparent from FIG. 15, when the above-mentioned polishing agent is used, the maximum surface roughness Rmax of the Al surface after polishing is constant regardless of the temperature of the polishing agent supplied, There was no problem in terms of wiring reliability.

In this embodiment, Al may contain a small amount of impurities. For example, Si 1.0 wt% or Cu
Even if a film made of an Al alloy containing 1.0% by weight is used as the object to be polished, the above effect is exhibited. Further, in the present example, an abrasive containing only silica particles as abrasive particles is used, but if the particle diameter of the abrasive particles is 100 nm or less and the pH of the abrasive is 7.5 or more, it is regarded as silica particles. An abrasive containing other particles as abrasive particles may be used. For example,
The effect of the present embodiment can be exhibited even by using an abrasive containing silica particles and alumina particles having a particle size of 100 nm or less. (Embodiment 4) FIG. 16 shows C using the polishing apparatus shown in FIG.
It is sectional drawing which shows the other example of the to-be-polished object which performs MP. The SiO ₂ film 60 is formed on the silicon substrate. Then, on the SiO ₂ film 60, wiring grooves (width 1 μm, 3 μm, 5 μm and 1
0 μm) is formed. A titanium nitride film 63 having a thickness of 50 nm is formed on the entire surface by DC magnetron sputtering.
To form. Then, the Cu film 64 is formed on the entire surface by the DC magnetron sputtering method. At this time, Cu
The film thickness of the film 64 was set to 450 nm so as to be higher than the groove step. In this way, the object 42 to be polished was produced.

This object to be polished was set on the sample holder 41 of the polishing apparatus shown in FIG. 12, and the object to be polished was subjected to CMP.
The polishing pad 43 has a total thickness of 1.5 mm and a Shore hardness of 66, which is formed by pasting a foamed polyurethane layer on a non-woven fabric.
.About.88 was used. As the abrasive 51, silica particles having an average particle diameter of 30 nm dispersed in hydrogen peroxide solution containing an oxidizing agent in an amount of 20% by weight were used. The polishing conditions were set as shown below. The polishing platen temperature was kept constant by the platen temperature controller 86.

Polishing pressure: 300 gf / cm ² Polishing platen temperature: 25 ° C. (room temperature) Polishing plate: 100 rpm rotation speed Sample holder: 100 rpm rotation speed The relationship between the dishing amount of Cu wiring and the polishing agent temperature at this time Graph and maximum surface roughness Rmax of Cu surface
17 and 18 are graphs showing the relationship between the polishing agent temperature and the polishing agent temperature. As is clear from FIG. 17, the dishing amount tends to decrease as the temperature of the polishing agent decreases. Therefore, the dishing of the object to be polished can be reduced by lowering the temperature of the polishing agent. Further, this effect was a phenomenon that appeared when the abrasive had a colloidal property. Further, as is apparent from FIG. 18, in the same manner as in Example 3, when the above-described polishing agent was used, the maximum surface roughness Rmax of the Cu surface after polishing did not depend on the temperature of the polishing agent supplied. It was constant and there was no problem in reliability of wiring.

In this embodiment, the Cu film is used as the object to be polished, but the above effect is exhibited even if Cu contains a small amount of impurities. Further, in Examples 3 and 4, the polishing pad is formed by laminating a foamed polyurethane layer on a non-woven fabric, but if the hardness is about the same, for example, non-woven fabric of polyester, polyether or the like. The above effect can be obtained by using a polishing pad obtained by impregnating these non-woven fabrics with a resin, or a polishing pad obtained by laminating two or more different types of pads.

According to the present invention, the surface of the insulating film on the semiconductor substrate is
A groove in which a wiring material is formed, or a groove in which a light (visible light, ultraviolet light, X-ray, etc.) absorber material is formed on a transparent (insulating) substrate (for example, It can also be applied to a phase mask made of Cr or W, an X-ray mask).

[0063]

As described above, the polishing method of the present invention is
A film to be polished is formed on a substrate having concave portions on its surface so as to fill at least the concave portions, and p containing abrasive particles and a solvent is added.
Since the film-to-be-polished is polished with a polishing agent of H7.5 or higher to selectively leave the film-to-be-polished in the recesses, scratches (roughness) and dishing generated on the wiring surface to the extent that there is no practical problem. Generation can be suppressed and polishing can be performed.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a polishing apparatus used in a polishing method of the present invention.

FIG. 2 is a sectional view for explaining an example of the polishing method of the present invention.

FIG. 3 is a graph showing the relationship between the particle size of abrasive particles and the maximum surface roughness of an Al film.

FIG. 4 is a graph showing the relationship between the pH of the polishing liquid and the maximum surface roughness.

FIG. 5 is an explanatory diagram for explaining the definition of specific resistance.

FIG. 6 is a graph showing the relationship between the specific resistance and the maximum surface roughness in each wiring width.

7A to 7C are cross-sectional views showing a state of a polishing surface due to a difference in pH of a polishing liquid.

FIG. 8: Dissolution rate and pH at average particle size of each abrasive particle
A graph showing the relationship with.

FIG. 9 is a graph showing the relationship between the polishing rate and pH of the average particle size of each abrasive particle.

FIG. 10 is a graph showing the relationship between the polishing rate and the average particle size of abrasive particles for Al, TiN, SiO ₂ and C.

FIG. 11 is a process sectional view for explaining another example of the polishing method of the present invention.

FIG. 12 is a schematic view showing another example of a polishing apparatus used in the polishing method of the present invention.

FIG. 13 is a cross-sectional view showing an example of an object to be polished used in the polishing method of the present invention.

FIG. 14 is a graph showing the relationship between the dishing amount and the polishing surface temperature.

FIG. 15 is a graph showing the relationship between maximum surface roughness and polishing surface temperature.

FIG. 16 is a cross-sectional view showing another example of the object to be polished used in the polishing method of the present invention.

FIG. 17 is a graph showing the relationship between the dishing amount and the polishing surface temperature.

FIG. 18 is a graph showing the relationship between the maximum surface roughness and the polishing surface temperature.

19A to 19G are process cross-sectional views for explaining a conventional polishing process.

[Explanation of symbols]

11, 41 ... Sample holder, 12, 42 ... Object to be polished, 1
3, 43 ... Polishing pad, 14, 44 ... Polishing plate, 15 ... Polishing liquid supply pipe, 16, 51 ... Abrasive,
21, 31 ... Silicon substrate, 22, 32, 60 ... SiO
₂ film, 23, 34, 61 ... Carbon film, 24, 24a, 3
3, 62 ... Al film, 25, 25a ... Al wiring, 45 ... Piping, 46 ... Plate temperature adjusting device, 47 ... Abrasive storage tank, 48 ... Propeller, 49 ... Abrasive supply pipe, 50 ... Discharge part, 52 ... Abrasive temperature control device, 53 ... Piping, 54 ... Tank temperature control device, 63 ... Titanium nitride film, 64 ... Cu
film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Nobuo Hayasaka No. 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Inside the Toshiba Research & Development Center (72) Inventor Haruo Okano Komukai-Toshiba, Kouki-ku, Kawasaki, Kanagawa Town No. 1 Toshiba Corporation Research & Development Center

Claims (9)

[Claims] 1. A step of forming a film to be polished made of a metal so as to fill at least the concave portion on a substrate having a concave portion on the surface thereof, and a polishing agent having a pH of 7.5 or more containing abrasive particles and a solvent is used. Polishing the film to be polished so that the film to be polished selectively remains in the recesses. 2. The polishing method according to claim 1, wherein the film to be polished is a film containing aluminum as a main component. 3. The polishing method according to claim 1, wherein the polishing particles include polishing particles made of silica. 4. The polishing method according to claim 1, wherein the particle size of the polishing particles is 100 nm or less. 5. A step of forming a film to be polished on a substrate having a recess on the surface so as to fill at least the recess, a solution for etching the film to be polished, a corrosion inhibitor for the film to be polished, and polishing. Polishing the film to be polished with an abrasive containing particles to selectively leave the film to be polished in the recesses. 6. The polishing method according to claim 5, wherein the corrosion inhibitor contains at least one substance selected from the group consisting of silicates and chromates. 7. The polishing method according to claim 5, wherein the corrosion inhibitor is generated by a reaction between the solution and the polishing particles. 8. The polishing method according to claim 7, wherein the polishing particles include silica particles, and the corrosion inhibitor is silicate ions and negatively charged silica. 9. The polishing method according to claim 1, wherein the polishing agent is supplied at a temperature of room temperature or lower to polish the film to be polished.