JPH11251276A - Polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing method and a polishing apparatus which dispenses with extending polishing time of a polished film and for using a special abrasive liquid suitable for a material forming the polished film, while reducing the polishing amount of a recess in the polished film. SOLUTION: A silicon oxide film 3 is formed as an insulation film on a circular silicon substrate 4, and an A1 interconnection 2 is formed on the oxide film 3 through lithography or etching. A silicon oxide film 1, which is a polished film, is then formed by plasma CVD. A circular polishing cloth 9 is positioned opposite to the silicon oxide film 1. Polishing liquid 8 containing polishing particles is supplied between the silicon oxide film 1 and the polishing cloth 9, and desired polishing can be performed in that convex portions are polished and recesses are not polished in the silicon oxide film 1 by maintaining P<=0.5×G×V during the polishing, where P is average pressure, G is viscosity and V is relative velocity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing method used in a process for manufacturing a semiconductor device, and more particularly to a process for planarizing an interlayer insulating film, which is one of the processes for planarizing a substrate surface, and forming an embedded metal wiring. Chemical mechanical polishing (Chemical polishing) used in the step of forming the embedded element isolation film, the step of forming the embedded capacitor, and the like.
The present invention relates to a polishing method such as Mechanical Polishing (hereinafter referred to as CMP).

[0002]

2. Description of the Related Art In recent years, an LSI (Large Scale) has been developed.
Various microfabrication techniques have been researched and developed for high integration and high performance of an integrated circuit.

[0003] The CMP technique is one of the techniques that have been studied to satisfy such demands for strict miniaturization. In particular, it is an indispensable technique in a multilayer wiring forming step such as planarization of an interlayer insulating film, formation of a metal plug, formation of a buried wiring, and a buried element isolation step.

A conventional polishing method will be described below with reference to FIG. FIG. 5A is a cross-sectional view showing a shape of an interlayer insulating film before polishing by a conventional polishing method.
FIG. 2B is a cross-sectional view illustrating a shape of the interlayer insulating film after polishing by a conventional polishing method.

[0005] As shown in FIG.
A silicon oxide film 3 is stacked on the substrate. The Al wiring 2 is arranged on the silicon oxide film 3. Polished film 1 which is a silicon oxide film is formed so as to cover Al wiring 2 and silicon oxide film 3. The polishing target film 1 has irregularities due to the shapes of the Al wiring 2 and the silicon oxide film 3. Also,
A polishing cloth (not shown) is provided to face the film 1 to be polished.

After the polishing is started, the polishing cloth comes into contact with the film 1 to be polished, and the polishing cloth is polished by the relative movement between the polishing cloth and the silicon substrate 4 so as to reduce the projections on the surface of the film 1 to be polished. .

Actually, not only the convex portions but also the concave portions of the film to be polished 1 are polished by the deformation of the shape of the polishing cloth. After polishing, as shown in FIG. 5B, an uneven portion is left on the surface of the film 1 to be polished. In addition, if the interval between the adjacent convex portions is relatively wide, the concave portion between the adjacent convex portions is polished by the polishing cloth, and the step of the uneven portion is further increased.

[0008]

In the LSI manufacturing process, planarization is required because the flatness is reduced to within a focus margin (allowable depth of focus) of lithography (exposure step) for forming a wiring pattern. That's why.

The focus margin becomes smaller due to the miniaturization of the design rule (minimum line width) accompanying the high integration of LSI, so that the flatness after processing required for the flattening step also becomes small.

[0010] In the conventional polishing method, the above-mentioned FIG.
As shown in (b), a step remains on the surface of the film-to-be-polished 1 after polishing. In order to reduce the level difference, it is sufficient to continue polishing, but for that purpose, there is a problem that the thickness of the film-to-be-polished 1 before polishing must be increased.

In addition, there is a problem that the polishing time required for flattening the film-to-be-polished 1 including polishing for eliminating a step after polishing becomes longer, and the manufacturing cost of the LSI increases. Conventionally, there has been a method as shown in FIG. 6 for solving such a problem.

FIG. 6 is a sectional view of an interlayer insulating film formed by another conventional polishing method. Of the uneven portions formed on the surface of the film-to-be-polished 1, in the concave portions between adjacent convex portions, a polishing-resistant film 5 made of a material having a lower polishing rate than the film-to-be-polished 1 made of silicon oxide is provided. There is a method of forming
No. 315308). The polishing resistant film 5 is made of, for example, Si3N
4.

However, the conventional polishing method having such a configuration has a problem in that the number of steps for forming the anti-polishing film 5 and the number of steps for removing after polishing are increased, and the steps are complicated. Further, by adding an organic compound having an extremely strong interaction with the polishing target film 1 to the polishing liquid, the average distance between the surface of the concave portion of the polishing target film 1 and the surface of the polishing cloth during polishing is reduced. There has been proposed a method of preferentially polishing only protrusions, which are larger than the average particle size of abrasive particles contained in the liquid (Japanese Patent Application Laid-Open No. 7-22970).

However, with the increase in the degree of integration and performance of LSIs, the type of the film 1 to be polished needs to be flattened. Therefore, an appropriate organic compound is selected for each material of the film 1 to be polished. Has a problem that development costs and a development period are required.

In view of the above, the present invention has been made in view of the above-described conventional problems, and does not require unnecessarily long polishing time for a film to be polished, reduces polishing of a concave portion of the film to be polished, An object of the present invention is to provide a polishing method and a polishing apparatus which do not require the development of a polishing liquid suitable for a material for forming a film to be polished.

[0016]

In order to achieve the above-mentioned object, a polishing method according to the present invention comprises an average pressure P [unit kPa: kilopascal] for pressing a substrate having a film to be polished against a polishing cloth. , The viscosity G [unit cp: centipoise] of the polishing liquid interposed between the film to be polished and the polishing cloth, and the relative velocity V [due to the relative motion between the substrate and the polishing cloth.
Unit: m / s] is a polishing method for polishing the film to be polished with the polishing cloth while maintaining a relationship of P ≦ 0.5 × G × V. Here, the unit of the average pressure P is kilopascal, the unit of the viscosity G is centipoise, and the unit of the velocity V is m / s.

Further, an average pressure P [kPa] of pressing a substrate having a film to be polished against a polishing cloth,
Viscosity G [cp] of polishing liquid interposed between the polishing cloth
And the relative velocity V [m / s] of the relative motion between the substrate and the polishing cloth have a relationship of P ≦ 0.5 × G × V. A polishing apparatus for polishing with the polishing liquid can also be configured.

Further, display means such as a display or a digital counter for displaying the pressure P, the viscosity G, or the relative speed V may be provided. In other words, by setting the product of the viscosity of the polishing liquid and the relative speed between the substrate and the polishing cloth larger than before, the pressure of the polishing liquid in the concave portions on the surface of the film to be polished is increased, so that the polishing particles and Contact with the film to be polished can be reduced, and polishing of a concave portion between adjacent convex portions can be reduced.

As a material for the substrate, silicon, quartz, sapphire, Al2O3, a group 3-5 compound, or the like can be used. The film to be polished is SiO2, α-S
i, poly Si, SiON, SiOF, BPSG (Bor
on-Phospho-Silicate Glas
s), PSG (Phospho-Silicate G)
las), SiN, Si3N4, Si, Al, W, A
It is made of a material containing g, Cu, Ti, TiN, Au, Pt and the like as main components.

The polishing particles contained in the polishing liquid are Si
O2, CeO2, Al2O3, Fe2O3, SiC, S
It is made of a material containing iN, ZrO2, TiO2 and the like as main components. As the polishing cloth, foamed polyurethane, polyurethane, non-woven fabric, or the like can be used.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a flowchart of the polishing method of the present invention, and FIG. 2 is a sectional view of a semiconductor device using the polishing method of the present invention.

First, the semiconductor element 10 to be polished will be described. A silicon oxide film 3 is formed as an insulating film on a circular silicon substrate 4 (substrate).

An Al wiring 2 having a width of 0.3 μm and a height of 0.4 μm is formed on the silicon oxide film 3 by lithography or etching. The distance between the wirings 2 is 0.3 μm, 3 μm, 30 μm,
There are five types, 00 micron and 3000 micron, which are formed as needed.

Thereafter, a silicon oxide film 1 (film to be polished) having a thickness of 1.3 μm as a film to be polished is formed by a plasma CVD method. Thus, the semiconductor element 10 includes the silicon substrate 4, the silicon oxide film 3, the Al wiring 2,
And a silicon oxide film 1.

A circular polishing pad 9 made of, for example, foamed polyurethane is arranged opposite the silicon oxide film 1.
The surface of the polishing pad 9 has some irregularities due to its material. Also,
A polishing liquid 8 containing abrasive particles is interposed between the silicon oxide film 1 and the polishing cloth 9.

Here, a driving device for relatively moving the polishing pad 9 and the silicon substrate 4 can be provided if necessary (not shown). The operation of a polishing method for polishing a semiconductor device having such a configuration will be described.

First, the semiconductor element 10 is arranged and fixed at a predetermined position of the polishing apparatus. Next, the viscosity G of the polishing liquid 8 that differs depending on the type of the polishing liquid 8 to be used is input to the polishing apparatus.

Next, in order to rotationally drive the polishing pad 9 and the silicon substrate 4, the respective rotational speeds are input to a predetermined rotating device. Relative velocity V between silicon substrate 4 and polishing cloth 9
, For example, at a rate of 2.5 meters per second.
Alternatively, the silicon substrate 4 is rotated (for example, relative movement in the direction of arrow 7 in the figure).

Next, the polishing cloth 9 is applied to the silicon oxide film 1.
For example, the pressure is set such that the average pressure P is pressed at 40 kPa (from the direction of arrow 6 in the figure). Next, it is calculated whether or not the relationship among the average pressure P, the viscosity G of the polishing liquid, and the relative speed V satisfies the relationship of P ≦ 0.5 × V × G (1).

If the result of the calculation satisfies the above equation (1), the operation proceeds to the next step. Also, the result of the calculation is
If the above equation (1) is not satisfied, the viscosity G, the relative velocity V, or the average pressure P of the polishing liquid 8 is reset.

Next, if the condition of equation (1) is satisfied,
Start polishing. First, the average particle size of the abrasive particles is, for example, 6
A polishing liquid 8 containing SiO 2 of 0 nanometer and having a viscosity G of 40 centipoise is supplied between the silicon oxide film 1 and the polishing cloth 9. The silicon oxide film 1 is polished by the supplied polishing liquid 8 and the relative movement of the polishing pad 9 and the silicon substrate 4.

Here, the pressure P, the viscosity G, and the speed V are each appropriately detected by various types of sensors and the like by detecting means (not shown), and based on the detected signals, a control system (not shown) performs polishing. Is operated so as to keep the relationship among the pressure P, the viscosity G, and the speed V at the relationship of Expression (1).

That is, during the polishing, the silicon oxide film
1 At least one of the pressure P, the viscosity G, and the speed V, which change depending on the state of the surface, the state of the polishing liquid 8, the state of the relative movement between the polishing pad 9 and the silicon substrate 4, etc. The viscosity G and the speed V can be changed so as to be set values, and the polishing can always be controlled to be performed in an optimum state.

In order to bring the surface of the silicon oxide film 1 into a desired polished state, the surface is first polished while maintaining the relation of the equation (1), and then the relation of P> 0.5 × V × G (2) Polishing can be performed while maintaining the above conditions.

At this time, the average pressure P, the viscosity G, or the relative speed V is set again. Further, the viscosity G, the relative speed V, or the average pressure P can be displayed by a display means such as a display or a digital counter, as necessary, during polishing of the silicon oxide film 1 or before and after the start of polishing.

Further, the shapes of the semiconductor element 10 before and after polishing by the polishing method of the present invention will be described with reference to FIG. FIG. 3A is a cross-sectional view of the semiconductor device 10 before polishing by the polishing method of the present invention, and FIG. 3B is a cross-sectional view of the semiconductor device 10 after polishing by the polishing method of the present invention.

Before polishing, as shown in FIG. 3A, irregularities reflecting the shape of the AL wiring 2 are formed on the surface of the silicon oxide film 1. The relationship between the pressure P, the viscosity G, and the speed V is maintained and polished as shown in Expression (1), thereby causing the arrangement of the Al wiring 2 as shown in FIG. A silicon oxide film 1 having a surface where almost no unevenness is observed is formed.

Conventionally, the average pressure was 40 kPa as in the present invention, but since the viscosity G was 20 centipoise and the speed V was 1 meter per second, irregularities remained on the silicon oxide film 1 even after polishing. (See FIG. 5B).

As described above, in the present invention, the polishing amount of the concave portion in the silicon oxide film 1 can be reduced as compared with the conventional polishing method. Therefore, the surface of the silicon oxide film 1 can be efficiently flattened.

The reason why such a polishing effect can be obtained will be described with reference to FIG. FIG. 4 is a sectional view of a semiconductor device for explaining the operation of the polishing method of the present invention. The surface of the polishing cloth 9 has a surface roughness for the purpose of holding the polishing liquid 8. When the surface roughness is small, that is, when the surface roughness is smaller than several tens times the average diameter of the abrasive particles 81, the polishing liquid 8 can be sufficiently supplied between the silicon oxide film 1 and the polishing cloth 9. Therefore, a desired polishing effect cannot be obtained.

Therefore, the polishing cloth 9 for obtaining a desired polishing effect has an amplitude 92 of the surface roughness and a wavelength 93 of the roughness.
However, a material having a range of several microns to several hundred microns, that is, a foam material or a nonwoven fabric is used. In addition, the amplitude 92
Is a half of the maximum height of the uneven portion formed in the vertical direction in the figure of the reference line 91 of the surface roughness of the polishing pad 9.

In the process of manufacturing the LSI, the irregularities existing in the silicon oxide film 1 have a height of about 1 μm, which is smaller than the surface roughness of the polishing pad 9. Therefore, the shape of the polishing liquid 8 layer formed between the silicon oxide film 1 and the polishing cloth 9 is determined substantially by the surface roughness of the polishing cloth 9.

Further, the polishing liquid 8 interposed between the silicon oxide film 1 and the polishing pad 9 also changes the direction of the relative speed (relative motion) due to the relative speed of the silicon oxide film 1 and the polishing pad 9 during polishing. As shown in FIG. 4, the polishing liquid 8 generates pressure by repeating compression and expansion along the surface roughness direction of the polishing pad 9. According to the theory of fluid lubrication, this pressure is determined by the viscosity, relative speed, and minimum thickness 82 of the polishing liquid 8 (the distance in the stacking direction in which the convex portion of the polishing pad 9 and the silicon oxide film 1 are opposed via the polishing liquid 8). ). According to the fluid lubrication theory, the higher the viscosity and relative velocity, or the smaller the minimum thickness 82 of the polishing liquid 8 film,
The generated pressure is large.

However, since the polishing liquid 8 contains the polishing particles 81, the minimum thickness 82 of the film of the polishing liquid 8 does not become smaller than the diameter of the polishing particles 81. That is, when the diameter of the polishing particles 81 is smaller than the diameter of the polishing particles 81, the polishing particles 81 and the film to be polished 1 come into contact with each other.

In the present invention as described above, in the conventional polishing method (FIG. 5), the limit of the pressure generated in the polishing liquid 8 was small and the polishing effect was low. By greatly improving the limit, the pressure of the polishing liquid 8 in the concave portions of the film 1 to be polished can be increased.
Therefore, the contact of the polishing particles 81 with the film 1 to be polished can be reduced, and the polishing effect can be greatly improved.

The present invention is not limited to the above embodiment,
It goes without saying that various modifications can be made without departing from the spirit of the invention. For example, the combination of the polishing cloth and the polishing liquid may be any combination as long as a desired polishing effect can be obtained.

[0047]

As described above, according to the present invention, the polishing of the concave portion can be reduced and the polishing can be performed to a desired thickness.

[Brief description of the drawings]

FIG. 1 is a flowchart of a polishing method according to the present invention.

FIG. 2 is a cross-sectional view of a semiconductor device to which the polishing method of the present invention is applied.

FIG. 3 is a cross-sectional view of a semiconductor device before and after polishing by the polishing method of the present invention.

FIG. 4 is a cross-sectional view of a semiconductor device for explaining the operation of the polishing method of the present invention.

FIG. 5 is a sectional view showing a shape of an interlayer insulating film before and after polishing by a conventional polishing method.

FIG. 6 is a cross-sectional view of an interlayer insulating film formed by another conventional polishing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon oxide film 2 Al wiring 3 Silicon oxide film 4 Silicon substrate 6 Average pressure 7 Relative speed 8 Polishing liquid 9 Polishing cloth 10 Semiconductor element

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yoshikuni Tateyama 8 Shinsugitacho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside Toshiba Yokohama Office

Claims (4)

[Claims] 1. An average pressure P [kPa] of pressing a substrate having a film to be polished against a polishing cloth, and a viscosity G [cp] of a polishing liquid interposed between the film to be polished and the polishing cloth. And the relative velocity V [m due to the relative movement between the substrate and the polishing cloth.
/ S], wherein the film to be polished is polished with the polishing cloth and the polishing liquid such that P ≦ 0.5 × G × V. 2. The polishing method according to claim 1, wherein the polishing is performed by changing at least one of the pressure, the viscosity, and the speed while polishing the film to be polished with the polishing cloth and the polishing liquid. Item 4. The polishing method according to Item 1. 3. An average pressure P [kPa] of pressing a substrate having a film to be polished against a polishing cloth, and a viscosity G [cp] of a polishing liquid interposed between the film to be polished and the polishing cloth. And the relative velocity V [m / by relative movement of the substrate and the polishing cloth.
polishing the film to be polished with the polishing cloth and the polishing liquid such that P ≦ 0.5 × G × V, and polishing the substrate provided with the film to be polished with a polishing cloth. Pressure [kPa], viscosity G [cp] of a polishing liquid interposed between the film to be polished and the polishing cloth, and relative velocity due to relative motion between the substrate and the polishing cloth. V [m / s]
Polishing in a relationship of P> 0.5 × G × V. 4. The polishing method according to claim 1, wherein the pressure P, the viscosity G, or the relative speed V is displayed.