Method for Adjusting Metal Polishing Rate and Reducing Defects Arisen in a Polishing Process

Abstract

The invention discloses a method for adjusting metal polishing rate and reducing defects arisen in a polishing process, in which a electric conduction system is additionally provided to a polishing apparatus to electrify the polishing fluid; in the polishing process, the polishing fluid flows through the polishing pad and the wafer to be polished, such that the polished metal surface of the wafer is electrically charged so as to control the oxidation of the polished metal surface of the wafer. The invention has solved the problem that the dishing and erosion defects are prone to be formed in the existing polishing process, the potential of the polishing fluid is changed by means of the additional electric conduction system and thus the polishing rate of the polished metal is controlled so as to reduce the dishing and erosion defects occurred in the polishing process.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is based upon and claims priority under 35 U.S.C. §119 to prior Chinese Patent Application No. 201110110366.0 filed on Apr. 29, 2011, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a semiconductor metal polishing technique, and more particularly, to a method for adjusting metal polishing rate and reducing defects arisen in a polishing process.

BACKGROUND

In the manufacture of wafers, as the upgrading of the process technology and the reduction of sizes of wires and grids, the lithograph technology has an increasing demand for non-uniformity of the wafer surface. IBM developed and introduced CMOS products in 1985, and successfully applied CMOS in manufacturing 64 MB DRAM in 1990. CMP (Chemical Mechanical Planarization) has been developed rapidly since 1995 and is used widely in semiconductor industry.

A polishing mechanism, taken copper polishing which is necessary in an advanced process for instance, is mainly based on an oxidation reaction of copper in a polishing fluid as follows:

1. If copper is at a relative high potential in the polishing fluid, copper will easily react with chemical compositions in the fluid to generate oxide(s) or copper ion(s);

2. If copper is at a relative low potential, its oxidation will be weaken or suppressed; contrary, such reaction is accelerated at a higher potential.

At present, the commonly used polishing stands perform polishing by a frication effect between a polishing pad and a wafer under the influence of a polishing fluid. Referring to FIG. 1, which is a schematic structural diagram of a polishing stand according to the prior art, since the polishing rate is different for different mediums, defects of so-called dishing and erosion are often caused. In view of process quality, a low-pressure polishing is usually used in the practical production for a better result. However, the pressure will have an impact on the polishing rate also, a low pressure corresponds to a lower polishing rate, which would not facilitate the improvement of productivity and the reduction of cost.

Chinese patent Application No. 200780041698.X, entitled “Method and Apparatus for Electrochemical Mechanical Polishing Nip Substrates” disclosed a method for accelerating polishing of a Nip substrate. However, the document does not relate to the area of producing an integrated circuit, but only refers to polishing Nip substrate. Obviously, the integrated circuit process requires a more accurate process control, and the metal polishing in the integrated circuit process is not suitable to be performed by using a single-directional/single-magnitude current or voltage. Moreover, the document does not relate to the phenomenon of cathodic protection resulted from the change of a current direction.

SUMMARY OF THE INVENTION

The present invention discloses a method for adjusting metal polishing rate and reducing defects arisen in a polishing process to solve the problem that dishing and erosion defects are prone to be formed in the existing polishing process.

The above object of the invention is achieved by the following technical solutions:

The invention provides a method for adjusting metal polishing rate and reducing defects arisen in a polishing process, comprising steps of: adding an electric conduction system to a polishing apparatus in order to electrify a polishing fluid; and in the polishing process, making the polishing fluid flow through a polishing pad and a wafer to be polished, such that a polished metal surface of the wafer is electrically charged and thereby an oxidation of the polished metal surface of the wafer is controlled.

The aforementioned method for adjusting metal polishing rate and reducing defects arisen in a polishing process may further comprise: providing a conducting element layer inside of a polishing turntable for polishing the wafer in the polishing apparatus, an edge portion of the conducting element layer being exposed to outside of a side edge of the polishing turntable, and the polishing fluid, when flowing down around the polishing turntable, contacting the conducting element layer.

According to the aforementioned method for adjusting metal polishing rate and reducing defects arisen in a polishing process, the conducting element layer may be grounded.

According to the aforementioned method for adjusting metal polishing rate and reducing defects arisen in a polishing process, the electric conduction system may provide a high potential to the polishing fluid, and the polished metal surface is at a higher potential in the polishing fluid, such that a reaction of the polished metal surface with chemical compositions in the polishing fluid is accelerated to generate metal oxide(s) or metal ion(s), and the accelerated oxidation reaction of the metal surface in turn results in an increased polishing rate, such that a scratch degree of the metal surface and a polishing pressure are reduced.

According to the aforementioned method for adjusting metal polishing rate and reducing defects arisen in a polishing process, the electric conduction system may provide a low potential to the polishing fluid, and the polished metal surface is at a lower potential in the polishing fluid. In such case, ions in the polishing fluid can suppress the reaction of the polished metal surface with the chemical compositions in the polishing fluid, so that the metal polishing rate is reduced and a more flat surface is thereby obtained.

The invention also provides an apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process, comprising a polishing stand, wherein the polishing stand is provided with an electric conduction system, and the electric conduction system has a voltage output terminal to contact the polishing fluid of the polishing stand.

In the aforementioned apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process, a conducting element layer may be provided inside of a polishing turntable of the polishing stand. The conducting element layer has an edge portion which is exposed to the outside of a side edge of the polishing turntable, and the conducting element layer has a leading-out terminal which is grounded.

To sum up, as the above technical solutions are introduced, the present invention has solved the problem that the dishing and erosion defects are prone to be formed in the existing polishing process, the potential of the polishing fluid is changed by means of the additionally arranged electric conduction system and thus the polishing rate of the polished metal is controlled, so as to achieve the object of reducing the dishing and erosion defects occurred in the polishing process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic structural diagram of a polishing stand according to the prior art;

FIG. 2 is a schematic structural diagram of an apparatus for adjusting a metal polishing rate and reducing defects arisen in a polishing process according to the invention;

FIG. 3 is a schematic structural diagram of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to a first embodiment of the invention;

FIG. 4 is a schematic structural diagram of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to a second embodiment of the invention;

FIG. 5 is a schematic structural diagram of a wafer before metal-polishing by means of the apparatus of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to the invention;

FIG. 6 is a schematic structural diagram of a wafer after polishing by means of a polishing process according to the prior art;

FIG. 7 is a schematic structural diagram of a wafer after the metal polishing by means of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to the invention; and

FIG. 8 is a graph of voltage versus PH of copper.

DETAILED DESCRIPTION OF THE EMBODIMENTS

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

FIG. 2 is a schematic structural diagram of an apparatus for adjusting a metal polishing rate and reducing defects arisen in a polishing process according to the invention. Refer to FIG. 2, a method for adjusting a metal polishing rate and reducing defects arisen in a polishing process according to the invention may comprise a step of adding an electric conduction system 401 to the polishing apparatus. The electric conduction system 401 provides an additional current and electrical field, and is connected to a polishing fluid outlet 301 of a polishing stand of the polishing apparatus in order to electrify a polishing fluid 302 from the outlet 301. In the polishing process, the polishing fluid 302 flows down from the polishing fluid outlet 301, and flows through a polishing pad 103; a wafer 201 is mounted on a wafer bracket 202, and a surface of the wafer 201 to be polished is pressed against the polishing pad 103 due to a pressure applied by the wafer bracket 202; the wafer bracket 202 rotates the wafer 201 while a polishing turntable 102 rotates the polish pad 103, wherein a rotation direction of the wafer 201 is opposite to that of the polishing pad 103, so that the wafer 201 can be polished. In the polishing process, the electrified polishing fluid 302 flows between the polishing pad 103 and the polished metal surface of the wafer 201, so that the polished metal surface of the wafer 201 is electrically charged. When the surface of the wafer 201 is polished to a different medium, because it is difficult to control the metal removal rate, dishing and erosion defects are prone to be formed; whereas after the surface of the wafer 201 is electrically charged, a potential of the surface of the wafer 201 will be changed (if the surface of the wafer is polished to a different medium), a chemical reaction on the polished metal surface of the wafer 201 may be controlled accordingly, such that the metal polishing rate is controllable. Once the metal on the surface of the wafer 201 is electrically charged, the metal surface can be protected, as a result, the dishing and erosion defects can be reduced in the polishing process.

The method according to the invention may further comprise a step of providing a conducting element layer 501 inside of the polishing turntable 102 of the apparatus. An edge portion of the conducting element layer 501 is exposed to outside of a side edge of the polishing turntable 102. The polishing fluid 302, when flowing down around the polishing turntable 102, contacts the conducting element layer 501 to make the conducting element layer 501 be grounded, so as to maintain a potential of the polished metal surface of the wafer 201 stable. As a result, stability of the polishing rate can be guaranteed. The polishing fluid 302 in the invention is an electrolyte fluid.

FIG. 8 is a graph of voltage vs. PH of copper. As shown from FIG. 8, the polishing mechanism of the copper polishing, which is taken as an example and is necessary in an advanced process, is mainly based on an oxidation reaction of copper in the polishing fluid: if copper is at a relative high potential in the polishing fluid, it can easily react with chemical compositions in the polishing fluid to generate oxide(s) or copper ion(s); if copper is at a relative low potential, the oxidation of copper will be weakened or suppressed, contrarily, such reaction will be accelerated at a higher potential.

The electric conduction system 401 according to the invention has a function of adjusting the potential of the polishing fluid 302. That is, in different processing steps, the electric conduction system may provide the surface of the wafer 201 with a different potential, so that the potential of the surface of the wafer 201 can be adapted to various processing step. When the polishing is processed to a certain stage, the surface metal of the wafer 201 may be brought to a low potential in order to reduce the metal polishing rate, so as to achieve an effect of reducing dishing and erosion defects. If the surface metal of the wafer 201 is brought to a high potential, the metal polishing rate is increased, so the pressure on the wafer 201 may be reduced, as a result, the effect of reducing the dishing and erosion defects can also be achieved.

FIG. 3 is a schematic structural diagram of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to a first embodiment of the invention. Refer to FIG. 3, according to the first embodiment of the invention, in the polishing process of the polished metal surface of the wafer 201, the electric conduction system 401 provides a high potential to the polishing fluid 302, so in the polishing fluid 302, the polished metal surface is at a relative high potential, which accelerates a reaction of the polished metal surface with chemical compositions in the polishing fluid 302 to generate metal oxide(s) or metal ion(s). In turn, the accelerated oxidation reaction of the metal surface results in an increased polishing rate, such that the polishing pressure is reduced, and a scratch degree of the metal surface is reduced as well.

FIG. 4 is a schematic structural diagram of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to a second embodiment of the invention. Refer to FIG. 4, in the polishing process of the polished metal surface of the wafer 201 according to the second embodiment of the invention, contrary to the first embodiment, the electric conduction system 401 provides a low potential to the polishing fluid 302, so in the polishing fluid 302, the metal surface being polished is at a relative low potential. In such case, ions in the polishing fluid 302 suppress the reaction of the polished metal surface with the chemical compositions in the polishing fluid, so that the metal polishing rate is reduced and a more flat (polished) surface is thereby obtained.

FIG. 2 is a schematic structural diagram of the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to the invention. Refer to FIG. 2, the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process comprises a polishing stand 101 provided with an electric conduction system 401. The electric conduction system 401 has a voltage output terminal to contact the polishing fluid outlet 301 of the polishing stand 101, so that the polishing fluid 302 is electrically charged, as a result, the polishing fluid 302 flows between the polishing pad 103 and the wafer 201 in the polishing process and makes the polished metal surface of the wafer be electrically charged, which produces an effect of controlling the metal polishing rate.

A conducting element layer 501 is provided inside of the polishing turntable 102 of the polishing stand 101 according to the invention. The conducting element layer 501 has an edge portion which is exposed to outside of the side edge of the polishing turntable 102, and has a leading-out terminal 502 which is grounded in order to maintain the stability of the potential of the surface of the wafer 201.

FIG. 5 is a schematic structural diagram of a wafer before metal-polishing which is performed by the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to the invention, and FIG. 6 is a schematic structural diagram of a wafer after polishing by means of a polishing process according to the prior art. Refer to FIGS. 5 and 6, it can be clearly seen that the surface of the wafer, after the polishing process of the prior art, dishing defect and erosion defect appear. FIG. 7 is a schematic structural diagram of a wafer after metal-polishing which is performed by the apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to the invention. As shown in FIG. 7, the wafer polished through the etching process of the invention has a very flat surface, and the dishing and erosion defects are effectively eliminated.

To sum up, by the above technical solutions, the invention has solved the problem that the dishing and erosion defects are prone to be formed in the existing polishing process, and by additionally providing the electric conduction system to change the potential of the polishing fluid and in turn control the polishing rate of the metal being polished, the invention has achieved the object of reducing the dishing and erosion defects occurred in the polishing process.

The specific embodiments of the invention have been described above, however, they are exemplifications only, and the invention does not intend to be limited to the above specific embodiments. For the person skilled in the art, any equivalent modification or substitution to the invention would fall into the scope of the invention. Therefore, any equivalent variation or modification that is made without departing from the spirit and scope of the invention should be covered by the scope of the invention.

Claims

1. A method for adjusting metal polishing rate and reducing defects arisen in a polishing process, comprising steps of: adding an electric conduction system to a polishing apparatus in order to electrify a polishing fluid; andin the polishing process, electrically charging a polished metal surface of a wafer to be polished by the polishing fluid flowing through a polishing pad and the wafer, and thereby controlling an oxidation of the polished metal surface of the wafer.

2. The method for adjusting metal polishing rate and reducing defects arisen in a polishing process according to claim 1, further comprising a step of providing a conducting element layer inside of a polishing turntable for polishing the wafer in the polishing apparatus, wherein an edge portion of the conducting element layer is exposed to outside of a side edge of the polishing turntable, and the polishing fluid, when flowing down around the polishing turntable, contacts the conducting element layer.

3. The method for adjusting metal polishing rate and reducing defects arisen in a polishing process according to claim 1, wherein the conducting element layer is grounded.

4. The method for adjusting metal polishing rate and reducing defects arisen in a polishing process according to claim 1, wherein the electric conduction system provides a high potential to the polishing fluid, and the polished metal surface is at a higher potential in the polishing fluid, so as to accelerate a reaction of the polished metal surface with chemical compositions in the polishing fluid to generate metal oxide(s) or metal ion(s), and the accelerated oxidation reaction of the metal surface in turn results in an increased polishing rate, such that a scratch degree of the metal surface and a polishing pressure are reduced.

5. The method for adjusting metal polishing rate and reducing defects arisen in a polishing process according to claim 1, wherein the electric conduction system provides a low potential to the polishing fluid, and the polished metal surface is at a lower potential in the polishing fluid, and ions in the polishing fluid suppress a reaction of the polished metal surface with chemical compositions in the polishing fluid, so that the metal polishing rate is reduced and a more flat surface is thereby obtained.

6. An apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process, comprising a polishing stand, wherein the polishing stand is provided with an electric conduction system, and the electric conduction system has a voltage output terminal to contact a polishing fluid of the polishing stand.

7. The apparatus for adjusting metal polishing rate and reducing defects arisen in a polishing process according to claim 6, wherein a conducting element layer is provided inside of a polishing turntable of the polishing stand, and has an edge which is exposed to outside of a side edge of the polishing turntable and a leading-out terminal which is grounded.