US20150306737A1

US20150306737A1 - Chemical mechanical polishing pad

Info

Publication number: US20150306737A1
Application number: US14/259,646
Authority: US
Inventors: Chang-Sheng Lin
Original assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Current assignee: Taiwan Semiconductor Manufacturing Co TSMC Ltd
Priority date: 2014-04-23
Filing date: 2014-04-23
Publication date: 2015-10-29

Abstract

The present disclosure relates to a radiance decomposable CMP pad, and an associated method to refresh the CMP pad. In some embodiments, the CMP pad has a polymer layer and some macro pores disposed therein. A monomer of the polymer layer has a photoactive compound unit.

Description

BACKGROUND

In the manufacture of integrated circuits (ICs), devices are formed on a wafer by forming various process layers, then selectively removing or patterning portions of those layers and depositing additional process layers thereon. An uppermost surface after a deposition step is usually non-planar because of previous selective patterning. A planarization process is performed in succession to remove excess portions and prepare a flat surface for the following process.
A chemical-mechanical polishing process (CMP process) is utilized for the planarization. The wafer to be processed is held upside down and forced against a rotating CMP pad. A slurry is disposed between the CMP pad and wafer surface. Due to the applied down force, this slurry, which includes chemicals that help chemically dissolve the uppermost surface of the wafer and abrasive particles that help physically wear away the uppermost surface, provides for wafer surface planarization.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 shows a structural view of a CMP system in accordance with some embodiments.

FIG. 2 shows a cross-sectional view of a CMP pad in accordance with some embodiments.

FIG. 3 shows a flow diagram of a method of CMP in accordance with some embodiments.

FIG. 4 shows a flow diagram illustrating a method of polishing in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.
Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.
Chemical-mechanical polishing (CMP) is a process utilized in the semiconductor fabrication industry for planarization. In a CMP process, a slurry including abrasive particles together with chemicals is applied on a CMP pad to react with the uppermost layer of a wafer and remove a non-planar portion thereof. The CMP pad and/or asperities theron can become deformed during the wafer polishing. Reaction residues, for example, or glazes adhering to the CMP pad, may affect subsequent CMP processes by reducing removal rates achieved by the CMP pad. For this reason, some CMP systems use a conditioning disk, for example a diamond disk, to remove such reaction residues. In some cases, the diamond disk may introduce over-conditioning in which case a surface profile of the CMP pad is damaged. In other cases, the diamond disk may introduce under-conditioning in which case residues are not removed completely. This over-conditioning or under-conditioning is difficult to precisely control, making precise planarization with diamond disks difficult to achieve. Also, to obtain the best conditioning results, CMP systems go through a large number of wafers, pads, and disks, as well as large amounts of slurry, cleaning chemical, and tool time. Thus, a more efficient process to remove residues and refresh the CMP pad properly is needed to keep stable polish performance.
Accordingly, the present disclosure relates to apparatus and methods which refresh CMP pads by irradiating UV decomposable CMP pads with ultraviolet (UV) light. This UV light repairs or reconditions a CMP pad surface that has been damaged or worn out by previous CMP processing. For example, during previous CMP processing, reaction residues can adhere to the CMP pad surface and introduce an uneven surface which can damage the wafer during CMP processing. The reaction residues can also cover portions of grooves on the CMP pad surface, which are designed to retain slurry. The reaction residues can comprise glazes generated by the chemical reactions which occur during CMP processing, portions of the processed wafer removed by the abrasive mechanical process, or portions of the CMP pad removed during the CMP processing.
To remove the thin damaged surface region of the CMP pad together with the reaction residues, if any, UV light is shone onto the surface of the CMP pad to decompose a very thin top portion of the CMP pads and thereby remove this thin top portion together with any reaction residues in succession by some aqueous solution. In this way, the CMP pad is refreshed for subsequent CMP processes. This surface reconditioning by UV irradiation simplifies CMP systems by removing or limiting the need for a conditioning disk. Further, compared to conventional conditioning disks, reconditioning by UV irradiation is more precise in that it can decompose a only a very thin layer of a CMP pad. For example, some embodiments of UV re-conditioning can remove a top portion of the CMP pad with a thickness of less than about 0.001 mil, while traditional mechanical removal of the CMP pad by the conditioning disk removes about 0.05 mil to about 0.01 mil in every refreshment cycle. Thus, the disclosed UV re-conditioning techniques for CMP pads can increase the useful lifetime of CMP pads by approximately 5 to 20 times for a given pad thickness. Also, UV light has a more precise control of the removal thickness which means a better stability.
In some embodiments, the UV decomposable CMP pad is formed by a polymer layer with photoactive units. These photoactive units react with UV light, such that the CMP pad can be decomposed by the UV light. In some embodiments, the method comprises placing a wafer face down on a CMP pad, applying a slurry between the wafer and the CMP pad and planarizing the wafer by applying a pressure between the wafer and the CMP pad. The CMP pad is then exposed to a radiance source, wherein a top portion of the CMP pad is decomposed uniformly and removed together with a reaction residue. Then the CMP pad is cleaned by applying an aqueous solution. By utilizing a disclosed CMP pad and exposing the CMP pad to the radiance source, the CMP pad is refreshed, thereby performing an optimized pad conditioning.
FIG. 1 shows a structural view 100 of a CMP system in accordance with some embodiments. The CMP system 100 can be utilized to polish metal, semiconductor or insulator layers which may include but are not limited to semiconductor thin films, integrated circuit thin films and to polish any other films, surfaces, and substrates where a CMP process is applied. A rotatable wafer carrier 108 is disposed face to a rotatable polishing platen 102. The rotatable wafer carrier 108 is utilized to hold a wafer 106 upside down, for example with active device structures face down and near the polishing platen 102. A CMP pad 104 is disposed on the rotatable polishing platen 102. The CMP pad 104 has a thickness of about 1 mm to about 4 mm. A CMP dispenser 110 is disposed above the CMP pad 104 to dispense a slurry 112 between the CMP pad 104 and the wafer 106. The slurry 112 can comprise a chemical mechanical compositions and at least one abrasive. The abrasive can be a metal oxide abrasive. Among other proper materials, the metal oxide abrasive can be selected from the group including Alumina, Zirconia, Germania, Silica, Cerium (IV) oxide (Ceria) and mixtures thereof. A radiation source 114 is disposed above the CMP pad 104. In some embodiments, the radiation source 114 is an ultraviolet (UV) source having a wavelength range from approximately 100 nm to approximately 380 nm. The UVsource may have an energy range from approximately 10 mJ/cm²to approximately 100 mJ/cm². The energy range of the UV source corresponds to an irradiating time to the CMP pad 104 in a range of several seconds to around one minute which is efficient and easy to control.
FIG. 2 shows a cross-sectional view of the CMP pad 104 in accordance with some embodiments. The CMP pad 104 comprises a first polymer layer 204. In some embodiments, the CMP pad 104 can further comprise macro pores 206 disposed in the polymer layer 204. The macro pores 206 are utilized for holding and transporting slurry to and from a surface (e.g. surface 212 or surface 214 after a refreshing cycle) of the CMP pad 104. The macro pores 206 can be distributed in all three dimensions of the polymer layer 204 randomly and uniformly. The macro pores 206 can have any suitable density or void volume. In some other embodiments, the macro pores 206 can be replaced and/or supplemented by structures such as grooves, channels, apertures or combinations thereof disposed in the first polymer layer 204. The macro pores are disposed within a significant depth of the first polymer layer 204 and help to retain a slurry during a polishing process. Notably, the first polymer layer 204 can be any CMP pad layer that comprises a suitable polymer or can be prepared from any suitable polymer. For example, the first polymer layer 204 may comprise polyurethane The first polymer layer 204 may comprise a microporous urethane film. The microporous urethane film can comprises a series of vertically oriented cylindrical pores.
In some embodiments, the CMP pad 104 further comprises a second polymer layer 202 can be disposed under the first polymer layer 204. In some embodiments, the second polymer layer 202 can be a polyester layer. The second polymer layer 202 may comprise polyurethane impregnated into a polyester non-woven fabric. The second polymer layer 202 can be used as a base material coated by the microporous urethane film. The second polymer layer 202 has a different hardness from the polymer layer 204, i.e., the second polymer layer 202 can be either harder or softer than the first polymer layer 204. The second polymer layer 202 can be a solid, non-porous layer. The second polymer layer 202 is not typically used as a polishing surface. The second polymer layer 202 helps to support the polymer layer 204 and improve CMP performance.
In some embodiments, a thickness of the first polymer layer 204 can be from about 40 mil to about 150 mil. A hardness of the first polymer layer 204 has a range of from approximately 5 shore A to approximately 80 shore D. A density of the first polymer layer 204 has a range of from approximately 0.2 g/ml to approximately 1.2 g/ml. A compressibility of the first polymer layer 204 has a range of from approximately 1% to approximately 30%.
In some embodiments, the first polymer layer 204 can comprise a copolymer which is derived from at least two different monomers. A photoactive compound (PAC) unit can be bonded to at least one of the monomers of the first polymer layer 204's polymer chain. For example, the PAC units can be bonded to a polyol monomer or a diisocyanate monomer of the polymer layer 204. Or the PAC unit can be an independent monomer bonded with other monomers of the polymer layer to form a polymer chain. The PAC unit can be attached to a terminal repeat unit or a non-terminal repeat unit of the polymer chain. Thus, the polymer layer 204 can be decomposable by exposing to the radiance source 114. A decomposed polymer layer can be dissolved in an aqueous solution. The PAC unit can be any suitable such unit. Existence of the PAC unit makes a top portion 208 of the polymer layer 204 decomposed with the exposure to the radiance source. For example, the PAC unit can comprise carboxylic of sulfonic acid with aromatic rings. For example, the PAC unit can comprise 9-anthracene carboxylic acid or 1,2-naphthoquinonediazide-5-sulfonic acid. In some embodiments, the PAC unit can comprise multi-aromatic rings, such as 2 to 7 aromatic rings that are bonded together. Some example structures of the PAC units are shown below:
wherein x represents an oxygen, sulfur, or nitrogen atom.
In some embodiments, the PAC units can be bonded to a polyol unit(Ω) or a diisocyanate unit (Σ) of a monomer of the polymer layer 204. The monomer of the polymer chain of the polymer layer 204 can be described by the following structures:
wherein x and y are positive integers, and PAC¹and PAC²can be same or different units.
In some other embodiments, the polymer layer 204 can comprise a polyol unit(Ω) and a diisocyanate unit (Σ) bonded together with the PAC unit. A monomer of the polymer chain of the polymer layer 204 can be described by the following structures:
(Σ)_z−(Ω)_x−(PAC)_yor (Σ)_z−(PAC)_y−(Ω)_x
wherein x, y and z are positive integers.
Still referring to FIG. 2, when the CMP pad 104 is exposed by the radiance source 114 for a selective period, the top portion 208 of a whole pad surface of the polymer layer 204 is decomposed uniformly and can be removed by an aqueous solution. In this way, a deformed or worn surface 212 is removed and replaced by a refreshed surface 214. The refreshed surface 214 becomes flat with designed asperities that can hold slurry well. Residues such as 210 are removed together with the top portion 208 of the polymer layer 204. In some embodiments, the top portion 208 of the polymer layer 204 has a thickness of from about 0.001 mil to 0.01 mil. The thickness of the top portion 208 to be removed can be controlled by power density and irradiation time of the radiance source 114.
FIG. 3 shows a flow diagram of a method 300 of CMP in accordance with some embodiments. The CMP method 300 can be configured to planarize a wide variety of wafer structures. Exemplary wafer structures include, but are not limited to: Al wiring, Cu wiring, W wiring, and the like.
At 302, a wafer is placed face down on a CMP pad. The wafer can be held by a wafer carrier which can include a plurality of variable-pressure chambers (not shown) for exerting either suction or pressure onto backside of the wafer.
At 304, a slurry is applied between the wafer and the CMP pad. The slurry comprises an abrasive to mechanically remove an uppermost portion of the wafer and a chemical to dissolve the uppermost portion of the wafer.
At 306, the wafer is planarized by applying a pressure between the wafer and the CMP pad. A general-purpose controller allows a variable down-force to be applied to the wafer carrier and a polishing platen to be rotated at variable and independent rates, and allows the slurry and/or other materials to be applied to the polishing pad attached on the polishing platen.
During operation, the wafer carrier is preferably rotated about spindle axis at a desired rate while the polishing platen is preferably rotated around the platen axis at an independent desired rate. In various embodiments, the slurry is comprised of slurry particles present during polishing. In various embodiments, the slurry particles are comprised of silica (SiO2) or alumina (Al2O3), depending on the surface to be polished. The combined action of the down-force of the wafer carrier, the respective rotations of the wafer carrier and the polishing platen, and the chemical and mechanical effects of the slurry combine to polish the surface of the wafer to a desired planarity and thickness. A residue can be formed on the CMP pad during the planarization, and the CMP pad can be deformed during the polishing. For example, the residue can introduce an uneven surface and cover the pores or grooves designed to retain the slurry.
At 308, the CMP pad is irradiated by a radiance source. In some embodiments, after polishing, the wafer carrier and the wafer are lifted and can be removed from top of the polishing platen. The deformed CMP pad can then be exposed to UV radiation from a UV radiation source. A top portion of the CMP pad is decomposed uniformly by the radiation. For example, in a refreshment cycle, a UV radiation can be applied for about 5 seconds to about 40 seconds, a thickness of about 0.001 mil of the CMP pad can be removed after a radiation scan. Notably, for traditional refreshment approach, a worn portion of the CVD pad is removed mechanically by a conditioning disk made of rigid material, for example, diamond. Typical remove thickness every cycle is about 0.005 mil to 0.01 mil. The disclosed approaches extend the CMP pad with a similar thickness about 5 to 10 times. Besides, more precise control of the top portion removal of the CMP pad introduces higher stability to the refreshment process. The disclosed approaches are faster and improve efficiency. In some embodiments, the UV radiation can be provided to the CMP pad intermittently or continuously as an actual CMP operation is going on. Thus, UV radiation can be provided to the CMP pad while the wafer and polishing platen are rotating in the presence of slurry while down-force is applied between wafer and polishing platen.
At 310, the CMP pad is cleaned by applying an aqueous solution. The deformed pad is generally subjected to a high-pressure spray of deionized water or other proper chemical solutions to remove slurry residue and other particulate matter from the pad. Other particulate matter may include wafer residue, CMP slurry, oxides, organic contaminants, mobile ions and metallic impurities.
By exposing the disclosed CMP pad to the radiation with proper time and radiation energy after it had been deformed by a polishing process, a thin top portion of the deformed CMP pad becomes soluble to the aqueous solution, and is removed together with reaction residues thereon. Method 300 refreshes the CMP pad quickly (about one minute for a refresh cycle) and efficiently with simplified CMP system configuration without a conditioning disk.
The methods of the present invention may be implemented in association with various types of monitoring components and systems, and any such system or group of components, either hardware and/or software, incorporating such a method is contemplated as falling within the scope of the present invention.
FIG. 4 shows a flow diagram illustrating a method of polishing incorporating a CMP pad condition monitoring process in accordance with some embodiments. The monitoring process for example, can be realized by applying a pad probe or optical scan over the CMP pad surface.
At 402, a CMP pad is forcefully pressed onto a wafer face with slurry in place to planarize the wafer face. A wafer carrier holding the wafer is preferably rotated about spindle axis at a desired rate while a polishing platen supporting the CMP pad is preferably rotated around platen axis at an independent desired rate. In various embodiments, a slurry comprised of slurry particles is present during polishing. The combined action of the down-force of the wafer carrier, the respective rotations of the wafer carrier and the polishing platen, and the chemical and mechanical effects of the slurry combine to polish the surface of the wafer to a desired planarity and thickness.
At 404, the processed wafer is unloaded. The wafer was held by the wafer carrier which includes a plurality of variable-pressure chambers (not shown) for exerting either suction or pressure onto backside of the wafer. The wafer carrier is removed from the top of the CMP pad and released the wafer after planarization.
At 406, it is determined whether the CMP pad reached a worn or spent conditionthrough the monitoring process. For example, in some embodiments, this worn or spent condition can be met if groove depths of the CMP pad are less than some predetermined groove depth, or if a frictional constant of the CMP pad is less than some predetermined frictional constant. In other embodiments, this worn or spent condition can be met if a thickness of the CMP pad is less than some predetermined thickness.
If the deformed CMP pad has not reached the worn or spent condition, thenno pad refreshment is needed. A possible cleaning process can be performed and a new wafer to be processed can be loaded at 412. A repeated process of 402 to 406 will be performed. Notably, “a new wafer” means another polishing cycle. It can be the same wafer after some additional fabrication processes or a different wafer.
If the deformed CMP pad has reached the worn or spent condition, thena refreshment is performed at 408. The CMP pad is irradiated by a radiance source, such as a UV light source. A top deformed portion of the CMP pad is decomposed as a result.
At 410, the CMP pad is cleaned by applying an aqueous solution. The deformed pad is generally subjected to a high-pressure spray of deionized water or other proper chemical solutions to remove slurry residue and other particulate matter from the pad. Other particulate matter may include wafer residue, CMP slurry, oxides, organic contaminants, mobile ions, and metallic impurities. The refreshed CMP pad is ready for a next polishing cycle started from loading a new wafer at 412.
The present disclosure is related to optimize CMP techniques that refresh a CMP pad. A CMP pad comprises a polymer layer with a PAC unit as part of its monomer such that it becomes soluble to certain aqueous solution after certain time of exposure to a radiance source. The CMP pad is refreshed by being exposed to the radiance source and cleaned by the aqueous solution in succession. As a result, better refreshment is achieved.
Thus, it will be appreciated that some embodiments relate to a CMP pad. The CMP pad comprises a polymer layer and some macro pores disposed therein. A monomer of the polymer comprises a photoactive compound unit.
Other embodiments relate to a CMP system. The CMP system comprises a rotatable wafer carrier to hold a wafer upside down to be processed and a CMP pad disposed uniformly on a rotatable polishing platen comprising a polymer layer. The CMP system further comprises a CMP dispenser to dispense a slurry between the CMP pad and the wafer. A monomer of the polymer layer comprises a photoactive compound (PAC) unit.
Still other embodiments relate to a method of chemical mechanical polishing. In this method, a wafer is placed face down on a CMP pad. Then a slurry is applied between the wafer and the CMP pad. Then the wafer is planarized by applying a pressure between the wafer and the CMP pad. A residue is formed on the CMP pad during the planarization. Then the CMP pad is irradiated by a radiance source and a top portion of the CMP pad is decomposed uniformly and removed together with the residue. At last, the CMP pad is cleaned by applying an aqueous solution.
The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

Claims

What is claimed is:

1. A chemical mechanical polishing (CMP) pad comprising a polymer layer and macro pores disposed therein, wherein a monomer of the polymer layer comprises a photoactive compound (PAC) unit.

2. The CMP pad of claim 1, wherein the polymer layer is decomposable through exposure to a radiance source.

3. The CMP pad of claim 2, wherein the radiance source is an ultraviolet (UV) source.

4. The CMP pad of claim 1, wherein the PAC unit comprises carboxylic of sulfonic acid with aromatic ring.

5. The CMP pad of claim 4, wherein the PAC unit comprises 9-anthracene carboxylic acid or 1,2-naphthoquinonediazide-5-sulfonic acid.

6. The CMP pad of claim 1, wherein the polymer layer comprises polyurethane.

7. The CMP pad of claim 1, wherein the polymer layer comprises a polyol unit (Ω) and a diisocyanate unit (Σ) wherein a PAC unit is bonded to the polyol unit or the diisocyanate.

8. The CMP pad of claim 1, wherein a polymer chain of the polymer layer comprises a structure of:

wherein x and y are positive integers, PAC¹and PAC²are same or different units.

9. The CMP pad of claim 1, wherein the polymer layer comprises polyol units (Ω), diisocyanate units (Σ) and PAC units in order of:

(Σ)_z−(Ω)_x−(PAC)_y

or (Σ)_z−(PAC)_y−(Ω)_x

wherein x, y, z and n are integers.

10. The CMP pad of claim 1, wherein the polymer layer comprises a copolymer.

11. A chemical mechanical polishing (CMP) system, comprising:

a rotatable wafer carrier to hold a wafer face down to be processed;

a CMP pad disposed uniformly on a rotatable polishing platen comprising a polymer layer; and

a CMP dispenser to dispense a slurry between the CMP pad and the wafer;

wherein a monomer of the polymer layer comprises a photoactive compound (PAC) unit.

12. The CMP system of claim 11 wherein the system is evidenced by an absence of a pad conditioning disk.

13. The CMP system of claim 11, wherein a plurality of macro pores are disposed in the polymer layer.

14. The CMP system of claim 11, further comprising a radiance source disposed above the CMP pad.

15. The CMP system of claim 14, wherein the radiance source is an ultraviolet source.

16. The CMP system of claim 15, wherein the ultraviolet source has a wavelength range from approximately 100 nm to approximately 380 nm.

17. The CMP system of claim 15, wherein the ultraviolet source has an energy range from approximately 10 mJ/cm²to approximately 100 mJ/cm².

18. A method of chemical mechanical polishing (CMP), the method comprising:

placing a wafer face down on a CMP pad;

applying a slurry between the wafer and the CMP pad;

planarizing the wafer by applying a pressure between the wafer and the CMP pad; wherein a residue is formed on the CMP pad during the planarization;

irradiating the CMP pad by a radiance source, wherein a top portion of the CMP pad is decomposed uniformly and removed together with the residue; and

cleaning the CMP pad by applying an aqueous solution.

19. The method according to claim 18, wherein the CMP pad is cleaned by applying high pressure deionized water.

20. The method according to claim 18, wherein the radiance source is ultraviolet source and having an irradiation time in a range of from approximately 5 seconds to approximately 40 seconds for an irradiating cycle.