Molded end point detection window for chemical mechanical planarization

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to endpoint detection in a chemical mechanical planarization process, and more particularly to endpoint detection using a preformed detection window.

2. Description of the Related Art

In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion regions are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then, metal CMP operations are performed to remove excess metallization.

A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material. In operation, the belt pad is put in motion and then a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood. The wafer may then be cleaned in a wafer cleaning system.

In the prior art, CMP systems typically implement belt, orbital, or brush stations in which belts, pads, or brushes are used to scrub, buff, and polish one or both sides of a wafer. Slurry is used to facilitate and enhance the CMP operation. Slurry is most usually introduced onto a moving preparation surface, e.g., belt, pad, brush, and the like, and distributed over the preparation surface as well as the surface of the semiconductor wafer being buffed, polished, or otherwise prepared by the CMP process. The distribution is generally accomplished by a combination of the movement of the preparation surface, the movement of the semiconductor wafer and the friction created between the semiconductor wafer and the preparation surface.

FIG. 1A

shows a cross sectional view of a dielectric layer

2

undergoing a fabrication process that is common in constructing damascene and dual damascene interconnect metallization lines. The dielectric layer

2

has a diffusion barrier layer

4

deposited over the etch-patterned surface of the dielectric layer

2

. The diffusion barrier layer, as is well known, is typically titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN) or a combination of tantalum nitride (TaN) and tantalum (Ta). Once the diffusion barrier layer

4

has been deposited to the desired thickness, a copper layer

6

is formed over the diffusion barrier layer in a way that fills the etched features in the dielectric layer

2

. Some excessive diffusion barrier and metallization material is also inevitably deposited over the field areas. In order to remove these overburden materials and to define the desired interconnect metallization lines and associated vias (not shown), a chemical mechanical planarization (CMP) operation is performed.

As mentioned above, the CMP operation is designed to remove the top metallization material from over the dielectric layer

2

. For instance, as shown in

FIG. 1B

, the overburden portion of the copper layer

6

and the diffusion barrier layer

4

have been removed. As is common in CMP operations, the CMP operation must continue until all of the overburden metallization and diffusion barrier material

4

is removed from over the dielectric layer

2

. However, in order to ensure that all the diffusion barrier layer

4

is removed from over the dielectric layer

2

, there needs to be a way of monitoring the process state and the state of the wafer surface during its CMP processing. This is commonly referred to as endpoint detection. Endpoint detection for copper is performed because copper cannot be successfully polished using a timed method. A timed polish does not work with copper because the removal rate from a CMP process is not stable enough for a timed polish of a copper layer. The removal rate for copper from a CMP process varies greatly. Hence, monitoring is needed to determine when the endpoint has been reached. In multi-step CMP operations there is a need to ascertain multiple endpoints: (1) to ensure that Cu is removed from over the diffusion barrier layer; (2) to ensure that the diffusion barrier layer is removed from over the dielectric layer. Thus, endpoint detection techniques are used to ensure that all of the desired overburden material is removed.

Many approaches have been proposed for the endpoint detection in CMP of metal. The prior art methods generally can be classified as direct and indirect detection of the physical state of polish. Direct methods use an explicit external signal source or chemical agent to probe the wafer state during the polish. The indirect methods on the other hand monitor the signal internally generated within the tool due to physical or chemical changes that occur naturally during the polishing process.

Indirect endpoint detection methods include monitoring: the temperature of the polishing pad/wafer surface, vibration of polishing tool, frictional forces between the pad and the polishing head, electrochemical potential of the slurry, and acoustic emission. Temperature methods exploit the exothermic process reaction as the polishing slurry reacts selectively with the metal film being polished. Friction-based methods in which motor current changes are monitored as different metal layers are polished can also typically be utilized.

Another endpoint detection method demodulates the acoustic emission resulting from the grinding process to yield information on the polishing process. Acoustic emission monitoring is generally used to detect the metal endpoint. The method monitors the grinding action that takes place during polishing. A microphone is positioned at a predetermined distance from the wafer to sense acoustical waves generated when the depth of material removal reaches a certain determinable distance from the interface to thereby generate output detection signals. All these methods provide a global measure of the polish state and have a strong dependence on process parameter settings and the selection of consumables. However, none of the methods except for the friction sensing have achieved some commercial success in the industry.

Direct endpoint detection methods monitor the wafer surface using acoustic wave velocity, optical reflectance and interference, impedance/conductance, electrochemical potential change due to the introduction of specific chemical agents. An approach to monitor the acoustic wave velocity propagated through the wafer/slurry to detect the metal endpoint is sometimes utilized. When there is a transition from one metal layer into another, the acoustic wave velocity changes and this has been used for the detection of endpoint. A method of endpoint detection using a sensor to monitor fluid pressure from a fluid bearing located under the polishing pad is also used at times. The sensor is used to detect a change in the fluid pressure during polishing, which corresponds to a change in the shear force when polishing transitions from one material layer to the next. Unfortunately, this method is not robust to process changes. Further, the endpoint detected is global, and thus the method cannot detect a local endpoint at a specific point on the wafer surface. Moreover, the method often utilized is restricted to a linear polisher, which requires an air bearing.

There have been many proposals to detect the endpoint using the optical reflectance from the wafer surface. They can be grouped into two categories: monitoring the reflected optical signal at a single wavelength using a laser source (such as, for example, 600 nm) or using a broad band light (such as, for example, 255 nm to 700 nm) source covering the full visible range of the electromagnetic spectrum. Another endpoint detection method that is sometimes utilized is the using of a single wavelength in which an optical signal from a laser source is impinged on the wafer surface and the reflected signal is monitored for endpoint detection. The change in the reflectivity as the polish transfers from one metal to another is used to detect the transition. Unfortunately, the single wavelength endpoint detection has a problem of being overly sensitive to the absolute intensity of the reflected light, which has a strong dependence on process parameter settings and the selection of consumables. In dielectric CMP applications, such single wavelength endpoint detection techniques also have a disadvantage that it can only measure the difference between the thickness of a wafer but typically cannot measure the actual thickness of the wafer.

Broad band methods rely on using information in multiple wavelengths of the electromagnetic spectrum. Such methods typically use a spectrometer to acquire an intensity spectrum of reflected light in the visible range of the optical spectrum. In metal CMP applications, the whole spectrum is used to calculate the end point detection (EPD signal). Significant shifts in the detection signal indicate the transition from one metal to another.

A common problem with current endpoint detection techniques is that some degree of over-etching is required to ensure that all of the conductive material (e.g., metallization material or diffusion barrier layer

4

) is removed from over the dielectric layer

2

to prevent inadvertent electrical interconnection between metallization lines. A side effect of improper endpoint detection or over-polishing is that dishing

8

occurs over the metallization layer that is desired to remain within the dielectric layer

2

. The dishing effect essentially removes more metallization material than desired and leaves a dish-like feature over the metallization lines. Dishing is known to impact the performance of the interconnect metallization lines in a negative way, and too much dishing can cause a desired integrated circuit to fail for its intended purpose. In view of the foregoing, there is a need for endpoint detection systems and methods that improve accuracy in endpoint detection.

FIG. 1C

shows a prior art belt CMP system

10

in which a pad

12

is designed to rotate around rollers

16

. As is common in belt CMP systems, a platen

14

is positioned under the pad

12

to provide a surface onto which a wafer will be applied using a carrier

18

(as shown in FIG.

1

D). The pad

12

also contains a pad slot

12

a

so end point detection may be conducted as described in FIG.

1

D.

FIG. 1D

shows a typical way of performing end-point detection using a rotary CMP system an optical detector

20

in which light is applied through the platen

14

, through the pad

12

and onto the surface of the wafer

24

being polished. In order to accomplish optical end-point detection, a pad slot

12

a

is formed into the pad

12

. In some embodiments, the pad

12

may include a number of pad slots

12

a

strategically placed in different locations of the pad

12

. Typically, the pad slot

12

a

is designed small enough to minimize the impact on the polishing operation. In addition to the pad slot

12

a

, a platen slot

22

is defined in the platen

14

. The platen slot

22

is designed to allow the optical beam to be passed through the platen

14

, through the pad

12

, and onto the desired surface of the wafer

24

during polishing.

By using the optical detector

20

, it is possible to ascertain a level of removal of certain films from the wafer surface. This detection technique is designed to measure the thickness of the film by inspecting the interference patterns received by the optical detector

20

. Additionally, conventional platens

14

are designed to strategically apply certain degrees of back pressure to the pad

12

to enable precision removal of the layers from the wafer

24

.

In typical end point detection systems such as shown in

FIG. 1C

, an optical opening is cut into a polishing belt. As shown in

FIG. 1B

, an optical opening is generally utilized within a polishing pad and a platen so a laser or light may be shined onto the wafer and a reflection may be received to determine the amount polished from the wafer.

FIG. 1E

shows a dual graph

40

of end point detection data obtained from utilizing a broad spectrum of light end point detection that illustrates polishing distance detection. In an upper graph

41

showing the reflected light intensity, a curve

42

shows the intensity level of reflection for different frequencies of a light utilized for end point detection. The upper graph

41

has a vertical axis that indicates intensity and a horizontal axis showing frequency. The curve

42

with the upper graph

41

shows the differing intensity of light reflection from a wafer depending on the different frequencies of optical signals transmitted to the wafer. The intensities of light reflection as shown by the curve

42

is the optimal optical signal transmission through an optical window without any slurry on top of it. Unfortunately, when the light is blocked by slurry as occurs in prior art flat optical window systems, intensity of the light transmitted to the wafer and received back from the wafer by an optical detection unit is decreased (signal/noise decreases) as shown by a curve

44

which is a typical prior art profile curve. Therefore the curve

42

is not achieved by prior art systems when slurry accumulates in the polishing window.

Once a fourier transform

50

is conducted, a peak

46

and a curve

48

are shown in a lower graph

43

showing end point detection (EPD) intensity. The lower graph

43

has a vertical axis of intensity and a horizontal axis of thickness. The peak

46

of the lower graph

43

is produced by way of the fourier transform

50

of the curve

42

, and the curve

48

is produced on the lower graph

43

by the fourier transform

50

of the curve

44

. If an optical signal received by the optical detection is weak, as shown by curve

44

, then the curve

48

is fuzzy and not as sharp as the peak

46

which results from reception of a strong optical signal by the light detection unit. Consequently, the curve

48

does not show as precise a film thickness polished as peak

46

. Therefore, the stronger the optical signal received, the clearer measurement of film thickness that is made by the optical detection unit. Therefore, it is highly advantageous for a strong optical signal to be able to pass to the wafer or reflect from the wafer through an optical window to reach the optical detection unit.

FIG. 1F

illustrates a prior art flat optical window system

60

for use during end point detection in a CMP process. In this example, a polishing pad

62

moves over platen

64

which in this example is a metallic table which may lend support to the polishing pad during the polishing action. A flat optical window

66

is attached to the polishing pad

62

, and during polishing moves over a platen opening

70

which is generally a hole exposing the flat optical window

66

to an optical detector

72

. Generally, flat optical windows of the prior art have a thickness of between 15 and 30 mils (a mil equals 1×10

−3

inch). As slurry

68

is deposited on top of the polishing pad

62

, the slurry

68

accumulates in a polishing pad hole above the flat optical window

66

. Unfortunately, the accumulation of slurry reduces reflection back of the optical signal to the optical detector

72

, especially for shorter wavelength signals.

Unfortunately the prior art method and apparatus of end point detections in CMP operations as described in reference to

FIGS. 1A

,

1

B,

1

C,

1

D,

1

E, and

1

F have various problems. The prior art apparatus also has problems with oxide removal where too much or too little may be removed due to inaccurate readings in optical endpoint detection resulting from accumulation of slurry in the flat optical window. Specifically, the accumulation of slurry often decreases the intensity of optical signal received by the optical detection unit from the wafer as shown in FIG.

1

E. Because the prior art optical windows are configured to be flat in a polishing pad opening, slurry dispensed during CMP pools in the polishing pad hole. As more and more slurry flows into the polishing pad hole, more optical signal interference is created. This may significantly reduce wafer polishing accuracy and resultant wafer production reliability. Such a decrease in wafer polishing accuracy may serve to significantly increase wafer production costs. Consequently, these problems arise due to the fact that the prior art polishing belt designs do not properly control and reduce slurry accumulation on top of the optical window.

Therefore, there is a need for a method and an apparatus that overcomes the problems of the prior art by having a polishing pad structure that reduces slurry accumulation over an optical window that further enables more consistent and effective end point detection for more accurate polishing in a CMP process.

SUMMARY OF THE INVENTION

Broadly speaking, the present invention fills these needs by providing a molded optical window for use with polishing pads for polishing a wafer during a chemical mechanical planarization (CMP) process. The apparatus includes a CMP pad with molded optical windows that resist accumulation of light blocking substances and therefore increase reception of light by an optical detection unit for end point detection. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.

In one embodiment, an optical window structure for use in chemical mechanical planarization is provided. The optical window structure includes a polishing pad and an optical window opening in the polishing pad. The optical window structure also includes a molded optical window attached to an underside of the polishing pad, a molded portion of the optical window at least partially protruding into the optical window opening in the polishing pad.

In another embodiment, a method to generate an optical window structure is provided The method includes providing a polishing pad, and generating an optical window opening in the polishing pad. The method also includes molding an optical window, and attaching the molded optical window to an underside of the polishing pad so that a molded portion of the optical window at least partially protrudes into the optical window opening.

In yet another embodiment, an optical window structure for use in chemical mechanical planarization is provided. The optical window structure includes a multi-layer polishing pad, and an optical window opening in the multi-layer polishing pad. The optical window structure also includes an optical window having a molded portion where the optical window is attached to an underside of the multi-layer polishing pad, and the molded portion of the optical window at least partially protrudes into the optical window opening.

In another embodiment, a method to generate an optical window structure is provided. The method includes providing a multi-layer polishing pad, and generating an optical window opening in the multi-layer polishing pad. The method also includes molding an optical window, and attaching the molded optical window the multi-layer polishing pad so that a molded portion of the optical window at least partially protrudes into the optical window opening.

The advantages of the present invention are numerous. Most notably, by constructing and utilizing a molded optical window structure in accordance the present invention, the polishing pad will be able to provide more efficient and effective planarization/polishing operations over wafer surfaces (e.g., metal and oxide surfaces). Furthermore, wafers placed through a CMP operation using the molded optical window structure are polished with better accuracy and more consistency. In addition, the increased wafer polishing efficiency leads to greater wafer production. The molded optical window keeps slurry from accumulating on top of an area where optical signal may travel. Therefore, an optical detection unit utilized during end point detection may transmit and receive optimal optical signals through the molded optical window to accurately determine the amount of polishing that has been completed in a CMP process. Moreover, the molded optical window may be generated in a more efficient and time consuming manner than other typical types of optical windows. The molded optical window may also enhance planarizations that require exacting end point detection such a dielectric shallow trench isolation.

Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings. To facilitate this description, like reference numerals designate like structural elements.

FIG. 1A

shows a cross sectional view of a dielectric layer undergoing a fabrication process that is common in constructing damascene and dual damascene interconnect metallization lines.

FIG. 1B

shows a cross sectional view of a dielectric layer after an overburden portion of the copper layer and a diffusion barrier layer have been removed

FIG. 1C

shows a prior art belt CMP system in which a pad is designed to rotate around rollers.

FIG. 1D

shows a typical way of performing end-point detection using a rotary CMP system an optical detector in which light is applied through the platen, through the pad and onto the surface of the wafer being polished.

FIG. 1E

shows a dual graph of end point detection data obtained from utilizing a broad spectrum of light end point detection that illustrates polishing distance detection.

FIG. 1F

illustrates a prior art flat optical window system for use during end point detection in a CMP process.

FIG. 2A

shows a top view of a CMP system according to one embodiment of the present invention.

FIG. 2B

shows a side view of a CMP system in accordance with one embodiment of the present invention.

FIG. 3

shows an optical window section of a polishing pad in accordance with one embodiment of the present invention.

FIG. 4

shows a cut-away side view of an optical detection area in accordance with one embodiment of the present invention.

FIG. 5

shows an optical window structure with a molded optical window in accordance with one embodiment of the present invention.

FIG. 6

shows another optical window structure with a molded optical window in accordance with one embodiment of the present invention.

FIG. 7A

illustrates a side view of an optical window structure in accordance with one embodiment of the present invention.

FIG. 7B

illustrates an optical window structure with a molded optical window in accordance with one embodiment of the present invention.

FIG. 8A

illustrates a top mold in accordance with one embodiment of the present invention.

FIG. 8B

illustrates a top mold with a removable connecting peg in accordance with one embodiment of the present invention.

FIG. 8C

shows a bottom mold in accordance with one embodiment of the present invention.

FIG. 8D

illustrates a bottom mold with removable connecting holes and in accordance with one embodiment of the present invention.

FIG. 9A

illustrates a molded optical window in accordance with one embodiment of the present invention.

FIG. 9B

shows a molded optical window from a top view in accordance with one embodiment of the present invention.

FIG. 9C

illustrates a side view of a molded optical window in accordance with one embodiment of the present invention.

FIG. 9D

shows a close up width view of the region molded optical window in accordance with one embodiment of the present invention.

FIG. 9E

shows a close up length view of the region of the molded optical window in accordance with one embodiment of the present invention.

FIG. 10

shows a flowchart which defines an exemplary molding process in accordance with one embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An invention is disclosed for a molded optical windows used in CMP where the molded optical windows are more resistant to slurry accumulation and therefore increase reception of light intensity by an optical detection unit due to less slurry in an optical window hole. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, by one of ordinary skill in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.

In general terms, the present invention is directed toward a molded optical window and a molded optical window structure. The molded optical window structure includes a polishing pad with a support layer and a molded optical window. The molded optical window may be configured to reduce slurry accumulation on top of it. In this way, the molded optical window may reduce the amount of optical transmission blocked by the slurry introduced during CMP. Consequently, the intensity of optical reflection received from the wafer surface through the molded optical window of the present invention may be stronger than if a prior art flat optical window is utilized thereby optimizing determination of the amount of polishing that has been completed in a CMP process. In this way, optical signals of optimal intensity may be transmitted and received by an optical detection unit located below the molded optical window structure and a platen to determine the amount of polishing that has been completed in a CMP process. Moreover, the molded optical window may be produced in a more efficient and cost effective manner than other typical optical windows.

In a preferable embodiment, a polishing pad of the molded optical window structure is preferably adhered to a support layer (which may include a cushioning layer and a reinforcement layer such as, for example a stainless steel layer or a Kevlar-type material, connected by an adhesive). A molded optical window may be attached to the polishing pad or the support layer in any way which enables the optical window to reduce the amount of slurry that may accumulate on a surface of the molded optical window such as, for example, by using adhesives.

The molded optical window structure may include a polishing pad in addition to any other structural component that may be utilized in conjunction with the polishing pad such as, for example, the cushioning layer, the support layer, a reinforcement layer, any molded optical window, etc. In a preferable embodiment, the reinforcement layer is a stainless steel belt or a Kevlar type material belt. The polishing pad within the molded optical window structure may be in either a generic pad form, a belt form, or any other form that may be utilized in a CMP process such as, for example, a seamless polymeric polishing pad, a seamless polymeric polishing belt, polymeric polishing pad, a linear belt polymeric polishing pad, polymeric polishing belt, a polishing layer, a polishing belt, etc. The polishing pad may be of a multi-layer variety that preferably includes a stainless steel or a Kevlar type material reinforcement layer. Furthermore, the molded optical window structure of the present invention may be utilized in any type of operation which may require controlled, efficient, and accurate polishing of any surface of any type of material.

FIG. 2A

shows a top view of a CMP system

100

according to one embodiment of the present invention. A polishing head

106

may be used to secure and hold a wafer

108

in place during processing. A polishing pad

102

preferably forms a continuous loop around rotating drums

104

. It should be understood that the polishing pad

102

may include a polishing layer with a support layer which may include a cushioning layer and a reinforcement layer. The polishing layer may be secured to the support layer by using a any type of glue or other adhesive material such as, for example a 3M 467 adhesive. In another embodiment, the polishing layer may be secured to support layer through a direct casting of polyurethane on top of the support layer. The polishing pad

102

preferably includes a molded optical window

208

of the present invention through which end point detection may be conducted.

The polishing pad

102

may rotate in a direction

112

indicated by the arrow. It should be understood that the polishing pad

102

may move at any speed to optimize the planarization process. In one embodiment, the polishing pad

102

may move at a speed of about 400 feet per minute. As the belt rotates, a polishing slurry

109

may be applied and spread over the surface of the polishing pad

102

by a slurry dispenser

111

. The polishing head

106

may then be used to lower the wafer

108

onto the surface of the polishing pad

102

. In this manner, the surface of the wafer

102

that is desired to be planarized is substantially smoothed.

In some cases, the CMP operation is used to planarize materials such as copper (or other metals), and in other cases, it may be used to remove layers of dielectric or combinations of dielectric and copper. Although the molded optical window described herein is shown in exemplary embodiments as being used in CMP applications, it should be appreciated that the molded optical window may be utilized in any suitable type of substrate processing application such as, for example applications involving, shallow trench isolation planarization, inter-level dielectric (ILD)/inter-metal dielectric (IMD) planarization, tungsten planarization, and poly-silicon planarization, etc. In one embodiment, the CMP operation utilizing the molded optical window

208

may be used to perform exacting planarization operations that require very accurate end point detection such as dielectric shallow trench isolation. The rate of planarization may be changed by adjusting the polishing pressure applied to the polishing pad

102

. The polishing rate is generally proportional to the amount of polishing pressure applied to the polishing pad

102

against a platen

118

. In one embodiment, the platen

118

may use an air bearing which is generally a pressurized air cushion between the platen

118

and the polishing pad

102

. It should be understood that the platen

118

may utilize any other type of bearing such as, for example, fluid bearing, etc. After the desired amount of material is removed from the surface of the wafer

101

, the polishing head

106

may be used to raise the wafer

108

off of the polishing pad

102

. The wafer is then ready to proceed to a wafer cleaning system.

In such an embodiment, the molded optical window

208

may be configured to keep slurry from accumulating on the molded optical window

208

so end point detection may be conducted in a more accurate manner thus resulting in better wafer polishing controllability. The molded optical window

208

of the present invention may also be configured for slurry removal during the CMP process by the pressurized air from the platen

118

by molding.

It should be appreciated that although the molded optical window

208

is shown in these exemplary embodiments as being used with a belt-type CMP system, it should be appreciated that the molded optical window

208

may be used in a rotary-type CMP system and an orbital-type CMP system. In generic terms, as known by those skilled in the art, a rotary-type CMP system has a polishing head and rotating platen with polishing pads mounted on the platen where the wafer is mounted on the head comes down to the rotating platen during polishing. In such an embodiment, the molded optical window

208

may be attached to either the polishing pad or the platen. As known by those skilled in the art, orbital-type CMP systems have a polishing head and a typically a smaller orbiting platen that rotates during polishing. The molded optical window

208

may be mounted on the polishing pad or the platen.

FIG. 2B

shows a side view of a CMP system

100

in accordance with one embodiment of the present invention. In this embodiment, the wafer

108

is lowered onto the polishing pad

102

by polishing head

106

. As this happens, the slurry

109

may be applied to the polishing pad

102

by the slurry dispenser

111

to enhance the polishing of the wafer

108

. An optical detection area

116

may include an optical window structure where end point detection may be conducted. Therefore, there may be a hole in the polishing pad

102

and the platen

118

through which optical signals may be transmitted and reflected. By use of the CMP system

100

, accurate polishing results may be obtained due to more precise polishing distance readings.

The many embodiments of the molded optical window and the optical window structures described herein may be utilized to planarize any suitable type of wafer such as, for example, 200 mm, 300 mm, etc. It should also be understood that the molded optical window and the optical window structures described herein may be used in any suitable CMP system such as, for example, in a belt-type CMP system as described in reference to

FIGS. 2A and 2B

, in a rotary-type CMP system, etc.

FIG. 3

shows an optical window section

200

of a polishing pad in accordance with one embodiment of the present invention. In this embodiment, the optical window section

200

includes an optical window opening

206

with a molded optical window

208

. Below the molded optical window

208

, an optical detection unit located below a hole or a transparent area in the platen may send optical signals through the hole and through the molded optical window

208

to a wafer and receive optical signals that are reflected back from the wafer through the molded optical window

208

. The molded optical window

208

may, in one embodiment, be produced in the manner described in reference to

FIGS. 8A through 8D

, and

FIG. 10

below. In this way, end point detection may be accurately conducted because the configuration of the molded optical window

208

reduces slurry accumulation on a top surface of the molded optical window

208

. It should be appreciated that the molded optical window

208

may be any shape or size that would enable optical signals to be sent to the wafer and reflected back from the wafer so an optical detection unit may determine the amount of polishing that has been conducted by CMP such as, for example, an oval, a circle, a rectangle, a square, or any other geometric or amorphous shape.

In one embodiment when a molded optical window is utilized (as discussed below), the optical window opening

206

has a length d

202

in the axis of polishing pad direction of between about 0.2 inch to about 2.0 inches. A width d

204

of the optical window opening

206

in the axis perpendicular to the polishing pad direction may be between about 0.1 inch to about 2.0 inches. In a preferable embodiment when the molded optical window is utilized, the length d

202

can be about 1.0 inch and the width d

204

may be about 0.6 inch. By use of the molded optical window

208

, slurry buildup may be kept to a minimum and optical signal transmission through a molded optical window structure may be kept at an optimal level.

FIG. 4

shows a cross sectional view of an optical detection area

116

during CMP in accordance with one embodiment of the present invention. In one embodiment, the polishing pad

102

has an optical window opening

206

. The optical window opening

206

may contain a molded optical window

208

that moves in a direction

255

to move closer to the wafer

108

during operation when air pressure

252

is applied from the platen

118

. Therefore, in this embodiment, the molded optical window

208

can remain partially protruded when the polishing pad

102

is rotating around the rollers. Then when the molded optical window

208

is rolling over the platen

118

, an air pressure

252

pushes on the molded optical window

208

so it protrudes further into the optical window opening

206

. The molded optical window

208

then takes a configuration as shown by the broken line. It should be understood that the optical window opening

206

may be any suitable dimension that would enable accurate end point detection and proper shaping of the molded optical window

206

. Different dimensions that may be utilized regarding the optical window opening

206

is described in detail in reference to FIG.

3

.

Slurry that may be preferably applied on the polishing pad can enter the optical window opening

260

and, in prior art systems, block optical signals coming in from a platen opening

258

. But, the molded optical window

208

is configured to controllably protrude into an optical window opening

206

and in one embodiment, the optical window

208

may protrude further into the optical window opening when the air pressure

252

is applied. The thickness of the molded optical window

208

may be managed to determine the amount of protrusion into the optical window opening

206

depending on the air pressure from the platen. Once the optical window opening

206

finishes passing over the platen and the air pressure

252

is not applied, the molded optical window

208

becomes reverts back the form before the air pressure

252

was applied. It should be appreciated that the molded optical window

208

may be any type of transparent or semi-transparent material that may be flexible and thin enough to controllably further protrude into the molded optical window with application of the air pressure

252

such as, for example, Mylar-type material, polyester, polyurethane, silicone etc. It should also be understood that the molded optical window

208

may be any suitable dimension that would enable proper end point detection in a CMP process. In one embodiment, the molded optical window

208

is made from a Mylar material enabling optical signal transmission that may be between about 1 mil to about 20 mil in thickness. The thickness may be varied depending on the amount of flexing is desired. In another embodiment, the molded optical window

208

can be about 2 mils in thickness. By use of such a molded optical window, the optical window structure as described herein reduces slurry buildup on a top surface of the molded optical window thereby optimizing optical signal transmission through the molded optical window.

FIG. 5

shows an optical window structure

280

with a molded optical window

208

in accordance with one embodiment of the present invention. In one embodiment, a molded optical window

208

is attached to a polishing pad

102

. A backing

253

may optionally be applied to a region of the back portion (side of the polishing pad

102

opposite the side that polishes a substrate) of the polishing pad

102

that the molded optical window

208

is does not cover. The backing

253

may be applied to the polishing pad

102

in any suitable manner such as for example, by adhesive, by pins, etc. In addition, the backing

253

may be any suitable material that can protect the back side of the polishing pad

102

such as, for example, polyethylene, urethane-based material, plastics, rubber, etc. In one embodiment, the backside

253

may be made out of polyethylene. Therefore, in one embodiment, the backing

253

and the molded optical window

253

form a substantially consistent surface along a back side of the polishing pad

102

. It should be understood that the molded optical window

208

may be any suitable dimension and may be made out of any suitable type of material. In one embodiment, the molded optical window

208

may protrude into the optical window opening before operation and further protrude into the optical window opening when air pressure is applied to the bottom portion of the molded optical window

208

as during a CMP operation.

In another embodiment, depending on the material utilized, the molded optical window

208

may not protrude further when pressurized air is applied from a platen. It should also be understood that the polishing pad

102

may be made out of any suitable type of material that can effectively polish a wafer such as, for example, polyurethane, cast urethane, and any other type of polymeric material such as, for example a Rodel IC-1000 pad, a Thomas West 813 pad, and the like. In addition, the polishing pad

102

may be any suitable dimension which would enable polishing of the wafer. In one embodiment, the polishing pad

102

is between about 20 mil to about 200 mil in thickness. In another embodiment, the polishing pad

102

is between about 30 mils to about 80 mils in thickness, and in a preferable embodiment, the polishing pad

102

is about 50 mils in thickness. It should also be understood that the molded optical window

208

may be attached to the polishing pad

102

in any suitable way such as, for example, by way of any type of adhesive, pins, etc. The distance d

283

may be any suitable distance as long as during operation, proper end point detection may be obtained through light (or other types of transmission) through the molded optical window

208

. In one embodiment, the molded optical window

208

may be attached to the polishing pad

102

over a distance d

283

of between 0.2 inch to 2.0 inches. In a preferable embodiment, the distance d

283

is about 0.5 inch.

When the molded optical window

208

further protrudes up into the optical window opening

206

, it moves in a direction

255

. Therefore, as the polishing pad

102

is polishing the wafer, slurry that was located on top of the molded optical window

208

falls away thus increasing optical signal intensity through and from the molded optical window

208

. It should be appreciated that the molded optical window

208

may protrude up any amount of distance which would permit better slurry draining from the surface of the molded optical window

208

and permit optimal optical signal transmission to and from an optical detection unit (which may be located below the molded optical window

208

). In this way, more accurate readings of CMP progress may be made.

The optical window structure

280

(and

280

′ below discussed in reference to

FIG. 6

) may be generated by providing a polishing pad and generating an optical window opening in the polishing pad, molding an optical window as discussed in reference to

FIGS. 8A-8B

, and

10

, and attaching the molded optical window the multi-layer polishing pad so that a molded portion of the optical window at least partially protrudes into the optical window opening. It should be appreciated that this methodology may apply to any suitable pad structure such as one described in reference to FIG.

6

.

FIG. 6

shows another optical window structure

280

′ with a molded optical window

208

′ in accordance with one embodiment of the present invention. In this embodiment, the optical window structure

300

includes the molded optical window

208

′ that is attached to the polishing pad

102

. As with the optical window structure

280

as described in reference to

FIG. 5

, the polishing pad

102

is shown with optionally backing

253

. The polishing pad

102

may be any thickness d

310

that enables efficient polishing of wafers. In one embodiment, the thickness d

310

of the polishing pad

102

may be between 0.02 inch to about 0.2 inch. In a preferable embodiment, the thickness d

310

is about 0.06 to about 0.08 inch. The molded optical window

208

′ may be attached to the polishing pad

312

in any suitable manner such as, for example, by any type of adhesive, pins, etc.

The molded optical window

208

′ may be any suitable type of material of any shape, size and construction that would enable optical signal transmission but limit the amount of slurry from accumulating between the molded optical window

208

′ and a wafer. In one embodiment, the molded optical window

208

′ may be a transparent, Mylar material. In another embodiment, the molded optical window

208

′may be polyester, polyurethane, silicone, etc. It should also be appreciated that a top surface of the molded optical window may be any suitable height that enables protrusion into the optical window opening and enables slurry to be evacuated. In one embodiment, the molded optical window

208

′ can be recessed below the top surface of the polishing pad

102

as shown by distance d

304

which may be between about 0.001 inch to about 0.05 inch. In a preferable embodiment, the distance d

304

can be about 0.01 inch. In one embodiment slurry may be outputted into polishing pad grooves as discussed below in reference to FIG.

13

. It should be appreciated that the molded optical window may be any suitable shape when seen from above such as, for example, an oval shape as described in further detail in reference to

FIG. 3

, circular, rectangular, etc. Therefore, the optical window structure

280

′ reduces slurry accumulation in an optical window opening and therefore maintains optimal optical signal transmission and reception by an optical detection unit. This enables accurate polishing utilizing advanced end point detection.

The optical window structure

280

′ may be generated by providing a multi-layer polishing pad and generating an optical window opening in the multi-layer polishing pad, molding an optical window as discussed in reference to

FIGS. 8A-8B

, and

10

, and attaching the molded optical window the multi-layer polishing pad so that a molded portion of the optical window at least partially protrudes into the optical window opening.

It should be appreciated that this methodology may apply to any multi-layer polishing pad structure such as one described in reference to FIG.

7

B.

FIG. 7A

illustrates a side view of an optical window structure

280

″ in accordance with one embodiment of the present invention. In this embodiment, the optical window structure

280

″ includes a polishing pad

102

, a support layer

330

, and a molded optical window

208

. The polishing pad

102

may be any type of pad with any type dimension that would enable accurate and efficient polishing such as, for example, an IC 1000 pad made by Rodel Inc. In one embodiment, the polishing pad

102

may be made up of a polymeric polishing belt and may be between about 0.02 inch and 0.2 inch thick. In another embodiment, the polishing pad

102

may be about 0.032 inch in thickness. In one embodiment, the support layer

330

includes a cushioning layer

330

a

and a reinforcement layer

330

b.

The reinforcement layer may be between about 0.005 inch to about 0.040 inches and is preferably made out of stainless steel although other types of supportive materials may be utilized such as, for example, kevlar, etc. The cushioning layer

330

a

may be made out of any type of material that may provide cushioning to the polishing pad

102

such as, for example, a polyurethane layer made by Thomas West, Inc. The molded optical window

208

may be held in place by an adhesive or by a mechanical connection such as, for example, a pin. When air pressure from an air bearing platen is applied to the bottom portion of the molded optical window

208

, the molded optical window

208

may move in a direction

255

. In this way, slurry may slide off thus optimizing optical signal transmission and reception in end point detection.

The optical window structure

280

″ may be generated by providing a multi-layer polishing pad and generating an optical window opening in the multi-layer polishing pad, molding an optical window as discussed in reference to

FIGS. 8A-8B

, and

10

, and attaching the molded optical window the multi-layer polishing pad so that a molded portion of the optical window at least partially protrudes into the optical window opening.

It should be appreciated that this methodology may apply to any multi-layer polishing pad structure such as one described in reference to FIG.

7

B.

FIG. 7B

illustrates an optical window structure

280

′″ with a molded optical window

208

″ in accordance with one embodiment of the present invention. In this embodiment, the optical window structure

280

′″ includes a polishing pad

102

, a support layer

330

, and the molded optical window

208

″. The support layer

330

includes a cushioning layer

330

a

and a reinforcement layer

330

b

which are connected to each other by any type of adhesive. The support layer

330

may also attached to the polishing pad

102

by an adhesive. Examples of adhesives include 3M 442, 3M 467MP, 3M 447, a rubber-based adhesive, etc. A gap between the molded optical window

208

″ and side wall of the polishing pad

102

may be any distance such as, for example, between about 0.02 inches to about 0.12 inches. In a preferable embodiment, the gap may be about 0.04 inches.

Slurry which would typically accumulate on prior art optical windows can be evacuated off of the molded optical window

208

″ into a groove or a plurality of grooves of the polishing pad

102

. Therefore, a top surface of the molded optical window

208

″may stay relatively clear of slurry thus enabling optimal transmission and reception of optical signals by an optical detection unit. Such optimization of optical signal transmission and reception enables better polishing distance measurement resolution thereby increasing accuracy of CMP procedures. This in turn may then increase wafer yield and decrease wafer production costs. In addition, the molded optical window

208

may extend the useful life of the polishing pad

102

and the support layer

330

because if for some reason, the molded optical window fails, then the optical window may be replaced (by re-adhesion) without disposing of the polishing pad

102

and the support layer

330

.

FIG. 8A

illustrates a top mold

400

in accordance with one embodiment of the present invention. The top mold

400

includes a connecting pegs

402

a

and

402

b

and a molding section

404

. The molding section

404

is an indentation in the top mold

400

where a portion of the molded optical window that protrudes into the optical window opening is formed.

FIG. 8B

illustrates a top mold

400

with a removable connecting peg

402

b

in accordance with one embodiment of the present invention. The top mold

400

a

shows a removable connecting peg

402

b.

The connecting pegs

402

a

and

402

b

may be utilized to connect with a bottom mold

440

as described in reference to

FIGS. 8C and 8D

.

FIG. 8C

shows a bottom mold

440

in accordance with one embodiment of the present invention. The bottom mold

440

fits together with the top mold

400

to mold a sheet of Mylar like material or any other suitable material such as, for example, polyester, polyurethane, silicon.

FIG. 8D

illustrates a bottom mold

440

with removable connecting holes

442

a

and

442

b

in accordance with one embodiment of the present invention. The bottom mold

440

shows the removable connecting holes

442

a

and

442

b

that may connect with connecting pegs

402

a

and

402

b

of the top mold

400

as discussed in reference to

FIGS. 8A and 8B

. It should be appreciated that although the bottom mold

440

has the indentation and the top mold

400

has the protrusion, there may be other embodiments where the top mold

400

has the protrusion and the bottom mold

440

has the indention.

Therefore, in one embodiment, the top mold

400

may be combined with the bottom mold

440

with an optical window film in between the molds

400

and

440

. By fitting connecting holes

442

a

and

442

b

of the bottom mold

440

with the connecting pegs

402

a

and

402

b

of the top mold

400

, the molds

400

and

440

may be connected so the indentation and the protrusion of the molds

400

and

440

molds the optical window film into the desired molded optical window

208

. In this way, the optical window film may be shaped by the molds

10

generate the molded optical window

208

. In one embodiment, the molds

400

and

440

may be heated during the molding process. It should be appreciated that the molding process may be adjusted for numerous variables such as, for example, temperature and molding time to enhance the process. In another embodiment, the molds

400

and

440

maybe configured to produce vacuum in the indentation portion to better form the molded optical window

208

.

FIG. 9A

illustrates a molded optical window

208

in accordance with one embodiment of the present invention. The molded optical window

208

is a molded portion of a optical window material

208

a

that is flat except for the protruding portion. It should be appreciated that the molded optical window

208

and the optical window material

208

a

that the molded optical window

208

is molded from may be made from any suitable material that can be molded and is at least semi-transparent such as, for example, Mylar-like material, polyester, polyurethane, silicone, etc.

FIG. 9B

shows a molded optical window

208

from a top view in accordance with one embodiment of the present invention. It should be appreciated that the molded optical window

208

, from the top view, may be any suitable geometrical shape such as, for example, oval, circular, square, rectangular, etc. In one embodiment, the molded optical window

208

is oval shaped where the oval is longer in the direction of the belt direction.

FIG. 9C

illustrates a side view of a molded optical window

208

in accordance with one embodiment of the present invention. The region

409

encircled by the broken line is a portion of the molded optical window

208

is the region that is discussed in further detail in reference to

FIGS. 9D and 9E

.

FIG. 9D

shows a close up width view of the region

409

molded optical window

208

in accordance with one embodiment of the present invention.

FIG. 9D

is A—A cross section view of FIG.

9

B. The molded optical window

208

may have any suitable type of dimension that may enable slurry removal and optical signals to penetrate the molded optical window

208

. The molded optical window

208

has a distance D

460

that shows a distance of a flat region at a furthermost protrusion region of the molded optical window

208

. It should be appreciated that the dimension distances shown herein may be any suitable dimensions as long as the molded optical window can remove slurry during CMP operation and enable end point detection. In one embodiment, the molded optical window has a distance D

460

of between about 0 inch to about 2 inches. In another embodiment, the distance D

460

is about 0.13 inch. In one embodiment, the molded optical window

208

has a distance D

462

of between about 0.01 inch to about 2.0 inches. In another embodiment, the distance D

462

is about 0.63 inch. In one embodiment, the distance D

464

is between about 0.2 inch to about 2.0 inches. In one embodiment, D

464

is about 0.83 inch. In one embodiment, the distance D

466

is between about 0 inch to about 1 inch. In another embodiment, the distance D

466

is about 0.25 inch.

FIG. 9E

shows a close up length view of the region

409

of the molded optical window

208

in accordance with one embodiment of the present invention.

FIG. 9E

is B—B cross section view of FIG.

9

B. The region

409

shows dimension distances of the molded optical window

208

. It should be appreciated that the dimension distances shown herein may be any suitable dimensions as long as the molded optical window can remove slurry during CMP operation and enable end point detection. In one embodiment, the molded optical window has a distance D

480

of between about 0.001 inch to about 0.5 inch. In another embodiment, the distance D

480

is about 0.068 inch. In one embodiment, the molded optical window

208

has a distance D

488

of between about 0.2 inch to about 2.0 inches. In another embodiment, the distance D

488

is about 1.22 inches. In one embodiment, the distance D

490

is between about 0.01 inch to about 2.0 inches. In one embodiment, D

490

is about 1.02 inches. In one embodiment, the distance D

492

is between about 0 to about 2 inches. In another embodiment, the distance D

492

is about 0.72 inch. In one embodiment, the distance D

494

is between about 0 inch to about 2 inches. In another embodiment, the distance D

494

is about 0.52 inch. In one embodiment, the radius D

496

is between about 0.1 to about 1.0 inch. In a preferable embodiment, the radius D

496

is 0.38 inch. In one embodiment, the radius D

498

is between about 0.1 inch to about 1.0 inch. In a preferable embodiment, the radius D

498

is about 0.38 inch. The thickness denoted by D

499

of the molded optical window, which in a preferable embodiment is made out of a Mylar material, is between about 1 mil to about 20 mil with a preferable thickness being 2 mil.

FIG.

10

. shows a flowchart

500

which defines an exemplary molding process in accordance with one embodiment of the present invention. Flowchart

500

begins with operation

502

which places an optical window material between a top mold and a bottom mold (as described in reference to

FIGS. 8A through 8D

) and connects the top mold and the bottom mold. In this way, the optical window material is sandwiched between the two mold sections. Then operation

504

heats the top mold and/or the bottom mold. It should be appreciated that the one or both of the molds may be heated by any suitable manner such as, for example, a heat gun or the mold(s) may be configured to be self heating etc. In addition, the magnitude of heat may be any suitable temperature as long as the optical window material is molded as desired.

After operation

504

, the method optionally moves to operation

506

which applies suction (e.g., vacuum) in an indented portion of the mold that has the indentation to better define and form the molded portion of the molded optical window. It should be appreciated that depending on the configuration and the manufacturing process, the top mold may have the indentation or the bottom mold may have the indentation with the complementary molds having a protrusion that fits into the indention. In this operation, the vacuum or suction pulls the portion of the optical window to be molded to the wall of the indentation thereby giving better control of the molding process. In one embodiment, opening(s) may be generated in the indented portion of the mold to generate vacuum in the indented portion. The opening may lead to a passage through the mold to be connectable to an outside suction or vacuum generating apparatus. After either operation

504

or

506

(if the optional operation

506

is conducted), then the method moves to operation

508

where the molded is kept at a heated state for a period of time. Then the method moves to operation

510

where the top mold and the bottom mold are allowed to cool down. Then in operation

512

, the top mold and the bottom mold are separated and the molded optical window is removed.

While this invention has been described in terms of several preferred embodiments, it will be appreciated that those skilled in the art upon reading the preceding specifications and studying the drawings will realize various alterations, additions, permutations and equivalents thereof. It is therefore intended that the present invention includes all such alterations, additions, permutations, and equivalents as fall within the true spirit and scope of the invention.

Number	Name	Date	Kind
6599765	Boyd et al.	Jul 2003	B1
6641470	Zhao et al.	Nov 2003	B1
20030084774	David	May 2003	A1

Molded end point detection window for chemical mechanical planarization

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

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Abstract

Description

Claims

US Referenced Citations (3)