RELATED APPLICATION

The present application claims priority from United States provisional patent application 63402035 filed on August 29, 2022 and United Sates provisional patent application 63428031 filed on November 25, 2022 with the United States patent office.

FIELD OF THE INVENTION

The present invention generally relates to a fluid delivery system for a chemical mechanical polishing(“CMP”) apparatus. The present invention also relates to a CMP apparatus employing the fluid delivery system and to a method of polishing a semiconductor wafer using the CMP apparatus. The fluid delivery system may deliver a plurality of fluids in a chemical mechanical polishing apparatus that is equipped with plurality of fluids, each with its own control valve.

BACKGROUND OF THE INVENTION

A CMP apparatus is used for polishing the front face or device side of a semiconductor wafer during the fabrication of semiconductor devices. The wafer is polished by pressing a rotating wafer held by a wafer holder, onto a rotating polishing pad while polishing slurry is dispensed onto the polishing pad. A diamond coated disk is optionally applied to the pad surface during or in between wafer polishing to roughen or texture the pad surface.

As the slurry is dispensed onto a rotating polishing pad, the rotation of the pad may cause some slurry to be thrown off the pad surface before reaching the wafer.

Additionally, slurry must traverse a narrow channel defined between the rotating polishing pad and the wafer from the wafer edge to the wafer center. Typically, the wafer holder may include a ring which presses against the pad to minimize potential for wafer slippage. This mechanism may also contribute towards slurry flow restriction, further reducing the slurry flow between the rotating polishing pad and the wafer. The retaining ring may contain openings or slots to enable slurry to flow under the wafer, however it still adds to the overall flow resistance.

Uniform spreading of the slurry across the pad surface is important for uniform film removal across the wafer surface. Polishing pad surface design contains several features to enable uniform distribution of slurry across the wafer surface. For example, polishing pads may contain grooves to channel slurry from the edge of the wafer to center of the wafer, and may also have micropores embedded in the pad surface enhance localized slurry availability. Additionally, a polishing pad surface may be textured with a 50 - 300 micron sized diamond coated disk to enhance slurry transport. All these three elements may be employed to work in concert for achieving a uniform polishing process.

Polishing pads may be hard, incompressible pads or soft pads. For oxide polishing, hard (Shore D >40) pads are generally used to achieve planarity. Soft pads (Shore D < 30) are generally used in other polishing processes to achieve improved uniformity and smooth surface. The hard pads and the soft pads may also be combined in an arrangement of stacked pads for customized applications.

Slurry composition consists of an abrasive component, typically a metal oxide like silicon dioxide or aluminum oxide and components that chemically react with the surface of the substrate. The chemistry of the slurry composition plays an important role in the polishing rate of the CMP process. For instance, when polishing oxide films, the rate of removal is twice as fast in a slurry that has a pH of 11 than with a slurry that has a pH of 7. A typical oxide polishing slurry composition consists of a colloidal suspension of silicon oxide particles with an average size of 50-100 nm suspended in an alkali solution at a pH larger than 10. A polishing rate of about 1200 Angstroms/min (or 0.12 micrometers per minute) can be achieved by using this slurry composition. Other abrasive components such as ceria suspensions (e g., suspensions of cerium oxide nanoparticles) may also be used for glass polishing where large amounts of silicon oxide must be removed. Ceria suspensions act as both the mechanical and the chemical agent in the slurry for achieving high polishing rates, i.e. , larger than 5000 Angstroms/min (or 0.5 micrometers per minute). Slurries for metal films such as copper generally contain hydrogen peroxide to oxidize the metal layer and carboxylic salts to complex the metal oxide along with surface passivation agents such as benzotriazole (BTA) to minimize removal of film in recessed features. Silicon oxide or alumina particles maybe used as abrasive agents, though silicon oxide is preferred due to better wafer surface finish.

Figure 1 illustrates a side view of a CMP assembly generally designated with numeral 100. The CMP assembly includes a wafer holder 104 with a wafer 106, a polishing pad 102, a polishing table 101 and a conventional slurry delivery arm 108 provided with a single nozzle. A slurry solution 110 is dispensed from the nozzle to the polishing pad 102 at a point location on the polishing pad 102. Some existing slurry arm designs may include multiple dispense points along the polishing pad radius to promote improved slurry distribution across the polishing pad. Alternatively, a single dispense slurry arm may be oscillated across the pad surface during the polishing process to better distribute the slurry across the rotating pad. Advanced slurry arms can improve slurry distribution across the polishing pad surface, however transporting slurry to the wafer 106 from a wafer edge to a wafer center remains a challenge and typically relies on the fluid transport properties of the polishing pad 102.

Examples of existing slurry dispensers and methods of injecting a polishing slurry are described in the following united states patent documents: US11318579 entitled “Multiple nozzle slurry dispense scheme,” US8523639 entitled “Self-cleaning and adjustable slurry delivery arm,” US6887132 entitled “Slurry distributor for chemical mechanical polishing apparatus and method of using the same,” US6398627 entitled “Slurry dispenser having multiple adjustable nozzles,” US9296088 entitled “Method and device for the injection of CMP slurry,” US8845395 entitled “Method and device for the injection of CMP slurry,” and LIS8197306 entitled “Method and device for the injection of CMP slurry.”

Generally, an existing polishing pad conditioning process may typically generate an RMS (Root Mean Square) surface roughness in the range of 3-8 micron and the polishing pad may have pores in the range of 25-50 micrometers. The fluid film thickness between the polishing pad and the wafer, during the polishing process may typically range from about 20 to about 40 micrometers. The slurry fluid layer under a 300 mm wafer may have a volume of about 0.7 ml for every 10 micrometer thickness (not accounting for the polishing pad texture volume). It follows, therefore, that according to existing slurry delivery systems and methods, a large slurry volume is wasted and, thus, concomitant process efficiency is low. This has cost and EHS (Environmental, Health and Safety) implications since a significant amount of slurry also needs to be treated as waste prior to discharge. In case of metal slurries, waste needs to be treated as hazardous waste which increases costs even further.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a slurry dispensing system for a CMP apparatus that does not have the drawbacks or shortcomings of the conventional slurry dispensing methods and systems.

It is also an object of the present invention to provide a CMP apparatus that employs the slurry dispensing system and a method of polishing a semiconductor wafer using the apparatus that do not have the drawbacks or shortcomings of the conventional CMP apparatuses and methods.

The present invention generally relates to a fluid delivery system for a CMP apparatus. The present invention also relates to a CMP apparatus employing the fluid delivery system and to a method of polishing a semiconductor wafer using the CMP apparatus. The fluid delivery system may deliver a plurality of fluids in a chemical mechanical polishing apparatus that is equipped with plurality of fluids, each with its own control valve.

Accordingly, an aspect of the present invention is directed to a fluid delivery system for dispensing slurry directly between a semiconductor wafer and a pad for a chemical mechanical polishing of the semiconductor wafer. The fluid delivery system comprises at least one fluid delivery nozzle affixed to a polishing table, wherein the fluid delivery nozzles outlet is substantially coplanar with a top surface of the polishing table, and wherein a mechanism is used to activate and deactivate the fluid delivery nozzles as they enter and exit from under the wafer holder.

In a preferred embodiment, The fluid delivery system comprises a plurality of fluid delivery nozzles affixed to a polishing table, wherein the fluid delivery nozzles outlets are substantially coplanar with a top surface of the polishing table, wherein the fluid delivery nozzles are arranged such that at least one fluid delivery nozzle is under the wafer holder at all times during the semiconductor wafer polishing process, and wherein a mechanism is used to activate and deactivate the fluid delivery nozzles as they enter and exit from under the wafer holder.

The fluid delivery nozzles may be low flow fan nozzles.

The fluid delivery nozzles may be a plurality of openings in a nozzle head assembly.

The nozzle head assembly may be multi-jet nozzle head assembly having plurality of nozzles arranged in one or more rows. The nozzles may be openings inside the body of the nozzle head assembly.

In an embodiment the nozzle head assembly may be an inkjet assembly.

More than one type of nozzles may be used. The nozzles may be disposed in an arrangement equi-distanced along the circumference at mid radius of the polishing table to supply slurry continuously during the semiconductor wafer polishing process.

The nozzles may be placed such that fluid is dispensed normal to the semiconductor wafer surface.

The fluid delivery system may comprise a first set of the plurality of nozzles configured to deliver a first fluid and a second set of the plurality of nozzles configured to deliver a second fluid which is different from the first fluid.

At least one of the first and second sets of the plurality of nozzles may be configured to dispense the first or second fluid respectively at an angle different from normal (perpendicular) to the surface of the semiconductor wafer.

A first set of nozzles, and a second set of nozzles for each of at least two different fluids may be placed 120 degrees from each other to provide continuous coverage of the semiconductor wafer surface that is polished during platen rotation.

According to another aspect of the present invention, an apparatus for chemical mechanical polishing of a semiconductor wafer is provided, the apparatus comprising: a wafer holder configured to hold the semiconductor wafer, rotate the semiconductor wafer and urge it against a polishing pad positioned on a polishing table, the polishing table with the polishing pad positioned on a top surface thereof, the polishing facing the semiconductor wafer, at least one nozzle assembly comprising a plurality of nozzles, each nozzle having an outlet that is coplanar or substantially coplanar with a top surface of the polishing table, wherein the plurality of nozzles are positioned below an opening of the polishing pad so that fluid ejected through the plurality of the nozzles reaches the surface of the semiconductor wafer that is being polished. The apparatus may in some embodiments comprise three nozzle assemblies spaced apart at 120 degrees from each other at a circumference having a radius one half the radius of the polishing table so that they can supply slurry continuously to the semiconductor surface during the semiconductor wafer polishing process.

In some embodiments, the at least one nozzle assembly may be positioned within a seat of the table below an opening of the polishing pad so that when fluid is ejected via the plurality of the nozzles the fluid can reach the surface of the semiconductor wafer that is being polished at an angle perpendicular to the surface of the semiconductor wafer.

The apparatus for the chemical mechanical polishing of a semiconductor wafer may comprise the fluid delivery system as disclosed in any of the examples provided herein and with any of the many possible described combinations.

In yet another aspect of the present invention, a method of polishing a semiconductor wafer, the method comprising: providing the apparatus as described above, placing the semiconductor wafer in the wafer holder, and pressing the wafer against the polishing pad, while supplying a fluid slurry through an opening in the pad using the plurality of the nozzles.

The slurry flow may be activated as a nozzle assembly passes under the wafer holder and terminated as the nozzle assembly exits from under the wafer holder.

The present invention comprises a fluid delivery system for dispensing slurry directly between the wafer and the pad in chemical mechanical polishing of semiconductor wafers. The fluid delivery system comprises of a set of fluid delivery nozzles affixed to the polishing table and substantially coplanar with its surface, such that at least one nozzle is under the wafer holder, at all times, during the polishing process. A mechanism is used to activate and deactivate the fluid delivery nozzles as they enter and exit from under the wafer holder.

In one embodiment, the nozzle may be a single spray nozzle capable of dispensing 5 - 500 ml/min. In another embodiment, the nozzle may be a piezo actuated nozzle or an array of piezo actuated nozzles. In another embodiment the piezo actuated nozzle array maybe a multi-jet nozzle head assembly, such as for example, an inkjet head assembly having a plurality of nozzles.

According to yet another embodiment, a chemical mechanical polishing system is provided which comprises: a polishing table comprising an opening at a top surface thereof; a polishing pad having a hole, the polishing pad being affixed on the top surface of the polishing table with the hole of the polishing pad being aligned with the opening of the polishing table; a semiconductor wafer holder configured to hold the semiconductor wafer over the polishing pad above the hole area of the polishing pad; a nozzle head assembly affixed to the polishing table inside the polishing table opening, the nozzle head assembly including a plurality of nozzles each nozzle having an outlet pointing to the hole of the polishing pad; wherein the nozzle head assembly is configured to inject a fluid to the wafer surface facing the hole of the polishing pad through the hole of the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the present invention will become apparent to the skilled person from the following detailed description and the appended drawings in which:

Figure 1 is a side view of a conventional chemical mechanical polishing setup. Figure 2 is a side view of fluid nozzles and slurry delivery integrated with the polishing table according to an embodiment of the present invention.

Figure 3 is a top view of the polishing table with preferred location for dispense nozzles along with wafer location on the table according to an embodiment of the present invention.

Figure 4 is a cross section view of the relative orientation of the multi-jet nozzle head assembly, according to an embodiment of the present invention.

Figure 5 shows two types of nozzles (a) multi-jet head with multiple nozzle openings and (b) a single nozzle opening, according to embodiments of the present invention.

Figure 6 illustrates an arrangement of wherein the wafer is larger than the polish table. A single nozzle head assembly is coplanar with the polish table and is affixed in the center of the polish table.

DETAILED DESRIPTION OF THE PREFERRED EMBODIMENT

Referring to the accompanying figures 2-6, the present invention discloses a slurry dispensing unit (also referred to as fluid delivery system) coupled to the polishing table 201 of a chemical mechanical polishing apparatus. The fluid delivery system comprises a nozzle head assembly 208 including a set of one or more fluid delivery nozzles. The nozzle head assembly 208 may be operably connected to the polishing table 201 . For example, the nozzle head assembly 208 may be affixed to the polishing table 201. In an embodiment, the nozzle head assembly 208 may be removably affixed to the polishing table 201 . In another embodiment, the nozzle head assembly 208 may be permanently affixed to the polishing table 201 . Preferably, each of the nozzles may have an outlet (or opening) that is coplanar or substantially coplanar or at the same height or level with the top surface of the polishing table 201.

In the embodiment of Figure 3, the fluid delivery system may include at least three nozzle head assemblies 208A, 208B, 208C spaced apart from each other at 120 degrees and positioned at a middle radius position of the polishing table 201 such that at least one nozzle head assembly is under the wafer 206 and the wafer holder 204, at all-times, during the polishing process. As polish table 201 rotates, fluid nozzle 208A passes under the wafer and valve 216A is activated to dispense fluid onto the wafer. As polish table continues to rotate, fluid nozzle 216A moves out from under the wafer and fluid nozzle 216B moves under the wafer and valve 216B is activated to dispense slurry, while 216A is shut off. In this way only the slurry nozzle under the wafer is actively dispensing slurry onto the wafer, while the other nozzles are off. This way, slurry waste may be prevented.

Referring to Figure 2, an embodiment of the slurry delivery setup is shown. Figure 2 is a side view of a slurry delivery system including a plurality of fluid nozzles as a part of at least one nozzle head assembly 208 integrated with the polishing table, according to an embodiment of the present invention. The nozzle head assembly 208 may be positioned inside an opening 211 of the polishing table 201. For example, the at least one nozzle head assembly 208 may be incorporated into the opening 211 of the polishing table (also referred to as platen) 201 and a top surface of the nozzle head assembly 208 may be substantially coplanar with the top surface of the polishing table 201. For example, the at least one nozzle head assembly 208 may be an Inkjet head assembly incorporated into the opening 211 of the polishing table (also referred to as platen) 201 so that a top surface of the nozzle head assembly 208 may be substantially coplanar with the top surface of the polishing table 201 .

A slurry supply line 212 may be connected to the multi-jet nozzle head assembly 208 through a rotary union 214 and a valve 216. The slurry supply line 212 may be in fluid communication with all the multiple nozzles of the multi-jet nozzle head assembly 208 and the slurry from the slurry supply line may divide and accelerate as it passes though the multiple nozzles to form multiple jets of slurry exiting the multi-jet nozzle head assembly 208. A point of use filter may optionally be added between the valve 216 and the multi-jet nozzle head assembly 208. A return loop 220 may be preferably connected through the multi-jet nozzle head assembly to minimize any settling of slurry. The nozzle array of the multi-jet nozzle head assembly may be aligned to the hole 203 in the polishing pad 202. Slurry 210 is dispensed directly onto the wafer 206, which is held in the wafer holder 204 above the polishing pad 202. As shown in figure 2 the hole 203 of the polishing pad 202 and the nozzle head assembly 208 may be positioned centrally below the wafer 206. The individual nozzles may for example have a circular crosssection, however, the present invention is not limited to only such configuration and any other shape cross section nozzle may be used. The individual nozzles may have a constant cross section along their entire length or may have a tapered cross-sectional shape with a larger inlet opening than outlet opening for increasing the speed of the slurry jets exiting the multi-jet nozzle head assembly 208. In an embodiment, the multi-jet nozzle head assembly may be an ink-jet type nozzle head assembly.

The slurry may be any suitable fluid used for CMP of semiconductor wafers, and may include, a carrier fluid such as, for example deionized water, one or more chemicals, abrasive particulates and helps remove excess material from the surface of the wafer through a combination of chemical reactions and mechanical abrasion.

Several types of nozzles may be suitable for the purposes of the present invention. In an embodiment, a low flow spray nozzle is installed for each slurry or polish fluid as well as DIW (deionized water). A fan profile flow nozzle may enable the slurry to be applied as a wide band across the wafer surface. Fan nozzles may be single orifice openings. All dispense lines may be pressurized so full flow can be achieved in a short time. Fast acting switching valves may be installed in each line to toggle the flow on and off rapidly. Low flow nozzles may have hole diameters less than 1 mm and may preferably be in the range of 200-800 microns. One such nozzle is product type 632.216 commercially available from Lechler USA having a spray angle of 90 degrees, a hole diameter of 406 micron and a dispense rate of 64 ml/min when operated at 10 Psi.

Another example, may be product 632.187 of the same company with a spray angle of 120 degrees and a flow rate of 45 ml/min when operated at 10 Psi. Flow rates may increase by 50% when operating at 20 Psi. These nozzles are available in PVDF, a suitable inert material for CMP applications.

In operation, a polishing process may operate at 30 - 120 rpm table speed, which translates to 2 sec to 0.5 sec per revolution. Suitable polishing tables include the polishing tables for Applied Materials Reflexion polisher which are approximately 30 inches in diameter, while Ebara polisher tables are approximately 28 - 31 inch diameter. At mid radius polish point on the polishing table, wafer diameter is —1/3 the circumference. So, a fluid nozzle will spend (1/3)*0.5 sec or 0.17 seconds under the wafer holder. A fast acting ON/OFF valve is provided to switch the flow as nozzle traverses under the wafer holder. Overall system can be optimized for response time and desired slurry flow rate. DIW line can be readily run at same or higher pressures to match response time. The overall flow rate is less of a concern for DIW and higher flow may be advantageous for overall pad cleaning as well. A separate set of nozzles which impinge DIW directly onto the pad surface may be installed for pad cleaning between polishes, pad breakin etc. Another aspect of wafer diameter and polishing table setup is that a given nozzle assembly is under the wafer holder for only 1/3 of the rotation. To provide continuous slurry or fluid to the wafer surface, 3 or more nozzle assemblies are installed along the polishing table circumference. Polishing table, mid radius location is preferred for traversing the diameter of the wafer. Typically, a sinusoidal or other oscillation function is applied to the wafer holder to smoothen our removal profile. It is understood that due to oscillation of the wafer holder the location of wafer center may not always coincide with the nozzle, and it is possible that for a brief period there may be no nozzle under the wafer holder supplying slurry to the wafer surface. The intent of the design is to have a nozzle under the wafer at substantially all the time so as to provide uniform slurry delivery. It may be sufficient to dispense slurry with one nozzle embedded in the polish table such that slurry is dispensed with every rotation of the polish table.

In another embodiment, a piezo operated nozzle assembly such as multi-jet nozzle head assembly (e.g., an inkjet head) is installed coplanar with the polishing table and a spray nozzle is installed for dispensing DIW. Since the piezo nozzles generate dispensing pressure independent of line pressure, inkjet nozzles can operate with low pressure slurry delivery and a high speed switching valve may not be required. Additionally, mutli-jet nozzles operate at high frequencies hence, slurry dispense response time is improved. For example, piezo nozzles in an inkjet head can operate at 20K Hz or greater and have multiple nozzles 10 - 100 micron in diameter range. For example, Epson S-800 series printheads have 800 nozzles with a droplet size of 7.5 nanoliter and operate at 48 KHz, dispensing 17.28 ml/min. A Rikoh MH2910F printheads have 384 nozzles with a droplet size of 50 nanoliters and operate at 24 KHz, dispensing 27.65 ml/min. An inkjet head, such as Rikoh MH2910F is designed for recirculation of jetting fluid and is especially suited for slurry suspensions. Inkjet slurry delivery, also enables slurry dispense profile across the wafer surface. The jetting frequency may be high when dispensing at the wafer edge and low when dispensing at the wafer center or vice vera. Alternatively, a sinusoidal profile maybe introduced so slurry volume can be modulated across the diameter in any desired profile. Additionally Piezo nozzles may also be suitable as they can dispense fluids in picoliter to microliter droplets.

In an embodiment, with 1 inch wide dispense width will cover -10% wafer area per pass, which translates to -30% area per pad revolution. Setup may include all one types of nozzle/nozzle arrays or a combination thereof.

At the beginning of polishing process, polishing table maybe operated at low rpm to allow more slurry onto the wafer surface. Additionally, slurry flow maybe maintained at high to further enhance initial coverage on the whole wafer. After about 5-6 polishing table revolutions, when entire wafer has been covered, polishing table speed maybe increased and/or flow rate may be reduced to a value necessary to maintain stable removal rate. Slurry flow rate across the wafer can be modulated directly by changing jetting frequency or jetting voltage as the multi-jet nozzle head assembly traverses the wafer. Slurry flow maybe also coupled with platen rpm to provide higher flow rate at high platen rpm and low flow rate at low rpm to account for differences in time spent by slurry dispense nozzles traversing the wafer diameter. At the end of polish step, DIW spray nozzle is turned on to quickly remove the slurry and polish by products from the interface. It is anticipated that significantly reduced DIW use will be effective in wafer clean at end of polish step.

The present invention slurry dispensing unit for a chemical mechanical polishing apparatus wherein fluid delivery nozzles are affixed and coplanar with the polishing table has therefore been amply described in the above description and in the drawings of Figures 2, 3, 4 and 5.

Figure 4 is a cross section view of the relative orientation of the multi-jet nozzle head assembly and nozzle, according to an embodiment of the present invention. A perpendicular or slanted orientation may be used. In figure 4 arrows 225 indicate the slurry being ejected from corresponding nozzle outlets from the nozzle head assembly 208 toward the surface of the wafer that is being treated at a normal angle (Figure 4(a)) and at less than 90 degrees angle (Figure 4(b)).

In Figure 5(a) an example of a multi-jet nozzle head 208 is illustrated having a plurality of nozzles 502, while Figure 5(b) shows a fan nozzle 504, where 506 is the nozzle opening. The plurality of nozzles 502 are spaced apart from each other at a regular interval and form two rows.

Fig. 6 illustrates an arrangement wherein the polish table is smaller than the wafer. Polish table contains the pad with slurry nozzle opening in the center and rotating pad is pressed against a rotating wafer. In this case the slurry is dispensed through an opening in the pad, except pad may always be present over the wafer surface. While the present invention has been described in an illustrative manner, it should be understood that the terminology used is intended to be in a nature of words of description rather than of limitation.

Furthermore, while the present invention has been described in terms of a preferred embodiment, it is to be appreciated that those skilled in the art will readily apply these teachings to other possible variations of the invention without departing from the scope of the present invention as defined in the appended claims.

List of numerals in the Figures

100 polishing assembly

102 polishig pad

104 wafer holder

106 wafer

101 platen (table)

108 conventional slurry delivery arm

110 slurry

210 slurry

214 rotary union

216 valve

208 nozzle head assembly (e.g., inkjet)

211 opening (seat) in polishing table for the nozzle head assembly

212 slurry supply line

220 slurry return line

203 opening in the pad 202

202 polishing pad

201 polishing table (platen)

204 wafer holder

206 wafer

304

225 arrows indicating ejected slurry angle toward the wafer

502 nozzles

504 Fan nozzle

506 nozzle opening