Method and apparatus for chemical mechanical polishing of large size wafer with capability of polishing individual die   

Any foregoing applications and all documents cited therein or during their prosecution (“application cited documents”) and all documents cited or referenced in the application cited documents, and all documents cited or referenced herein (“herein cited documents”), and all documents cited or referenced in herein cited documents, together with any manufacturer\'s instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention.

FIELD OF THE INVENTION

This invention relates to a method of chemical mechanical polishing (CMP) for microelectronics applications. Specifically, the invention is directed to an apparatus of chemical mechanical polishing used for large size patterned/blanket wafer polishing, a process allowing polishing an individual die at a time, and a method for chemical mechanical polishing slurry and process evaluation.

Chemical mechanical polishing has become an essential technology for fabrication of semiconductor devices and recording head for hard disk drives. In a typical chemical mechanical polishing (CMP) process, the wafer to be polished is held by a rotating carrier or polishing head, the pad is mounted on a rotating platen or table, and the slurry is delivered into the space between the wafer and the pad. Generally, the wafer, blanket or with patterns, has a thin film of metal, oxide, polysilicon, or other materials. The polyurethane pad, with grooves and asperities on the surface, brings slurry to be in contact with the wafer and takes removed residues away from the polish zone. The slurry, containing abrasives, oxidizer, complexing agent, inhibiting agent, passivating agent, surfactant, and with an appropriate pH, provides chemical reaction to soften the wafer surface and mechanical removal to remove the reacted layer by abrasive particles. Abrasive-free slurry is also known (U.S. Pat. Nos. 6,800,218 and 6,451,697), in which the abrasive particles and surfactant used to stabilize the colloidal system are removed.

A CMP apparatus, or CMP polisher, is an equipment to realize the CMP process. A typical CMP polisher mainly consists of three parts: the carrier, the platen, and a slurry delivery system. Besides holding the wafer, the carrier also provides the functions of rotating the wafer and adjusting down force & back pressure. The platen rotates the pad to polish the wafer, which, generally, is located below the wafer to be polished. In an orbital CMP polisher, the pad has an orbital motion and thus each point on the pad describes a circle along an orbit. The relative motion between the wafer and the pad is important for a uniform material removal from every point on the wafer surface. Ideally, it is expected to achieve the same or similar velocity for each point on the wafer relative to the pad, which can be realized by maintaining the same or similar rotation speed and the same rotation direction for both the carrier and the platen in rotational polisher. Atypical polisher is designed to polish the entire wafer.

It is commonly accepted that, in a production environment, a uniform polishing of the entire wafer is a prerequisite to achieve the desired global planarity. For a simple evaluation of CMP process or consumables such as slurry, it is desirable to polish only a small portion of the wafer in order to cut down the cost of using up the entire wafer with single evaluation. This is often accomplished by using a small bench top polisher and a small patterned wafer (e.g. 2″ diameter) cut out from a larger wafer (e.g. 8″). Due to the practical difficulty in producing a 2″ wafer with smooth edge, only 4 to 5 2″ wafers can be produced from a single 8″ wafer. Furthermore, on the 2″ wafers produced by this method only one die is usable. Another motivation for adapting this approach is the ever increasing cost and complexity of a full wafer or production polisher. Therefore, a polisher that is capable of polishing a small portion of the wafer without cutting the wafer down to small pieces is certainly a valuable tool for CMP process and consumable evaluation. This invention addresses this issue with an inventive polisher design.

When Chemical Mechanical Polishing was first adopted for wafer processing by semiconductor industry, the wafer sizes were 2 to 6″ in diameter. The traditional silicon grinder/polisher design was essentially adopted without much modification. As matter of fact, the basic platform has practically unchanged for the past twenty years since the adaptation of CMP into wafer processing such as dielectric, metal, and copper planarization. It is widely recognized that, with the ever increase in wafer size, a number of scale up issues are becoming more and more apparent. Significant effort has been spent and complicated schemes must be in place to maintain the within-wafer-non-uniformity for wafers larger than 200 mm. Due slurry residence time increase, the temperature profile underneath the wafer during the polishing is significantly different from that for smaller wafers. It is increasingly difficult to optimize planarity at global level without severe over polishing at some local levels. Furthermore, a compromise of such at lower level poses greater threat on defectivity at higher level. This will only become even more severe for 450 mm wafers and beyond. In other words, with the significant increase in wafer size and challenges to maintain within wafer uniformity and defectivity, the conventional design is no longer a best choice. This invention addresses this issue with a set of new polisher design that can meet the challenges for large wafer processing while maintaining the control on local and global planarity.

SUMMARY

Unlike the design in a conventional polisher, the new design described in this invention places the focus on each individual dies that need to be processed. In another word, at least with one of the designs, there will be many small arms that will work parallel on different dies individually. According to the present invention, the forgoing and other aspects are achieved by but not limited to a platen to hold the wafer, a multiple-arm system with polish heads to hold the pad, a slurry delivery system, a pressure control system, a separate pad conditioning disk, a part to collect used slurry, and a system consisting of motor(s) to drive the polish head and drainage for used slurry. As a variation of the design described above, a small section of the wafer that contains several dies can be polished together. When several such sections are polished in concert, the entire wafer is processed at the same time. As a further modification of the design described above, an even larger portion of the wafer can be polished using a pad similar to the wafer in size. Such a device contains the needed sensors to report information such as slurry viscosity, static etch rate, dynamic etch rate, polishing rate at low down force, and friction between the pad and wafer upon initial contacts. The main application of this device is to provide useful information on the characteristics and performance of consumables such as slurry and pad.

Another aspect of the present invention is a method of manufacturing a semiconductor device. The method is achieved by using the present invention and a slurry to planarize a thin film on the wafer, such as Cu or Cu alloy film on a dielectric layer, oxide, barrier layer, or low material on wafer surface by CMP.

The third aspect of the present invention is an effective and efficient method to achieve planarization on the selected area on the wafer surface or the entire wafer.

In an embodiment of the present invention as shown in FIG. 1, the wafer is hold on the platen, which is fixed and located below the multiple arms with polish heads, whereas the pads are attached to these polishing heads. The pad selection is mainly based on the film to be polished (copper, dielectric, barrier, metal, etc). There will be multiple sets of these polishing heads. Therefore, while one set is in operation of polishing, the other sets can be either conditioned or exchanged. This should eliminate or significantly reduce the tool down time. Whenever it is desired, the wafer can be covered by a specifically designed mask (FIG. 2) with the same number of windows as that of the dies on the wafer. These windows can be open, if the die located at the window will be polished; or closed so that the thin film is protected by the cover.

It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in U.S. Patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.

Additional aspects of the present invention are apparent to those skilled in this technology from the following detailed description, wherein embodiments of the present invention are described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the overall design of a polisher with multiple polishing heads.

FIG. 2 depicts a schematic of a polishing head.

FIG. 3 depicts a schematic of a wafer holder and mask for patterned wafer.

FIG. 4 depicts a schematic of a single armed pad on a typical die.

FIG. 5 depicts a schematic of a slurry delivery system.

FIG. 6 depicts the overall design of a polisher with a single polishing head (top view).

FIG. 7 depicts the overall design of a polisher with a single polishing head (side view).

FIG. 8 depicts a schematic of a single polishing head.

FIG. 9 depicts a schematic of a disk that holds the polishing pad.

FIG. 10 depicts a schematic of a cam that drives the pad holder.

FIG. 11 depicts a schematic of an 8″ wafer holder.

FIG. 12 depicts a schematic of a slurry evaluator.

FIG. 13. shows the capability of six axis magnetic levitation stage designed for photolithographic application.

FIG. 14 shows the basic principle of using levitation technique to measure viscosity of a fluid.

FIG. 15 shows the simulation of material removal rate vs. inter plate distance between the pad and wafer.

FIG. 16 depicts the schematic of a polisher uses polishing tape.

The present invention enables effective and efficient planarization of large wafer (12″, 18″,and beyond) with the capability of polishing individual die that need to be processed and easy control of within wafer uniformity, providing advantages over conventional CMP polisher. The present inventive design departs significantly from the traditional polisher design by focusing on each individual dies that need to be processed.

Aspects of the present invention are implemented by employing single polishing head with pad or multi-arms with polishing head to process one die or multiple dies on the wafer surface. In addition, the wafer is stationary. Conventional CMP polisher employs a large single pad, but only a portion of the pad is used as polish area. With this platform, it is difficult to process lager and lager wafers without the increase of pad size and the footprint of a polisher. The present invention overcomes this difficulty by switching the relative positions of the wafer and the pad and employing a set of polishing head each equipped with a small pad. Therefore, the footprint of a polisher according to present invention is only approximately 1/20 of the size of a conventional polisher. Furthermore, the wafer holder can be easily upgraded to accommodate larger wafers. More specifically, the new polisher can scale down to polish 2″ wafers and up to handle 18″ without any further capital investment. As a result of such extendibility, the cost of ownership of such a polisher will be significantly lower than that of a conventional polisher. Without having to provide movement of large platen and heavy wafer carrier, the energy consumption by the new polisher will be significantly lower that its counterpart with a conventional design.

One of the embodiments of the present invention is achieved by many small arms with small pieces of pad at the bottom that work parallel on dies individually, as shown in FIG. 1. These arms are fixed to a disk that has the same number of holes as that of the dies on the wafer, as shown in FIG. 2. Each arm corresponds to a hole where the arm can be fixed or removed according to the processing requirement of the die corresponding to the hole. The disk is driven by a motor with a mechanic rod to do an oscillatory movement. Therefore, each pad will also move in the same manner on the corresponding die surface, as shown in FIGS. 3 and 4. FIG. 4 also shows that movement of a single pad on a typical die, the relative velocity and central location between the pad and wafer are mechanically controlled and computer programmed to vary during the polishing. The net averaging effect of these variations is to allow each location on the wafer to experience the polishing tape from all directions.

The slurry is supplied to each die on the patterned wafer individually and the slurry delivery can be turned off if necessary, as shown in FIG. 5. A slurry collection system is designed around the wafer holder to collect the used slurry in the case that the used slurry is needed to be collected for further analysis. The operation of the polishing process on the present invention is, but not limited to, performed on a tilted new polisher in order to provide a better slurry fluid mechanics on the wafer surface. The tilting of the present invention can be obtained, but not limited, by adjustable legs whose heights can be adjusted to a required level. The angle of the tilted wafer surface can be 10 to 45 degrees. The pressure control is realized by a pressure control cell at the end of each arm. The conditioning of the pad can be done, but not limited, by replacing the wafer with a conditioning disk with the same size as the wafer after every operation.

Another example of the embodiments of the present invention is using a single polish head and a wafer holder, as shown in FIG. 6. The positions of both of the polish head and the wafer can be adjusted by adjusting levers in X and Y directions, respectively. The detailed design of the two position adjusting levers is schematically shown in FIG. 10 and 12. Combination of the two adjustment levers make it possible for the polish head to reach any die(s) desired to be polished on the wafer surface. The polish head is connected with a motor, which is located in a container fixed to the adjusting lever. The down force during polishing process can be controlled by several pressure control cells inside the polish head, which are shown in FIG. 7. The disk holding the pad, as shown in FIG. 8, moves along a small orbit with radius 3-10 mm and thereby the relative velocity between every point on the pad and the polish are on the wafer surface is the same. The relative velocity between the pad and the wafer can be adjusted by changing the motor speed as well as the orbit radius. The orbital motion of the pad can be achieved, but not limited, by a cam whose center has an offset with the axle of the motor, as shown in FIG. 9. The wafer holder, as shown in FIG. 10, can be changeable and with different size for wafers with different size. Correspondingly, the position adjustment levers for polish head as well as the wafer are also changeable according to the requirement of the wafer size. But only one polisher is used. The conditioning of the pad is achieved by a separate conditioning disk that is located near the wafer holder and its position can be given by the polish head adjusting lever (FIG. 10). For blanket wafer, there are totally seven polish areas on the wafer surface; for patterned wafer, there are as many as ten polish areas. In this way, the wafer utilization is effectively and efficiently improved. During the polishing process, only the polish area on the wafer surface is open and the rest area is covered and protected by a specifically designed mask. Also, a slurry collection channel is given with the wafer holder to collect the used slurry for further analysis. The tilting of the present invention can be achieved, but not limited, by adjustable legs whose heights can be adjusted to a required level.

In an embodiment of the present invention, a single arm can have multiple types of pad, for example, a hard pad for copper polishing and a soft pad for barrier polishing. There will be no need to have multiple platens. A significant saving in space and increase in throughput. As each individual die is polished separately, there will be no cross contamination issue among dies. The defect causing entity will be localized. There will be no defect propagation like what usually happened on a conventional polisher.

One variation on the polishing head is to replace the conventional solid rigid pad with a softer more flexible polishing tape as shown in FIG. 11. There are several advantages of using a tape over polishing pad. A tape can be manufactured to contain various chemical components such as soft abrasives, releasable chemicals, surfactants, etc. The polishing performance can be improved by the presence of these components in situ. It is much easier to clean, purify, and reuse of a polishing tape. The operation of a polisher that uses polishing tape can be more automated and continuous. There are two further variations when a polishing tape is used. One is to use a roller to hold and guide the polishing tape. The down force and relative polishing speed is determined by the lateral movement of the roller. As the absolute contact area between the roller and the wafer is relatively small, the rollers have to be moved laterally to increase the contact surface area.

The rotation speed will be determined by the size of the roller. For example, if a linear velocity of 1.0 m/sec is desired and the diameter of a roller is 10 mm, the rotation speed should be about 600 rpm. An alternative to the roller approach, a solid block with a low friction surface can also be used to guide the tape towards the wafer. The gap between the tape and the wafer can be adjusted by a magnetic levitation current. A repulsive current can create a actual gap between the tape and the wafer. This is particularly useful for static and dynamic etch rate measurement for slurry. An attractive current can exert the desired pressure between the tape and the wafer. This down force can range from 0.01 psi to 10 psi. This is particularly useful for the polishing of a wafer that uses soft and fragile low k dielectric materials. Furthermore, the solid block can be replaced by a porous material through which a positive air pressure can be applied. The porosity of the material can lead to a small gap between the guiding block and the tape. The gap between the block and the tape can eliminate the complication created by the friction between them and give closer contact between the tape and the wafer at microscopic level.

Another variation of the invention is to use the said device to evaluate slurry and its performance on a polishing process. One example is illustrated in FIG. 12 in which a slurry chamber with adjustable volume houses a carrier for polishing pad and a carrier for wafer.

FIG. 12 shows a schematic of a slurry evaluator that can be used to characterize polishing slurry for viscosity, friction upon contact between a pad and a wafer in the presence of a slurry, static etch rate with various fluid movements, and removal rate upon contact between a pad and wafer and various low down forces. The relative velocity and distance between the pad carrier and wafer carrier are mechanically controlled and computer programmed to vary during the polishing. The net averaging effect of these variations is goal is to allow each location on the wafer to experience the pad from all directions.

Both carriers are vertically positioned and can counter rotate to each other at an adjustable rotation speed. Both carriers can be driven by a simple DC motor with an effective seal to prevent the interference of slurry. The lateral position of the carrier for wafer is typically fixed. The lateral position of the pad is adjustable. The adjustment can be accomplished with a second motor that is connected to Motor A. A more desirable mechanism for the control is through Magnetic Levitation Currents. Several patents such as U.S. Pat. No. 6,750,625 teach the design and application of magnetic levitation mechanism to control a stage in a precision manor that matches the requirement for photolithography (FIG. 13—A reproduction of work published by C. H. Meng and Z. P. Zhang on the capability of a six axis magnetic levitation stage designed for photolithographic application in the semiconductor industry).

In addition patents such as U.S. Pat. No. 6,559,567 teach the design and application of electromagnetic rotary drive. More specifically, Schob et al teaches the use of senor arrangement in an electromagnetic rotary device to measure the fluid property such as viscosity (U.S. Pat. No. 6,355,998). In this inventive device, an electromagnetic design can be implemented to control the lateral and rotary movements of a pad carrier. When the pad and the wafer are kept at far enough distance, the disturbance created by the pad movement on the wafer film is minimal. The removal rate measured under such condition can be considered as static etch rate or something close. The resistance exerted on the movement of the pad carrier is mainly due the slurry viscosity. When the distance between the pad and wafer carrier is getting smaller, the disturbance created by the pad movement on the wafer surface significantly aids the transport of the fluid. The removal rate measured under this circumstance should be viewed as a dynamic etch rate. When the pad and wafer surfaces starts to make a contact, the material removal on the wafer surface should increase significantly. The material removal shall increase as the relative pressure between the wafer and the pad increases. The removal rate may eventually reach it plateau as shown in FIG. 14 (a reproduction of a drawing published by Levitronix technique to measure viscosity of a fluid (U.S. Pat. No. 6,640,617).

The initial slope and intercept describes the slurry\'s static etch characteristics. The second slope and intercept describes the slurry\'s polishing characteristics for the wafer film. The combination of these two sets of information may provide valuable insight about the planarization capability of this slurry. This information can not be obtained directly with blanket wafer with the current polishers.

The schematic of a polisher in FIG. 16 also show that uses tape to replace polishing pad, the relative speed and location between the tape center and die on the wafer are mechanically controlled and computer programmed to vary during the polishing. The net averaging effect of these variations is goal is to allow each location on the wafer to experience the polishing tape from all directions.

Other advantages of the present invention include but not limited to: (1) Easy implementation of complete E-CMP. There will be no electrical contact loss issues and thereby the advantages of ECM can be fully utilized; (2) All types of endpoint detection systems can be implemented. Unlike conventional polisher, the implementation of optical, electrical, or frictional endpoint detection system is easy. There will be no slurry interference issues. Each die are will have its own endpoint detection system. If a feedback loop control is present, there will be no more need for over polishing as each die can stop polishing as soon as it reaches to the endpoint. (3) For interlayer dielectric polishing, it is desirable to have the global planarity correction. While the wafer will still remain stationary, a single orbital polisher wheel will come along. The unique design of this polishing wheel will have the same linear velocity under the arm for the majority of the area. When program properly, it should reach global planarity with a single polish head. (4) Greater productivity. There will be no down time due to pad conditioning, pad change, and ex-situ conditioning of the pad. During the change of wafers, the pads will be conditioned at the same time. (5) The cost of the pad will be much less than the cost in conventional polisher because of the small size of the pad. Also, the within-pad non-uniformity due to conditioning is eliminated.

And, the pad can be easily changed during wafer switching.

The invention is further described by the following numbered paragraphs: 1. A method of chemical mechanical polishing of a surface of a substrate to remove selected portions thereof comprising: (i) maintaining at least a portion of the surface of the substrate in sliding fractional contact with the polishing pad until the selected portions of the surface of the substrate are removed; (ii) polishing one area on a blanket/patterned wafer, containing one or more dies, using a single polishing head with a small piece of commercial CMP pad or a pad under evaluation; and (iii) polishing a patterned wafer using multi-arm polishing head with each polishing arm corresponding to a die on the patterned wafer. 2. The method of paragraph 1, wherein the die(s) on the patterned wafer desired to be polished is processed and the remaining dies are protected by a cover or a mask. 3. The method of paragraph 1, wherein only a portion of the surface of the substrate is polished by a single polish head or multi-arm polish head with multiple pads while the rest area of the surface of the substrate to be polished is protected. 4. An apparatus for chemical mechanical polishing of a surface of a substrate to remove selected portions thereof comprising: (i) a fixed platen to hold the wafer to be polished, the wafer holder is changeable, and the size of the holder adjustable to fit different size of the wafer; (ii) a cam with an offset with the motor axle to make orbital motion of the polishing pad and achieves the same relative velocity between each point on the pad and the area to be polished; (iii) a device for providing an oscillatory motion on the surface of a single die; (iv) a disk to hold the multi-arm polish head system; (v) a slurry delivery system in which the slurry can be supplied to each individual die on the patterned wafer separately; (vi) a two-motor system, one motor rotates the disk that holds the second motor and the second motor rotates the pad in a same rotation speed and the same direction as that of the first motor and thus the same relative velocity between each point on the pad and the area to be polished is achieved; (vii) a two-lever adjustment system to control the position of the polish head and the wafer whereby all the dies on the patterned wafer can be polished; (viii) adjustable legs for tilting the whole apparatus; (ix) a slurry collection system to collect used slurry; and (x) a replaceable pad conditioning disk. 5. The apparatus of paragraph 4, wherein the tubes of the slurry delivery system are distributed in parallel. 6. A device for the evaluation of the performance and characteristics of a slurry comprising of a slurry chamber, a rotary wafer carrier that is vertically placed and fixed on lateral movement, a rotary pad carrier that is movable along its lateral axis, a sensor which measures the film thickness change in-situ, and a sensor which measures the resistance exerted on to the rotary movement of the pad carrier. 7. The device of paragraph 6, lateral and rotary movements for the pad and wafer carriers are accomplished by DC motors. 8. The device of paragraph 6, lateral and rotary movements of the pad carrier are accomplished by the use of a magnetic levitation system. 9. The device of paragraph 6, the film thickness change is measured by 14-point probe or Eddy current system for metal films. 10. The device of paragraph 9, wherein the film is a dielectric film and the measurement is made by an optical sensor. 11. The device of paragraph 10, wherein an acoustic sensor for measuring the film thickness change for metal and non-metal is simultaneously used. 12. A polisher that utilizes polishing tape for IC wafer processing comprising of a slurry delivery system, a tape management system, a guiding system for the tape, and optionally a system for tape cleaning, conditioning, and re-use. 13. The polisher of paragraph 12, the tape can be made with natural, process natural materials or synthetic materials. Processed natural materials include but are not limited to silk, cotton and paper. The tape can be made of entirely synthetic materials such as polyethylene, polypropylene, and polystyrene. The tape materials can be hydrophobic or hydrophilic. The materials can be made into porous or non-porous. Furthermore, the tape can contain releasable materials such as complexing agent, catalyst, surfactant, lubricant, and/or abrasive particles. The tape can also contain functional groups that can chemically interact with slurry and the wafer film. 14. The polisher of paragraph 12, wherein the tape management system may include but not limited to control the tape tension, the tape movement, the tape cleaning, conditioning, embossment of temporary patterns shortly before it reaches the wafer, and a flipping mechanism that allows the use of either side of the tape at will. 15. The polisher of paragraph 12, wherein the tape guiding system may include a solid roller or a block that controls the distance between the tape and the wafer. When a solid block is used to guide the relative distance between the wafer and the tape, the block may contain a magnetic material that responses to levitation current which may create a gap between the tape and the wafer. The electromagnetic current can also control the relative pressure between the tape and wafer. In another preferred embodiment, the guiding block can also be porous and allow air stream to pass through. As a result, the exiting air stream will create a small gap between the block and the tape. This gap is adjustable.

It is to be understood that the present invention is capable of use in various other combinations and is capable of changes and modifications within the scope of the inventive concept as expressed herein.