HK1019716A - A chemical mechanical polishing system and method therefor - Google Patents

Description

Chemical mechanical polishing system and method thereof

no marking

The present invention relates generally to Chemical Mechanical Planarization (CMP) systems, and more particularly to pumps used in CMP systems.

Chemical mechanical planarization (also known as chemical mechanical polishing) is a proven process in advanced integrated circuit manufacturing. CMP is used at almost all stages of semiconductor device fabrication. Chemical mechanical planarization produces fine structures by local planarization, which produces a high density of vias and interconnect layers over the entire wafer. Materials for CMP in integrated circuit fabrication processes include single and poly-silicon, oxide, nitride, polyimide, aluminum, tungsten, and copper.

At this point, the cost of chemical mechanical planarization has proven cost effective for components such as average high-priced microprocessors, ASICs (application specific integrated circuits), and other semi-custom integrated circuits. The main area of use is in the formation of high density multilayer interconnects required in these types of integrated circuits. Commercial devices such as memory and the like have little or no use of CMP for cost reasons.

Successful implementation of chemical mechanical planarization for high volume integrated circuit designs has shown that most semiconductor manufacturers have accepted this technology. Semiconductor manufacturers have driven the development of CMP in several areas. The first area is cost, as mentioned above, the CMP process is not used in the manufacture of integrated circuits for the manufacture of goods, since any increase in manufacturing cost affects yield. Most of the research on CMP is in the area of reducing the cost per wafer of the CMP process. Significant advances in CMP cost reduction will increase the viability of manufacturing lower profit margin integrated circuits. A second area is the reduction of the size or footprint of CMP equipment. The smaller footprint reduces the cost of all people. Current designs of chemical mechanical planarization apparatus occupy a significant amount of floor space in semiconductor processing equipment.

A third area to emphasize is manufacturing throughput and reliability. CMP device manufacturers are focusing their efforts to develop machines that planarize more wafers in less time. Only the reliability of the CMP apparatus is also increased, the throughput is significantly increased. A fourth area of research is in semiconductor material removal devices. Semiconductor companies rely to some extent on a limited number of chemical suppliers of slurries or polishing agents used in different removal processes. The semiconductor industry has not developed some slurries, but comes from other areas such as the glass polishing industry. Research is inevitably directed to the high performance slurry industry dedicated to the processing of specific semiconductor wafers. Developments in slurry composition directly affect removal rate, particle statistics, selectivity, and particle agglomeration size. The final field of research is post-CMP processing. For example, post-CMP cleaning, integration, and metrology are areas where device manufacturers began to provide specific devices for CMP processes.

It would therefore be advantageous to have a chemical mechanical planarization apparatus that provides reliability in a manufacturing environment. It would be further advantageous if the chemical mechanical planarization apparatus could reduce the cost of polishing each wafer.

FIG. 1 is a cross-sectional view of a peristaltic pump used in a chemical mechanical planarization apparatus for transferring slurry;

FIG. 2 is a top view of a Chemical Mechanical Planarization (CMP) apparatus in accordance with the present invention;

FIG. 3 is a side view of the Chemical Mechanical Planarization (CMP) apparatus of FIG. 2 in accordance with the present invention;

FIG. 4 is a cross-sectional view of a diaphragm pump used in the chemical mechanical planarization apparatus according to the present invention; and

figure 5 is a schematic representation of a slurry delivery system for a chemical mechanical planarization apparatus in accordance with the present invention.

The main component used in a Chemical Mechanical Planarization (CMP) process is a polishing slurry. A slurry is a mixture of abrasives and chemicals that mechanically and chemically remove material from a semiconductor wafer. The chemicals used in the slurry depend on the type of material to be removed. Generally, the chemical substance is acidic or basic and has strong corrosiveness. During the process of wafer polishing, the slurry is a consumable that needs to be continually replenished. This is a major cost consuming factor in the CMP process.

Other examples of consumables in a CMP process are deionized water and polishing pads. Polishing pads, which typically comprise polyurethane or some other polishing medium, are generally the second costly expense in the CMP process. The pad cost per wafer is typically on the order of 25% of the cost of polishing agent per wafer. Other consumables account for less than 5% of the cost per wafer polishing slurry. Clearly, the greatest gain in reducing the cost of chemical mechanical planarization per wafer is the cost of the polishing slurry.

The slurry delivery system is a component of a chemical mechanical planarization apparatus. A slurry delivery system provides a polishing agent to a semiconductor wafer to be polished. Current CMP apparatuses use peristaltic pumps to deliver polishing agents to semiconductor wafers. Peristaltic pumps are used by CMP device manufacturers because they can isolate the media to be delivered from any pump components. This protects critical pump components from abrasive and corrosive polishing agents.

Fig. 1 is a cross-sectional view of a peristaltic pump 12 for delivering slurry in a chemical mechanical planarization apparatus. The isolation means of the peristaltic pump is an elastic tube 13. Ideally, the elastomeric tube may prevent penetration of chemicals in the slurry. For example, the elastic tube 13 is generally made of a silane or n-butadiene (norprene) type compound. The polishing agent is delivered through the flexible tube 13. By confining the slurry within the elastomeric tube 13, the slurry does not come into contact with any component of the peristaltic pump 12. One end of the elastic tube 13 is connected to an Input (IN) receiving the slurry, while the other end of the elastic tube 13 is connected to an Output (OUT) of the peristaltic pump 12.

The rotating portion 14 rotates within a housing 16 of the peristaltic pump 12. The rotating portion 14 is connected to a motor (not shown). Fixed to the rotating portion 14 is a roller 15 that continuously presses the elastic tube 13. A minimum of two rollers are used in peristaltic pumps, and some pumps are designed with many rollers. As the rollers rotate within the housing 16, the slurry is pushed or squeezed through the elastomeric tube 13. The peristaltic pump has the advantage that no internal leakage occurs. Leakage will only occur if the tube breaks. The amount of material delivered by the peristaltic pump 12 is determined by the inner diameter of the tube, durometer, wall thickness, and delivery pressure. The rate of output delivery can be varied by varying the pump speed.

Generally, peristaltic pumps 12 are simple, efficient, and easy to maintain. However, there are problems with the placement of the peristaltic pump 12 in a chemical mechanical planarization apparatus that delivers slurry. In general, the retention or drying of the slurry from which material is removed from the semiconductor wafer within the delivery system can have dire consequences including hardening, caking, and settling. If allowed to settle or dry, the slurry will clog the delivery system, causing the system to fail or damage the wafer.

To avoid the above-mentioned problems, most slurry delivery systems circulate the slurry as much as possible. Furthermore, in the case where the polishing agent cannot be circulated, the system is flushed with water. Flushing with water often causes the elastic tube 13 to rupture due to high water delivery pressure. Problems occur due to the rollers 15 pushing the flexible tube 13 against the housing 16 preventing the flow of water. The hydraulic pressure at the input of the peristaltic pump 12 causes the elastic tube 13 to expand and rupture.

As previously mentioned, the highest cost of consumption in chemical mechanical planarization processes is the polishing agent. In theory, a predetermined amount of material can be uniformly removed from the surface of a semiconductor wafer with a minimum required amount of slurry delivered by a chemical mechanical planarization apparatus. Assuming less than the minimum required amount of polishing agent, uneven planarization or even damage to the wafer will result. If it is larger than the minimum required amount of the polishing agent, the slurry will be wasted, thereby increasing the manufacturing cost. Semiconductor manufacturers often provide excessive slurry because the long-term cost of the polishing agent is less than the cost of a damaged semiconductor wafer.

In a manufacturing environment, the amount of slurry delivered is negatively affected by variations in peristaltic pump 12 over time. The variations in the delivery of the peristaltic pump 12 are affected by the maintenance cycle of the elastic tube 13. The maintenance period is determined by the acceptable time period for shutting down the CMP apparatus to prevent the elastic tube 13 from breaking to cause a sudden failure. Generally, maintenance of the peristaltic pump 12 to replace the elastic tube 13 is on the order of once a month.

Another factor to consider in determining the rate of slurry delivery is the input pressure. The internal pressure that the polish imparts to the peristaltic pump 12 (from the entire slurry delivery system) varies significantly, for example, pressures in the range of 1406.2 to 7031.0 kilograms per square meter (2-10 pounds per square inch) are common. Generally, the entire slurry delivery system is able to provide a slurry pressure that exceeds what the flexible tube 13 can tolerate. The peristaltic pump is sensitive to the input pressure of the slurry. In fact, the delivery rate increases with higher delivery pressure because as the pressure increases, the elastomeric tube 13 expands and becomes larger in volume. An on-board slurry delivery system configured with a CMP apparatus delivers greater than a minimum required amount of slurry at a minimum input pressure. Thus, when the input pressure of the slurry is higher than the minimum pressure, a large amount of the slurry is wasted.

The rate of delivery is also affected by the plastic deformation of the elastic tube 13. The rollers continuously squeeze or extrude the resilient tube 13 to deliver the polish. Initially, after being flattened by the rollers 15, the elastic tube 13 will spring back to its original shape. Continuously, plastic deformation occurs, and the elastic tube 13 does not rebound by the amount that should be, thereby changing the volume delivered. In other words, the elastic tube 13 is hardened or deformed with time. The rate of slurry delivery also affects plastic deformation. Increasing the slurry delivery rate (increasing the speed of the peristaltic pump 12) accelerates the rate at which the elastic tube 13 deforms plastic over time. All of the problems listed above tend to reduce the rate of slurry delivery over time.

Chemical mechanical planarization apparatus manufacturers do not currently provide any type of real-time detection of slurry flow. Semiconductor manufacturers do not want the flow rate of the slurry to be below the minimum required so the slurry flow rate is compensated by a high initial delivery rate. The high initial delivery rate ensures that the minimum acceptable slurry flow is met until the elastomeric tube 13 is routinely replaced for maintenance. The high initial delivery rate wastes slurry due to the more slurry delivery system provides than is needed. It can be estimated that more than about 25% of the slurry is wasted by the increased delivery rate of a typical chemical mechanical planarization system. During the planarization process, polishing agents in excess of 50% of the minimum required amount are less common.

Fig. 2 is a top view of a Chemical Mechanical Planarization (CMP) apparatus 21. CMP apparatus 21 includes platen 22, Deionized (DI) water valve 23, multi-input valve 24, pump 25, dispense rod manifold 26, dispense rod 27, conditioning arm 28, driven valve 29, vacuum generator 30, and wafer carrier arm 31.

The platen 22 supports various polishing media and chemistries that planarize the process side of the semiconductor wafer. The platen 22 is made of metal such as aluminum or stainless steel. A motor (not shown) is connected to the platen 22. The platen 22 can rotate, orbit, or move linearly at a user-selected surface speed.

The deionized water valve 23 has an input and an output. The input is connected to a DI water source. A control circuit (not shown) opens or closes the DI water valve 23. When the DI water valve 23 is open, DI water supply is provided to the multi-input valve 24. The multiple input valve 24 is capable of delivering different materials to the dispensing rod 27. One example of the types of materials that may be input to multi-input valve 24 are chemicals, slurries, and deionized water. In one embodiment of CMP apparatus 21, multi-input valve 24 has a first input connected to DI water valve 23, a second input connected to a source of slurry, and an output. Control circuitry (not shown) closes all of the inputs to multiple input valves 24 or opens any combination of valves to produce a flow of selected material to the output of multiple input valves 24.

The pump 25 delivers material received from the multi-input valve 24 to the dispensing wand manifold 26. The delivery rate provided by pump 25 is selected by the user. The minimum flow rate change over time and the different conditions allow the material flow to be regulated around the minimum required flow rate, reducing waste of chemicals, slurry and DI water. An input of pump 25 is connected to an input and an output of multiple input valve 24.

The dispensing rod manifold 26 allows chemicals, slurry and deionized water to flow to the dispensing rod 27. The distribution rod manifold 26 has an output and an input connected to the pump 25. Another measure utilizes a pump to supply each material to the dispensing rod 27. For example, chemicals, slurry and DI water each have a pump connected to the dispensing wand manifold 26. The use of multiple pumps allows different materials to be accurately mixed in different combinations by controlling the flow rate of each material with a corresponding pump. The dispense rod 27 dispenses chemicals, slurry and deionized water to the polishing medium surface. The dispensing rod 27 has at least one aperture for dispensing material to the surface of the polishing medium. The distribution rods 27 overhang and extend above the platen 22 to ensure that material is distributed to most surfaces of the polishing medium.

Wafer carrier arm 31 suspends the semiconductor wafer above the surface of the polishing medium. Wafer carrier arm 31 applies a user-selected downward force to the polishing medium surface. Generally, the wafer holder arm 31 is capable of rotational movement as well as linear movement. The semiconductor wafer is held on the wafer carrier by vacuum. Wafer carrier 31 has a first input and a second input.

The vacuum generator 30 is a vacuum source for the wafer carrier 31. The vacuum generator 30 generates and controls a vacuum degree by which the wafer carrier performs wafer pickup. If a vacuum source is not available at the manufacturing facility, the vacuum generator 30 is not required. Vacuum generator 30 has a port connected to a first input of wafer carrier arm 31. Driven valve 29 supplies gas to wafer carrier arm 31 to eject the wafer after planarization is complete. During planarization to control wafer distribution, the gas also applies pressure to the backside of the wafer to control wafer distribution. In an embodiment of CMP apparatus 21, the gas is nitrogen. The driven valve 29 has an output connected to a nitrogen source and a second input connected to a wafer holder arm 31.

The abrasive end effector is applied to the polishing medium surface using an adjustment arm 28. The abrasive end effector planarizes the polishing medium surface and cleans or roughens the surface for chemical transport. The adjustment arm 28 is generally capable of both rotational and translational movement. The pressure or downward force pressing the end effector against the surface of the polishing medium is controlled by the adjustment arm 28.

Fig. 3 is a side view of the Chemical Mechanical Planarization (CMP) apparatus 21 shown in fig. 2. As shown in fig. 3, adjustment arm 28 includes a pad conditioner connection 32 and an end effector 33. CMP apparatus 21 further includes polishing medium 34, carrier membrane 35, carrier ring 36, carrier assembly 37, mechanical mount 38, heat exchanger 39, housing 40, and semiconductor wafer 77.

A polishing medium 34 is placed on the platen 22. Typically, the polishing medium 34 is secured to the platen 22 using a pressure sensitive adhesive. The polishing media 34 provides a suitable surface to which the polishing agent is directed. Polishing medium 34 provides chemical support and micro-conformity to the overall and local wafer surface regularity. Typically, polishing medium 34 is a polyurethane pad that includes small holes or sharp angled grooves in the exposed surface of the chemical delivery.

The carrier assembly 37 is attached to the wafer arm 31. The carrier assembly 37 provides a base for rotating the semiconductor wafer 77 relative to the platen 22. The carrier assembly 37 also applies a downward force to the semiconductor wafer 77 causing it to be urged against the polishing medium 34. A motor (not shown) allows the user to control the rotation of the carriage assembly 37. The carrier assembly 37 includes vacuum and gas passages to hold the semiconductor wafer 77 during planarization, distribution of the semiconductor wafer 77, and ejection of the semiconductor wafer 77 after planarization.

The carrier ring 36 is connected to a carrier assembly 37. The carrier ring 36 concentrically aligns the semiconductor wafer 77 with the carrier assembly 37 and physically constrains the semiconductor wafer 77 from lateral movement. The carriage membrane 35 is attached to a surface of a carriage assembly 37. The carrier film 35 provides the semiconductor wafer 77 with a surface having suitable frictional characteristics to prevent rotation due to sliding relative to the carrier assembly 37 during planarization. In addition, the carrier film 35 has slight elasticity to facilitate the planarization process.

Pad conditioner connection 32 is connected to conditioning arm 28. Pad conditioner connection 32 allows for angular compliance between platen 22 and manipulator 33. The end effector abrades polishing medium 34 to achieve planarity and facilitates the delivery of chemicals to the surface of semiconductor wafer 77 to be planarized.

The chemical reaction is very sensitive to temperature. It is known that the rate of reaction generally increases with temperature. In chemical mechanical planarization, the temperature of the planarization process is maintained within a certain range to control the reaction rate. The temperature is controlled by a heat exchanger 39. A heat exchanger 39 is connected to the platen 22 for heating and cooling. For example, when a wafer batch is first started for planarization, the temperature is about room temperature. The heat exchanger 39 heats the platen 22 so that the CMP process is above a predetermined minimum temperature to ensure that a minimum chemical reaction rate occurs. Generally, the heat exchanger 39 uses ethylene glycol as a temperature transfer/control mechanism to heat or cool the platen 22. The continuous running of the wafer through the chemical mechanical planarization process generates heat, e.g., the carrier assembly 37 retains the heat. Increasing the temperature at which the CMP process occurs increases the rate of the chemical reaction. Platen 22 is cooled by heat exchanger 39 to ensure that the CMP process is below a predetermined maximum temperature so that maximum reaction is not exceeded.

The mechanical mount 38 raises the chemical mechanical planarization unit 21 above floor level, allowing floor mounted drip trays that are not integral with the polishing unit. The mechanical mount 38 also has an adjustable configuration to level the CMP apparatus 21 and is designed to absorb or isolate vibrations.

The chemical mechanical planarization unit 21 is placed within the unit housing 40. As previously mentioned, the CMP process uses corrosive materials that are harmful to humans and the environment. The device housing 40 prevents escape of particles and chemical vapors. All moving parts of CMP apparatus 21 are placed within apparatus housing 40 to prevent injury.

The operation of the chemical mechanical planarization apparatus 21 is described as follows. No particular sequence of steps is specified or implied in the operating specification, and is determined in large part by the type of semiconductor wafer being polished. The heat exchanger 39 heats the platen 22 to a predetermined temperature to ensure that the chemicals in the slurry have a minimum reaction rate when the chemical mechanical planarization process is initiated. The motor drives the platen 22 to place the polishing medium 34 in one of a rotational, orbital, or linear motion.

The wafer carrier 31 moves to pick up the semiconductor wafer 77 placed at a predetermined position. Turning on the vacuum generator provides vacuum to the carriage assembly 37. The carrier assembly 37 is aligned with the semiconductor wafer 77 and moved so that the surface of the carrier assembly is in contact with the unprocessed side of the semiconductor wafer 77. The carrier film 35 is bonded to a surface of the carrier assembly 37. The vacuum and carrier film 35 hold the semiconductor wafer 77 on the surface of the carrier assembly 37. The carrier ring 36 confines the semiconductor wafer 77 to the center on the surface of the carrier assembly 37.

The multiple input valve 24 is opened to provide slurry to the pump 25. A pump 25 provides slurry to a dispensing rod manifold 26. The slurry flows through the dispense rod manifold 26 to the dispense rod 27 where it is delivered to the surface of the polishing media 34. Periodically, the deionized water valve 23 is opened to supply water instead of the slurry through the dispensing rod 27 to prevent it from hardening in the dispensing rod 27. The movement of the platen 22 helps to distribute the polishing agent across the surface of the polishing medium 34. Generally, the slurry is delivered at a constant rate throughout the polishing process.

Wafer carrier 31 is then returned to the position of polishing medium 34. Wafer carrier 31 contacts semiconductor wafer 77 with polishing medium 34. The polishing agent covers the polishing media 34. The wafer carrier 31 applies a downward force to the semiconductor wafer 77 to promote friction between the slurry and the semiconductor wafer 77. Polishing medium 34 is designed for chemical transport, allowing the slurry chemistry to flow under semiconductor wafer 77 even if it is pressed against the polishing medium. As heat increases within the system, the heat exchanger 39 changes from heating the platen 22 to cooling the platen 22 to control the rate of chemical reaction.

It should be noted that the platen 22 has been previously described as being capable of mechanical polishing for moving placement relative to the semiconductor wafer 77. Instead, the platen 22 may be fixed in position and the carriage assembly 37 may be placed in rotational, orbital or translational motion. Generally, both the platen 22 and the carriage assembly 37 are movable to facilitate mechanical polishing.

After the chemical mechanical planarization process is complete, the wafer carrier 31 lifts the carrier assembly 37 off of the polishing medium 34. The wafer carrier 31 moves the semiconductor wafer 77 to a predetermined area for cleaning. The wafer carrier 31 then moves the semiconductor wafer 77 to a position where the wafer is unloaded. Thereafter, vacuum generator 30 is closed and driven valve 29 is opened to provide gas to cradle assembly 37 to eject semiconductor wafer 77.

The consistency of the chemical mechanical planarization process is maintained by periodically conditioning the polishing medium 34, commonly referred to as pad conditioning. Pad conditioning facilitates removal of slurry and particles that have been built up and embedded within polishing medium 34. Pad conditioning also planarizes the surface and roughens the protrusions of polishing medium 34 to facilitate chemical transport. Pad conditioning may be achieved by a conditioning arm 28. The adjustment arm 28 is moved to bring the end effector 33 into contact with the polishing medium 34. The surface of the end effector 33 is coated with industrial diamond or other abrasive surface that conditions the polishing medium 34. A pad conditioner connection 32 is between the conditioning arm 28 and the end effector 33 to allow angular compliance between the platen 22 and the end effector 33. The adjustment arm 28 is capable of both rotation and horizontal movement to assist in pad adjustment. Pad conditioning is accomplished by adjusting the new pad during the planarization process, between wafer starts, and before wafer processing.

As previously described, the peristaltic pump used in the process of delivering the polishing agent (slurry) in the chemical mechanical planarization apparatus does not supply the polishing agent at a constant rate. The delivery rate decreases with time. The peristaltic pump is set to a high delivery rate to compensate for the decrease in rate over time to ensure that a sufficient amount of polishing agent is provided to the polishing medium to planarize the semiconductor wafer without damage. The high rate of delivery provides more polishing agent than is needed, and typically more than 25% of the delivered polishing agent is not needed and is wasted in the planarization process.

Experimental studies have shown that the minimum delivery rate of the polishing agent can be defined for each type of planarization process. If less than the minimum delivery rate of the polishing agent, this may result in non-uniformity in the planarization of the wafer, a reduction in the polishing rate, or even wafer damage. If it is larger than the minimum required amount of the polishing agent, the slurry will be wasted, thereby increasing the manufacturing cost. Thus requiring a pump that provides an accurate constant delivery rate over time. One such pump is a positive displacement pump. Positive displacement pumps displace or pump a fixed volume of material during each evacuation cycle. For example, peristaltic pumps are not positive displacement pumps because the volume of material delivered varies directly with input pressure, varying inversely with time. One example of a positive displacement pump is a diaphragm pump. Diaphragm pumps deliver a fixed volume of material independent of input pressure variations.

Fig. 4 is a sectional view of a diaphragm pump 41 used in the chemical mechanical planarization apparatus according to the present invention. The diaphragm pump 41 isolates the moving parts from the corrosive chemicals of the slurry. Generally, all of the wet surfaces of the diaphragm pump 41 are polymer components that are inert to the polishing agent. The diaphragm pump comprises an input, an output, a piston 42, a rotary member 43, a diaphragm 44, a check valve 45, a check valve 46 and a chamber 47.

A diaphragm 44 is shown secured to the surface of the piston 42. The diaphragm 44 isolates the moving parts of the diaphragm pump 41 from the corrosive chemicals of the slurry. Another measure is that the piston compresses a small amount of hydraulic liquid instead of the diaphragm. The advantage of using a pressurized liquid is the equalization of the pressure on the membrane. A motor (not shown) rotates the rotary member 43. The rotary member 43 is connected to the piston 42, and the rotary motion is converted into the reciprocating motion to move the piston 42.

Check valve 45 allows the polishing agent to enter the diaphragm pump 41. The chamber 47 changes in volume depending on the position of the piston. Chamber 47 has a maximum volume at the bottom of the stroke of piston 42. The input of the diaphragm pump 41 under pressure provides the polishing agent. The pressure opens the check valve 45 allowing the polishing agent to enter and fill the chamber 47. The upward movement of the piston 42 closes the check valve 45 against the input pressure of the polish. When the piston 42 is at the top of the stroke, the chamber 47 has a minimum volume. The piston 42 pushes the check valve 46 open and delivers an amount of polish volume equal to the difference between the maximum and minimum chamber 47 volumes. Check valve 45 and check valve 46 prevent backflow through diaphragm pump 41. In other words, the polishing agent does not flow in the opposite or opposite direction (output to input) through the diaphragm pump 41.

The diaphragm 44 is not deformed to some extent in the case of plastic deformation. The range of movement of the piston 42 is such that the diaphragm 44 returns to its original shape after each pumping cycle. There is little maintenance requirement on the diaphragm pump 41, thereby substantially reducing the downtime of the chemical mechanical planarization apparatus. Generally, the maintenance cycle of the diaphragm pump 41 is two years to replace the diaphragm and five years to replace the motor drive assembly. The diaphragm pump 41 has a path from input to output regardless of the position of the piston 42. The input pressure of the polishing agent delivers the polishing agent into the chamber 47 and also opens the check valve 46. Once chamber 47 is full, the polishing agent will flow out of diaphragm pump 41, wasting polishing agent. This problem can be solved by keeping check valve 46 closed during the return stroke when chamber 47 fills piston 42.

Fig. 5 is a diagram of a slurry delivery system 51 for a chemical mechanical planarization apparatus in accordance with the present invention. Slurry delivery system 51 includes check valve 52, diaphragm pump 53, check valve 54, backpressure valve 55, dispense rod manifold 57, dispense rod 58, and platen 59.

The check valve 52 includes an input and an output that receive the polishing agent. The polish flowed in the direction indicated by the arrow. The check valve 52 has a passageway that can be blocked to terminate the flow of the polishing agent. The passage is blocked and the polishing agent attempts to flow in the opposite direction (backflow) as indicated by the arrow. In other words, the check valve 52 allows the polish to flow in only one direction (into the pump).

The diaphragm pump 53 has an input connected to the check valve 52 and an output providing a polishing agent. The input pressure of the polishing agent changes significantly. The diaphragm pump 53 is a positive displacement pump thereby providing a fixed volume of polishing agent at the output per pump cycle. The diaphragm pump 53 is capable of generating a high output pressure to drive the polishing agent downward.

The check valve 54 includes an input and an output connected to the diaphragm pump 53. The polish flowed in the direction indicated by the arrow. The check valve 54 operates similarly to the check valve 52, including a passage that can be blocked to terminate the flow of the polishing agent. The passage through the diaphragm pump 53 is blocked by the check valves 52 and 54 and the polishing agent attempts to flow in the opposite direction indicated by the arrows.

The use of a back pressure valve 55 in the slurry delivery system 51 eliminates the problem of waste of polishing slurry flowing through the diaphragm pump 53 due to the pressure of the polishing slurry at the input of the check valve 52. The input pressure of the polish opens the check valve 52, filling the chamber of the diaphragm pump 53, and opens the check valve 54 to allow the polish to flow out of the pump. The back pressure valve 55 creates a pressure differential across the check valve 54 such that the pressure differential closes the check valve 54 to prevent unwanted backflow of the polish.

The backpressure valve 55 includes inputs, outputs, passages 61, valves 63, and feedback control 64 (optional). The input of the backpressure valve 55 is connected to the output of the check valve 54 and to the passage 61. The passage 61 is blocked by a valve 63. When the valve 63 is open, the passage 61 forms an adjacent passage from the input to the output of the backpressure valve 55. A predetermined pressure is applied to valve 63 by pressure control 56 to seal or block passageway 61. The valve 63 is opened by an input supplying the polishing agent to the back pressure valve 55 whose pressure exceeds a predetermined pressure. Feedback 64 allows regulation to a predetermined pressure.

The pressure differential across the check valve 54 is created by setting the predetermined pressure of the pressure control 56 to a pressure greater than the maximum input pressure of the polish at the input of the check valve 52. For example, assume that the input pressure of the polish at the input of the check valve 52 varies in the range of 1406.2 to 7031.0 kilograms per square meter (2 to 10 pounds per square inch). The maximum input pressure was 7031.0 kilograms per square meter. The pressure control 56 is set to provide pressure per square meter on the valve 63 to ensure that 10546.5 kilograms per square meter (15 pounds per square inch) check valve 54 closes until the diaphragm pump 53 is ready to deliver a precise volume of polish. During the return stroke of the diaphragm pump 53, a minimum pressure differential of 3515.5 kilograms per square meter (5 pounds per square inch) holds the check valve 54 closed. A maximum pressure differential of 9140.3 kilograms per square meter (13 pounds per square inch) occurs when the polish pressure is 1406.2 kilograms per square meter (2 pounds per square inch) at the input of the check valve 52. The diaphragm pump 53 is capable of pumping the polish at pressures in excess of 10546.5 kilograms per square meter (15 pounds per square inch).

The pumping cycle shows how waste is minimized in the slurry delivery system 51. Initially, assume that the diaphragm pump 53 is at the uppermost portion of the stroke delivering a metered amount of polish. The piston begins to unblock the chamber of the diaphragm pump 53 on the return stroke. The pressure at the output of the check valve 54 is greater than the pressure at the input of the check valve 54 which keeps the valve closed. The input pressure of the polish at the output of the check valve 52 opens the check valve 52 to fill the chamber of the diaphragm pump 53 until the piston reaches the bottom of the return stroke (the chamber is filled to maximum volume). The upward stroke of the piston creates pressure at the input of the check valve 54. The polishing agent consists of a liquid and a solid material and is therefore not compressible. The pressure generated by the diaphragm pump 53 exceeds the predetermined pressure applied to the valve 63 by the pressure control 56 which opens the check valve 54 and the valve 63. The volume within the piston discharge chamber of the diaphragm pump 53 delivers the polish at the output of the back pressure valve 55. Note that at each pumping cycle, the piston displaces a precise volume within the chamber, independent of the pressure at the input of the check valve 52.

In an embodiment of the backpressure valve 55, a predetermined pressure is mechanically generated to keep the valve 63 closed. Generally, the spring provides pressure to keep the valve 63 closed. The magnitude of the pressure is controlled by a screw arrangement which can compress or decompress a spring to increase and decrease, respectively, a predetermined pressure. Generally, mechanically adjusting the back pressure valve enables a predetermined pressure alone that is sufficient for most applications.

Feedback 64 can be adjusted to a predetermined pressure provided by pressure control 56 that keeps valve 63 closed. The change in polish pressure at the input of the check valve 52 can be detected and increased or decreased to a predetermined pressure that keeps the valve 63 closed, thereby providing a constant polish pressure at the output of the backpressure valve 55. Adjustment of the predetermined pressure may result in a constant or adjustable pressure differential across check valve 54. Pneumatic or electrical feedback may be used to compensate for variations in polish pressure at the input of the check valve 52. The pressure at which the holding valve 63 is closed is varied using the controlled compressed gas. Electrically generated pressure changes may be accomplished by a motor or solenoid.

Most commercially available back pressure valves have a flat surface valve that seals the valve against another flat surface within the passage of the device. The use of this common type of back pressure valve generates a pressure wave in the system that can damage the diaphragm pump. For example, when the back pressure valve is closed after a volume of polish is delivered, a pressure wave is transmitted toward the diaphragm pump. The pressure wave also reflects back from the diaphragm due to "teapot" or chatter as the valve intermittently allows the slurry to flow through the valve during the pump stroke. The worst case is that the pressure wave hits the membrane of the membrane pump, and the force breaks the membrane, destroying the pump.

With a back pressure valve having a valve with a tapered surface blocking the passage in the back pressure valve, the magnitude and frequency of the pressure wave is significantly reduced or diminished. The sealing surface within the passageway may or may not have a taper corresponding to the tapered surface of the valve. For example, the valve 63 is shown as an arcuate surface. Ryan Herco Company names the back pressure valves as PLAST-O-MATIC, some valves having an arcuate surface.

The distribution stem manifold 57 has an input and an output connected to the backpressure valve 55. The dispense rod 58 has an output connected to the dispense rod manifold 57 and an output providing a polishing slurry. The dispensing bar 58 is suspended above a platen 59. An amount of polishing agent equal to the amount discharged by the piston of the diaphragm pump 53 flows through the dispensing rod manifold 57 and the dispensing rod 58 and is dispensed onto the surface of the polishing medium on the platen 59. The movement of the platen 59 is due to the polishing agent on the surface. The semiconductor wafer is placed in contact with a polishing agent and a polishing medium. It should be noted that chemical mechanical planarization apparatuses utilize several types of motions to mechanically polish semiconductor wafers. For example, rotary, orbital, and horizontal motion is used on a platen or wafer carrier to create motion between a semiconductor wafer and a polishing medium.

By now it should be appreciated that there has now been provided apparatus and methods for planarizing semiconductor wafers. The CMP apparatus includes a platen that supports a semiconductor wafer during a planarization process. The polishing media on the platen provides a surface suitable for polishing agents. The diaphragm pump pumps the polish to the dispensing strip. The diaphragm pump is a positive displacement pump that provides a fixed volume of polishing agent during each pumping cycle. The accuracy and reliability of the diaphragm pump allows the flow rate to be set near the minimum required amount to reduce polishing agent waste. The reliability of the pump significantly extends the maintenance time. A dispensing rod is suspended from the platen and dispenses the polishing agent to the polishing medium. The process side of the semiconductor wafer is placed in contact with a polishing medium to aid in planarization. The platen, the semiconductor wafer, or both are moved to planarize the semiconductor wafer.

The check valve is placed before or after the membrane pump. The check valve may prevent the flow of the polishing agent in a direction opposite to the pumping direction. A back pressure valve is placed downstream of the diaphragm pump output, creating a pressure differential across the check valve at the output of the diaphragm pump. The back pressure valve (flowing the polish) is set to a maximum pressure of the polish above the diaphragm pump input (or the input of a check valve connected to the diaphragm pump input). The back pressure valve prevents the flow of the polishing agent through the membrane pump due to the pressure of the polishing agent at the pump input.

The back pressure valve includes a passage through which a polishing agent flows. The back pressure valve has a valve with a tapered surface to prevent harmful pressure waves from being generated within the system when the valve is closed. The valve is held closed by the pressure provided by the pressure control.

Further control of the downstream pressure is obtained by opening a back pressure valve at the control pressure. If the pressure at the input of the diaphragm pump increases/decreases, the pressure at which the back-pressure valve is opened also increases/decreases. Generally, pressure compensation creates a pressure differential across a check valve of the output of the diaphragm pump.

A fixed and precise volume of polishing agent can be delivered using a diaphragm pump, check valve and back pressure valve. The delivery rate is set at or near the minimum flow rate required to ensure that wafer planarization is constant. There is no waste of polish due to the substantial cost savings associated with using the minimum amount required. The maintenance and reliability of the slurry delivery system is also improved, extending the maintenance time period and increasing wafer productivity.

Claims (5)

1. A chemical mechanical planarization apparatus, characterized by:

a platen (22) for supporting a semiconductor wafer (77);

a diaphragm pump (12) having an input for outputting and receiving a polishing agent; and

a dispense rod (27) having an input connected to the output of the diaphragm pump (12) and an output providing the polishing agent to planarize the semiconductor wafer (77).

2. A chemical mechanical planarization process for a semiconductor wafer, characterized by comprising the steps of:

pumping the polishing agent onto the surface of the polishing medium (22,34) with a positive displacement pump (12);

distributing the polishing agent on the surface of the polishing medium (22, 34);

placing a process side of a semiconductor wafer (77) in contact with the surface of the polishing medium (22, 34);

moving at least one of the polishing media (22,34) or the semiconductor wafer (77) to remove material from the semiconductor wafer (77).

3. The method of claim 2, further comprising the steps of:

providing the polishing agent to the positive displacement pump (12); and

preventing reverse flow of the polish through the positive displacement pump (12).

4. A method of chemical mechanical planarization, comprising the steps of:

providing a polishing medium (22, 34);

providing a polishing agent;

pumping the polishing agent to the polishing medium with a diaphragm pump (12);

dispensing the polishing agent to the polishing medium when a pressure of the polishing agent at the output of the diaphragm pump (12) exceeds a predetermined pressure, the predetermined pressure exceeding a maximum pressure of the polishing agent at the input of the diaphragm pump (12);

distributing the polishing agent to a surface of the polishing medium (22, 34);

placing a semiconductor wafer (77) in contact with the polishing medium (22, 34); and

-moving at least one of said polishing media (22,34) or semiconductor wafer (77).

5. The method of claim 4, further comprising the step of preventing reverse flow of the polishing agent through the diaphragm pump (12).