System and method for producing ammonia solutions with reduced dissolved carrier gas and oxygen content

Abstract

To provide a system for supplying a rinsing liquid comprising ultra-pure water and ammonia gas.SOLUTION: A system (100) for supplying a rinsing liquid including ultrapure water and ammonia gas includes an ultrapure water source (102) configured to supply ultrapure water to a contactor (110), a gas mixture source configured to supply ammonia gas and a carrier gas to the contactor (110), a control unit configured to maintain an operating pressure of the contactor (110) below a pressure threshold, the contactor (110) configured to generate the rinsing liquid, and a pump (150) configured to deliver the rinsing liquid including a gas partial pressure below the pressure threshold to an outlet.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This application relates generally to systems and methods used in wet cleaning operations during the manufacture of semiconductor devices. In particular, this application relates to systems and methods for generating and delivering deionized water having a desired concentration of NH3 for use in semiconductor manufacturing processes. [Background technology]

[0002] The processing of wafers, lithography masks, flat panels, and solar panels involves wet processing with a variety of chemicals. These chemicals must be rinsed off before the treated wafers or panels are dried. Deionized water (DI water) and ultrapure water (used interchangeably herein) are commonly used in semiconductor device manufacturing processes for rinsing or wet cleaning operations.

[0003] However, the use of substantially non-conductive liquids such as DI water in semiconductor manufacturing processes can result in charge accumulation on the surface of the wafer. This is particularly problematic in manufacturing processes that use rotating wafer tools, because electro-osmotic effects created by contact between the wafer and the DI water used in cleaning operations can cause charge accumulation and resulting electrostatic discharge events. These discharge events can damage or destroy structures on the wafer or cause contaminants and unwanted particles to adhere to the wafer. Therefore, it is desirable to use a rinse liquid that has a higher conductivity than ultrapure water to avoid the generation of static charges during the rinsing process.

[0004] Existing systems often use conductive cleaning fluids to reduce charge build-up on wafers during wet cleaning operations. For example, a gas such as carbon dioxide (CO2) can be dissolved in DI water to produce deionized carbonated (DI-CO2) water. However, the acidity of DI-CO2 water can undesirably etch acid-sensitive materials such as copper, cobalt, and other metals commonly used in the back-end of line (BEOL) stages of wafer manufacturing.

[0005] Another approach uses ammonia (NH3) instead of CO2. For example, a dilute solution of NH3 in DI water is commonly used on wafers or panels with exposed metal layers. By dissolving NH3 in DI water, an alkaline solution with a substantially lower etch rate than DI-CO2 can be made for use in wet cleaning operations.

[0006] However, processing machines (e.g., single-wafer spin tools) typically rinse each wafer in a separate chamber, and a fabrication facility may operate multiple processing machines independently, although each machine is connected to a common source of resources used during manufacturing, such as a DI water supply for wafer rinsing. Furthermore, the processing of each chamber is rarely synchronized, resulting in randomly varying demand for rinse fluids.

[0007] Supplying freshly prepared conductive rinse solutions with precise amounts of dissolved NH3 can pose technical challenges that are only complicated given the randomly varying flow rates required to service asynchronous processing tools. For example, NH3 can be supplied as a concentrated solution or as a gas. Due to the high solubility of NH3 in DI water, using NH3 in its gas phase results in total absorption of NH3 in the DI water. However, NH3 gas is too reactive in DI water, so if the NH3 flow rate is low enough, there is a high risk of DI water backflowing into the NH3 gas supply line and NH3 valve. This can lead to serious control problems, since the flow characteristics of the valve are very different for a gas-filled valve and a water-filled valve. Therefore, it is difficult to maintain a steady flow of NH3 gas into the DI water under such conditions, especially if the gas flow is interrupted during the normal course of the manufacturing process. It is even more difficult to produce a rinse solution with a small but precise amount of ammonia gas dissolved in the DI water.

[0008] US Patent No. 5,999,336 discloses an apparatus for generating and delivering a conductive cleaning solution comprising DI water having a desired concentration of dissolved NH3 to prevent charge build-up on the wafer surface when used in semiconductor manufacturing processes such as wet cleaning operations. To address the above issues caused by the absorption of NH3 into the DI water, a carrier gas such as nitrogen can be used to facilitate the dissolution process. The resulting rinse solution has a partial pressure equal to or greater than atmospheric pressure due to the carrier gas.

[0009] This gas partial pressure can be problematic in certain applications. The pressure drop through the delivery nozzle can cause bubbles to form at the moment the rinse liquid is applied to the wafer surface. These bubbles can attach to the wafer surface and damage structures formed thereon. Another problem can be due to dissolved oxygen in the rinse liquid, which can corrode metal structures formed on the wafer. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] US Patent Application Publication No. 2018 / 0133665 Summary of the Invention [Problem to be solved by the invention]

[0011] In light of the above, there is a continuing need for systems and methods for generating and delivering a rinse solution comprising DI water having a subatmospheric gas partial pressure and a desired concentration of dissolved NH3. Additionally, there is a need for systems and methods for reducing and / or removing dissolved oxygen from the rinse solution. The techniques described herein allow for precise control of gas partial pressure by controlling the carrier gas flow. Additionally, the concepts described herein provide an oxygen reduction system that reduces oxygen content in the rinse solution while mitigating ammonia stripping. [Means for solving the problem]

[0012] The technology, in one aspect, features a system for supplying a rinse solution including ultrapure water and ammonia gas. The system includes an ultrapure water source in fluid communication with the contactor. The ultrapure water source is configured to supply the ultrapure water to the contactor. The system further includes a gas mixture source in fluid communication with the contactor. The gas mixture source is configured to supply the ammonia gas and a carrier gas to the contactor. The system further includes a control unit in fluid communication with the contactor. The control unit is configured to adjust a flow rate of the ultrapure water such that an operating pressure of the contactor is maintained below a pressure threshold. The system further includes a compressor in fluid communication with the contactor. The compressor is configured to remove residual transfer gas from the contactor. The contactor is configured to generate a rinse solution having ultrapure water and a concentration of ammonia gas dissolved therein. The system further includes a pump in fluid communication between the contactor and an outlet. The pump is configured to deliver the rinse solution to the outlet having a gas partial pressure below a pressure threshold.

[0013] The technique may further include any of the following features: In some embodiments, the control unit is configured to adjust a flow rate of ultra-pure water at an inlet of the contactor to control an operating pressure of the contactor.

[0014] In some embodiments, the liquid level in the contactor is controlled by adjusting the flow rate of the carrier gas. In some embodiments, the liquid level in the contactor is controlled by adjusting the flow rate of the residual transfer gas.

[0015] In some embodiments, the operating pressure of the contactor is in the range of about 0.4 to about 0.95 bar (about 40 to about 95 kPa) absolute pressure. For example, in some embodiments, the operating pressure of the contactor is about 0.6 bar (60 kPa) absolute pressure.

[0016] In some embodiments, the pressure threshold is about atmospheric pressure. In some embodiments, the rinsing liquid is delivered to the wafer. For example, in some embodiments, the system further includes a nozzle in fluid communication with the outlet. The nozzle can be configured to deliver the rinsing liquid to the wafer.

[0017] In some embodiments, the system further includes a membrane contactor in fluid communication with the outlet. For example, in some embodiments, the membrane contactor can be configured to strip oxygen from the rinse liquid.

[0018] In some embodiments, the system further includes a pressure sensor in fluid communication with the contactor. For example, in some embodiments, the pressure sensor can be configured to monitor an operating pressure of the contactor.

[0019] In some embodiments, the gas mixture source includes an ammonia gas source and a carrier gas source. For example, in some embodiments, the ammonia gas source is configured to supply ammonia gas to the contactor. In some embodiments, the carrier gas source is configured to supply a carrier gas to the contactor.

[0020] In some embodiments, the ultrapure water, ammonia gas, and carrier gas are mixed prior to entering the contactor. In some embodiments, the contactor is a packed column or packed tower type contactor.

[0021] In another aspect, the technology features a method of providing a rinse liquid comprising ultrapure water having a gas partial pressure below atmospheric pressure and a desired concentration of dissolved ammonia gas. The method includes providing ultrapure water and a gas mixture to a contactor. The gas mixture includes ammonia gas and a carrier gas. The method further includes monitoring an operating pressure of the contactor using a pressure sensor in fluid communication with the contactor. The method also includes generating a rinse liquid in the contactor. The rinse liquid includes ultrapure water and a concentration of ammonia gas dissolved therein. The method further includes regulating a flow rate of the ultrapure water using a control unit in fluid communication with the pressure sensor such that an operating pressure of the contactor is maintained below atmospheric pressure. The method also includes removing residual transfer gas from the contactor using a compressor in fluid communication with the contactor. The method further includes delivering the rinse liquid to the outlet using a pump in fluid communication between the contactor and the outlet. The rinse liquid has a gas partial pressure below atmospheric pressure.

[0022] In another aspect, the technology features a system for supplying a rinsing liquid. The system includes a rinsing liquid source in fluid communication with a membrane contactor. The rinsing liquid source is configured to supply a rinsing liquid having a first oxygen concentration. The system further includes a nitrogen gas source in fluid communication with the membrane contactor. The nitrogen source is configured to supply nitrogen gas to the membrane contactor. The system also includes a nozzle in fluid communication with the membrane contactor. The nozzle is configured to adjust a flow rate of the nitrogen gas. Additionally, the system includes a membrane contactor configured to generate a stripped rinsing liquid from the rinsing liquid. The stripped rinsing liquid has a second oxygen concentration lower than the first oxygen concentration.

[0023] This technique may further include any of the following features: In some embodiments, the system further includes a pump in fluid communication between the membrane contactor and the outlet. The pump may be configured to deliver the stripped rinsing liquid to the outlet. In some embodiments, the pump is a vacuum pump. For example, in some embodiments, the pump is a chemically inert diaphragm pump or a water ring pump.

[0024] Advantages of the systems and methods described herein, together with further advantages, will be better understood by reference to the following description taken in conjunction with the accompanying drawings, in which: The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the described embodiments by way of example only, in which: [Brief description of the drawings]

[0025] [Figure 1] FIG. 1 is a block diagram of an exemplary system for providing a rinse liquid comprising DI water having a subatmospheric gas partial pressure and a desired concentration of dissolved NH3, in accordance with an embodiment of the technology described herein. [Diagram 2] FIG. 2 is a diagram illustrating the generation of bubbles caused by rinsing fluid being dispensed from a dispensing nozzle onto a wafer in accordance with an embodiment of the technology described herein. [Diagram 3] FIG. 3 is a block diagram of an exemplary system for understanding and mitigating bubble generation in a rinse solution in accordance with an embodiment of the technology described herein. [Figure 4] FIG. 4 is a graph illustrating the results of tests using devices of three different designs that were characterized using a system according to an embodiment of the technology described herein. [Diagram 5] FIG. 5 illustrates an exemplary tube formed into a spiral shape according to embodiments of the technology described herein. [Figure 6] FIG. 6 is a graph showing a comparison of oxygen concentration at the outlet of an apparatus for generating and delivering a conductive cleaning solution comprising DI water with a desired concentration of dissolved NH3 with and without an oxygen removal unit according to an embodiment of the technology described herein. [Figure 7] FIG. 7 is a graph showing the effect of N2 gas flow on oxygen concentration in the outlet according to an embodiment of the technology described herein. [Figure 8] FIG. 8 is a block diagram of an exemplary system for providing a rinse solution comprising DI water with a desired concentration of dissolved NH3 having reduced oxygen content, in accordance with an embodiment of the technology described herein. [Figure 9] FIG. 9 is a flow diagram of a method 900 for providing a rinse solution comprising DI water with a desired concentration of dissolved NH 3 in accordance with an embodiment of the technology described herein. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] In some embodiments, the systems and methods described herein can include one or more mechanisms or methods for generating and delivering a rinse solution that includes DI water having a gas partial pressure below atmospheric pressure and a desired concentration of dissolved NH3. The systems and methods described herein can include one or more mechanisms or methods for reducing and / or removing dissolved oxygen from the rinse solution. The systems and methods described herein can include one or more mechanisms or methods for precisely controlling gas partial pressure by controlling carrier gas flow. The systems and methods described herein can include one or more mechanisms or methods for an oxygen reduction system that reduces oxygen content in the rinse solution while mitigating ammonia stripping.

[0027] FIG. 1 is a block diagram of an exemplary system 100 for supplying a rinse liquid comprising DI water having a subatmospheric gas partial pressure and a desired concentration of dissolved NH3. The system 100 includes at least one ultrapure water source 102, at least one carrier gas source 104, and at least one ammonia gas source 106. Optionally, in some embodiments, the carrier gas source 104 and the ammonia gas source 106 include a gas mixture source. The carrier gas 104 and the ammonia gas 106 can be added to the ultrapure water 102 before entering the contactor 110, although one skilled in the art will appreciate that the carrier gas 104 and / or the ammonia gas 106 can be added anywhere to the ultrapure water in the system 100. In some embodiments, the contactor 110 is a packed column or packed tower type contactor. Optionally, any type, number, or type of contactor 110 can be used.

[0028] The contactor 110 operates at a pressure below atmospheric pressure. The operating pressure within the contactor 110 is monitored by at least one pressure sensor 120. The pressure sensor 120 is connected to a control unit (not shown) that adjusts an operating variable, such as the flow rate of the ultrapure water 102. Thus, the pressure sensor 120 may be configured at the inlet to maintain the operating pressure, although one skilled in the art will appreciate that the pressure sensor 120 may be configured elsewhere in the contactor 110. The system 100 includes at least one compressor 140 that may be configured to remove residual transfer gas from the contactor 110 with an exhaust 142. In one embodiment, the system 100 includes a level sensor 125 that may be configured to monitor the liquid level within the contactor 110.

[0029] The system 100 includes at least one pump 150. In one embodiment, the pump 150 may be configured to deliver the rinsing liquid 160 to the wafer or panel processing machine at a required pressure. In some embodiments, the pump 150 may include a centrifugal pump. For example, the pump 150 may be selectively operable and configured not to operate if the pump 150 is not fully filled with at least one of the carrier gas, the ammonia gas, the residual gas, the ultrapure water, and / or the rinsing liquid. For example, at the start-up of the system 100, the pump 150 may not be full of liquid. Thus, the contactor 110 may be temporarily pressurized during the start-up procedure to allow some water to flow from the contactor 110 to the pump 150. The start-up phase is over when the contactor 110 has the required liquid level and a minimum liquid flow is achieved.

[0030] The pressure within the contactor 110 may be controlled by adjusting the water flow to the contactor. In some embodiments, the controlled pressure inside the contactor 110 ranges from about 0.4 to about 0.95 bar (about 40 kPa to about 95 kPa) absolute, although one of ordinary skill in the art would understand that the contactor 110 can operate at any of a variety of pressures. In some embodiments, the controlled pressure inside the contactor 110 is 0.6 bar (60 kPa) absolute. In some embodiments, the carrier gas 104 is nitrogen (N2) gas. Optionally, any of a variety of alternative gases can be used.

[0031] The lower limit of pressure in the contactor 110 is determined by the operation of the pump 150, which pressurizes the liquid to provide the pressure. Low pressure causes cavitation inside the pump 150. This cavitation is desirable to avoid, as it can lead to particles in the liquid. Particles are unnecessary in semiconductor processes, as they can contaminate and damage structures formed on the wafer during fabrication. In some embodiments, the pump 150 is a bearingless pump that operates on the principle of magnetic levitation. This type of pump has a very low pressure at which cavitation occurs. Such pumps are advantageous for the present application. In one example, the pump 150 is a Levitronix BPS 2000 pump system.

[0032] In some embodiments, the pump 150 can introduce heat into the exiting liquid, which can have a significant impact on the operation of the system 100 at low liquid flow rates where temperatures can be significantly higher downstream of the pump 150. As the temperature of the liquid changes, the electrical conductivity of the liquid can change.

[0033] In some embodiments, the temperature increase due to the pumping action of pump 150 is used as feedback to a controller that adjusts the NH3 feed rate accordingly to achieve a constant conductivity. In some embodiments, a heat exchanger is used to control the temperature of the exiting liquid, where the cooling stream is temperature controlled. In some embodiments, a Peltier element is used to control the temperature of the exiting liquid.

[0034] Operating the contactor 110 at very low internal pressure can have drawbacks, such as higher pumping energy required, resulting in higher costs at low flow rates, and increased temperatures.

[0035] The upper limit of pressure in the contactor 110 is given by the partial pressure exerted by the carrier gas 104, which can cause bubble generation when the liquid is dispensed onto a wafer in a single wafer processing tool. One of the key factors that can cause bubble generation is the partial pressure of dissolved gas in the liquid. Bubble nucleation in the liquid can occur when the gas partial pressure is higher than the liquid static pressure. Bubble nucleation can occur with particles as bubble nuclei. The low particle concentration in ultrapure water can inhibit this mechanism.

[0036] Another mechanism that can cause bubble generation is fluctuations in liquid flow, for example in turbulent flows, which can create short-lived localized conditions of very low liquid pressure, low enough to cause spontaneous bubble nucleation.

[0037] In addition, the shape of the nozzle can cause the generation of bubbles. A smooth nozzle will not cause bubbles in the rinse solution with a carrier gas partial pressure below ambient pressure. However, the use of a sharp nozzle can cause bubbles to be generated when the partial pressure of the dissolved carrier gas is low.

[0038] The contactor 110 requires a pressure lower than the desired partial pressure exerted by the carrier gas in the liquid to allow removal of the carrier gas from the liquid. Additionally, the techniques described herein can avoid the generation of bubbles in the liquid dispenser by providing a liquid with a low gas partial pressure. FIG. 2, described below, is a diagram 200 illustrating the generation of bubbles caused by the rinsing liquid being dispensed onto the wafer from a dispensing nozzle. A pressure (absolute) of about 0.95 bar (about 95 kPa) can avoid bubbles at the dispensing nozzle under substantially optimal conditions. In one embodiment, a pressure of 0.6 bar (60 kPa) inside the contactor 110 allows stable operation even under unfavorable conditions. The generation of bubbles can be further reduced by selecting a dispenser geometry that avoids sharp gradients in the liquid flow rate. A configuration for understanding and mitigating the generation of bubbles in the rinsing liquid is described below in conjunction with FIG. 3.

[0039] The flow of carrier gas (e.g., N2) through the system 100 may have certain constraints. For example, a high flow rate of carrier gas 104 increases the amount of NH3 stripped into the exhaust gas 142, which is undesirable. Furthermore, a high flow rate of carrier gas 104 requires the compressor 140 to use a pump with a larger diaphragm, which adds undesirable costs. Furthermore, the gas inside the contactor 110, due to its working principle, is more or less saturated with water vapor. When the pressure of such gas increases, the pressure of the water vapor increases above the saturation pressure, which results in condensation of water.

[0040] Certain types of compressors require oil for lubrication, which causes oil contamination of the exiting gas. Such oil contamination is undesirable. Therefore, in some embodiments, an oil-free diaphragm pump is used in the compressor 140 to compress the exhaust gas. Diaphragm pumps are robust devices that can be used with corrosive gases and can withstand humid gases.

[0041] The exhaust gas stream contains undesirable water droplets at the outlet of the compressor 140. In some embodiments, the exhaust gas 142 is diluted with dry gas. The dry gas may be added between the nozzle 130 and the compressor 140 or downstream of the compressor 140. The amount of dry gas added may be selected such that the relative humidity of the compressed exhaust gas is less than 100%.

[0042] In other embodiments, the exhaust gas is heated by a heat exchanger or heated tubes to an amount such that at the temperature achieved the relative humidity is less than 100%. The carrier gas 104 acts to transport NH3 106 to the contactor 110. In general, the time delay occurs as a function of the length of the corresponding gas pipe. A large time delay is undesirable when the liquid flow rate changes dynamically, as it will affect the stability of the concentration of dissolved NH3 in the liquid. A fast system reaction is required when the liquid flow rate changes dynamically to avoid overshooting or undershooting the resulting NH3 concentration in the rinse liquid. When the pressure increases, DI water is sent to the gas line. This is undesirable because NH3 gas is too reactive with DI water, so there is a high risk that DI water will backflow into the NH3 gas supply line and the NH3 valve if the NH3 flow rate is low enough. Therefore, some reaction time is required to detect this case and close the corresponding valve.

[0043] In some embodiments, the flow rate of the carrier gas is set between 1 slm and 20 slm. In some embodiments, the flow rate of the carrier gas is 2 slm at a pressure (absolute) of 0.6 bar (60 kPa) in the contactor 110.

[0044] Using the above systems and techniques, the partial pressure exerted by the carrier gas in the dispensed rinsing liquid 160 can be made lower than ambient pressure. In some embodiments, the system 100 can meet the rinsing liquid 160 demands for a typical single wafer tool or other tool, for example, rinsing the surface of a flat panel. The flow rate of the rinsing liquid 160 can range from 0.5 liters per minute to 100 liters per minute. In certain embodiments, at least a second flow of DI water is mixed into the flow through the contactor 110 to achieve a higher liquid outlet flow of up to 140 liters per minute.

[0045] 2, a diagram 200 illustrates bubble generation 230 caused by rinsing fluid 210 dispensed from a dispensing nozzle 220 onto a wafer 240. As noted above, a single wafer tool can use multiple chambers. A single dispense nozzle 220 can be used to supply liquid to the wafer 240 in each chamber. In some embodiments, the dispensed flow in each chamber can be independent of the actual number of chambers using the rinsing fluid 210. This can be accomplished by a pressure drop in the dispense nozzle 220 or an upstream valve that is typically greater than the pressure drop of the liquid flowing in the liquid distribution tube.

[0046] 3 is a block diagram of a system 300 for understanding and mitigating bubble generation in rinse solutions. A liquid having dissolved oxygen is created using an ozonated water supply system 305 and supplied in Liquid Out as DIO3. In some embodiments, the ozonated water supply system 305 is a LIQUOZON device from MKS Instruments Inc. that operates without ozone generation, although alternative ozonated water supply systems can be used.

[0047] Liquid flows through porous membrane device 310 and is then delivered to device under test 320. Gas inside membrane device 310 is trapped between valves 330 and 332. The gas pressure equalizes over time with the gas partial pressure of the liquid flowing through membrane device 310. Pressure gauge 340 is used to directly measure the partial pressure of the liquid.

[0048] The pressure downstream of the device under test 320 is kept constant by a control loop consisting of a pressure gauge 342, a PID controller 350, and a flow regulator valve 360. The air bubble content in the liquid is measured with two devices 370 and 372. In the illustrated embodiment, the two devices 370 and 372 include optical measurement devices, although any of a variety of devices can be used.

[0049] 4 is a graph showing the results of using three different designs of device under test 320 that were characterized using system 300: (1) a smooth membrane valve from Gemu Group, (2) a valve with sharp edges from Futurestar Corporation, and (3) a bent tube having an outer diameter of about 0.25 inches (6.35 mm) and an inner diameter of about 0.15 inches (3.95 mm).

[0050] For characterization, valves 330 and 332 were adjusted to give the same flow rate at a defined pressure drop. The length of the tubing was chosen to give approximately the same flow rate at this pressure drop. Referring to the results in FIG. 4, supersaturation is defined as the difference in the measured pressures, i.e., the pressure measured by pressure gauge 342 minus the pressure measured by pressure gauge 340. Positive supersaturation means that the gas partial pressure is higher than the liquid pressure. Negative supersaturation means that the liquid pressure is higher than the gas partial pressure.

[0051] The air bubble content of the liquid flowing from the device under test 320 was optically measured using device 370. As shown, the bent tube and the smooth membrane valve from Gemu Group produced the least amount of air bubbles. In some embodiments, the membrane value is used to set the pressure drop. Optionally, a tube formed into a helical shape is used to set the pressure drop. FIG. 5 shows an exemplary tube 500 formed into a helical shape. The pressure drop can be achieved by selecting the appropriate number of turns and the appropriate diameter of the helix.

[0052] As manufacturing processes evolve and feature geometries continue to increase in complexity and decrease in size, rinsing of wafers with exposed metal layers becomes a substantially more demanding and precise process. Rinsing of silicon wafers is often combined with surface oxidation to reduce the susceptibility to surface contamination. Rinsing of metals on the other side of the wafer must avoid surface oxidation, as this can lead to undesirable corrosion and etching of the metal in the rinsing solution.

[0053] The techniques described herein reduce the oxygen content of the rinse solution. The causes of oxygen contamination of the rinse solution were analyzed. There are two sources of oxygen contamination caused during the rinse process: the rinse solution itself and the effect of the rinse solution flow on the wafer.

[0054] The main source of oxygen in the rinse solution is the oxygen in the liquid chemicals that make up the rinse solution. The liquid chemicals are often stored in plastic containers to avoid metal contamination. The plastic containers allow oxygen to permeate the liquid during storage. Thus, the liquid chemicals can become saturated with atmospheric oxygen over time. In the systems described herein, this source of oxygen in the rinse solution is avoided because no liquid chemicals are used to generate the rinse solution. For example, the systems described herein use clean gases and ultrapure water. The gases are processed in metal containers and pipes that are impermeable to atmospheric oxygen.

[0055] Ultrapure water (UPW) is generally the liquid with the lowest oxygen concentration available in a semiconductor fabrication facility. UPW is typically prepared immediately prior to use, and oxygen is removed before the UPW is distributed to the various processing tools in the semiconductor fabrication facility.

[0056] Considering these factors and conditions, the remaining source of oxygen contamination is the penetration of oxygen into the pipes and tubing used to handle and distribute the rinse solution. Thus, the source of oxygen contamination has been characterized.

[0057] Oxygen permeation into plastic pipes and tubes occurs according to known processes. In one embodiment, tubes made from perfluoroalkoxy (PFA) may be used. This material is chosen for aggressive and highly reactive liquids used in semiconductor manufacturing processes due to its high inertness. PFA is compatible with most chemicals and can be used at high temperatures. Tubing and fittings made from this material are readily available. However, PFA has the disadvantage of having a relatively high gas permeability coefficient. Optionally, the tubes may be manufactured from a variety of materials that provide high inertness and availability.

[0058] UPW distribution tubing in semiconductor manufacturing facilities is typically made from polyvinylidene fluoride (PVDF). PVDF has a much lower oxygen permeability coefficient than PFA. Therefore, the UPW itself maintains low oxygen content throughout the entire distribution pipe except for the last line used to connect to the semiconductor manufacturing tool. This connection is often made from PFA because of its high flexibility. It has a higher tube surface to liquid flow ratio than the main distribution tube made from PVDF.

[0059] These lines may also experience flow stagnation in the event of tool maintenance or shutdown. The results of this analysis are that the overall contribution of small diameter PFA tubing to oxygen contamination has a measurable effect. Therefore, the technique described herein uses nitrogen purged double containment for the PFA inlet and outlet tubes of the NH3 dissolution device. This configuration is effective in avoiding oxygen penetration into the rinse solution and requires only moderate effort to implement and achieve.

[0060] By combining oxygen removal with the NH3 dissolution system 100, further reduction in oxygen content can be achieved. FIG. 6 is a graph showing a comparison of oxygen concentration at the outlet of an apparatus (such as that described in U.S. Patent No. 5,399,633) for generating and delivering a conductive cleaning solution comprising DI water with a desired concentration of dissolved NH3 with and without an oxygen removal unit.

[0061] In some embodiments, the oxygen removal unit is a commercially available membrane contactor type 3M® Liqui-Cel® EXF-4x28 series, although any type and number of oxygen removal units can be used. It can operate with 28 slm N2 gas flow at atmospheric pressure. The quality of the N2 can be substantially grade 5.6.

[0062] The oxygen removal capacity of such modules is high enough to be effective in some processes. However, the oxygen removal capacity can be increased if it is also operated at a lower N2 gas flow rate. Figure 7 is a graph showing the effect of N2 gas flow on the oxygen concentration in the outlet. It is not necessary to operate the membrane contactor at vacuum pressure. This adds an undesirable cost to the vacuum pump.

[0063] The membrane contactor is selected to have a low pressure drop for the liquid flow and be chemically compatible with the NH3 solution. Low pressure drop for the liquid flow is important to avoid energy input to the liquid due to the pumping action of the pump. High energy requirements for pumping would cause undesirable temperature changes in the liquid.

[0064] 8 is a block diagram of an exemplary system 800 for providing a rinse solution 860 comprising DI water with a desired concentration of dissolved NH3 with reduced oxygen content. Similar to system 100, system 800 includes an ultrapure water source 802, a carrier gas source 804, an ammonia gas source 806, a contactor 810, a pressure sensor 820, a level sensor 825, and an exhaust 842. System 800 includes a membrane contactor 870 in combination with an NH3 dissolution system, such as system 100, described above in connection with FIG. 1. System 800 also includes a nitrogen gas source 880 and a pump 850.

[0065] To avoid wet off-gas from the membrane contactor 870, the membrane contactor 870 can be operated at a pressure above ambient pressure. The N2 flow rate from the nitrogen gas source 880 can be adjusted by two fixed nozzles 890 and 892. The inner diameters of the nozzles 890 and 892 are selected such that the N2 pressure in the contactor 810 is higher than ambient pressure and lower than the liquid pressure in the contactor 810. The expansion of the N2 gas in the nozzles 890 reduces the relative humidity of the N2 below the saturation point, avoiding liquid water at the gas outlet of the membrane contactor 870.

[0066] In some cases, it may be preferable to have the gas partial pressure in the rinsing liquid 860 lower than ambient pressure. Thus, the membrane contactor 870 can be operated at a N2 pressure lower than ambient pressure, and a vacuum pump 850 can be used at the gas outlet of the membrane contactor 870. The vacuum pump 850 can be a chemically inert diaphragm pump or a water ring pump.

[0067] As mentioned above, the solubility of NH3 is high compared to the solubilities of other dissolved gases. Therefore, the stripping efficiency of NH3 in the membrane contactor 870 is surprisingly low. The flow rate of N2 can be adjusted to achieve less than 1% NH3 loss while maintaining a sufficiently high oxygen removal rate.

[0068] 9 is a flow diagram of a method 900 for providing a rinse solution comprising ultrapure water having a subatmospheric gas partial pressure and a desired concentration of dissolved ammonia gas, according to embodiments of the technology described herein. The ultrapure water and gas mixture may be provided to a contactor (902). In some embodiments, the contactor is a packed column or packed tower type contactor.

[0069] The gas mixture includes ammonia gas and a carrier gas, as described above in connection with Figure 1. For example, using system 100, ultrapure water source 102 can supply ultrapure water to contactor 110, carrier gas source 104 can supply carrier gas to contactor 110, and ammonia gas source 106 can supply ammonia gas to contactor 110. In some embodiments, the ultrapure water, ammonia gas, and carrier gas are mixed prior to entering the contactor.

[0070] The operating pressure of the contactor can be monitored using a pressure sensor in fluid communication with the contactor (904). For example, using the system 100, the operating pressure of the contactor 110 can be monitored using the pressure sensor 120.

[0071] A rinsing solution may be generated in the contactor (906). As described above in connection with Figure 1, the rinsing solution includes ultra-pure water and ammonia gas at a concentration dissolved therein. For example, the system 100 may be used to generate the rinsing solution 160 in the contactor 110.

[0072] The flow rate of the ultrapure water may be adjusted (908) using a control unit in fluid communication with the pressure sensor. As previously described in connection with FIG. 1, the flow rate of the ultrapure water may be adjusted such that the operating pressure of the contactor is kept below atmospheric pressure. For example, using the system 100, the flow rate of the ultrapure water provided by the ultrapure water source 102 may be adjusted using a control unit in fluid communication with the pressure sensor 120. In some embodiments, the control unit is configured to adjust the flow rate of the ultrapure water at the inlet of the contactor 110. In some embodiments, the operating pressure of the contactor 110 is controlled by adjusting the flow rate of the carrier gas. In other embodiments, the operating pressure of the contactor 110 is controlled by adjusting the flow rate of the residual transfer gas.

[0073] In some embodiments, the operating pressure of the contactor 110 is in the range of about 0.4 to about 0.95 bar (about 40 to about 95 kPa) absolute pressure. For example, in some embodiments, the operating pressure of the contactor is about 0.6 bar (about 60 kPa) absolute pressure.

[0074] Residual transfer gas may be removed from the contactor using a compressor in fluid communication with the contactor (910). For example, using system 100, residual transfer gas may be removed from contactor 110 using compressor 140.

[0075] The rinsing liquid may then be pumped to the outlet using a pump in fluid communication between the contactor and the outlet (912). As described above, the rinsing liquid has a gas partial pressure that is less than atmospheric pressure. For example, using system 100, rinsing liquid 160 may be pumped to the outlet using pump 150.

[0076] In some embodiments, the rinsing fluid 160 is delivered to the wafer. For example, in some embodiments, a dispensing nozzle 220 in fluid communication with the outlet is configured to deliver the rinsing fluid 210 to the wafer 240.

[0077] In some embodiments, using the system 800, the membrane contactor 870 in fluid communication with the outlet is configured to strip oxygen from the rinsing liquid 860. For example, in some embodiments, the system 800 for supplying the stripped rinsing liquid 860 may include a rinsing liquid source in fluid communication with the membrane contactor 870. The rinsing liquid source may be configured to supply a rinsing liquid having a first oxygen concentration. In some embodiments, the system 800 may include a nitrogen gas source 880 in fluid communication with the membrane contactor 870. For example, in some embodiments, the nitrogen gas source 880 may be configured to supply nitrogen gas to the membrane contactor 870. In some embodiments, the system 800 may include a nozzle 890 in fluid communication with the membrane contactor 870. For example, the nozzle 890 may be configured to adjust the flow rate of the nitrogen gas. In some embodiments, the system 800 may include two nozzles 890 and 892, and both nozzles 890 and 892 may be configured to adjust the flow rate of the nitrogen gas. In some embodiments, the membrane contactor 870 can be configured to generate a stripped rinse solution 860 from the provided rinse solution. As described above in connection with FIG. 8, the stripped rinse solution 860 has a second oxygen concentration that is lower than the first oxygen concentration.

[0078] As described in detail above, an apparatus such as that described in the '891 patent can provide a very dilute ammonia solution for use in a manufacturing rinse process. The solution can be prepared by dissolving ammonia gas directly in water. The ammonia gas is diluted with nitrogen gas to avoid the ammonia fountain effect inside the apparatus. The ammonia fountain effect occurs when water and ammonia gas come into contact, the water absorbs the ammonia, and a vacuum is created. Additional traces of dissolved nitrogen and oxygen gas cannot be ignored and can affect the manufacturing process. For example, dissolved nitrogen can cause microbubbles on the wafer surface, causing defects in structures on the wafer, and traces of oxygen in the liquid can corrode metals. The system and method described in detail above address these concerns by precisely controlling the gas partial pressure of the rinse liquid and stripping the oxygen content from the rinse liquid before application to the wafer.

[0079] Variations, modifications, and other embodiments of what is described herein will occur to those skilled in the art without departing from the spirit and scope of the invention. Accordingly, the invention is not limited to only the foregoing illustrative description. The technical ideas contained in this disclosure are described below as appendices. [Appendix 1] 1. A system for supplying a rinse liquid comprising ultrapure water and ammonia gas, comprising: an ultrapure water source in fluid communication with the contactor and configured to supply ultrapure water to the contactor; a gas mixture source in fluid communication with the contactor and configured to supply ammonia gas and a carrier gas to the contactor; a control unit in fluid communication with the contactor, the control unit configured to adjust a flow rate of ultra-pure water such that an operating pressure of the contactor is maintained below a pressure threshold; a compressor in fluid communication with the contactor and configured to remove residual transfer gas from the contactor; the contactor configured to generate a rinsing liquid, the rinsing liquid comprising ultrapure water and ammonia gas at a dissolved concentration therein; a pump in fluid communication between the contactor and an outlet, the pump configured to deliver a rinse liquid to the outlet, the rinse liquid comprising a gas partial pressure below the pressure threshold. [Appendix 2] 2. The system of claim 1, wherein the control unit is configured to adjust a flow rate of ultrapure water at an inlet of the contactor. [Appendix 3] 2. The system of claim 1, wherein the liquid level in the contactor is controlled by adjusting the flow rate of the carrier gas. [Appendix 4] 2. The system of claim 1, wherein the liquid level in the contactor is controlled by adjusting the flow rate of the residual transfer gas. [Appendix 5] 2. The system of claim 1, wherein the operating pressure of the contactor comprises a pressure (absolute) in the range of about 0.4 to about 0.95 bar (about 40 to about 95 kPa). [Appendix 6] 6. The system of claim 5, wherein the operating pressure of the contactor comprises a pressure (absolute) of about 0.6 bar (about 60 kPa). [Appendix 7] 2. The system of claim 1, wherein the pressure threshold is atmospheric pressure. [Appendix 8] 2. The system of claim 1, wherein the rinsing liquid is delivered to the wafer. [Appendix 9] 2. The system of claim 1, further comprising a nozzle in fluid communication with the outlet, the nozzle configured to deliver the rinsing liquid to the wafer. [Appendix 10] 2. The system of claim 1, further comprising a membrane contactor in fluid communication with the outlet, the membrane contactor configured to remove oxygen from the rinsing liquid. [Appendix 11] 2. The system of claim 1, further comprising a pressure sensor in fluid communication with the contactor, the pressure sensor configured to monitor an operating pressure of the contactor. [Appendix 12] 2. The system of claim 1, wherein the gas mixture source comprises an ammonia gas source and a carrier gas source, the ammonia gas source configured to supply ammonia gas to the contactor, and the carrier gas source configured to supply a carrier gas to the contactor. [Appendix 13] 2. The system of claim 1, wherein the ultrapure water, the ammonia gas, and the carrier gas are mixed prior to entering the contactor. [Appendix 14] 2. The system of claim 1, wherein the contactor is a packed column or packed tower type contactor. [Appendix 15] A method for supplying a rinse liquid containing ultrapure water having a gas partial pressure lower than atmospheric pressure and having ammonia gas dissolved therein at a desired concentration, comprising: supplying ultra-pure water and a gas mixture including ammonia gas and a carrier gas to a contactor; monitoring an operating pressure of the contactor using a pressure sensor in fluid communication with the contactor; generating a rinse solution in the contactor, the rinse solution including the ultrapure water and ammonia gas at a dissolved concentration therein; regulating the flow rate of the ultrapure water using a control unit in fluid communication with the pressure sensor such that an operating pressure of the contactor is maintained below atmospheric pressure; removing residual transfer gas from the contactor using a compressor in fluid communication with the contactor; delivering the rinse solution, comprising a subatmospheric gas partial pressure, to the outlet using a pump in fluid communication between the contactor and an outlet. [Appendix 16] 16. The method of claim 15, wherein the contactor is a packed column or packed tower type contactor. [Appendix 17] a membrane contactor in fluid communication with the outlet and configured to receive a rinse fluid via the outlet, the rinse fluid comprising a first oxygen concentration; a nitrogen gas source in fluid communication with the membrane contactor, the nitrogen gas source configured to supply nitrogen gas to the membrane contactor; a nozzle in fluid communication with the membrane contactor, the nozzle configured to adjust the flow rate of the nitrogen gas; 2. The system of claim 1, wherein the membrane contactor is configured to remove oxygen from the received rinsing solution to produce a rinsing solution comprising a second oxygen concentration from the received rinsing solution that is lower than the first oxygen concentration. [Appendix 18] If the outlet is the first outlet, 18. The system of claim 17, further comprising a pump in fluid communication between the membrane contactor and a second outlet, the pump configured to deliver the rinse solution containing the second oxygen concentration produced in the membrane contactor to the second outlet. [Appendix 19] 20. The system of claim 18, wherein the pump in fluid communication between the membrane contactor and the second outlet is a vacuum pump. [Appendix 20] 20. The system of claim 19, wherein the vacuum pump is a chemically inert diaphragm pump or a water ring pump.

Claims

1. 1. A system for supplying a rinse liquid comprising ultrapure water and ammonia gas, comprising: an ultrapure water source in fluid communication with the contactor and configured to supply ultrapure water to the contactor; a gas mixture source in fluid communication with the contactor and configured to supply ammonia gas and a carrier gas to the contactor; a control unit in fluid communication with the contactor, the control unit configured to maintain an operating pressure of the contactor below a pressure threshold; the contactor configured to generate a rinsing liquid, the rinsing liquid comprising ultrapure water and ammonia gas at a dissolved concentration therein; a pump in fluid communication between the contactor and an outlet, the pump configured to deliver a rinse liquid to the outlet, the rinse liquid comprising a gas partial pressure below the pressure threshold.

2. The system of claim 1 , wherein the control unit is configured to adjust a flow rate of ultra-pure water to maintain an operating pressure of the contactor below the pressure threshold.

3. 10. The system of claim 1, wherein the liquid level in the contactor is controlled by adjusting the flow rate of the carrier gas.

4. 10. The system of claim 1, wherein the contactor liquid level is controlled by adjusting the flow rate of a residual transfer gas.

5. 10. The system of claim 1, wherein the contactor operating pressure comprises a pressure (absolute) in the range of about 0.4 to about 0.95 bar (about 40 to about 95 kPa).

6. 6. The system of claim 5, wherein the contactor operating pressure comprises a pressure (absolute) of about 0.6 bar (about 60 kPa).

7. The system of claim 1 , wherein the pressure threshold is atmospheric pressure.

8. The system of claim 1 , wherein the rinsing fluid is delivered to a wafer.

9. The system of claim 1 , further comprising a nozzle in fluid communication with the outlet, the nozzle configured to deliver the rinsing liquid to the wafer.

10. 10. The system of claim 1, further comprising a membrane contactor in fluid communication with the outlet, the membrane contactor configured to remove oxygen from the rinse liquid.

11. The system of claim 1 , further comprising a pressure sensor in fluid communication with the contactor, the pressure sensor configured to monitor an operating pressure of the contactor.

12. 2. The system of claim 1, wherein the gas mixture source comprises an ammonia gas source and a carrier gas source, the ammonia gas source configured to supply ammonia gas to the contactor and the carrier gas source configured to supply a carrier gas to the contactor.

13. 10. The system of claim 1, wherein the ultra-pure water, the ammonia gas, and the carrier gas are mixed prior to entering the contactor.

14. 10. The system of claim 1, wherein the contactor is a packed column or a packed tower type contactor.

15. a membrane contactor in fluid communication with the outlet and configured to receive a rinse fluid from the outlet, the rinse fluid comprising a first oxygen concentration; a nitrogen gas source in fluid communication with the membrane contactor, the nitrogen gas source configured to supply nitrogen gas to the membrane contactor; a nozzle in fluid communication with the membrane contactor, the nozzle configured to adjust the flow rate of the nitrogen gas; 2. The system of claim 1, wherein the membrane contactor is configured to remove oxygen from the received rinse solution to produce a rinse solution comprising a second oxygen concentration from the received rinse solution that is lower than the first oxygen concentration.

16. A method for supplying a rinse liquid containing ultrapure water having a gas partial pressure lower than atmospheric pressure and having ammonia gas dissolved therein at a desired concentration, comprising: supplying ultra-pure water and a gas mixture including ammonia gas and a carrier gas to a contactor; monitoring an operating pressure of the contactor using a pressure sensor in fluid communication with the contactor; generating a rinse solution in the contactor, the rinse solution including the ultrapure water and ammonia gas at a dissolved concentration therein; using a control unit in fluid communication with the pressure sensor to maintain an operating pressure of the contactor below atmospheric pressure; and pumping the rinse solution, the rinse solution comprising a subatmospheric gas partial pressure, to the outlet using a pump in fluid communication between the contactor and an outlet.

17. 17. The method of claim 16, wherein the contactor is a packed column or packed tower type contactor.

Images