CN1856651A - Detection of contaminants within fluid pumped by a vacuum pump - Google Patents

Abstract

A vacuum pump has, in fluid communication with a location intermediate an inlet thereof for receiving fluid and an outlet thereof for exhausting pumped fluid, a sensor for receiving at least part of the fluid received by the pump and for sensing the presence of one or more contaminants therein.

Description

Detection of Contaminants in Fluid Pumped by Vacuum Pumps

The present invention relates to the detection of contaminants in fluids pumped with vacuum pumps, and in particular molecular vacuum pumps.

Many manufacturing processes and tests are highly sensitive to contamination and are therefore performed in vacuum or partial vacuum environments. Especially in the production of semiconductor devices, certain manufacturing processes such as erosion, deposition, and ion implantation require vacuum conditions to ensure the chemical purity of the process, as well as to obtain the correct physical conditions suitable for forming active plasmas or providing uniform processes ( Molecular mean free path, etc.). More recently, extreme ultraviolet (EUV) projection printing processes have been devised where reflective surfaces of optical components are highly susceptible to damage in the presence of water or hydrocarbon contamination.

In order to guarantee the ambient conditions for such sensitive vacuum processes, it is very advantageous to have local pressure sensing means that can distinguish contaminant gas species from other gases deliberately introduced into the vacuum chamber. These other gases may be reactive gases, or inert gases, which are required to create the necessary pressure and flow conditions.

Various methods exist in the prior art for species-selective gas pressure measurement.

(1). Residual Gas Analyzer (RGA)

In the prior art, partial pressure analyzers are used to measure the gas composition in vacuum chambers. Such RGAs are typically quadrupole mass spectrometers (QMS), which are very expensive and generally only capable of measuring at low levels of total pressure. In this method, a spectrum is generated which corresponds to the partial pressure of the ions present and as their mass-to-charge ratio (m/z). Typically, gas molecules present in the system dissociate in the ion source, producing smaller ions, which typically appear as lower m/z values in the spectrum.

(2). Sampling residual gas analysis

Figure 1 illustrates an arrangement where the total pressure exceeds the level allowed by the pressure sensing device. Chamber 1 is pumped by a pump 2, typically a turbomolecular pump 2, and a primary pump 3, typically a positive displacement pump. The RGA 4 is connected to the auxiliary chamber 6 , which is connected to the chamber via the current limiting device 5 . The auxiliary chamber 6 is equipped with an additional molecular pump 7 and a positive displacement pump 8 which allows the RGA 4 to operate at an acceptable overall pressure level. This system allows the measurement of the most abundant gaseous species in chamber 1 , but cannot measure gaseous species with very low partial pressures; typically, measurements are limited to relative levels of the order of 50 parts per billion. The additional suction arrangement of the molecular pump 7 and the positive displacement pump 8 also leads to a very expensive system.

(3). Transient residual gas analysis

In order to measure oil return from a suction arrangement it is known to connect the RGA to a vacuum chamber upstream of the pump arrangement. Once the system has reached final pressure, the RGA is closed, allowing the nearby surfaces of the chamber to cool and thus adsorb the oil vapor present in the chamber. When the RGA is turned on again, the concomitant temperature increase causes a rapid desorption of the oil gas, which is detected in the RGA. This results in a highly amplified "spike" of detected oil and gas, which then begins to decay when thermal equilibrium is established again. This amplified response can be used to improve the sensitivity of the measurement system.

(4). Countercurrent residual gas analysis

An alternative approach (often applied in helium leak detection) is to connect the RGA in a counter-flow configuration, as schematically shown in Figure 2. In this arrangement, RGA4 is connected to the inlet of molecular pump 2 . The outlet of this pump 2 is connected to a positive displacement pump 3 which is also connected to chamber 1 . When molecular pump 2 maintains RGA4 at a sufficiently low total pressure, helium is allowed to flow back through molecular pump 2, and thus the arrangement is based on the fact that the compressibility of molecular pump 2 is low for certain gas species, especially light Gases such as helium.

This arrangement provides an improvement in the relative sensitivity of the RGA to gases such as helium, but is not suitable for other gases such as water vapor or hydrocarbons. Since the sensitivity of the device to each gaseous species depends on the compressibility of the molecular pump for that particular species, the system is not suitable for use as a multi-gas analyzer. This method works for helium because molecular pumps have poor compressibility for helium, but is ineffective for most heavy hydrocarbon contaminants because molecular pumps exhibit high compressibility for these heavy molecules. The high cost of the analyzer and the additional pump 2 is also disadvantageous.

(5). Pump Auxiliary Leakage Detection

When the helium leak detection is used in a large vacuum system with its own vacuum pump, the response speed can be improved by connecting the helium leak detector to the foreline of the vacuum pump instead of directly to the vacuum chamber. The response speed in leak detection is related to the S/V ratio, where S is the pumping speed of the leak detection system and V is the volume of the vacuum chamber. Most leak detectors have low suction speeds in the range of a few liters/second, and therefore for large vacuum chambers with correspondingly large vacuum pumps, by connecting them in series with these large vacuum pumps, the effectiveness of the leak detector The suction speed is greatly increased. While this method is very advantageous for helium leak detection, it is impractical for detecting hydrocarbon contamination in chambers due to the high concentration of hydrocarbon contamination typically present in the foreline (often by the primary pump cause).

(6).GC-MS inlet concentrator

In gas chromatography-mass spectrometry (GC-MS), the gas being analyzed can be detected by a variety of techniques, including quadruple frequency analyzers, time-of-flight (TOF) and other methods. To increase the sensitivity of these methods, the "inlet Concentrator", also known as "purification and ventilation" device. These devices consist of a small chamber filled with an adsorbent material, such as activated carbon, whose temperature can be varied. The device is exposed to the gas to be analyzed and then heated rapidly to dissipate any accumulated gas in a short time. The increased concentration improves the sensitivity of the detection device.

(7). Temperature Programmable Desorption Spectroscopy (TPDS)

In this analytical method, gases are adsorbed onto an adsorption layer kept at a low temperature, and the temperature is then raised at a steady-state controlled rate (typically a few K/s). The gas thus dispersed is then detected with a suitable detector, such as a quadrupled mass spectrometer (QMS), but a time-of-flight (TOF) spectrometer may also be used. This method provides a gas pressure spectrum as a function of temperature, which can be interpreted to indicate the relative abundance of gases with different surface binding energies, thus providing valuable information about the gas composition. For example, in Figure 3, the QMS output is shown for formic acid adsorbed to a copper matrix with atomic weight values of m/z=2 and 44. This shows only weakly adsorbed hydrogen (m/z=2), which desorbs at about 280K, and hydrogen and carbon dioxide (m/z=44) desorbed at about 470K.

(8).Gas selective capacitive measuring device

An alternative is to use gas-selective measurement devices, such as capacitive sensors, in which a dielectric material, often a thin-film polymer, changes properties in response to the presence of water vapor. A disadvantage of such devices is that they are only sensitive to certain gaseous species (water vapor in this example), and they also generally have a low absolute sensitivity. They are also prone to drifting. However, because they are only sensitive to specific gas species, they can be measured at low relative partial pressures, where the species of interest is a small fraction of the other gases present. They also have the advantage of being less expensive than residual gas analyzers.

(9).Quartz crystal microbalance (QCM)

These devices are based on measuring the mass of contaminants adsorbed (condensed) onto the surface of the device. The device consists of a quartz crystal, excited by a high-frequency voltage, whose natural frequency is affected by the additional mass due to the adsorbed material. These devices are substance-independent in that they respond only to gases condensing on their surfaces, and their ability to discriminate gases can be improved by coating appropriate materials on their surfaces or by operating the devices at different temperatures, including cryogenic temperatures. Change.

(10).Surface acoustic wave (SAW) sensor

These devices are similar to QCMs, but are based on waves propagating on the surface of the device rather than traveling through its bulk. This greatly improves their sensitivity to small amounts of material adsorbed to their surface.

(11). Metal oxide conductive sensor

These devices use thin layers of metal oxides, usually deposited using chemical vapor deposition (CVD) methods, to create a sensing layer whose conductivity is sensitive to the adsorption material. Special fabrication techniques allow the deposition of arrays of such thin-film devices, each sensitive to a specific set of materials, onto individual substrates. Because these devices rely on oxidation, they are prone to drift in the vacuum environment, which is oxygen-reduced.

(12).Solid electrochemical battery

These sensors consist of a solid electrolyte between two electrodes and are based on detecting the current carried by oxidizing negative ions or the voltage generated. These are suitable for measuring hydrocarbon contamination, but have detection limits that are higher than the limits required in many applications. They should also be operated at high temperatures in order to promote negative ion conduction. In some cases, the electrolyte allows oxygen to diffuse from the atmosphere into the vacuum system, which itself can be a source of process contamination.

These prior art methods (1) to (12) described above have various disadvantages which make them unsuitable for use as methods for quantitatively measuring partial pressure in process applications.

(A). Cost

Prior art methods (1) to (7) basically rely on quadruple frequency mass analyzers or similar high-cost detection devices. In most cases they also require an auxiliary vacuum chamber with its own vacuum pumping equipment. The cost of such systems is often prohibitive for widespread use in many processes.

(B). Explain

Interpretation of quadruple mass spectrometer data is complicated by the fragmentation of large hydrocarbon molecules in the ion source and requires skilled operator interpretation to determine the parent chemical composition from the fragmentation patterns of the light fragments. This makes it unsuitable for automatic process control software.

(C).Sensitivity

RGA has difficulty in discriminating small partial pressures in other mild gas environments. In particular, it is difficult to detect water in an intense argon environment, since doubly ionized argon occurs at 20 amu and water occurs at 18 amu. Also, splitting hydrocarbons produces C ₃ H ₄ ⁺ (40 amu) fragments as well as other fragments with masses close to 40 amu. These are also difficult to identify in the presence of argon. Argon is frequently used in semiconductor manufacturing processes as well as in EUV lithography tools. The low cost of sensors (8) to (11) does not likewise have the disadvantage of being influenced by other gases, but generally has poor sensitivity.

(D).Response speed

The response speed of the sampled residual gas analyzer of the prior art method (2) is low because, referring again to FIG.

(E). The effect on the vacuum system

Prior art methods (6) and (7) involve temperature regulation and are generally used for analytical purposes in order to determine only the relative concentrations of different species. They are generally considered unsuitable for the quantitative measurement of partial pressure in process applications because temperature fluctuations cause increased concentrations of contaminants which adversely affect the process. Typically, this improvement in sensitivity by thermoregulation is determined by the "pulse-to-pulse ratio" - ie the ratio of the time the surface is heated to the time it is kept cool.

(F).Heat radiation and conduction

RGAs as well as solid state electrochemical cells should operate at high temperatures, they transfer heat to the vacuum system by conduction or radiation. This is very disadvantageous in lithography or metrology systems, which are very sensitive to temperature changes.

(G). Charged particles

RGAs typically produce energetic charged particles (ions or electrons) that are also very detrimental to the process.

(H) Pollution generated

Some sensors also generate contamination. In the case of solid state electrochemical cells, diffusion of oxygen from the atmosphere can contaminate the process.

In conclusion, since contamination can be highly damaging to expensive components, it is important that the sensing device is very sensitive to low levels of contamination and also has a fast response time so that it can be adequately protected by the process control software.

In a first aspect, the present invention provides apparatus comprising a vacuum pump having an inlet for receiving fluid and an outlet for discharging aspirated fluid, and in fluid communication with a location intermediate the inlet and outlet for receiving A sensor that receives at least a portion of the fluid and is used to detect the presence of one or more contaminants therein.

Accordingly, a sensor for detecting the presence of one or more contaminants therein is disposed intermediate the pump inlet and the pump outlet. Accordingly, the partial pressure of the contaminant or contaminants detected by the sensor is controlled by the flow of fluid received by the pump inlet, and thus any return flow from the primary pump connected to the pump outlet has a positive effect on the partial pressure of the contaminants. minimal impact.

Preferably, the pump comprises at least first and second suction stations, and said location is located between the first and second stations. Sensitivity of the sensor is increased by operating the sensor at a location where contaminants in the received fluid are compressed to a higher partial pressure by the first suction station of the pump. For example, if the suction speed of the first station is S _a and _that of the second station _is S _b , then the partial pressure of the contaminant at the sensor _, p _s , _is related to The partial pressure _p in the chamber is dependent. Also, the suction effect of the second station keeps the sensor free from contamination present in the foreline.

One of the stations preferably comprises a molecular station. For example, one of the stations may comprise a turbo-molecular station and/or one of the stations may comprise a molecular drag station.

The sensor is preferably connected externally to the pump, in which case the pump comprises a port at said location, a device comprising means for delivering fluid from said port towards the sensor. The device preferably has a housing housing the pump and sensor. Control means may be provided to control the pump and sensor, preferably housed in a common housing.

Preferably, in use, the sensor is sensitive to contaminants in the fluid, such as water vapor or hydrocarbons, substantially independently of the pressure of non-contaminants in the fluid. The sensor is preferably only sensitive to one or more selected contaminants, which provides an easily interpretable sensor output signal and process using automated process control software. Preferably, the sensor is arranged to provide an output indicative of the partial pressure of the contaminant in the fluid.

The sensor can be a quartz crystal microbalance sensor, a surface acoustic wave sensor, or a capacitive-type sensor.

In one embodiment, the sensor is combined with an inlet concentrator to increase its sensitivity, or to improve its ability to discriminate between different gaseous species. The temperature regulation in the inlet concentrator can be essentially stepped, which allows the accumulation of pollutants while the surface is at a lower temperature and rapidly desorbs these accumulated pollutants when the temperature increases rapidly, thereby forming pollutants The large transient concentration of , which is easily sensed.

Optionally, this temperature regulation can be substantially saw-toothed, which allows pollutants to accumulate at lower temperatures and desorb more slowly as the temperature is gradually increased, so that pollutants with lower binding energies are desorb at higher temperatures, and those contaminants with higher binding energies desorb at higher temperatures, thereby providing the ability to identify contaminants with different binding energies. In another alternative, the temperature regulation may be substantially in the form of ramp pulses.

The sensor may include a surface coated with a material for absorbing one or more pollutants. Means may be provided for cooling the sensor to a temperature below ambient temperature, which may improve the sensor's ability to adsorb contaminants of interest.

The apparatus preferably comprises a primary pump connected to the pump outlet for pumping fluid discharged from the vacuum pump. The inlet can be in fluid communication with the vacuum chamber to receive fluid therefrom.

Apparatus according to any preceding claim, wherein the contaminants comprise at least one of water and hydrocarbons.

The present invention also provides in combination a vacuum pump having an inlet for receiving fluid and an outlet for discharging suction fluid, and a sensor in fluid communication with a location intermediate the inlet and outlet for At least a portion of the fluid received by the pump is received and used to detect the presence of one or more contaminants therein.

The present invention also provides a method for detecting the presence of one or more contaminants in an aspirated fluid, comprising receiving fluid at an inlet of a vacuum pump; and receiving the pump from a location intermediate the inlet and outlet of the vacuum pump At least a portion of the fluid is transmitted to a sensor for detecting the presence of one or more contaminants therein.

Features related to the apparatus aspect of the invention are equally applicable to the method aspect of the invention, and vice versa.

Preferred features of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 schematically shows an arrangement of a sampling residual gas analyzer;

Figure 2 schematically illustrates an arrangement of a countercurrent residual gas analyzer;

Figure 3 is a graph showing the desorption spectrum of adsorbed formic acid;

Figure 4 illustrates an embodiment of the invention; and

Figures 5(a) to (c) illustrate various forms of temperature regulation that can be applied to the sensor of Figure 4 .

Referring to FIG. 4, a pump 12, such as a turbomolecular, molecular drag, or compound turbomolecular/molecular drag pump has an inlet 15 connected to the vacuum chamber 11 by an inlet pipe or conduit, and is connected to a second vacuum pump 13 by an outlet pipe or conduit. For example outlet 17 of a dry primary pump. The pump 12 has a first suction portion 12a, and a second suction portion 12b. The first pumping section 12a comprises at least one pumping station, eg at least one turbomolecular station, and the second pumping section 12b comprises at least one pumping station, eg at least one molecular drag station.

A local pressure sensor, or measuring device 14 is connected to the molecular pump port intermediate the pump inlet 15 and the pump outlet 17 via a connecting pipe or conduit 16 . The partial pressure measuring device 14 may be of the QCM (Quartz Crystal Microbalance), SAW (Surface Acoustic Wave) or capacitive type (or similar specific gas sensor), and may also use temperature adjustment to increase its sensitivity, or to improve its discrimination between different gases material capacity. As illustrated in FIG. 4 , a controller 18 may be provided to control the pump 12 and the local pressure measuring device 14 , wherein the pump 12 , the local pressure measuring device 14 and the controller 18 are preferably located in a common housing 19 .

The temperature adjustment can be basically in the form of steps, as shown in Figure 5(a), can be basically in the form of sawtooth, as shown in Figure 5(b), or basically in the form of ramp pulses, as shown in Figure 5(c) shown. The effect of the step regulation is to allow accumulation of pollutants when the surface is at a lower temperature, and rapid desorption of these accumulated pollutants when the temperature increases rapidly, thereby creating a high transient concentration of pollutants, which is easily sensed. The effect of sawtooth regulation is that pollutants accumulate at lower temperatures and then desorb more slowly as the temperature is stepped up so that pollutants with lower binding energies desorb at lower temperatures and those with Higher binding energy contaminants desorb at higher temperatures, thereby providing the ability to identify contaminants with different binding energies.

In use, contaminant gases present in the chamber 11 are sucked by the pump suction portion 12a closest to the pump inlet and compressed to a higher pressure by the suction portion 12a. With this arrangement, the pressure of the pollutant gas is increased such that the pollutant can be more easily detected by the local pressure measuring means 14 .

Contaminant gases may also be present in the vicinity of the outlet duct 17 of this pump 12 due to contamination present in its bearings and lubrication system or its motor drive system, or due to contamination present in the second vacuum pump 14 . Typically, these contaminants do not affect the process chamber 11 because the pump suction portions 12a, 12b provide an effective barrier against these contaminants. It is important, however, that the local pressure measuring device 14 does not respond to buildup of contamination in the outlet conduit. This is ensured by the suction effect of the suction section 12 adjacent to the outlet duct 17 .

The present invention has several significant advantages over the prior art methods (1) to (12) described above.

(A). Cost

The present invention overcomes the cost disadvantage of residual gas analyzers by using lower cost gas selective measurement devices. When the present invention is applied to a vacuum system already using a molecular pump, no additional suction device is required. The absolute sensitivity of the gas selective measuring device is increased by connecting the device at a location in the system where the total pressure is higher.

(B). Explain

The output of this sensor, sensitive only to the contaminant of interest, is inherently easy to interpret and the process uses automated process control software.

(C).Sensitivity

The invention increases the sensitivity of the sensor by operating the sensor in a region where the contaminants present in the vacuum chamber have been compressed to a higher partial pressure. If the suction speed of the suction part 12a of the pump 12 is S _a , and the suction speed of the pump 12 suction part 12b is S _b , the partial pressure p _s of the pollutant at the sensor is passed by the relationship p _s =p _c ×S _a /S _b is related to the partial pressure p _c in the chamber. Furthermore, the suction effect of the suction portion 12a of the pump 12 ensures that the sensor is not affected by contamination present in the foreline.

(D).Response speed

Response speed is increased by using the pumping speed of the first part 12a of the pump 12 to draw contaminants into the sensor.

(E). The effect on the vacuum system

The suction effect of the first part 12a of the molecular pump 12 prevents the process chamber 11 from being adversely affected by fluctuations in the pressure of the contaminants due to temperature regulation. It also insulates the process chamber from contaminants generated by the sensor itself.

(F).Thermal effect

Since the sensor is located away from the process chamber, thermal effects due to the sensor itself or due to radiation or conduction of the temperature regulation in the inlet concentrator are greatly reduced.

In summary, the vacuum pump has, in fluid communication with a location intermediate an inlet for receiving fluid and an outlet for discharging aspirated fluid, for receiving at least a portion of the fluid received by the pump and for sensing the presence of a A sensor for the presence of one or more pollutants.

Claims (30)

1. equipment, comprise aspirator, described aspirator has the outlet that is used to receive the inlet of fluid and is used to discharge the suction fluid, and forms fluid with the entrance and exit position intermediate and is communicated with and is used to receive by at least a portion of the fluid of described aspirator reception and is used to survey the wherein sensor of the existence of one or more pollutants.

2. equipment 1 according to claim 1 is characterized in that, described aspirator comprises at least the first and second suction stations, and described position is between described first and second stations.

3. equipment according to claim 2 is characterized in that, one in these stations comprises the branch substation.

4. according to claim 2 or 3 described equipment, it is characterized in that one in these stations comprises the turbo-molecular station.

5. according to each described equipment in the claim 2 to 4, it is characterized in that one in these stations comprises molecular drag stage.

6. according to the described equipment of each claim of front, it is characterized in that described aspirator comprises port in described position, described equipment comprises from the device of described port towards the sensor conveyance fluid.

7. according to the described equipment of each claim of front, it is characterized in that, comprise the housing that is used to hold described aspirator and sensor.

8. according to the described equipment of each claim of front, it is characterized in that, comprise the device that is used to control described aspirator and sensor.

9. equipment according to claim 8 is characterized in that, comprises the housing that is used for described control gear.

10. according to the described equipment of each claim of front, it is characterized in that in use, described sensor is independent of the pollutant sensitivity in the pressure versus flow body of uncontamination thing in the fluid substantially.

11., it is characterized in that sensor is set to provide the output that can indicate the local compression of pollutant in the fluid according to the described equipment of each claim of front.

12., it is characterized in that described sensor is the little balance sensor of quartz crystal according to the described equipment of each claim of front.

13., it is characterized in that described sensor is a saw sensor according to each described equipment in the claim 1 to 11.

14. equipment according to claim 13 is characterized in that, the pollutant for the treatment of sensing is a hydrocarbon.

15., it is characterized in that described sensor is the solid electro-chemical cell according to each described equipment in the claim 1 to 11.

16. equipment according to claim 15 is characterized in that, the pollutant for the treatment of sensing is a hydrocarbon.

17., it is characterized in that described sensor is gas-selectively capacitor element according to each described equipment in the claim 1 to 11.

18. equipment according to claim 17 is characterized in that, the pollutant for the treatment of sensing is a water vapour.

19., it is characterized in that described sensor is provided with temperature regulation according to the described equipment of each claim of front.

20. equipment according to claim 19 is characterized in that, described temperature regulation is stepped form substantially.

21. equipment according to claim 19 is characterized in that, described temperature regulation is sawtooth form substantially.

22. equipment according to claim 19 is characterized in that, described temperature regulation is the inclined-plane pulse shape substantially.

23., it is characterized in that described sensor has the surface that applies the material be used to absorb one or more pollutants according to the described equipment of each claim of front.

24. according to the described equipment of each claim of front, it is characterized in that, comprise the device that sensor is cooled to be lower than the temperature of environment temperature.

25. according to the described equipment of each claim of front, it is characterized in that, comprise that the backing pump that is connected to outlet is to be used for suction from described aspirator fluid discharged.

26., it is characterized in that described inlet forms fluid with vacuum chamber and is communicated with to be used for receiving fluid from it according to the described equipment of each claim of front.

27., it is characterized in that described pollutant comprises at least a in water and the hydrocarbon according to the described equipment of each claim of front.

28. vacuum pump that combines, it has the outlet that is used to receive the inlet of fluid and is used to discharge the suction fluid, and forms fluid with the entrance and exit position intermediate and is communicated with and is used to receive by at least a portion of the fluid of described pump reception and is used to survey the wherein sensor of the existence of one or more pollutants.

29. a method is used for surveying the existence of one or more pollutants of suction fluid, is included in the vacuum pump inlet place and receives fluid; And at least a portion of the fluid that described pump is received from described vacuum pump inlet and outlet position in the middle is transferred to sensor to be used to survey the existence of one or more pollutants wherein.

30. a method is used for surveying the existence of one or more pollutants of suction fluid, is included in place, the first suction station and receives fluid; And be transported to the second suction station and second fluid streams is transported to sensor to survey the existence of one or more pollutants wherein from the described first suction station with first strand of suction fluid.

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