Load lock gauge

Abstract

The loadlock pressure gauge comprises a housing configured to be coupled to a loadlock vacuum chamber. The housing supports an absolute vacuum pressure sensor providing an instantaneous high vacuum pressure signal over a range of high vacuum pressures, and a diaphragm differential pressure sensor providing an instantaneous differential pressure signal between the loadlock pressure and ambient pressure. The housing further supports an absolute ambient pressure sensor. A low vacuum absolute pressure is calculated from the instantaneous differential pressure signal and the instantaneous ambient pressure signal. A controller of the housing can recalibrate the diaphragm differential pressure sensor based on a measured voltage of the sensor and a measured ambient pressure during normal operation of the gauge through routine cycling of pressure in the loadlock.

Description

Related applications

[0001] This application is a continuation of U.S. Patent Application No. 17 / 154,698, filed on January 21, 2021. All teachings of the above application are incorporated herein by reference. [Background technology]

[0002] A load lock is a standard mechanism for industrial and laboratory vacuum process chambers. As shown in Figure 1, the sample 102 is fed into the load lock 106 through the load lock port 104, while the load lock 106 is vented to ambient (atmospheric) pressure. Most load locks are expected to remain particle-free when exposed to the ambient pressure. Once the sample is placed inside and secured, the load lock port is closed and pump-down towards a high vacuum begins through the vacuum pump 108. When the pressure in the load lock is sufficiently low, the transfer port 110 is opened to connect the load lock chamber 106 to the process chamber 112, which has its own vacuum pump 112 and pressure gauge 107. The sample is then transferred through the transfer port to the process chamber in which it will be processed. Once the process is complete, the sample is returned to the load lock, which is still under high vacuum, the transfer port is closed, and the load lock is vented so that the processed sample can be removed when the load lock port is opened to the surroundings or to a front-opening unified pod (FOUP).

[0003] There are several important requirements for the proper operation of the load lock.

[0004] The load lock must remain particle-free at all times. This requires ensuring that when the load lock port is opened, it is slightly positive pressure relative to the ambient pressure. This guarantees that when the load lock port is opened, any airflow will escape from the chamber, preventing dust particles from the room from entering the load lock chamber. If there is no inflow of ambient air, dust intrusion is avoided. Accurate differential pressure measurement between the load lock chamber and the ambient pressure is necessary to ensure that the load lock port is opened only when the pressure in the load lock chamber is greater than the ambient pressure. A load lock pressure gauge is expected to provide a very accurate measurement of the differential.

[0005] The load lock pressure must also be carefully monitored during pump-down. The transfer port is opened only when the pressure is low enough to prevent the transfer of dust particles from the load lock chamber to the process chamber. Generally, a pressure of less than 1 Torr is required in the load lock chamber to prevent dust particles from being stirred up into the high-vacuum process chamber during transfer. Accurate absolute pressure measurement in the high-vacuum load lock chamber is required and is requested by the load lock operator.

[0006] Therefore, the load lock chamber needs to be fitted with a high-precision pressure measuring gauge capable of performing two very important measurements with high accuracy: a. Before opening the load lock port to ambient conditions, measure the differential pressure between the load lock chamber and the surroundings. b. In particular, measure the absolute pressure inside the load lock chamber under high vacuum before opening the transfer port to the process chamber.

[0007] Gauges used for pressure monitoring and control in load lock chambers are often called load lock gauges.

[0008] A load lock gauge that met the above requirements was disclosed in U.S. Patent No. 6,672,171 (Patent Document 1). The gauge included both a high vacuum absolute pressure sensor in the form of a micro-electromechanical system (MEMS) Pirani sensor, particularly a MicroPirani® gauge, and a differential pressure sensor in the form of a differential diaphragm sensor having one side of the diaphragm exposed to the load lock pressure and the opposite side of the diaphragm exposed to ambient pressure. While the device met the above requirements, the MEMS Pirani gauge, which provided the high accuracy at the high vacuum pressure required to control the transfer port, had an accuracy of only about + / -25% at ambient pressure. However, some process engineers had an expectation for accurate absolute pressure measurement at the load lock throughout the pressure range from ambient to high vacuum. U.S. Patent No. 6,909,975 (Patent Document 2) addressed that additional requirement.

[0009] In one embodiment of U.S. Patent No. 6,909,975, the differential pressure sensor was replaced with two absolute pressure sensors: a piezoresistive diaphragm absolute pressure sensor that was accurate at the low vacuum pressure of the load lock, and an absolute pressure sensor that was accurate at the ambient pressure outside the load lock. The differential pressure requirement for opening the load lock port was then met by calculating the difference between the low vacuum pressure sensor and the ambient pressure sensor. The full absolute pressure range was obtained by using a Pirani sensor at high vacuum, an absolute piezoresistive diaphragm sensor at low vacuum, and a mixture of the two outputs at intermediate vacuum levels. An early embodiment of that embodiment was the MKS390 pressure gauge. The MKS390 gauge included a MEMS Pirani sensor, an absolute piezoresistive diaphragm sensor, and a barometer. It further included an ionization pressure gauge, as also proposed in U.S. Patent No. 6,909,975, to provide very high vacuum absolute pressure readings at even higher vacuums than that which could be supported by the Pirani sensor.

[0010] The difficulty in using individual absolute gauges to calculate the differential pressure of an object lies in the fact that the differential pressure of the object is not directly detected, and calculations based on pressures detected by separate sensors are prone to errors. Process engineers prefer highly reliable direct differential readings from differential diaphragm sensors.

[0011] U.S. Patent No. 6,909,975 presented a method in which the output of a diaphragm differential pressure sensor could be used to provide accurate absolute pressure readings at low vacuum pressures. Thus, a correlation coefficient between absolute pressure and differential pressure measurements was taken where the absolute pressure in the chamber could be accurately and reliably measured, and the correlation coefficient was preserved. The differential pressure measurement was then adjusted with the correlation coefficient to provide a virtual absolute pressure measurement. While the correlation coefficient could be taken and preserved at atmospheric pressure when the differential pressure measured zero, a preferred method was to measure the output of the differential pressure sensor at a high vacuum equal to the negative ambient pressure, and to preserve the absolute value as the correlation coefficient. This correlation coefficient could then be added to the differential output of the differential pressure sensor to provide absolute pressure readings across the entire pressure range of the load lock. The output of the Pirani sensor then provided accurate high-vacuum absolute pressure readings, the virtual absolute pressure calculated from the differential pressure sensor output provided the absolute pressure at low vacuum, and a mixture of the two provided the absolute pressure at intermediate vacuum pressures. This approach was used in the highly successful MKS901P gauge, which was the most widely used load lock gauge in the industry for over a decade.

[0012] The MKS901P gauge is based on a MEMS Pirani sensor for absolute high vacuum (low pressure) output and a differential piezoresistive diaphragm (DPRD) sensor for differential output and low vacuum virtual pressure output. Each time the load lock is pumped to less than approximately 1 Torr, the absolute value of the differential pressure is measured and stored in memory as a positive number of constant magnitude. This is essentially a highly accurate, up-to-date measurement of the ambient pressure performed by the DPRD itself. Thereafter, all differential readings from the DPRD can be subtracted from this constant value to provide the absolute pressure in the load lock chamber. Since the DPRD is used to generate the stored value of the ambient pressure (during pump-down) and then, during venting, to calculate the load lock chamber pressure, the readings are more accurate at low vacuum than those provided by the Pirani sensor. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] U.S. Patent No. 6,672,171 [Patent Document 2] U.S. Patent No. 6909975 [Overview of the Initiative] [Problems that the invention aims to solve]

[0014] The MKS901P gauge uses the virtual pressure approach of U.S. Patent No. 6,909,975 to provide the highly accurate high vacuum pressure required from a Pirani sensor to control the transfer port, the highly accurate differential pressure to control the load lock port, and even highly accurate absolute pressure at low vacuum. To maintain its highly accurate low vacuum absolute pressure, it is crucial that the correlation coefficient corresponds to the actual ambient pressure. Therefore, the correlation coefficient is updated whenever the load lock pressure is reduced to high vacuum. However, ambient pressure fluctuations of + / -10 Torr can occur throughout the day. If the correlation coefficient is not updated sufficiently, ambient pressure fluctuations can lead to inaccuracies in the low vacuum absolute pressure readings. While these readings are not critical for the differential pressure at the transfer port or load lock port, they are worse than optimal. To provide even better accuracy, even at low vacuum pressure, another absolute pressure sensor, such as the absolute piezoresistive diaphragm sensor used in the MKS390 product, could be added to the gauge. However, such sensors significantly increase the overall cost of the gauge and have the undesirable drawback of hysteresis. [Means for solving the problem]

[0015] To improve the accuracy of absolute low vacuum pressure readings derived from diaphragm differential pressure sensors at a reasonable cost, absolute ambient pressure sensors are added to the gauge. Such gauges include a diaphragm exposed to a reference vacuum on one side and ambient pressure on the opposite side. They are widely used as barometers, for example, in altimeters, and thus provide highly accurate ambient pressure readings at a low additional cost. By including an ambient pressure sensor in the gauge, it is no longer necessary to store correlation coefficients in specific process conditions. Rather, accurate instantaneous ambient pressure can be added to the differential pressure with high accuracy over the entire range of load lock pressure. The ambient pressure sensor included in the gauge also enables synchronization of the Pirani gauge with respect to ambient pressure, and automatic recalibration of the differential pressure sensor during normal operating cycles based on the detected ambient pressure.

[0016] The pressure gauge comprises a housing configured to be coupled to a vacuum chamber. An absolute vacuum pressure sensor within the housing is configured to be exposed to the vacuum chamber and is operable at high vacuum to provide an accurate instantaneous high vacuum pressure signal over a high vacuum pressure range. A diaphragm differential pressure sensor within the housing comprises a diaphragm configured so that one side is exposed to the vacuum chamber and the opposite side is exposed to ambient pressure to provide an instantaneous differential pressure signal. An absolute ambient pressure sensor within the housing is exposed to ambient pressure to provide an instantaneous ambient pressure signal. A controller within the housing receives the high vacuum pressure signal from the absolute vacuum pressure sensor, the differential pressure signal from the diaphragm differential pressure sensor, and the ambient pressure signal from the ambient pressure sensor. The controller calculates the calculated absolute pressure in the vacuum chamber from the instantaneous differential pressure signal and the instantaneous ambient pressure signal, both of which are detected over a low vacuum pressure range. The controller provides, as outputs, a differential pressure output from the diaphragm differential pressure sensor signal, an absolute vacuum pressure output taken from the absolute vacuum pressure sensor signal at high vacuum, and an absolute vacuum pressure output from the calculated absolute pressure at low vacuum.

[0017] The controller may be further configured to calibrate the diaphragm differential pressure sensor based on the ambient pressure bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at ambient pressure, the full-scale bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at full-scale high vacuum, and the full-scale ambient pressure measured by the absolute ambient pressure sensor when the vacuum chamber is at full-scale high vacuum.

[0018] The controller may be configured to calibrate the diaphragm differential pressure sensor by measuring the ambient pressure bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at ambient pressure, measuring the full-scale bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at full-scale high vacuum, and measuring the full-scale ambient pressure with an absolute pressure sensor when the vacuum chamber is at full-scale high vacuum. The controller may determine the gain of the diaphragm differential pressure sensor from the ambient pressure bridge voltage, the full-scale bridge voltage, and the full-scale ambient pressure. Thereafter, the instantaneous differential pressure signal may be determined from the instantaneous bridge voltage, the ambient pressure bridge voltage, and the gain. The gain may be

[0019] a = (V b,0 - V b,FS ) / P amb,FS

[0020] calculated from, where a is the gain, V b,0 is the ambient pressure bridge voltage, V b,FS is the full-scale bridge voltage, and P amb,FS is the full-scale ambient pressure. The pressure difference may be

[0021] P D = (V b - V b,0 ) / a

[0022] calculated from, where P D is the instantaneous pressure difference and V b is the instantaneous voltage from the diaphragm differential pressure signal.

[0023] The pressure gauge may further provide an output of the instantaneous ambient pressure from the absolute ambient pressure signal.

[0024] The absolute vacuum pressure sensor may have an accuracy of 7% or better at a high vacuum pressure of 5 Torr. The calculated absolute pressure from the instantaneous differential pressure readings may have an accuracy of 1% or better at 60 Torr.

[0025] The controller may be configured to calculate a mixed pressure at intermediate vacuum pressures from an instantaneous high vacuum pressure signal and a calculated absolute pressure. The controller may output as a chamber pressure signal an instantaneous high vacuum pressure signal over a high vacuum pressure range, a calculated absolute pressure over a low vacuum pressure range, and a mixed pressure at intermediate vacuum pressures.

[0026] The controller may be configured to zero out the absolute vacuum pressure signal at ambient pressure.

[0027] The absolute vacuum pressure sensor may be a thermal conductivity sensor, such as a MEMS Pirani sensor. The diaphragm differential pressure sensor may be a differential piezoresistive diaphragm pressure sensor. Other differential diaphragm gauges may also be used, but piezoresistive gauges have the advantage of being small and inexpensive. The absolute ambient pressure sensor may comprise a diaphragm that is exposed to a reference vacuum on one side and to ambient pressure on the opposite side.

[0028] In a method for controlling the load lock port and transfer port of a load lock, an instantaneous high vacuum pressure signal may be provided from an absolute vacuum pressure sensor. An instantaneous differential pressure signal may be provided from a diaphragm differential pressure sensor having a diaphragm exposed to the load lock on one side and to ambient pressure on the opposite side. An instantaneous ambient pressure signal may be provided from an absolute ambient pressure sensor. In an electronic controller, the calculated absolute ambient pressure may be calculated from the instantaneous differential pressure signal and the instantaneous ambient pressure signal. The transfer port is opened to the high vacuum chamber only after the load lock has reached a sufficiently low pressure, as indicated by the instantaneous high vacuum pressure signal from the absolute vacuum pressure sensor. The load lock port is opened to the ambient only after the instantaneous differential pressure signal from the diaphragm differential pressure sensor indicates a load lock pressure at least as high as the ambient pressure. The absolute vacuum pressure output from the controller is an absolute vacuum pressure output taken from the high vacuum absolute vacuum pressure sensor and the calculated low vacuum absolute pressure. [Brief explanation of the drawing]

[0029] The foregoing is evident from the following more specific description of exemplary embodiments as shown in the attached drawings, where similar reference numerals refer to the same parts through different drawings. The drawings are not necessarily to scale, and instead the emphasis is on illustrating embodiments. [Figure 1] This is a schematic diagram of a load lock with a load lock gauge, where the load lock is coupled to the process chamber. [Figure 2] This is a cross-sectional view of a load lock pressure gauge embodying the present invention. [Figure 3A] Figure 2 is a schematic cross-sectional view of the diaphragm differential pressure sensor in one of the three different pressure conditions of the load lock. [Figure 3B] Figure 2 is a schematic cross-sectional view of the diaphragm differential pressure sensor in yet another of the three different pressure conditions of the load lock. [Figure 3C] Figure 2 is a schematic cross-sectional view of the diaphragm differential pressure sensor in yet another of the three different pressure conditions of the load lock. [Figure 4] Figure 2 is a schematic cross-sectional view of the ambient pressure sensor. [Figure 5] Figure 2 is a schematic cross-sectional view of a MEMS Pirani gauge. [Figure 6] Figure 2 is a flowchart of the pressure measurement loop for the gauge. [Figure 7] These are graphs of the bridge voltage output from the differential pressure sensors, plotted against the differential pressure, as shown in Figures 3A-C. [Figure 8A] This is a flowchart of the pressure gauge controller microprocessor for determining the differential pressure sensor offset. [Figure 8B] This is a flowchart of the controller microprocessor for determining the gradient and performing full-scale calibration of a differential pressure sensor. [Figure 9] This is a schematic diagram of a system similar to Figure 1, but with an additional very high vacuum pressure sensor coupled to the load lock. [Modes for carrying out the invention]

[0030] An exemplary embodiment is described below.

[0031] Multiple sensor gauges offer the ability to accurately measure both absolute and differential pressure in load lock chambers across the full pressure range, without the limitations of current equipment. MEMS Pirani sensors provide high vacuum absolute pressure for transfer port control. Differential piezoresistive diaphragm (DPRD) pressure sensors provide the single-sensor differential pressure measurement that industry has come to expect from the MKS901P and its load lock switch.

[0032] The addition of a barometer enables real-time updates of ambient pressure measurements, providing the latest absolute pressure inside the load lock chamber from the differential pressure sensor and improving the fixed ambient pressure correlation coefficient, which is stored by the 901P and updated only during load lock pump-downs. This eliminates the need to perform repeated pump-downs throughout the day to know the ambient pressure and calculate the accurate load lock chamber absolute pressure from DPRD measurements.

[0033] There are also opportunities to synchronize sensors.

[0034] Whenever the high vacuum inside the load lock chamber is less than approximately 0.5 Torr, the differential sensor can synchronize with the ambient sensor. When the absolute pressure is less than 0.5 Torr, which is the approximate accuracy of a barometer, it can be ensured that the ambient sensor and DPRD read within the same approximately 0.5 Torr. Otherwise, the differential pressure sensor can be automatically recalibrated as discussed below. The ambient sensor continues to track the transitioning ambient pressure with high accuracy, ensuring accurate calculation of the load lock chamber absolute pressure. The ambient sensor is precisely calibrated before use and can be relied upon during operation for reliable measurement of ambient pressure.

[0035] The MEMS Pirani atmospheric readings can be synchronized each time the load lock chamber is vented to the ambient pressure. At this point, the differential sensor reads zero differential pressure, and the Pirani synchronizes with the barometer. This improves the accuracy of the Pirani sensor at near ambient pressure.

[0036] Figure 2 shows a pressure gauge having a specific application as a load lock gauge, which is based on but improves upon the MKS901P gauge. Block 202 has a flange 204 for mounting the gauge to the side of the load lock chamber. Volume 206 within the block is exposed to the load lock chamber. A conduit 208 from volume 206 through the block exposes tube 210 to the load lock pressure. Tube 210 extends to a differential pressure sensor 212, which may be a differential piezoresistive diaphragm sensor (DPRD) (the gauge is shown only as a solid block in Figure 2; further details are shown in Figures 3A-C). The differential sensor 212 is mounted on a sensor board 213, which includes a protective can 215 that allows exposure of the differential sensor to ambient pressure from outside the gauge.

[0037] The second conduit 214 of block 202 extends to a volume 216 into which the MEMS Pirani absolute pressure sensor 218 is exposed (the sensor 218 is shown only as a solid block in this figure and is described further in relation to Figure 5). The Pirani gauge 218 is suspended below the sensor board 213 by electrical pins 219.

[0038] An additional sensor not available in the 901P gauge is an ambient pressure sensor 220, which may be a conventional barometer. Sensor 220 is exposed only to ambient pressure. Barometers are widely available with high accuracy of less than ±2 Torr. Through recalibration, their accuracy can be improved to ±0.5 Torr, preferably ±0.25 Torr, or better. Barometers typically include temperature compensation.

[0039] Additional electronic components, including the controller microprocessor 226, are mounted on board 213 and microprocessor board 222. The sensors and electronic components are enclosed within a protective housing 223. Communication with the pressure gauge is made via an electrical connection 224. As will be discussed in detail below, the microprocessor 226 is responsible for pressure measurement and output. In particular, the microprocessor is responsible for pressure synchronization of the Pirani sensor and synchronization and calibration of the differential diaphragm sensor.

[0040] Figures 3A-3C are schematic diagrams of the differential pressure sensor 212 in three different states. The sensor includes a diaphragm 302 exposed to the ambient pressure of the upper volume 304. Its opposite side is exposed to the load lock pressure in a chamber 306 that is in fluid communication with the tube 210. The diaphragm 302 may be made of, for example, silicon and has a piezoresistive strain element mounted on it. When the pressures in volumes 304 and 306 are the same, the diaphragm has zero deflection, as shown in Figure 3A, and a calibrated device provides a zero differential pressure output. When positive pressure is applied to the load lock, the diaphragm is pushed upward, as shown in Figure 3B, providing a voltage output that is converted into a positive differential pressure output. When the load lock is evacuated, the diaphragm is pulled downward, as in Figure 3C, and the sensor outputs a negative voltage output that is converted into a negative differential pressure reading. This is a direct, gas-type-independent differential pressure reading.

[0041] Figure 4 is a schematic diagram of a barometer used in an ambient pressure sensor. It also includes a diaphragm, such as a silicon diaphragm 402, whose top surface is exposed to a volume 404 that is exposed to ambient pressure through a hole 408 in the housing 410. The bottom surface of the diaphragm 402 is exposed to a closed chamber of reference pressure. The sensor may be a piezoresistive diaphragm sensor that provides a voltage output by bending the diaphragm driven by the ambient pressure relative to the reference pressure in the chamber 406. When properly calibrated, the voltage output is converted into a very accurate reading of the ambient pressure.

[0042] The high vacuum absolute pressure sensor 218 is a thermal conductivity sensor, in particular a MEMS Pirani sensor. Other sensors, such as wire-based Pirani sensors, may also be used. A thermal conductivity sensor measures pressure based on the relationship between the temperature of a heated sensor resistance and the amount of heating power applied to the sensor resistance. For example, a thin wire (sensor resistance) is heated to a constant temperature (T s The amount of heating power required to maintain the wire at a certain temperature may be monitored. As the gas pressure increases, the thermal conductivity of the gas increases, and the gas removes more heat from the heated wire, increasing the heating power required to maintain the wire at a constant temperature. A gas species-dependent calibration curve that correlates heating power with pressure enables pressure measurement. Calibration is typically performed in a factory against pure nitrogen gas. This is an indirect pressure measurement where heating power is proportional to the gas pressure.

[0043] This principle is used in the well-known Pirani gauge, where heat loss is measured in a Wheatstone bridge network that serves both to heat the sensing element and to measure its resistance. In the Pirani gauge, the temperature-sensing resistor is connected as one arm of the Wheatstone bridge. The temperature-sensing resistor is mounted in a chamber exposed to a vacuum environment where pressure is measured.

[0044] Conventional Pirani gauges are calibrated to several known pressures to determine the relationship between gas pressure and power loss to the gas or bridge voltage. In this case, assuming end losses and radiation losses remain constant, the unknown pressure of the gas may be directly determined by the power lost to the gas or related to the bridge voltage in the bridge balance.

[0045] The specific thermal conductivity sensor used here is a MEMS Pirani sensor, as shown in Figure 5. This sensor includes a silicon nitride film 502 extending throughout a chamber having volumes 504 and 506. Volumes 504 and 506 communicate with volume 216 of a pressure gauge, which is therefore the load lock pressure. The resistive element to be heated is formed on the film 502 at 508. Due to the geometric shape of the sensor, convection cannot occur within the cavity, and consequently, the sensor is not affected by its mounting position. Gas molecules are transferred by diffusion only to the heated element, where the heat loss to the gas is measured. Similar to conventional Pirani gauges, heat is conducted from the heated resistor to the ambient gas at 510 and 512 from the resistive element on the film 502. As with conventional Pirani sensors, as the gas pressure increases, the thermal conductivity of the gas increases, and the gas takes more heat from the heated resistor, increasing the heating power required to maintain the wire at a constant temperature. The calibration curve correlates heating power with pressure. MEMS Pirani sensors provide very accurate pressure readings in high vacuum and are therefore particularly suitable for controlling transfer ports to high vacuum process chambers. However, as mentioned above, they are not as accurate at higher pressures that approach ambient pressure.

[0046] To obtain accurate absolute pressure readings at low vacuum without requiring expensive and potentially inaccurate absolute pressure sensors, this system determines the absolute pressure of the load lock from the differential pressure detected by a DPRD sensor. Since the differential pressure is related to the ambient pressure, the absolute vacuum pressure can be determined by adding the ambient pressure. This calculation is similar to the approach in U.S. Patent No. 6,909,975, except that the actual instantaneous ambient pressure is used in the calculation rather than a conserved correlation coefficient. If both sides of the differential pressure sensor are exposed to the ambient pressure, the differential pressure reading is zero. Therefore, calculating the absolute pressure from the ambient differential pressure requires that the ambient pressure detected by the barometer be added to the differential pressure. Similarly, in load locks evacuated to lower pressures, their absolute pressures are: P LL =P D +Pamb (1) It can be calculated from, where P LL This is the absolute pressure of the load lock, P D This is the differential pressure, P amb This represents the instantaneous ambient pressure detected by the barometer, i.e., the ambient pressure at the moment of calculation.

[0047] The load lock pressure gauge derives the absolute pressure output P of the load lock pressure from the Pirani gauge at high vacuum (very low pressure) and from the differential pressure of the DPRD sensor plus the ambient pressure from the barometer at low vacuum (pressure closer to ambient pressure). LL Provides load lock pressure P LL A single output for this purpose transitions from the Pirani measurement to the differential plus ambient measurement, so if the load lock gas is anything other than the sensor calibrated to pure nitrogen gas, the difference between the two measurements can be expected. To avoid the step in output due to that transition, a technique well-known in industry and used in the MKS901P product is to mix the two measurements over a pressure range. In one example of mixing, two factory-set thresholds are defined when the measurements are taken either individually from the Pirani sensor, individually from the differential and barometer sensors, or as a mixture of the two. Threshold P X,L If the value falls below this threshold, only the Pirani measurement is used. X,H If it exceeds P D and P amb Only measurements calculated from are used. Between those thresholds, some form of mixture is used from pure Pirani measurements to pure P D Plus P amb This allows for continuous transitions up to the measured value. The mixing may be linear or nonlinear, but near the lower threshold, the mixed value is weighted more towards the Pirani measured value, and towards the upper threshold, the measured value is weighted more towards the calculated measured value. A typical lower threshold is 20 Torr, which may be user-configurable, and an upper threshold is 60 Torr, which may also be user-configurable.

[0048] The upper and lower thresholds may be the same, or they may be simple values ​​P. XFor example, it may be set to approximately 40 Torr. In either case, there is no mixing, but a rapid transition between readings as pressure up and down, and pressure output P during the transition. LL There are possible steps.

[0049] Figure 6 is a flowchart of pressure measurement by a pressure gauge via a measurement loop. In any order, at 602, the load lock pressure is measured by a Pirani sensor; at 604, the difference between the load lock pressure and ambient pressure is measured by a DPRD sensor; and at 606, the ambient pressure is measured by a barometer. Each of these measurements is available to the load lock operator through the measurement loop. At 608, the Pirani pressure reading P MP The lower mixed threshold P X,L It is determined whether it is smaller or smaller. If so, at 610, the load lock pressure P LL is P MP It is set to be equal to . If the Pirani pressure at 608 is not less than the lower threshold, then at 612, the Pirani pressure is equal to the upper mixed threshold P X,H It is compared to the load lock pressure P if the Pirani pressure exceeds its threshold in 614. LL P D and P amb It is taken to be equal to the sum of the two. If the Pirani pressure is not below the lower threshold and not above the upper threshold, the pressure is in the mixed pressure range, and in 616, the load lock pressure P LL P is the Pirani pressure P MP And the calculated pressure P D Plus P amb The pressure is determined from the mixture of the following. The pressure defined in step 610, 614, or 616 is made available to the user. The system then loops back to take another set of measurements. During operation, the pressure P provided by the Pirani sensor is MP , differential pressure P provided by DPRD D P provided by the barometer amb , and the determined load lock pressure P LL It is available to users for both control and monitoring purposes.

[0050] The DPRD sensor is factory calibrated and has an accuracy of ±1% Torr or better. The sensor output is very stable and linear (typically better than 0.1% linearity and better than ±1% repeatability over the pressure range), and the sensor maintains its calibration well. However, over time there may be voltage offset and gain variations that need to be maintained to maintain accuracy. Having real-time ambient pressure measurements during operation allows for periodic calibration of the DPRD during normal operation.

[0051] The output signal from the DPRD is approximately linear to the bridge voltage V, which is related to the differential pressure on the diaphragm. b The relationship between the bridge voltage and differential voltage is shown in Figure 7. LL P amb Equal to, therefore, P D When the load lock chamber is exposed to the ambient light, the bridge voltage is offset somewhat V, such that V is equal to 0. b,0 When the load lock is evacuated to vacuum pressure, the bridge voltage becomes more negative. LL Since it is almost 0, usually less than 1.2 Torr, and probably around 0.5 Torr, the maximum negative deflection of the DPRD diaphragm is towards the load lock pressure, and the full-scale bridge voltage V b,FS P D =-P amb,FS It is reached at V. b and P D The relationship is approximately linear, as follows:

[0052] V b =V b,0 V b,0 -V b,FS ) / P amb,FS )P D (2)

[0053] Here, V b,0 This is the voltage offset at zero differential pressure. D The gain applied is the gradient a in Figure 7.

[0054] a=(V b,0 -V b,FS ) / P amb,FS (3)

[0055] This can be seen from this equation: b = offset = V b,0 Simplifying equation 2, we get the pressure difference P. D teeth,

[0056] P D =(V b -b) / a (4)

[0057] That is the case.

[0058] The MKS901P gauge is factory calibrated. This calibration is typically done for the lifespan of the gauge, but the gauge is also calibrated for differential pressure P D The gauges can be recalibrated in the field by using a special code via communication connection 22 to determine the offset b and gradient a for subsequent measurements, using an accurate external ambient pressure calibration gauge, and by operating the load lock gauge through ambient and high-pressure conditions. The gauges disclosed herein can self-calibrate during normal operation.

[0059] Whenever the load lock is exposed to the surroundings, offset V is indicated by the system controller via communication input 224. b,0 This can be checked, and the saved value can be updated as needed. Then, at approximately zero load lock pressure, the full-scale V b,FS and P amb,FSBoth can be measured to enable the calculation of the gradient (gain) a. This allows the DPRD calibration parameters for the offset and gradient to be re-determined in each cycle of operation as needed. During operation, the calibration procedure performed by the pressure gauge microprocessor 226 may be substantially the same as that performed at the factory. A major advantage of including the ambient pressure sensor 220 in the pressure gauge is that the procedure can be performed automatically in the field whenever it is determined to be necessary, for example, when the absolute pressure indicated by the differential pressure calculation at high vacuum does not match a negative number of the measured ambient pressure.

[0060] Figure 8A shows the determination of the offset under microprocessor control. In 802, for example, when the load lock is vented to the surroundings when signaled by the system controller, the load lock pressure P LL The ambient pressure is V amb Equal to, differential P D It is known to be zero. In 804, when the load lock is vented, P D Bridge voltage V at =0 b V is b,0 However, voltage V is passed through a high-resolution analog-to-digital converter. b The voltage is measured by reading it. The measured voltage is stored in the calibration memory of the 806 as voltage offset b.

[0061] The gradient is determined for full-scale calibration in the microprocessor procedure shown in Figure 8B. The load lock is pumped down to approximately zero load lock pressure, within barometer accuracy, as measured by the Pirani sensor during normal operation. At that pressure, in 808, the pressure difference is -P amb,FS It is equal to the full-scale bridge voltage V at 810. b,FS The exact full-scale ambient pressure P is measured. amb,FS This is measured using a barometer. In 812, V b,FS and P amb,FSBoth are stored in the calibration memory. In 814, the gradient of FIG. 7, which is the gain applied to determine the differential pressure, is calculated. That gradient a is stored in the calibration memory in 816.

[0062] After that, the stored value V b,0 and a are combined with the instantaneous voltage V of any pressure in order to calculate the pressure differential P D using Equation (4). The load lock pressure P b can be calculated by Equation (1) using the real-time measurement values of P LL and P D and P amb . Temperature compensation of the DPRD measurement value may also be provided, such as 901P.

[0063] In addition to the multi-sensor embodiments described herein, the scope of the present disclosure can be extended to very high vacuum and ultra-high vacuum levels by adding a fourth sensor, such as an ionization sensor, to the array as shown at 902 in FIG. 9. When an ionization gauge (low-temperature or high-temperature embodiment) is added, here the user can handle a load lock chamber that needs to be pumped down to a much lower pressure than the Pirani sensor can monitor before the transfer valve is activated. Such multi-sensors are very versatile when enabling an accurate vent around the load lock chamber and when verifying the high-vacuum level before transferring a sample to the process chamber at high vacuum (very low pressure).

[0064]

[0065] ​This disclosure has long focused on the addition of standard barometric pressure sensors to provide real-time, continuous ambient pressure measurements. Barometers are unique in that they enable the measurement of ambient pressure between sea level and the highest peak with very high resolution. They are commonly used as altimeters. However, the scope of this disclosure extends beyond those standard sensors and includes any sensing technology capable of accurately measuring ambient pressure. This includes high-end diaphragm deflection sensors, such as piezoresistive capacitive and optical deflection diaphragm sensors.

[0066] This system is not limited to the use of differential piezoresistive diaphragm sensors. Apparatus may similarly be constructed using differential diaphragm sensors based on optical and capacitive measurements of differential diaphragm deflection. Capacitive and optical diaphragm deflection pressure sensors can be made from, for example, metal, ceramic, or sapphire films.

[0067] All patents, published applications, and references cited herein are incorporated in their entirety by reference.

[0068] While exemplary embodiments have been illustrated and described in detail, it will be understood by those skilled in the art that various modifications may be made to the form and details without departing from the scope of the embodiments included in the appended claims. Furthermore, the present invention includes the following embodiments. [Aspect 1] A housing configured to be coupled to a vacuum chamber, An absolute vacuum pressure sensor within a housing, configured to be exposed to the vacuum chamber and capable of operating in high vacuum to provide an accurate instantaneous high vacuum pressure signal, A diaphragm differential pressure sensor in a housing, comprising a diaphragm configured such that one side is exposed to the vacuum chamber and the opposite side is exposed to ambient pressure, in order to provide an instantaneous differential pressure signal, To provide an instantaneous ambient pressure signal, an absolute ambient pressure sensor within the housing is exposed to ambient pressure, A controller within the housing receives the high vacuum pressure signal from the absolute vacuum pressure sensor, the differential pressure signal from the diaphragm differential pressure sensor, and the ambient pressure signal from the ambient pressure sensor. Equipped with, The controller calculates the calculated absolute pressure of the vacuum chamber from the instantaneous differential pressure signal and the instantaneous ambient pressure signal, both of which are detected throughout the vacuum pressure range. The controller provides, as outputs, a differential pressure output from the diaphragm differential pressure sensor signal, an absolute vacuum pressure output taken from the absolute vacuum pressure sensor signal in high vacuum, and an absolute vacuum pressure output from the calculated absolute pressure in low vacuum. Pressure gauge. [Aspect 2] The aforementioned controller The ambient pressure bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at ambient pressure, The full-scale bridge voltage of the diaphragm differential pressure sensor when the vacuum chamber is at full-scale high vacuum, and Full-scale ambient pressure measured by the absolute ambient pressure sensor Based on this, the diaphragm differential pressure sensor is further configured to calibrate the diaphragm differential pressure sensor. A pressure gauge as described in Embodiment 1. [Aspect 3] The aforementioned controller The ambient pressure bridge voltage of the diaphragm differential pressure sensor is measured when the vacuum chamber is at ambient pressure. The full-scale bridge voltage of the diaphragm differential pressure sensor is measured when the vacuum chamber is in a full-scale high vacuum state. The absolute ambient pressure sensor measures the full-scale ambient pressure, and The gain of the diaphragm differential pressure sensor is determined from the ambient pressure bridge voltage, the full-scale bridge voltage, and the full-scale ambient pressure. The diaphragm differential pressure sensor is further configured to be calibrated by the above, Subsequently, the instantaneous differential pressure signal is determined from the instantaneous bridge voltage, the ambient pressure bridge voltage, and the gain. A pressure gauge as described in Embodiment 1. [Aspect 4] The gain is a=(V b,0 -V b,FS ) / P amb,FS It is calculated from, and here, a is the gain, V b,0 This is the ambient pressure bridge voltage, V b,FS This is the full-scale bridge voltage, and, P amb,FS This is the full-scale ambient pressure, and, The pressure difference is P D =(V b -V b,0 ) / a It is calculated from, and here, P D This is the instantaneous pressure difference, V b This is the instantaneous voltage from the diaphragm differential pressure sensor. A pressure gauge as described in embodiment 3. [Aspect 5] The pressure meter according to embodiment 1, wherein the controller further provides an output of instantaneous ambient pressure from the absolute ambient pressure signal. [Aspect 6] The pressure gauge according to embodiment 1, wherein the absolute vacuum pressure sensor has an accuracy of 7% or more at a high vacuum pressure of 5 Torr. [Aspect 7] The pressure gauge according to embodiment 1, wherein the calculated absolute pressure from the instantaneous differential pressure reading has an accuracy of 1% or more at 60 Torr. [Aspect 8] The aforementioned controller At an intermediate vacuum pressure, the mixed pressure is calculated from the instantaneous high vacuum pressure signal and the calculated absolute pressure. The chamber pressure signal outputs the instantaneous high vacuum pressure signal over the high vacuum pressure range, the calculated absolute pressure over the low vacuum pressure range, and the mixed pressure at the intermediate vacuum pressure. It is configured in such a way. A pressure gauge as described in Embodiment 1. [Aspect 9] The pressure gauge according to embodiment 1, wherein the controller is configured to set the absolute vacuum pressure signal to zero at ambient pressure. [Aspect 10] The pressure gauge according to embodiment 1, wherein the absolute vacuum pressure sensor is a thermal conductivity sensor. [Aspect 11] The pressure gauge according to embodiment 10, wherein the thermal conductivity sensor is a MEMS Pirani sensor. [Aspect 12] The pressure gauge according to embodiment 1, wherein the diaphragm differential pressure sensor is a differential piezoresistive diaphragm pressure sensor. [Aspect 13] The pressure gauge according to embodiment 1, wherein the absolute ambient pressure sensor comprises a diaphragm that is exposed to a reference vacuum on one side and to ambient pressure on the opposite side. [Aspect 14] A method for controlling the load lock port and transfer port of a load lock, To provide an instantaneous high vacuum pressure signal from an absolute vacuum pressure sensor, To provide an instantaneous differential pressure signal from a diaphragm differential pressure sensor having a diaphragm exposed to the load lock on one side and exposed to ambient pressure on the opposite side, To provide an instantaneous ambient pressure signal from an absolute ambient pressure sensor, In the electronic controller, the calculated absolute ambient pressure is calculated from the instantaneous differential pressure signal and the instantaneous ambient pressure signal, The transfer port is opened to the high vacuum chamber only after the load lock has reached a sufficiently low pressure, as indicated by the instantaneous high vacuum pressure signal from the absolute vacuum pressure sensor. The load lock port is opened to the surroundings only after the instantaneous differential pressure signal from the diaphragm differential pressure sensor indicates a load lock pressure at least as high as the ambient pressure. The controller provides an absolute vacuum pressure output. Includes, The absolute vacuum pressure output is taken from the high vacuum absolute vacuum pressure sensor and the low vacuum calculated absolute pressure. method. [Aspect 15] The aforementioned controller When the load lock is ambient pressure, the ambient pressure bridge voltage of the diaphragm differential pressure sensor, The full-scale bridge voltage of the diaphragm differential pressure sensor when the load lock is at full-scale high vacuum, and Full-scale ambient pressure measured by the absolute ambient pressure sensor Based on this, the diaphragm differential pressure sensor is further calibrated. The method described in Embodiment 14. [Aspect 16] The aforementioned controller The ambient pressure bridge voltage of the diaphragm differential pressure sensor is measured when the load lock is exposed to ambient pressure. The full-scale bridge voltage of the diaphragm differential pressure sensor is measured when the load lock is at full-scale high vacuum. When the load lock is at full-scale high vacuum, the absolute ambient pressure sensor measures the full-scale ambient pressure, and, In the controller, the gain of the diaphragm differential pressure sensor is calculated from the ambient pressure bridge voltage, the full-scale bridge voltage, and the full-scale ambient pressure. The diaphragm differential pressure sensor is further calibrated by this, Subsequently, the instantaneous differential reading is calculated from the instantaneous bridge voltage, the ambient pressure bridge voltage, and the gain. The method described in Embodiment 14. [Aspect 17] The gain is a=(V b,0 -V b,FS ) / P amb,FS It is calculated from, and here, a is the gain, V b,0 This is the ambient pressure bridge voltage, V b,FS This is the full-scale bridge voltage, and, P amb,FS This is the full-scale ambient pressure, and, The pressure difference is P D =(V b -V b,0 ) / a It is calculated from, and here, P D This is the instantaneous pressure difference, V b This is the instantaneous voltage from the diaphragm differential pressure sensor. The method described in Embodiment 14. [Aspect 18] The method according to embodiment 14, wherein the controller further provides an output of instantaneous ambient pressure from the instantaneous absolute ambient pressure signal. [Aspect 19] The method according to embodiment 14, wherein the controller calculates a mixed pressure from the instantaneous high vacuum pressure signal and the calculated absolute pressure signal at an intermediate vacuum pressure. [Aspect 20] The method according to embodiment 14, further comprising setting the absolute vacuum pressure signal to zero at ambient pressure.

Claims

1. A housing configured to be coupled to a vacuum chamber, An absolute vacuum pressure sensor within the housing, configured to be exposed to the vacuum chamber and capable of operating in high vacuum to provide an instantaneous high vacuum pressure signal, A diaphragm differential pressure sensor in a housing, comprising a diaphragm configured such that one side is exposed to the vacuum chamber and the opposite side is exposed to ambient pressure, in order to provide an instantaneous differential pressure signal calculated from the instantaneous sensor voltage output and from calibration parameters consisting of stored voltage offset and gain, To provide an instantaneous ambient pressure signal, an absolute ambient pressure sensor within the housing is exposed to ambient pressure, A controller within the housing receives the instantaneous high vacuum pressure signal from the absolute vacuum pressure sensor, the instantaneous differential pressure signal from the diaphragm differential pressure sensor, and the instantaneous ambient pressure signal from the absolute ambient pressure sensor. Equipped with, The controller calculates the calculated absolute pressure of the vacuum chamber from the instantaneous differential pressure signal and the instantaneous ambient pressure signal, both of which are detected throughout the vacuum pressure range. The controller provides the user with the following outputs: a differential pressure output from the instantaneous differential pressure signal, an absolute vacuum pressure output taken from the instantaneous high vacuum pressure signal in high vacuum, and an absolute vacuum pressure output from the calculated absolute pressure in low vacuum. The controller is further configured to recalibrate the diaphragm differential pressure sensor for providing the instantaneous differential pressure signal by updating the stored calibration parameters. The update of the saved calibration parameters is performed as follows: The ambient pressure voltage offset of the diaphragm differential pressure sensor is measured when the vacuum chamber is at ambient pressure, The full-scale voltage output of the diaphragm differential pressure sensor is measured when the vacuum chamber is in a full-scale high vacuum state. The absolute ambient pressure sensor measures the full-scale ambient pressure, The gain of the diaphragm differential pressure sensor is determined from the measured ambient pressure voltage offset, the measured full-scale voltage output, and the measured full-scale ambient pressure. The measured ambient pressure voltage offset and the determined gain are stored as the calibration parameters. The instantaneous differential pressure signal is then calculated from the instantaneous sensor voltage output of the diaphragm differential pressure sensor and the updated calibration parameters. Pressure gauge.

2. The gain is a=(V ｂ，０ -V ｂ，ＦＳ ) / P ａｍｂ，ＦＳ It is calculated from, and here, a is the gain, V ｂ，０ This is the ambient pressure voltage offset, V ｂ，ＦＳ This is the full-scale voltage output, and, P ａｍｂ，ＦＳ This is the full-scale ambient pressure, and also, The aforementioned instantaneous differential pressure signal, P Ｄ =(N ｂ -V ｂ，０ ) / a It is calculated from, and here, P Ｄ This is the instantaneous differential pressure signal, V ｂ This is the instantaneous sensor voltage output from the diaphragm differential pressure sensor. The pressure gauge according to claim 1.

3. The pressure meter according to claim 1, wherein the controller further provides an output of instantaneous ambient pressure from the instantaneous ambient pressure signal.

4. The pressure gauge according to claim 1, wherein the absolute vacuum pressure sensor has an error of ±7% or less at a high vacuum pressure of 5 Torr.

5. The pressure gauge according to claim 1, wherein the calculated absolute pressure from the instantaneous differential pressure signal has an error of ±1% or less at 60 Torr.

6. The aforementioned controller At an intermediate vacuum pressure, the mixed pressure is calculated from the instantaneous high vacuum pressure signal and the calculated absolute pressure. The chamber pressure signal outputs the instantaneous high vacuum pressure signal over the high vacuum pressure range, the calculated absolute pressure over the low vacuum pressure range, and the mixed pressure at the intermediate vacuum pressure. It is configured in such a way. The pressure gauge according to claim 1.

7. The pressure gauge according to claim 1, wherein the controller is configured to reduce the absolute vacuum pressure output to zero at ambient pressure.

8. The pressure gauge according to claim 1, wherein the absolute vacuum pressure sensor is a thermal conductivity sensor.

9. The pressure gauge according to claim 8, wherein the thermal conductivity sensor is a MEMS Pirani sensor.

10. The pressure gauge according to claim 1, wherein the diaphragm differential pressure sensor is a differential piezoresistive diaphragm pressure sensor.

11. The pressure gauge according to claim 1, wherein the absolute ambient pressure sensor comprises a diaphragm that is exposed to a reference vacuum on one side and to ambient pressure on the opposite side.

12. A method for controlling the load lock port and transfer port of a load lock, To provide an instantaneous high vacuum pressure signal from an absolute vacuum pressure sensor, A diaphragm differential pressure sensor provides an instantaneous differential pressure signal from a diaphragm having a diaphragm exposed to the load lock on one side and exposed to ambient pressure on the opposite side, the instantaneous differential pressure signal is calculated from the instantaneous sensor voltage output and from calibration parameters consisting of stored voltage offset and gain, To provide an instantaneous ambient pressure signal from an absolute ambient pressure sensor, In the controller, the calculated absolute pressure is calculated from the instantaneous differential pressure signal and the instantaneous ambient pressure signal, The transfer port is opened to the vacuum chamber only after the load lock has reached a sufficiently low pressure, as indicated by the instantaneous high vacuum pressure signal from the absolute vacuum pressure sensor. The load lock port is opened to the surroundings only after the instantaneous differential pressure signal from the diaphragm differential pressure sensor indicates a load lock pressure that is at least as high as the ambient pressure. The controller provides an absolute vacuum pressure output, and the absolute vacuum pressure output is taken from the high vacuum absolute vacuum pressure sensor and the low vacuum calculated absolute pressure. The controller recalibrates the diaphragm differential pressure sensor for providing the instantaneous differential pressure signal by updating the stored calibration parameters. Includes, The update of the saved calibration parameters is performed as follows: The ambient pressure voltage offset of the diaphragm differential pressure sensor is measured when the vacuum chamber is at ambient pressure, The full-scale voltage output of the diaphragm differential pressure sensor is measured when the vacuum chamber is in a full-scale high vacuum state. The absolute ambient pressure sensor measures the full-scale ambient pressure, The gain of the diaphragm differential pressure sensor is determined from the measured ambient pressure voltage offset, the measured full-scale voltage output, and the measured full-scale ambient pressure. The measured ambient pressure voltage offset and the determined gain are stored as the calibration parameters. The instantaneous differential pressure signal is then calculated from the instantaneous sensor voltage output of the diaphragm differential pressure sensor and the updated calibration parameters. method.

13. The gain is a=(V ｂ，０ -V ｂ，ＦＳ ) / P ａｍｂ，ＦＳ It is calculated from, and here, a is the gain, V ｂ，０ This is the ambient pressure voltage offset, V ｂ，ＦＳ This is the full-scale voltage output, and, P ａｍｂ，ＦＳ This is the full-scale ambient pressure, and also, The aforementioned instantaneous differential pressure signal, P Ｄ =(N ｂ -V ｂ，０ ) / a It is calculated from, and here, P Ｄ This is the instantaneous differential pressure signal, V ｂ This is the instantaneous sensor voltage output from the diaphragm differential pressure sensor. The method according to claim 12.

14. The method according to claim 12, wherein the controller further provides an output of instantaneous ambient pressure from the instantaneous ambient pressure signal.

15. The method according to claim 12, wherein the controller calculates a mixed pressure from the instantaneous high vacuum pressure signal and the calculated absolute pressure at an intermediate vacuum pressure.

16. The method according to claim 12, further comprising making the absolute vacuum pressure output at ambient pressure zero.

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