TW201804083A - Method for reducing pressure in a load lock and related pump unit - Google Patents

Abstract

The invention relates to a method for reducing the pressure in a load lock for a substrate at atmospheric pressure using a pump unit (1) having a rough-vacuum pump (2) and a high-vacuum pump (3) arranged upstream of said rough-vacuum pump (2) in the direction of flow of the gases being pumped, characterized in that, during the pressure drop and until the pressure in the load lock reaches a predefined low-pressure threshold, the rotational speed of the high-vacuum pump (3) is controlled as a function of an operating parameter of the high-vacuum pump (3) to increase the flow rate (SoR) generated by the high-vacuum pump such that the flow rate (SoR) generated by the high-vacuum pump falls within a range in which the upper value is six times the flow rate (So1) generated by the rough-vacuum pump and the lower value is 1.3 times the flow rate (So1) generated by the rough-vacuum pump. The invention also relates to a pump unit for implementing said method for reducing pressure.

Description

Method for reducing pressure in load lock and related pump unit

The present invention relates to a method for reducing the pressure in a load lock for a substrate (such as a flat panel display or a photovoltaic substrate) from atmospheric pressure to low pressure for loading in a processing chamber maintained at a low pressure. And a method for unloading the substrate. The invention also relates to a related pump unit for implementing the method for reducing pressure.

In some manufacturing methods, an important step involves processing a substrate in a processing chamber under a controlled extremely low pressure atmosphere. In order to maintain an acceptable yield and to avoid the presence of impurities and contaminants, the atmosphere near the substrate is first reduced to a low pressure with a load lock communicating with the processing chamber.

To do this, the load lock has a sealed enclosure with a first door that joins the interior of the enclosure with an area under atmospheric pressure, such as a clean room, for load At least one substrate. The enclosure of the load lock is connected to a pump unit, which is designed to reduce the pressure in the enclosure to a low pressure similar to the pressure inside the processing chamber, so that the substrate can be transferred To the processing chamber. The load lock also has a second door for unloading the substrate into the processing chamber after vacuumization. The load lock is also typically used to raise the pressure of the substrate after it has been processed and unloaded at atmospheric pressure.

However, each time a substrate is loaded or unloaded, the pressure in the enclosure of the load lock must be alternately lowered and then raised, which involves frequent use of the pump unit. Furthermore, the vacuum is not immediately generated in the load lock, which limits the overall speed of the process. This limitation is even more severe if the substrate is large. This is especially true for the manufacture of flat panel displays or photovoltaic substrates, where the enclosure of the load lock must be large enough to accommodate one or more flat panels. For example, currently, the enclosures used to make load locks for flat plates typically have a large volume of about 500-1000 liters (and occasionally greater than 5000 liters), so the pump must be implemented as quickly as possible.

In particular, a power pump unit is used for this purpose to provide a suction pump significantly when the load lock is opened and the pressure in the enclosure is at atmospheric pressure.

The pump unit usually has one or more rough vacuum pumps and one high vacuum pump, such as a Roots single-stage vacuum pump. The high vacuum pump is disposed on the upstream side of the rough vacuum pump in the direction of flow of the pumped gas. The main purpose of the pump is to improve the performance of the pump unit at low pressure. Total pumping speed.

The flow rate produced by the high vacuum pump may be about 5 times the flow rate produced by the rough vacuum pump. When the load lock is opened, the presence of the high gas flow rate can generate significant pressure at the discharge port of the high vacuum pump, which can reach 4 bar (or 3 bar relative). This high overpressure causes high power consumption of the high vacuum pump and blockage on the inlet side of the rough vacuum pump, posing a risk of failure to both the rough vacuum pump and the rough vacuum pump.

To prevent this, a known solution involves providing a pipe that connects the inlet of the rough vacuum pump to the inlet of the high vacuum pump. The pipeline is sheathed with a bypass valve, which is designed to open when the pressure difference between the inlet side of the high vacuum pump and the discharge port is too high, and the bypass valve is designed to be between 50 and 80 millimeters. Open under maximum pressure difference between bars. Therefore, the bypass valve is opened at the beginning of the pressure drop to communicate the excess air flow from the discharge port to the inlet side of the high vacuum pump. The bypass valve is then closed when the upstream / downstream pressure difference of the high vacuum pump is below 50 or 80 mbar. At high pressures, the pressure drop is therefore only implemented by the rough vacuum pump, and the role of the high vacuum pump is limited to participating in the "regulation" of the airflow.

The bypass valve thus helps protect the rough vacuum pump by diverting excess airflow. This bypass also helps to thermally protect the high vacuum pump from excessive pressure by preventing the high vacuum pump's discharge pressure.

The pressure drop in the load lock causes the pressure drop in the high vacuum pump and the discharge port of the enclosure of the bypass valve, thus allowing the high vacuum The pump is able to compress the gas to be pumped starting from the pressure inside the load lock (which is typically about 200 mbar).

However, this prior art device has some disadvantages.

When the pressure drop begins, the initial total pumping speed of the pump unit is low because the pumping is provided only by the rough vacuum pump.

In addition, before the pressure in the load lock reaches several millibars, the power consumed by the high vacuum pump is very high and is lost due to the bypass of the air flow.

Another problem is the fact that the bypass valve system is operated in pulses, which opens and closes cyclically and is extremely fast, obviously due to the principle of the cylindrical pumping principle of the volumetric high vacuum pump. This creates the risk of premature mechanical wear of the bypass valve and therefore the risk of leakage. Furthermore, the pulsating operation of the bypass valve causes a lot of noise.

In addition, the gas flowing through the pipe of the bypass valve is hot due to the compression of the high vacuum pump. These recovered hot gases will also overheat the high vacuum pump.

Therefore, one of the objects of the invention is to propose a method for reducing the pressure in a load lock and an associated pump unit, which at least partially solves the previous problem by allowing a higher pumping speed at the beginning of the pressure drop Technical problems while reducing the power consumed by the high vacuum pump.

Another object of the present invention is to protect the rough vacuum pump and the high vacuum pump from being exposed to the load lock member under atmospheric pressure. Risk of injury related to excess gas flow when opened.

Another object of the invention is to reduce the risk of wear of the bypass valve caused by "recovered" hot gas and the risk of overheating of the high vacuum pump.

To this end, the present invention relates to a method for reducing the pressure in a load lock for a substrate at atmospheric pressure using a pump unit having a rough vacuum pump and a high vacuum pump. It is arranged upstream of the direction of flow of the pumped gas of the rough vacuum pump, and is characterized in that the high vacuum is during the pressure drop and before the pressure in the load lock reaches a predetermined low pressure threshold. The speed of the pump is controlled as a function of an operating parameter of the high vacuum pump to increase the flow rate generated by the high vacuum pump so that the flow rate generated by the high vacuum pump falls within a range. The upper limit of this range is 6 times the flow rate generated by the rough vacuum pump and the lower limit is 1.3 times the flow rate generated by the rough vacuum pump.

The pressure reduction method of the present invention, individually or in combination, includes one or more of the following features:-the operating parameter of the high vacuum pump is a parameter of the motor of the high vacuum pump,-when the high vacuum is detected When the value of an operating parameter of the pump has exceeded a predetermined trigger threshold for a first predetermined time, the control of the rotation speed of the high vacuum pump is as a function of the operating parameter of the high vacuum pump. Initially, if the value of the operating parameter of the high vacuum pump is longer than a predetermined safety threshold value for a longer time than a second predetermined time, the speed of the high vacuum pump is forced to decrease, -If the value of the operating parameter of the high vacuum pump is less than a predetermined waiting threshold time longer than a third predetermined time, the rotation speed of the high vacuum pump is set to a standby rotation speed.

The invention also relates to a pump unit, which includes a rough vacuum pump and a high vacuum pump, the high vacuum pump is arranged upstream of the flow direction of the pumped gas of the rough vacuum pump and has a A variable frequency drive, characterized in that the high vacuum pump includes a control unit that is connected to the variable frequency drive and is configured to control the high vacuum as a function of a signal representing an operating parameter of the high vacuum pump The rotation speed of the pump is such that during the pressure drop and before the pressure in the load lock reaches a predetermined low pressure threshold, the flow rate generated by the high vacuum pump is increased to fall within a range. The upper limit is 6 times the flow rate generated by the rough vacuum pump and the lower limit is 1.3 times the flow rate generated by the rough vacuum pump.

According to a specific embodiment, the rough vacuum pump includes a pressure relief module for a pumping stage.

The signal representing the operating parameters of the high vacuum pump is, for example, a parameter of the motor of the high vacuum pump, such as current or power, for example.

According to an exemplary embodiment, the pump unit has a bypass pipe that connects the inlet of the rough vacuum pump to the inlet of the high vacuum pump, and the bypass pipe has a discharge module that is designed to It opens when the suction pressure of the rough vacuum pump exceeds the suction pressure of the high vacuum pump by a predetermined exceeding value between 100 and 400 mbar.

The high vacuum pump is, for example, a Roots vacuum pump.

During the pressure drop and the pressure in the load lock reaches Prior to a predetermined low pressure threshold, the flow rate produced by the high vacuum pump is maintained to be 1.3 times greater than the flow rate produced by the rough vacuum pump and 6 times greater than the flow rate produced by the rough vacuum pump. Xiao can optimize the ratio between the flow rate produced by the rough vacuum pump and the flow rate produced by the high vacuum pump. More specifically, the flow rate generated by the high vacuum pump is maintained at a level suitable for a high initial gas flow, that is, less than 6 times the flow rate generated by the rough vacuum pump. At the same time, the generated flow rate is optimized for the rough vacuum pump, which is greater than 1.3 times the flow rate generated by the rough vacuum pump to ensure that the gas is compressed as quickly as possible.

The pressure difference between the inlet side and the exhaust port of the high vacuum pump is kept below a value between 150 and 300 mbar. The pipe and the bypass valve of the device according to the prior art, which is designed to open when the pressure difference in the high vacuum pump reaches between 50 and 80 mbar, can be removed. However, for safety reasons, the pump unit may include a discharge module that is designed to have a pressure difference between the inlet side of the high vacuum pump and the discharge port of more than 100 to 400 mbar. A high value of 打开 is opened, which depends on the value of the ratio between the flow rates being used and the safety settings of the machine, so that the vacuum pump is protected, especially during the period when the speed control is applicable.

Once the rotation speed of the high vacuum pump is controlled, the high vacuum pump is no longer "short circuited" as in the case of a pressure of 200 mbar in the load lock of the prior art, Instead, it is used as the actual first pumping stage of the rough vacuum pump. The operating characteristics of the high vacuum pump are thus adapted to the rough vacuum pump The pump's capacity makes the high vacuum pump practically efficient from atmospheric pressure. This significantly reduces the power consumption from the pressure drop and increases the total pumping speed of the pump unit, thereby shortening the pressure drop time within the load lock. For example, in a pressure range between 1000 mbar and 20 mbar, the pumping speed is increased by 20-50% compared to the pumping speed of the prior art device. In addition, the total pressure drop time between a transfer pressure of approximately 1000 mbar to approximately 0.1 mbar in the enclosure of a 500 liter load lock was shortened from 25 seconds to 20 seconds, ie, approximately 20%.

Furthermore, given that the exhaust module opens at a higher pressure than the bypass valve of the prior art, and the ratio between the flow rate of the rough vacuum pump and the high vacuum pump is optimized, the high vacuum pump The discharge pressure drops rapidly, so that the discharge module opens for only a short time. The exhaust module is subject to limited stress, so it wears slowly and produces less noise. In addition, a limited amount of gas flows through the bypass pipe, which prevents the high vacuum pump from being overheated by the hot compressed gas.

1‧‧‧pu unit

2‧‧‧ rough vacuum pump

3‧‧‧High Vacuum Pump

T1‧‧‧The first pumping stage

T2‧‧‧Second pumping stage

T3‧‧‧The third pumping stage

T4‧‧‧The fourth pumping stage

T5‧‧‧Fifth pumping stage

4‧‧‧ entrance

5‧‧‧ emission port

6‧‧‧ check valve

7‧‧‧ Motor

8‧‧‧ Variable Frequency Drive

9‧‧‧Control unit (processing unit)

10‧‧‧ Pipeline

11‧‧‧ entrance

12‧‧‧ Valve

13‧‧‧channel

14‧‧‧ Valve

P1‧‧‧Discharge pressure

Other features and benefits of the present invention are provided in the following description, which is provided as a non-limiting example with reference to the accompanying drawings, wherein: FIG. 1 is a schematic diagram of a pump unit according to the present invention, and FIG. 2 is A graph showing the pressure drop in a load lock connected to the pump unit of FIG. 1, where the x-axis is the pressure in the enclosure of the load lock (in millibars) and the right y-axis is high vacuum The rotation frequency of the pump (in Hz) and the left y-axis are the power consumed by the high-vacuum pump (in kW). Figure 3 is a graph similar to Figure 2, where the right y-axis is the high-vacuum pump. The ratio of the flow rate generated by the pump to the flow rate generated by the rough vacuum pump, and FIG. 4 is a graph showing the rough vacuum pump alone during the pressure drop, the pump unit according to the present invention, and the previous The pump speed (in m ³ / h) of the technical pump device is expressed as a function of the pressure in the enclosure of the load lock (in mbar).

In these figures, the same components are labeled with the same component symbols.

"Atmospheric pressure" refers to the pressure outside the load lock of the substrate, such as the pressure in the room in which the clean room work is performed, that is, about 10 ⁵ Pascals (1000 mbar) or slightly higher pressure for Promote the direction of flow towards the outside of the enclosure.

"Generated flow rate" (or volume generated) refers to the capacity corresponding to the volume driven by the vacuum pumped rotor multiplied by the number of revolutions per minute.

Fig. 1 shows an exemplary pump unit 1 designed to be connected to a enclosure of a load lock via an isolation valve (not shown).

In a known manner, the load lock has a sealed enclosure with a first door that connects the interior of the enclosure with a large enclosure. Pneumatic areas (such as clean rooms) are joined to load at least one large substrate, such as a flat panel display or a photovoltaic substrate. This load lock usually has a volume between 500 and 500 liters.

The load lock also has a second door for unloading the substrate into a processing chamber after vacuumization, and a device for injecting inert gas to restore atmospheric pressure after the substrate is transferred.

The pump unit 1 includes a rough vacuum pump 2 and a high vacuum pump 3, which are arranged upstream of the rough vacuum pump 2 in the flow direction of the pumped gas.

The rough vacuum pump 2 is, for example, a multi-stage dry vacuum pump with rotating leaf petals, such as a Roots pump with two or three leaflets (double leaflets, trilobes). According to other embodiments not described, the rough vacuum pump includes several pumps connected in series or in parallel. In addition, other conventional pumping principles can be used for this rough vacuum pump.

The rough vacuum pump 2 which is schematically shown in FIG. 1 for the sake of example has five pumping stages T1, T2, T3, T4, T5, which are connected in series with each other, wherein the generated flow rate follows The position of the pumping stage in the series decreases, and a pumped gas flows between an inlet 4 and a discharge port 5 between the pumping stages.

Generally, a rotating lobe type Roots vacuum pump has two rotors of the same shape, which are loaded on two shafts extending through the pumping stages T1, T2, T3, T4, T5 and are subjected to the rough vacuum The motor of pump 2 (not shown) is rotationally driven in the opposite direction inside the stator. During the rotation, the sucked gas is trapped in the rotor and the stator before being discharged. Free space between the children. The pump system works without the mechanical contact between the rotor and the stator of the rough vacuum pump 2, which completely eliminates the need for lubricant between the pumping stages T1, T2, T3, T4, and T5.

In the illustrated example, the first pumping stage T1 of the rough vacuum pump 2 has a generated flow rate So1 of about 600 m ³ / h, and the second pumping stage T2 has a flow rate of about 400 m ³ / The generated flow rate So2 of h, the third pumping stage T3 has a generated flow rate So3 of about 200m ³ / h and the last two pumping stages T4, T5 have a generated rate of about 100m ³ / h Flow rate So4, So5. Because the generated flow rates change as a function of the pressure range, these values correspond to the maximum value of the rough vacuum pump 2 with a fixed pump flow rate and speed at steady state operation and about 65 Hz. .

The rough vacuum pump 2 also has a check valve 6 near the exhaust port 5 at the exit of the last pumping stage T5 to prevent the pumped gas from flowing back into the rough vacuum pump 2.

The high vacuum pump 3 is a volumetric vacuum pump like the rough vacuum pump 2, that is, a pump that uses a piston, a rotor, a blade, and a valve to suck in, transfer, and then discharge the gas to be pumped. Pu.

The high vacuum pump 3 is, for example, a single-stage rotor-based vacuum pump (which has only one pumping stage), such as a Roots pump or the like, such as a claw pump.

In operation, the maximum generated flow rate SoR of the high vacuum pump 3 at the maximum speed (ie, about 70 Hz) in the optimum pressure range is, for example, about 3000 m ³ / h.

The high vacuum pump 3 includes a motor 7 (for example, a different Step motor), an inverter drive 8 for driving the motor 7 (which drives the rotors), and a control unit 9 connected to the inverter drive 8.

The control unit 9 is configured to represent a high vacuum pump 3 during a pressure drop in the load lock at atmospheric pressure and before the pressure in the load lock reaches a predetermined low pressure threshold. The function of the signal of the operating parameter controls the rotation speed of the rotor of the high vacuum pump 3 as a function of increasing the generated flow rate, so that the flow rate SoR generated by the high vacuum pump is within a range. The upper limit of the range is 6 times the flow rate So1 generated by the rough vacuum pump and the lower limit is 1.3 times the flow rate So1 generated by the rough vacuum pump.

The predetermined low-pressure threshold is, for example, 20 mbar. Below this value, the rotation speed of the high vacuum pump 3 is set to the maximum value, which is 70 Hz in this example.

The pressure difference between the inlet side of the high vacuum pump and the discharge port is kept below a value between 150 and 300 mbar.

The signal representing an operating parameter is, for example, a discharge pressure P1 of the high vacuum pump or a parameter of the motor 7 of the high vacuum pump 3.

In the latter example, the parameter of the motor 7 of the high vacuum pump 3 may be a current (which represents power consumption), or directly the consumed power. These signals can be received from a variable frequency drive 8 connected to the motor 7. Therefore, the control of the high-vacuum pump 3 is automatic, because the control requires neither information from the load lock nor the addition of a pressure sensor at the inlet 4 of the rough vacuum pump 2.

The control that controls the rotation speed of the rotor of the high vacuum pump 3 as a function of a signal representing an operating parameter of the high vacuum pump 3 is a closed-loop control: when the discharge pressure P1 or the current of the motor 7 Or, when the pressure increases and the generated flow rate approaches or exceeds the upper limit of the allowed range, the rotation speed is slowed or reduced.

The pump unit 1 also includes a pipe 10 that connects the inlet 4 of the rough vacuum pump 2 to the inlet 11 of the high vacuum pump 3.

The pipeline 10 has a discharge module, such as a valve 12 driven by the processing unit 9, and is configured to have a pressure difference between the inlet side of the high vacuum pump 3 and the discharge port of more than 100 to 400. A predetermined excess value ΔP between millibars is opened when the excess value ΔP is defined according to the selected proportion of the generated flow rate and according to the mechanical safety settings.

For example, for a ratio of the maximum generated flow rate of about 4.5, the pressure difference of the high vacuum pump 3 is maintained at a pressure of less than about 250 mbar at all times. The emission module thus be constructed to open in the rough vacuum pump suction pressure P1 exceeds the high vacuum pump suction pressure P _asp over a predetermined value △ P (e.g., 300 mbar) time.

In addition, in order to absorb the high initial airflow caused by the vacuumization of the load lock member at atmospheric pressure, the rough vacuum pump 2 is designed to absorb and forward this high initial airflow while consuming as little as possible electric power. To do this, the rough vacuum pump 2 includes, for example, a pressure relief module for the pumping stage.

In fact, although the flow rate SoR produced by the high vacuum pump is adjusted to match the flow rate So1 produced by the rough vacuum pump (i.e., the rough true The flow rate generated by the first pumping stage T1 of the air pump 2), the second or third pumping stages T2, T3 sequentially limit the total flow rate produced by the rough vacuum pump 2. Therefore, in order to allow the rough vacuum pump 2 to absorb many sporadic pump flows (which is equivalent to the suction pressure P1 in this example, which is limited to the opening pressure of the exhaust module, that is, 300 mbar), the release The compression module is connected to the output of a low-pressure pumping stage (for example, the second pumping stage T2).

The pressure relief module includes, for example, a channel 13 that connects the output of the low-pressure stage (T1 or T2) to the discharge port 5 of the rough vacuum pump 2. The channel 13 is provided with a valve 14.

The graphs in Figures 2, 3, and 4 showing examples of pressure drops in a 500 liter load lock are discussed below.

In the initial stage, the rotation speed of the high-vacuum pump 3 is at a standby speed, for example, about 30 Hz, to limit power consumption.

After a substrate is loaded into the enclosure of the load lock under atmospheric pressure, the load lock opens the isolation valve and isolates the enclosure under atmospheric pressure from the pump unit 1 (t1).

For a relatively short period of time (approximately a few seconds), the high vacuum pump 3 compresses the excess gas from the enclosure, increases the discharge pressure P1 of the high vacuum pump, and reduces the speed (Figure 2). Curve V).

When the pressure difference between the inlet side of the high-vacuum pump 3 and the discharge port exceeds 300 mbar, the discharge module of the pipeline 10 is opened, thereby limiting the discharge pressure P1 of the high-vacuum pump from rising. The gas flow is absorbed by the first two pumping stages T1, T2 of the rough vacuum pump 2, and then from the second The pumping stage T2 is output by the pressure relief module toward the discharge port 5 of the rough vacuum pump 2.

When an operating parameter of the high vacuum pump 3 (for example, the power consumption of the high vacuum pump 3 (curve P in FIG. 2)) exceeds a predetermined trigger threshold value for a predetermined first time, the The processing unit 9 can trigger a pressure drop cycle. The processing unit 9 then controls the rotation speed of the high-vacuum pump 3 as a function of an operating parameter of the high-vacuum pump 3 (such as the power consumption of the motor 7) (such as the curve P of FIGS. 2 and 3) ( Curve V) in FIG. 2 is used to increase the flow rate SoR generated by the high vacuum pump, so that the flow rate SoR generated by the high vacuum pump is greater than 1.3 times the flow rate So1 generated by the rough vacuum pump. It is less than 4.5 times the flow rate So1 generated by the rough vacuum pump, as shown in the example shown in FIG. 3 (curve R).

In view of the increase in power consumed by the high vacuum pump 3, the flow rate SoR generated by the high vacuum pump still remains less than 4.5 times the flow rate So1 generated by the rough vacuum pump, and the processing unit 9 orders an increase in the speed (The curve V between t1 and t2 in Fig. 2), causing the ratio between the generated flow velocities to increase from 1.3 to 4.5. The consumed power then stabilizes at about 17 kW (Figure 3). This consumed power is required to maintain effective compression of the rough vacuum pump 2 and the high vacuum pump 3 thermally and mechanically at the exhaust port of the high vacuum pump 3.

In addition, the upper limit value of the power consumed by the high vacuum pump 3 can be set for safety purposes. If the value of the parameter of the motor 7 of the high vacuum pump 3 is greater than a predetermined safety threshold value and lasts longer than a second predetermined time, the rotation speed of the high vacuum pump 3 is forcibly reduced. . This precaution is more specifically applicable to large-volume load locks, such as load locks of more than 100m ³ , and these pump units are made to be suitable for small-volume load locks of about 2m ³ to 20m ³ . This prevents the high vacuum pump 3 from overheating.

It can be seen that between the atmospheric pressure (t1) and the predetermined low pressure threshold (for example, 20 mbar (t2)), the flow rate SoR generated by the high vacuum pump and the rough vacuum pump station The ratio between the produced flow rates So1 is maintained between 1.3 and 4.5.

Keeping the ratio between the generated flow rates below 4.5 ensures that the flow rate SoR produced by the high vacuum pump is tolerable for the rough vacuum pump 2. This limits excessive consumption and the high vacuum pump 3 provides compression anyway. The pressure difference between the inlet side of the high vacuum pump 3 and the exhaust port is kept below a value between 150 and 350 mbar.

The high vacuum pump 3 is no longer "short-circuited" like the prior art devices.

By comparison, FIG. 4 shows the pumping speed of a pump unit 1 (curve A) during the pressure drop in a load lock, the pumping speed of the rough vacuum pump 2 (curve B), and according to the prior art Pumping speed (curve C) of the device, the prior art device has a rough vacuum pump and a high vacuum pump, which are similar to the rough vacuum pump and the high vacuum pump in the pump unit 1 according to the present invention, and It has a bypass valve which is designed for high vacuum pumps with 60 mbar and a fixed speed.

In a device according to the prior art, the high vacuum pump and There is no improvement in the total pumping speed between 200 mbar and atmospheric pressure, the pressure drop being provided solely by the rough vacuum pump. The role of the high vacuum pump (whose rotation speed is set to a fixed maximum speed) is therefore limited to assisting the airflow consumed by the side pass (curves B and C between t1 and ta).

Therefore, due to the adjusted ratio of the generated flow rates SoR and So1, the high vacuum pump 3 of the pump unit 1 according to the present invention is used as the actual first pump of the rough vacuum pump 2. stage. The high vacuum pump 3 is thus practically efficient from atmospheric pressure (t1 of curve A in FIG. 4). The efficiency of the high vacuum pump of the device according to the prior art only catches up with the efficiency of the high vacuum pump 3 of the pump unit 1 around 5 mbar (tb).

This significantly reduces the power consumed by the pump unit 1 and increases the total pumping speed from the pressure drop, thereby reducing the time for the pressure drop in the load lock. In this example, at 200 mbar, the total pumping speed is increased by 40% compared to a device according to the prior art.

Furthermore, because the exhaust module is not subject to much stress, the exhaust module wears out more slowly and is less noisy. In addition, a limited amount of gas flows through the bypass duct 10, which prevents the high vacuum pump 3 from being overheated by the previously compressed hot gas.

When the pressure in the load lock member reaches the predetermined low pressure threshold value (t2 on the curve B in FIG. 4), the set point of the rotation speed of the high vacuum pump 3 is set to a maximum value of 70 Hz. The discharge pressure P1 of the high vacuum pump decreases, reducing the power consumption of the high vacuum pump (Figures 2 and 3) Curve P). At these low pressure values in the load lock, the power consumed is about 2 kW. Below this predetermined low pressure in the load lock, the pumps of the rough vacuum pump and the high vacuum pumps 2 and 3 can be conventionally implemented without changing the rotation speed of the high vacuum pump 3 Because the pump flow and power consumption are extremely low.

At extremely low pressure (over t3), for example, while waiting for the load lock to be opened to the processing chamber for substrate transfer, if the value of the parameter of the motor of the high vacuum pump 3 is lower than a second If the predetermined threshold value lasts longer than a second predetermined time (for example, 2kW for several minutes), the speed of the high vacuum pump 3 can be set to a standby speed, which is lower than the 70Hz Maximum speed to limit power consumption.

1‧‧‧pu unit

2‧‧‧ rough vacuum pump

3‧‧‧High Vacuum Pump

4‧‧‧ entrance

5‧‧‧ emission port

6‧‧‧ check valve

7‧‧‧ Motor

8‧‧‧ Variable Frequency Drive

9‧‧‧Control unit (processing unit)

10‧‧‧ Pipeline

11‧‧‧ entrance

12‧‧‧ Valve

13‧‧‧channel

14‧‧‧ Valve

T1‧‧‧The first pumping stage

T2‧‧‧Second pumping stage

T3‧‧‧The third pumping stage

T4‧‧‧The fourth pumping stage

T5‧‧‧Fifth pumping stage

Claims (12)

A method for reducing the pressure in a load lock for atmospheric pressure using a pump unit (1), the pump unit has a rough vacuum pump (2) and a high vacuum pump (3) ), Which is arranged upstream of the rough vacuum pump (2) in the direction of flow of the pumped gas, and is characterized in that the pressure in the load lock member reaches a predetermined low pressure threshold during the pressure drop Before the value, the rotation speed of the high vacuum pump (3) is controlled as a function of an operating parameter of the high vacuum pump (3), so as to increase the flow rate (SoR) generated by the high vacuum pump, The flow rate (SoR) generated by the high vacuum pump falls within a range, the upper limit value of the range is 6 times the flow rate (So1) generated by the rough vacuum pump, and the lower limit value is the rough vacuum pump. The generated flow rate (So1) is 1.3 times. For example, the method for reducing pressure in item 1 of the patent application range, wherein the operating parameter of the high vacuum pump (3) is a parameter of the motor (7) of the high vacuum pump (3). For example, the method for reducing pressure in item 1 or 2 of the scope of patent application, wherein when it is detected that an operation parameter value of the high vacuum pump (3) has exceeded a predetermined trigger threshold value for a first predetermined time The control of the rotation speed of the high vacuum pump (3) is started as a function of the operating parameters of the high vacuum pump (3). For example, the method for reducing pressure in the first scope of the patent application, wherein if the value of the operating parameter of the high vacuum pump (3) is greater than a predetermined safety threshold value for a time longer than a second predetermined time, then The speed of the high vacuum pump (3) is forced to decrease. For example, if the method for reducing pressure in item 1 of the patent scope is applied, if the value of the operating parameter of the high vacuum pump (3) is less than a predetermined waiting threshold value for a longer time than a third predetermined time, then The speed of the high vacuum pump (3) is set to a standby speed. A pump unit includes a rough vacuum pump (2) and a high vacuum pump (3). The high vacuum pump (3) is arranged in the rough vacuum pump (2) in a gas pumped state. Upstream of the flow direction and has a variable frequency drive (8), characterized in that the high vacuum pump (3) includes a control unit (9), which is connected to the variable frequency drive (8) and is constructed as a representative A function of a signal of an operating parameter of the high vacuum pump (3) controls the rotation speed of the high vacuum pump (3) as a function of the pressure during the pressure drop and within the load lock member to reach a predetermined low pressure threshold Before the value, the flow rate (SoR) generated by the high vacuum pump is increased to fall within a range, and the upper limit value of the range is 6 times and the lower limit of the flow rate (So1) generated by the rough vacuum pump. The value is 1.3 times the flow rate (So1) produced by this rough vacuum pump. For example, the pump unit of the scope of patent application No. 6 in which the rough vacuum Pump (2) includes a pressure relief module for the pumping stages (T1, T2). For example, the pump unit of the patent application scope item 6 or 7, wherein the signal representing the operating parameters of the high vacuum pump (3) is a parameter of the motor (7) of the high vacuum pump (3). For example, the pump unit of the eighth patent application range, wherein the parameter of the motor (7) of the high vacuum pump (3) is a current. For example, the pump unit of the eighth patent application range, wherein the parameter of the motor (7) of the high vacuum pump (3) is power. For example, the pump unit of the patent application No. 6 wherein the pump unit has a bypass pipe (10) which connects the inlet (4) of the rough vacuum pump (2) to the high vacuum pump (3) The inlet (11), the bypass pipe (10) has a discharge module, which is designed to make the suction pressure (P1) of the rough vacuum pump exceed the suction pressure (P _asp ) of the high vacuum pump It opens when a predetermined exceeding value (ΔP) between 100 and 400 mbar is reached. For example, the pump unit of the sixth scope of the patent application, wherein the high vacuum pump (3) is a Roots vacuum pump.