In the semiconductor industry, microelectronic components are built up on the plane surface of a single crystal. During the production process, layers with particular electrical properties (insulators, conductors and layers with certain conductive properties) are applied on top of each other. Due to the different properties of adjacent layers, electronic components such as transistors, capacitors, resistors, etc. are created.
Vacuum technology is used in many different processes during the production of integrated circuits, such as doping the semiconductor base material, building up layers, structuring and also in analyzing. Production takes place in cleanrooms. Vacuum pumps are used either directly on the production machinery in the cleanroom or in a separate pump floor (basement) underneath the cleanroom.
The processes place different requirements on the pumps used. Processes without corrosive, toxic or condensable media can be operated with pumps that are not specially equipped for handling corrosive gases. These processes include
Load locks and transfer chambers
PVD (Physical Vapor Deposition) of metals without a reactive gas atmosphere
Implanters (Beam Line and End Station)
Annealing (baking out crystal defects) under vacuum or an inert gas atmosphere
Wafer inspection
The pumps used (L series) are described in Chapter 4.6.3. Using the pumps directly in the cleanroom means not only that fore-vacuum lines to the pump basement and any heating required can be dispensed with, but also that conductivity losses can be reduced and reproducible installations with high process stability can be realized.
Medium duty applications can involve corrosive chemicals with a tendency to condense, but do not generate particles. This type of application includes different processes such as
Oxidation, ashing
RTP (Rapid Thermal Processing; wafer processing in high-temperature processes with halogen lighting with a high rating)
Dry etching of polycrystalline silicone, aluminum or tungsten
Implanters (sources)
Certain CVD processes
The pumps used (P series) are described in Chapter 4.6.4. For safety reasons and owing to the proximity to the waste gas purification system, process pumps are often installed in a basement.
The most demanding processes (harsh processes, H-series pumps) make it necessary to handle particles, highly corrosive chemicals or reaction by-products and chemicals or reaction by-products with a tendency to condensate. Examples of such processes are:
MOCVD (Metal Organic Chemical Vapor Deposition) of titanium nitride
Isotropic dry etching of dielectrics
HDP CVD (High Density Plasma Chemical Vapor Deposition) of silicon dioxide
SACVD (Sub Atmospheric Chemical Vapor Deposition) of silicon dioxide
SACVD HARP (Sub Atmospheric Chemical Vapor Deposition, High Aspect Ratio Process) of silicon dioxide
Combinations of turbomolecular pumps (see Chapter 4.9.3.2) and dry-running process pumps are sometimes also used for these processes.
The previously mentioned processes for P and H pumps use chemicals with, for example,
High toxicity, such as arsine (AsH3) or phosphine (PH3)
High corrosiveness such as plasma activated nitrogen trifluoride (NF3), sulfur hexafluoride (SF6), fluorocarbons, etc
Highly oxidizing properties such as plasma activated oxygen or ozone
Metalorganic chemicals such as tetraethyl orthosilicate (TEOS), trisilylamine (TSA)
Extensive knowledge of vacuum technology and vacuum process technology is required to define a practicable solution with long-term stability and minimum cost of ownership. This, for instance, includes defining the pump working temperature in order to prevent condensation due to too low a temperature, powder formation at too high a temperature or blockage of the pump if the chemicals remain in the pump body for too long. In addition precise controlling of the temperature pattern is often necessary not only in the pump itself but also in the production plant, fore-vacuum line and exhaust gas line.
Vacuum processes in the solar industry and in display manufacture are often similar to the processes used in the semiconductor industry. Due to the larger surfaces to be coated in these industry sectors, the gas throughputs are higher however, and require pumps with correspondingly high pumping speeds.
As an example: in the solar industry, antireflective layers and silicon nitride layers which passivate the surface are applied to the solar cells in a plasma CVD process to better harvest the sun’s light. These are not only deposited on the substrate as desired, but also on the walls of the vacuum chamber. The process chamber must be cleaned at the latest when the layers which have accumulated on the walls no longer allow a controlled vacuum process. This is done by in-situ plasma cleaning with the strongly oxidizing agent NF3. If the pump (in this case the AD 73 KH, see Chapter 4.6.5) is operated at too low a temperature, then, as shown in Figure 4.10, the reaction product ammonium hexafluorosilicate is deposited in the pumping station. An ideal process control includes not only a process compatible pump and a tried-and-tested and qualified set of operating parameters but also:
A heated fore-vacuum line to prevent condensation there
In the case of a vertical fore-vacuum line a protective device to prevent objects from falling off into the pump (e. g. a T-piece with a blank flange at the perpendicular lower end and with an output horizontal to the pump)
A soft-start valve to prevent particles from being raised
A shut-off valve at the pump inlet for continuous operation of the pump at high temperatures even during maintenance work on the fore-vacuum line
A leak detector connection in the fore-vacuum line, as near as possible to the backing pump. Leaks would result in the formation of silicone dioxide particles.
A heated exhaust gas line between the pump and the exhaust gas cleaning system
An exhaust gas cleaning system
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Figure 4.10: Condensation of ammonium hexafluorosilicate (NH4)2SIF6 in a Roots pump operated at too low a temperature
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Figure 4.11: Operating principle of a multi-stage Roots pump, process pump
As with the pumps described in the preceding section, the Roots vacuum pumps described in this chapter belong to the category of technically dry-running rotary displacement vacuum pumps. In this section we are dealing with pumps for corrosive processes and the pumps derived from these for load locks and transfer chambers.
In the pump, two synchronously counter-rotating rotors (1) rotate contactlessly in a single housing (2) (Figure 4.11). The rotors have a figure-eight configuration and are separated from one another by a narrow gap. Four to six pairs of rotors are located on the rotor shafts. Each rotor cavity is separated from the others by stator disks with a gas orifice. The gas conveyed is pumped from the inlet port (3) to the outlet port. The vertical pumping direction is always important in process pumps. The space between the various stages in the outfall channels can be used as particle traps as a result. This is the best way to avoid blockage of the pump.
Because there is no friction in the suction chamber, a Roots vacuum pump can be operated at high rotation speeds of up to 6,000 rpm. The symmetrical distribution of the rotor mass around the shaft axis also results in perfect dynamic balancing, which means that the pump operates extremely quietly in spite of its high speeds.
To avoid the condensation of chemicals in the pump and the silencer, these can be tempered by regulating the cooling water flow or heated electrically with heating sleeves. If the outlet silencer is arranged separately, this requires an additional heating sleeve. Integrating the outlet silencer directly on the pump block not only reduces energy costs by dispensing with an additional heater but also makes installation easier.
Advantages of multi-stage Roots pumps in a corrosive gas version include:
Ideal adjustment to the vacuum process concerned by adjusting the temperature, the purge gas throughput and the rotation speed.
No lubricant in the gas displacement area
No operating fluid disposal problems
High reliability and system uptime
Long service intervals, low power consumption and media consumption of cooling water and flushing gas, and low cost of ownership as a result
Small footprint, with good integration and savings in cleanrooms and pump levels
Extensive controlling options, local or remote control, integration in a monitoring network
Minimal leak rate
Ideal backing pump for turbopumps and Roots pumps in corrosive processes
Certified to UL/CSA and SEMI S2
Dust and particles
Process pumps are exposed to particles that are conveyed to the pump from process chambers and fore-vacuum lines. In addition, particles and deposits that may result from the condensation of reaction byproducts in the pumps themselves must also be tolerated. Ideally, it is possible to avoid the formation of particles and deposits by using adjustable heating and controlled temperature patterns. By pumping in a vertical direction, any particles drop out of the pump stage and remain in the outfall channel to the next stage. After the next ventilation and the subsequent pump-down, the particles will be discharged by the displaced gas into the next stage that follows. This discharging mechanism expels more than 98 % of the particles generated from the inlet to the outlet. This means that a central exhaust gas cleaning system which captures and disposes of not just process chemicals but also particles can be provided at the pump outlet. High-maintenance traps and filters on the intake side can be avoided wherever possible in vacuum solutions for corrosive, toxic and condensable media.
Corrosive gases
Multi-stage Roots pumps of the P and H series are specially designed for corrosive gas processes in the semiconductor, solar and coating industry for flat screens. Both the metal rotors and stators as well as the elastomer materials of the pumps are made of highly corrosion-resistant materials.
Leakage rate
The high tightness and the protection from gases diffusing back from the ambient air or an exhaust gas cleaning system or scrubber through a non-return valve make multi-stage Roots pumps the perfect solution for corrosive gas applications. Encapsulated motors are also part of the anti-leak concept.
The ACP 120 is an entry-level model of water cooled multi-stage Roots pumps. Pumps in the ACP series are not suitable for pumping down large quantities of corrosive gases. However, ACP series pumps can be used to handle at least traces of corrosive gases. In this case, inert gas purge is used in which the bearings are protected with an inert gas curtain and process gases are diluted by introducing inert gas into the pump stages.
The ACP 120 can either be operated as a stand-alone pump or in combination with a Roots pump as an ACG 600 pumping station that is an ideal solution for industrial use and which benefits from the design of corrosive gas versions for the semiconductor industry. ACP/ACG pumps are ideally suited for clean processes through their friction-free design. They achieve excellent long-term stability and long maintenance intervals.
Lock pumps for the semiconductor industry have an ”L“ for ”load lock“ in their designation. In contrast to the ACP 120 described above, they are equipped with a housing and a controller. A frequency converter ensures globally reproducible performance parameters irrespective of the mains voltage and frequency.
L-series pumps are fitted with an operating hour counter, status lights and a and can be operated in a local and remote control mode between local and remote control mode.
Inlet and outlet flanges are fitted to the rear of the pump as well as an input-output interface which allows it to be linked to the control unit of a semiconductor production machine. A serial interface is optionally available to enable the pump, for example, to be connected to a monitoring network. Connections for water cooling and an optional energy-saving option are also located on the rear of the pumps (see Figure 4.13).
The optional energy-saving option (Energy Saving, ES) integrated in the pump housing reduces the pump power consumption by up to 50 %. The cost of ownership for the operator is significantly reduced as a result. Besides saving energy, the A 100 L ES can attain an ultimate pressure of 7 · 10-4 hPa. The noise level is also reduced by 3 dB(A).
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Figure 4.12: ACP 120
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Figure 4.13: A 100 L rear side with connections
By keeping the pump surfaces free, the units can also be stacked and therefore minimize the space taken in the cleanroom of a semiconductor fab or in a the basement. Thanks to its combination of a minimal footprint, stackability, high pumping speed even at atmospheric pressure, energy-saving option, low ultimate pressure and high reliability and long-term stability, the L series is the ideal solution for all load-lock processes.
The low final pressure and the reduced noise level make them attractive for analytical and research and development applications.
In coating process, specially in the production of semiconductors, flat screens and in the solar industry, as demonstrated in the introduction to this chapter, the corrosion resistance of vacuum pumps is of great significance. Besides the process compatibility, the small footprint and the low operating costs are particularly important pump parameters. The P series meets these requirements by lowering power input up to 53 % compared to the previous model while maintaining the same footprint.
This pump series is based on the A 103 P dry-running process pump. We have taken two models from the series and supplemented them with Roots pumps for enhanced pumping speeds and gas throughput in the process pressure range. The power input is kept low due to the six-stage design of the A 103 P and an energy-efficient motor. The six-stage design of the A 103 P reduces the differential pressures between the various stages and also the power input of the pump. Besides the sixth stage, the large-dimensioned inlet stage and the high rotation speed allow for a high pumping speed and a low ultimate pressure.
Placing the silencer on the outlet side directly on the pump block makes for a compact pump design and energy savings through direct heating of the silencer by the pump block without the need for an additional heating sleeve. Temperature-controlled and continuously monitored heating of the entire pump is necessary to prevent the condensation of reaction byproducts.
Due to the P series standby option, not only does the pump use less cooling water, but it also reduces flushing gas consumption beyond the process operation which results in the reduction of operating costs.
Extensive activating and controlling options allow not only a manual control mode but also control through a system control and connection to a monitoring network. Important parameters can be outputted directly and exported for statistical evaluation.
The P series is CE and SEMI S2 compliant.
The ongoing development of processes especially in the semiconductor and solar industry places constantly new demands on the vacuum pumps used. Based on the proven technology of multi-stage Roots pumps, Pfeiffer Vacuum provides the perfect solution for demanding processes in these industry sectors with its H series. The gas throughput at the process pressure, the particle tolerance and the resistance to condensation have been significantly increased in comparison with previous pump solutions.
As with the P (for Process) series pumps, H series (for Harsh Process) pumps are equipped with a temperature control and an inert gas flushing system. The parameter range for optimizing adjustment to the process is far wider, however, than in pumps in the P series.
This pump series is based on the A 203 H dry-running process pump. We have taken three additional models from the series and supplemented them with Roots pumps for enhanced pumping speeds and gas throughput in the process pressure range. Due to the use of specific materials, the corrosive gas equipment of these pumps also makes it possible to use strong oxidizing agents such as NF3. The broad temperature range of the pumps enables them to adapt to widely differing processes such as tungsten deposition at low temperatures or nitride deposition at high temperatures. A highly efficient motor results in energy savings at low pressures and provides good startup properties after pump downtime due to its high torque.
The models in the A3H series are ideally compatible with pumps in the P series thanks to their identical interfaces and identical media connections. This means that if a process is changed on an existing production plant, optimized pump solutions can be obtained with a minimum of installation work by exchanging the pumps.
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Figure 4.14: A 203 H cross-section
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Figure 4.15: A 1503 H process pumping station
Supplementing the A 1803 H model with a third Roots stage provides a compact and extremely powerful pumping station with maximum pumping speeds for CVD processes. The AD 73 KH uses a frequency- controlled Roots pump with a rated pumping speed of 4,500 m³ · h-1 in its own frame over the dry-running process pump. Installation is easy due to the modular structure and the various pumps in the pumping station can be taken out singly and maintained in the event of servicing work. The frequency converter of the Roots pump on the intake side allows adjustment to the process parameters over a broad gas throughput range and for widely differing process gases.
Pfeiffer Vacuum monitors the dynamic development of processes in the various sectors of industry on an ongoing basis and will continue in the future to deliver optimized pump solutions to meet these requirements. An initial overview is given in Chapter 8, Contamination Management Solutions.
4.6.6.1 Water cooled process pumps
The pumping speed and final pressure of the ACP 120 / ACP 120 G can be increased further increased by combining them with a Roots pumps. Optimized pump versions are available for larger volumes.
The technical data provided are given for a mains frequency of 50 Hz. Standard not more than 1 m3. Special versions of A 203 H and A 1803 H type pumps are suitable for volumes of up to 50 m3.
Multi-stage Roots pumps for noncorrosive applications | |||
Model | Pumping speed | Ultimate pressure with/without purge gas | Applications |
ACP 120 | 95 m³ · h-1 | 3 · 10-2 hPa | Load locks and transfer chambers with a volume of up to 1 m3, noncorrosive gases, noble gases, regeneration of cryo pumps, backing pumps for turbopumps with noncorrosive gases |
ACP 120 G | 95 m³ · h-1 | 9 · 10-2 with 35 slm purge gas | |
A100 L | 100 m³ · h-1 | 6.6 · 10-3 hPa | |
A100 L ES | 100 m³ · h-1 | 7 · 10-4 hPa | |
Table 4.16: Performance data for water cooled multi-stage Roots pumps for noncorrosive applications
Multi-stage Roots pumps for corrosive applications | |||
Model | Pumping speed | Ultimate pressure with/without purge gas | Applications |
A 103 P | 120 m³ · h-1 | 6.5 · 10-3 hPa 2.6 · 10-2 hPa with 20 slm purge gas | Dry etching (oxide and poly) Ashing Stripping RTP Implantation |
A 603 P | 480 m³ · h-1 | 5 · 10-4 hPa 2 · 10-3 hPa with 20 slm purge gas | |
A 1003 P | 900 m³ · h-1 | 3 · 10-4 hPa 1 · 10-3 hPa with 20 slm purge gas | |
Table 4.17:Performance data for P series water cooled multi-stage Roots pumps for corrosive applications
Diaphragm Pumps | |||
Model | Pumping speed | Ultimate pressure with/without purge gas | Applications |
A 203 H | 130 m³ · h-1 | 6 · 10-2 hPa 5 · 10-1 with 50 slm purge gas | Metal etching CVD (PECVD, SACVD, LPCVD) ALD Epitaxy Dry etching |
A 803 H | 600 m³ · h-1 | 1 · 10-3 hPa 1 · 10-2 hPa with 50 slm purge gas | |
A 1503 H | 1,100 m³ · h-1 | 2 · 10-3 hPa 9 · 10-3 hPa with 50 slm purge gas | |
A 1803 H | 1,650 m³ · h-1 | 2 · 10-3 hPa 9 · 10-3 hPa with 50 slm purge gas | |
AD 73 KH | 4,700 m³ · h-1 | 8 · 10-4 hPa 3 · 10-3 hPa with 50 slm purge gas | |
Table 4.18: Performance data for H series water cooled multi-stage Roots pumps for corrosive applications (harsh processes)
4.6.6.2 Accessories
Seismic brackets kit
A seismic brackets kit enables the pump to be fixed in place at its site of operation, and prevents any displacement due to earthquakes and the fore-vacuum line from becoming detached.
Remote control
Remote control allows the pump parameters to be set and saved in the integrated memory of the pump. Pump parameters can be displayed in real time.
Interfaces
Customized interfaces between the pump and the system control can be supplied to provide a link to production plant control units.
Water connections
The water connections on the pumps and the appropriate quick fitting couplings to connect cooling water lines are available in brass and stainless steel versions to provide the best possible corrosion stability.
The accessories listed are not recommended or available for every type of pump described in this chapter. Additional accessories, such as for additional interfaces, electrical safety, connections or safe shipping, can be supplied on request.
