AW-903eR Plasma Etch RIE

AW-903eR Plasma Etch System Basic Configuration:

1. Chamber :

The AW-903eR chamber employs a diode reactor design. The Chamber is at ground potential and functions as the cathode for this scheme. The Chuck is the anode in the scheme.The size of the gap between the upper and lower surfaces of the reactor (also known as the reactor) for the AW-901e and AW-903e systems are different.

As a first step in plasma generation, the vacuum valve on the Pressure Controller evacuates the Reaction Chamber to a low pressure. The Gas  Delivery module then introduces process gases. RF power is supplied to one electrode (the Chuck), and the voltage differential between that electrode and another electrode (the Chamber) generates a plasma. A sapphire rod and a fiber-optic cable provide optical evaluation of the
plasma, the characteristics of which depend on the gas chemistry, pressure, and RF power used. The cable carries the optical signal from the Chamber to the endpoint module. The Chamber, which is made of aluminum, is electrically grounded, and the Chuck is connected to the positive lead of the RF generator. The lower ceramic of the Chamber provides a sealing surface for the O-ring on the Chuck module and acts as an insulator between the Chuck and the Chamber.

2. AC Module:

The AC Module (ACM) receives AC power from the PDM and distributes AC voltage to • the DC Power Supply, •Controllers and • RF Generator  modules within the system. The module contains:

• • The main 200-240 VAC, 20 amp, primary AC power connector.
• • Line filter.
• • 24 VAC transformer for interlock and AC control relays.
• • Two 115-VAC, 2-amp, service outlets (on front of module) and a terminal strip for AC distribution to other system peripheral equipment.
• • Circuit breakers and contact relays that control power to the other modules in the machine

 3. DC Modules:

The DC modules receive AC power (200+ VAC) from the AC module. They convert the AC power into DC power via the DC power Distribution PCB 
for distribution to the• Endpoint PCB,• Gas/Pressure Interface PCB, Interface Matching Network PCB ( IMN),• Front Panel Display PCB ,• Receiver Interface PCB (If Applicable),• Sender Interface PCB (If Applicable) ,• Shuttle Interface PCB (If Applicable) , • Temperature Interface PCB, • Autotune RF Matching Network PCB etc.

4. Endpoint/Optical Emission

When RF is turned on, the plasma is initialized and “ionized molecules” are formed. The energy released as excited molecules relax is in the form of
light (photon),. The frequencies, or wave lengths, of the light emission spectrum is specific to the “excited moleculers” present in the reactor. By  monitoring decreases in etchant species or increases in etchant by-product, process endpoint can be determined and the data can be stored for further analysis. To achieve endpoint, various parameters must be set up in the etch step(s) of the recipe. The Process Engineer adjusts several recipe parameters to detect the desired endpoint. 
The Photodiode Endpoint PCB contains the digital and analog circuits required to monitor an etch process and determine the end of an etch
sequence. This circuit has the ability to monitor two separate photodiodes as well as both positive and negative DC Bias. The two photodiodes, Cell A and Cell B, are identical. The silicon photodiodes are broadband light detectors, therefore an optical filter is required to detect the strength of  emissions at specific wavelengths. The Endpoint board is designed to accept any filter on either diode. However, to be consistent, we have standard locations for filters. In general, the negativegoing emissions are in the A position, and the positive-going in B. Optical signals can be powerful tools for the Process Engineer to determine endpoint and analyze etching problems. Signals sent from optical diodes are analyzed by the system software and displayed on the system screens and (optionally) the chart recorder.

5. Gas Delivery Module

The Gas Delivery Module provides the controlled delivery of all process gases to the Chamber upon demand. The Control Computer creates the
timing of delivery, quantity and the total time of each gas delivered. The Mass Flow Controllers control gas flow. Up to four process gases can be
used, as well as a manually adjusted clean channel gas (O2) for plasma cleaning.

6. Pressure/Vacuum

On the top plate, left side, as viewed from the front. There are several key components that comprise the pressure vacuum module:

• • Capacitance Manometer: analog device, 0-10VDC output = 0-10Torr. The manometer is heated to 40C to to maintain output stability  independent of ambient temperature. A 4-hour warm-up period must be allowed before adjusting the zero.
• • Atmospheric Sensor: analog device, ~5VDC to ~0VDC = 0Torr to 760Torr. No adjustments are made.
• • Test Port: There are two different vacuum connections: VCR and Ultra Torr. Port is enabled manually via toggle switch located on Front Panel Display (90Xe).
• • Pressure Controller : The UPC controls the flow of N2.into the foreline of the vacuum pump to control the reactor pressure to the setpoint pressure. Reactor and setpoint pressures are inputted to the pressure controller.
• • Vacuum Valve: The Vacuum Valve is used to isolate the chamber from the vacuum pump. It is connected to the process chamber and vacuum pump lines via KF-40 flanges on, 1.5 inch diameter plumbing and is actuated by clean dry air (80 psig) that is controlled by a solenoid valve. The vacuum valve is bypassed with a smaller pneumatically controlled  valve with ¼ inch plumbing for soft-pump feature. Both valves receive the same pneumatic signal, but the pneumatic delivery to the main vacuum valve is metered to achieve full open in 12-17 seconds for softpump. Also, there are two switches mounted to the end of the main vacuum valve – one is wired NO, the other is wired NC. The RF enable signal is disabled until the main vacuum valve is fully open.
• • Vacuum Pump connection: This is a KF-40 vacuum flange located at the left-rear of the tool.

7. RF Delivery

The RF Delivery module is located in the front-center of the chassis. The module is accessible via a hinged panel. To gain access to the lever that
releases the hinged panel, the top panel between the cassette elevators must be opened. A 5/32 inch socket-head screw at the top of the On/Off panel
releases the top cover. 
The RF Delivery module is responsible for delivery and control of RF power from the RF Generator to the process chamber. The RF Delivery module
contains several components, or sub-modules:

• Matching Network: The matching network module is located on the left side of the RF Delivery module. The matching network automatically adjusts two capacitors to match the output impedance of the RF generator (50 ) to the variable impedance of the reactor. The matching network currently does not interface with the system controller. The auto tuning feature is independently controlled by the auto tune PCB, which is mounted to the side of the matching network. Also mounted to the side of the matching network is the phase/magnitude detector, through which the RF signal passes before going into the matching network. The DC output of this device is fed to the autotune PCB, the  amplitude of which is proportinal to the amount of reflected power. The autotune PCB adjusts the tuning capacitors in a direction that minimizes the output of the phase/mag detector. The matching network also contains a DC bias sensing circuit just before the RF output. A signal from the DC bias sensing circuit in the Matching Network is fed out the rear of the matching network module to the Endpoint PCB via BNC connection. 
• DC BIAS THEORY: Electrically, the reactor behaves like a capacitor. The chamber body and the lower electrode makeup the two plates of the capacitor. The upper electrode is at ground potential and the lower electrode is at RF potential. The upper electrode (chamber body) is larger than the lower electrode in that it has more surface area. Electrons have virtually no mass and essentially all of them migrate to the lower electrode when the RF signal is positive. Conversely, all the electrons  migrate to the upper electrode (chamber) when the RF signal is negative. Since the same number of electrons make it to the smaller electrode (lower) as do to the larger electrode (upper), the density of electrons is greater at the  lower electrode as compared to the upper electrode. Therefore, the lower electrode has a net negative charge to ground, a -DC bias. A DC potential exists at the lower electrode because the upper and lower electrodes are not the same size. If the lower electrode is anodized, no DC bias is present at the sensing circuit because anodization (Al2O3) is an insulator. Note that ceramic chamber parts are Al2O3. If DC bias is present on systems with anodized lower electrodes, then a breach in anodization has occurred. A breach in anodization does not necessarily adversely affect the process results. 
• Interface Matching Network PCB (IMN): Although the IMN PCB is not mounted to the RF Delivery module, it is connected in series with it. The data ribbon cable from the main control board connects to the IMN. The RF enable (digital), RF setpoint (analog),RF forward and reflected power feedback signals (analog) are delivered. The RF enable signal is sent to the vacuum valve (see Vacuum Valve Interlock below). All other signals are sent to the RF Interface PCB (see below). The IMN PCB also interfaces to the controller the atmospheric sensor (analog) signal. 

• RF Interface PCB (RFI): This interface card is located at the front-bottom of the RF Delivery module. The RFI PCB interfaces the controller signals, such as RF enable (digital), RF setpoint (analog), RF forward and reflected power feedback signals (analog).

• RF Generator: The RF generator is located remotely up to 2.7 meters (9 feet) from the etcher. The interface connection between the RFG and the etcher consists of two cables: the RF cable, which connects to phase/mag detector on the side of the matching network, and the data cable, which connects to J4 on the RF Interface PCB. The data cable transmits the RF setpoint (analog to RFG), the RF enable signal (digital to RFG) and the RF forward and reflected power information (analog from RFG).

• RF Meters: There are two hour-meters mounted to the upper display One meter can be reset to zero (push button near meter), the other cannot. The meters are activated by the RF enable signal from the RF interface PCB and indicate RF-on hours.

• RF Vacuum Interlock: There are two switches mounted to the end of the main vacuum valve – one is wired NO, the other is wired NC. The RF enable signal (digital) is disabled via these switches until the main vacuum valve is fully open. The RF enable signal is routed from the IMN PCB, through the vacuum valve switches and back to the IMN PCB. RF power is connected to the Chuck to generate a plasma.