EpiSoft MBE & Deposition Control System
Initially developed for MBE applications, EpiSoft provides a unique approach to deposition process and overall system control. It is built around the principle of defining the growth process in terms of deposition events (growth rates, doping levels...) as opposed to low level parameters (temperature, voltage, flow rate...); we call this growth-oriented approach SOC (Structure-Oriented Control):
- SOC defines the structure in terms of a series of "events" (e.g. thickness or time specified steps) analogous to "drawing" the required structure. "High" level parameters (such as thickness, growth rate, doping level) are internally converted to "low" level values (such as temperature, voltage) as they are required.
- SOC permits unprecedented ease of definition of and control over deposited features. For example, a linear composition ramp can be defined in a single step, as opposed to a complex list of temperatures as required by low level parameter definition. More importantly, the required data profile can be much more precisely applied than possible using manual (low-level) programming.
- Growth data can be simply and intuitively analysed graphically: for example, comparison of intended composition, growth rate, doping levels with actual values.
SOC is achieved through maintaining detailed "calibration" information (easily modified to reflect source digression) between the high and low level parameters within the EpiCAD software, which is only applied at the moment of communicating with the deposition system. The benefits of SOC extend well beyond the above:
- All aspects of controlling the system can use SOC, from vacuum pressure monitoring to gas flow control, from shutter/valve status to real (as opposed to indicated) substrate temperature.
- SOC allows automated correction for source instabilities/drifts, such as MBE source depletion
- SOC makes possible sharing of expertise across labs and even between different deposition systems.
- Sophisticated alarm conditions and actions can be readily defined and invoked to ensure correct and safe operation of the systems.
EpiSoft has a 20 year history in controlling MBE and other deposition systems:
- Used by some of the world's leading research and production facilities
- Has been applied to most material systems: III-V, mixed-IV, II-VI, metals, HTSC, organics...
- Provides a unified interface for most technologies: effusion sources, e-beam sources, sputtering, gas lines, ablation...
- Installed on all leading manufacturers (Veeco, VG, Riber...) as well as custom systems
The EpiSoft system comprises 2 parts: the PC-based EpiCAD software and the EpiFrame hardware interface unit which connects the PC to the deposition system compontents.
The EpiFrame is a 19" rack-mounting, 1U high interface unit fitted as standard with:
- 4x serial ports (individually configurable as RS232, RS422 or RS485)
- 20x opto-isolated digital inputs
- 8x ±10V analogue inputs
- Either 2 or 8 ±10V analogue outputs
- Digital outputs from one of the following: 16x relays, 21x relays, 32x TTL-level, 32x opto-isolated.
Most applications can be more than adequately controlled using a single EpiFrame unit, but if necessary, up to 8 Epiframes can be daisy-chained to provide what is in effect unlimited interfacing.
All aspects of the EpiFrame, such as serial settings (baud rate, parity etc.), analogue ranges, comms watchdogs are user-selectable from within the EpiCAD software.
EpiCAD is an object-oriented environment essentially based around user-definition of P-Loops (process loops), ports (communication ports), sensors (digital input events) and flags (digital output events). Each object has a range of user-defined attributes which allow it to simulate operation of a deposition component (such as substrate, source, dopant, interlock, shutter, valve...). EpiCAD contains a knowledge base as to how the different objects interact in a real deposition process.
In addition to SOC discussed above, EpiCAD provides a host of features including:
- The Calibration Maintenance facility provides SOC with the relationship between high and low level parameters via a range of weighted fitting functions, and fast, easy re-calibration which mimics the way many deposition sources operate. Even consumption-based auto-correction of source depletion is supported.
- EpiList editors use an intuitive event based paradigm to allow fast creation of deposition "recipes" of unlimited size. Thanks to SOC, all recipes are reusable without modification, even if source calibrations have changed! Includes automatic error checking, on-the-fly recipe editing during run, nested repeat sequences and much more...
- Data Acquisition. This fully user-defined facility provides for continuous logging of all system data, as well as separate recipe-related data acquisition. Data is presented graphically with full user-definition of resolution, zoom, time-span etc. Data can be exported as ASCII for spread-sheet import.
- Comprehensive, multi-level user-defined alarm condition and actions for system protection and security
- Slaving of process loops, for example, for automated operation of multi-zone sources
- Dual sensor operation, for example, thermocouple AND pyrometer control over substrate temperature
- Definition and assignment of multiple valve combinations to growth conditions (e.g. as line run, vent, purge, off...)
- AND MUCH MORE!