Sensors & trandsucers
are calibrated using a Gravimetric System that records weight change over time in a cylinder supplying gas to a master MFC to derive a flow rate. Measurements are taken in a temperature-controlled room to eliminate any bias due to air buoyancy and the system includes an electronic balance that is not susceptible to the effects of vibration. The Gravimetric System was the subject of a
feature in the June 2018 issue of Instrumentation magazine. What does an MFC having ISO/IEC 17025
certification mean to you as a user? When you unbox a new unit, you know that the degree of uncertainty between the figures on the spec sheet and actual performance are within acceptable limits of accuracy and repeatability. Regarding the vaporisation step, there are
several techniques available; and are worthy of a separate article at a later date. For now, we will stick with closed-loop ‘instruments.’ Concentration monitors are used to verify
(in real-time) that the precursor recipe going into the chamber is correct. Most high- performance monitors use the non-dispersive infrared absorptiometry (NDIR) double-beam method. Following verification of the recipe in its
vapour/gaseous state a mass flow meter would be used, though an MFC can also be used (it is just a case of setting the valve to fully open).
Reaction time
The monitoring of conditions within the chamber during the manufacturing process/stage is of paramount importance. For example, in dry coating applications (as well as the drying phases of others) moisture levels must be closely monitored. In other examples, such as plasma-enhanced chemical vapour deposition (PECVD), the effectiveness of the sputtering can be determined through gas analysis. Etching can be monitored and therefore controlled too. For all applications, an RGA can be used to detect gas leaks and contaminations, as well as determining partial and total gas pressures. RGAs can also be used to verify that the chamber has been successfully flushed of chemicals - such as CF4 and F2 – following cleaning, in readiness for the next batch. Process equipment manufacturers are
favouring compact RGAs, as their small form-factor enables their use in low- vacuum and high-vacuum pressures without
the need for differential pumps; perfect for sputtering applications. Lastly, a second gas concentration monitor could be employed, this time in the exhaust line, to verify that the processes have taken place as intended; and again, that chamber cleaning was successful.
in contRol
In a closed-loop control environment, the overall accuracy, repeatability and reproducibility of the manufacturing process is dependent on all the individual instruments possessing those characteristics too. It only takes one weak link in the chain and the high value product is at risk. For this reason, single-sourcing from OEMs
that provide the full spectrum of process and control products, and which are best-in-class and appropriately certified, is a sound strategy. Also, there is an increasing need for in-line, in- situ material characterisation (using analytic techniques traditionally associated with the scientific laboratory – a subject for another day) and if the OEM can provide those too then that is even better.
HoRiBa UK
www.horiba.com
Figure 2 - ISO/IEC 17025 certification requires the provision of traceability all the way back to SI units.
Instrumentation Monthly February 2019
35
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80
