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About the MPG HLL
MPG HLL Frequently Asked Questions

 

 

     
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  Why is our cleanroom illumination yellow by default?
       
  Photochemical processing is the reason for the yellow illumination:
The photoresist is insensitive to this type of light only.
  Photo of MPG HLL cleanroom with different types of illuminations
         
         
  Our Most Frequently Asked Question      
         
  A frequently asked question is, why our detector fabrication is not undertaken by “conventional” silicon foundries for microelectronics, assuming this would save resources and would rely on a constantly upgraded industrial technology.   Photo of wafer boats containing wafers to be inserted into a MPG HLL furnace  
       
  In fact our fabrication process is totally different. A direct transfer to microelectronics industry or an adaptation of electronic industry standards is impossible: Dedicated detector manufacturing requires extraordinary time and effort. In contrast to other fabrication processes, there are four reasons for not outsourcing our ultra-pure silicon wafer processing:
     
         
I     Purity      
         
  The purity of the silicon we use is more than 1,000-times higher than electronic industry silicon. In consequence the cleanliness of the silicon must be maintained throughout the entire fabrication process of up to 500 individual steps. This requires an extraordinary care concerning the cleanroom itself, the fabrication tools employed in the process, the chemicals used as well as the cleaning procedures before and after every individual step.   Photo of a MPG HLL eRosita chip inspection  
         
         
II    Fully Double Sided Process      
         
  Contrary to electronics industry, we take advantage of a fully double sided process, i.e. both wafer surfaces contain electronic structures. Correspondingly the wafer must be handled only within a small well defined rim-area during the entire fabrication process. And the development of dedicated handling robots and process tools is mandatory.   Photo of a
        MPG HLL silicon wafer being inspected before processing  
         
         
III   Large Feature Sizes      
         
  The size of our double sided monolithic circuits can be as large as 100 cm². Optical inspections with data based monitoring systems are required: Every production step and wafer is scanned in detail. These inspections consume nearly half of the production time – in a typical state-of-the-art project corresponding to five of ten months total production time.   Photo of the MPG HLL XMM Charge Coupled Device  
         
         
IV    Combined Electronic and Detector Fabrication Process  
         
  The MPG HLL is one of the few places in the world where a monolithic integration of electronics into the detector fabrication process (signal processing, first amplification) has successfully been solved without degrading the detector performance. Producing fully depleted, i.e. fully sensitive devices with low leakage currents in a radiation hard process is the rationale for future optimizations. The achievements of our research as well as our projects, experiments and collaborations translate the philosophy mentioned above into detector properties.   Photo of MPG HLL DEPFET pixel matrixes and integrated readout electronics  
         
     
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Photo of the MPG HLL cleanroom data-based monitoring system inspection.