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The Meeting was held at CERN 3.February 2000 (14:00 Room 13-3-005).
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Contents:
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• Participants

• Transparencies

• Presentations and Comments
  Michael Moll
  Gianluigi Casse
  Laci Andricek
  Janet Carter
  Petra Riedler
  Alberto Messineo
  Renate Wunstorf
  Frederic Teubert

• Discussion and Conclusions / Next Meeting

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Participants  (top of page)
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Transparencies    (top of page)
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Copies of the transparencies have been send to all participants. Those who have not attended the meeting are invited to ask for a copy (michael.moll@cern.ch ).

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Presentation: Michael Moll RD48    (top of page)
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A more detailed description of most of the presented data can be found in the recent RD48 STATUS REPORT. The report is available on the Web: http://cern.ch/rd48 or ask me for a copy ( michael.moll@cern.ch ).

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Part I - taken from the STATUS REPORT (Executive Summary)
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The Key results of the RD48 collaboration are:

* The leakage current damage parameter is material independent (no impurity, resistivity or conduction type dependence). It has been linked to defect clusters which are not affected by the material. Annealing of the leakage current is also material independent. The damage parameter and its annealing has been shown to scale ideally with NIEL (non ionising energy loss), i.e. with-out any remaining particle or energy dependence.

* Effective doping changes can be improved by oxygenation of the material (factor 3) Such improvement is only observed when the radiation environment contains a significant charged parti-cle component. This has been understood in terms of the production of larger numbers of iso-lated vacancy/interstitial pairs during charged particle irradiation.

* Lower resistivity oxygenated material is beneficial for detectors that operate in a radiation environment dominated by reactor energy neutrons.

* Reverse annealing has been linked to defect clusters. After proton irradiation, this process is found to saturate at high fluence (>2 1014p.cm-2 ) for oxygenated silicon. This provides a significant safety margin. In addition, the time constant for the process is found to be a factor 4 larger. This would allow detectors to remain at room temperature for longer periods during mainte-nance periods and thus offers a substantial safety margin.

* Detailed correlations have been found between microscopic defect formation and macroscopic damage parameters. Defect kinetics models and device models can predict macroscopic behavior well, even for hadron irradiation.

* A macroscopic damage parameter model has been developed which can be used to predict detector parameters in a given radiation environment. This model has been used already in operational projections for major LHC experiments.

The key technological results of the project are:

* Two methods were found to highly oxygenate silicon. Firstly, at the ingot growing stage. Secondly by diffusion of oxygen into ANY wafer using a high temperature drive-in (a minimum of 16 hours at 1150C seems to be sufficient).

* This technology has been successfully transferred to several silicon detector manufacturers (SINTEF, Micron, ST, CIS) and full-scale microstrip detectors produced.

The following work needs to be performed in the next few months:

* The minimum diffusion time required to give radiation hardening needs further study. The bene-ficial effect that oxygen has on the reverse annealing process needs more work. As this effect is crucial to the maximum maintenance period that can be used by the experiments, it needs further investigation. This work is extremely time consuming.

* The physics of bulk damage should be the same in full-scale detectors as in simple diodes. Nev-ertheless, bulk damage parameters should be extracted from irradiated strip detectors and com-pared to the well-measured parameters obtained with diodes.

* The violation of NIEL by charged hadrons in oxygenated material needs further study. Testing with radiation sources that better represent the environment in the LHC experiments needs to be performed. The neutron spectrum in the LHC experiments extends to much higher energy than for reactor sources. There are good reasons to believe that oxygenated
silicon will perform better than standard material in such a neutron environment.

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Part II - not included in the STATUS REPORT
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An important point not mentioned in the status report (new data) is the wide spread in the damage parameter beta for standard material:

A set of silicon diodes produced by ST Microelectronics on standard Wacker silicon with different resistivity (1 to 15Kohmcm) and different orientation (<111> and <100>) was irradiated with 24 GeV/c protons. Some of the diodes were less radiation hard than expected from previous experiments on standard silicon and some were radiation harder (almost as
good as oxygenated silicon diodes). This fluctuation of the beta factor was found to be independent of the resistivity and the crystal orientation. Up to now it is not clear which material property is responsible for this behavior (SIMS measurements are under way).

However, for the oxygenated silicon such a variation was so far not observed. This leads to the preliminary conclusion that the oxygenation process gives a reproducible good result with respect to the radiation hardness of the diodes while for material bought as "standard silicon" a wide variation can be possible. Even a less radiation hard behavior than expected from our previous experiments on standard silicon and   published in the STATUS REPORT is possible!

An important question is whether such a fluctuation is also observed after irradiation of the same set of diodes with neutrons. Such an irradiation experiment is foreseen.

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Presentation: Gianluigi Casse - ATLAS SCT    (top of page)
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* Comparison of oxygenated (DOFZ-48h at 1100C) and standard test diodes produced by Micron show a strong improvement for the radiation hardness of the oxygenated diodes (about 150 V (300mum) after 2.5e14 p/cm2).

* Two techniques used for oxygenation leading to the same radiation hardness of final diodes:
a) Oxygenated from SiO2 coating + 48h 1100C
b) Oxygenated from surface implant + 48h 1100C

* ATLAS Barrel detectors produced from oxygenated and standard silicon by MICRON show no difference in their properties prior to irradiation. (Oxygenation: 110h at 1100C)

* After irradiation with 3e14 p/cm2 the improvement for the oxygenated Barrel detectors compared to the standard ones is about 50 V. Deduced from CCE measurements with laser (1064nm) and 106 Ru-source (maximum CCE arbitrarily scaled to one for both kind of measurements - see transparencies).

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Presentation: Laci Andricek - ATLAS SCT   (top of page)
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* Comparison of oxygenated (280mum, 24h 1150C), standard (280mum) and thin standard (260mum) ATLAS W12 detectors produced by CIS

* before irradiation: no difference between standard and oxygenated detector

* after irradiation with 3e14p/cm2 (24GeV/c) and annealing for 7d at 25C:

- Oxygenated/Standard: Currents after irradiation are very similar and at the level expected from other irradiations
-CV measurements
--> 30V to 40V lower depletion voltage for the oxygenated detectors.
- Source measurement with fast analogue readout (SCT128a):
--> for oxygenated detectors CCE plateau around 300V, about 60 V lower than for the standard detector
--> oxygenated and standard detector give 92% of the signal that was measured on the unirradiated detectors

Conclusions:

* Even in the annealing state at the minimum of the depletion voltage oxygen enriched detectors give the same signal at 60 V lower voltage
* Using thin detectors, one has to got as low as 250microns to get the same performance as an oxygen enriched detector (in this radiation field and at this point of the annealing).

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Comments: Janet Carter ATLAS   (top of page)
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* Investigations on irradiated oxygenated/standard SINTEF detectors are presently under way.
(Contact person: DAVE ROBINSON)
* First (preliminary) results show that one of the oxygenated detectors behaves like a standard detector.
* CV: Approx. 50 V improvement for the oxygenated detectors (preliminary)

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Comments: Petra Riedler CMS-Pixel    (top of page)
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CSEM is currently producing CMS-Pixel detectors. 8 high resistivity and 8 low resistivity detectors produced on standard silicon have already been delivered and 8 oxygenated detectors are expected to be delivered in the next 2-3 weeks. An irradiation experiment with 24 GeV/c protons is scheduled for April.


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Comments: Alberto Messineo CMS    (top of page)
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" CSM started the prototypes production of Silicon Oxygenated micro-strp detectors with the ST Company.
We have 16 wafers oxygenated available and 5 wafers not oxygenated produced from the same batch and processed in the same line.
Each wafer contains 1 standard prototypes micro-strip detector, in real size, plus test structures as diodes, baby micro-strip detectors etc.
6 oxygenated together with 4 not oxygenated have been irradiated at CERN last November, with a maximum fluence of 3*10^14 24 GeV protons. The irradiation has been performed at low temperature and under bias; and after irradiation no annealing has been performed. Together with micro-strip detectors irradiation have been performed on  diodes and baby detectors for a total number of 17 structures.
We plan to perform electrical tests in the next weeks, hopefully to have results for the next Rose-collaboration meeting.
Future plans consists on beam test with MIP at CERN in the next months (April-May).

New oxygenated prototypes will be designed and committed to companies."


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Comments: Renate Wunstorf ATLAS-Pixel    (top of page)
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ATLAS - Pixel Collaboration will order oxygenated silicon (24hours at 1150C) !!

* The order of 3000 tiles is in preparation.

* Oxygenated prototypes have been produced at 2 vendors

--> behavior before irradiation is perfect
--> behavior after irradiation is presently under study (80 MeV protons).
However, same good results as with diodes are expected, since only bulk effect are seen after irradiation.

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Comments: Frederic Teubert LHCb    (top of page)
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"LHCb still has as a priority thin detectors, but the option to use oxygenated detectors is not excluded. Several detectors from Micron have been ordered (p on n detectors of different thickness 300 um, 220 um and 140 um), some of them oxygenated. Probably some oxygenated detectors from Hamamatsu (300 um) will be available and tested.
LHCb expects to reach a conclusion on the technology by the end of 2000.
Some of the results shown by ROSE, ATLAS and CMS need to be adapted to the special conditions of LHCb (mainly very non-uniform radiation). LHCb needs also to look at what is the effect on the resolution, and not only improvements on Vdep or CCE. LHCb expects to have the first results of this tests for the next meeting with RD48 in June."

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Discussion   (top of page)
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== Annealing experiments ==

Since the reverse annealing is strongly suppressed and slowed down in oxygenated silicon, annealing experiments should be performed with full size detectors.

Laci/ATLAS-SCT:
a) For an annealing into the minimum of the depletion voltage currently 7d at 25C are used.
b) For a long term annealing an annealing of 21d at 25C is suggested.

Michael/RD48:
It would be very interesting to compare a fully reverse annealed full size detector with a fully annealed diode of the same wafer. This could be done with the ATLAS - CIS structures (irradiated diodes and detectors available) and the CMS- ST Microelectronics structures (irradiated diodes and detectors available). For this experiment a higher annealing temperature (60C or 80C) would be better (better comparison with previous ROSE experiments).


== SIMS measurements ===

ATLAS and CMS are interested in common SIMS measurements in order to find out why for the full size detectors an improvement of only 50 V is seen while from the data published by the ROSE collaboration an improvement in the order of 120 V is expected.

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Next Meeting    (top of page)
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Will be held at CERN in the at the 15th of June 2000 (afternoon).

Before this meeting there will be a ROSE Workshop at CERN at the 16-17 of March 2000

------ http://cern.ch/RD48/5th-workshop/5th-workshop.htm -----------

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Michael Moll Tel: +41 22 76 74280
Division EP-MIC-SD Fax: +41 22 76 79075
CERN Email: michael.moll@cern.ch
CH-1211 Geneve 23 WWW: http://sesam.desy.de/~moll
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