High Resistivity Magnetic Czochralski Research Articles

Strip Detectors Processed on High-Resistivity 6-inch Diameter Magnetic Czochralski Silicon (MCz-Si) Substrates

Tracking detectors for future high-luminosity particle physics experiments have to be simultaneously radiation hard and cost efficient. This paper describes processing and characterization of p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> (n-type silicon bulk) detectors made of high-resistivity Magnetic Czochralski silicon (MCz-Si) substrates with 6-inch wafer diameter. The processing was carried out on a line used for large-scale production of sensors using standard fabrication methods, such as implanting polysilicon resistors to bias individual sensor strips. Special care was taken to avoid the creation of Thermal Donors (TD) during processing. The sensors have a full depletion voltage of 120-150 V which are uniform over the investigated sensors. All of the leakage current densities were below 55 nA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> at 200 V bias voltage. A strip sensor with 768 channels was attached to readout electronics and tested in particle beam with a data acquisition (DAQ) similar to the system used by the CMS experiment at the CERN LHC. The test beam results show a signal-to-noise ratio greater than 40 for the test beam sensor. The results demonstrate that MCz-Si detectors can reliably be manufactured in the industrial scale semiconductor process.

Development of Radiation Hard Particle Detectors Made of Czochralski Grown Silicon

Tracking detectors to be used in the future high-luminosity particle physics experiments have to be simultaneously radiation hard and cost e cient. Magnetic Czochralski silicon wafers can be grown with su ciently high resistivity (several kΩ cm) and well-controlled high oxygen concentration. Signi cant research and development activity aiming to develop particle detectors made of high resistivity magnetic Czochralski silicon has been ongoing during the past decade. Beam test results presented in this paper show that n-type magnetic Czochralski silicon strip detectors can be operated with acceptable signal-to-noise ratio at least up to a 1 MeV neutron equivalent (neq) uence of 1 × 10 cm−2. The improved radiation hardness, compared to more commonly used oat zone silicon, can be explained by the more bene cial electric eld distribution inside the detector bulk. We have demonstrated a S/N of > 10 for full-size strip detectors attached to readout electronics at a uence of 1 × 10 neq/cm. These ndings are supporting our transient current technique measurements.

MCz diode response as a high-dose gamma radiation dosimeter

This work presents the preliminary results obtained with a high-resistivity magnetic Czochralski (MCz) silicon diode processed at the Helsinki Institute of Physics as a high-dose gamma dosimeter in radiation processing. The irradiation was performed using a 60Co source (Gammacell 220, MDS Nordion) within total doses from 100 Gy up to 3 kGy at a dose rate of 3 kGy/h. In this interval, the dosimetric response of the diode is linear with a correlation coefficient ( r 2 ) higher than 0.993. However, without any irradiation procedure, the device showed a small sensitivity dependence on the accumulated dose. For total dose of 3 kGy, the observed decrease was about 2%. To clarify the origin of this possible radiation damage effect, some studies are under way.

Evaluation of Surface Passivation Layers for Bulk Lifetime Estimation of High Resistivity Silicon for Radiation Detectors

In order to identify an appropriate low-temperature surface passivation that could be used for bulk lifetime estimation of high resistivity (HR) (&gt; 1 k·cm) silicon for radiation detectors, different passivating layers were evaluated on n-type and p-type standard Czochralski (CZ), HR magnetic CZ and HR float zone (FZ) substrates. Minority carrier lifetime measurements were performed by means of a μW-PCD set-up. The results show that SiNx PECVD layers deposited at low temperatures (≤ 250°C) may be used to evaluate the impact of different processing steps and treatments on the substrate characteristics for radiation detectors. First results are obtained about a preliminary thermal treatment experiment to evaluate the thermal stability of the passivating layers, as well as the potential impact of the generation of thermal donors on minority carrier lifetime.

Low-temperature TCT characterization of heavily proton irradiated p-type magnetic Czochralski silicon detectors

n +/p −/p + pad detectors processed at the Microelectronics Center of Helsinki University of Technology on boron-doped p-type high-resistivity magnetic Czochralski (MCz-Si) silicon substrates have been investigated by the transient current technique (TCT) measurements between 100 and 240 K. The detectors were irradiated by 9 MeV protons at the Accelerator Laboratory of University of Helsinki up to 1 MeV neutron equivalent fluence of 2×10 15 n/cm 2. In some of the detectors the thermal donors (TD) were introduced by intentional heat treatment at 430 °C. Hole trapping time constants and full depletion voltage values were extracted from the TCT data. We observed that hole trapping times in the order of 10 ns were found in heavily (above 1×10 15 n eq/cm 2) irradiated samples. These detectors could be fully depleted below 500 V in the temperature range of 140–180 K.

Intentional thermal donor activation in magnetic Czochralski silicon

We have made a quantitative study about the thermal activation of thermal donors in high resistivity magnetic Czochralski silicon. The thermal donor activation has been performed through a thermal treatment at 430 °C up to a total time of 80 min. The space charge density after each annealing step has been extracted from capacitance–voltage measurements. If the starting material is boron-doped p-type high-resistivity Czochralski silicon, the thermal donor generation process can be utilized in order to produce p +/n −/n + detectors. The last thermal process step, i.e. the sintering of aluminum, is intentionally carried out at the temperature where thermal donors are created. According to our results, we have improved the previously reported model of the thermal donor generation.

Recent progress of CERN RD50 Collaboration

The objective of the CERN RD50 Collaboration is to develop radiation hard semiconductor detectors for very high luminosity colliders, in particular, for the upgrade of the large hadron collider (LHC) which itself is scheduled to be operational in 2007. The approach of the RD50 has two major research lines, material engineering and device engineering. These are further subdivided into projects covering defect characterization and engineering, new detector materials, detector characterization, new detector structures and full detector systems. Presently, 264 members from 53 institutes are actively participating in the RD50 Collaboration. Detectors made of defect engineered substrates, e.g. high resistivity magnetic Czochralski (MCz-Si), epitaxial silicon (Epi-Si) on Czochralski silicon (Cz-Si) substrate, intentionally thermal donor (TD) compensated p-type MCz-Si and oxygen enriched (DOFZ) silicon, have been demonstrated by the RD50 Collaboration. An overview and highlights of the results of these defect engineering techniques were given in this report.

Processing and first characterization of detectors made with high resistivity n- and p-type Czochralski silicon

We report on the design, manufacturing and first characterisation of pad diodes, test structures and microstrip detectors processed with high resistivity magnetic Czochralski (MCz) p- and n-type Si. The pre-irradiation study on newly processed microstrip detectors and test structures show a good overall quality of the processed wafers. After irradiation with 24 GeV/ c protons up to 4×10 14 cm -2 the characterisation of n-on-p and p-on-n MCz Si sensors with the C– V method show a decrease of the full depletion voltage and no space charge sign inversion. Microscopic characterisation has been performed to study the role of thermal donors in Czochralski Si. No evidence of thermal donor activation was observed in n-type MCz Si detectors if contact sintering was performed at a temperature lower than 380 °C and the final passivation oxide was omitted.

Gamma radiation induced space charge sign inversion and re-inversion in p-type MCZ Si detectors and in proton-irradiated n-type MCZ Si detectors

Positive space charge build-up was observed in proton—and neutron—irradiated high-resistivity magnetic Czochralski (MCZ) n-type Si detectors after gamma radiation. Space charge sign re-inversion (SCSRI) from negative to positive was achieved at the high dose of 454 Mrad in a low-fluence proton irradiated MCZ Si detector. No SCSRI has been observed yet for low-fluence neutron-irradiated MCZ Si detectors at the highest dose in this study (662 Mrad), but positive space charge is building up, and SCSRI is expected at higher doses. Up to the highest dose in this study, the double junction or double peak electric field distribution is still preserved even after SCSRI. No SCSRI was observed in control FZ Si detectors. Space charge sign inversion was also observed in high-resistivity as-processed MCZ p-type Si detectors after gamma radiation.

Radiation hardness of high resistivity magnetic Czochralski silicon detectors after gamma, neutron, and proton radiations

High resistivity magnetic Czochralski Si detectors were irradiated with /sup 60/Co gamma rays, neutrons, and protons to various doses/fluences, along with control float zone Si detectors. 1) It has been found that for gamma radiation, magnetic Czochralski Si detectors behave similarly to the high-temperature, long-time (HTLT) oxygenated float zone Si detectors. There is no space charge sign inversion and there is a buildup of positive space charges. The rate for this buildup is much higher than that for the oxygenated Si detectors and is proportional to the oxygen concentration. 2) For neutron radiation, there is little difference between magnetic Czochralski and control float zone silicon detectors. Space charge sign inversion is observed for both materials. The introduction rate of deep acceptors (beta) for magnetic Czochralski Si detectors is slightly less than that for control float zone Si detectors, and 3) for proton radiation (10 and 20 MeV), although the space charge sign inversion is also observed for magnetic Czochralski Si detectors, the 1-MeV neutron-equivalent space charge sign inversion fluence is about three times higher than that of magnetic Czochralski Si detectors irradiated with neutrons. Also, the acceptor introduction rate beta is about half of that for oxygenated Si detectors. Thus, high resistivity magnetic Czochralski Si behaves in a similar manner to the HTLT oxygenated float zone Si detectors and is even more radiation resistant to damage caused by charged particles.