PUBLISHABLE EXECUTIVE SUMMARY The last period of the Chemaph project,-extended by one additional month in order to include the time for an interesting synchrotron radiation experiment on selected, optimised, GeTe samples to take place- was characterized by an intense experimental activity on improvement of growth and characterization of chalcogenide materials. Following the Reviewers' suggestions, a project flow chart for the remaining time of the project was set in January, including recovering plans in case of failure of the main plan. The effort on deposition by MOCVD was carried out on three fronts: N2-based, standard MOCVD (horizontal tube reactor at MDM), H2 activated liquid injection MOCVD (close coupled showerhead reactor at AIXTRON) and hot wire - liquid injection MOCVD using N2 (vertical tube reactor at VU). A strict interaction between AIXTRON and MDM was set, in order to both evaluate the effectiveness of hydrogen in the process activation and to exchange data/information/characterization results, to reciprocally sustain advances in the respective deposition processes. The final aim was obviously to overcome the difficulties found in the achievement of bidimensional growth of uniform GST layers, so that all the subsequent milestones of the project could be achieved. Although the effectiveness of hydrogen in improving the morphology cannot be assessed optimized layers were obtained at AIXTRON by conventional thermal MOCVD using low pressure, low temperature processes. Best layers showed reversible phase change behaviour after nanopuls laser irradiation. At MDM, after a wide investigation of the deposition parameters within the limits of the system, an upgrade was decided in order to reach low deposition pressures (p<= 10 mbar). The upgrade consisted in the heating/isolation of the gas lines carrying the metalorganic precursors and letting them into the reaction chamber. Such installation was performed by Aixtron/MDM personnel in July 2008 and was necessary to allow the working temperature of 45°C for the thermostat baths containing the precursor bubblers. In such a way it could be possible to prevent the condensation of the precursor vapors along the gas lines, thus a sensitive decrease of the source molar flow. Improved layers were then deposited with morphology similar to the one reached at AIXTRON. At VU, after several reactor reconstructions, the hot wire -liquid injection MOCVD method was used for the deposition of Ge2Sb2Te5 and GeTe, finalized to the fabrication of prototype memory cells. Unfortunately, although an effort was made in order to optimize the handling and timing of the different steps involved in the fabrication of the device, no better results were obtained. By the optimized MOCVD process for Ge2Sb2Te5, depositions were also tried in VU with the aim of demonstrating the MOCVD capability of filling very aggressive, high aspect ratio (AR) structures supplied by Numonyx. Preliminary results show that the MOCVD layer has a very good conformality on structure with an AR around 1:1, while for a very aggressive AR (5:1) the film thickness at the bottom of the trench is reduced. In any case some chalcogenide has been deposited also at the bottom of the high AR trenches, proving the expected well superior performances of the MOCVD approach in term of film conformality with respect to the PVD technique. During this reporting period, the precursor supply by SAFC totally satisfied the needs of the growth teams, with an impressive effort due to the increasing needs related to the large out put of the deposition tool (working on 12 inches wafers) at AIXTRON. The precursor for doped-GST, namely tBuHNNH2, was also supplied in time to MDM and VU. Growths at VU of N-doped chalcogenide materials just started in October 2008. The material characterization, assessed during the first two reporting periods, supported the growth teams with on time responses. An increased involvement was set at MDM and AIXTRON, in order to face increasing needs for chemical, structural and morphological characterization, also including sample exchanges and reciprocal visits. A strong effort was also made at CSIC for providing functional characterization of new materials produced at AIXTRON, MDM and VU. The results are encouraging in terms of demonstrating phase change in samples produced by each of the three MOCVD systems. Moreover, two additional experimental studies were promoted by CSIC in order to contribute to a better understanding of the structural dynamics underpinning the physics of phase-change memory devices. - One ultrafast optical experiment, performed in collaboration with Davide Boschetto and Barbara Mansart from LOA-ENSTA in Palaiseau, France, where the coherent phonon signal was measured via optical reflectivity in single and double pump-probe experiments on GeTe films. - A combined ultrafast optical-X-ray experiment, to be performed in November at PSI, Villigen, Switzerland, aiming at the detection of the coherent phonon and related structural dynamics of the ferroelectric phase transition in crystalline GeTe. 4 Due to the high surface roughness over the wide area pieces necessary for the 3? method, the thermal conductivity of chalcogenide materials produced at VU was not evaluated at MDM. Since the consortium decided that it could be interesting to have an estimate of the thermal conductivity of some materials deposited by HW-CVD, it was agreed to perform some measurements in collaboration with the University of Bordeaux (TREFLE laboratory) that has a world-famous experience in thermal characterization of materials. The measurements were performed by photothermal radiometry and the results turned out to be in agreement with those found in the literature for the same class of materials. Due to the novelty of the subject, the results obtained during this last reporting period, although not at the expected level, where published in international journals and were presented at different conferences. In particular, the Chemaph Consortium was deeply involved in the organization of Symposium H Materials and Emerging Technologies for Non-Volatile-Memory Devices of EMRS 2008, Spring Meeting, Strasbourg, France and was also represented by two invited talks, one oral and one poster contribution. The success of SAFC in developing advanced precursor technologies has resulted in a new product range specifically targetted at the PCM market. Individual Ge, Sb and Te sources have been identified and robust synthesis and purification processes suited to a production environment have been established. A press release detailing the new products was well received and customer interest has been high. SAFC will continue to work to bring the optimum chemicals to the semiconductor industry to meet current and future requirements. Ahead of schedule AIXTRON has realized a first production prototype for the deposition of GST on 300 mm wafers. Analyzing the status of the process development after the second year AIXTRON decided to use the existing Tricent® technology as basis for the GST production tool. The systems provide for production necessary high deposition rate, high throughput and lower cost of ownership by employing unique processing technique enabled by a proprietary pulsed injection vaporizer called TriJet. In a first step the precursor delivery system was adapted to the GST precursors and up coming additional safety issues have been addressed. The demonstrated good conformality of the MOCVD film on Numonyx high aspect ratio structures represents an important achievement of the project and it proves that this technique is mandatory for the fabrication of alternative PCM cell architecture (full-confined PCM cells). On the other side, the electrical properties of the MOCVD deposited film are still in the validation phase and only a preliminary assessment has been achieved. It follows that the PVD deposited GST still remains the reference material for the PCM cell fabrication, even if there is interest to continue the evaluation of the MOCVD technique through demo activities from equipment suppliers.
CHEMAPH-2008-third periodic activity report
wiemer c
2008
Abstract
PUBLISHABLE EXECUTIVE SUMMARY The last period of the Chemaph project,-extended by one additional month in order to include the time for an interesting synchrotron radiation experiment on selected, optimised, GeTe samples to take place- was characterized by an intense experimental activity on improvement of growth and characterization of chalcogenide materials. Following the Reviewers' suggestions, a project flow chart for the remaining time of the project was set in January, including recovering plans in case of failure of the main plan. The effort on deposition by MOCVD was carried out on three fronts: N2-based, standard MOCVD (horizontal tube reactor at MDM), H2 activated liquid injection MOCVD (close coupled showerhead reactor at AIXTRON) and hot wire - liquid injection MOCVD using N2 (vertical tube reactor at VU). A strict interaction between AIXTRON and MDM was set, in order to both evaluate the effectiveness of hydrogen in the process activation and to exchange data/information/characterization results, to reciprocally sustain advances in the respective deposition processes. The final aim was obviously to overcome the difficulties found in the achievement of bidimensional growth of uniform GST layers, so that all the subsequent milestones of the project could be achieved. Although the effectiveness of hydrogen in improving the morphology cannot be assessed optimized layers were obtained at AIXTRON by conventional thermal MOCVD using low pressure, low temperature processes. Best layers showed reversible phase change behaviour after nanopuls laser irradiation. At MDM, after a wide investigation of the deposition parameters within the limits of the system, an upgrade was decided in order to reach low deposition pressures (p<= 10 mbar). The upgrade consisted in the heating/isolation of the gas lines carrying the metalorganic precursors and letting them into the reaction chamber. Such installation was performed by Aixtron/MDM personnel in July 2008 and was necessary to allow the working temperature of 45°C for the thermostat baths containing the precursor bubblers. In such a way it could be possible to prevent the condensation of the precursor vapors along the gas lines, thus a sensitive decrease of the source molar flow. Improved layers were then deposited with morphology similar to the one reached at AIXTRON. At VU, after several reactor reconstructions, the hot wire -liquid injection MOCVD method was used for the deposition of Ge2Sb2Te5 and GeTe, finalized to the fabrication of prototype memory cells. Unfortunately, although an effort was made in order to optimize the handling and timing of the different steps involved in the fabrication of the device, no better results were obtained. By the optimized MOCVD process for Ge2Sb2Te5, depositions were also tried in VU with the aim of demonstrating the MOCVD capability of filling very aggressive, high aspect ratio (AR) structures supplied by Numonyx. Preliminary results show that the MOCVD layer has a very good conformality on structure with an AR around 1:1, while for a very aggressive AR (5:1) the film thickness at the bottom of the trench is reduced. In any case some chalcogenide has been deposited also at the bottom of the high AR trenches, proving the expected well superior performances of the MOCVD approach in term of film conformality with respect to the PVD technique. During this reporting period, the precursor supply by SAFC totally satisfied the needs of the growth teams, with an impressive effort due to the increasing needs related to the large out put of the deposition tool (working on 12 inches wafers) at AIXTRON. The precursor for doped-GST, namely tBuHNNH2, was also supplied in time to MDM and VU. Growths at VU of N-doped chalcogenide materials just started in October 2008. The material characterization, assessed during the first two reporting periods, supported the growth teams with on time responses. An increased involvement was set at MDM and AIXTRON, in order to face increasing needs for chemical, structural and morphological characterization, also including sample exchanges and reciprocal visits. A strong effort was also made at CSIC for providing functional characterization of new materials produced at AIXTRON, MDM and VU. The results are encouraging in terms of demonstrating phase change in samples produced by each of the three MOCVD systems. Moreover, two additional experimental studies were promoted by CSIC in order to contribute to a better understanding of the structural dynamics underpinning the physics of phase-change memory devices. - One ultrafast optical experiment, performed in collaboration with Davide Boschetto and Barbara Mansart from LOA-ENSTA in Palaiseau, France, where the coherent phonon signal was measured via optical reflectivity in single and double pump-probe experiments on GeTe films. - A combined ultrafast optical-X-ray experiment, to be performed in November at PSI, Villigen, Switzerland, aiming at the detection of the coherent phonon and related structural dynamics of the ferroelectric phase transition in crystalline GeTe. 4 Due to the high surface roughness over the wide area pieces necessary for the 3? method, the thermal conductivity of chalcogenide materials produced at VU was not evaluated at MDM. Since the consortium decided that it could be interesting to have an estimate of the thermal conductivity of some materials deposited by HW-CVD, it was agreed to perform some measurements in collaboration with the University of Bordeaux (TREFLE laboratory) that has a world-famous experience in thermal characterization of materials. The measurements were performed by photothermal radiometry and the results turned out to be in agreement with those found in the literature for the same class of materials. Due to the novelty of the subject, the results obtained during this last reporting period, although not at the expected level, where published in international journals and were presented at different conferences. In particular, the Chemaph Consortium was deeply involved in the organization of Symposium H Materials and Emerging Technologies for Non-Volatile-Memory Devices of EMRS 2008, Spring Meeting, Strasbourg, France and was also represented by two invited talks, one oral and one poster contribution. The success of SAFC in developing advanced precursor technologies has resulted in a new product range specifically targetted at the PCM market. Individual Ge, Sb and Te sources have been identified and robust synthesis and purification processes suited to a production environment have been established. A press release detailing the new products was well received and customer interest has been high. SAFC will continue to work to bring the optimum chemicals to the semiconductor industry to meet current and future requirements. Ahead of schedule AIXTRON has realized a first production prototype for the deposition of GST on 300 mm wafers. Analyzing the status of the process development after the second year AIXTRON decided to use the existing Tricent® technology as basis for the GST production tool. The systems provide for production necessary high deposition rate, high throughput and lower cost of ownership by employing unique processing technique enabled by a proprietary pulsed injection vaporizer called TriJet. In a first step the precursor delivery system was adapted to the GST precursors and up coming additional safety issues have been addressed. The demonstrated good conformality of the MOCVD film on Numonyx high aspect ratio structures represents an important achievement of the project and it proves that this technique is mandatory for the fabrication of alternative PCM cell architecture (full-confined PCM cells). On the other side, the electrical properties of the MOCVD deposited film are still in the validation phase and only a preliminary assessment has been achieved. It follows that the PVD deposited GST still remains the reference material for the PCM cell fabrication, even if there is interest to continue the evaluation of the MOCVD technique through demo activities from equipment suppliers.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
