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Berg, Sören
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Publications (10 of 110) Show all publications
Särhammar, E., Nyberg, T. & Berg, S. (2016). Applying "the upgraded Berg model" to predict hysteresis free reactive sputtering. In: : . Paper presented at 58th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 25-30, 2015, Santa Clara, CA (pp. 34-38). , 290
Open this publication in new window or tab >>Applying "the upgraded Berg model" to predict hysteresis free reactive sputtering
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Reactive sputtering is a popular process to deposit oxides, nitrides, and several other compounds. Unfortunately, this process mostly exhibits a hysteresis effect. The hysteresis causes a delicate choice of either a high deposition rate but not a fully oxidized/nitrided film or a fully formed compound film but at a significantly lower deposition rate. For high reactivity target material/reactive gas systems, the hysteresis forces the process to flip quite abrupt between these two conditions. Process control may therefore be quite critical. In this work we will use the original "Berg model" as well as the newly published "upgraded Berg model" to illustrate how hysteresis is generated. We have selected one simple graph (reactive gas flow vs. partial pressure) that gives clear indications of how the process may be affected in such a way as to decrease or even eliminate the hysteresis. Specific values of target size and composition, gas mixture as well as total pressure and pumping speed are processing parameters that may be selected in a way to eliminate hysteresis. We will show that this behavior is predicted by the simulations and also refer to experimental evidence for such behavior.

Keywords
Reactive sputtering, Hysteresis, Modeling, Thin film
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-297548 (URN)10.1016/j.surfcoat.2016.02.029 (DOI)000374370600007 ()
External cooperation:
Conference
58th Annual Technical Conference of the Society-of-Vacuum-Coaters (SVC), APR 25-30, 2015, Santa Clara, CA
Available from: 2016-06-27 Created: 2016-06-23 Last updated: 2016-08-30Bibliographically approved
Särhammar, E., Nyberg, T. & Berg, S. (2015). Applying "the upgraded Berg model" to predict hysteresis free reactive sputtering. Surface & Coatings Technology, 279, 39-43
Open this publication in new window or tab >>Applying "the upgraded Berg model" to predict hysteresis free reactive sputtering
2015 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 279, p. 39-43Article in journal (Refereed) Published
Abstract [en]

Reactive sputtering is a popular process to deposit oxides, nitrides, and several other compounds. Unfortunately, this process mostly exhibits a hysteresis effect. The hysteresis causes a delicate choice of either a high deposition rate but not a fully oxidized/nitrided film or a fully formed compound film but at a significantly lower deposition rate. For high reactivity target material/reactive gas systems, the hysteresis forces the process to flip quite abrupt between these two conditions. Process control may therefore be quite critical. In this work we will use the original "Berg model" as well as the newly published "upgraded Berg model" to illustrate how hysteresis is generated. We have selected one simple graph (reactive gas flow vs. partial pressure) that gives clear indications of how the process may be affected in such a way as to decrease or even eliminate the hysteresis. Specific values of target size and composition, gas mixture as well as total pressure and pumping speed are processing parameters that may be selected in a way to eliminate hysteresis. We will show that this behavior is predicted by the simulations and also refer to experimental evidence for such behavior.

Keywords
Reactive sputtering, Hysteresis, Modeling, Thin film
National Category
Materials Engineering
Identifiers
urn:nbn:se:uu:diva-264811 (URN)10.1016/j.surfcoat.2015.07.054 (DOI)000361864500006 ()
Available from: 2015-11-02 Created: 2015-10-19 Last updated: 2017-12-01Bibliographically approved
Särhammar, E., Berg, S. & Nyberg, T. (2014). Hysteresis-free high rate reactive sputtering of niobium oxide, tantalumoxide, and aluminum oxide. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, 2, 041517
Open this publication in new window or tab >>Hysteresis-free high rate reactive sputtering of niobium oxide, tantalumoxide, and aluminum oxide
2014 (English)In: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 2, p. 041517-Article in journal (Refereed) Published
Abstract [en]

This work reports on experimental studies of reactive sputtering from targets consisting of a metaland its oxide. The composition of the targets varied from pure metal to pure oxide of Al, Ta, and Nb. This combines features from both the metal target and oxide target in reactive sputtering. If a certain relation between the metal and oxide parts is chosen, it may be possible to obtain a high deposition rate, due to the metal part, and a hysteresis-free process, due to the oxide part. The aim of this work is to quantify the achievable boost in oxide deposition rate from a hysteresis-free process by using a target consisting of segments of a metal and its oxide. Such an increase has been previously demonstrated for Ti using a homogeneous substoichiometric target. The achievable gain in deposition rate depends on transformation mechanisms from oxide to suboxides due to preferential sputtering of oxygen. Such mechanisms are different for different materials and the achievable gain is therefore material dependent. For the investigated materials, the authors have demonstrated oxide deposition rates that are 1.5–10 times higher than what is possible from metal targets in compound mode. However, although the principle is demonstrated for oxides of Al, Ta,and Nb, a similar behavior is expected for most oxides.

Keywords
Reactive sputtering, hysteresis elimination
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-229205 (URN)10.1116/1.4885399 (DOI)000338718400029 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
Berg, S., Särhammar, E. & Nyberg, T. (2014). Upgrading the “Berg-model” for reactive sputtering processes. Thin Solid Films, 565, 186-192
Open this publication in new window or tab >>Upgrading the “Berg-model” for reactive sputtering processes
2014 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 565, p. 186-192Article, review/survey (Refereed) Published
Abstract [en]

Several phenomena are neglected in the original “Berg model” in order to provide a simple model of the reactive sputtering process. There exist situations, however, where this simplified treatment limits the usefulness of the model. To partly correct for this, we introduce an upgraded version of the basic model. We abandon the simplifying assumption that compound targets are sputter eroded as molecules. Instead, the molecule is split and individual atoms will be sputter ejected. Also, the effect of ionized reactive gas atoms implanted into the target will be considered. We outline how to modify the original model to include these effects. Still, the mathematical treatment is maintained simple so that the new model may serve as an easy-to-understand tutorial of the complex mechanisms of reactive sputtering.

Keywords
Reactive sputtering, Hysteresis, Modelling
National Category
Other Physics Topics Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-229204 (URN)10.1016/j.tsf.2014.02.063 (DOI)000341054600030 ()
Funder
Swedish Foundation for Strategic Research
Available from: 2014-08-05 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
Särhammar, E., Strijckmans, K., Nyberg, T., Van Steenberge, S., Berg, S. & Depla, D. (2013). A study of the process pressure influence in reactive sputtering aiming at hysteresis elimination. Surface & Coatings Technology, 232, 357-361
Open this publication in new window or tab >>A study of the process pressure influence in reactive sputtering aiming at hysteresis elimination
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2013 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 232, p. 357-361Article in journal (Refereed) Published
Abstract [en]

Reactive sputtering processes operating at different argon pressures (ranging from 0.3 to 2.7 Pa) have been studied for a number of gas/metal target combinations (Al, Mg, Y in Ar/O-2 and Ti in Ar/N-2). To transcend local deposition conditions, experiments were performed in three different deposition systems. Both experiments and process modeling show the existence of conditions where the hysteresis width may be significantly decreased or even be totally eliminated. This behavior is pronounced for low reactivity gas/metal target combinations such as Al/O-2 and Ti/N-2. It is suggested that for such gas/metal target combinations the direct ion implantation of the reactive gas will be the dominating poisoning mechanism at low total pressure. At elevated total pressure, however, this will no longer be the case. Here, the chemisorption may dominate. For chemisorption-dominated processes, it has been shown earlier that low reactivity materials will exhibit small hysteresis widths and sometimes also be hysteresis free. For materials like Mg and Y, the effect was, as expected, small due to the high affinity of oxygen for these metals.

Keywords
Reactive sputtering, Hysteresis, Elevated pressure, Modeling
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-214001 (URN)10.1016/j.surfcoat.2013.05.035 (DOI)000327691300047 ()
Available from: 2014-01-06 Created: 2014-01-06 Last updated: 2017-12-06Bibliographically approved
Kubart, T., Nyberg, T. & Berg, S. (2012). High rate reactive magnetron sputtering of oxides using sputtering yield amplification. Paper presented at 13th International Conference on Plasma Surface Engineering PSE, September 2012, Garmisch-Partenkirchen, Germany.
Open this publication in new window or tab >>High rate reactive magnetron sputtering of oxides using sputtering yield amplification
2012 (English)Conference paper, Oral presentation only (Refereed)
Abstract [en]

In this contribution, we summarize our work on increasing the deposition rate in reactive magnetron sputtering by sputtering yield amplification. Modelling of the sputtering process predicts that a very high deposition rate increase by more than 100 % may be achieved for oxides. Comparable values were measured experimentally using a setup suitable for up-scaling.

In sputtering yield amplification the target is doped with a heavy dopant in order to reflect the recoils created in a collision cascade towards the surface and thus increase the number of atoms sputtered from the surface. In order to realize the process, an experimental system for serial co-sputtering has been built and used for experimental studies. The dopants are introduced from an auxiliary cathode onto the primary rotating target and incorporated into the target surface by recoil implantation during sputtering. A necessary requirement for suitable doping elements is high atomic mass. Another important parameter is the surface binding energy as demonstrated by comparison of W and Bi, two heavy elements with very different surface binding energies. Using a dynamical model of the sputtering process, the performance of various doping elements is evaluated.

Reactive sputtering of Al and Ti targets with W and Bi doping was performed.  The deposition rate of Al2O3 can be increased by 80 % by W doping of the Al target in very good agreement with predictions. For TiO2, however, an increase by more than 100 % was observed, substantially higher than predicted. Finally, the optical properties of W doped Al2O3 and TiO2 thin films are briefly discussed.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-190005 (URN)
Conference
13th International Conference on Plasma Surface Engineering PSE, September 2012, Garmisch-Partenkirchen, Germany
Available from: 2013-01-07 Created: 2013-01-07 Last updated: 2013-04-08
Kubart, T., Schmidt, R. M., Austgen, M., Nyberg, T., Pflug, A., Siemers, M., . . . Berg, S. (2012). Modelling of sputtering yield amplification in serial reactive magnetron co-sputtering. Surface & Coatings Technology, 206(24), 5055-5059
Open this publication in new window or tab >>Modelling of sputtering yield amplification in serial reactive magnetron co-sputtering
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2012 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 206, no 24, p. 5055-5059Article in journal (Refereed) Published
Abstract [en]

Serial magnetron co-sputtering can be used to increase the deposition rate in reactive deposition of thin films. The increase in deposition rate is achieved by sputtering yield amplification through doping the sputtering target by a heavy element. The dopant is introduced by means of sputtering from an auxiliary target onto a rotating primary magnetron. During sputtering of the primary target, the dopant is implanted into the target surface. Here we present a model describing the serial co-sputtering technique. The model is based on the binary collision approximation and takes into account the dynamical sputtering and mixing at the target surface. As an example, W and Bi doping in reactive sputter deposition of Al2O3 is analyzed. W is shown to be very efficient dopant which can increase the deposition rate for oxide up to 100% with 1.6 at.% of W in the resulting coating. Doping by Bi is not very effective due to the low surface binding energy of Bi. The simulations show that sputtering yield amplification can be realized in the serial co-sputtering setup with rotating magnetrons.

Keywords
Reactive sputtering, Magnetron sputtering, Deposition rate, Oxide thin films, TRIDYN, Sputtering yield amplification
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-181406 (URN)10.1016/j.surfcoat.2012.06.005 (DOI)000307492500006 ()
Available from: 2012-09-28 Created: 2012-09-24 Last updated: 2017-12-07Bibliographically approved
Kubart, T., Nyberg, T., Berg, S., Austgen, M., Koehl, D., Wuttig, M., . . . Siemers, M. (2011). Serial magnetron co-sputtering: Sputtering yield amplification and process modelling. In: E-MRS 2011 Spring Meeting: . Paper presented at E-MRS 2011 Spring Meeting.
Open this publication in new window or tab >>Serial magnetron co-sputtering: Sputtering yield amplification and process modelling
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2011 (English)In: E-MRS 2011 Spring Meeting, 2011Conference paper, Published paper (Refereed)
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-156571 (URN)
Conference
E-MRS 2011 Spring Meeting
Projects
VWIII
Available from: 2011-08-04 Created: 2011-08-04 Last updated: 2016-04-19
Austgen, M., Koehl, D., Zalden, P., Kubart, T., Nyberg, T., Pflug, A., . . . Wuttig, M. (2011). Sputter yield amplification by tungsten doping of Al(2)O(3) employing reactive serial co-sputtering: process characteristics and resulting film properties. Journal of Physics D: Applied Physics, 44(34), 345501
Open this publication in new window or tab >>Sputter yield amplification by tungsten doping of Al(2)O(3) employing reactive serial co-sputtering: process characteristics and resulting film properties
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2011 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 44, no 34, p. 345501-Article in journal (Refereed) Published
Abstract [en]

The deposition rate of reactively sputtered Al(2)O(3) coatings is demonstrated to increase by 80% upon tungsten doping of the used aluminium target. This effect is based on the recoil of the sputtering species at implanted dopants below the target surface and is termed sputter yield amplification. For the investigation of this effect, a novel type of magnetron sputter deposition system is employed that facilitates serial co-sputtering. In this technique doping of the elementary target is enabled by a dynamic sputtering process from an auxiliary cathode. In our case, the rotating aluminium target is dynamically coated with tungsten from this auxiliary cathode. Since the primary target rotates, the auxiliary cathode is placed in series with the primary erosion zone. The deposition rate of Al(2)O(3) can be considerably increased in this process already for very low concentrations of approximately 1% of tungsten in the resulting film. A characterization of the dynamics of reactive sputtering as a function of target rotation speed is performed.

National Category
Physical Sciences Engineering and Technology
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-159251 (URN)10.1088/0022-3727/44/34/345501 (DOI)000294761500015 ()
Available from: 2011-09-26 Created: 2011-09-26 Last updated: 2017-12-08Bibliographically approved
Schmidt, R., Kubart, T., Austgen, M., Wagner, D., Nyberg, T., Pflug, A., . . . Wuttig, M. (2011). Sputter Yield Amplification of reactively sputtered TiO2. In: : . Paper presented at 10th International Conference on Reactive Sputter Deposition, RSD 2011, Linkoping, December 8-9.
Open this publication in new window or tab >>Sputter Yield Amplification of reactively sputtered TiO2
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2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

TiO2 is a material with attractive properties which have led to various applications such as anti-reflective coatings [1] or self cleaning surfaces [2]. One of the most applied deposition techniques used for TiO2 is reactive magnetron sputtering. Unfortunately TiO2 suffers from a comparatively low deposition rate when reactively sputtered.  To increase the deposition rate, Sputter Yield Amplification (SYA) can be used through recoil of the sputtering species at implanted heavy dopants below the target surface [3,4]. Here we present experimental results showing a large increase of the TiO2 deposition rate when doped with Tungsten.

 

Although SYA has been proposed earlier [5], the production of doped targets was complicated. We have built a designated sputter deposition tool which enables systematic studies of SYA. In this study the rate increase by SYA is investigated for two different dopants, namely Tungsten and Bismuth. Bismuth was chosen since it is the heaviest non-radioactive material available. Our experiments show that the rate increase of TiO2 by Bismuth is surprisingly low. Tungsten on the other hand results in a large rate increase of 160% in DC and 220% in HiPIMS mode. A number of additional experiments have been carried out to verify and explain this observation. Finally TRIDYN [6] simulations have been performed which reproduce the experimental results.

National Category
Ceramics Fusion, Plasma and Space Physics
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-164336 (URN)
Conference
10th International Conference on Reactive Sputter Deposition, RSD 2011, Linkoping, December 8-9
Available from: 2011-12-19 Created: 2011-12-19 Last updated: 2016-04-20
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