Browsing by Author "Tuominen, Marko"

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  • Combining Experimental and DFT Investigation of the Mechanism Involved in Thermal Etching of Titanium Nitride Using Alternate Exposures of NbF5 and CCl4, or CCl4 Only
    (2021-11-23) Sharma, Varun; Kondati Natarajan, Suresh; Elliott, Simon D.; Blomberg, Tom; Haukka, Suvi; Givens, Michael E.; Tuominen, Marko; Ritala, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Thermally activated chemical vapor-phase etching of titanium nitride (TiN) is studied by utilizing either alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4) or by using CCl4 alone. Nitrogen (N2) gas purge steps are carried out in between every reactant exposure. Titanium nitride is etched in a non-self-limiting way by NbF5–CCl4 based binary chemistry or by CCl4 at temperatures between 370 and 460 °C. Spectroscopic ellipsometry and a weight balance are used to calculate the etch per cycle. For the binary chemistry, an etch per cycle of ≈0.8 Å is obtained for 0.5 and 3 s long exposures of NbF5 and CCl4, respectively at 460 °C. On the contrary, under the same conditions, the etch process with CCl4 alone gives an etch per cycle of about 0.5 Å. In the CCl4-only etch process, the thickness of TiN films removed at 460 °C varies linearly with the number of etch cycles. Furthermore, CCl4 alone is able to etch TiN selectively over other materials such as Al2O3, SiO2, and Si3N4. X-ray photoelectron spectroscopy and bright field transmission electron microscopy are used for studying the post-etch surfaces. To understand possible reaction products and energetics, first-principles calculations are carried out with density functional theory. From thermochemical analysis of possible reaction models, it is found that NbF5 alone cannot etch TiN while CCl4 alone can etch it at high temperatures. The predicted byproducts of the reaction between the CCl4 gas molecules and TiN surface are TiCl3 and ClCN. Similarly, TiF4, NbFCl3, and ClCN are predicted to be the likely products when TiN is exposed to both NbF5 and CCl4. A more favorable etch reaction is predicted when TiN is exposed to both NbF5 and CCl4 (ΔG = −2.7 eV at 640 K) as compared to exposure to CCl4 only (ΔG = −2 eV at 640 K) process. This indicates that an enhanced etch rate is possible when TiN is exposed alternately to both NbF5 and CCl4, which is in close agreement with the experimental results.
  • Deposition of aluminium, hafnium and zirkonium oxide thin films for gate oxide applications
    (2002) Laitinen, Otto
     Helsinki University of Technology | Master's thesis
  • Microscratch testing method for systematic evaluation of the adhesion of atomic layer deposited thin films on silicon
    (2016-01-01) Kilpi, Lauri; Ylivaara, Oili M. E.; Vaajoki, Antti; Malm, Jari; Sintonen, Sakari; Tuominen, Marko; Puurunen, Riikka L.; Ronkainen, Helena
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    The scratch test method is widely used for adhesion evaluation of thin films and coatings. Usual critical load criteria designed for scratch testing of coatings were not applicable to thin atomic layer deposition (ALD) films on silicon wafers. Thus, the bases for critical load evaluation were established and the critical loads suitable for ALD coating adhesion evaluation on silicon wafers were determined in this paper as LCSi1, LCSi2, LCALD1, and LCALD2, representing the failure points of the silicon substrate and the coating delamination points of the ALD coating. The adhesion performance of the ALD Al2O3, TiO2, TiN, and TaCN+Ru coatings with a thickness range between 20 and 600 nm and deposition temperature between 30 and 410°C on silicon wafers was investigated. In addition, the impact of the annealing process after deposition on adhesion was evaluated for selected cases. The tests carried out using scratch and Scotch tape test showed that the coating deposition and annealing temperature, thickness of the coating, and surface pretreatments of the Si wafer had an impact on the adhesion performance of the ALD coatings on the silicon wafer. There was also an improved load carrying capacity due to Al2O3, the magnitude of which depended on the coating thickness and the deposition temperature. The tape tests were carried out for selected coatings as a comparison. The results show that the scratch test is a useful and applicable tool for adhesion evaluation of ALD coatings, even when carried out for thin (20 nm thick) coatings.
  • Seostettujen alumiinigalliumarsenidikalvojen valmistus ja ominaisuudet
    (1993) Tuominen, Marko
     Helsinki University of Technology | Master's thesis
  • Thermal Atomic Layer Etching of Aluminum Oxide (Al2O3) Using Sequential Exposures of Niobium Pentafluoride (NbF5) and Carbon Tetrachloride (CCl4)
    (2021-04-27) Sharma, Varun; Blomberg, Tom; Haukka, Suvi; Givens, Michael E.; Tuominen, Marko; Ritala, Mikko; Elliott, Simon
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Thermal atomic layer etching (ALEt) of amorphous Al2O3 was performed by alternate exposures of niobium pentafluoride (NbF5) and carbon tetrachloride (CCl4). The ALEt of Al2O3 is observed at temperatures from 380 to 460 °C. The etched thickness and the etch rate were determined using spectroscopic ellipsometry and verified by X-ray reflectivity. The maximum etch rate of about 1.4 Å/cycle and a linear increase of the removed film thickness with the number of etch cycles were obtained at a temperature of 460 °C. With the help of density functional theory calculations, an etch mechanism is proposed where NbF5 converts part of the Al2O3 surface into an AlF3 or aluminum oxyfluoride layer, which upon reacting with CCl4 is converted into volatile halide-containing byproducts, thus etching away the converted portion of the material. Consistent with this, a significant surface fluorine content of about 55 at. % was revealed when the elemental depth profile analysis of a thick NbF5-Treated Al2O3 layer was performed by X-ray photoelectron spectroscopy. The surface morphology of the reference, pre-, and postetch Al2O3 surfaces was analyzed using atomic force microscopy and bright-field transmission electron microscopy. Moreover, it is found that this process chemistry is able to etch Al2O3 selectively over silicon dioxide (SiO2) and silicon nitride (Si3N4).
  • Thermal gas-phase etching of titanium nitride (TiN) by thionyl chloride (SOCl2)
    (2021-02-28) Sharma, Varun; Blomberg, Tom; Haukka, Suvi; Cembella, Shaun; Givens, MIchael E.; Tuominen, Marko; Odedra, Rajesh; Graff, Wes; Ritala, Mikko
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    In this work, thermal based gas-phase etching of titanium nitride (TiN) is demonstrated using thionyl chloride (SOCl2) as a novel etchant. A single etchant is utilised in a pulsed fashion to etch TiN. This type of etching technique may also be considered as a chemical gas-phase or dry etching. The removed TiN amount was measured by various techniques like spectroscopic ellipsometry (SE), weighing balance and in some cases X-ray reflectometry (XRR). Additionally, the post-etch surfaces were analysed with X-ray photoelectron spectroscopy (XPS) and bright field transmission electron microscopy (BF-TEM). The surface roughness and morphology of before and after etching TiN films were measured using atomic force microscopy (AFM). The etch per cycle (EPC) was calculated and is plotted as a function of SOCl2 pulse time, purge time after SOCl2 exposure, number of etch cycles and etch temperature (Tetch). An increase in EPC with an increase in SOCl2 pulse time as well as etch temperature was observed. SOCl2 is able to etch TiN starting from 270 °C with an EPC of about 0.03 Å to almost 1.2 Å at 370 °C. Arrhenius plot determined the activation energy (Ea) of about 25 kcal/mol for TiN etching by SOCl2. In addition, the etch selectivity between different substrates such as silicon dioxide (SiO2), silicon nitride (Si3N4) and aluminum oxide (Al2O3) was investigated on blanket as well as 3D structures. Moreover, thermodynamic calculations were performed for various possible etch reactions. Titanium from TiN is proposed to be etched in the form of either titanium trichloride (TiCl3) or titanium tetrachloride (TiCl4). Nitrogen from TiN films may form volatile by-products such as diatomic nitrogen (N2), nitrous oxide (N2O) and nitrogen dioxide (NO2).
  • Tribological properties of thin films made by atomic layer deposition sliding against silicon
    (2018-01-01) Kilpi, Lauri; Ylivaara, Oili M.E.; Vaajoki, Antti; Liu, Xuwen; Rontu, Ville; Sintonen, Sakari; Haimi, Eero; Malm, Jari; Bosund, Markus; Tuominen, Marko; Sajavaara, Timo; Lipsanen, Harri; Hannula, Simo Pekka; Puurunen, Riikka L.; Ronkainen, Helena
     A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
    Interfacial phenomena, such as adhesion, friction, and wear, can dominate the performance and reliability of microelectromechanical (MEMS) devices. Here, thin films made by atomic layer deposition (ALD) were tested for their tribological properties. Tribological tests were carried out with silicon counterpart sliding against ALD thin films in order to simulate the contacts occurring in the MEMS devices. The counterpart was sliding in a linear reciprocating motion against the ALD films with the total sliding distances of 5 and 20 m. Al2O3 and TiO2 coatings with different deposition temperatures were investigated in addition to Al2O3-TiO2-nanolaminate, TiN, NbN, TiAlCN, a-C:H [diamondlike carbon (DLC)] coatings, and uncoated Si. The formation of the tribolayer in the contact area was the dominating phenomenon for friction and wear performance. Hardness, elastic modulus, and crystallinity of the materials were also investigated. The nitride coatings had the most favorable friction and wear performance of the ALD coatings, yet lower friction coefficient was measured with DLC a-C:H coating. These results help us to take steps toward improved coating solutions in, e.g., MEMS applications.