Can RF Sputtering cause the the ejected target to ionise?

  1. Hello,

    I am currently working on sputtering method for thin film deposition of III-Nitrides. The target used was a gallium nitride (GaN) plate and plasma generation was achieved by radio frequency (RF).

    After running the sample through phase analysis, interestingly a gallium oxide (Ga2O3) peak has been observed, indicating that not only Ga2O3 has been deposited, but it is also crystalline in nature.

    My only explanation is as follows
    1. After being bombarded by the argon (Ar) ions, the GaN molecules will be dislodged by energy transfer and move away to the substrate.
    2. While passing the area with RF radiation, the Ga-N bond breaks, leaving Ga and N ions to be deposited on the surface.
    3. Due to the residual oxygen (O) inside the growth chamber at low vacuum, the N and O will face competition to be adsorbed to the Ga dangling bond
    4. Therefore, Ga2O3 can be formed

    Is this plausible? Can the neutral Ga-N bond that is passing in the RF region somehow get broken? I am saying this because since the RF is energetic enough to ionise an inert gas (Ar), it could also could break a covalent bond of GaN.

    Pardon me if I got the facts wrong.

    Thank you for reading this.
     
  2. jcsd
  3. ZapperZ

    ZapperZ 29,763
    Staff Emeritus
    Science Advisor
    Gold Member

    You should double check this by figuring out the bonding strength of GaN.

    Zz.
     
  4. The bonding strength of Ga-N is 8.92 ev/atom [1],
    Whereas the bonding strength of Ar is 4.73 kJ/mol [2]. Converting this, I got ~0.049 eV/atom.

    It can be seen that Ga to N bonding has a higher bonding strength compared to Ar. However, in my opinion, I should determine the energy given by the RF radiation. Is this the right track?

    Reference
    [1] W. A. Harrison, Electronic Structure and Properties of Solids, Freeman, San Francisco, (1980)
    [2] http://www.webelements.com/argon/bond_enthalpies.html
     
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