to Thin Film Deposition

							          Ruhr-Universität Bochum




 Introduction to
Thin Film Deposition




          Dipl.-Ing. Egmont Semmler
                                       Ruhr-Universität Bochum




                            Overview

•   What is thin film deposition ?

•   Techniques

•   General problems of thin film deposition

•   Sputter etching

•   Sputtering in multifrequency CCP discharges

•   Summary



                                       Dipl.-Ing. Egmont Semmler   Slide 2 / 12
                                         Ruhr-Universität Bochum




                What is thin film deposition ?
•   Bring some coating of any kind on a
    given surface to modify its nature

     – Semiconductor industry
     – Medical applications
     – Optics (telescope mirror)

•   Applications
                                                 Structure of a telescope mirror

     –   Smooth out uneven surfaces (i.e. mirrors)
     –   Layers for better adhesion of two or more components
     –   Magnetic layers for recording media
     –   Glass coatings of plastic bottles
     –   Organic layers on implants (i.e. bone-like tissue on Ti-implants)

                                         Dipl.-Ing. Egmont Semmler         Slide 3 / 12
                                            Ruhr-Universität Bochum




                Techniques – CVD / PECVD
•   (PE)CVD = (Plasma Enhanced) Chemical Vapour Deposition

•   Conventional CVD : Deposit a thin film out of a selected gas, aerosol or
    both
     – Deposition process is of pure chemical nature
     – Example : 3 Si + 4 NH3     Si3N4 + 6 H2
         • Substrate temperature = 1200 °C, chamber pressure = 1 bar


•   Plasma Enhanced CVD
     – Dissociation and activation of gases (i.e. NH3)
     – Desired film can be produced with lower temperatures at the
       substrate (~ 300 °C, 30 Pa) : 3 SiH4 + 4 NH3    Si3N4 + 12 H2
     – Directed deposition is possible through sheath above the substrate
     – Problem : stoichiometry of the film changes
         • Implantation of H+- Ions in the Si3N4 – film
                                            Dipl.-Ing. Egmont Semmler   Slide 4 / 12
                                       Ruhr-Universität Bochum




      Techniques – Spraying / Dust / Evaporation / PVD
                                                  Powder
•   Plasma spraying :
                                                                     Substrate


                                     Argon Ion
                                    Beam Source
•   Dusty Plasmas (DPCVD)
     – Clustering of atoms polymerization         high
       deposition rates

•   Evaporation
     – Target material is heated up to evaporation temperatures (chamber
       pressure 10-4 Pa)
     – Target atoms move and deposit on nearby (~50 cm) substrate

•   PVD = Physical Vapour Deposition      Sputter deposition

                                       Dipl.-Ing. Egmont Semmler   Slide 5 / 12
                                         Ruhr-Universität Bochum




            Techniques – Sputter deposition
•   Extract a target atom by means of
    heavy ion (or electron)
    bombardment (high sheath
    voltages) and let it condense on a
    nearby substrate

•   Reactive Sputtering : Extracted
    atoms chemically react with the
    sputtering gas and the product
    condenses on the substrate

•   Different reactor types are used :
     – Inductively Coupled Plasma
     – Capacitively Coupled Plasma
     – DC discharges
     – Ion Beam Sources
     – Magnetrons
                                         Dipl.-Ing. Egmont Semmler   Slide 6 / 12
                                           Ruhr-Universität Bochum




            Techniques – Sputter deposition
•   Problems in sputter deposition                     Ar +
                                                                       Ar +

                                                                  Si
     – Backscattering to the target
                                                                                  Si

     – Resputtering from the substrate                        Target
         • Net particle target substrate flux must be substantially higher than
           substrate target flux


     – Film contamination due to sputtering of the target holder etc.

     – Reactive sputtering : Other chemical reactions take place and form
       non-volatile products which contaminate the film

     – Radiation damage from high energetic photons emitted by excited
       background gas atoms
                                           Dipl.-Ing. Egmont Semmler          Slide 7 / 12
                                           Ruhr-Universität Bochum




       General problems of thin film deposition
•   Thin film adhesion on the substrate

     – Resistance to mechanical stress and stability in a defined
       temperature region

     – Some countermeasures to reduce adhesion problems :
         • Cleaning of the substrate prior to deposition (remove oxide layer)

         • Pre-deposit one or more intermediate layers with good adhesion to each
           other (i.e. oxides)

         • Heating of the substrate supports interdiffusion adhesion

         • Uneven substrate surface promotes mechanical interlocking



                                           Dipl.-Ing. Egmont Semmler            Slide 8 / 12
                                       Ruhr-Universität Bochum




       General problems of thin film deposition
•   Contamination of the film with other atom species as the target




•   Radiation damage from high energetic photons
•   Unwanted deposition of non-volatile by-products (reactive sputtering)
•   Unequal film thickness on the substrate due to inhomogeneous
    condensation process
•   Uniform film deposition on trench-like geometries
•   Roughness of the deposited film must be small for further processing
•   Deposition of alloys, complex molecules or organic material
                                       Dipl.-Ing. Egmont Semmler      Slide 9 / 12
                                        Ruhr-Universität Bochum




                      Sputter - Etching
•   Basically the same as the sputtering, with additional chemical
    interactions between the substrate surface and the reactive discharge
    gas

•   Substrate + discharge ions   Main product should be volatile
     – Plasma ashing (etching of carbon layers with oxygen plasma)

•   Ion-assisted sputter-etching
     – Chemical interactions of the reactive ions with the substrate at low
        kinetic ion energies, assisted by an inactive sputtering background
        gas (i.e. Ar)

•   Reactive ion etching (RIE)
     – Like ion-aided sputter-etching without background gas. Reactive
       ions need high kinetic energies and the flux of reactive ion species
       must be substantially higher than ion-assisted sputter-etching

                                        Dipl.-Ing. Egmont Semmler     Slide 10 / 12
                                          Ruhr-Universität Bochum




    Sputtering in multifrequency CCP discharges

•   Better control of substrate and target sheath voltages through individual
    biases and rf excitation

•   Higher rf frequencies for the discharge leads to smaller losses in the
    electrode sheath region

•   Plasma reactor will be designed as both, a RIE-machine and a
    sputtering machine.

•   Aim : Investigations in the field of sputter depositing magnetic layers
     – Magnetron sputtering of magnetic targets is inefficient
     – Applications of thin magnetic films
         • Microelectromagnetic devices (i.e. on-wafer sensors)
         • Magnetic recording media (computer harddisks)
                                          Dipl.-Ing. Egmont Semmler     Slide 11 / 12
                                          Ruhr-Universität Bochum




                                Summary
•   What is thin film deposition ?

•   Techniques
     – (PE)CVD
     – PVD
     – Sputter deposition

•   General problems of thin film deposition
     – Thin film adhesion to the substrate
     – Contamination, Radiation, uniform deposition etc.

•   Sputter etching
     – Ion aided sputter etching
     – Reactive Ion Etching (RIE)

•   Sputtering in multifrequency CCP discharges

•   Questions

                                          Dipl.-Ing. Egmont Semmler   Slide 12 / 12