Tsuyoshi Moriya

Reduction of Particle Contamination in Plasma-Etching Equipment by Dehydration of Chamber Wall

The mechanism of particle generation is investigated in order to prevent defects formed on wafers in the plasma etching of multi-layered films composed of tungsten silicide (WSi) and polycrystalline silicon (poly-Si). Particles are measured by an in situ monitoring system using laser light scattering during the etching process. The particles are composed of AlF3, which is presumably generated by reacting the coating material Al2O3 on the etching chamber wall with plasma containing fluorine atoms, F in the presence of H2O absorbed into the chamber parts and materials. We demonstrated successfully that dehydration of the chamber parts and materials by plasma discharge suppresses particle generation.

Generation of positively charged particles at an anode and transport to device wafers in a real radio frequency plasma etching chamber for tungsten etch-back process

The transport path of particles, that have flaked off a grounded anode of a real parallel-plate radio frequency (rf) plasma etching equipment for tungsten etch-back processing to device wafers on the cathode, is measured by using an in situ monitoring system that measures laser light scattered by the particles. A few particles appear constantly only near the grounded anode while rf power is being supplied. These particles have parabolic trajectories that open upward. Few particles are observed near the wafer. On the other hand, at the timing of the turning off of rf power, many particles appear near the anode. Their trajectories from the anode to the chamber wall are sharply curved. Near the wafer, which has a negative self-bias voltage, almost all the particles’ trajectories are from the chamber wall to the wafer. Therefore, the particles move from the anode to the device wafer on the cathode and keep away from the after-glow plasma as well as from the bulk plasma. These particles are then attracted to t...

Observation of the trajectories of particles in process equipment by an in situ monitoring system using a laser light scattering method

An in situ scattered laser light measurement system, which can detect individual particles and observe their trajectories, has been produced experimentally and has been used with tungsten (W) etchback reactive ion etching (RIE) equipment. The particles which are smaller than 100 nm in size can be detected during plasma emission if the stray light that is caused by the laser light is properly suppressed. The trajectories of the particles are successfully observed in the W etchback RIE chamber by using this system under mass production conditions. Not only the appearance of the particle but also the direction of particle trajectory correlate distinctly with the specific operating state of the equipment. When the rf power was turned off, many of the particles that were observed seemed to be drawn towards the wafer. On the other hand, during injection of the N2 purge gas to the process chamber, the few particles that were frequently observed seemed to fall down, away from the wafer.

Annealing Properties of Defects in B^+- and F^+-Implanted Si Studied Using Monoenergetic Positron Beams

Annealing properties of defects in F+- and B+-implanted Si were studied using monoenergetic positron beams. For F+-implanted specimen with a dose of 2×1013 F/cm2, before annealing treatment, the mean size of the open volume of defects was estimated to be close to the size of divacancies. After rapid thermal annealing (RTA) at 700° C, vacancy-fluorine complexes and vacancy clusters were formed. The mean size of the open volume for the vacancy-fluorine complexes was estimated to be close to the size of monovacancies, and their annealing temperature was determined to be 800° C. For F+-implanted specimen with a dose of 4×1015 F/cm2, complexes between vacancy clusters and fluorine atoms were introduced during solid-phase epitaxial growth of the amorphous region, and they were observed even after RTA at 1100° C. Effects of additional B+ implantation on annealing properties of defects are also discussed.

Capture of flaked particles during plasma etching by a negatively biased electrode

A bias electrode was installed inside an etching chamber to investigate the effect of bias voltage on particle behavior. To detect flaked particles individually and to determine their trajectories, an in situ particle monitoring system which employs laser light scattering was employed. Consequently, it was found that particles were attracted when negative voltage was supplied to the bias electrode. However, particles were pushed toward the wafer when positive voltage was applied. It was thus clarified that the flaked particles have positive charges, and concluded that negative bias voltage can control their behavior and keep the wafer surface particle free, without serious affect on the etching process.

Particle reduction and control in plasma etching equipment

Particles within plasma etching equipment stick to the wafer and cause defects, resulting in large scale integrated circuit (LSI) yield reduction. We observed the behavior of particles resuspended in a vacuum chamber using a laser light scattering method. Investigating the influences of gases, static electricity, and plasma on particle resuspension, we found out that particles are not only suspended by the shock wave or gas viscous force generated when the valve opens or when the gas is introduced into the chamber, but also are resuspended due to electromagnetic stress caused by electrostatic chuck voltage application or radio frequency discharge. If, on the other hand, stable plasma generation is assured, particles are positively charged and receive repelling force within the ion sheath; as a consequence, particle resuspension is suppressed. We developed a method that can suppress particle resuspension by avoiding the production of a shock wave and electromagnetic stress during the wafer processes. We also developed a method that can effectively remove particles before the beginning of processes that use gas viscosity, the shock wave, and the electromagnetic stress.

Effects of Recoil-Implanted Oxygen on Depth Profiles of Defects and Annealing Processes in P+-Implanted Si Studied Using Monoenergetic Positron Beams

Effects of oxygen atoms recoiled from SiO2 films on depth profiles of defects and annealing processes in P+-implanted Si were studied using monoenergetic positron beams. For an epitaxial Si specimen, the depth profile of defects was found to be shifted toward the surface by recoil implantation of oxygen atoms. This was attributed to the formation of vacancy-oxygen complexes and a resultant decrease in the diffusion length of vacancy-type defects. The recoiled oxygen atoms stabilized amorphous regions introduced by P+-implantation, and the annealing of these regions was observed after rapid thermal annealing (RTA) at 700° C. For a Czochralski-grown Si specimen fabricated by through-oxide implantation, the recoiled oxygen atoms introduced interstitial-type defects upon RTA below the SiO2/Si interface, and such defects were dissociated by annealing at 1000° C.

Defects in Ion-Implanted 3C-SiC Probed by a Monoenergetic Positron Beam

Defects introduced by 200-keV N2+- or Al+-implantation into 3C–SiC were probed by a monoenergetic positron beam. Depth profiles of the defects were determined from measurements of Doppler broadening profiles of the annihilation radiation as a function of incident positron energy. For ion implanted specimens at high substrate temperature (≥800° C), the major species of defects was identified to be vacancy clusters. The depth profile of vacancy-type defects was found to be shifted towards the surface of the specimen by implantation at high temperatures. Upon furnace annealing after the implantation, an agglomeration of vacancy-type defects was observed, and interstitial clusters were introduced below the vacancy-rich region.

Reduction of particle contamination in an actual plasma etching process

To reduce particle contamination in plasma etching equipment, a strategy to control particles behavior were developed. The methods include the following techniques: a non-plasma particle cleaning (NPPC) with an in situ particle monitor (ISPM), a pre-purge gas sequence, a control of cross over pressure and a chucking voltage application during plasma discharge. Before the application of these methods, 12 particles in average and 52 particles at maximum were detected on a 300 mm wafer during the RF time of 220 hours. The particle level was decreased to less than 1 particle in average and 4 particles at maximum after the application of these measures without any modification of the chamber hardware and process recipe. From a trend of the ISPM counts during NPPC, a spike of ISPM count was observed. This spike suggests that there are some problems in the chamber at this time. After 85 times of NPPC, the spikes of ISPM count were observed repeatedly. These spikes are thought to mean that the chamber becomes dirty. A slightly high particle level is detected just after chamber maintenance. The major part of particles, which are larger than 1 micron, consists of carbon and fluorine. These particles are considered to come from the downstream of the chamber. A novel method to reduce these particles is developed and verified experimentally.

Fluorine-Related Defects in BF2+-Implanted Si Probed by Monoenergetic Positron Beams

Fluorine-related defects in 30-keV BF2+-implanted Si were probed using monoenergetic positron beams. From measurements of Doppler broadening profiles of the annihilation radiation as a function of incident positron energy and those of lifetime spectra of positrons, depth profiles of defects and the species of the defects were determined. For an as-implanted specimen, the major species of the defects below the amorphous region was identified to be divacancies. Upon rapid thermal annealing above 700 °C, solid phase epitaxial growth of the amorphous region started, but no shift of the depth profile of defects detected by the positron annihilation technique was observed. During the regrowth of the amorphous region, vacancy-fluorine complexes were introduced. The complexes between vacancy clusters and fluorine atoms were observed even after 1100 °C annealing.