Natsuko Ito

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.

Real-time monitoring of scattered laser light by a single particle of several tens of nanometers in the etching chamber in relation to its status with the equipment

In order to detect a single particle of several tens of nanometers and to clarify the relationship between particle outbreak and the workings of wafer processing equipment, a scattered laser light measurement system has been produced experimentally. The system is composed of a high frequency pulse-laser oscillator, a two-dimensional charge-coupled device image processor, and a status-signal processor connected to the wafer process equipment. By using this system, in situ monitoring of a single particle of several tens of nanometers that flakes off films deposited on the upper ground electrode of the plasma etching chamber, and observation of its trajectory are successfully demonstrated for real tungsten etchback processing. Moreover, data from the system show that, after processing several hundred wafers, the outbreak of particles in the etching chamber had a correlation with specific workings of the etching equipment, such as turning off the rf power and the injection of purge gas to the chamber. The sca...

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.

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.

The application of in situ monitor of extremely rarefied particle clouds grown thermally above wafers by using laser light scattering method to the development of the mass-production condition of the tungsten thermal chemical vapor deposition

It has been successfully demonstrated that the scattered-light intensity of thermally grown particle clouds consisting of particles of less than 20 nm in size above wafers in a real tungsten (W) chemical vapor deposition (CVD) chamber correlate well with both the surface roughness of the W-CVD film measured by atomic force microscopy and with the gas-flow ratio SiH4/WF6. In addition, we can observe the appearance and motion of particle clouds corresponding to the transient variation of the ratio SiH4/WF6 at the conversion of gases and at the change of the flow ratio. These features of our in situ particle monitor enable us to achieve the mass-production conditions for particle-free and smooth surfaces of W films with short cycle time. Moreover, our particle monitor is sensitive enough to adopt in the development of process conditions as the reduction of design rules for large-scale integrated circuit proceeds. Therefore, applying our in situ particle monitor above wafers for developing mass-production con...