Takashi Namura

Charge buildup in magnetized process plasma

The charge buildup in a magnetron etcher has been studied experimentally for two different magnet arrangements and theoretically on the basis of an equivalent circuit model. Wafer charging measured with a metal-Si3N4-SiO2-Si (MNOS) capacitor is negative along the centerline of the magnet poles and positive between the magnets in both cases. Wafer charging is explained either by curtent crowding at the center of the magnet poles or by the nonambipolar diffusion effect.

Experimental and Theoretical Study of the Charge Build-Up in an ECR Etcher

The charge build-up in an electron cyclotron resonance (ECR) etcher has been studied experimentally and theoretically. The experimental results show that the charge build-up profiles of the wafer are convex and positive, and are detected only when the RF bias exists. We have derived a simplified equivalent circuit model for the wafer in an ECR etcher. The charge build-up profile predicted with the simplified equivalent circuit model shows a good agreement with the experimental results. It is concluded that the variation of plasma potential caused by the radial RF current across the magnetic field results in the charge build-up.

Charge Build-Up and Uniformity Control in Magnetically Enhanced Reactive Ion Etching Using a Curved Lateral Magnetic Field.

The effectiveness of a curved lateral magnetic field has been examined in magnetically enhanced reactive ion etching (MERIE). It is demonstrated that both charge build-up and etching nonuniformity are suppressed at the same time when the offset angle of dipole magnets is adjusted to 10°. Theoretical analysis of electron flow in the curved lateral magnetic field suggests that the plasma electron multiplication effect along E×B drift motion is compensated by the divergence of the drift motion at the optimum condition, and it results in uniform plasma generation. Although the definite mechanism of charge build-up is still not clear, this study indicates the importance of plasma uniformity in controlling the charge build-up in a MERIE system.

Wafer charging in different types of plasma etchers

Wafer charging in barrel etchers, reactive ion etching (RIE) etchers, magnetron RIE (MRIE) etchers and electron cyclotron resonance (ECR) etchers are characterized. The charging voltages were measured by using electrically programmable non-volatile memories. The charging profile for the barrel etchers and the RIE etcher depends critically on the electrode arrangements and wafer locations, while that in the MRIE etchers and the ECR etchers depends on the structure of the magnetic field. Even in the case of a non-divergent magnetic field ECR etcher, wafer charging is built-up when an RF bias is applied to the wafer stage. By analyzing these results, two charging mechanisms are distinguished. One is the plasma nonuniformity around the wafer, which depends on the RF electrode and the wafer location. The other is the anisotropy of the magnetized plasma, which depends on the structure of the magnetic field. Some of the charging profiles due to the former effect is reproduced by using an equivalent circuit model. It is found from the model that even in the uniform density plasma, wafer charging is induced by the RF current which causes a plasma potential variation across the wafer surface.

Effects of permanent magnet arrangements and antenna locations on the generation of multicusp electron cyclotron resonance plasma

A comparative study on the generation of 2.45‐GHz multicusp electron cyclotron resonance (ECR) plasma is performed. Looped cusp structures such as the ring‐cusp give a low‐power and low‐pressure ignition, and vice versa, indicating an importance to keep the electron trajetory of gradient‐B drift motion inside the chamber even in the case of ECR plasmas. The importance of the antenna location in such multicusp fields is elucidated by comparison in two cases of the axial antenna located in the weak magnetic field region, generating a hydrogen plasma of limited density (ne<7.4×1010 cm−3), and a radial antenna located in the strong magnetic field region, generating an overdense plasma (ne∼2×1011 cm−3).

Detailed measurements and simplified modeling of wafer charging in different barrel reactor configurations

The detailed profiles of the wafer charging in different barrel reactor configurations have been obtained by using the electrically erasable–programmable read‐only memory devices. Charging profile in a parallel electrode system depends strongly on the wafer orientation with respect to the rf electric field, while minor changes are observed by the use of floating Al etch tunnel and by the reduction of the wafer‐to‐wafer separation. On the other hand, no wafer charging is detected in a co‐axial electrode system. A simplified equivalent circuit model, which represents the potential in 2‐dimensional rf plasma–wafer system, has been proposed. The charging profile derived from the simplified model coincides with the experimental results. This model gives an analytical explanation of the gate charging.

Evaluation of Device Charging in Ion Implantation

Device charging in the ion implantation is evaluated by using two different types of electrically erasable-programmable read-only memory (EEPROM) devices and two different types of metal-oxide-semiconductor (MOS) capacitors. The averaged charging voltage is measured by the turn-on voltage shift (ΔVT) of a grounded source EEPROM, while the transient charging effect is detected by a floating source EEPROM. The yield of the MOS capacitor reaches its maximum when the grounded source EEPROM shows the minimum ΔVT. The effects of the charge-collecting electrode area and substrate type of the MOS capacitor are also examined.

Evaluation of ion implantation charging by using EEPROM

Abstract Ion implantation charging has been studied by evaluation of the threshold voltage shift (ΔVt) of EEPROM devices. The threshold voltage shifted proportionally with the variation of the electron emission current. This method allows the uniformity of charging within a wafer to be evaluated exactly, and has also shown excellent repeatability. The oxide breakdown frequency of the MOS capacitor showed good agreement with the threshold voltage shift. Consequently, the EEPROM threshold voltage shift measurement was found to be very useful in the development of systems which retard charge buildup.

Epitaxial Lateral Overgrowth (ELO) of Silicon on the Whole Surface

In order to obtain a SOI layer over the whole surface, techniques using two ELO processes are presented. In the first ELO process, the silicon epitaxial layer grows vertically through openings between the SiO2 stripes and laterally across SiO2 stripes. In the second ELO process, the silicon epitaxial layer grows laterally over the new SiO2 layer linking the SiO2 stripes at the bottom of the trench etched in the silicon epitaxial layer, between the SiO2 stripes.

Evaluation of charge build-up in wafer processing by using MOS capacitors with charge collecting electrodes

The charge build-up evaluation technique in semiconductor wafer processing such as ion implantation and plasma processing by using the MOS capacitor with charge collecting electrode (antenna) has been proposed. The estimation of charge build-up during ion implantation has been successfully demonstrated by using this technique. The charge detection sensitivity of a small area MOS capacitor can be improved by using the antenna structure. To estimate charge build-up quantitatively, gate oxide thickness, substrate type, capacitor area and antenna ratio should be carefully chosen. This technique is very useful to estimate charge build-up in conjunction with other charge build-up detection techniques such as EEPROM.