Yasuhiro Morikawa

Low-k materials etching in magnetic neutral loop discharge plasma

Low-k materials etching for FLARE™ and a porous silica were carried out in a magnetic neutral loop discharge plasma at low pressure, below 1 Pa. Fluorinated carbon molecules were used as etching gases for porous silica. The etch rate of the porous silica was approximately two times higher than that of thermal SiO2. This result means that consumption of perfluoro compound (PFC) gases is suppressed below at approximately half volumes. And organic low-k materials etching where ammonia gas or a gas mixture of nitrogen and hydrogen were used instead of PFC gas is an environmentally friendly process. After investigating an influence of a N2/H2 mixture ratio in the organic materials etch process, a good experimental condition to get a low microloading profile was found at a N2 ratio of 70%–80%. Under this condition N2+ and N2H+ ions were dominant, and the signal intensity of the N2H+ ion showed a maximum value in the mass spectrum. This may mean N2+ and N2H+ ions play an important role for a low microloading etc...

Very uniform and high aspect ratio anisotropy SiO2 etching process in magnetic neutral loop discharge plasma

Magnetic neutral loop discharge (NLD) plasma is a new type for dry etching process characterized by effective coupling of the input electric field electron electron motion near the magnetic neutral loop (NL) region. Therefore, dense plasma can be produced and controlled spatially by changing the position of the NL. Uniformity was controlled by changing the radius of NL temporally during the etching using a repetition frequency of 0.1 Hz, so that the deviation of the SiO2 etch rate was within 2% (3σ) on 200-mm-diam wafer. In nanoscale pattern etching processes, we found that CHF2+ ions played an important role in very high aspect ratio profile etching. In CHF2+ ion-rich plasma, ZEP photoresist patterned 20 nm space was successfully etched 800 nm in depth at the pressure of about 0.3 Pa, using CH2F2, C4F8, and O2.

Application of magnetic neutral loop discharge plasma in deep silica etching

The electron temperature Te is one of the key parameters for process plasma because the decomposition of most reactive gases depends on the kinetic energy of electrons in the plasma. Pressure is another important parameter in the etching process for microelectromechanical systems (MEMS). Low pressure can avoid etch product substrate redepositing by reducing the collision between neutral particles and etch products in the gas phase. Also, low pressure may reduce the scattering of incident ions in the sheath that may reduce the negative taper angle for trench etching. Therefore, this study is focused on low pressure (<0.67 Pa), low Te plasma production for optical MEMS etching processes. To reduce the Te and keep the high density of the plasma, use of a parallel turn antenna was proposed and it was applied in magnetic neutral loop discharge plasma, where the Te is desirably reduced to about 2.5 eV while the density is about 1.2×1011 cm−3 at pressure of 0.2 Pa. With this improvement in plasma production, fus...

Etching Characteristics of Organic Polymers in the Magnetic Neutral Loop Discharge Plasma.

Etchings of organic low-k materials, FLARE, SiLK and polyimide films were carried out in a N2-dominant mixed gas plasma generated by a magnetic neutral loop discharge (NLD) method at a low pressure below 1 Pa. The results showed that the uppermost layers on the top surface and sidewall surface were composed of tightly bonded C–N sp3, so anisotropic profiles were obtained in the case of the N2-dominant mixture ratio of the N2 + H2 plasma. Based on this result, we also investigated polyimide deep etching under the same condition, and successfully obtained an anisotropic etched profile with the depth of about 8 µm and the linewidth of about 0.5 µm (aspect ratio of 16).

Reaction of the fluorine atom and molecule with the hydrogen-terminated Si(111) surface

To establish the self-limiting reaction process that is necessary to achieve the atomic layer-by-layer etching for the damageless fabrication of nanometer-electronics devices, the initial reaction of fluorine (F) atoms and F2 molecules with hydrogen (H)-terminated Si(111) was studied employing a combined system of Fourier transform infrared (FTIR)-attenuated total reflection (ATR) and x-ray photoelectron spectroscopy (XPS). In the ATR measurement, peaks of 2086 cm−1 (B2) and 2090 cm−1 (B3) newly appeared instead of a decrease in the original Si–H peak at 2083 cm−1 (B1) with initial exposure of XeF2. The sum area of B1, B2, and B3 peaks until ∼2000 L was almost constant. This implies that B2 and B3 peaks also resulted from Si–H bonds. The XPS measurement revealed that the initial exposure of XeF2 generated nonbonded F atoms at first, followed by SiF1 bonds. Based on the good correspondence between ATR and XPS results, first the F atoms penetrate just underneath the Si–H bond, generating the B2 peak. After ...

Etching characteristics of porous silica (k=1.9) in neutral loop discharge plasma

Etching characteristics of a porous silica material (ISM-1.5™ produced in ULVAC, Inc.) were investigated and compared with those of thermal oxide. The etch rate of porous silica in magnetic neutral loop discharge plasma was approximately two times higher than that of thermal SiO2 film when linear saturated perfluorocarbon compounds were used. This may be due to the low film density of the porous silica. However, in the case of C4F8 (octafluorocyclobutane) plasma, the etch rate ratio to SiO2 was about 1.45. When C4F6 (CF2=CFCF=CF2: hexafluorobutadiene) was used, the etch rate ratio was also very low (0.6). So, the etch rate strongly depended on the gas structure, whereas the SiO2 etch rate did not depend on the gas species and was almost constant. Through mass spectrometry and x-ray photoelectron spectroscopy measurements, it was deduced that the fluorocarbon polymer formed in the pore suppressed the etch rate of porous silica in C4F8 or C4F6 plasmas.

Magnetic Neutral Loop Discharge (NLD) Plasma and Application to SiO2 Etching Process

The applicability of the magnetic neutral loop discharge (NLD) plasma etching apparatus to the 0.1 µm wafer process was experimentally verified. Variation of the SiO2 etch rate was obtained to within 1.3% (2% as 3σ value) on a 200 mm wafer, by applying a functional current to the magnetic coil with 0.1 Hz. A superfine trench pattern with a width of 20–50 nm and a depth of 800 nm was also successfully fabricated with an electron beam resist mask in a C4F8 + CH2F2 plasma at 0.3 Pa.

Investigations of Surface Reactions in Neutral Loop Discharge Plasma for High-Aspect-Ratio SiO2 Etching

The relationship between fine etching and gas structure in magnetic neutral loop discharge (NLD) plasma has been investigated using C4F8, C3F8, and CF3FOC=CF2 (HFE-216) gases. It was found that CF3+ ions were effectively generated in the HFE-216 plasma compared with those in the C4F8 or C3F8 plasma under the same conditions. Hydrofluorocarbon (HFC) gases such as CH2F2 (HFC-32) and CH3CHF2 (HFC-152a) were also employed to realize highly selective etching for SiO2 to the photoresist. C1s X-ray photoelectron spectra showed a prevalence of C–C and C–CFx bonds in the films deposited on the surface in the HFC plasma. This implies that the deposited film was mainly composed of carbon atoms. It was also found from X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared (FTIR) analyses that the chemical state of fluorine in this film was not C–F, but H–C–F. This may lead to the realization of microloading free etching with high resist selectivity in the HFE-216/HFC-152a mixture plasma. Studies on the relationship between etch performance and thin H–C–F polymer film formation were carried out in the HFE-216/HFC-152a mixture plasma. It can be thought that the interaction of the H–C–F film on the surface and CxFy species from the plasma is very low compared with that of a C–F film. The H–C–F film on the sidewall may play serve as a lubricant and may transport etchants to the bottom of the etched pattern. As a result, 50-nm-diameter holes and 40 nm space patterns with aspect ratios of 18 and 22.5, respectively, were successfully fabricated in the HFE-216 + HFC-152a + O2 plasma. The H–C–F film formation on the etched surface enables high-aspect-ratio etching with high selectivity.

CH4/N2 Plasma Etching for Organic Low-k Dielectric Material

The etching of an organic low-dielectric-constant (low-k) material, FLARE, with gas mixtures of CH4/N2 and H2/N2 was investigated in a magnetic neutral loop discharge (NLD) plasma system. The hole-etching profile of FLARE with a SiO2 hard mask and reactive ion etching (RIE) lag characteristics (the etch rate depends on the hole size) were studied for hole diameters from 0.16 to 0.4 µm. We discuss the role of CH4 in organic low-k etching and consider the etching mechanism in a CH4/N2 plasma in comparison with that in a H2/N2 plasma. Etching with no RIE lag was achieved at a CH4 concentration of about 30% with a total flow of 100 sccm, pressure of 0.4 Pa, source power of 1000 W, and bias power of 200 W in a CH4/N2 plasma. FLARE etching profiles with a perpendicular or normal taper and no microtrenching were obtained with CH4 concentrations below about 70%. We used X-ray photoelectron spectroscopy (XPS) to evaluate films deposited on a Si substrate during etching under several plasma conditions to clarify the mechanism of the organic low-k material etching.

Fabrication of ultra-fine vias in low CTE Build-up Films using a novel dry etching technology

An ultra-fine vias pattern below 10 μm with low surface-roughness in a low-CTE Build-up film was achieved by a new fabrication. In this method, a DFR (Dry Film Resist) mask was formed on ABF (Ajinomoto Build-up Film) by the photolithography process. There were achieved ultra-fine vias through the use of a dry etching method. In the last years the number of high performance mobile devices, such as smart phones or tablet PCs, increases widely and accordingly data traffic augments rapidly. Devices for these equipments require high-rate processing capabilities, high-density packaging possibilities and low power consumptions. Thus the demand for packed semiconductor chips with high density of components is growing. In order to accomplish high-density packaging, miniaturization of wiring in organic package is needful. To obtain vias in a build-up film, the laser drilling process is widely used but there are three major restricting difficulties. The first is that it is impossible to make ultra-fine vias because of laser wave length limitation. The second is that wet desmear process to remove residuals is necessary. Finally, film surface gets rough when wet desmear is used and hence the performances of devices in high frequency are affected.