Takafumi Tokunaga

Analysis of SiO2-to-Si3N4 selectivity in reactive ion etching using additional O2 gas

The mechanism for control of the Si3N4 etch rate in a self-aligned contact process when C4F8/Ar/O2 gas is used was investigated. The Si3N4 surfaces after dry etching were analyzed by x-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. After dry etching, a polymer-like residue film less than 15 nm thick and an oxidized layer between the polymer layer and the Si3N4 surface were observed. In the CF polymer layer, the etching product of CN or CNO was characterized. CN or CNO components are widely distributed in the CF polymer layer, while the SiO2 layer is more localized on the Si3N4 surfaces. We found that the thicknesses of the CF polymer and SiO2 layer strongly depend on the Si3N4 etch rate, which is determined by the flow rate of the additional O2 gas. The thickness of the CF polymer, which was decreased from 10.1 to 4.1 nm, is considered to act as an inhibitor. The thickness of the SiO2 layer, which is easy to etch, was increased from 1.4 to 2.7 nm. The CF polymer thickne...

Low-energy Ion-scattering Spectroscopic Analysis of Structural Damage in Si Substrate under Ultrathin SiO2 after Gate Etching

The relationship between wafer-bias power during over-etching and structural damage induced in Si(100) substrate under ultrathin SiO2 layers by gate etching was examined by low-energy ion-scattering spectroscopy (LEIS) and high-resolution X-ray photoelectron spectroscopy. The crystal structure of the topmost surface of the Si substrate was modified when the residual SiO2 layer was 2.5 nm thick at a wafer-bias RF power of 70 W during over-etching. This structural damage was shown to be due to ions coming from plasma irradiation because the residual SiO2 thickness was close to the projected ion range at an ion energy of 310 eV (which was estimated from the Vpp of the bias voltage when the RF power was 70 W).

In-situ After-treatment Using Low-energy Dry-etching with a CF4/O2 Gas Mixture to Remove Reactive Ion Etching Damage

We have investigated a new method of in-situ after-treatment that precisely and anisotropically removes dry-etching damage induced by reactive-ion etching (RIE) of SiO2, especially in self-aligned contact (SAC) processing, through, low-energy etching in the dry-etching chamber after the RIE. This in-situ after-treatment with a CF4/Ar gas mixture and with a CF4/O2 gas mixture were examined. The after-treatment with the CF4/O2 gas almost completely removed both the chemical damage and the crystalline damage. On the other hand, although RIE damage could be reduced by after-treatment with the CF4/Ar gas mixture, severe crystal damage remained. The after-treatment with the CF4/O2 gas mixture could precisely remove the surface damage and allowed us to control the surface roughness during removal of RIE damage.

LOW-ENERGY ION SCATTERING MEASUREMENT OF NEAR-SURFACE DAMAGE INDUCED BY THE SIO2 DRY-ETCHING PROCESS

Si(100) surface crystallinity after dry etching was measured using low-energy ion scattering spectroscopy (LEIS). We used 4-keV He+ ions as the incident beam, and neutral particles back-scattered at 180° were detected. A heavily damaged layer was observed immediately after reactive ion etching. After the heavily damaged layer was removed using a post-etch treatment, channeling and focusing effects were observed. The presence of a modified layer was confirmed even after the suboxide-rich layers were removed, because the channeling and focusing effects were slightly weaker than those of the surface without dry etching.

Evaluation of Charge Passed through Gate-Oxide Films Using a Charging Damage Measurement Electrode

A charging damage measurement electrode was used to model device structures. The charge passed through gate-oxide films (Qp) was measured in a cavity-resonator-type electron cyclotron resonance (ECR) plasma etcher for 12-inch wafers and the reduction of charging damage was investigated. Parallel circuits composed of resistors and condensers were modeled after the current–voltage (I–V) characteristics of the gate-oxide film. The electron shading effect was introduced by mounting a Si chip with line and space (L&S)-patterned photoresist on the probe, which corresponded to the gate electrode. The reduction of charging damage using the time modulation (TM) bias was determined by evaluating Qp and the damaged test element group (TEG) wafer. This charging damage measurement electrode is effective for investigating the reduction of charging damage in particular, of the etcher used for 12-inch wafers.

Using Auger Electron Spectroscopy for Chemical Analysis of Plasma Damage Induced by Reactive Ion Etching of SiO2

Surface damage induced by reactive ion etching (RIE) at the bottom of the pattern was investigated in terms of chemical information by Auger electron spectroscopy (AES). The Si-L23VV line shape was changed during the removal of the damage by chemical dry etching after RIE. The relationship between the changing of the Si-L23VV line shape and the chemically damaged layer, which contains SiOx and SiC, was investigated by X-ray photoelectron spectroscopy (XPS) and AES for nonpatterned wafers. The height of the peaks at 90 eV and 79 eV in the Si-L23VV spectra were correlated with the amounts of chemical damage in the layer measured by XPS. The thickness of the residual SiOx damage was estimated from the relationship between the Si-L23VV line shape and the thickness of the SiOx layer. This relationship was applied to the chemical analysis for patterned wafers. The line shape of the Si-L23VV spectrum from the bottom of the pattern was also changed as the chemical-dry-etching time increased.

Effects Of Multichamber Processing On Reliability Of Submicron Vias

This paper describes effects of spin-on-glass (SOG) planarization layer etchback process on reliability of submicron vias for multilevel metalization. Resistance values of double-level metal via chains containing 4,000-200,000 vias in the 0.8-2.0 um size range have been measured. Mass spectra for outgas from SOG films have been studied in more detail. The SOG etchback process and the subsequent P-SiO layer deposition process have been executed in a multichamber CVD system. The multichamber processing can reduce the emission of outgas which degrades via yield and reliability.