Mark A. Jaso

Chemical‐Mechanical Polishing for Fabricating Patterned W Metal Features as Chip Interconnects

Interconnect features of W metal, recessed in an dielectric, can be formed using a novel chemical‐mechanical polish process. Mechanical action, to continually disrupt a surface passivating film on W, and chemical action, to remove W, appear to be requirements for workability of the process. A trial process chemistry using a ferricyanide etchant is described. Removal of the W is discussed in terms of competition between an etching reaction which dissolves W and a passivation reaction to reform on the surface of the W. This novel processing technology is compared with earlier methods of fabricating metal interconnect structures.

Surface analysis of realistic semiconductor microstructures

The geometrical and insulating properties of regular arrays of oxide masked silicon trenches formed by reactive ion etching have been utilized to enable in situ x‐ray photoelectron spectroscopy of specific parts of the trench structures. Different surface portions of the sample structure are differentiated by using (i) grazing incidence x‐ray irradiation which results in shadowing of the trench bottoms and (ii) electrostatic charging of the insulating portions (e.g., the oxide mask) which shifts spectral features. We demonstrate the usefulness of this approach in analyzing the composition of the film passivating the silicon trench sidewall for a SF6/O2 trench etching process.

Selective Dry Etching of Germanium with Respect to Silicon and Vice Versa

It is shown that germanium is more rapidly etched than silicon in conventional fluorine‐, chlorine‐, and bromine‐based low‐pressure plasmas and that a high Ge/Si etch rate ratio ERR can be readily obtained. The etching of Ge induced by plasma‐generated fluorine atoms relies much less on ion bombardment than the etching of Si. A very high Ge/Si ERR (40) may therefore be achieved for plasma etching conditions or for reactive ion etching at high pressure (250 mtorr) where the importance of ion bombardment effects on the etching is reduced. For reactive ion etching at low pressure where the etching is strongly ion‐enhanced, the Ge/Si etch rate ratio is reduced to 3. Silicon may be more rapidly etched than Ge in a gas mixture of . A Si/Ge etch rate ratio greater than 70 is demonstrated in this work. Both the formation of carbonaceous material and an involatile germanium‐sulfide compound on the Ge surface are important in reducing the reaction of fluorine with the substrate and lowering the Ge etch rate. It is also shown that this RIE approach may be used to selectively etch Si over a alloy.

Transient fluorocarbon film thickness effects near the silicon dioxide/silicon interface in selective silicon dioxide reactive ion etching

We have utilized an on‐line ellipsometer to perform real time measurement of the thickness of fluorocarbon films formed on Si during overetching in selective silicon dioxide reactive ion etching (RIE) using CF4/H2. Employing an ultrahigh vacuum surface analysis system interfaced via a transfer chamber to the RIE system, x‐ray photoelectron spectroscopy analysis was also performed on reactive ion etched SiO2 just before the encounter of the SiO2/Si interface (≂3‐nm SiO2 remaining) during etching and for Si just after etching through the interface (overetch time <15 s). The SiO2 surface was essentially free of fluorocarbon film. The formation of the fluorocarbon film on Si after etching through the SiO2/Si interface was shown to occur very fast and achieve a near steady‐state thickness value within ≂15 s for our etching conditions.

Mechanism of the Slow-Down of the Silicon Etch Rate by a Fluorocarbon Overlayer in CF 4 /H 2 Reactive Ion Etching of Silicon

We have utilized an ultrahigh vacuum surface analysis system interfaced via a load-lock to a flexible diode dry etching apparatus to study vacuum transferred CF 4 /H 2 reactive ion etched silicon surfaces by X-ray photoemission spectroscopy (XPS). From the observation and analysis of silicon-fluorine bonding underneath the fluorocarbon film and the dependence of the abundance of fluorosilyl species on the thickness of the fluorocarbon overlayer, the role of the fluorocarbon film in the slow-down of the Si etch rate has been elucidated: The role of the fluorocarbon film is to “protect” the Si surface from attack of fluorine, rather than prevent the escape of SiF 4 etch product.

In situ spatially resolved surface characterization of realistic semiconductor structure after reactive ion etching process

The properties of a patterned semiconductor structure have been utilized to enable spatially resolved analysis of the surface chemistry of a contact hole reactive ion etching process by x‐ray photoemission spectroscopy. The topography of the semiconductor structure in combination with angle resolved analysis has been used to cause geometrical shadowing and to enable selective area analysis. Differences in the conduction characteristics of silicon and photoresist and concomitant electrostatic charging of the insulating photoresist layer made fluorocarbon films on photoresist and silicon nonequivalent and allowed to unambiguously assign their spatial origin.

A photoemission investigation of surface processes affecting the reactive ion etching of TiSi2 in CF4

Photoemission was used to probe the surface modifications which occur while etching TiSi2 in CF4 plasmas. Fluorination of the silicide leads to the depletion of Si from the surface region and the formation of a relatively thick (∼15–20 A) overlayer with an average stoichiometry of TiF3. An identical overlayer also forms on pure Ti. The overlayer is primarily composed of a single fluorinated species and apparently does not contain a distribution of different species as in the case of fluorinated Si. This observation strongly suggests that the limiting factor in the etching of these materials is the further reaction/sputtering of this stable, nonvolatile fluoride. Also, as in the case of Si etching in halocarbon plasmas, CFx films were found to form with increasing addition of H2. Significant differences in the quantity and composition of the films were found compared to those formed on Si substrates, with Si exhibiting a higher tendency to promote CFx film growth.