Michinari Yamanaka

Improved Metal Gate Process by Simultaneous Gate-Oxide Nitridation during W/WNx Gate Formation.

The improvement of gate dielectric reliability by simultaneous gate dielectric nitridation during W/WNx gate sputtering deposition was investigated. The time-to-breakdown (tbd) of the W/WNx gate metal-oxide-semiconductor (MOS) capacitor was improved compared to that of the W gate by increasing the N2 flow ratio (RN) during the reactive sputtering deposition of the WNx gate with an N2–Ar gas mixture. The surface nitridation of the gate dielectric of the W/WNx gate MOS capacitor was confirmed to occur simultaneously with the reactive sputtering deposition of the WNx layer. The improvement of the gate dielectric reliability was achieved by the nitridation, which terminated the dangling bonds formed in the gate dielectric surface during the metal gate sputtering process. Other characteristics of the W/WNx gate electrode were also demonstrated. The W/WNx gate provides low resistivity, a near-mid-gap work function and a good gate etch profile.

Radical behavior in inductively coupled fluorocarbon plasma for SiO2 etching

Silicon dioxide etching in an inductively coupled plasma (ICP) using a multispiral coil (MSC) has been studied on the basis of CFx (x=1, 2) radical measurement employing a laser-induced fluorescence (LIF) technique. Fundamental radical behaviors in the MSC-ICP including a pulsed operation have been investigated for CF4 gas chemistry; radical composition and distribution are strongly dependent on chamber wall conditions and on the pulse modulation period as well as the time-averaged ICP power, because of dissociation and extinction kinetics. Moreover, radical behaviors in fluorocarbon plasmas including C4F8 and CHF3 have been examined in relation to the SiO2 etching characteristics. The dependence of radical densities on gas chemistry and on ICP power in the MSC-ICP has been characterized and has been found to correlate with the SiO2 etch rate and selectivity to Si. The results demonstrate that the control of radical behavior is crucial in realizing selective SiO2 etching using the MSC-ICP.

Highly Selective SiO2 Etching Using Inductively Coupled Plasma Source with a Multispiral Coil

To exploit the highly selective SiO2 etching in an inductively coupled plasma (ICP) with a multispiral coil (MSC), the effects of chamber wall heating and pulse modulation have been examined, employing a laser-induced fluorescence (LIF) technique to detect CFx (x=1, 2) radicals. It was found that chamber wall heating up to 100°C in a CHF3/C4F8 plasma leads to a drastic increase in the SiO2 selectivity to Si, accompanied by an increase in the radical densities. A further increase in the selectivity of SiO2 up to ~45 was realized by pulse modulation whereby the CF2 radical density increases with shortening of the modulation period to 20 µs. The resultant high selectivity could be brought about by controlling the production and extinction processes of the radicals in the MSC-ICP.

Contact Hole Etch Scaling toward 0.1 µm

Reactive ion etching (RIE)-lag, i.e., the dependence of contact etched depth D on contact diameter , for deep quarter micron contact hole etching has been studied down to 0.1 µm contact. The nonlinearity between and D was found to be successfully converted into a linear relationship with reciprocal plots of and modified contact etched depth (D+h), taking into account the resist thickness h. In addition, by introducing the dependence on etching time t as the intercept in the relationship, the simple experimental equation was proposed in a new form to describe RIE-lag. This permits the prediction of etching rates of smaller contacts in the future and will be useful to investigate the etching mechanism.

Spatial and Temporal Behavior of Radicals in Inductively Coupled Plasm for SiO2 Etching

Fluorocarbon CFx (x=1, 2) radicals in an inductively coupled plasma (ICP) have been measured using a spatially and temporally resolved laser-induced fluorescence (LIF) technique. Hollow profiles in the radial and axial distributions for the radicals in C4F8 ICPs, in contrast to uniform radial profiles near the substrate, suggest a destructive character within the ICP bulk and a small surface loss probability on the chamber wall. Temporal change of the CF2 radical distribution in the afterglow ICP was found to be dominated by the slow diffusion and wall-reflection processes.

Effect of Thin Tungsten Oxide on Resistance Increase in Annealed Aluminum/Chemical Vapor Deposited Tungsten Interconnects

Aluminum/chemical vapor deposited tungsten (Al/CVD-W) interconnects shows an undesirable large increase in sheet resistance due to Al-W reaction during annealing at 450°C. The effect of native oxides on W surfaces on the resistance increase has been studied. When there is no native oxides on W surfaces, the narrower interconnects show a larger increase in sheet resistance after annealing due to the nonuniform formation of WAl 12 . On the other hand, the interconnects with the native oxide at the Al/W interface show a large increase in sheet resistance, which has little dependence on linewidth. This is because WAl 12 formation is suppressed by Al 2 (WO 3 ) 4 and WAl 5 formation.

Suppression of Resistance Increase in Annealed Al/W Interconnects by Capacitively Coupled Plasma Nitridation on W Surface.

The suppression of the resistance increase in annealed Al/chemical vapor deposition (CVD)-W interconnects has been achieved by exposing the W surface to N2 plasma before Al deposition. The N2 plasma was generated in a capacitively coupled parallel-plate reactor. This process forms a thin WN x layer at the interface between the Al and the W layer. The WN x layer prevents Al-W alloy formation during annealing at 450°C. With this N2 plasma treatment, the resistance increase after annealing at 450°C is suppressed to only 10% compared to 140-180% in samples without the N2 plasma treatment. The N/W ratio and the thickness of the WN x layer are about 1.1 and 4 nm, respectively. The WN x layer formed in our experiment is found to be thicker and have a higher N concentration than the WN x layer formed by electron cyclotron resonance (ECR) plasma nitridation. This is probably due to the large self-bias voltage of the N 2 plasma generated in a capacitively coupled parallel-plate reactor.

A Novel Al/TiN/CVD-W Structure to Eliminate Resistance Anomaly in Deep Submicron Al/CVD-W Interconnects

The sheet resistance increase of Al/chemical vapor deposition (CVD)-W interconnects after low-temperature annealing has been investigated. Anomalous sheet resistance increase depending on the linewidth in sub-half-micron Al-Si-Cu/CVD-W lines after 450°C annealing is found for the first time. The sheet resistance increase of the Al/CVD-W lines becomes larger for narrower linewidth after annealing. It is considered that this anomalous sheet resistance increase is due to more nonuniform high-resistivity WAl 12 formation in the narrower lines. Using a TiN interlayer to eliminate WAl 12 formation, sub-half-micron lines of a new Al-Si-Cu/TiN/CVD-W structure have demonstrated sufficiently low line resistance even after 450°C annealing for 300 min and exhibited 6 times longer electromigration (EM) lifetime compared with the previous Al-Si-Cu/CVD-W structure. This longer EM lifetime is also attributed to the suppression of WAl 12 formation. This structure is one of the most promising interconnect structures for realising sub-half-micron interconnects in future ULSIs

Transformation of dense contact holes in oxide etching

For the semiconductor fabrication, the advanced photolithography technology of the high resolution by short wavelength, such as ArF, is studied. However, the photo resist used for present ArF lithography is deficient in the resistance for dry etching. In this study, it is investigated that the formation of the dense contact holes with the ArF resist mask.

Transformation of Dense Contact Holes during SiO2 Etching

The profile transformation that occurs during SiO2 etching using an ArF positive resist is a serious problem. We investigate the characteristic transformation of the dense contact holes. Under the high-selectivity etch condition, the deformation of dense contact holes occurs only in the direction of the closest adjoining contact holes. Since the patterns have a small flat part at the top of the photoresist, deposition of a small amount of fluorocarbon can exist on the flat part. Therefore, the recession of the photoresist at the facet part progresses rapidly and erosion of the photoresist occurs. On the other hand, the deposition of fluorocarbon progresses at the spacious top of the photoresist. This fluorocarbon suppresses the recession of the photoresist at the facet part and overhangs the contact hole. Accordingly, the dense contact holes change from a circular shape to rectangular shape.