Hans-Olof Blom

Modeling of reactive sputtering of compound materials

An experimentally verified useful new model for reactive sputtering is presented. By considering the total system (target erosion, gas injection, chamber wall deposition, reactive gas gettering at all surfaces, etc.) during deposition it is possible to evaluate quite simple relationships between processing parameters. We have expanded earlier treatments to include these phenomena. The model involves that gettering of the reactive gas takes place at the target and at the walls opposite to the target. Arguments are also presented for how the sputtered materials (elemental target atoms and the formed compound) contribute to the formation of the surface composition of the walls opposite to the sputtering electrode. The mass flow of the reactive gas has been chosen as the independent parameter in this presentation. Results for partial pressure and sputter rate are presented. The theoretical values are compared with experimental results from reactive sputtering of TiN. It is also pointed out that the calculated...

Predicting thin‐film stoichiometry in reactive sputtering

The electrical, optical, and mechanical properties of a compound film depend strongly on the composition of the film. Therefore, it is interesting to study a wide variety of compositions of many new compound materials. Reactive sputtering is a widely used technique to produce compound thin films. With this technique it is possible to fabricate thin films with different compositions. However, it has not yet, to any great extent, been possible to predict the composition of the sputtered film. In this article we will present a model that enables us to predict both sputtering rate and film composition during reactive sputtering. The results point out that there exists a very simple linear relationship between processing parameters for maintaining constant thin‐film composition in the reactive sputtering process. Based on these results, it is possible for the first time to combine information of both sputtering rate and film composition into the same graphical representation. Access to this new and simple grap...

Microloading effect in reactive ion etching

The etch rate of silicon, during reactive ion etching (RIE), depends on the total exposed area. This is called the loading effect. However, local variations in the pattern density will, in a similar way, cause local variations in the etch rate. This effect is caused by a local depletion of reactive species and is called the microloading effect. Silicon wafers patterned with silicon dioxide have been etched in order to study the microloading effect. The pattern consists of a large exposed area and narrow lines at different distances from the edge of the large area. This arrangement makes it possible to study how the distance from the large area, which depletes the etchants, influences the etch rate. The influence of different processing parameters like, e.g., pressure, gas flow rate, and flow direction on the microloading effect have been investigated. It has been found that the microloading effect is small (<10%) compared to other pattern dependent nonuniformities. It is also shown that the nonuniformitie...

Process modeling of reactive sputtering

Reactive sputtering is a very complex and nonlinear process. There are many parameters involved. Normally it is not possible to vary a single parameter independently of the others. It is therefore very difficult to characterize the process based on experimental observations. A better understanding of the reactive sputtering mechanism is needed. We have suggested a simple model for the reactive sputtering process. This model is primarily based on well‐known gas kinetics, transferred to this application. With this model it is possible to theoretically predict different processing conditions and actually study the influence of a change in an individual parameter value. The results may then be used to predict optimal experimental conditions. With this technique it is also possible to study means of affecting the well‐known hysteresis effect. This article is specially devoted to explain the width of the hysteresis region and how it is affected by the sputtering intensity. Experimental results are presented tha...

A comparative study of the diffusion barrier properties of TiN and ZrN

Abstract The usefulness of Ti/TiN and Zr/ZrN bilayers as low resistivity contacts and diffusion barriers between doped silicon and aluminium was examined. The metal nitride layers were formed by reactive sputtering from elemental targets in Ar-N2 mixtures. Analytical results obtained using Rutherford backscattering spectroscopy (RBS) showed that the as-deposited layers were stoichiometric. X-ray diffactometry revealed that the as-deposited films were polycrystalline. The respective RBS spectra showed that no detectable intermixing occured between aluminium and silicon after heat treatment up to 550°C for 30 min for either combinations. Furthermore, RBS analysis indicated that arsenic implanted in the silicon was snow ploughed during the formation of zirconium silicide, which is essential for the formation of low resistivity ohmic contacts. In contrast, arsenic was observed to diffuse through the titanium silicide layer during its formation. Finally, the possibility of in situ deposition of a multilayered structure of Zr/ZrN/Al and the formation of zirconium silicide during the post-metal anneal without aluminium-silicon intermixing was examined.

The use of nitrogen flow as a deposition rate control in reactive sputtering

It is well known in reactive sputtering that the deposition rate generally drops drastically at a high enough partial pressure level of the active gas to form a compound on the target surface. At the point where the deposition rate drops, there exists a simple relationship between the consumed nitrogen and the deposition rate of stoichiometric films. This abrupt decrease in deposition rate can be measured indirectly by monitoring the processing gas by mass spectroscopy (MS) and studying the discharge by optical emission spectroscopy (OES). We have shown that it is possible to select a desired deposition rate by simply choosing a correct mass flow value of the active gas (nitrogen) while maintaining correct stoichiometry of the sputtered film. This can be achieved by presetting the mass flow of the nitrogen. Thereafter, the rf power is increased to the transition level, where the surface of the target changes from compound to elemental. The combination of mass flow control and diagnostic tools (MS) and (OE...

SELECTIVE SIO2-TO-SI3N4 ETCHING IN INDUCTIVELY COUPLED FLUOROCARBON PLASMAS : ANGULAR DEPENDENCE OF SIO2 AND SI3N4 ETCHING RATES

In the fabrication of microstructures in SiO2, etch selectivity of SiO2 to masking, etch stop, and underlayer materials need to be maintained at corners and inclined surfaces. The angular dependence of the SiO2-to-Si3N4 etch selectivity mechanism in a high density fluorocarbon plasma has been studied using V-groove structures. The SiO2 etch rate on 54.7° inclined surfaces is lower than on flat surfaces, while the SiO2 etch yield (atoms/ion) is a factor of 1.33 higher. The results are consistent with a chemical sputtering mechanism. The Si3N4 etch yield is greater by a factor of 2.8 for 54.7° inclined surfaces than for flat surfaces. This large enhancement is explained by a fluorocarbon surface passivation mechanism that controls Si3N4 etching. The fluorocarbon deposition is decreased at 54.7° whereas the fluorocarbon etching rate is increased at 54.7°. This produces a thinner steady-state fluorocarbon film on the inclined Si3N4 surface, and results in a large enhancement of the Si3N4 etch yield.

Generation of Oxide Nanopatterns by Combining Self-Assembly of S-Layer Proteins and Area-Selective Atomic Layer Deposition

We report an effective method to fabricate two-dimensional (2D) periodic oxide nanopatterns using S-layer proteins as a template. Specifically, S-layer proteins with a unit cell dimension of 20 nm were reassembled on silicon substrate to form 2D arrays with ordered pores of nearly identical sizes (9 nm). Octadecyltrichlorosilane (ODTS) was utilized to selectively react with the S-layer proteins, but not the Si surface exposed through the pores defined by the proteins. Because of the different surface functional groups on the ODTS-modified S-layer proteins and Si surface, area-selective atomic layer deposition of metal oxide-based high-k materials, such as hafnium oxide, in the pores was achieved. The periodic metal oxide nanopatterns were generated on Si substrate after selective removal of the ODTS-modified S-layer proteins. These nanopatterns of high-k materials are expected to facilitate further downscaling of logic and memory nanoelectronic devices.

Effects of post–deposition annealing on the material characteristics of ultrathin HfO2 films on silicon

High quality HfO2 films were deposited on p-type Si(100) wafers by an atomic layer deposition scheme. The deposited films were smooth, amorphous, and stoichiometric, as determined by atomic force microscopy, x-ray diffraction, and x-ray photoelectron spectroscopy, respectively. The as-deposited films showed a very small interfacial layer between the HfO2 and silicon. The index of refraction of the film was determined to be slightly smaller than that of bulk HfO2 by spectroscopic ellipsometry. The films annealed in O2 and NH3 at 800°C showed a growth of the interfacial layer, which resembles a SiO2-rich dielectric layer. Short-range order in the as-deposited films was determined to be monoclinic by the extended x-ray absorption fine structure measurements, and signs of crystallization were observed in the O2 annealed sample. The films appeared to be polycrystalline upon high temperature (800°C) annealing as confirmed by high-resolution transmission electron microscopy. Annealing in the forming gas (450°C) ...

Simulation and dielectric characterization of reactive dc magnetron cosputtered (Ta2O5)1−x(TiO2)x thin films

New capacitor material with high dielectric constant is needed for future integrated capacitor structures. Tantalum pentoxide (Ta2O5) is considered as one of the most promising candidates. In this article, thin films of (Ta2O5)1−x(TiO2)x were grown utilizing reactive dc magnetron cosputtering of tantalum and titanium in an argon/oxygen atmosphere. By varying the input power at the targets, the composition of the thin film is easily controlled. The composition of the films was analyzed with elastic recoil detection analysis revealing the titanium oxide content (x ranging from 0 to 0.40). The presented results indicate that reactive sputter deposited tantalum pentoxide, with or without the addition of titanium, exhibits the properties required to meet the demands for future dielectric materials in integrated capacitors. The dielectric constant for metal-insulator-semiconductor structures is about 20 and the leakage current density is below 10 nA/cm2 at 0.5 MV/cm, if the annealing temperature does not exceed...