George Andrew Antonelli

Optical pump and probe measurement of the thermal conductivity of low-k dielectric thin films

We report on measurements of the thermal conductivity of a number of amorphous materials, including fluorinated silicate glass and carbon-doped oxides. These materials are of interest to the microelectronics industry for use as insulators in microprocessors. The samples measured were in the form of thin films deposited onto silicon substrates. Measurements were made using an optical technique in which the film is heated with a picosecond light pulse, and a time-delayed, probe light pulse is used to measure the temperature of the film as a function of time. We find that the thermal conductivity of these low-k dielectrics is reduced by as much as a factor of 5 with respect to amorphous SiO2. Most measurements were made at room temperature, but for two samples we additionally report on measurements for the temperature range 150–375 K. Results for the thermal conductivity for these materials are compared to theories of heat flow in amorphous solids.

Optical pump-probe measurements of sound velocity and thermal conductivity of hydrogenated amorphous carbon films

In this paper, we report the measurements of the thermal conductivity and longitudinal sound velocity of four types of hydrogenated amorphous carbon films. The measurements were made with an ultrafast optical pump-probe apparatus. The films were deposited at various temperatures by plasma enhanced chemical vapor deposition. The films are of a low density (1.0–1.4 g cm−3) and are found to have sound velocities that range from as low as 3 km/s to as high as 10 km/s. The thermal conductivities are between 0.6 and 1.4 W/mK which are low compared to amorphous SiO2 but are larger than published measurements of thin films of similar composition and density by a factor of 2–3.

Picosecond ultrasonic experiments with water and its application to the measurement of nanostructures

The propagation of ultrashort sound pulses in water has been studied by using the picosecond ultrasonic technique and a pulse time-of-flight technique for measuring the depths of deep channels in Si-based nanostructure was demonstrated. The sound pulses were generated when light was absorbed in a metal transducer film and detected by a time-delayed probe light pulse. First, the attenuation and velocity of sound of frequency 4.8 GHz in water were measured through an analysis of the Brillouin frequency oscillations in the reflectivity of the probe light. Measurements at frequencies up to about 11 GHz were made by sending a sound pulse across a thin layer of water and measuring the change in shape of the returning echo due to the attenuation of the different Fourier components. Second, we also report on proof-of-concept ultrasonic experiments to acquire spatial profile information from nanostructures, where sound pulses propagate down narrow channels in patterned nanostructures. We have been able to detect a...

Designing Ultra Low-k Dielectric Materials for Ease of Patterning

Organosilicate materials with dielectric constants (k) ranging from 3.0 to 2.2 are in production or under development for use as interlayer dielectric materials in advanced interconnect logic technology. The dielectric constant of these materials is lowered through the addition of porosity which lowers the film density, making the patterning of these materials difficult. The etching kinetics and surface roughening of a series of low-k dielectric materials with varying porosity and composition were investigated as a function of ion beam angle in a 7% C4F8/Ar chemistry in an inductively-coupled plasma reactor. A similar set of low-k samples were patterned in a single damascene scheme. With a basic understanding of the etching process, we will show that it is possible to proactively design a low-k material that is optimized for a given patterning. A case study will be used to illustrate this point.

Picosecond ultrasonic study of surface acoustic waves on titanium nitride nanostructures

We have measured surface acoustic waves on nanostructured TiN wires overlaid on multiple thin films on a silicon substrate using the ultrafast pump-probe technique known as picosecond ultrasonics. We find a prominent oscillation in the range of 11–54 GHz for samples with varying pitch ranging from 420 nm down to 168 nm. We find that the observed oscillation increases monotonically in frequency with decrease in pitch, but that the increase is not linear. By comparing our data to two-dimensional mechanical simulations of the nanostructures, we find that the type of surface oscillation to which we are sensitive changes depending on the pitch of the sample. Surface waves on substrates that are loaded by thin films can take multiple forms, including Rayleigh-like waves, Sezawa waves, and radiative (leaky) surface waves. We describe evidence for detection of modes that display characteristics of these three surface wave types.

Advances in metrology for the determination of Young's modulus for low-k dielectric thin films

As the semiconductor nano-electronics industry progresses toward incorporating increasingly lower dielectric constant materials as the inter layer dielectric (ILD) in Cu interconnect structures, thermo-mechanical reliability is becoming an increasing concern due to the inherent fragility of these materials. Therefore, the need for metrologies to assess the mechanical properties and elastic constants of low-k dielectric materials is great. Unfortunately, traditional techniques such as nano-indentation are being increasingly challenged as target low-k ILD thicknesses decrease below 100 nm for sub 16 nm technologies. In this light, we demonstrate the applicability of two new techniques, Brillouin Light Scattering and Contact Resonance Atomic Force Microscopy, for the determination of Young’s modulus for low-k dielectric thin films. We show that these techniques yield values that are in agreement with standard nano-indentation measurements and are capable at film thickness on the order of 100 nm or less.

Patterning with Amorphous Carbon Thin Films

Amorphous carbon hard mask films grown with plasma enhanced chemical vapor deposition are an enabling technology for advanced front-end-of-line patterning technologies. These films must have a low etch rate and be weakly roughened in dielectric etch chemistries, high transparency at lithography alignment wavelengths, and the mechanical properties to mitigate elastic instabilities such as line bending. The deposition process affects all of these parameters through the resulting structure and composition. Highly graphitic films deposited at 550°C are common; however, other process spaces relying on ion bombardment rather than temperature can create less graphitic films with improved film properties like transparency, hardness, and etch selectivity.

Studies of the Coefficient of Thermal Expansion of Low-k ILD Materials by X-Ray Reflectivity

The electrical and mechanical properties of low-k dielectric materials have received a great deal of attention in recent years; however, measurements of thermal properties such as the coefficient of thermal expansion remain minimal. This absence of data is due in part to the limited number of experimental techniques capable of measuring this parameter. Even when data does exist, it has generally not been collected on samples of a thickness relevant to current and future integrated processes. We present a procedure for using x-ray reflectivity to measure the coefficient of thermal expansion of sub-micron dielectric thin films. In particular, we elucidate the thin film mechanics required to extract this parameter for a supported film as opposed to a free-standing film. Results of measurements for a series of plasma-enhanced chemical vapor deposited and spin-on low-k dielectric thin films will be provided and compared.

Ultrafast opto-acoustics applied to the study of material nanostructures

The propagation of ultra-short sound pulses in water has been studied using an ultrafast opto-acoustic technique. A pulse time-of-flight technique for measuring the depths of deep channels in Si-based nanostructures was demonstrated. We report in these proof-of-concept ultrasonic experiments how spatial profile information of nanostructures can be acquired, where sound pulses propagate down narrow channels in patterned nanostructures. We have been able to detect acoustic echoes for sound propagating along a channel as narrow as 35 nm with depth to width ratios exceeding 10:1.

Picosecond ultrasonic study of surface acoustic waves on periodically patterned layered nanostructures

&NA; We have used the ultrafast pump–probe technique known as picosecond ultrasonics to generate and detect surface acoustic waves on a structure consisting of nanoscale Al lines on SiO2 on Si. We report results from ten samples with varying pitch (1000–140 nm) and SiO2 film thickness (112 nm or 60 nm), and compare our results to an isotropic elastic calculation and a coarse‐grained molecular dynamics simulation. In all cases we are able to detect and identify a Rayleigh‐like surface acoustic wave with wavelength equal to the pitch of the lines and frequency in the range of 5–24 GHz. In some samples, we are able to detect additional, higher frequency surface acoustic waves or independent modes of the Al lines with frequencies close to 50 GHz. We also describe the effects of probe beam polarization on the measurements sensitivity to the different surface modes. HighlightsAn ultrafast optical pump‐probe technique is used to generate and detect surface acoustic waves on a nanostructure.Vibrational modes up to 50 GHz are identified and compared to molecular dynamics simulations of the structure.Significant effects of probe beam polarization on the detected frequencies are also described.