John Robert McNeil

Ion-assisted deposition of optical thin films: low energy vs high energy bombardment

Oxygen ion-assisted deposition of SiO2 and TiO2 has been investigated as a function of ion energy (30–500 eV) and current density (0–300 μA/cm2) at the optic. It is shown that both low and high energy ion bombardment improve SiO2 film stoichiometry, although slightly greater improvement is realized for the low energy case. For TiO2 films, low energy bombardment improves stoichiometry, while high energy bombardment is clearly detrimental. A reduction in H content by a factor of 10 is observed in SiO2 films deposited with high energy ion bombardment. Durable films are produced at low substrate temperatures (50–100°C). Film stress characteristics are discussed.

Metrology of subwavelength photoresist gratings using optical scatterometry

The widths and overall profiles of dielectric grating lines can be determined by measuring the intensity of diffracted laser light from the sample over a specified range of incident beam angles. This technique, known as 2‐Θ scatterometry, is able to accurately and precisely measure photoresist structures in the subhalf micron regime. Moreover, a 2‐Θ scatterometer is capable of making measurements in a rapid and nondestructive manner. To test this technique we measured five identically processed wafers with nominal 0.5 μm line/0.5 μm space grating patterns. Each wafer comprised gratings in a Shipley 89131 negative photoresist exposed in a matrix of incremental exposure doses and focus settings. The scatterometry results were consistent with cross‐sectional and top‐down scanning electron microscopy (SEM) measurements of the same structures. The average deviation of 11 scatterometer linewidth measurements from top‐down SEM measurements, over a broad exposure range, is 14.5 nm. In addition, the repeatability ...

Multiparameter grating metrology using optical scatterometry

Scatterometry, the analysis of light diffraction from periodic structures, is shown to be a versatile metrology technique applicable to a number of processes involved in the production of microelectronic devices. We have demonstrated that the scatterometer measurement technique is robust to changes in the thickness of underlying films. Indeed, there is sufficient information in one signature to determine four process parameters at once, namely the linewidth and thickness of the photoresist grating, and the thicknesses of two underlying film layers. Results from determining these dimensions on a 25 wafer study show excellent agreement between the scatterometry measurements and measurements made with other metrology instruments [top-down and cross-section scanning electron microscopy (SEM) and ellipsometer]. In particular, measurements of nominal 0.35 μm lines agree well with cross-section SEM measurements; the average bias is −1.7 nm. Similarly, for nominal 0.25 μm lines, the average bias is −7.3 nm. In ad...

Ellipsometric scatterometry for the metrology of sub-0.1-μm-linewidth structures

We describe a modification to our existing scatterometry technique for extracting the relative phase and amplitude of the electric field diffracted from a grating. This modification represents a novel combination of aspects of ellipsometry and scatterometry to provide improved sensitivity to small variations in the linewidth of subwavelength gratings compared with conventional scatterometer measurements. We present preliminary theoretical and experimental results that illustrate the possibility of the ellipsometric scatterometry technique providing a metrology tool for characterizing sub-0.1-mum-linewidth.

Use of diffracted light from latent images to improve lithography control

As the microelectronics industry strives to achieve smaller device design geometries, control of linewidth, or critical dimension (CD), becomes increasingly important. Currently, CD uniformity is controlled by exposing large numbers of samples for a fixed exposure time which is determined in advance by calibration techniques. This type of control does not accommodate variations in optical properties of the wafers that may occur during manufacturing. In this work, a relationship is demonstrated between the intensity of light diffracted from a latent image consisting of a periodic pattern in the undeveloped photoresist and the amount of energy absorbed by the resist material (the exposure dose). This relationship is used to simulate exposure control of photoresist on surfaces having slight variations in optical properties, representative of those found in operating process lines. We demonstrate that linewidth uniformity of the developed photoresist can be greatly improved when the intensity of diffracted li...

Grating line shape characterization using scatterometry

Identification of dimensional parameters of an arbitrarily shaped grating using scatter characteristics is presented. A rigorous diffraction model is used to predict the scatter from a known grating structure, and utilizing this information we perform the inverse problem of predicting line shape from a measurement of the scatter.

Properties of TiO2 and SiO2 thin films deposited using ion assisted deposition

TiO2 and SiO2 films deposited using ion assisted deposition are investigated as a function of ion energy and current density. Optical constants, possible ion source contaminants, and optical scatter are examined for samples deposited at ambient (∼75°C) and elevated (∼250°C) substrate temperatures.

Linewidth measurement of gratings on photomasks: a simple technique

A novel laser scatterometer linewidth measurement tool has been developed for critical dimension metrology of photomasks. Calculation of the linewidth is based on a rigorous theoretical model, thus eliminating the need for calibrations. In addition the effect of the glass substrate on which the photomask grating is placed is explicitly taken into account. The experimental arrangement consists of a chrome photomask diffraction grating that is illuminated with a laser. A rigorous theoretical model is used to provide a lookup table that gives the power in the transmitted zero-order beam as a function of the linewidth for a fixed pitch of the grating. The predicted linewidth values are compared with those that are obtained by using commercial optical linewidth measurement systems, and excellent agreement is obtained.

Surface Figuring Using Neutral Ion Beams

During recent years, economic and technological pressures have driven research for higher performance optical fabrication techniques. Among the candidate figuring technologies is ion beam sputtering in which material is removed from the optical surface by the kinetic interaction of ions and atoms or molecules of the surface. The first use of sputtering as a means for optical figuring occurred in the mid 1960s [1,2], and the technique has been investigated by several groups since that time. The prior work was done primarily with ion sources producing high energy (20KeV and above), low current (fraction of a milliampere), narrow (usually less than one millimeter) ion beams. The low current directly translates to low removal rates, while the high energy contributes to radiation damage, ion implantation, and other effects. In the present work the low current, high energy source is replaced with a Kaufman broad-beam ion source[3]. These sources produce higher ion currents at lower energies, thus giving faster removal with minimal surface damage. The ion beam produced by a Kaufman ion source consists of a number of ions traveling in a (typi-cally) slightly diverging beam, along with an equal flux of lower energy electrons. The electrons are injected into the ion beam to reduce electrostatic repulsion in the beam, but also to prevent the charging of dielectric targets.

Scatterometry for CD measurements of etched structures

Scatterometry, the characterization of periodic structures via diffracted light analysis, has been shown to be a versatile technique for measuring critical dimensions in photoresist as small as 0.160 micrometer. Rapid, non-destructive and inexpensive, scatterometry has the potential to be applied to other microlithographic features as well. This paper discusses applications of scatterometry in the measurement of etched sub-um poly-Si line/space patterns. Since etched features represent the final dimensions of a finished product, the characterization of such features is important. Initial attempts at measuring the etched linewidth and height using scatterometry assumed the sidewalls were perfectly vertical. Although results from these two parameter predictions were good, our measurement algorithms suggested that the etch profiles were not square. Thus, sidewall angle was left as an unknown in our model and three parameter predictions were made. These improved results from measuring the linewidth, height and sidewall angle are presented, and comparisons to SEM measurements of the same samples are made. Finally, experiments to determine the repeatability of the scatterometer for measuring etched features were performed. Results show that the repeatability of the instrument, for both static and dynamic measurements of nominal 0.25 micrometer structures, is sub-nanometer for all parameters measured; the 3(sigma) repeatability for static CD measurements is 0.63 nm, and for dynamic measurements is 0.78 nm.