Patricia B. Smith

Low temperature, low pressure CdZnS films produced by metalorganic chemical vapor deposition

CdxZn(1−x)S thin films were deposited on (100) Si at low temperature and low pressure from the reaction of dimethylzinc, dimethylcadmium, and hydrogen sulfide. A possible application of mixed metal‐sulfide films as novel insulators in metal–insulator–semiconductor structures in HgCdTe‐based infrared devices provides the motivation for studying the physical properties of the CdZnS films. The films were produced over a 25 to 125 °C range of deposition temperature, and deposition pressure less than 1 Torr. No carrier or diluent gases were used. The polycrystalline films have been characterized by x‐ray photoelectron spectroscopy (XPS), scanning electron microscopy, Rutherford backscattering spectroscopy (RBS), and x‐ray diffraction. Films with cadmium fractions of zero to 0.75 have been produced and characterized. The growth rate ranges from 4 to 145 A/s. XPS indicates 1%–2 at. % oxygen contamination in the films, and about 3 at. % carbon within the bulk of the films. The cadmium mole fraction was determined...

Examination of hydrogen etched mercury cadmium telluride by spectroscopic ellipsometry

The incorporation of dry etch processes for mercury cadmium telluride (HgCdTe) infrared device fabrication is becoming critical for the infrared community as we advance toward the production of high‐density devices. Dry etch processes are cleaner than wet etch processes. In addition, dry etches are highly anisotropic and are capable of producing the small features required by the more advanced device architectures. However, the incorporation of dry etch processes into device fabrication often affects the surface quality, producing roughened surfaces and variations in composition. Consequently, the identification of suitable dry etch processes to produce high quality infrared devices is essential. In this investigation, three different plasma etching tools (reactive ion etching, electron cyclotron resonance, and remote microwave) were used to etch HgCdTe with hydrogen. The hydrogen interaction with HgCdTe at similar etch depths was examined with spectroscopic ellipsometry and atomic force microscopy. Varia...

Optical characterization of heterojunction bipolar transistors

We report the nondestructive, optical characterization of a heterojunction bipolar transistor (HBT) structure using photoreflectance spectroscopy (PR) and spectral ellipsometry (SE). The PR results show good agreement with capacitance-voltage (C-V) measurements for the dopant concentration in the n-GaAs collector layer. We find that PR provides a reasonable N/sub d/ for the emitter layer; whereas C-V analysis of the thin emitter layer provides only an upper-limit to the dopant concentration, PR provides a useful means of obtaining emitter and collector dopant concentrations quickly and nondestructively. We have developed a detailed SE model of the HBT structure and applied this model to obtain alloy compositions and layer thicknesses for the upper five of the nine HBT layers. Combining the structure and dopant concentration data obtained from critical layers of the HBT, we can screen the epitaxial material for potentially harmful structural deviations.

Ellipsometric studies of low‐temperature metalorganic chemical vapor deposited ZnS thin films

The most common techniques used for the determination of thin film thickness are profilometry, spectrophotometry, and ellipsometry. Spectrophotometers require the refractive index of the film (generally assumed to be transparent) as an input parameter. Profilometers yield nonreproducible and often inaccurate film thickness measurements when the films exhibit rough surface structure. Ellipsometric analyses of polycrystalline metalorganic chemical vapor deposition (MOCVD) ZnS films which assume that the thin films are single, uniform, transparent layers do not produce reliable or self‐consistent optical parameters or thickness values for the films. We employed multiple wavelength ellipsometry to analyze thin, polycrystalline MOCVD ZnS films. A two‐layer model incorporating absorption and surface roughness was used to determine the thicknesses of the two layers self‐consistently at wavelengths of 4050, 5461, and 6328 A. The optical constants of the two layers are related through the Bruggeman effective mediu...

248-nm photolithography compatibility on low-k dielectrics in BEOL interconnects

Printing small geometries using wavelength of 248 nm on low- k materials is not a plug-in photolithography process from one technology to other technology node. In this paper, a method of film characterization of low-k dielectric materials will be discussed. For a characterization of chemical vapor deposited low-k dielectric materials, a positive tone deep UV (DUV) chemically amplified photoresist (CAR) was used as a poisoning gauge. In early development state of low-k dielectrics and copper dual damascene interconnects in back-end-of-line processes, unstable patterning behaviors were observed in spite of using an organic bottom antireflective coating layers on low-k substrates. The initial work was focused on finding the source of lot-to-lot critical dimension (CD) variations and understanding what causes this problem as well. Study indicated a strong correlation that photo CD depended on time interval between photolithography process and previous process step. Significant photo CD shift was introduced by short cycle time from thin film deposition to photolithography process and post via etch clean process to trench photolithography process. To minimize photo CD variations, the process optimizations were necessary in low- k dielectric film deposition, rework, via etch process, and post via etch clean process. As parallel efforts to improve lot-to-lot CD control, various photoresist system, different ambient annealing conditions, various surface organic and inorganic capping techniques were tested. In this experiments, time interval between processes was tightly controlled and maximized the worst case of scenario. Fresh and aged low-k dielectric films were analyzed using time-of- flight secondary ion mass spectrometry and x-ray photoelectron spectroscopy techniques. This work suggested that N2 containing in the film or introducing N2 into low-k dielectric film caused lot-ot-lot photo CD variations.

Integrated fault detection capability for Spreeta biosensors

This paper presents integrated fault detection capability of the Spreeta biosensor technology. A specific feature is discussed based on multi-point image characterization. Multi-point image characterization provides a means to monitor biosensor surface damage, as well as sample anomalies such as macroparticulates are bubbles.

Characterization of AlGaAs/GaAs Heterojunction Bipolar Transistors Using Photoreflectance and Spectral Ellipsometry

Photoreflectance spectroscopy (PR) and spectral ellipsometry (SE) have been used to characterize the doping and structure of heterojunction bipolar transistors (HBT). This information provides a more complete description of the epitaxial HBT structure than is possible by relying solely on electrical characterization of specially processed test structures. Additional benefit is derived from the nondestructive nature of both SE and PR. The measurements are fast enough to be implemented on all production-bound HBT material. We describe our recent results comparing capacitance-voltage measurements with PRderived doping levels in the emitter layer of the HBT. We also describe some work comparing SE fit results with Auger electron spectroscopy depth profiles for InGaAs contact layer composition and thickness.

In-situ monitoring for HgCdTe device fabrication

In situ monitoring provides numerous advantages in the fabrication of HgCdTe-based infrared devices. Two in situ monitoring techniques are currently being investigated in our laboratory: optical emission spectroscopy (OES) and ellipsometry. OES is ideal for end point detection, for monitoring reactor integrity, and it also provides chemical information. Ellipsometry is a technique useful for the determination of film thickness and surface roughness. Process control can be readily achieved through the implementation of these two in situ measurement techniques. Examples of the use of OES for end point detection during the plasma etching of }fgCdTe and ZnS are discussed. In situ ellips.ometry is being pursued for monitoring the mild plasma etching of bromine/ methanol polished HgCdTe surfaces prior to in situ passivation and insulator deposition. To support the utility of in si.u ellipsoriietry, our initial studies using ex situ ellipsoinetry measurements of plasma etched HgCdTe are highlighted. The advantages of in situ monitoring for multistep vacuum processing, including contamination reduction and improved process control, are presented.

Hydrogen in metallo-organic chemically vapor-deposited ZnS thin films determined by nuclear resonance reaction analysis

Nuclear resonance reaction analysis was used to determine hydrogen concentrationin polycrystalline metallo-organic chemically vapor-deposited ZnS films produced at low substrate temperatures and pressures. This method of hydrogen content determination is quantitative and non-destructive. Other available depth profile methods, such as secondary-ion mass spectroscopy (SIMS), are destructive and of limited quantitative use, as SIMS depends upon knowing accurate ionization yields for each type of matrix studied. Also, the nuclear resonance reaction analysis technique is not susceptible to vacuum artifacts associated with ion-sputtering techniques. Alteration of the H2S-to-(CH3)2Zn flow rate ratio of reactants indicates that the hydrogen in the ZnS films is associated with the dimethylzinc, and not the hydrogen sulfide reactant. Variation in the substrate deposition temperature Ts resulted in the decreased hydrogen concentration at increased Ts (in the range 50–150°C). Hydrogen concentrations varied from about 1 × 1020 to 2.0 × 1021 atoms cm−3.