X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
2000-10-10
2002-08-13
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S090000
Reexamination Certificate
active
06434217
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This disclosure relates to determining material properties, and more particularly to a system and method for determining thickness and composition of layers.
2. Description of the Related Art
Characteristic analysis of layers within measurement samples is desirable for many applications. For example, the amount and type of adhesive applied to a tape product or the amount and type of metal or paint applied to a device for corrosion protection is critical for functionality of the products. Often, the most important characteristics of the layer include thickness, composition and uniformity. The method and system as described herein are discussed primarily with respect to the analysis of thin films within semiconductor devices. The term “thin film” is commonly used within the semiconductor industry when referring to layers deposited upon a semiconductor wafer during the fabrication of a transistor.
As production volumes and efforts to improve process control increase in the integrated circuit fabrication industry, the ability to accurately characterize semiconductor processes and the materials associated with such processes in a timely manner becomes more critical. Inaccurate analysis of one or more process parameters within the processing of a semiconductor wafer may hinder or prohibit the function of a transistor, leading to a reduction in production efficiency and transistor quality. The characterization of thin films is especially important, since the effectiveness and reliability of thin films play an important, central role in the operation of a transistor. Therefore, thin films must be accurately analyzed in order to meet a transistor's functionality requirements. Unfortunately, many current analysis techniques employ complex, expensive systems that do not coincide with the desire to increase production efficiency and improve process control within the semiconductor industry.
In order for a thin film to be effective, it must conform to strict electrical, chemical, and structural requirements. Specialized materials are selected for thin films to perform specific functions of the transistor. These materials may include, but are not limited to, metallic, semiconducting, and dielectric materials or a combination of them. Often thin films are doped with impurities to heighten the effectiveness of the material used. Thus, the composition of the material must be closely monitored to insure the correct material or combination of materials is applied, along with insuring the correct amount of material is applied. Accordingly, the composition, thickness and uniformity of a thin film all play crucial roles in the function of a transistor.
At present, it is difficult to find an analytical technique suitable for use in a semiconductor fabrication area that can characterize in a simple, accurate and cost-effective manner the thickness, uniformity and composition of a thin film. Many current techniques require expensive and large pieces of equipment that are not used within a fabrication area due to size and cleanliness requirements. Several of these techniques actually destroy the sample being measured, thus increasing the manufacturing cost and time requirements. It is nonetheless useful to discuss some of the analytical tools used currently in the semiconductor industry, for these tools do point out some difficulties and shortcomings associated with characterizing thin films.
One of the analytical methods in current use is Secondary Ion Mass Spectroscopy (hereinafter referred to as SIMS). In SIMS, a sample to be studied is bombarded with a primary beam of energetic ions. These ions sputter away ionized particles, or secondary ions, from the surface of the sample. The secondary ions are directed into a mass spectrometer, which identifies the ions as a function of their mass to charge ratio. Continued sputtering dislodges particles and secondary ions located below the surface of the sample. Thus, SIMS has the ability to analyze elements embedded within the sample as a function of sample depth. Therefore, SIMS can be used to measure the amount of material embedded within a thin film.
Although SIMS depth resolution, lateral resolution, and sensitivity continue to improve year after year, several drawbacks are inherent with SIMS measurements. The biggest drawback is the fact that SIMS is a destructive technique. SIMS sputters away layer after layer of material from the surface of the sample; thus, it is not feasible to use SIMS as a bench-top process control station, which could monitor the amount of material embedded within a thin film. Also, SIMS is a very bulky, complex, expensive method requiring complicated, maintenance-intensive machinery. For instance, SIMS instruments typically occupy an entire room in a mid-sized laboratory and consist of several vacuum pumps, valves, powerful magnets, energy filters, ion sources, and complex data analysis tools.
Another technique, which may be used in the semiconductor industry, is Auger electron spectroscopy (hereinafter referred to as AES). In AES, an energetic, primary electron beam is directed at the surface of a sample. The primary electron beam interacts with atoms at and near the surface of the sample, dislodging electrons from energy shells of the sample. As an energy shell is vacated, an electron within a higher energy state may fill the vacant position. The electron filling the once-vacant state releases energy characteristic of the transition in energy levels. This energy then interacts with the atom and ejects an electron of a lower energy state. Such an ejected electron is termed an Auger electron and has energy characteristic of the process, which caused its ejection. Because an ejected Auger electron has an energy characteristic of the energy levels of the atom from which it is ejected, one may determine the composition of the sample being studied by measuring the Auger electrons. Because Auger electrons cannot escape from great depths within the bulk of a sample, AES is considered a surface-sensitive analysis technique. It is commonly used to study materials present at a depth within fifty Angstroms from the sample's surface.
In order to study the composition of a sample deeper below the surface, it is necessary to sputter away atoms from the surface of the sample being studied. Thus, to measure the quantity of materials embedded within a thin film deeper than approximately fifty Angstroms, ion sputtering must often be used. Although providing excellent lateral resolution and possessing the ability to probe very small areas, AES suffers from the same major drawback as does SIMS—when probing beneath the surface of a thin film, sputtering is required which effectively destroys the sample. Also, like SIMS, AES requires expensive, complex machinery, which may become maintenance intensive. A typical AES system consists of vacuum pumps (AES is most effective when carried out at pressures of approximately 10
−10
torr and lower) and an ion beam for sputtering the sample.
Another technique, which may be utilized in microelectronics characterization, is X-ray Photoelectron Spectroscopy (hereinafter referred to as XPS). In this technique, an x-ray beam is directed at a sample, and the interaction of x-ray photons with the atoms of the sample causes the ejection of electrons from the sample. The kinetic energy of the ejected electrons is characteristic of the sample being studied. Like AES, only electrons from the top 1-10 monolayers are emitted from the sample. Thus, XPS is similarly a surface-sensitive technique. Like AES, if XPS is to probe within the thin film, destructive sputtering must be employed. Also, similar to AES, XPS systems are quite complex, expensive, and may become maintenance intensive. A typical system consists of powerful vacuum pumps, an electrostatic energy analyzer, and a complicated data analysis system.
X-ray Emission Spectroscopy (hereinafter referred to as XES) is yet another technique in use in the semiconductor field for the purpose of analyzi
Hossain Tim Z.
Pickelsimer Bruce L.
Advanced Micro Devices , Inc.
Conley & Rose & Tayon P.C.
Kevin L. Daffer
Porta David P.
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