Radiant energy – Invisible radiant energy responsive electric signalling – Ultraviolet light responsive means
Reexamination Certificate
2001-10-29
2004-02-03
Porta, David (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Ultraviolet light responsive means
C250S372000
Reexamination Certificate
active
06686594
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to a method and apparatus for analyzing effluent streams from various process tools used to make semiconductors, and in particular, to an on-line UV-Visible analyzer system for measuring the concentrations of homonuclear diatomic halogens (F
2
, Cl
2
, Br
2
, and I
2
) in a gas flow stream, and methods for using the analyzer system.
2. Description of the Related Art
In the manufacture of integrated circuits (IC), sequences of thin film deposition and etching steps are performed in order to construct several complete electrical circuits (chips) on monolithic substrate wafers. The general principles of IC manufacturing are described in a publication entitled Handbook of Semiconductor Manufacturing Technology, Y. Nishi and R. Doery editors, Marcel Dekker, New York, N.Y. 2000.
In a typical manufacturing sequence, molecular gases containing halogen atoms are often used in processes to remove materials, either from an integrated circuit substrate or, from the internal components of deposition equipment. The process that removes material from integrated circuit substrates is typically referred to as etching, while the process for removing deposits on the inner walls of the deposition tools is called chamber cleaning. Chamber cleaning is necessary to maintain the quality of the film produced in the deposition processes. Etching is necessary to produce the desired circuit structure on the substrates.
Molecular gases containing halogens are often used in film removal processes because reactions with certain critical substrate materials form energetically stable, gaseous byproducts. These byproducts evolve from the substrate or process tool surface. They are then easily removed from the process equipment by vacuum pumping. In a typical process step, silicon dioxide (SiO
2
) is deposited as an electrical insulating layer on the surface of a silicon wafer for example, by a plasma enhanced chemical vapor deposition (PECVD) process. Other thermal deposition processes are known to produce semiconductor films. After removal of the wafer from the process chamber, residual SiO
2
remains on the inside of the process chamber and must be removed to prevent the formation of particles. In some processes, a gas containing fluorine such as NF
3
or C
2
F
6
is converted in an electrical discharge plasma to atomic fluorine, according to the reaction:
This plasma can be generated between electrodes located in the deposition chamber. In this case, the process is termed “in situ plasma chamber cleaning”. The plasma can also be generated upstream of the process chamber in which case it is termed “remote plasma downstream chamber cleaning”.
Atomic fluorine reacts with SiO
2
to form volatile byproducts SiF
4
and O
2
, according to the reaction:
A competing process is the recombination of atomic fluorine radicals to form molecular fluorine by the reaction:
2F.→F
2(g)
(3)
In most processes, the rate of reaction (1) is constant. As SiO
2
is removed from the process chamber, the rate of reaction (2) slows. This results in an increase in the number density of atomic fluorine in the process chamber and a subsequent increase in the rate of reaction (3). The time when the residual SiO
2
is completely removed from the internal components of the process chamber is called the “endpoint”. The endpoint is marked by a plateau in the atomic fluorine (F.) number density and in the molecular fluorine (F
2
) emission rate. Process control and optimization requires accurate determination of the endpoint to terminate the cleaning process.
For in situ plasma cleaning processes, an electrical discharge exists in the vicinity of the residual film being removed. There is an emission of light from the discharge at wavelengths specific to gases present in the discharge. One method for determining the endpoint of an in situ cleaning process is to monitor light emission from atomic fluorine. At the endpoint, this signal increases to a constant value due to the increase in fluorine concentration within the process chamber.
In remote plasma cleaning, the plasma is formed upstream of the process chamber containing the residual film. By the time the radical species flow into the process chamber, optical emission from the reactant gases ceases. Therefore, optical emission cannot be used to determine the endpoint.
Another method for determining the endpoint is to monitor the concentrations or flow rates of product species in the gas effluent from the process tool. In U.S. Pat. No. 6,079,426 patentees disclose a method to determine the endpoint by monitoring either the change in pressure in the process tool when the exhaust capacity is fixed, or the degree that the exhaust pump must be throttled to maintain a constant pressure. In other words, this method monitors the changes in the exhaust pump throughput. This method is only applicable to processes in which the number of atoms or molecules generated in the process changes by a measurable amount as endpoint is reached. Unfortunately, most of the chamber cleaning procedures use large amounts of inert diluent gases (e.g. Helium) in addition to reactive gases, hence the changes in the number of atoms or molecules generated by the plasma processes are greatly diluted by the large inert gas flow and may become too small to provide an accurate indicator of the end point.
Methods that directly monitor chemical species within the process effluent are more desirable from a process control perspective.
In U.S. Pat. No. 5,812,403 patentees disclose an infrared absorption endpoint monitor based on the absorption of infrared light by species present within the exhaust gas of a process tool. This endpoint detection method is specific to processes that form species that absorb infrared light in a specific band of infrared wavelengths. It is highly desirable to have a widely applicable system that can detect the endpoint following chemical vapor deposition of any material in which a molecular species containing a halogen is used as the reactant. A large number of deposition residues are removed by reactions with halogen-containing gases. These include tungsten, silicon, silicon dioxide, and silicon nitride. It is also desirable to have a system that is independent of the energy source used in the chamber cleaning process.
An IC process effluent stream may contain one or more homonuclear diatomic halogen gases. For example, NF
3
, and C
2
F
6
based chamber cleaning processes emit F
2
in the process effluent stream. Use of ClF
3
in chamber cleaning emits both Cl2 and F2. Use of fluorocarbons such as C4F8 and C4F6 etc. in dielectric plasma etching may emit F2. Use of HBr and BCl3 in conductor (for example, polysilicon and metals) plasma etching leads to emission of Cl2 and Br2. These homonuclear diatomic halogen gases (such as F2, Cl2, Br2, and I2) are highly toxic, reactive, and corrosive. The amounts of these halogen gases released from a semiconductor fabrication site cannot exceed government mandated limits. Therefore, homonuclear diatomic halogen gases must be quantified prior to release to the environment or an abatement system.
Typical instruments used to measure concentrations of effluent species in real-time include infrared and mass spectrometers. Both techniques have severe limitations in this application.
In U.S. Pat. No. 6,154,284, patentees disclose use of a tunable diode laser absorption spectrometer (TDLAS) to quantify species in an IC process effluent stream. TDLAS is a special kind of infrared spectrometer. Other types of infrared spectrometers include non-dispersive infrared (NDIR) and Fourier Transform Infrared (FTIR) types.
Infrared spectrometers determine the concentration of various species in a gas cell by measuring the decrease in the intensity of infrared radiation traversing the cell due to absorption. The degree of absorption is dependent on the concentration of each absorbing species. The pattern of infrared absorption as a function of wavelength, or “spectrum” is unique
Ji Bing
Karwacki, Jr. Eugene Joseph
Langan John Giles
Maroulis Peter James
Ridgeway Robert Gordon
Air Products and Chemicals Inc.
Chase Geoffrey L.
Porta David
Sung Christine
LandOfFree
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