Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-05-27
2002-11-05
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S339110
Reexamination Certificate
active
06476393
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a surface state monitoring method and apparatus for performing in-situ monitoring of surface states of semiconductor substrates by infrared spectroscopy at fabrication sites of semiconductor devices.
Various requirements at fabrication sites of semiconductor devices require surface states of the semiconductor substrates being accurately grasped.
To give an example, in the field of semiconductor integrated circuits of memory devices, such as DRAM (Dynamic Random Access Memory), etc., and of logic devices, to form a gate insulation film having dielectric breakdown voltage of a required value, it is very important that surface states of a semiconductor substrate are administered. As a device has higher integration, the gate insulation film at the time of the fabrication of the device is made thinner, and the device has a design that the function for insulating an electric field (about 4×10
6
V/cm) of a MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor) in operation has a small margin. Generally, a gate insulation film is formed by thermal oxidation. In forming a gate insulation film by thermal oxidation, in a case of surface contamination, as of metal contamination, chemical contamination, organic contamination or others is present, there is a risk that dielectric breakdown of the formed gate insulation film may be induced. It is known that organic contaminants stayed on the substrate surfaces after the gate insulation film has been formed results in insulation deterioration.
Plasma etching is widely used in steps of patterning device structures. In the plasma etching process, to set optimum plasma etching conditions and to detect the end point of the plasma etching, it is very effective to know adsorption states, chemical bonding states, structures and thicknesses of reaction layers, etc. of surface states of semiconductor wafers. The plasma etching process is determined by dynamic balance in adsorption, reaction and elimination processes between influxes of radical ions, etc. fed in gas phase and outfluxes from semiconductor substrate surfaces.
Recently, semiconductor devices have elements increasingly micronized, and are made increasingly three dimensional. This makes it difficult for cleaning solutions to intrude into micronized regions or steep steps or to be replaced there. In consideration of future further micronization, dry cleaning is noted. For example, to remove organic contaminants staying on silicon substrates reaction with ozone or oxygen excited by UV radiation is effective. Oxygen molecules are dissolved to oxygen atoms by light of a below 242 nm wavelength. The organic contaminants are oxidized by the oxygen atoms and solved into H
2
O, O
2
, CO, CO
2
, etc. of high vapor pressures. Organic bonds, such as C—C, C—H, C—O, etc. can be dissolved by UV radiation. Thus, knowing surface states of semiconductor substrates is very important also to control parameters for the dry cleaning, such as an optimum amount of radiation, wavelength, oxygen amount, etc.
Native oxide films formed on the surfaces of silicon substrates are not usable in devices because their thickness cannot be controlled. Accordingly, it is preferable that when a device is fabricated on a silicon substrate, native oxide film on the silicon substrate is removed, and silicon bonds on the surfaces are terminated with hydrogen to stabilize the surfaces of the silicon substrate. This is because hydrogen can be eliminated at a relatively low temperature of about 500° C., and the termination with hydrogen relatively little affects the following processes. Most of silicon atoms on the surfaces of a silicon substrate subjected to UV ozone cleaning and hydrogen fluoride etching are terminated with hydrogen, and Si═H
2
and Si—H are formed. Accordingly, if a state of the termination with hydrogen on silicon substrate surfaces, temperature dependency of the elimination of terminating hydrogen can be monitored, the silicon substrate surfaces at the start of semiconductor processing can be kept in a suitable state. Higher quality and higher yields can be expected.
Thus, it is very important to know a surface state of a semiconductor substrate in a fabrication process of a semiconductor device, and various monitoring methods and apparatuses have been proposed and locally practiced.
Means for monitoring a surface state of a semiconductor substrate by internal multiple reflection of infrared radiation is provided by, e.g., FT-IR (Fourier-transform spectroscopy) apparatus or the special use marketed by Perkin-Elmer Co., U.S.A. For wider applications of the means Graseby Specac Limited, for example, markets various accessories.
In the conventional surface state monitoring method using this means, as exemplified in
FIG. 41A
, a substrate-to-be-monitored
102
is cut into, e.g., a 40 mm×10 mm strip, and infrared radiation emitted from an infrared radiation source
104
is passed through the substrate-to-be-monitored
102
to monitor states of the substrate surfaces. Otherwise, as exemplified in
FIG. 41B
, a substrate-to-be-monitored
102
has the end tapered, and infrared radiation is incident on the end surface of the substrate-to-be-monitored
102
to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored. Otherwise, as exemplified in
FIG. 41C
, infrared radiation is incident on a substrate-to-be-monitored via a prism
106
positioned above the substrate to undergo multiple reflection inside the substrate, whereby a surface state of the substrate is monitored.
The basic principle of monitoring a surface state of a substrate by applying infrared radiation to a substrate to cause the infrared radiation to undergo multiple reflection inside the substrate is that spectra of frequency components of evanescent waves oozing when light reflects on the substrate surfaces are resonance-absorbed when they agree with molecular vibrational frequencies of organic contaminants on the substrate surfaces are measured, whereby kinds and amounts of the organic contaminants can be determined. The basic principle also has a function that information of organic contaminants on substrate surfaces is gradually made more exact. A signal vs. noise ratio (S/N ratio) is also improved.
However, these monitoring methods needs cutting a substrate-to-be-monitored into strips, additionally machining a substrate-to-be-monitored, or disposing a prism above a substrate-to-be-monitored. These monitoring methods have not been usable in the in-situ monitoring at site of fabricating semiconductor devices.
Methods of monitoring organic contaminants on semiconductor substrates are known thermal desorption GC/MS (Gas Chromatography/Mass Spectroscopy), APIMS (Atmospheric Pressure Ionization Mass Spectroscopy), TDS (Thermal Desorption Spectroscopy), etc. However, these methods are not suitable to be used in in-situ monitoring at site of fabricating semiconductors for reasons that these methods cannot directly observe large wafers of, e.g., above 300 mm-diameters which are expected to be developed, and need vacuum ambient atmosphere, and have low throughputs, and other reasons.
As described above, the above-described conventional surface state monitoring methods are not usable in the in-situ monitoring at site of fabricating semiconductor devices because the monitoring by these method is destructive, or these methods are not suitable for monitoring large semiconductor wafers. Surface state monitoring methods and apparatuses which permit the in-situ monitoring of substrate surfaces at site of fabricating semiconductor devices, and permit large wafers to be monitored have been expected.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a surface state monitoring method and apparatus which enable, at the site of fabricating a semiconductor device, in-situ monitoring of surface states of a substrate-to-be-monitored by infrared radiation spectroscopy of internal multiple reflection.
The above-described ob
Endo Michiaki
Maeda Yasuhiro
Miyamoto Nobuo
Niwano Michio
Yoshida Haruo
Advantest. Corp
Gagliardi Albert
Hannaher Constantine
Muramatsu & Associates
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