Active solid-state devices (e.g. – transistors – solid-state diode – With specified dopant – Deep level dopant
Reexamination Certificate
1999-05-18
2001-09-18
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
With specified dopant
Deep level dopant
C117S013000
Reexamination Certificate
active
06291874
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for producing a silicon single crystal wafer for particle monitoring having few pits on its wafer surface with high productivity.
2. Related Art
Particles adhered to a silicon single crystal wafer used for semiconductor devices may cause pattern breakage or the like during the production of semiconductor devices. In particular, because the pattern width of the most advanced devices (64M DRAM) is extremely small, i.e., 0.3 &mgr;m, production of such patterns suffers from abnormalities (failure) such as pattern breakage even by the presence of particles of 0.1 &mgr;m, and its production yield in the production of devices is markedly reduced. Therefore, particles adhered to silicon wafers must be decreased as far as possible.
To this end, in the production process of silicon wafers, particle counters are used to strictly control such particles (search of generation source, evaluation of cleaning effect, control of clean level of clean room, inspection of final products before shipment, etc.).
The measurement method of conventional particle counters involves, for example, irradiating a laser beam spot of around 10-100 &mgr;m on a wafer for monitoring of which particles are measured (wafer for particle monitoring), and effectively condensing feeble lights scattered by the particles through multiple optical fibers, integrating spheres or the like, which condensed lights are converted into electric signals by photoelectric devices. Therefore, conventional particle counters count the number of spots (bright spots) on the wafer surface where light scattering is caused.
By the way, minute crystal defects are generated during the growth of silicon single crystals, and they do not disappear during the cooling of crystals, and remain in the processed and produced wafers as they are. When these wafers are cleaned in a mixed solution of aqueous ammonia (NH
4
OH+water) and aqueous hydrogen peroxide (H
2
O
2
+water) as generally conducted so as to remove the particles, hollows (pits) are formed on the wafer surfaces because etching rate is faster in the crystal defect sites (such pits are called crystal originated particles, COPs).
If such silicon wafers are used as wafers for particle monitoring, and particle number is counted on such wafers by the above particle counter, light scattering by not only particles actually adhered to the wafer surfaces, but also light scattering by such pits are detected. Thus, there has been a disadvantage that a true particle number cannot be obtained.
In particular, it has been known that a wafer produced from a silicon single crystal pulled by the CZ method generates much more COPs compared with a wafer produced from a silicon single crystal produced by the floating zone melting method (FZ method) and an epitaxial wafer comprising a wafer produced by the CZ method on which a silicon single crystal thin film is grown.
On the other hand, it has also been known that, in order to decrease crystal defects (COPs) introduced into silicon single crystals during their growth in the CZ method, marked improvement can be obtained by using an extremely low crystal growth rate (for example, 0.4 mm/min or less; see, for example, Japanese Patent Application Laid-open No. 2-267195).
However, if the crystal growth rate is simply lowered from the conventional rate of 1 mm/min or more to 0.4 mm/min or less, the productivity of single crystals would be halved or further reduced, and the cost would be markedly increased, even though COPs may be improved. This remained as a problem not only in the production of wafers used for devices, but also in the production of wafers for particle monitoring used for particle measurement.
SUMMARY OF THE INVENTION
The present invention has been accomplished in view of the aforementioned problems, and its object is to obtain silicon single crystals for particle monitoring having few crystal defects with high productivity by the CZ method.
To achieve the aforementioned object, the present invention provides a method for producing a silicon single crystal wafer for particle monitoring, characterized by comprising growing a silicon single crystal ingot doped with nitrogen by the Czochralski method, and processing the single crystal ingot into wafers to produce the silicon single crystal wafer for particle monitoring.
By doping a single crystal ingot with nitrogen during growing it by the CZ method as in the aforementioned method, growth of crystal defects occurring during the crystal growth can be suppressed. Further, as a result of suppression of the growth of crystal defects, the crystal growth rate can be made faster, and hence the productivity of crystals can be markedly improved.
In the aforementioned method, when the single crystal ingot doped with nitrogen is grown by the Czochralski method, concentration of nitrogen doped into the single crystal ingot is preferably controlled to be in a range of 1×10
10
to 5×10
15
atoms/cm
3
.
The above range is defined, because the concentration of 1×10
10
atoms/cm
3
or more is preferred for sufficiently suppressing the growth of crystal defects, and because the concentration of 5×10
15
atoms/cm
3
or less is preferred in order not to inhibit the single crystallization of silicon crystals.
In the aforementioned method, after the single crystal ingot was processed into wafers to produce a silicon single crystal wafer, the silicon single crystal wafer is preferably subjected to a heat treatment so that nitrogen contained in a wafer surface portion should be out-diffused.
If the silicon single crystal wafer is subjected to a heat treatment so that nitrogen contained in a wafer surface portion should be out-diffused, the wafer surface layer would have extremely few crystal defects, and generation of oxide precipitate defects on the wafer surface due to acceleration of oxygen precipitation by nitrogen should be prevented, because the nitrogen is out-diffused. Further, when oxygen is also out-diffused at the same time by the heat treatment, the surface defect density can further be reduced. Therefore, the resulting wafers would become particularly suitable for wafers for particle monitoring.
Further, when the single crystal ingot doped with nitrogen is grown by the Czochralski method, concentration of oxygen contained in the single crystal ingot is preferably controlled to be 1.2×10
18
atoms/cm
3
or less (value according to ASTM '79).
Such a low oxygen concentration can further suppress the growth of crystal defects, and prevent the formation of oxide precipitates in the surface layer. Thus, the resulting wafers would become further suitable ones as wafer for the monitoring.
A silicon single crystal wafer for particle monitoring produced by the production method of the present invention is, for example, a silicon single crystal wafer for particle monitoring obtained by processing a silicon single crystal ingot into wafers, which ingot has been produced by the Czochralski method while doped with nitrogen.
In this wafer, the nitrogen concentration may be in a range of 1×10
10
to 5×10
15
atoms/cm
3
, the nitrogen contained in a wafer surface portion may be out-diffused by a heat treatment, and the oxygen concentration may be 1.2×10
18
atoms/cm
3
or less.
Such a silicon single crystal wafer for particle monitoring having the aforementioned characteristics would have extremely few crystal defects in the surface layer. In particular, such a wafer may have a crystal defect density of the wafer surface of 30 defects/cm
2
or less, and use of such a wafer realizes accurate particle counting. Therefore, it is very useful for control of device fabrication process and the like.
According to the present invention, silicon single crystal wafers for particle monitoring having few crystal defects on wafer surfaces can be produced with high productivity. If the particle measurement is performed by using the silicon single crystal wafer for particle monitoring of
Miki Katsuhiko
Tamatsuka Masaro
Hoang Quoc
Hogan & Hartson L.L.P.
Nelms David
Shin-Etsu Handotai & Co., Ltd.
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