Silicon wafer and epitaxial silicon wafer utilizing same

Details Silicon wafer and epitaxial silicon wafer utilizing same Silicon wafer and epitaxial silicon wafer utilizing same

2001-12-18

2003-05-27

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Composite

Of silicon containing

C428S064200, C117S932000, C423S348000

Reexamination Certificate

active

06569535

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a silicon wafer to be used as a semiconductor material and having a very low surface defect density with bulk micro defects (BMDs) uniformly and sufficiently abundantly formed therein, and to an epitaxial silicon wafer derived from the silicon wafer by forming an epitaxial layer thereon.
DESCRIPTION OF THE PRIOR ART
Semiconductor silicon wafers are sliced from silicon single crystals and the method most widely employed for the production of such silicon single crystals is the Czochralski method (CZ method) of pulling single crystals.
The CZ method comprises dipping a seed crystal in a molten silicon placed in a quartz crucible and pulling up the seed crystal to thereby allow a single crystal to grow. With the advancement in the technology of pulling silicon single crystals, it has now become possible to produce less defective, dislocation-free, large single crystals. Semiconductor devices are produced from wafers or substrates prepared from single crystals via a large number of processes. In the course thereof, the substrates are subjected to a large number of physical treatments, chemical treatments and, further, thermal treatments, including treatments in a severe thermal environment, such as high temperature treatments at 1,150° C. or above. Thus, problems are produced not only by such defects as oxygen-induced stacking faults (hereinafter referred to as “OSFs”), which manifest themselves in device manufacturing processes and lower the performance characteristics of the devices, but also by micro defects, namely grown-in defects, which are formed in the step of crystal growth and greatly affect the performance characteristics of the devices.
FIG. 1
shows the results of an observation of the distribution of typical grown-in defects. This is a schematic representation of the results of an observation of the distribution of micro defects, by X-ray topography, on a wafer sliced from a single crystal just after growing, immersed in an aqueous solution of copper nitrate for deposition of copper and then subjected to heat treatment. On this wafer, OSFs are found distributed in a ring-like manner. Inside the ring, there are detected defects having a size of about 0.1 to 0.2 &mgr;m, called laser scattering tomography defects or crystal-originated particles (COPs), for instance, at a density of about 10
5
to 10
6
defects/cm
3
and, outside the ring, there is a region where there are about 10
3
to 10
4
defects/cm
3
called dislocation clusters with a size of about 10 &mgr;m.
OSFs are stacking faults caused by interstitial atoms and formed on the occasion of thermal oxidation treatment. When formed and grown on the wafer surface, which constitutes active regions of devices, they cause a leakage current and deteriorate the device characteristics. Dislocation clusters, another kind of grown-in defects, too, give no good devices when these are formed thereon. Laser scattering tomography defects act as a factor lowering the time-zero dielectric breakdown characteristic.
Generally, the sites of occurrence of the above defects are greatly influenced by the pulling rate on the occasion of single crystal pulling and by the temperature distribution within the single crystal just after solidification. For example, when a single crystal is grown while gradually lowering the pulling rate and it is examined for the distribution of various defects in a plane cut longitudinally along the pulling axis in the center of the crystal, the results schematically shown in
FIG. 2
are obtained. Thus, in the stage of higher pulling rates after shoulder formation and attainment of a desired single crystal diameter, there are ring-forming OSFs in the peripheral portion of the crystal and the inside is a region where a large number of laser scattering tomography defects occur. With the decrease in pulling rate, the diameter of ring-forming OSFs becomes gradually smaller and finally null, whereupon the whole wafer surface becomes a region of occurrence of dislocation cluster defects alone, which corresponds to the region outside the ring-forming OSFs shown in FIG.
1
. Thus,
FIG. 1
shows the wafer sliced at position A in
FIG. 2
or from a single crystal grown at the corresponding pulling rate.
In pulling up single crystals in the art, the pulling rate in single crystal growth has been increased and so controlled that the site of ring-forming OSFs, which is a region allowing high density occurrence of OSFs, may be shifted to the outer periphery of the crystal, since laser scattering tomography defects are not so adversely influential than dislocation clusters, and for the effect of productivity improvement.
However, various investigations have been made to provide methods of producing single crystals from which wafers can be obtained with the number of these defects being reduced as far as possible. Upon more detailed observation of the wafer shown in
FIG. 1
, there is found an oxygen precipitation promoted region, which is defect-free and in which oxygen precipitation tends to occur, just outside and adjacent to the ring-forming OSFs and, outside that region, there is an oxygen precipitation inhibited region, which is defect-free and in which oxygen precipitation hardly occurs, then followed by a region allowing the occurrence of dislocation cluster defects. There is also a denuded zone inside the ring-forming OSF region between that region and the laser scattering tomography defect region. The state of distribution of these ring-forming OSF region and the neighboring regions varies depending on the temperature distribution within the single crystal just after pulling up and/or the pulling rate and, in these oxygen precipitation promoted region and oxygen precipitation inhibited region, the occurrence of grown-in defects is very infrequent. Therefore, technologies have been developed to enlarge such portions to the whole single crystal to thereby obtain defect-free wafers.
Thus, according to the invention disclosed in Japanese Patent Application Laid-open No. H08-330316, for instance, the temperature gradient within crystal G (°C./mm) in the pulling axis direction in the temperature range from the melting point to 1,300° C. is controlled so that the ratio V/G (where V is the pulling rate (mm/min) in single crystal growth) in the internal portion from the center of the crystal to 30 mm from the periphery may amount to between 0.20 and 0.22 [mm
2
/(°C.·min)] and this ratio may be gradually increased toward the periphery. By carrying out the pulling in that manner, the denuded zone comprising the oxygen precipitation promoted region and oxygen precipitation inhibited region outside the OSF ring alone can be extended to the whole section perpendicular to the pulling axis, hence to the whole single crystal. In this case, it is indicated that the positions of the crucible and heater, the position of the semiconical thermal radiator made of carbon and disposed around the growing single crystal, the structure of the thermal insulator around the heater and other various conditions should be examined by overall heat transfer calculations so that the above temperature conditions may be selected for the crystal growth.
If schematically illustrated in the same manner as in
FIG. 2
, the case where this method is employed may be illustrated as shown in FIG.
3
. That is, when a single crystal grown while gradually decreasing the pulling rate is examined for the distribution of various defects in a section cut longitudinally along the crystal center pulling axis, it is found that the V-shaped region of occurrence of ring-forming OSFs as shown in
FIG. 2
is converted to a U-shaped one by changing the temperature distribution within the single crystal just after pulling up. Thus, when a single crystal is grown at a pulling rate indicated by E, the whole crystal is occupied by a denuded zone and defect-free wafers can thus be obtained.
For attaining such a defect-free state, however, the condition ranges are restricted and it is not easy to stably realize

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