Single-crystal – oriented-crystal – and epitaxy growth processes; – Processes of growth from liquid or supercritical state – Having pulling during growth
Reexamination Certificate
2001-10-24
2003-07-15
Hiteshew, Felisa (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Processes of growth from liquid or supercritical state
Having pulling during growth
C117S030000, C117S032000, C117S917000
Reexamination Certificate
active
06592662
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a manufacturing method for a silicon single crystal, using a CZ method (a Czochralski Method) pulling the silicon single crystal from a silicon metal contained in a crucible. More particularly, the invention relates to a method obtaining a high quality silicon single crystal by controlling an interstitial oxygen concentration in the silicon single crystal with a high precision and a silicon single crystal that can be realized by the method for the first time.
DESCRIPTION OF THE BACKGROUND ART
In order to produce a silicon single crystal wafer used in fabrication of semiconductor devices, there has been widely used a silicon single crystal manufactured by a Czochralski method (hereinafter also referred to as a CZ method or a pulling method), which is advantageous in growing a large size crystal. A manufacturing method according to the Czochralski method is, as is well known to the general public, such that a seed crystal is dipped into a silicon melt obtained by melting in a quartz crucible of a single crystal growth apparatus and thereafter, the dipped seed crystal in the melt is slowly pulled upward while rotating the seed crystal in a direction opposite to that of the quartz crucible, resulting in growth of a silicon single crystal in an almost cylindrical shape.
Since a quartz crucible is used for holding a silicon melt in a manufacturing method for a silicon single crystal according to a Czochralski method, the quartz of a crucible wall reacts with the silicon melt to dissolve oxygen atoms into the silicon melt and ad as a result, the silicon is incorporated into the single crystal during growth through the melt. For this reason, a silicon single crystal manufactured by a CZ method includes oxygen atoms in supersaturation and a mechanical strength of the silicon single crystal in processing into wafers increases in the presence of the oxygen atoms in supersaturation. Therefore, characteristically, not only does a silicon wafer from such a single crystal come to have a large resistance force against various thermal strains received when the semiconductor elements are fabricated thereon, but dislocations such as slippage are also difficult to be produced therein (see K. Sumino: Semiconductor Silicon 1981, Electrochem. Soc., Penington 1981 p. 208).
Furthermore, while oxygen in super saturation existing in a wafer is transformed into oxide precipitates (bulk micro defects, which is hereinafter abbreviated as BMD) by a heat treatment of the wafer after a single crystal is processed into wafers, but in a case where BMDs are introduced in a region remote from an element forming region in a surface layer of the silicon wafer, the BMDs serves as getter sinks collecting impurities existing in the wafer and therefore, capture various impurities introduced into a wafer during an element's forming process, thus performing a role to keep clean the element forming region. This method is called intrinsic gettering (hereinafter abbreviated as IG) and IG has been widely used as a gettering method when elements are fabricated on a wafer.
However, on the other hand, as interstitial oxygen existing in a wafer increases, a forming amount of BMDs also increase and with the forming amount in excess, especially, in a wafer surface layer which is an element forming region, the BMDs are a cause for a leakage failure at element junction interfaces, which in turn invites deterioration in element characteristics, resulting in loss of an essential function of a semiconductor integrated circuit by chance. Therefore, it is very important when semiconductor elements are fabricated in the surface layer of a wafer to keep an interstitial oxygen concentration in a CZ method silicon single crystal at a proper value, which produces a problem of how to control an interstitial oxygen concentration in a crystal at proper value in order to take care of a high density and high degree of integration of a semiconductor device, such that the control of an interstitial oxygen concentration have further become an important factor in maintaining a product quality of an integrated circuit.
In growth of a silicon single crystal by a CZ method, as an amount of a silicon melt contained in a quarts crucible decreases, a contact area between a wall of the quartz crucible and the silicon melt decreases. As a result, oxygen dissolved from the crucible wall also decreases, in turn an oxygen concentration in the latter half of a grown crystal decreases to a value equal to or less than a desired value, and thereby, there arises a chance to be unable to ensure a necessary quality. As a measure to improve this problem, proposal has been made on a method for adjusting an amount of oxygen supplied into the silicon melt from the quartz crucible wall by increasing a rotation speed of a crucible with progress in growth of a single crystal, that is as a pulled amount of a single crystal ingot is increased.
In this method, however, it has been said to be hard to achieve a high precision control of an interstitial oxygen concentration adapting to growth of a single crystal since, in a quartz crucible of as large a size as a diameter in excess of 200 mm, there exists a distance between a crucible wall supplying oxygen and a crystal growth interface, which in turn causes a delay in time for a melt to reach the crystal growth interface. As a result, in a case where a large size crystal equal to or more than, especially, 200 mm in diameter is pulled, there has been an inevitable limitation on control to suppress variations in interstitial oxygen concentration due to the above inconvenience.
On the other hand, as a method for controlling an interstitial oxygen concentration in a silicon single crystal, there is disclosed in JP A 81-104791, for example, a MCZ method whereby to grow a single crystal under application of a magnetic field (a magnetic field applied Czochralski method, which is also called magnetic field applied pulling method), in which a proposal is made on a technique that an interstitial oxygen concentration is efficiently reduced. In one aspect of this method, however, somewhat troublesome faults have been encountered in setting of and adjustment for growing conditions of a single crystal since an oxygen concentration is excessively low by chance depending on growth conditions for a single crystal when a BMD density is desired at a necessary and sufficient level in a wafer, therefore, a special technique is required to be performed for achieving a high oxygen concentration on a specific target quality of a crystal and a growth state of the crystal.
As a means for solving such problems, methods have been proposed: one of JP A 92-31386 in which a magnetic field is altered in strength according to a growth length of a crystal such that an interstitial oxygen concentration along the crystal growth axis direction is kept constant and the other of JP A 93-194077 in which a rotation speed of a crucible filled with a melt is controlled so as to adjust an oxygen concentration in a grown crystal.
In growth of a silicon single crystal according to a MCZ method, interstitial oxygen existing in a silicon single crystal originates from oxygen in the silicon melt dissolved from a quartz crucible, similar to an ordinary CZ method, and the oxygen in the melt is incorporated into the crystal through a crystal growth interface. In the MCZ method, however, by growing a silicon single crystal under application of a magnetic field to a silicon melt, a turbulent in the melt produced by thermal convection in the melt and rotation of a crucible can be efficiently suppressed, so an amount of oxygen supplied to a region in the vicinity of a crystal growth interface is caused low, with the result that a single crystal of a low oxygen concentration can be grown. This is a mechanism enabling a low oxygen crystal to be grown in an MCZ method.
According to a prior art MCZ method, however, in use of a large size quarts crucible for growth of a single crystal as large a diameter as to exceed 200 mm, as describe
Fusegawa Izumi
Hoshi Ryoji
Inokoshi Kouichi
Ohta Tomohiko
Hiteshew Felisa
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
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