Semiconductor device manufacturing: process – With measuring or testing
Reexamination Certificate
1999-12-20
2002-01-08
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
With measuring or testing
C117S014000, C438S660000
Reexamination Certificate
active
06337219
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a silicon single crystal to be used as a semiconductor device and a silicon wafer manufactured from the grown silicon single crystal.
BACKGROUND ART
A silicon single crystal used as a semiconductor highly integrated circuit material is mainly manufactured by the Czochralski method (hereafter referred to as the CZ method)
When the silicon single crystal is grown by the CZ method, it is known that when the single crystal is processed to a wafer and then thermally treated at a high temperature, a ring-shaped oxidation induced stacking fault, which is called an OSF ring, is caused.
When the OSF ring is caused in the single crystal, there is about 10
5
to 10
6
cm
−3
of a grown-in defect, which is related to a point defect (vacancy) degrading the gate oxide integrity (GOI) characteristics of a MOS-type device, on the inside area of the OSF ring. This grown-in defect seems to have a hollow in it and has an octahedron base structure.
The quality of the silicon single crystal can be controlled by adjusting the positions of such areas.
For example, (1) when the OSF ring is made to disappear on the outermost periphery of the crystal, a crystal which contains no OSF ring and no grown-in defects (dislocation cluster) due to an interstitial silicon can be obtained; (2) when the OSF ring is generated between the center and the outermost periphery of the crystal, and the pulling rate and oxygen concentration of the crystal are adjusted, a crystal having extremely reduced size of OSF nuclei and a wide grown-in defect-free area formed on the ring and its outside area can be obtained; and (3) when the OSF ring is made disappear at the center, a crystal completely free from the grown-in defect on its entire surface can be obtained.
Here, the OSF ring includes a generally observable OSF ring and a latent OSF ring which has a very small OSF nuclei and cannot be seen without using special means.
It is known that the position where the OSF ring is formed is determined by the V/G value calculated from the temperature gradient G from the melting point to 1300° C. in the silicon single crystal pulled and a pulling rate V. It is recognized that a crystal having the OSF ring at a predetermined position can be obtained by keeping the V/G value at a predetermined value while pulling the crystal.
For example, the invention described in Japanese Patent Laid-Open Publication No. Hei 8-330316 discloses a method which calculates a temperature distribution in a furnace by heat transfer calculations in view of a hot zone structure of a CZ furnace, calculates the G value from the temperature distribution in a direction of a crystal length, and determines the pulling rate V according to a pulling length according to the G distribution.
The invention described in Japanese Patent Laid-Open Publication No. Hei 8-268794 measures the temperature distribution at a predetermined position in the crystal by a radiation thermometer or measures the temperature distribution near the surface of the crystal by thermocouples, and makes heat transfer calculation of a temperature gradient G within the crystal or calculates it on-line from a regression formula obtained by experiments. And, there is described a method of controlling the pulling rate V so that the V/G value becomes constant according to the G value.
Thus, it is made possible to produce or disappear the OSF ring at a target position by controlling the V/G value.
Also, supersaturated oxygen is contained in the silicon single crystal produced by the CZ method. When heat treatment is performed in a device forming process after processing the single crystal into wafers, a heat-treatment originated fine defect (oxygen precipitate) is formed due to the supersaturated oxygen contained in the single crystal.
When the oxygen precipitates are present in the device active region of the wafer surface layer, a junction leakage current characteristic is degraded.
On the other hand, when the oxygen precipitates are present in the wafer, it is effective to remove contaminants mingled during the device forming process from the device active region. In other words, an intrinsic gettering layer (called IG layer) is formed.
In order to effectively use the oxygen precipitates formed by the supersaturated oxygen contained in the crystal grown by the CZ method, the wafer formed from the silicon single crystal is subjected to a high-temperature heat treatment at a temperature about 1150° C. to out diffuse oxygen in the wafer surface zone, so that the oxygen concentration in the wafer surface layer is lowered, and a denuded zone (DZ) where an oxygen precipitate or a defect caused is not present, is formed on the wafer surface. Then, the heat treatment is further performed at a temperature between 500° C. to 900° C. to form an oxygen precipitation nucleus within the wafer in order to form an IG layer (hereafter this method is called the DZ-IG treating method).
By performing the aforesaid treatment, a high-quality wafer can be produced in which the device active region on the wafer surface layer is free from defects, while an absorbing layer for removing a contaminant from the device active region is present within the wafer.
The aforesaid method of adjusting the OSF ring forming position has the following problems.
Specifically, the invention described in Japanese Patent Laid-Open Publication No. Hei 8-330316 is the method which calculates G from the hot zone structure of the CZ furnace and determines V in order to have a predetermined V/G value and has disadvantages (a) the accuracy of the heat transfer calculation is poor, and (b) it takes time to calculate. Though the hot zone is worn and degraded with the number of pulling times, a change of G involved in such wearing and degradation is hardly taken into account. It was difficult to accurately control the V/G value because of these problems.
The invention described in Japanese Patent Laid-Open Publication No. Hei 8-268794 is the method which measures a temperature gradient of the crystal surface through online by a radiation thermometer or thermocouples and controls V according to the G value calculated from the measured value to keep the V/G value at a constant level. This method has problems, such as; (a) when the radiation thermometer is used to measure the light reflected from the surface of a melt, the inner wall of a chamber and the surface of the crystal is penetrated with stray light, and the crystal surface temperature cannot be measured accurately; (b) when a thermocouple is used to measure the crystal surface temperature, the thermocouple is influenced by heat radiation from the melt or a heater even if it is mounted near the surface of the crystal, therefore the crystal surface temperature cannot be measured accurately. Besides this, even if the temperature is measured by the aforesaid methods, the measured temperature is a temperature of the crystal surface and not a measured value of the actual temperature within the crystal having the OSF ring formed therein. The temperature inside the crystal is merely estimated from the surface temperature, therefore it is difficult to control the OSF ring diameter with high precision.
Thus, it is not easy to correctly know the G value which is the temperature gradient within the single crystal at the time of being pulled.
The DZ treating method which is used as a treating method for forming the aforesaid high-quality wafer has the following disadvantages.
The DZ treating method out-diffuses the supersaturated oxygen present on the wafer surface zone by the high-temperature heat treatment and decreases undetected oxygen precipitates present on the wafer surface layer or secondary defects induced by the oxygen precipitates by selective etching used for evaluation.
However, the aforesaid DZ-IG treating method cannot eliminate the grown-in defects formed at crystal pulling.
Specifically, the oxygen precipitates are eliminated from the wafer surface layer by the treatment of out diffusion of oxygen, but the grow
Kanesaka & Takeuchi
Lee Calvin
Smith Matthew
Sumitomo Metal Industries Ltd.
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