Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Ion implantation of dopant into semiconductor region
Reexamination Certificate
2001-11-28
2003-12-30
Zarabian, Amir (Department: 2822)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Ion implantation of dopant into semiconductor region
C438S906000
Reexamination Certificate
active
06670261
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a manufacturing process for an annealed wafer capable of suppressing a change in resistivity due to an increase in a boron concentration in the vicinity of a wafer surface after annealing in an Ar atmosphere.
BACKGROUND ART
It has been known that there exist defects named so-called grown-in defects such as COP (Crystal Originated Particle), oxide precipitates and so on in a CZ silicon wafer. A proposal has been made on a heat treatment performed in a hydrogen atmosphere (hereinafter may be referred to as “hydrogen annealing”) as a method for annihilating grown-in detects in the vicinity of a wafer surface. This heat treatment is required to use hydrogen at a temperature of 1000° C. or higher, so it is necessary to take a countermeasure from the viewpoint of safety. Therefore, the furnace is required to be modified with a sealed structure for increasing airtightness and an explosion-proof apparatus as a measure against an explosion.
Meanwhile, it has been recently found that even a heat treatment carried out in an argon atmosphere (hereinafter may be referred to as “Ar annealing”) can annihilate the grown-in defects in the level equal to hydrogen annealing. Ar annealing is not explosive and then safer compared with hydrogen. Although the Ar annealing has an advantage to need no measure in a safety aspect, it has also been known that the annealing displays a characteristic behavior to a silicon wafer. An example of such a characteristic behavior is a phenomenon that tiny pits are easily formed on a wafer surface subjected to the Ar annealing.
This is caused by the following mechanism. An oxide film is formed by very small amounts of oxygen and water as impurities included in a raw material gas, or oxygen and water in the outside air involved through the furnace opening of the reaction tube in a heat treatment process, and then the oxide film is allowed to react with silicon (Si) according to the following reaction:
SiO
2
+Si→2SiO
As a result of the reaction, Si is etched and the etched portion is observed as pits. The pits serve as a cause for degrading a local surface roughness (micro-roughness) and a long-period surface roughness (haze) on a wafer surface. Thus, an Ar gas is sensitive to a trace of impurities and small changes in the environment such as fluctuations in temperature, so the Ar gas has a demerit of difficulty in handling.
However, according to a technique disclosed in JP A 98-144697, the following is taught: When a silicon wafer containing boron as a dopant is subjected to hydrogen annealing or Ar annealing, for the hydrogen annealing, boron in the wafer outdiffuses to reduce a boron concentration in the vicinity of a wafer surface, while for the Ar annealing, there occurs none of such a phenomenon as observed in the hydrogen annealing and a boron concentration does not decrease in a surface layer of a wafer.
That is, the Ar annealing has not only an advantage in a safety aspect, but also another advantage with respect to a wafer characteristic in that after annealing, no change occurs in resistivity in the vicinity of a wafer surface; therefore, an importance of the Ar annealing has grown.
In the mean time, in a process associated with manufacture of an annealed wafer in an atmosphere of an inert gas represented by Ar or in a hydrogen atmosphere, it has been customary that a mirror finished wafer to be annealed is prepared, contaminants attached on a surface of the wafer, such as heavy metals, organic substances and so on are removed by wet cleaning and the wafer is dried, followed by loading the wafer into a heat treatment furnace.
Where a mirror finished silicon wafer is cleaned, cleaning liquids (chemical liquids) of various compositions are used and a general cleaning method is of a proper combination of SC-1 (a liquid mixture of ammonia, hydrogen peroxide and water) cleaning, DHF (dilute hydrofluoric acid aqueous solution) cleaning and SC-2 (a liquid mixture of hydrogen chloride, hydrogen peroxide and water) cleaning.
Then, a cleaning process has been generally performed adopting SC-1 or SC-2 in the final stage in a cleaning process to finish a wafer so as to have a hydrophilic surface on which a natural oxide film is formed by the cleaning solution. This process is similar to wet cleaning of wafers before the wafers are loaded into a heat treatment furnace; after a natural oxide film is formed on a surface of each wafer to finish it hydrophilic, the wafers are loaded into a heat treatment furnace.
However, in the course of repeated experiments performed by the inventors about Ar annealing, it was found that a phenomenon occurred that is entirely contrary to reduction in a boron concentration in the vicinity of a wafer surface that has been observed in hydrogen annealing. That is, when Ar annealing was performed, there was observed a trend that a boron concentration increases in the vicinity of a wafer surface and furthermore, an increment is subtly different according to an annealing batch. Such a phenomenon is desirably to be suppressed to the possible lowest level because it varies resistivity in the vicinity of a wafer surface, which exerts an adverse influence on device characteristics.
The inventors have made an investigation of a contamination source increasing a boron concentration on a surface region of a wafer after Ar annealing and the outcome thereof showed that no contamination source exists in a heat treatment furnace itself but a cause is boron attached onto a wafer surface immediately before annealing. That is, it has been known that a wafer after cleaning is exposed to an environmental atmosphere (air) in a clean room before loading the wafer into a heat treatment furnace and boron builds up in the air from a filter provided for cleaning the air and the boron in the air attaches onto a wafer surface (for example, see JP A 93-253447). It has been estimated that such boron attached on a wafer surface diffuses in the vicinity of a wafer surface during Ar annealing, which increases a boron concentration therein.
Such a phenomenon of boron contamination in a clean room was reported in the past. As one example, it is described in JP A 95-58303 that boron contamination caused by air in a clean room is detected at the bonding interface of a bonding substrate. Furthermore, a problem is pointed out in JP Application No. 99-277255, applied for a patent by the applicant separately, that when a polysilicon film is deposited on a wafer surface, boron contamination is detected at the interface.
However, the above two boron contamination cases were problems which were created at an interface. That is, in these cases, the problems were caused by the fact that boron once attached onto a wafer surface is sandwiched between the wafer and another wafer or polysilicon and cut-off from escape with the result that the boron diffuses into the wafer bulk during a heat treatment. In contrast to this, in case of Ar annealing which the inventors investigated, although a wafer surface during a heat treatment is in a perfectly free state, boron contamination occurs and besides, as described above, in case of hydrogen annealing where a wafer surface during a heat treatment is likewise a free state, a problem arose that boron in a wafer outdiffuses and thereby a boron concentration decreases to the contrary. Therefore, it was absolutely unexpectable phenomenon that a boron concentration on a wafer surface increases in Ar annealing.
The above-mentioned JP A 98-144697 describes that a boron concentration in the vicinity of a wafer surface does not increase even after Ar annealing is performed and a concentration profile is flat in the depth direction. But since a boron concentration of a wafer used therein is high of 1×10
18
/cm
3
or higher, it is considered that the boron concentration profile is hardly affected even when boron attached on a wafer surface diffuses into the interior of the wafer unless a great amount of boron contamination occurs.
It is an object of the present invention to provide a manufact
Akiyama Shoji
Kobayashi Norihiro
Nagoya Takatoshi
Tamatsuka Masaro
Arent Fox Kintner Plotkin & Kahn
Perkins Pamela E
Shin-Etsu Handotai & Co., Ltd.
LandOfFree
Production method for annealed wafer does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Production method for annealed wafer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Production method for annealed wafer will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3142436