Method of producing a bonded wafer and the bonded wafer

Details Method of producing a bonded wafer and the bonded wafer Method of producing a bonded wafer and the bonded wafer

2002-09-17

2004-01-20

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating of substrate containing semiconductor region or of...

By reaction with substrate

C117S002000

Reexamination Certificate

active

06680260

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of producing a bonded wafer having very few crystal defects on and near the surface and a bonded SOI wafer.
BACKGROUND ART
SOI (silicon on insulator) has a buried oxide film (BOX: Buried OXide) as a insulator film right below a silicon layer that is to be a region for fabrication of device, and is expected to be a silicon material for high speed device with electric power saving performance. One of methods for producing a SOI wafer is a bonding method wherein two silicon single crystal wafers, one of which is to be a bond wafer (a substrate that is to be a SOI layer on which a device is fabricated), and the other of which is to be a base wafer (a substrate supporting the SOI layer) are bonded via a oxide film, and then thickness of the bond wafer is decreased to form a SOI structure. The method has an advantage that crystallinity of the SOI layer is excellent, and insulating property of BOX is high, but has a disadvantage that quality of the SOI layer is influenced much by quality of the bond wafer.
Specifically, it has been known that there exist micro crystal defects (Grown-in defects) such as COP (Crystal Originated Particles) that is a void type defect or the like in a silicon wafer produced according to Czochralski method, which adversely affects characteristics of the device such as oxide dielectric breakdown voltage. In order to solve the problem, there have been known that visible defects can be reduced by using, as a substrate for a bond wafer, a wafer wherein a CZ wafer is subjected to annealing in a hydrogen atmosphere or an epitaxial wafer wherein an epitaxial layer is formed on a CZ wafer (See Japanese Patent Application Laid-open (kokai) No. 9-22993 and Japanese Patent Application Laid-open (kokai) No. 9-260619).
However, two heat treatments, namely heat treatment such as hydrogen annealing or epitaxial growth and heat treatment for forming a buried oxide film, which may lead to increase of cost and lowering of through put.
In the case of the epitaxial wafer, haze (surface roughness) is generated on the surface of the epitaxial layer, or projection called mound is sometimes formed. They may cause bonding failure when the wafers are bonded. Accordingly, it is sometimes necessary to polish the surface of the epitaxial layer before bonding in that case.
On the other hand, crystal defects are reduced by hydrogen annealing only at layer quite near the surface (about 0.5 &mgr;m from the surface), and thus, if a SOI wafer having a thickness more than the value is produced, an area where crystal defects are not reduced is exposed. Therefore, crystal defects in the whole SOI layer cannot be reduced, unless any measures are taken, for example, further hydrogen annealing is conducted after SOI wafer is produced. Furthermore, according to annealing with hydrogen, quartz tube, a boat made of SiC or the like are always etched, and contamination with metal impurities or the like are caused thereby.
Furthermore, when heat treatment is conducted in a hydrogen atmosphere, it is necessary to take out the wafer after replacing the atmosphere in the heat treatment furnace with nitrogen gas for safety. At that time, the surface of the wafer is locally etched with slight amount of oxygen and water vapor contained in nitrogen gas, which may degrading surface roughness such as haze or the like, which may lead to bonding failure when they are bonded.
Recently, it has been reported that there can be produced CZ wafer wherein Grown-in defects are significantly reduced if crystal is pulled with strictly controlling a growth rate and temperature gradient of solid-liquid interface while single crystal is grown according to Czochralski method. It can be easily expected that SOI wafer having few defects in SOI layer can be produced if such a wafer is used as a bond wafer. However, if the crystal is pulled under such significantly strict growing condition may naturally lead to lowering in yield, resulting in significant increase of cost for production.
On the other hand, single crystal produced according to FZ method has no COP defects as observed in CZ single crystal, but FZ crystal having a diameter more than 150 mm cannot be produced at commercial level. Although FZ crystal having a diameter of 200 mm can be produced at experimental level, there is no hope for producing a large diameter wafer having a diameter of 300 mm, 400 mm in the future.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problems. A main object of the present invention is to provide a SOI wafer that has a SOI layer having few crystal defects and high quality in high productivity, in high yield and with low cost by using a wafer wherein grown-in defects in a surface-layer part of silicon single crystal wafer produced by CZ method are eliminated or reduced effectively by heat treatment as a bond wafer of a bonded wafer.
To achieve the above mentioned object, the present invention provides a method of producing a bonded SOI wafer comprising bonding a bond wafer and a base wafer via an oxide film and then reducing thickness of the bond wafer, wherein a silicon single crystal ingot is grown according to Czochralski method, the single crystal ingot is then sliced to produce a silicon single crystal wafer, the silicon single crystal wafer is subjected to heat treatment in a non-oxidizing atmosphere at a temperature of 1100° C. to 1300° C. for one minute or more and continuously to a heat treatment in an oxidizing atmosphere at a temperature of 700° C. to 1300° C. for one minute or more without cooling the wafer to a temperature less than 700° C. to provide a silicon single crystal wafer wherein a silicon oxide film is formed on the surface, and the resultant wafer is used as the bond wafer.
As described above, if the wafer produced according to Czochralski method is subjected to heat treatment in a non-oxidizing atmosphere at a temperature of 1100° C. to 1300° C. for one minute or more and continuously to a heat treatment in an oxidizing atmosphere at a temperature of 700° C. to 1300° C. for one minute or more without cooling the wafer to a temperature less than 700° C. to provide a silicon single crystal wafer wherein a silicon oxide film is formed on the surface, and the resultant wafer is used as the bond wafer, a silicon single crystal wafer having high quality wherein Grown-in defects near the surface of the wafer that are harmful for fabrication of semiconductor device can be eliminated or decreased in short time can be used as a bond wafer, so that SOI wafer that has a SOI layer having few crystal defects and high quality can be produced in high productivity, in high yield with low cost.
The present invention also provides a method of producing a bonded SOI wafer comprising bonding a bond wafer and a base wafer via an oxide film and then reducing thickness of the bond wafer, wherein a silicon single crystal ingot is grown according to Czochralski method, the single crystal ingot is then sliced to produce a silicon single crystal wafer, the silicon single crystal wafer is subjected to heat treatment in a non-oxidizing atmosphere at a temperature of 1100° C. to 1300° C. for one minute or more and continuously to a heat treatment in an oxidizing atmosphere at a temperature of 700° C. to 1300° C. for one minute or more without cooling the wafer to a temperature less than 700° C. to provide a silicon single crystal wafer wherein a silicon oxide film is formed on the surface, at least one of hydrogen ions and rare gas ions are implanted into the surface via a silicon oxide film of the wafer to form an ion implanted layer, and the resultant wafer is used as the bond wafer, which is then brought into close contact with the base wafer via the silicon oxide film of the bond wafer, followed by delamination at the ion implanted layer by heat treatment.
As described above, in method of producing a bonded SOI wafer, by using the method wherein the wafer produced according to Czochralski method is subjected to heat treatment in a

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