Silicon single crystal wafer, epitaxial silicon wafer, and...

Details Silicon single crystal wafer, epitaxial silicon wafer, and... Silicon single crystal wafer, epitaxial silicon wafer, and...

2000-04-18

2002-11-12

Chaudhuri, Olik (Department: 2813)

Metal treatment

Barrier layer stock material, p-n type

With recess, void, dislocation, grain boundaries or channel...

C117S020000, C117S021000, C438S497000, C438S500000

Reexamination Certificate

active

06478883

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an epitaxial silicon single crystal wafer for the manufacture of semiconductor devices with reduced heavy metal impurities present in an epitaxial layer, which impurities degrade reliability of the devices, and a boron-doped silicon single crystal wafer, antimony-doped silicon single crystal wafer, and phosphorus-doped silicon single crystal wafer, which serve as a substrate of the epitaxial wafer, as well as methods for producing them.
BACKGROUND ART
Epitaxial silicon single crystal wafers have long been widely used as wafers for the manufacture of discrete semiconductors, bipolar ICs and so forth because of their excellent characteristics. Moreover, as also for MOS LSIs, they are widely used for microprocessor units or flash memory devices because of their excellent soft error and latch up characteristics. Furthermore, in order to improve poor reliability of DRAMs caused by the so-called grown-in defects, which are introduced at the time of the production of silicon single crystals, the need of epitaxial silicon single crystal wafers has been increasingly enlarged.
However, existence of heavy metal impurities on epitaxial silicon single crystal wafers used for such semiconductor devices yields poor characteristics of the semiconductor devices. In particular, as a degree of cleanness required for the latest devices, it is considered that heavy metal impurity concentration must be 1×10
10
atoms/cm
2
or less, and therefore heavy metal impurities existing on silicon wafers must be reduced as much as possible.
Moreover, in recent researches, it has been pointed out that, even in such epitaxial wafers, influence of the grown-in defects present at surfaces of substrate wafers may be manifested depending on conditions of the epitaxial processes and thickness of the epitaxial layer after the epitaxial growth (Kimura et al., Journal of Japanese Association of Crystal Growth, Vol. 24, No. 5, p.444, 1997).
In particular, N-type substrates doped with antimony (referred to as “antimony-doped silicon single crystal wafers” hereinafter) used for low resistance devices have a higher grown-in defect density compared with usual P-type substrates doped with boron (referred to as “boron-doped silicon single crystal wafers” hereinafter), because the atomic radius of antimony is larger than that of silicon. Therefore, they have a problem that they suffer from much more significant influence of grown-in defects after the epitaxial growth compared with other substrates.
The importance of gettering techniques has become increasingly higher as one of the techniques for reducing such heavy metal impurities. In the production of the epitaxial silicon single crystal wafers for logic devices, p
++
type substrates consisting of boron-doped silicon single crystal wafers having a very high boron concentration expressed in terms of a resistivity of less than 10 m&OHgr;·cm (referred to as “very highly boron-doped silicon single crystal wafer” hereinafter) have conventionally been used as substrate wafers for performing epitaxial growth, and they have afforded a higher device yield compared with substrate wafers consisting of p
+
type substrates of a high boron concentration that exhibit a resistivity of from 10 m&OHgr;·cm to 100 m&OHgr;·cm (referred to as “highly boron-doped silicon single crystal wafer” hereinafter). However, the very high boron concentration of the very highly boron-doped silicon single crystal wafer causes a problem that boron impurities in the substrates are once released into the gaseous phase and enter into the epitaxial growth layer again, which is called auto doping.
As countermeasures against such auto doping, for example, the epitaxial growth has been performed under reduced pressure atmosphere, or CVD oxide films have been provided on back surfaces of the substrates. However, there has been a problem that these treatments all lead to reduction of productivity, increase of cost and so forth.
Therefore, it was expected to use highly boron-doped silicon single crystal wafers, which did not require any countermeasure against the auto doping, as the substrate for performing epitaxial growth. However, gettering of the highly boron-doped silicon single crystal wafers having a low oxygen concentration is segregation type gettering attained by boron atoms. Therefore, they suffer from a problem of lower gettering ability for heavy metal impurities of copper, nickel and so forth compared with relaxation type gettering attained by oxide precipitates.
On the other hand, in the production of epitaxial silicon single crystal wafers for CCDs, N-type substrates such as N-type substrate doped with phosphorus (referred to as “phosphorus-doped silicon single crystal wafers” hereinafter), and antimony-doped silicon single crystal wafers have conventionally been used as the substrate for performing epitaxial growth. However, these N-type substrates also have a problem that oxygen precipitation is harder to occur in them compared with the boron-doped silicon single crystal wafers. Insufficiency of the gettering ability due to such an insufficient amount of oxygen precipitation in N-type substrates is a detrimental problem for devices sensitive to crystal defects resulting from heavy metal impurities, such as CCDs.
In particular, as for the antimony-doped silicon single crystal wafers, when a silicon single crystal ingot doped with antimony is grown by the Czochralski method, it is extremely difficult to maintain the oxygen concentration in a portion having a high antimony concentration obtained in the latter half of the growth of the single crystal ingot, because of evaporation of antimony oxide. For this reason, the oxygen concentration becomes low, and oxygen precipitation of silicon wafers cut out from such a portion is inhibited. Thus, gettering ability required for the device production cannot be obtained.
However, if it is attempted to obtain, in the antimony-doped silicon single crystal wafers or the phosphorus-doped silicon single crystal wafers, an amount of precipitated oxygen comparable to that obtained in the boron-doped silicon single crystal wafers, there would be caused a problem that prolonged oxygen precipitation heat treatment is required compared with the boron-doped silicon single crystal wafers, which leads to reduced productivity.
Specifically, as for the phosphorus-doped silicon single crystal wafers, for example, performed is a heat treatment called IG heat treatment comprising a first stage heat treatment at a high temperature of 1100° C. or higher, a heat treatment for formation of precipitation nuclei at about 600-700° C. as the second stage, and a heat treatment for formation of oxide precipitates at about 1000° C. as the third stage, for several hours for each stage.
On the other hand, if the oxygen concentration of wafers can be elevated in order to increase the oxygen precipitation of these highly boron-doped silicon single crystal wafers, antimony-doped silicon single crystal wafers and phosphorus-doped silicon single crystal wafers, oxygen precipitation would be promoted, and thus the period required for such heat treatments may be shortened. However, the amount of precipitated oxygen in wafers becomes excessive, and it will cause problems such as deformation of wafers and reduction of wafer strength. Moreover, when an epitaxial layer is formed on the surfaces of these silicon single crystal wafers, there would be caused a problem that harmful defects are generated in the epitaxial layer due to out-diffusion of oxygen impurities, and adversely affect the characteristics of semiconductor devices.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished in order to solve these problems, and its major object is to produce and supply a silicon wafer for epitaxial growth consisting of a highly boron-doped silicon single crystal wafer, an antimony-doped silicon single crystal wafer or a phosphorus-doped silicon single crystal wafer, which allows easy oxygen precipitation and exhibits high g

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