Semiconductor device manufacturing: process – Formation of electrically isolated lateral semiconductive... – Total dielectric isolation
Reexamination Certificate
2002-09-09
2004-07-27
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Formation of electrically isolated lateral semiconductive...
Total dielectric isolation
C438S407000, C438S423000, C438S769000
Reexamination Certificate
active
06767801
ABSTRACT:
TECHNICAL FIELD
This invention relates to a SOI substrate having a buried oxide layer disposed near the surface of a silicon substrate and a single crystal silicon layer [hereinafter referred to as “SOI (silicon-on-insulator) layer”] superposed thereon. More particularly, it relates to a SOI substrate obtained by the SIMOX (Separation by IMplanted OXygen) technology and a method for the production thereof.
BACKGROUND ART
As the SOI substrate having a single crystal silicon layer formed on such an insulation material as silicon oxide, SIMOX wafers and bonded wafers have been mainly known. The SIMOX wafer is a SOI substrate which is obtained by implanting oxygen ions into the interior of a single crystal silicon substrate and subsequently performing an annealing treatment on the substrate thereby inducing a chemical reaction between the oxygen ions and the silicon atoms in the substrate and consequently giving rise to a buried oxide (BOX) layer in the substrate. The bonded wafer is a SOI substrate which is obtained by joining two single crystal silicon wafers across an interposed oxide layer and then transforming either of the two wafers into a thin film.
The MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor) which is formed in the SOI layer of such a SOI substrate is capable of repressing the short channel effect which becomes more severe as design rule of device fabrication process becomes smaller, and allowing a saving in the power consumption involved in the operation thereof in addition to excelling in radiation hardened characteristics and avoidance of latchup and exhibiting high reliability. Further, it is capable of exalting the signal transmission speed and realizing high speed operation of the device because the operating region of the device is electrically isolated from the substrate itself. By this reason, the SOI substrate acquires a prospect of becoming a high-performance semiconductor substrate for the application of MOS-LSI in the next generation.
Among other species of the SOI substrate, the SIMOX wafer possesses the characteristic feature of particularly excelling in the uniformity of thickness of the SOI layer. In the SIMOX wafer, the SOI layer can be formed in a thickness of not more than 0.3 &mgr;m and also the SOI layer having a thickness in the neighborhood of or even not more than 0.1 &mgr;m can be controlled satisfactorily in thickness. Particularly, the SOI layer measuring not more than 0.1 &mgr;m in thickness is often utilized in the formation a MOS-LSI adapted for the fully depleted type operation. Since, in this case, the thickness of the SOI layer itself has proportionality with the threshold voltage of the MOSFET operation, the uniformity in thickness of the SOI layer constitutes itself an important factor for the manufacture of a high-performance device in a high yield. From this point of view, the SIMOX wafer which excels in the uniformity of thickness of the SOI layer acquires a bright prospect of becoming a substrate for use in the MOSFET of the next generation.
In the manufacture of a SIMOX substrate, the implantation of oxygen ions is generally effected by the use of a single accelerating energy, typically an energy approximating closely to 200 keV. It is well known that, in this case, only when the amount of oxygen ions to be implanted is either in a region of not less than 1.5×10
18
pieces/cm
2
or in a limited region in the range of 2.5-4.5×10
17
pieces/cm
2
, the SIMOX structure obtained after a heat treatment at an elevated temperature is enabled to acquire a buried oxide layer of satisfactory continuous and uniform quality (as disclosed in S. Nakashima and K. Izumi, Journal of Materials Research, Vol. 8, 523 (1993), for example). As respects these species of SIMOX substrate that are manufactured by implanting oxygen ions in such amounts as mentioned above, it is customary to designate the species of SIMOX manufactured by implanting oxygen ions in an amount in the former range as high-dose SIMOX substrates and the species of SIMOX manufactured by implanting oxygen ions in an amount in the latter range as low-dose SIMOX substrates.
The high-dose SIMOX substrates and the low-dose SIMOX substrates respectively possess specific characteristics of their own and find utility in particular applications which are appropriate for these specific characteristics. Of these species, the low-dose SIMOX substrates acquire a prospect of decreasing the threading dislocation density in the surface silicon layer and realizing low production cost as well because the amount of oxygen ions to be implanted therein is comparatively small. The low-dose SIMOX substrates meanwhile have the problem of leak defects generation in the buried oxide layer and insulation resistance deficiency with a high probability because of the small thickness of the buried oxide layer.
As a measure to contribute to the improvement of the quality of the buried oxide layer of the low-dose SIMOX substrate, the internal thermal oxidation process (hereinafter referred to as an “ITOX process”) has been proposed (U.S. Pat. No. 5,658,809 and U.S. Pat. No. 5,918,136 or S. Nakashima et al., Journal of Electrochemical Society, Vol. 143, page 244 (1996)). According to the ITOX process, the treatment of oxidation at an elevated temperature induces growth of a thermal oxide film on the surface of a substrate and growth of an oxide film in a certain amount on the upper interface of a buried oxide film as well and consequently renders addition to the thickness of a buried oxide film possible. It is reported that this process produces the consequence of feasibilizing both the repression of leak defects and the improvement in insulation resistance in the buried oxide layer.
The surface silicon layer in the low-dose SIMOX substrate still contains threading dislocations at a density in the approximate range of 10
2
-10
4
pieces/cm
2
or in a higher range, though repressed as compared with the high-dose SIMOX substrate. It has been pointed out that when the ITOX treatment (internal oxidation treatment) is carried out at a generally adopted elevated temperature of about 1350° C. in the process for the production of such a low-dose SIMOX substrate, depressions measuring approximately 2 &mgr;m in diameter and 10 nm in depth and centering around the sites of threading dislocations are generated on the surface of the SOI layer (W. P. Maszara et al., Proceedings 1997 IEEE International SOI Conference, page 18). Typically, the fully depleted type device using a SOI of a thickness of not more than 100 nm has the threshold voltage of its operation vary with the thickness of the SOI layer. Since the depressions mentioned above affect the local variation of the SOI thickness, the fully depleted type device which is manufactured on such a substrate has the possibility of imposing a restriction on the performance of operation thereof.
In the ITOX technique mentioned above, since the effect of the internal oxidation which is relied on to produce an increment in the thickness of the buried oxide film induces growth of a surface oxide film in a thickness of not less than 10 times the increment in the buried oxide film, the surface silicon layer inevitably has the thickness thereof decrease. An effort to secure an increment in the buried oxide film owing to the effect of internal oxidation for the purpose of improving the quality of the buried oxide layer has no alternative but to decrease the thickness of the surface silicon layer, with the result that the produced silicon layer will impose a restriction on the thickness thereof. Otherwise, an effort to secure a prescribed surface silicon layer in the eventually produced SIMOX structure entails the necessity for limiting the amount of an oxide on the surface of the substrate, with the result that the degree with which the buried oxide layer is improved in quality will have its own limit.
The low-dose SIMOX substrate manufactured by the use of the ITOX process, though improved in the quality of the buried oxide layer by the ITOX effect
Kawamura Keisuke
Matsumura Atsuki
Mizutani Toshiyuki
Kenyon & Kenyon
Nippon Steel Corporation
Picardat Kevin M.
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