Semiconductor device manufacturing: process – Introduction of conductivity modifying dopant into... – Ion implantation of dopant into semiconductor region
Reexamination Certificate
1998-07-07
2001-04-24
Wilczewski, Mary (Department: 2812)
Semiconductor device manufacturing: process
Introduction of conductivity modifying dopant into...
Ion implantation of dopant into semiconductor region
C438S370000, C438S480000, C438S440000
Reexamination Certificate
active
06221743
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for processing a substrate in which occurrence of defects after ion implantation can be suitably prevented, for example, in a Si semiconductor substrate.
2. Description of the Prior Art
In the field of manufacturing Si semiconductors, recently, SOI (Silicon on Insulator) technique capable of providing a high-speed, low-power consumption LSI is advancingly developed, and SIMOX (Separation by Implanted Oxygen) has attracted attention as a method for manufacturing a wafer necessary for this.
According to this method, oxygen atom ion O
+
is implanted to a Si wafer
20
heated to 500-650° C. by ion implantation in the order of 10
17
-10
18
/cm
2
as shown in FIG.
2
(
a
). The accelerating voltage in this ion implantation is set to about 200 kV, whereby the oxygen ion is dosed to the area of several 10 to several 100 nm from the surface (hereinafter referred to as a dosing area
21
).
A heating treatment to a temperature equal to or higher than 1300° C. for 6-10 hours (high-temperature annealing) is successively performed in an inert gas such as Ar or an mixture gas of Ar and oxygen added thereto. The oxygen atom implanted to the dosing area
21
is reacted with Si by this annealing to form a buried oxide film
22
formed of silicon dioxide (SiO
2
) having a substantially uniform thickness in a specified depth from the surface as shown in FIG.
2
(
b
).
By use of a substrate having the buried oxide film
22
thus formed thereon (hereinafter referred to as a SIMOX substrate
20
′), a device formation is performed in a Si layer
23
of 10-500 nm on the surface side from the buried oxide film
22
, or the part insulated from a Si base layer
24
on the lower side by the buried oxide film
22
to form an element, whereby a high-speed, low-power consumption LSI can be manufactured.
However, the conventional SIMOX substrate
20
′ formed according to the above method has a problem in that defects as reduce the manufacturing yield or reliability can not be sufficiently reduced in the manufacture of an ULSI (IC with ultra-high integration degree) in which integration of elements is further advanced.
Namely, in the above-described manufacturing process, in the substrate
20
after ion implantation, crystal defects such as atomic vacancies Dv . . . in the surface Si layer
23
, substitutional lattice defects Dc . . . in which O atom is substituted by Si atom, interstitial lattice detects Di . . . in which O atom is penetrated between atoms, and the like occur in large quantities according to the ion implantation as shown in FIG.
2
(
c
). The high-temperature annealing after ion implantation leads to a behavior as these crystal defects are mutually integrated, resulting in a change to defects of a larger level as large vacancies PV (Piled up Vacancies), stacking fault SF, or dislocation DF as shown in FIG.
2
(
d
), and these are existing in the SIMOX substrate
20
′. Further, the buried oxide film
22
is not necessarily a chemically stable SiO
2
layer.
Although it is conventionally adapted to change the temperature, time, temperature rising speed or the like in the annealing in order to reduce such defects, dislocation of a high density in the order of 10
9
/cm
2
still remains in a high dose substrate having a dose of about 2×10
18
/cm
2
. It is also reported that the dislocation density can be significantly reduced by changing the dose of oxygen ion to about 4×10
17
/cm
2
. However, it is the actual state that the dislocation density is about 10
2
/cm
2
even in that case, which is still insufficient to be applied to ULSI.
SUMMARY OF THE INVENTION
The present invention has been achieved to solve the above-mentioned problems. An object of the present invention is to provide a method for processing a substrate in which occurrence of defects after ion implantation can be suitably prevented to a substrate functionalized by ion implantation as the above-mentioned SIMOX substrate, or a substrate reformed in the vicinity of the surface by ion implantation.
As the earnest studies on the relation between high-temperature annealing condition after ion implantation and occurrence of defects in order to attain the above object, the present inventors have found that the high gas pressure in annealing has a significant effect on the behavior of crystal defects occurring according to ion implantation, and attained the present invention.
Namely, a method for processing a substrate according to the present invention in which occurrence of defects after ion implantation can be prevented, for example, in a Si semiconductor substrate is characterized by annealing the substrate under a pressurized gas atmosphere in order to suppress the integration of crystal defects occurring according to ion implantation.
When the annealing is performed under the pressurized gas atmosphere, the behavior of crystal defects becomes different from the previous one. Namely, under the atmospheric pressure or vacuum, the crystal defects in the substrate are laid in thermodynamically more stable state by being collected in a specific part, resulting in the formation of dislocation or large vacancies. In the pressurized state, on the other hand, the structure having a smaller volume is thermodynamically more stabile. Thus, the behavior as increases crystal distortion is arrested to form a state where the crystal defects are uniformly dispersed, and the vacancies can be also extinguished. At a result, occurrence of defects by the integration of crystal defects can be prevented.
When a specified element ion is collectively implanted to a specified depth from the surface of a substrate to be processed, and the implanted element is then reacted with the constituting element of the substrate to be processed by the above-mentioned annealing under pressurized gas atmosphere to form a compound layer, occurrence of defects which was previously apt to be caused in the critical surfaces of the compound layer with the bases (base material) nipping it can be also prevented.
Namely, the formation of the compound as described above generally accompanies a volume expansion. In this case, a stress is generated in the critical surface with the base material, whereby a large quantity of dislocations and, further, defects such as micro-cracks in an extreme case occur in the base material. Although a volume contraction accompanied by the compound formation is also known, large vacancies are formed in the vicinity of the critical surface in such cases.
In the thermal treatment accompanying the generation of a compound as described above, the dislocation or cracking can be prevented by heating to a temperature such that the constituting atom can be diffused in the pressurized state, and vacancies can be extinguished when formed.
Accordingly, when a compound layer formed of silicon dioxide is formed by annealing under a pressurized gas atmosphere by use of a silicon monocrystal substrate as the substrate to be processed and oxygen as the element to be ion-implanted, a substrate having a buried oxide layer in which lattice defects such as atomic vacancies and interstitial atoms in ion implantation are never changed to large defects, or a specific tissue or defect never occurs in the vicinity of the critical surface of the compound layer with the base material can be formed. Thus, a Si semiconductor substrate of good quality suitable for manufacture of ULSI can be provided.
REFERENCES:
patent: 5658809 (1997-08-01), Nakashima
patent: 5895274 (1999-04-01), Lane et al.
patent: 5918136 (1999-06-01), Nakashima
S. Wolf, Silicon Processing for the VLSI era, vol. 1, 1997, 216-218.
Fujikawa Takao
Masuoka Itaru
Narukawa Yutaka
Suzuki Kohei
Goodwin David
Kabushiki Kaisha Kobe Seiko Sho
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Wilczewski Mary
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