JPH0417327A - Ion implantation - Google Patents

Abstract

PURPOSE:To enable a method of breaking down a part below the mask edge as a desired dopant is injected to be executed sufficiently in advance without increases in energy and dose by implanting other ions obliquely to the substrate surface just before implantation of desired dopant ions and then by implanting intrinsic dopant ions. CONSTITUTION:In ion implantation whereby ions are implanted selectively only into a desired region with the surface of a target substrate 1 of crystal structure partially masked, other ions are implanted obliquely into the substrate surface just before implantation of desired dopant ions, and then intrinsic dopant ions are implanted. For example, a polysilicon 2a serving as a gate electrode and a mask is grown on a silicon wafer 1 via an oxide film 6 and then patterned. Next, silicon ions are implanted obliquely from an ion implantation direction 4b with an angle of 45 deg. to the wafer surface at an acceleration energy 4eKeV and a dose 2X10<14>cm-<2>. Thereafter, baron is injected at an acceleration energy of 5KeV and a dose 2X10<14>cm-<2> with ion implantation direction 5 set vertical to the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an ion implantation method as an impurity introduction technique in a semiconductor device manufacturing process.

[Conventional technology]

It is desirable that semiconductor devices used in large-scale integrated circuits be as fine as possible, and large quantities of semiconductor devices with well-matched individual characteristics are required. In this fine semiconductor device, it is necessary to form a shallow junction between a p-type semiconductor and an n-type semiconductor in order to suppress the microshape effect, such as the short channel effect of a MOS transistor. In addition, semiconductors are almost always crystals.9 When forming shallow junctions in such crystal targets using conventional ion implantation, the implanted ions scatter along the crystal axis due to scattering with the crystal constituent atoms within the crystal. If the ions are oriented in the same direction, the implanted ions are forced to move in the direction of the atomic array (channeling motion) due to the electrical potential of the regular atomic arrays in the crystal. This channeling effect becomes more pronounced when the implant energy is lowered to obtain a shallow junction because it penetrates too deeply and cannot form a shallow junction. Furthermore, it is difficult to lower the implantation energy too much because of the divergence and fluctuation of the implantation beam. Therefore, conventional technology has been used to prevent channeling when implanting desired ions by implanting another ion to destroy the target crystal and make it amorphous just before implanting the desired dopant ions. being developed.

However, for example, in a MOS transistor, by forming a shallow source/drain junction, the lateral direction of the simultaneously patterned portion becomes much smaller, reducing the overlap capacitance between the gate and the source/drain, and improving the high-speed operation of the device. Although this conventional method is effective in suppressing channeling in the direction of implantation depth, it is not possible to suppress curling in the lateral direction.

[Problem to be solved by the invention]

However, when making a crystal amorphous to suppress channeling by ion implantation, the target surface that can be implanted is generally not flat and is often selectively patterned by the mask material. The substrate crystal structure cannot be sufficiently destroyed in the portion shaded by the structural difference, so that channeling cannot be prevented when desired dopant ions implanted later reach this portion. This is due to the fact that by lowering the implantation energy and reducing the thickness of the ion-implanted layer, the spread under the mask can be suppressed at the same time.For MOS transistors, etc., conventional methods are insufficient to destroy the crystals under the mask. Therefore, there is a problem in that the source/drain and gate overlap and the effect is lost. Alternatively, it may be possible to use the conventional method and increase the energy and implantation amount to sufficiently destroy the crystals directly below the mask, but this would destroy the crystals too much and require a large amount of heat treatment to recover. Considering this, it is desirable that the energy and injection amount be as low as possible, and there is a problem that they cannot be increased.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an ion implantation method that can sufficiently destroy the portion below the edge of a mask before implanting a desired dopant without increasing energy or implantation amount.

[Means to solve the problem]

In order to achieve the above object, the ion implantation method of the present invention is an ion implantation method in which a part of the surface of a target substrate having a crystal structure is masked and ions are selectively implanted only in a desired region, and a desired dopant is Immediately before ion implantation, another ion is implanted obliquely to the substrate surface, and then the original dopant ions are implanted.

[Effect]

Next, the present invention will be explained in detail. FIG. 1 is a diagram schematically showing the ion implantation method of the present invention. In FIG. 1, in the ion implantation method of the present invention, a mask 2 is applied to a part of the surface of a target crystal substrate 1 having a crystal structure, and ion implantation is performed for the purpose of destroying the crystal structure in the region to be implanted in advance.
Substrate 1 toward region 3 where the crystal structure is destroyed by implantation.
Since the ion implantation is performed obliquely with respect to the surface of the mask 2, as shown by the ion beam direction 4, the implanted ions can reach below the mask 2 and sufficiently destroy the crystal. A schematic diagram of the case using the conventional method is shown in FIG. As shown in FIG. 2, in the conventional method, ions are implanted in the ion implantation beam direction 4a or in a direction perpendicular to the surface of the substrate 1, so that it is difficult to destroy the crystal under the mask.

〔Example〕

Hereinafter, a typical embodiment of the present invention relating to an ion implantation method will be described with reference to the drawings. In FIG. 3, reference numeral 1 denotes a target crystal substrate, or in this case, an n-type single crystal silicon wafer having a clean surface (100) plane orientation was used. An oxide film 6 was grown on this silicon wafer 1, and polysilicon 2a to be used as a gate electrode and a mask was grown on it to a thickness of 0.5 μm, and then patterned by dry etching. In order to destroy the crystal structure in advance, silicon ions, which are the same atoms as the substrate, are accelerated with an energy of 40 keV using the oxide film 6 and polysilicon 2a as a mask 2.
, implantation volume 2 x 10” CI+-, 4 to wafer surface
Ions were implanted obliquely from a silicon ion implantation direction 4b having an angle of 5°. After that, the holon ion implantation direction 5 of boron, which is the original p-type dopant, is set perpendicular to the wafer, and the acceleration energy is 5 keV.
A ρn junction was selectively formed by implanting at an implantation amount of 2×10”−2.

Current technology is only capable of measuring the lateral self-dispersion of impurity dopants in the microstructure of semiconductor silicon.

However, there are computer simulation techniques based on detailed and reliable theory that can estimate the lateral self-destruction of impurity dopants and the degree of substrate crystal destruction. Figures 4(a) and 4(b) show the results of calculating how much the crystal structure is destroyed by silicon ion implantation for the purpose of partially destroying the crystal structure. FIG. 4(a) shows, in a wafer cross section, the degree of crystal destruction after silicon ion implantation at an angle of 45° in this example. FIG. 4(b) shows the degree of crystal destruction within the wafer cross section when this crystal structure is partially destroyed by the conventional method, that is, when silicon ions are implanted perpendicularly to the wafer. The numerical value in the figure is the ratio of the atomic number density displaced by ion implantation to the original crystal atomic density, and represents the degree of damage to the crystal. As is clear from the figure, it can be seen that in the present invention, the degree of destruction of the crystal structure is greater at the end portions of the mask. Further, FIGS. 5(a) and 5(b) show the isoconcentration line distribution of the boron concentration within the cross section of the wafer after boron, which is the original dopant, is implanted as in the example. Figure 5 (
Figure a) shows the result of implanting silicon in advance at an angle of 45° to destroy the crystal structure and then implanting boron as in this embodiment. On the other hand, FIG. 5(b) shows the result of implanting silicon vertically using the conventional method to partially destroy the crystal 411 structure, and then implanting boron. Figure 5 (
The values of the isodensity lines in a) and (b) are the same. According to the conventional method, as shown in FIG. 4(b), the crystal structure at the edge of the mask is not sufficiently destroyed, so the spread of boron toward the edge of the mask is suppressed as shown in FIG. 5(b). It has not been. On the other hand, in the present invention, as shown in FIG. 4(a), the crystal structure is sufficiently destroyed to the edge of the mask before the holons are implanted, so as shown in FIG. 5(a). The lateral distribution is suppressed to the same extent as when implanted into an amorphous material. The lateral overlap directly under the gate as read from FIGS. 5(a) and 5(b) is suppressed to 75%.

〔Effect of the invention〕

According to the ion implantation method of the present invention, the crystal is partially destroyed by ion implantation with a beam perpendicular to the wafer in the shallow junction formation step in which the original dopant is implanted after the crystal is preprocessed and destroyed. Compared to the conventional method,
This has the effect that the crystal under the mask can be destroyed without increasing the ion acceleration energy and the implantation amount, and that lateral self-destruction under the mask can be suppressed.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram showing a state of partial destruction of a crystal caused by the ion implantation method according to the present invention, FIG. 2 is a diagram showing a state by a conventional ion implantation method, and FIG. A diagram showing an embodiment of the inventive method, FIG. 4(a) is a diagram showing the degree of partial damage to a crystal obtained by the ion implantation method of the present invention, and FIG. 4fb) is a diagram showing the degree of damage by the conventional method. figure,
FIG. 5(a) is a cross-sectional isoconcentration diagram of boron ions in silicon obtained by the ion implantation method of the present invention.
b) is an isoconcentration diagram of boron ions according to the conventional method. 1...Target crystal substrate 2...Mask 3...A region where the crystal structure is destroyed by implantation 4...
Ion implantation beam direction that pre-destroys the crystal structure 5... Desired dopant ion implantation direction Patent applicant
Naka Kanno, Representative Patent Attorney, NEC Co., Ltd.
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Claims (1)

[Claims] (1) An ion implantation method in which ions are selectively implanted only into desired regions by masking a part of the surface of a target substrate with a crystal structure, and immediately before implanting desired dopant ions, another ion is implanted into the substrate surface. An ion implantation method characterized by implanting the dopant ions obliquely to the dopant, and then implanting the original dopant ions.