JPH04368122A - Ion implantation method of semiconductor device - Google Patents

Abstract

PURPOSE:To improve uniformity of through-ion implantation wherein ions are implanted in a semiconductor substrate through a thin film. CONSTITUTION:Through.ion implantation is a useful method which is resistive to impurity contamination and can reduce channeling at the time of ion implantation, because a film (insulating film or the like) protects the surface of a semiconductor substrate. Irregularity of film thickness, however, exerts an influence upon uniformity. In the case of a thin film, irregularity is reduced, but reduction effect of channeling is also decreased. In an ion implanter of parallel scan system, an ion beam enters parallel with the semiconductor substrate, and channeling is reduced. As a result, the above ion implanter is used, and ions are implanted through a thin film which reduces film thickness irregularity. Thereby uniformity is improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for implanting ions into a semiconductor substrate.

0002

[Prior Art] Compound semiconductors, especially GaAs, are Si
Currently, LS
Research on integration is being actively conducted. This GaAsLSI
Ion implantation technology, which is the main technology in the manufacturing process, is widely used because of its excellent uniformity and reproducibility. The major issues faced by this ion implantation technology are (1) Vth (field effect transistor) of FET (field effect transistor);
Improved in-plane uniformity of FET Vth (threshold voltage) (2) Improved reproducibility of FET Vth (threshold voltage) (
3) There are three points to improve the yield of Vth (threshold voltage) of FET.

These problems largely depend on the performance of the ion implanter. FIG. 5 shows the positional relationship between the ion beam and the semiconductor substrate during ion implantation. In the general angle scanning type ion implantation equipment currently in use, the parallelism of the ion beam at the semiconductor substrate position is not good (approximately ±1.5° (Δ in Figure 5) within a 3-inch substrate). Distribution of Vth due to channeling caused by the difference in incidence angle of injection (
Unilateral flow distribution; for example, J. Kasahara et.
al, “THE EFFECT OF CHAN
NELING ON THE LSI-GRAD
E UNIFORMITY OFGaAs-FET
s BY ION IMPLANTATION”
, GaAsIC Symposium, p, 37.1
985) occurs. Furthermore, when performing ion implantation, a resist is applied directly to the GaAs surface and ions are implanted. Bare implantation is performed, but since various chemicals are used in the process of applying and peeling off the resist that serves as the ion implantation mask, there is also the problem that the GaAs surface is contaminated with impurities, deteriorating uniformity and reproducibility.

One method for improving the in-plane distribution of channeling is through implantation in which ions are implanted through a thin film. This method corrects the difference in ion incidence angle by scattering ions within a thin film, and performs uniform ion implantation. Furthermore, since the GaAs surface is protected by a thin film, there is no problem with contamination of the GaAs surface.

[0005]

As mentioned above, through ion implantation eliminates the problem of contamination of the GaAs surface. Furthermore, since ions are scattered within the thin film, channeling is less likely to occur. However, with through ion implantation through a thin film, there is a concern about instability as changes in film thickness and film quality directly affect the implantation distribution. For example, Table 1 shows the contact width when the film thickness uniformity/reproducibility is ±5%.

[0006]

[Table 1]

The thickness of the thin film required to prevent channeling varies depending on the ion implantation conditions, but is approximately 1000 Å thick.
The above is necessary. Even if completely uniform ion implantation could be performed, the thickness of the ion implanted layer would vary by ±50 Å. Here, the film thickness of the ion implantation layer of high performance FET is ~
1000 Å, and Vth (film thickness of ion implantation layer)
2, the variation in Vth is ±
This results in a change of 10% (1.052≒1.10). In reality, since variations in ion implantation are also added, the variations in Vth become even larger, resulting in a value that is insufficient for practical use.

Therefore, in order to put through injection into practical use, it is necessary to prevent channeling by making the film as thin as possible.

[0009]

[Means for Solving the Problems] In view of the above points, the present invention implants ions into a semiconductor substrate formed with a film thickness (preferably 100 Å or less) using an ion implantation device scanned by a parallel scan method. The purpose is to provide a method for forming semiconductor elements with excellent performance with good uniformity and reproducibility.

0010

[Effect] Recently, the parallelism of the ion beam has been improved (3
(±0.3% or less within an inch substrate) A parallel scan type ion implanter has been developed. The inventor thought that through implantation using a parallel scan type ion implanter would be effective in solving these problems. That is, since the angular difference is small, channeling is difficult to occur in the first place, and it is expected that even if the thickness of the thin film is made thin, there will be a sufficient effect in preventing channeling. The results are shown below.

Here, the tilt angle φ and the rotation speed R of the target holder during ion implantation were used as parameters. A 3-inch semi-insulating GaAs substrate was used as the semiconductor substrate, and a 100 Å silicon nitride film (SiNx) was deposited on the surface by plasma CVD (p-CVD), and 28Si+ was deposited at 30k.
Ion implantation was performed at eV 1×10 13 [cm −2 ]. Uniformity was evaluated by thermal wave measurement (Uchitomi et al. "Evaluation of GaAs ion-implanted layer by endothermal measurement" IEICE Technical Report ED87-137)
p. 19). The results are shown in FIG.

[0012] Uniformity is determined by tilt angle θ, azimuth angle φ, and rotation speed R.
It depends on both. This dependence is thought to be due to the channel that the GaAs crystal has, and the width of the change is as small as 0.3 to 0.5% (in a similar experiment using a "bare implantation + angle scan type ion implanter", ~12%
[Mizutani et al. "Optimization of GaAs wafer surface orientation in ion implantation" 1990 Spring Society of Applied Physics 29P-D
-1]). After all, tilt angle θ = 10°, azimuth angle φ = 20
The best uniformity was obtained at 0.3%. This value is the best value for "through implantation + angle scan type ion implanter" ~
More than 1%.

[0013]

[Examples] Examples of the present invention will be described below.

(Example 1) In FIG. 1, 1 is a semi-insulating GaAs substrate, and 2 is a substrate with a thickness of 10 formed by p-CVD.
0 Å SiNx. 28Si+ was implanted at 30keV 1×1013 [c
m-2] ion implantation. The tilt angle θ is 10° and the azimuth angle φ is 20°. At this time, the uniformity was 0.3%.

(Example 2) FIG. 2 shows the results under the same conditions as FIG. 1.
FIG. 2 is a schematic diagram of a place where selective ion implantation can be performed to form an FET. 3 indicates a region into which selective ions have been implanted. Since the ion implantation part of Example 2 has no essential difference from Example 1, the same degree of uniformity can be obtained. (Example 3) In FIG. 3, 4 is a deposited metal thin film. In this example, it is Ti. FIG. 4 shows the performance of a Ti ion-implanted device (a graph that evaluates the damage introduced by ion implantation by measuring the extinction coefficient of the semiconductor substrate. The extinction coefficient before ion implantation is about 0.35). ~40
It can be seen that Ti of 0 Å almost completely stops ion penetration into GaAs. From this figure, the Ti film thickness is 40 Å.
It was set to When a metal is used as the thin film, charge up due to ion implantation can be prevented, thereby further improving the uniformity (see Japanese Patent Laid-Open No. 2-22817).

[0016] In all of the above examples, 0.3%
It was found that the following uniformity could be obtained. This is a good value that could not be obtained with conventional through ion implantation.

[0017]

As described in detail above, by using the method of ion implantation into a semiconductor substrate according to the present invention, more uniform ion implantation can be performed than with conventional ion implantation methods.

Furthermore, since the thickness of the through-implantation thin film can be reduced, the implanted layer can be made thinner and highly concentrated by low-energy ion implantation, so that the characteristics of the formed semiconductor element are high.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining one embodiment of the present invention.

FIG. 2 is a diagram for explaining one embodiment of the present invention.

FIG. 3 is a diagram for explaining one embodiment of the present invention.

FIG. 4 is a diagram showing the ion implantation blocking ability with respect to the film thickness of a Ti thin film.

FIG. 5 is a diagram showing the positional relationship between an ion beam and a semiconductor substrate during ion implantation.

FIG. 6 is a characteristic diagram using the tilt angle, azimuth angle, and rotation speed of the target holder during ion implantation as parameters.

Claims (2)

[Claims] 1. A method for manufacturing a semiconductor device, characterized in that an ion implantation apparatus in which an ion beam is scanned in a parallel scanning manner is used when implanting ions into a semiconductor substrate. 1. A method for ion implantation of a semiconductor device, characterized in that: is formed. 2. An ion implantation method for a semiconductor device, wherein the thickness of the thin film is 100 Å or less.