JP2643695B2 - Boron ion implantation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for implanting boron ions into a semiconductor substrate without performing mass analysis.

[0002]

2. Description of the Related Art In some cases, ion implantation is performed without mass spectrometry in order to simplify an apparatus configuration. In such a case, conventionally, an ion source (for example, a Freeman-type ion source or a bucket-type ion source) that generates plasma by arc discharge has been used, and ions extracted from such an ion source have been implanted into a semiconductor substrate.

[0003]

However, when an ion source that generates plasma by arc discharge is used, the energy of electrons for converting the ion source gas into plasma is high, and ions of various masses are generated at the same time. Specifically, when diborane (B ₂ H ₆ ) is used as the ion source gas, BH _x ⁺ and B ₂ H _x ⁺ (x = 1 to 6, the same applies hereinafter)
Order but occurs when injected without such ions mass spectrometry, the difference in mass, in particular by the mass difference between B and B _2, since the implantation depth is different, clean in the depth direction of the implanted ions There is a problem that a concentration distribution cannot be obtained.

[0004] Such a problem is particularly serious in ion implantation into a semiconductor substrate in which control of the ion concentration distribution in the depth direction is very important.

Accordingly, an object of the present invention is to provide an implantation method capable of implanting ions of uniform mass when implanting boron ions into a semiconductor substrate without performing mass analysis.

[0006]

To achieve the above object, the boron ion implantation method of the present invention uses a high-frequency discharge type ion source for generating plasma by high-frequency discharge for generating boron ions. Diborane diluted with hydrogen is used as an ion source gas to be introduced into the ion source , whereby B ₂ H _x ⁺ (x = 1
6) is preferentially extracted .

[0007]

[Action] As a result of conducting various experiments, according to the above method,
It was found that BH _x ⁺ was scarcely contained in the ions extracted from the ion source, and most of the ions were in the form of B ₂ H _x ⁺ .

This is considered to be due to the following reasons. In other words, the energy of the electrons is relatively small in order to decompose diborane into B ₂ H _x ⁺ by colliding the electrons, whereas large energy is required to be decomposed into BH _x ⁺ . For ion source for generating a plasma by a conventional arc discharge, the electron energy increases since the DC voltage for the arc discharge directly becomes the electron acceleration energy, thus not diborane B ₂ H _x ⁺ only B
Decomposes to H _x ⁺ . On the other hand, in the case of an ion source that generates plasma by high-frequency discharge, the period of the alternating electric field is too fast for the electrons to sufficiently follow, so that the electrons are not accelerated to the energy equivalent to the high-frequency voltage. , Only smaller energies. Therefore, there is no energy to decompose diborane to BH _x ⁺ , and most of the energy is decomposed to B ₂ H _x ⁺ .

Therefore, according to the implantation method of the present invention, even when boron ions are implanted into a semiconductor substrate without performing mass analysis, ions having a uniform mass can be implanted.

[0010]

First, a theoretical comparison between the case where B ₂ H _x ⁺ is extracted and ion-implanted and the case where BH _x ⁺ is extracted and ion-implanted is as follows. However, since two ions are contained in one ion, the amount of boron is doubled. In addition, in order to implant the same depth as in the case of the above, one ion contains two boron and has twice the mass, so that twice the energy is required. In this case, if the extraction voltage V of the ion source is doubled, not only can the ion implantation be performed to the same depth as in the case described above, but also the beam current extracted from the ion source increases in proportion to V ^3/2. So
The injection volume and thus the throughput is greatly increased.

Next, the results of an experiment of boron implantation into a silicon substrate using a high-frequency discharge ion source and diborane as an ion source gas according to the present invention will be described.

At this time, the gas introduced into the ion source is B ₂
A mixed gas of H ₆ and H ₂ with the former concentration of 5%, input high frequency power of 20 W, ion energy of 30 keV
And The injection amount was set to 5 × 10 ¹⁵ ions / cm ² .

After the implantation, the result of evaluating the distribution of boron in the depth direction using a secondary ion mass spectrometer is shown by a solid line as an example in FIG. During the drawing, for comparison, by selecting the B ¹¹ by mass spectrometric analysis indicated by a broken line as a comparative example distributions injected with the same ion energy as described above.

As shown in the figure, in the case of the embodiment, the peak position of the implanted ions is almost half the depth of the comparative example. Further, the peak concentration of B ¹¹ is determined by the concentration calculated from the amount of implanted ions (that is, 1.5 × 10 ^21).
Pcs / cm ³ ). In other words, these results are in accordance with the above-mentioned theory, and the curves of the examples are as clean as those of the comparative example. From these facts, in the case of the examples, BH _x ⁺ is hardly contained in the ions extracted from the ion source. Not included, mostly B ₂
It can be seen that it is H _x ⁺ .

As can be seen from FIG. 1, since no mass spectrometry was performed in the case of the embodiment, B ^{11 which} is an isotope of B ¹¹ was used.
¹⁰ is also injected, which is also the same depth as B ^11, moreover the amount because 1/10 of B ^11, no particular hindrance.

[0016]

As described above, according to the present invention, since most of the ions extracted from the ion source are in the form of B ₂ H _x ⁺ , boron ions are implanted into the semiconductor substrate without mass analysis. In this case, ions having a uniform mass can be implanted. As a result, a clean concentration distribution of the implanted ions in the depth direction can be obtained. Moreover, Ho
Extracting and implanting elemental ions in the form of B ₂ H _x ⁺
Can be drawn out and injected in the form of BH _x ⁺
Twice the amount of boron implanted at the same beam current
be able to. Moreover, to achieve the same implantation depth,
Be if B ₂ H _x ⁺ a the extraction voltage V of the ion source to double
Can be extracted from the ion source
Since the beam current increases in proportion to ^{V3 / 2} , a large
Beam current can be easily obtained. Both reasons
Therefore, according to the present invention, the injection amount and thus the processing capacity can be increased.
Can be increased sharply.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a concentration distribution of boron ions in a depth direction by an implantation method according to the present invention.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaaki Nukayama 47, Umezu Takaune-cho, Ukyo-ku, Kyoto-shi, Nissin Electric Co., Ltd. (56) References JP-A-2-224376 (JP, A) JP-A Heisei 1-243358 (JP, A)

Claims (1)

(57) [Claims] In a method for implanting boron ions into a semiconductor substrate without mass analysis, a high-frequency discharge type ion source for generating plasma by high-frequency discharge is used for generating the boron ions, and the boron ions are introduced into the ion source. the ion source gas, diborane diluted with hydrogen,
Thereby, B ₂ H _x ⁺ (x = 1 to
6. A boron ion implantation method, wherein 6) is preferentially extracted .