JPS60135882A - Measurement of diameter of ion beam - Google Patents

Abstract

PURPOSE:To make it possible to accurately measure the diameter of ion beam condensed in a sub-micron order, by measuring the diameter of ion beam by utilizing a boundary present on the surface of a flat semiconductor crystal. CONSTITUTION:When ion beam is allowed to vertically irradiate the surface of a semiconductor 1, secondary electrons 4 are emitted from the semiconductor 1 and the intensity of the electrons 4 is measured by a secondary electron intensity measuring apparatus 5. When ion beam 3 is scanned in this state and irradiated so as to traverse the boundary of two regions 1a, 1b, the intensities of emitted secondary electrons are changed in the regions 1a, 1b. Therefore, the diameter of the ion beam is calculated by the product of a time required in changing the intensity of secondary electrons from etaa to etab and the scanning speed of the ion beam.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the diameter of an ion beam when implanting ions into a semiconductor substrate crystal using acceleration energy.

In order to form optical devices such as lasers, light emitting diodes, and photodetectors, and electronic devices such as transistors and diodes on semiconductor substrates, impurities,
The recently proposed maskless ion implantation method, which uses a focused ion beam to directly dope impurity ions into a semiconductor substrate, requires complicated mask creation and positioning. In order to form a device according to dimensions, it is essential to accurately determine the diameter of the focused impurity ion beam.

The conventional method for measuring the diameter of an ion beam is to scan the focused beam perpendicularly to the knife edge, measure the change in beam current as it crosses the knife edge using a Faraday cup, and measure the beam current change from the current rise point 9. The diameter of the beam was being measured. However, the ion beam has a high sputtering yield, and the knife edge is scraped and retreats during measurement, making measurement accuracy unreliable. In addition, a line pattern of gold, which emits a large amount of secondary electrons, is placed on the Si crystal, etc., and the focused ion beam is scanned perpendicularly to this line pattern (to ensure that the beam crosses the boundary between the Si and gold). A method is also known in which the diameter of the beam is measured from the change in the emission ratio of secondary electrons as it traverses the ion beam.However, during this method 5 measurement, the edges of the gold line pattern may be affected due to scattering caused by the ion beam. □ was gradually damaged, reducing measurement accuracy.

An object of the present invention is to provide a method for measuring the diameter of an ion beam with high precision and good reproducibility. The ion beam is perpendicular to the boundary and scanned across the boundary, and the secondary electron intensities of the two regions emitted by the scanning of the ion beam are falsely detected. It is characterized by measuring the diameter of the ion beam by the intensity ratio of .

Next, the present invention will be explained with reference to FIG. 1. l is a semiconductor and is constructed by joining two regions /lL+/6 having different characteristics. As a semiconductor l constructed by joining regions having such different characteristics, Gap
Semiconductors having a heterojunction structure such as S and AlGaAs, or semiconductors having a pn junction can be cited.

When the surface of this semiconductor 1 is irradiated perpendicularly with the ion beam 3 whose diameter is to be measured, secondary electrons are emitted from the semiconductor, and the intensity of the emitted secondary electrons is greater than that of an electron multiplier. Measurement is performed using a secondary electron intensity measuring device according to step 3.

If the ion beam 3 is scanned in this state and irradiated across the boundary λ of the two regions /αe'b, the energy of the ion beam 3 will not change, but the characteristics of the secondary electron emitting surface of the semiconductor will change depending on the region /αe'b. Since α and region /b are different, the strength of the emitted secondary electrons changes accordingly. That is, when scanning the semiconductor region lα, as shown in FIG. A signal with varying strength and strength ηb will be received. Therefore, the diameter of the ion beam can be determined by the product of the time during which the intensity of the secondary electrons changes from ηα to ηb and the scanning speed of the ion beam. Actually, there are two semiconductor regions 1a,
For example, the width of the boundary where /b joins is about 10 to 201 in the case of a heterojunction structure, and 3 in the case of a p-" junction.
It has a width of 0X or less.

Therefore, in the process in which the secondary electron □ intensity changes from ηα to ηb, the time reference related to measuring the diameter of the ion beam varies depending on the shape of the current intensity distribution of the ion beam.
Normally, the intensity distribution of an ion beam is often Gaussian, so in this case, assuming that the change from ηα to ηb is 100, the time it takes for the ion beam to reach a point from a point α that has changed by 16 degrees to a point that has changed by 84 degrees is assumed to be 100. For a time corresponding to the diameter d, even beam diameters on the order of submicrons can be accurately measured.

However, the current intensity distribution of the ion beam falls on the differential of the curve shown in Figure 2, and in the case of a Gaussian distribution, the point α-
The width between the gaps (variation width of 16%-84%) corresponds to the width of the 1/g point of the peak of the current intensity distribution.

The semiconductor surface on which the ion beam is scanned must be smooth, and the two regions lα and /b must be on the same plane. From this point of view, if the valve opening plane of a heterojunction semiconductor formed by the molecular beam crystal growth method (MBE method) is used as the scanning plane of the ion beam, it will be flat and the width of the heterojunction boundary will be 20 mm.
Since it is less than If the semiconductor surface to be scanned by the ion beam is not sufficiently flat, or if the boundary has a step, sputtering will occur due to the ion beam, so it may be necessary to polish and smooth it using a known polishing method. Use as a.

As mentioned above, this invention measures the diameter of the ion beam using the boundary on the flat semiconductor crystal surface, so the beam diameter is measured with good reproducibility without damaging the boundary due to ion beam sputtering. can do. Furthermore, since the width of the boundary can be formed on the order of ^, it is possible to accurately measure the diameter of a beam focused on the order of submicrons.

Next, embodiments of this invention will be described.

A 5 μm thick non-doped GcLAs layer is grown on a GaAs substrate by molecular beam crystal growth, and a 7 μm thick A layer is grown on top of it.
A JGI0LAg layer was grown. This laminate is folded,
Two ion beams of different diameters, large and small, were scanned over the interfold surface having this GaAtt-=AlGαA8 boundary, and the intensity of secondary electrons was measured using an electron multiplier. Figure 5 (W) shows the secondary electron output characteristics when scanning an ion beam with a small diameter, and Figure 3 (b) shows the output characteristics of secondary electrons when scanning an ion beam with a large diameter. It is a characteristic diagram. From the above measurement results, the diameter of the former ion beam is 0.07 μm, and the diameter of the latter ion beam is 0.2 μm.
It was 6 μm.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing the method of measuring the ion beam diameter according to the present invention, Fig. 2 is a graph showing the irradiation position of the ion beam and the state of change in secondary electron intensity, and Fig. 5 (8).
(6) is an output characteristic diagram of secondary electrons when a semiconductor is scanned with an ion beam. /P/Semiconductor, Co...Boundary, 3...Ion beam,
G: Secondary electron, S: Secondary electron intensity measuring device. Patent applicant Director of the Agency of Industrial Science and Technology Yoda # Department Figure 4 Figure 2 1 A Nine beam irradiation A 1 Figure 3 (a) (b)

Claims (1)

[Claims] An ion beam is scanned perpendicularly across the boundary of two bonded semiconductor regions with different characteristics, and the intensity of secondary electrons emitted from the two regions by irradiation with the ion beam is measured. A method for measuring the diameter of an ion beam, characterized in that the diameter of the ion beam is measured from the intensity ratio of secondary electrons in two regions obtained.