JPS61292844A - Method for determining shape of ion beam - Google Patents

Abstract

PURPOSE:To enable even the diameter of the thin portion of a focused ion beam with small intensity to be measured by irradiating the beam along parallel lines on a silicon plate while changing the scanning speed for each line to form a pattern consisting of linear areas with different secondary ion emission rates and scanning the beam across the pattern in order to determine the variation in the secondary electron emission of the pattern. CONSTITUTION:Ga ions are irradiated along parallel lines with a length of about 60mum on a silicon plate while changing the scanning sped for each area (3mum/s, 6mum/s, 30mum/s, 60mum/s...). As the result, the width of the resulting noncrystallized linear area becomes larger for the slower irradiation speed. The widths of the resulting noncrystallized linear areas (a1, a2, a3...) for the different scanning speeds (3mum/s, 6mum/s, 30mum/s...) are measured in order to observe the pattern resulting from Ga ion irradiation. The shape of the ion beam can be determined by plotting the thus obtained data on a graph paper where the vertical axis of the graph uses a logarithmic scale.

Description

[Detailed Description of the Invention] [Summary] In the manufacturing of semiconductor devices, applications are being developed that use focused ion beams in processes such as processing using ion beams, ion implantation without using a mask, and ion beam exposure. However, we will explain how to measure the beam shape or beam profile with high precision, including the beam tail.

[Industrial application field]

The present invention relates to a method for measuring a fine ion beam shape,
This invention relates to a method for easily measuring a beam profile over a wide range, including the current density distribution at the base of the beam.

Sputtering, drilling, and etching using gas or metal ions are widely used as semiconductor manufacturing processes, but these processes usually do not require focusing the ions into a beam.

Methods of focusing tangential ions into a narrow beam and utilizing them include ion beam processing, ion implantation by beam scanning without using a mask, and lithography in which resist is directly exposed to ion beam. has been in the spotlight.

However, there is currently no method for accurately measuring the diameter of this ion beam, and it is only estimated empirically using a simple method, and there is a need for a highly accurate measuring method.

[Conventional technology]

Some known conventional ion beam diameter measurement methods will be briefly described.

The first method, called the Naifetsu method, scans the ion beam 1 in the direction of the arrow as shown in Figure 4.
When the tip is scanned to the top of the knife-shaped part 2, the current flowing through the ammeter 4 connected to the collector 3 is measured as a function of the beam irradiation position, as shown in Fig. 5 ( become.

By differentiating this current value with respect to the moving distance, the intensity distribution of the ion beam current with respect to the beam position can be obtained as shown in FIG. From this, the beam shape can be estimated.

As a second method, as shown in FIG. 7, a substrate 5 with a boundary between substances A and B having different secondary electron emission rates on the surface is prepared, and a beam is emitted from A to A in the same manner as in the first method. The secondary electron multiplier tube 6 measures the emitted secondary electron current by scanning.

As a result, a current value curve as shown in FIG. 8 is obtained, and by differentiating this with respect to distance as before, the beam shape can be determined.

A third method is to process etching grooves of several widths in a metal thin film or semiconductor layer on a substrate, and then scan the etching grooves in the lateral direction with an ion beam. This is a method of determining the beam diameter from the measurement and its resolution.

Furthermore, as a fourth method, there is a method of using an ion beam as a scanning microscope to scan a substrate having a pattern with a known line width in advance and estimating the beam shape from the resolution.

[Problem that the invention seeks to solve]

Generally, the intensity distribution of an ion beam is assumed to be a Gaussian distribution type, and the beam diameter at which the intensity takes a value of 1/e of the peak value is approximately called the diameter of the ion beam.

The measurement method described above is at its best in determining this approximate beam diameter. The shape of the tail of the current density, which is several orders of magnitude lower than the peak, has hardly been measured.

The reason is that the total beam current value is very small, typically 10
01) It is less than A, and it is extremely difficult to separate and measure the distribution at the base, and even when measuring the approximate beam diameter of 1/e, the beam diameter is extremely small at 0.1 to 0.2 μm. Another reason is that ions have a larger mass than electrons and cannot be repeatedly measured due to sputtering.

In maskless ion implantation using a focused ion beam from a metal ion source, it is necessary to measure the beam spread at a current density that is at least three to four orders of magnitude lower than the peak.

In the conventional method, it is only one digit at most.

[Means for solving problems]

The above problem is solved by irradiating a substrate such as a semiconductor with a focused ion beam while changing its scanning speed to form a plurality of, for example, parallel linear patterns with different secondary electron emissivities.

Thereafter, by scanning the beam across the pattern, changes in the secondary electron emission pattern of the pattern are detected as a secondary electron image, and the shape of the focused ion beam is measured. This problem can be solved by using an ion beam measurement method.

[Effect]

By irradiating the substrate with an ion beam, the surface of the substrate is made amorphous and the secondary electron emission rate is reduced.

By changing the scanning speed of the ion beam on the substrate, it is possible to change the width of the amorphous region, and by slowing down the scanning, it is possible to form a pattern that is amorphous up to the base of the ion beam. .

That is, by controlling the scanning speed, it is possible to measure the beam diameter at the base of the beam, which is several orders of magnitude lower than the beam center.

[Example] A case will be described in which gallium (Ga) is used as the focused ion and silicon (Si) is used as the semiconductor device. G
A case will be described in which Ga ions extracted from the liquid metal ion source in a are focused by an electrostatic lens and scanned over a silicon substrate.

In the scanning region, Ga is injected and the crystal becomes amorphous. As a result, the secondary electron emission rate in the Ga irradiated region is lower than that in the non-irradiated region. When this is observed using a scanning ion microscope using Ga ions, the amorphous region is observed as black.

The present invention attempts to measure the intensity distribution of the focused ion beam itself by utilizing the above properties.

In FIG. 1, a Ga ion beam 1 is accelerated at 100 K e V and irradiated onto a silicon substrate 7 with a current value of 40 pA.

The irradiation is carried out over a region approximately 60 μm in length on the silicon substrate at an initial scanning speed of 3 μm/s. Next, the irradiation position is shifted to the adjacent one, and irradiation scanning is performed in parallel with only the scanning speed changed to 6 μm/s.

Furthermore, 30 μm/s, 60 μm/s, 300 μm
73. While changing the scanning speed at a ratio such as 600 μm/s,
A silicon substrate is irradiated with Ga ions.

This is shown in a partially enlarged view in FIG. The slower the irradiation speed,
A pattern is obtained in which the width of the line that becomes amorphous is expanded.

To observe this pattern, when an ion microscope image is observed by scanning at high speed using the same focused ion beam, patterns with different line widths that have been amorphous in the previous scan are observed.

In other words, the pattern width scanned at the slowest speed of 3 μm/3 is at
Then, when the scanning speed is increased to 6 μm/s, 30 pm/s, etc., the pattern width is measured as at+aff, etc., respectively.

FIG. 3 is obtained by plotting these data on graph paper with a logarithmic scale on the vertical axis. Since the vertical axis represents the current density of the beam, the position of the vertical axis corresponding to each scanning speed is 1. The width at the center of the beam using scales such as 2.10.20.100 is theoretically 0, so it is difficult to determine, but it can be estimated from the shapes of the curves on both sides.

With the above method, the profile of the ion beam including the base portion can be measured with high precision, and since the total ion beam current value is known, the current density at the base portion of the beam can also be calculated.

〔Effect of the invention〕

As explained above, the ion beam shape measurement method of the present invention makes it possible to accurately measure the current density at the base of the beam, which has rarely been measured in the past.
This is an expansion that contributes to improving the quality of semiconductor device manufacturing.

[Brief Description of the Drawings] Figures 1 and 2 are conceptual diagrams for explaining the measurement method of the present invention, Figure 3 is ion beam shape data in the example, Figures 4 and 5, FIG. 6 is a diagram illustrating a method for measuring an ion beam diameter using the conventional Knifezi method, and FIGS. 7 and 8 are diagrams explaining a method for measuring an ion beam diameter using a conventional secondary electron method. In the drawings, 1 is a focused ion beam, 2 is a knife component, 3 is a collector, 4 is an ammeter, 5 is a substrate, 6 is a secondary electron multiplier, and 7 is a silicon substrate. Fig. 1, it4: 2nd FzJ distance (μm) ion beam h-shape of 1st height J row Z- Fig. 3 Fig. 4 Fig. 5 Fig. 6 Figure 7 Figure 8

Claims (1)

[Claims] After irradiating the substrate (7) with a focused ion beam (1) while changing its scanning speed to form a plurality of linear patterns with different secondary electron emissivities, the pattern is A method for measuring an ion beam shape, comprising: scanning a beam across the pattern to detect a change in the amount of secondary electron emission of the pattern, and measuring the shape of the focused ion beam.