JPS59122904A - Ion beam film thickness measuring device - Google Patents

Abstract

PURPOSE:To make it possible to measure the thickness of each layer of sample constituting layers, by detecting a slight change in a sample absorbing current value based on the change in a layer to be etched, by performing phase detection using a lock in amplifier, wherein a modulating signal that modulates the potential of a sample is made to be a reference signal. CONSTITUTION:An ion beam IB is projected on a sample 4 comprising a plurality of layers 4a-4b through a condenser lens 2 and an objective lens 3. The output signal from a modulator 5, which generates a modulating voltage at a constant frequency f0, is applied on the sample 4 by a modulating transformer 6. In order to detect the ion beam current that is absorbed by the sample 4, the sample 4 is coupled to a preamplifier 7 by CR. The output signal of the amplifier 7 is supplied to a lock in amplifier 8, and its output is supplied to a recorder 9. A measuring person uses the data associated to a standard sample, and converts the data, which shows the etching time of each layer of the sample obtained from the recorder 9 into the data, which shows the thickness of each layer. Thus, the thickness of each layer of the sample can be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for measuring the film thickness of each layer of a sample while etching the sample by irradiating the sample with a plurality of layers made of different materials by irradiating the sample with an ion beam.

The thickness of each layer of a sample consisting of multiple layers of different materials is
When measuring while etching a sample by irradiating it with an ion beam, the conventional method was as follows.

The first type of device analyzes the energy of Auger electrons generated from the sample during ion beam irradiation, detects changes in the spectrum, and detects that etching has progressed to a new layer. The layer thickness was measured based on such detection.

In the second type of device, secondary ions generated from the sample are guided to a mass spectrometer for mass analysis, changes in the layer are detected from changes in the mass spectra, and based on these detections, the changes in the layer are determined. The thickness was being measured.

Therefore, all of these conventional devices required large-sized auxiliary equipment such as an energy analyzer or a mass spectrometer.

The present invention has been made to solve these conventional drawbacks, and includes an ion beam source, a focusing lens for narrowly focusing and irradiating the ion beam from the ion beam source onto the sample, and means for applying a periodic modulation voltage; a detection means for detecting the ion beam current absorbed by the sample; and phase detection of the detection signal detected by the detection means in synchronization with the application of the modulation voltage. The present invention is characterized in that it comprises a phase detector for the purpose of the present invention, and means for displaying or recording the output signal of the phase detector.

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

In FIG. 1 showing an embodiment of the present invention, 1 is an ion source, and an ion beam IB from this ion source 1 is focused by a focusing lens 2 and then focused onto a sample 4 by an objective lens 3. irradiated. As is clear from FIG. 2, which shows the cross section of the sample 4, there are a plurality of layers 4a made of different materials.

It consists of 4b, 4c, 4d... 5 is Figure 3<
This is a modulator that generates a modulation voltage of a constant frequency fo as shown in a>, and the output signal of this modulator 5 is applied to the sample 4 by a modulation transformer 6.

In order to detect the ion beam current absorbed by sample 4,
The sample 4 is CR-coupled to the preamplifier 7 via the secondary winding of the transformer 6. The output signal of the preamplifier 7 is supplied to a lock-in amplifier 8 to which a reference signal synchronized with the modulation signal of the modulator 5 is supplied. The output signal of the lock-in amplifier 8 is supplied to a recorder 9.

In such a configuration, when the sample 4 is irradiated with the ion beam 1B from the ion source 1, the material on the surface of the sample 4 is sputtered, and the sample 4 is etched. On this occasion,
Secondary ions etc. are generated from the sample 4, and the charges carried by the incident ions are absorbed by the sample 4, but the signal voltage shown in Figure 3 (a) is applied to the sample 4. Therefore, the absorbed current signal supplied from the sample 4 to the preamplifier becomes as shown in FIG. 3(b).

This signal from the preamplifier 7 is supplied to the lock-in amplifier 8, but on this day, the twin-in amplifier 8 is supplied with a modulation signal synchronized with the modulation signal from the modulator 5.
The output signal of this lock-in amplifier is as shown by A in FIG.

As the etching of the sample 4 progresses and the etched surface of the sample 4 changes from the first layer 4e to the second layer 4b, the etching depth per unit time increases due to changes in the elements constituting the layer. As etching rate) changes,
The amount of secondary ions etc. ejected from the sample surface changes. The amount of current absorbed by the sample 4 varies slightly from the total ion current incident on the sample. As a result, the detection signal of the lock-in amplifier 8 changes from the value indicated by A to the value indicated by I in FIG. This change is so small that it cannot be detected with the normal amount of current, etc., but if it were to be detected, the detection signal would be as shown by the dotted line in the same figure, but at the boundary between layers, it would not be possible to detect it. Since the output signal of the in-amplifier has the same shape as that obtained by differentiating the detection signal of this ammeter, the layer boundaries can be clearly known from the output signal of the lock-in amplifier 8. Similarly, as the etching progresses further and the layer changes, a differential waveform will appear in the detection signal of the lock-in amplifier 8 and the level of the signal will change each time this change occurs.

Such a signal is supplied to a recorder 9 which is swept at a constant speed and recorded. A measurer observes the signal from such a recorder and determines the time required to etch each layer from the distance between adjacent differential waveforms. On the other hand, the person measuring each layer 4a and 4b.

Standard samples 4At having the same material as 4C, 4d... and known thickness 4B, 4G, 4D... (not shown)
are prepared, each of these standard samples is etched in advance under the same equipment conditions, and the time required for etching the known thickness is measured for each. Using the data regarding this standard sample, the measurer can measure the thickness of each layer of the sample by replacing the data representing the etching time of each layer of the sample obtained from the recorder with the data representing the thickness of each layer. can do.

As is clear from the above description, in the present invention, a slight change in the sample absorption current value due to a change in the etched layer is detected in phase by a lock-in amplifier that uses a modulation signal that modulates the potential of the sample as a reference signal. Since it is detected by wave detection, it is possible to measure the thickness of each layer that makes up the sample without using a large energy analyzer or mass spectrometer.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention, FIG. 2 is a diagram showing a cross section of a sample, and FIG. 3 is an output of each circuit element of the embodiment device shown in FIG. 1. Diagram for showing signals,
FIG. 4 is a diagram for illustrating the output signal of the lock-in amplifier. 1: ion source, 2: focusing lens, 3: objective lens, 4:
Sample, 5: Modulator, 6: Modulation transformer, 7: Preamplifier, 820 twin amplifier, 9: Recorder. Patent applicant JEOL Ltd. Representative Ito-husband X: Ward ~3 ■ Figure 2

Claims (1)

[Claims] an ion beam source, a focusing lens for narrowly focusing and irradiating the ion beam from the ion beam source onto a sample, means for applying a periodic modulation voltage to the sample, and an ion beam absorbed by the sample. a detection means for detecting current; a phase detector for phase-detecting the detection signal detected by the detection means in synchronization with application of the modulation voltage; and displaying an output signal of the phase detector. or recording means.