JPH0410345A - Processing method using focused ion beam - Google Patents

Abstract

PURPOSE:To repeatedly carry out grooving process with an optional pitch by altering voltage to be applied to a deflector which scans ion beam on a specimen. CONSTITUTION:An ion beam optical system consists of a specimen stage 8 on which a specimen 7 is mounted, a highly bright liquid metal ion source 1, a drawing electrode 2 to draw out ion beam of the ion source 1, a first lens electrode 3 and a second lens electrode 5 to focus the drawn ion beam 6, a deflection electrode 4 to scan in a process region of the specimen 7, and a secondary electron detector 9 to detect secondary electrons generated from the specimen 7. The ion beam 6 is focused by the ion beam optical system, scanned on the specimen 7 linearly to carry out sputtering and grooving process repeatedly. At that time, scanning pitch of the ion beam 6 is altered on the specimen 7 by altering the voltage applied to a deflector. As a result, grooving process with an optional pitch can be repeated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a focused ion beam processing method, and is applicable to ultrafine processing of % traps, diffraction gratings in optical integrated circuits, quantum wires in quantum devices, etc. This invention relates to a focused ion beam processing method.

[Conventional technology]

Generally, there are elements such as micro LSIs, optical integrated circuits, quantum wires, etc. that have a repeating groove pattern with a fine pitch. Processing methods for forming such a groove pattern include interference exposure, laser beam lithography, and the like.

Here, as an element having such a repeating groove pattern with a fine pitch, a diffraction grating is provided inside the semiconductor laser, and a laser that oscillates in a single mode due to the wavelength selectivity of the diffraction grating is used.
ibuted Feedbaokbaok: Distributed feedback type) laser, DRB (Distributed B
ragg Refleator: Distributed Bragg reflection type)
Think laser.

FIG. 2 shows a diffraction grating 21 used in a DFB laser.
to guide the wave.

Conventionally, as a method for manufacturing such a diffraction grating 51,
Technical Digest, First International Meeting on Advanced Processing and Characterization, Japan Technologies, Tokyo.

1989 (Japan Society on Applied
Physics and American Vacuum Society) pages 81 to 84 (Teoh-nioal
Digest, First International
onal Meeting onAdvanoed P
rooessing and Charaoteriz
ation Te-chnologiea, Tok
yo, 1989 (Japan 5ooietyyo
fApplied Physios and Amer
ioan Vaouum 5oaiet)')pp81
-84). This is He −Cd
A diffraction grating is manufactured by using a laser, splitting the laser beam into two by a half mirror, converting it into a spherical wave by a lens, and using an exposure method using interference light from three beams of spherical waves.

[Problem to be solved by the invention]

In the above conventional technology, the diffraction grating is patterned using laser beam interference, so the pitch of the diffraction grating is asymmetrical linear distribution (the pitch changes linearly), symmetric quadratic distribution (the pitch changes linearly), etc. ), pseudo-like distribution, etc.

There has been a problem in that it is difficult to manufacture a diffraction grating that is limited to a specific pattern and has an arbitrary pitch.

In addition, the pitch of the diffraction grating is also determined by the oscillation wavelengths H and -C of the laser beam.
d laser, wavelength 525. There was a problem in that it was impossible to manufacture anything with V2 or lower.

The object of the present invention is to provide a fine LS including such a diffraction grating.
When processing fine groove patterns such as I-patterns and quantum wire patterns, it is possible to create grooves with arbitrary pitches.
Moreover, the object is to provide a means for processing at fine pitches.

[Means for solving problem a]

In order to achieve the above objects, the present invention consists of a liquid metal ion source, an ion beam optical system for extracting and focusing the ion beam from the ion source, and a deflector for scanning the ion beam on the sample. This is done using ion beam processing equipment and sputter processing.

In addition, in the case of the present invention, when the pitch of the repeated grooves is fine, in order to prevent processing due to overlapping grooves around the beam diameter of the focused ion beam, a thin film is formed on the upper surface of the sample to be processed.
Sputter processing was performed on the film to form a loop groove, and after processing, the thin film was removed.

The present invention further sets the thickness hl of the thin film formed on the sample to the depth h2. The sputtering rate η1 of the thin film, the sputtering rate η2 of the sample, and the minimum and maximum values of the sum of adjacent ion beam current densities were set.

[Effect]

In a focused ion beam processing device, an ion beam is focused by an ion beam optical system to a depth of several tens of nanometers, and the sample is scanned in a straight line to perform sputter processing.
By changing the voltage applied to the deflector at this time, it is possible to change the scanning pitch of the ion beam on the sample and to process the back grooves at any desired pitch.

In addition, when machining fine pitches, the peripheral parts of the beam diameter overlap, resulting in the wall part of the groove being machined.
Therefore, a thin film is formed on the sample to be processed in advance, sputtering is performed on the thin film, and the thin film is removed after processing. By doing so, the processing by overlapping beams in the peripheral portion of the beam diameter is performed only on the thin film and does not reach the sample to be processed.

In addition, the thickness of the thin film formed on the top surface of the sample to be processed is
It is determined from the fact that the product of ion beam current, processing time, and sputtering rate is proportional to processing method δ. First, the maximum value 14 of the ion beam current density for processing adjacent processing grooves is determined. If the minimum value is 12, the ratio r becomes r=12/11. Also, if the thickness of the thin film formed on the sample is 1, < the depth h2 to be processed for repeat groove processing, and the sputtering rate of the thin film η is a small sample. When the sputtering rate η2 is, the ion beam electric power tItt,
At the maximum value of 1°, the processing time of the thin film is h,
/i, η The processing time for a small sample is proportional to h2/i, η2. On the other hand, when the ion beam current density is at the minimum value of 12, the thin film processing time is proportional to h,/12η, and the sample processing time becomes zero because the sample is not processed. When the current density reaches the maximum value 1. and the total machining time at the minimum value of 12 are equal.

〔Example〕

An embodiment of the present invention will be explained below with reference to FIG.

As shown in FIG. 1, the focused ion beam processing apparatus of this embodiment includes a sample 7, an ion beam optical system, and a t@ controller.

The ion beam optical system includes a sample stage 8 on which the sample 7 is placed.
, a high-intensity liquid metal ion source located above the sample 7 1.
An extraction electrode 2 for extracting ions from the liquid metal ion source 1, and an extraction electrode 2 for extracting ion beams from the liquid metal ion source 1, and an extraction electrode 2 for extracting ion beams from the liquid metal ion source 1, and an extraction electrode 2 for extracting ion beams from the liquid metal ion source 1.
It consists of a lens electrode 3, a second lens electrode 5, a deflection electrode/pole 4 for scanning the processing area of the sample 7, and a secondary electron detector 9 for detecting secondary electrons generated from the sample 7.

The power source/controller includes an extraction power source 10 that applies an extraction voltage to the extraction electrode 2. Acceleration power source for accelerating the extracted ion beam 17. #c-Lens electrode 5, a first lens power supply 11 that applies a lens voltage to the second lens electrode 5, a second lens power supply 15, a deflection voltage amplifier 12 that amplifies the deflection signal and applies a deflection voltage to the deflection electrode 4. , a microcomputer 15 for setting processing conditions, a deflection signal generator 14 for generating a deflection signal matching the processing conditions, and a monitor 16 for displaying the secondary electron signal from the secondary electron detector 8 as a scanning ion microscope image. .

Next, the operation will be explained.

The sample processed by the ion beam is DF shown in Figure 5.
This is a portion of the diffraction grating 21 of the B semiconductor laser. In the semiconductor laser beam shown in FIG. 5, the lower cladding layer 3 is
2. The active layer 23 and the waveguide layer 22 are sequentially formed from the bottom layer by liquid phase epitaxial growth to form a laminated structure as shown in FIG. 4(a), and then as shown in FIG. 4(b). ,
A diffraction grating 21 is formed on the waveguide layer 22 by sputtering using a focused ion beam processing device. Thereafter, as shown in FIG. 5, the upper cladding layer 55 and subsequent layers are formed by liquid phase epitaxial growth, and laterally etched to form stripes so as to leave only the necessary width as the active layer 23. In order to confine the laser stripe, the laser stripe portion is buried by liquid phase epitaxial growth.

Next, the waveguide layer 2 is
2, a method for forming the diffraction grating 21 by sputtering will be described.

As the sample 7, as shown in FIG. 4(a), a substrate 51 with layers up to the waveguide layer 22 is used. In FIG. 1, an extraction voltage of about 10 KV is applied to the extraction electrode 2 by the extraction power supply 10 to extract the ion beam 6 from the liquid metal ion source 1. Here, G is used as the liquid metal ion source. The extracted ion beam 6 is accelerated by an acceleration power source 17 of more than 20 KV, and the first lens power source 11 and the second lens power source 13 accelerate the first lens electrode 3 and the second lens electrode 5 at around 10 KV. A first lens voltage and a second lens voltage are applied to focus on the surface of the sample 7. The beam diameter on the sample surface is 60. It will be about.

The deflection electrode 4 is connected to a deflection voltage amplifier 12 which applies a voltage (X-direction deflection voltage vx is constant, Y-direction deflection voltage v: sawtooth wave) so that the ion beam 6 scans linearly in the Y direction on the surface of the sample 7. Apply by. This produces a diffraction grating. The processing time is determined based on the depth of the grooves of the diffraction grating and the sputtering rate of the processed sample. After the processing is completed, a voltage is applied to the blacking electrode (not shown) to cut the ion beam through the planking aperture. Then, a voltage (Δvx
(d constant) is added to the X-direction deflection voltage vx to obtain (vx+Δv
x) is applied by the deflection voltage amplifier 12, and the blanking electrode (I-OFF) is turned off to start processing again.

By pressing the button ↑ and clicking the button, the waveguide/1i22 can be processed into the diffraction grating 211 as shown in FIG. 4(b)K.

In addition, the position, length, pitch, number % depth of the diffraction grating 21 to be processed are inputted in advance to the microcomputer 15. deflection voltage vx
1 Pitch voltage Δv, 1 Calculate. Also, calculate the processing time t + it from the depth of the grooves of the diffraction grating and the sputtering rate of the sample,
The end point of machining is detected from the number of pieces.

In addition, in order to process a diffraction grating with an arbitrary pitch, the pitch value or bust formula is input into the microcomputer 15 in advance, and the pitch is changed each time the process is performed.

By the way, when performing processing by sputtering in this way, the processing depth is 8tri, which is considered to be proportional to the current density distribution of the ion beam. Generally, the ion beam current density distribution is assumed to be a Kawass distribution as shown in FIG. 5(a), and the full width at half maximum (FWHM) d is 1/2 of the maximum value. 50
is called the beam diameter. Therefore, as shown in Figure 5(a), the beam diameter d at which the current density reaches the maximum value of 10 cm,
is 1.82 do, and it is thought that approximately 10% of this part is processed. In this case, beam diameter qdo=
Since it is 60 nm, even if d:1109n, if the center processing depth is 1100n, 10nru processing will be required.

By the way, when the ion beam klI is scanned in contact with the ion beam, the machining depth of the sample is considered to be proportional to the sum of the current density distributions of adjacent ion beams. In this case, if the pitch of adjacently scanning ion beams is d2, as d2 becomes smaller, the amount of processing becomes larger when the current density distributions overlap. However, as shown in sg5 diagram (b), d2
==130 nm, the sum of the current density distribution is 12 /i+ = [10, where the maximum value is 14 and the minimum value is 12
8, when the center is machined to a depth of -g 1100n, the periphery is machined to a depth of 8nrn, and the processing depth at the periphery is small until about d2=120nm.

Next, a second embodiment of the present invention will be explained with reference to FIG.

The focused ion beam processing vcIf in this embodiment is the same as that in the first embodiment. Further, as in the first embodiment, the sample 7 to be processed also has a lower cladding layer 52, a substrate 31,
The active layer 23 and the waveguide layer 22 are formed by liquid phase epitaxial growth in order from the bottom layer (the top two layers are shown in FIG. 5(a)). When sputtering the diffraction grating 21 on the 22,? ! The difference is that, as shown in FIG. 45(b), a time-saving film 41 is formed on the waveguide layer 22.

By the way, generally, as shown in Fig. 1, the pitch △ of the diffraction grating 21 of the DFBλ laser is △=m−n (where λ: oscillation wavelength, n: refractive index, 9m: order), and the pitch △ of the first-order diffraction grating 21 is The pitch is G, A, 130 nm.

Therefore, when sputtering a G, A, first order diffraction grating using the focused ion beam processing apparatus shown in FIG. Processing is possible without machining the convex portion.

However, if the beam diameter and beam position of the ion beam change for some reason, the beam diameters overlap as shown in Figure 7 (a), and the convexity of the diffraction grating as shown in Figure 7 (b) K. parts are processed.

Further, when the pitch of the diffraction grating requires processing smaller than 1+Onm, processing as shown in FIG. 7(b) is performed.

Here, we will discuss the case where the pitch is son.

In this case, since the sum of the current densities of adjacent ion beams is a2=sonm, as shown in FIG. 5(c),
If the maximum value of beam diameters with large overlaps is 11 and the minimum value is 12, then 12/i = 158.With the overlap of beams as shown in Fig. 7(a), Figure 7 (
b) As shown in K, the convex portion of the diffraction grating is processed.

When performing such fine processing, in this embodiment, a temporary maintenance film 41 is formed on the waveguide layer 22, as shown in FIG. 6(b). The thickness of the - protection film 41 is determined from the sputtering rate of the material of the - protection film 41 by the ion beam and the ratio of the sputtering rate of the waveguide layer 22 to the current density, 12/i.

- The thickness h of the protective film 41 is the machining depth of the diffraction grating 8 h.
When the sputtering rate η of the protective film 41 is 2% and the sputtering rate η2% of the waveguide layer 22 is the current density ratio r=i2/11η1r, it can be determined as h, ≧π7h2.

Using this, when the sputtering rates of the materials of the protective film 41 and the waveguide layer 22 are approximately the same, the depth of the diffraction grating of the waveguide layer 220 is set to 1100 nm.

From the current density ratio i2/1, the thickness of the protective film 41 is 15 when -
0 nm (however, a minimum of 138 nm is required).

Moreover, when the sputtering rate of the material of the protective film 41 is -, the sputtering rate of the material of the protective film 41 is
If you adopt something as small as 1/2 of 2.

The thickness of the time protection S film 41 is 7 nm.

- After the protective film 41 is formed, grooves are formed as shown in FIG. 6(b).The processing procedure is the same as in the first embodiment. However, since the processing involves two layers, the temporary protection film 41 and the waveguide layer 22, it is necessary to increase the processing time.

The processing depth by the ion beam is proportional to the sputtering rate and the current density by the ion beam. Therefore, as shown in FIG.
When 100n is processed, in the part corresponding to 1/2 pitch of the diffraction grating, -Tokiho ii! The membrane 41 is processed,
The waveguide layer 220 portion remains unprocessed. However, in general, in sputter processing using an ion beam, the sputtering rate is dependent on the incident angle of the ion beam, and the central portion of the ion beam tends to be processed deeply at an acute angle. Therefore, the thickness of the - protection film 41 can be made smaller than in the case described above.

After processing, a shape as shown in FIG. 6(d) is obtained.

Next, as shown in FIG. 6(e), the protective film 41 is selectively removed from the waveguide layer 221C, and a fine diffraction grating 21 is obtained.

The temporary retention film 41 is made of, for example, a highly heat-resistant polyimide resin, and the method of forming the retention #I film 41 is coating with a spinner, and the removal of the temporary retention film 41 during processing is by dissolving with an organic solvent or 02 Performed by plasma heating,
In addition, even if it is a metal, if the material has a low sputtering rate and can be etched selectively to the waveguide layer 22, the protective film 41 is formed by sputter deposition or the like, and after processing with an ion beam, it is etched by RIE. (Reactive ion etching) By wet etching, the time-retaining film 4
1 is removable.

Incidentally, in this embodiment and the first embodiment, there is a possibility that crystal lattice defects may occur due to incident ions at the location where sputtering is performed using an ion beam. In this case, there is a method of removing the damaged portion by annealing by heat treatment or etching. In the first embodiment, as shown in FIG. 8(a), the portion damaged by etching is removed by making the waveguide layer 22 thicker before processing with an ion beam, and after processing, the waveguide layer 22 is thickened. The removed portion 51 is removed by etching the entire surface. In addition, in the second embodiment, as shown in Section 8 (b), after processing with the ion beam, -Jibo #! etching the removed part 51 before removing the gland 41, or
1 and removed portion 51 (i--removed by etching at the same time.

Although the diffraction grating has been described above, the present invention also provides a fine LS
It is clear that the present invention can also be applied to processing I patterns, wrinkled thin line patterns, and other repeating groove patterns.

〔Effect of the invention〕

According to the present invention, since grooves are repeatedly formed by sputtering using a focused ion beam processing device, processing at an arbitrary pitch can be performed.

Also, when the pitch of repeated groove machining is fine.

Since sputtering is performed after forming a thin film on the upper surface of the sample to be processed, fine processing can be performed without being affected by the beam diameter I#.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a focused ion beam processing device that is an embodiment of the present invention, Fig. 2 is a perspective view of a diffraction grating, and Fig. 5 is a perspective view of a semiconductor laser to be processed in an embodiment of the present invention. 4 is an explanatory diagram of the processing method according to one embodiment of the present invention, FIG. 5 is an explanatory diagram showing the ion beam current density of one embodiment of the present invention and the second embodiment, and FIG. An explanatory diagram showing the processing method of the second embodiment of the invention, FIG. 7 is an explanatory diagram showing the processing state of the second embodiment of the invention without the temporary protective film, and FIG. FIG. 6 is an explanatory diagram showing a method of etching the damaged portion of the first and second embodiments.

Claims (1)

[Scope of Claims] 1. A focused ion beam processing device consisting of an ion source, an ion beam optical system that extracts and focuses an ion beam from the ion source, and a deflection system that scans the ion beam on a sample. A focused ion beam processing method, characterized in that the ion beam is scanned and sputtered on the sample at an arbitrary pitch by changing an applied voltage, thereby repeatedly forming grooves at an arbitrary pitch. 2. In claim 1, when performing sputter processing by scanning the ion beam over the sample, a protective film is temporarily formed on the sample surface, and after the formation of the protective film, scanning is performed at an arbitrary fine pitch. A focused ion beam processing method in which the protective film is temporarily removed after processing to perform repeated groove processing at an arbitrary fine pitch. 3. In claim 2, the thickness of the temporary protective film formed on the sample surface is determined by the processing depth h of the repeated groove processing, the sputtering rate η_1 of the temporary protective film, the sputtering rate η_2 of the sample, and the thickness of the adjacent ion beam. A focused ion beam processing method in which the ratio of the minimum value and the maximum value of the sum of current densities is η_1/η_2(r/1−r)h or more.