JP3397390B2 - Processing method using focused ion beam - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focused ion beam processing method for scanning a material to be processed by scanning the material to be processed with a finely focused ion beam.

[0002]

2. Description of the Related Art In the processing using a focused ion beam, an ion beam from an ion source is finely focused on a material to be processed by a focusing lens, and the ion beam is two-dimensionally scanned stepwise at a processing portion. At this time, when performing ion beam irradiation by deflecting and scanning the ion beam, the step feed frequency (processing frequency) and the number of scan repetitions (frame number) that give the desired dose amount are determined, and the step at this frequency is determined. By performing the deflection scanning (frame scanning) by the operation repeatedly, the processing by the ion beam is performed. Usually, this processing frequency is fixed, and it is rarely set off-line and discontinuously.

[0003]

Various kinds of processing can be performed by using the focused ion beam device described above, but there are difficult problems depending on the type of processing. For example, it is necessary to use a certain specific material and perform three-dimensional molding of a certain shape in that material. For example, when processing for micromachines, adjustment of rotation and inclination of the material to be processed, specific scanning signal There are many problems in the occurrence of noise and current modulation. There are numerous technical difficulties in solving these problems, and even if these problems are overcome, the conventional focused ion beam processing apparatus does not allow precise processing of free-form surfaces. It is considered impossible to do.

The present invention has been made in view of the above circumstances, and an object thereof is to realize a processing method using a focused ion beam capable of precisely processing a free curved surface of a material to be processed.

[0005]

According to a first aspect of the present invention, there is provided a focused ion beam processing method, wherein an ion beam is finely focused on a material to be processed, and the ion beam is repeatedly scanned in a processing area on the material. In the ion beam processing method for processing the surface of a material, when the step feed frequency (processing frequency) of the ion beam is modulated according to the irradiation position of the ion beam ,
If the frequency is below a certain value, the etching rate will increase
It is characterized in that for performing modulation based on the relationship of the change processing frequency and the etching rate. In the method for processing with a focused ion beam according to the second aspect of the invention, the surface of the material is processed by finely focusing the ion beam on the material to be processed and repeatedly scanning the ion beam in the processing area on the material. In the ion beam processing method, when the step feed frequency (processing frequency) of the ion beam is modulated according to the irradiation position of the ion beam,
The composition of the material of the ion beam irradiation area is determined , and the processing frequency determined in advance according to this composition is below a certain value.
It is characterized in that for performing modulation based on the relationship of the working frequency and the etching rate of each workpiece material etching rate becomes below greatly changes.

[0006]

First, the processing frequency will be described by taking rectangular etching processing with an ion beam as an example. The processing frequency f in the focused ion beam device is the reciprocal of the time (1 / f) for irradiating a point on the material to be processed with the ion beam, and defines the scanning speed of the ion beam during processing. Now, the processing of the processing width x and the depth y is performed in this processing area (x
Xy) It is assumed that irradiation with a focused spot ion beam is performed on the whole at intervals of s. In this case, the time t _f irradiation is performed once ion beam machining entire region ₍₁ frame processing time) is expressed as follows.

T _f = x · y / (s ² · f) It is assumed that the ion beam irradiation of this one frame has processed to the depth d. When the number of repetitions of frame irradiation is n, the total processing time t _T and the processing depth D are as follows.

D = nd t _T = nt _{f The} etching rate ε can be experimentally obtained from the above equation.

Ε = x · y · D / (t _T · Ip) In the above equation, Ip is the probe current of the ion beam. As is well known, the etching rate ε is experimentally a function of the material M to be processed, and the dependence on the probe current is small in a certain current density range. Therefore, when processing a certain substance, in the case of the focused ion beam apparatus up to now, the processing frequency f is fixed to a certain value in consideration of a constant ε, and the probe current I which is another processing parameter is fixed.
p, the number of repeated scans n, the processing time t _{f for} one frame, etc. were selected appropriately.

In the present invention, the machining frequency f is a function f = f (x, y) of the machining position (x, y), and this value is modulated online during machining and given to the machining position (x, y). A free-form surface can be drawn on the material surface by changing the dose amount.

That is, I want to process in a computer
Enter the data of the etching rate of the material. Next
You can use the terminal to input the formula or numerical value of the three-dimensional surface you want to process.
Do it. Each point about the processing area with a computer etc.
Processing frequency to give a dose equivalent tof
(X, y) and the number of frames n
Let's calculate using values such as Great and probe current,
This is output and the beam irradiation corresponding to each point is performed.
By applying the firing time (processing frequency), the processing speed can be
Have each point defined. This is the frame number n
By repeating the process, free-form three-dimensional molding processing is possible.
It becomes Noh. Then how to calculate f (x, y)
Will be described in more detail using a simple example.

Here, as shown in FIG. 1, a free curve which can be expressed by the function z = Z (x, y) <0 is given to the material M as follows.
With current Ip and frame number n, f (x,
The value of y) is shown by approximate calculation. The origin of z in this coordinate system is the surface of the material before processing. Further, here, for simplification of calculation, it is assumed that the beam current is evenly distributed only within the square of s ² as the irradiation interval s of the spot beam. Further, assuming that the etching rate ε is ε ₀ irrespective of the frequency, the processing depth D can be expressed as follows by the above equation.

D = ε ₀ · Ip · n / [s ² · f (x, y)] As a result, the following equation holds. Z (x, y) = − ε ₀ · Ip · n / [s ² · f (x,
y)] Therefore, f (x, y) is as follows.

[0014]       f (x, y) = − ε₀・ Ip ・ n / [s^Two・ Z (x, y)] (1) The above calculation shows that the etching rate depends on the processing frequency.
That is the case. Theoretically, the etching rate
Is the mass number of ions, acceleration energy, current density, material
Material (chemical composition, chemical bond energy, etc.) and temperature
It is thought that it depends on which one. Here ionic
Fix the beam condition and material, and set the etching rate and material.
Consider the relationship with temperature. Etch by raising the material temperature
Is increased due to the decrease in binding energy
Because it is considered, the total processing time t _TConstant,
Experiments on the machining frequency dependence of the etching rate ε
Performed in a wide frequency range. If the processing frequency is low,
When the machining frequency is high, the local temperature reached at the work point is
Because it is thought that it can be made higher than
It The result is shown in FIG.

As is apparent from FIG. 2, the etching rate shows a large frequency dependence when the processing frequency is below a certain value. This shows that the etching rate ε, which has been treated as a substantially constant value depending on the substance, can be changed in a fairly wide range.
Now, the processing frequency dependence of the etching rate ε is ε (f)
When expressed by, the formula (1) can be expressed as follows.

F (x, y) = − ε (f) · Ip · n / [s ² · Z (x, y)] (2) Here, ε for various substances in the computer system
The data of (f) is stored in advance, and for example, the value of ε at f = 1 kHz, ε (1 kHz), is substituted into the above equation (2) to generate a f ₁ (x, y) table of the primary f. create. Next, the value of ε (f ₁ ) is obtained from the stored data based on the first-order f ₁ obtained for each point (x, y), and f is obtained.
= F ₂ is recalculated. This calculation is repeated for each point until the following relation holds.

| F _n (x, y) −f _n−1 (x, y) | ≦ δ (3) By performing such calculation processing, optimum processing using the processing frequency dependence of the etching rate is performed. The frequency can be calculated. As a result, it becomes possible to perform machining with higher efficiency and accuracy using the formula (1).

[0018]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 3 shows an example of an ion beam processing apparatus for carrying out the present invention, and 1 is an ion gun.
The ion beam IB generated from the ion gun 1 and accelerated is
The focusing lens 2 and the objective lens 3 finely focus the light on the material 4 to be processed. Further, the ion beam is deflected by the deflector 5. The ion gun 1 is controlled by an ion gun control circuit 6, and the focusing lens 2 and the objective lens 3 are controlled in lens strength by a lens control circuit 7.
The gun control circuit 6 and the lens control circuit 7 is connected to the probe current setting circuit 8.

A scanning signal is supplied to the deflector 5 from the deflection control circuit 9, and the deflection control circuit 9 includes a frame number setting circuit 10, a processing area setting circuit 11, a processing frequency setting circuit 12, and the like. ing. This frame number setting circuit 1
0, processing area setting circuit 11, processing frequency setting circuit 12,
The probe current setting circuit 8 includes a computer system 13
It is configured to be controlled by the control computer 14 therein. An arithmetic circuit 15 is provided in the computer system 13, and the arithmetic circuit 15 performs an arithmetic operation based on the data from the input terminal 16 and stores the value in the memory 17. The operation of such a configuration will be described below.

In processing the material to be processed 4, the ion beam from the ion source 1 is finely focused on the material 4 by the focusing lens 2 and the objective lens 3, and the ion beam is deflected by the deflector 5.
By scanning with an ion beam over the material 4. Here, the probe current value of the ion beam IB with which the material 4 is irradiated is set in the probe current setting circuit 8. The probe current setting circuit 8 controls the ion control circuit 6 to adjust the extraction voltage of the ions in the ion gun 1 according to the set probe current value, and controls the lens control circuit 7 to control each lens. The intensity is adjusted so that the material 4 is irradiated with the ion beam having the desired current value Ip. The number of frames n is set in the number-of-frames setting circuit 10, and the processing area (x, y) is set in the processing area setting circuit 11.

Here, the data of the etching rate of the material 4 to be processed is inputted into the computer 14 in advance. Next, with respect to the material to be processed 4, an expression or a numerical value of a three-dimensional surface to be processed is input from the input terminal 16. The arithmetic circuit 15 in the computer system 13 calculates the equation (2) and the equation (3) based on each input numerical value.
Is calculated for each point in the processing area. Then, the calculation result is stored in the memory 17.

Now, at the time of actual processing, the computer 1
4 is a memory 1 for each machining point in the machining area (x, y)
The processing frequency setting circuit 1 in the deflection control circuit 9 reads out the data of each processing frequency f (x, y) stored in
Transfer within 2. The deflection control circuit 9 supplies the deflector 5 with a deflection signal according to the set number of frames, the processing area, and the processing frequency. As a result, in the material portion to be processed deeper, the processing frequency is lowered, and the ion beam stays in one place for a relatively long time, so that the surface of the material 4 to be processed is processed into a desired curved surface.

FIG. 4 shows another embodiment of the present invention.
In this embodiment, a detector 20 is provided in addition to the embodiment of FIG. The detector 20 detects secondary electrons, X-rays, secondary ions, etc. generated based on the irradiation of the material 4 with an ion beam. The output signal of the detector 20 is an image data processing circuit 21. Is supplied to. The image data processing circuit 21 determines the composition of the material portion irradiated with the ion beam, and the determined composition information is supplied to and stored in the memory 22 in the computer system 13.

Now, with regard to two types of processing, that is, non-selective etching and selective etching, when two compositions A and B are locally present in the processing region of the material to be processed 4 with such a configuration. explain. The frequency dependence of the etching rates of the substances A and B is shown in FIG.

In the case of non-selective etching, the image data processing circuit 21 determines the composition of the substance in the portion irradiated with the ion beam based on the detection signal from the detector 20. When the composition of the material portion being processed is A, the computer 13 sets the processing frequency to the processing frequency a in FIG. 5 and sets the value in the processing frequency setting circuit 12. as a result,
The material is processed at an etching rate ε ₁ .

Next, when the composition of the material portion being processed is B, the computer 13 sets the processing frequency to the processing frequency b in FIG. 5, and sets the value in the processing frequency setting circuit 12. As a result, the material is processed at the etching rate ε ₁ . Therefore, non-selective etching, that is, processing is always performed at the same processing speed regardless of the material to be processed.
As a result, the irregularities on the side surface and the bottom surface, which are problems in the ordinary focused ion beam processing apparatus, are suppressed to a minimum, and the optimum processing is performed for micromachines that require accurate processing accuracy.

Next, selective etching will be described. Until now, selective etching has been performed using a corrosive gas or the like. In many cases, corrosive gas is toxic, and it imposes a burden on the device itself, so that maintenance of the device, protection of the device, and the like have become major problems. In the example of FIG.
When the composition of the part irradiated with the ion beam is A,
The processing frequency a'in FIG. 5 is selected. Further, when the composition of the portion irradiated with the ion beam is B, the processing frequency b ′ in FIG. 5 is selected. As is apparent from FIG. 5, the etching rate ε when the processing frequency is a '
₂ and the etching rate ε _{3 at} the processing frequency b ′ greatly differ in value. As a result, the composition is A and B
It becomes possible to carry out selective etching with the portion. This selective etching is effective for removing a specific film of the multilayer film.

[0028]

As described above, according to the focused ion beam processing method of the present invention, the ion beam is finely focused on the material to be processed, and the ion beam is repeatedly scanned in the processing area on the material to make the material. in the ion beam processing method for performing surface treatment of, when performing modulation in accordance stepwise feed frequency of the ion beam (processing frequency) the irradiation position of the ion beam, obtained in advance, the processing frequency
If the value is below a certain value, the etching rate will change significantly.
Since that was so processed frequency and on the basis of the relationship of etching rates performing modulation can be performed precisely machining free-form surface of the work piece. In addition, the composition of the material of the ion beam irradiation portion is determined, and etching is performed when the processing frequency, which has been determined in advance according to this composition, falls below a certain value.
Since rate is to perform the modulation on the basis of the relationship between processing frequencies and the etching rate of each workpiece material varies greatly, it is possible to arbitrarily perform selective etching or non-selective etching.

[Brief description of drawings]

FIG. 1 is a diagram showing a free curve to be processed.

FIG. 2 is a diagram showing a relationship between an etching rate and a processing frequency.

FIG. 3 is a diagram showing an example of an ion beam processing apparatus for carrying out the present invention.

FIG. 4 is a diagram showing another example of an ion beam processing apparatus for carrying out the present invention.

FIG. 5 is a diagram showing a relationship between an etching rate and a processing frequency.

[Explanation of symbols]

1 ion gun 2 Focusing lens 3 Objective lens 4 Material to be processed 5 deflector 6 Ion gun control circuit 7 Lens control circuit 8 Probe current setting circuit 9 Deflection control circuit 13 Computer system 16 Input terminal 17 memory

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Claims (2)

(57) [Claims] 1. An ion beam processing method in which an ion beam is finely focused on a material to be processed, and the surface of the material is processed by repeatedly scanning the ion beam in a processing region on the material. When the (machining frequency) is modulated according to the irradiation position of the ion beam, it etches when the machining frequency, which was previously obtained, is below a certain value.
Working method by focused ion beam and performing modulation on the basis of the relationship between processing frequencies and etching rate Great changes greatly. 2. An ion beam processing method in which an ion beam is narrowly focused on a material to be processed, and the surface of the material is processed by repeatedly scanning the ion beam in a processing region on the material. When the (machining frequency) is modulated according to the irradiation position of the ion beam, the composition of the material of the irradiation part of the ion beam is determined, and according to this composition , the processing frequency, which was obtained in advance , falls below a certain value. Na
That the working method by focused ion beam and performing modulation on the basis of the relationship between processing frequencies and the etching rate of each workpiece material etching rate varies greatly.