JPH07256473A - Multistage etching method for solid object utilizing photodecomposition - Google Patents

Abstract

PURPOSE:To increase a processing speed of etching and to simplify a processing stage by irradiating an etching object with light of the size to generate photodecomposition by cutting intermolecular bonds by one photon dissociation or multiphoton dissociation. CONSTITUTION:The surface of a quartz glass substrate 10 which is the etching object is subjected to preliminary irradiation to irradiate the surface with 100 pulses of a laser beam A of, for example, wavelength 160nm at laser fluence of 200mJ/cm<2> which is irradiation energy as a first stage. The Si-O bonds of a preliminary irradiation region 12 are cut and SiO2 is formed. The preirradiated region 11 of the quartz glass substrate 10 is irradiated with 10 pulses of a laser beam B of, for example, wavelength 266nm at laser fluence of 2J/cm<2> as a second stage. As a result, only the preirradiated region 12 is selectively abraded and an abrasion region 14 is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-step etching method for solids using photolysis, and more particularly to a multi-step etching method for solids using photolysis by one-photon dissociation or multiphoton dissociation.

[0002]

2. Description of the Related Art Conventionally, a substance having an absorption edge of light at a wavelength shorter than ultraviolet has a strong binding energy between constituent atoms.
It is known that processing such as etching is difficult.

For example, quartz glass has a light absorption edge of 17
Since it is around 0 nm and the binding energy is about 8 eV, the conventional etching method using laser light, ion beam light or plasma has a problem that the etching processing speed is slow.

That is, it is possible to obtain light having a large irradiation energy in vacuum ultraviolet having a wavelength of 190 nm or less (in the case of laser light, a laser light having a large laser fluence).
At present, it is extremely difficult to perform etching processing such as laser ablation on a material having a high binding energy at a high speed without damaging the material.

For example, existing ultraviolet lasers (excimer
Ablation also occurs with lasers and Nd: YAG laser fourth harmonics, but since there is almost no absorption in the substrate, a large laser fluence is required, which causes thermal processing to dominate, resulting in significant damage to the processed part. There is a problem such as giving.

Further, when a fine pattern is processed by using an ion beam or plasma, it is necessary to provide a resist by a photolithography process, so that the processing process becomes complicated and the work becomes complicated. The point was pointed out.

On the other hand, in order to perform processing at high speed, wet etching using hydrofluoric acid is generally performed. In this case as well, however, it is necessary to provide a resist by a photolithography process. It has been pointed out that the working process becomes complicated and the work becomes complicated similarly to the above, and undercutting due to isotropic etching has been a problem especially in the case of fine processing.

The present invention has been made in view of the above-mentioned various problems of the prior art, and an object of the present invention is to increase the processing speed of etching, fine pattern processing and wet processing. -An object of the present invention is to provide a solid multi-step etching method utilizing photolysis, which eliminates the need to provide a resist during etching, simplifies the processing step, has low damage, and improves workability.

[0009]

In order to achieve the above object, the method of multi-step etching of solids utilizing photolysis according to the present invention has a large absorption for an object to be etched and an irradiation energy of at least 1. The first step of irradiating with light having a size that breaks the interatomic bond by photon dissociation or multiphoton dissociation, and causes photolysis without causing thermal damage, and at least the first of the above-mentioned object. The second step of etching the region irradiated with light in the step.

[0010]

[Function] Light having a short wavelength, that is, light having a large photon energy (short wavelength light), or light having a short pulse width, that is, light having a large peak power intensity (ultra-short pulse light) is first applied to the solid surface. (Hereinafter, this light irradiation is referred to as “pre-irradiation”), and the bonds between atoms in the solid are broken by the one-photon dissociation or the multi-photon dissociation by the preliminary irradiation. As a result, the light absorption edge of the pre-irradiated region shifts to the long wavelength side, and the pre-irradiated region can be selectively and rapidly etched by the etching process.

For example, when pre-irradiating an object, pre-irradiation for reducing and projecting light onto a solid surface as an object through a mask is performed, and only a region pre-irradiated through the mask is one-photon dissociated. Alternatively, it is possible to perform fine patterning by etching only the pre-irradiated region without providing a resist by the photolithography process, which is modified by cutting the bonds of atoms in the solid by multiphoton dissociation. Become.

That is, when laser ablation is used as an etching means after the pre-irradiation, the pre-irradiation shifts the light absorption edge of the object to the long wavelength side, so that the pre-irradiation has almost no absorption. However, if the laser light having strong absorption is irradiated after the preliminary irradiation, the energy of the laser light is absorbed only in the pre-irradiated area, and only the pre-irradiated area can be selectively and without a resist. It can be etched at high speed.

On the other hand, when wet etching is used as the etching means after the pre-irradiation, the etching rate of the region where the interatomic bond is broken by the pre-irradiation is the same as the etching rate of the region where the pre-irradiation is not performed. By comparison, the speed is much faster, so that the etching of fine patterning can be performed without providing a resist by the photolithography process by utilizing the difference in etching rate between the pre-irradiated area and the non-pre-irradiated area. it can.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a solid multi-stage etching method utilizing photolysis according to the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a method of multi-step etching of solids using photolysis according to an embodiment of the present invention, in which laser ablation is performed after pre-irradiation.

In this embodiment, first, as a first step, the quartz glass substrate 10 (Si
O ₂ : the light absorption edge of the quartz glass substrate 10 in this example is about 170 nm), and a wavelength of 160 nm
Pre-irradiation is performed by irradiating 100 pulses of the laser light A of No. ² with a laser fluence of 200 mJ / cm ² as irradiation energy (FIG. 1A).

The diameter of the spot size of the laser beam A on the surface of the quartz glass substrate 10 is about 200 μm.
mφ.

In this way, when the surface of the quartz glass substrate 10 is pre-irradiated with the laser light A, the Si--O bond in the pre-irradiated region 12 is broken, and SiO _x (x <x
2) will be formed (FIG.1 (b)).

Next, as a second step, the quartz glass substrate 1
Laser ablation is performed as an etching process performed on the 0 surface. That is, the laser beam B having a wavelength of 266 nm is formed on the preliminary irradiation region 12 of the quartz glass substrate 10.
Is irradiated with 10 pulses of laser fluence at ² J / cm ² (FIG. 1 (c)).

The diameter of the spot size of the laser beam B on the surface of the quartz glass substrate 10 is about 1 mmφ.
Is.

Thus, the laser beam B in the second step
As a result of this irradiation, only the pre-irradiation region 12 is selectively ablated, and the ablation region 14 is formed (FIG. 1D).

The threshold value of the laser fluence when the laser ablation is performed on the quartz glass substrate 10 only with the laser beam having the wavelength of 266 nm is about 2.
It is 1 J / cm ² , and ablation does not occur below this value.

However, after the preliminary irradiation, the ablation occurs as described above even when the laser beam having the wavelength of 266 nm is irradiated with the laser fluence of ² J / cm ^{2 which} is lower than the above threshold value. .

FIGS. 2 to 4 show the processed shape of the quartz glass substrate 10 which has been subjected to the etching process by the steps described with reference to FIGS. 1 (a) to 1 (d). That is, FIGS. 2 to 4 are shown in FIGS.
3 is an enlarged view of the processed state of the surface of the quartz glass substrate 10 shown in FIG. 3, in which the vertical axis represents the etching depth and the horizontal axis represents the etching width.

FIG. 2 shows the quartz glass substrate 10 immediately after the preliminary irradiation with the laser light A having a wavelength of 160 nm in the first step.
However, there is no ablation and no change in shape is observed.

For comparison, FIG. 3 shows the quartz glass substrate 10 in the case where only the laser beam B having a wavelength of 266 nm in the second step is irradiated without performing the preliminary irradiation in the first step.
However, in this case also, no ablation occurs and no change in shape is observed.

Then, in FIG. 4, the wavelength 160 of the first step is shown.
The state of the quartz glass substrate 10 when the laser beam B having a wavelength of 266 nm in the second step is irradiated after the preliminary irradiation with the laser beam A having a wavelength of 0.1 nm is shown, and unlike FIG. 2 and FIG. Has occurred, depth of about 40
A groove of μm is formed.

The etching rate in the second step at this time is 0.4 μm / s, which is extremely high as compared with the conventional etching method. Further, as described above, the spot size diameter of the laser light A on the surface of the quartz glass substrate 10 in the preliminary irradiation is about 200 μmφ, and the spot size of the laser light B on the surface of the quartz glass substrate 10 in the laser ablation is smaller than the spot size. The diameter was about 1 mmφ, whereas the diameter of the ablation in FIG. 4 was about 200 μmφ, and it was confirmed that only the preliminary irradiation region was ablated.

Thus, by performing the laser ablation of the second step after the preliminary irradiation, effective ablation can be performed.

Further, FIG. 5 shows the result of performing the processing of the first step and the second step by changing only the wavelength of the laser beam used for the preliminary irradiation in the above-mentioned embodiment.

As is clear from FIG. 5, no ablation occurs in pre-irradiation of any wavelength by pre-irradiation alone.

However, as described above, the wavelength 160
wavelength of 2nd step after pre-irradiation with laser light of nm
When irradiated with a 66 nm laser beam, the wavelength is 171n
m of laser light is pre-irradiated and then the wavelength of the second step is set to 26
Ablation occurred on the quartz glass substrate 10 when the laser light of 6 nm was irradiated.

Therefore, from the above,
In the process, it can be seen that preliminary irradiation with laser light having a wavelength component of 171 nm or less is effective. Since this wavelength of 171 nm substantially coincides with about 170 nm, which is the wavelength at the light absorption edge of the quartz glass substrate 10,
By pre-irradiating the object to be etched with light having large absorption, photodissociation that breaks interatomic bonds can be generated in the pre-irradiated region, and as a result, high-speed etching is performed in the second step. . Hereinafter, this point will be described in detail.

FIGS. 6 to 7 show the bonding states of atoms in the pre-irradiated region pre-irradiated in the first step shown in FIG.
The results evaluated by line photoelectron spectroscopy (XPS) are shown.

FIG. 6 relates to the Si-2p orbital. The Si-2p orbital spectrum of the quartz glass substrate 10 pre-irradiated in the first step shown in FIG. 1 shows the Si-2p orbital spectrum of the quartz glass substrate 10 not pre-irradiated. Compared with the Si-2p orbital spectrum, the peak is shifted to the low energy side of 0.2 eV to 0.3 eV.

Here, it is generally known that in oxides, the binding energy decreases as the oxidation number decreases, and the peak shifts to the low energy side. Therefore, the shift of the peak to the low energy side in FIG. 6 is that the O of SiO ₂ is photodissociated by the preliminary irradiation,
That is, the Si—O bond is broken, resulting in SiO _x (x <2)
Is generated.

Although FIG. 7 relates to the O-1s orbit, it is 5 in the O-1s orbit spectrum of the quartz glass substrate 10 pre-irradiated in the first step shown in FIG.
In addition to the peak near 35 eV, 531 eV to 532 e
Another peak is observed near V. This 531e
The binding energy near V to 532 eV almost coincides with the spectrum of energy from a simple oxygen atom having no bond, and the Si—O bond is cut by preliminary irradiation to generate an oxygen atom, and SiO _x ( x <
2) is generated.

As described above, in the above embodiment,
Due to the preliminary irradiation in the first step, S in the quartz glass substrate 10
The i-O bond is broken and SiO _x (x <2) is generated. Then, this SiO _x (x <2) has a large absorption for light with a wavelength of 266 nm. For example, S
The absorption coefficient of iO is 3 × 10 for a wavelength of 240 nm.
It is about ⁵ cm ^{−1 and} about 1.7 × 10 ⁵ cm ⁻¹ for a wavelength of 300 nm.

Therefore, SiO _x (x <2) is generated in the region pre-irradiated in the first step and has a large absorption for the light of the wavelength of 266 nm. As a result, the second step causes When light with a wavelength of 266 nm is irradiated, light energy is accumulated in SiO _x (x <2) for the light irradiation, and ablation occurs.

Then, for example, in the above-described embodiment, when the preliminary irradiation for reducing projection exposure of the laser beam through the mask on the surface of the quartz glass substrate 10 in the first step, only the area pre-irradiated through the mask is 1 Atoms in the solid are cut and modified by photon dissociation or multiphoton dissociation, and only the pre-irradiated area is etched by the second step in the second step for fine patterning without providing a resist by the photolithography step. You will be able to do it.

The above embodiment may be modified as follows.

(1) Numerical values such as wavelength, pulse width, laser fluence, and pulse number of the laser beam for pre-irradiation in the first step and the laser beam for laser ablation in the second step depend on the object to be etched. Of course, it may be changed appropriately.

(2) In the above embodiment, the case where a quartz glass substrate having a light absorption edge having a wavelength shorter than ultraviolet is etched has been described. However, other light absorption edges having a wavelength shorter than ultraviolet are used. Of course, it may be used when etching a material or a material whose light absorption edge is longer than ultraviolet light.

(3) In the above embodiment, the case of performing laser ablation as the second step has been described, but wet etching may be performed.

When wet etching is performed as the second step, the etching rate of the region where the interatomic bonds are broken by the preliminary irradiation is significantly higher than the etching rate of the region where the preliminary irradiation is not performed. Because of the high speed, the etching of fine patterning can be performed without providing a resist by the photolithography process by utilizing the difference in etching rate between the pre-irradiated region and the region not pre-irradiated.

(4) In the above embodiment, the preliminary irradiation in the first step was performed only with the laser beam having the wavelength of 160 nm, and the laser ablation in the second step was performed only with the laser beam having the wavelength of 266 nm. Pre-irradiation with laser light of a plurality of wavelengths in one step, or laser ablation with laser light of a plurality of wavelengths in the second step, respectively. The first step and the second step may be combined.

As described above, if the preliminary irradiation of the first step is performed by irradiation with a plurality of laser beams, it becomes possible to change the broken state of interatomic bonds by selecting the wavelength of each laser beam. Since it becomes possible to shift the absorption edge of light in multiple stages, it becomes possible to ablate only specific constituent portions sequentially by the laser ablation in the second step.

(5) The depth of the preliminary irradiation region is controlled by controlling the wavelength of the laser beam for the preliminary irradiation in the first step, and the ablation depth in the laser ablation or the wet etching in the second step is controlled. May be controlled.

(6) In the above embodiments and modifications, description has been made only about the case where the pre-irradiation is performed by laser light, but the present invention is not limited to this, and an object to be etched by one-photon dissociation or multi-photon dissociation. The light source is not limited to a laser as long as it is light having irradiation energy of a magnitude that breaks the interatomic bond of to cause photolysis.

(7) It is a matter of course that the above-described embodiment and the modified examples (1) to (6) may be appropriately combined and implemented.

[0051]

Since the present invention is constructed as described above, it has the following effects.

Irradiation with light having a large absorption in an object to be etched, the irradiation energy of which is such that at least one photon dissociation or multiphoton dissociation breaks an interatomic bond to cause photolysis. Since it has a first step and a second step of etching the area irradiated with light by at least the first step of the object, the light has a strong absorption in the object to be etched, That is, light with large photon energy (short wavelength light),
Alternatively, when light having a short pulse width, that is, light having a large peak power intensity (ultra-short pulse light) is first pre-irradiated on the surface of the solid object, the atoms in the solid are dissociated by one-photon dissociation or multi-photon dissociation by the pre-irradiation. You can break the bond between them.

Therefore, the light absorption edge of the pre-irradiated region is shifted to the long wavelength side, so that the pre-irradiated region can be selectively and rapidly etched by the etching process. Become.

That is, according to the solid multi-step etching method utilizing photolysis of the present invention, the etching processing speed can be increased, and fine pattern processing and wet etching can be performed.
There is no need to provide a resist during etching, and the processing steps can be simplified, so that workability can be greatly improved.

Further, since the pre-irradiation lowers the binding energy of the irradiation region, the thermal action is hardly given in the etching in the second step, and the damage due to it can be reduced.

[Brief description of drawings]

FIG. 1A to FIG. 1D are explanatory views showing a multi-step solid etching method using photolysis according to an embodiment of the present invention.

FIG. 2 is a graph enlarging the processing state of the surface of the quartz glass substrate with the etching depth on the vertical axis and the etching width on the horizontal axis, and showing the preliminary of laser light with a wavelength of 160 nm in the first step. The state immediately after irradiation is shown.

FIG. 3 is a graph enlarging the processing state of the surface of the quartz glass substrate with the etching depth on the vertical axis and the etching width on the horizontal axis, without performing preliminary irradiation in the first step. Shows a state in the case of irradiating only a laser beam having a wavelength of 266 nm in the second step.

FIG. 4 is a graph enlarging the processing state of the surface of the quartz glass substrate with the etching depth on the vertical axis and the etching width on the horizontal axis, and showing the preliminary of laser light of wavelength 160 nm in the first step. After the irradiation, the wavelength of the second step 2
The state when irradiated with a 66 nm laser beam is shown.

FIG. 5 is a table showing measurement results when the processes of the first step and the second step are performed by changing only the wavelength of the laser beam used for the preliminary irradiation.

FIG. 6 is a graph showing the results of evaluation of the bonding state of atoms in the pre-irradiated region pre-irradiated in the first step by X-ray photoelectron spectroscopy (XPS), showing the evaluation results regarding the Si-2p orbital. .

FIG. 7 is a graph showing the results of evaluation of the bonding state of atoms in the pre-irradiated region that was pre-irradiated in the first step by X-ray photoelectron spectroscopy (XPS), showing the evaluation results regarding the O-1s orbital. .

[Explanation of symbols]

10 Quartz glass substrate 12 Pre-irradiation area 14 Ablation area A Laser light of 160 nm wavelength (100 pulses of laser fluence 200 mJ / cm ² ) B Laser light of 266 nm wavelength (10 pulses of laser fluence ² J / cm ² )

Continuation of the front page (72) Inventor Koichi Toyota, Hirosawa No. 2-1, Hirosawa, Wako City, Saitama Prefecture

Claims (3)

[Claims] 1. Light having a large absorption for an object to be etched, the irradiation energy being at least one photon dissociation or multiphoton dissociation to break interatomic bonds to cause photolysis. Utilizing photodecomposition characterized in that it has a first step of irradiating light, which is a depth, and a second step of etching the region of the object irradiated with light by at least the first step. Method for multi-step etching of solids. 2. The method of multi-step etching of solids using photolysis according to claim 1, wherein the second step is a laser ablation process. 3. The method of multi-step etching of solid using photolysis according to claim 1, wherein the second step is a wet etching process.