JP2004268206A - Wet etching method of processing object substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form a fine three-dimensional image without using a photolithography technology. <P>SOLUTION: A first step S1 selectively irradiates FIB onto a processing object substrate such as a monocrystal silicon substrate. In that case, dose quantity of the FIB, a dot pitch, and accelerating voltage are adjusted according to the height of a projecting part to be formed. The masking effect to an etching liquid is revealed in an FIB irradiation part by this FIB irradiation. A second step S2 removes a natural oxide film formed on a substrate surface by being processed by a buffered hydrofluoric acid (BHF). After performing flowing water cleaning in a third step S3, ultrasonic cleaning is performed by using pure water and acetone in a fourth step S4. A fifth step S5 etches the FIB irradiation surface of the processing object substrate by being soaked in a KOH aqueous solution. Afterwards, a sixth step S6 observes a level difference by AFM for confirmation. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for wet etching a substrate to be processed, and more particularly to a method for producing a fine three-dimensional structure by combining a focused ion beam (FIB) with wet etching.
[0002]
[Prior art]
It is known that when a focused ion beam is irradiated on the surface of single crystal silicon, the etching property with respect to an etchant changes, and a method of selectively etching single crystal silicon without using a lithography technique utilizing this property is known. (For example, see Non-Patent Document 1). This method is a method of obtaining a planar pattern by performing etching utilizing the fact that a masking effect is developed in a focused ion beam irradiation region. In this method, a structure having a three-dimensional shape is formed. I couldn't do that.
On the other hand, in the field of micro optical systems using micro lenses, diffraction gratings, and MEMS (micro electro mechanical systems), it is required to form structures having different heights and three-dimensional structures having variable heights. ing. A conventional method of manufacturing this kind of structure is to perform exposure using a gray scale mask (a mask having different ultraviolet transmittance regions) and develop it to form a photoresist film having a variable thickness on a workpiece. In this method, the shape of a photoresist is transferred to a workpiece by performing dry etching (for example, see Patent Document 1).
[0003]
[Non-patent document 1]
Jpn. J. Phys. Vol. 39 (2000) pp. 2186-2188
[Patent Document 1]
JP-A-2003-15275
[Problems to be solved by the invention]
In the method using the above-described gray scale exposure method, a gray scale mask having a complicated shape is required, and since photolithography is used, many man-hours are required, resulting in an increase in product cost.
An object of the present invention is to make it possible to form a three-dimensional structure having different heights or changing heights with a small number of steps.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, according to the present invention, a target substrate is irradiated with a focused ion beam having different irradiation conditions, and wet etching is performed to perform etching on the target substrate in accordance with the focused ion beam irradiation condition. A method for wet etching a substrate to be processed, characterized by forming workpieces of different sizes.
[0006]
Further, according to the present invention, in order to solve the above-described problems, according to the present invention, a focused ion beam having different irradiation conditions is irradiated onto a substrate to be processed, and wet etching is performed to determine whether or not focused ion beam irradiation is performed on the substrate to be processed and focusing. A wet etching method for a substrate to be processed, wherein a workpiece having a different etching depth is formed according to ion beam irradiation conditions is provided.
Preferably, the irradiation conditions for differentiating the focused ion beam are one or more of a dose, a dot pitch, and an acceleration voltage.
Preferably, the etching time is controlled to control the difference in etching depth between regions having different focused ion beam irradiation conditions.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
In the following embodiments, examples using a single crystal silicon substrate will be described. FIG. 1 is a diagram showing a flow of processing according to the embodiment of the present invention. In the first step S1, to form a partially SiO ₂ mask (100) plane of the single crystal silicon substrate is selectively irradiated with the FIB region where the SiO ₂ is not formed in the mask. At this time, the dose of the FIB, the dot pitch, and the acceleration voltage are adjusted according to the height of the projection to be formed. Ga ⁺ , Si ^2+, or the like is used as the ion species of FIB. Due to this FIB irradiation, a masking effect on the etchant is exerted on the FIB irradiated portion as described later. This masking effect changes depending on the FIB irradiation conditions. In the second step S2, a natural oxide film formed on the substrate surface is removed by processing with buffered hydrofluoric acid (BHF). After performing running water cleaning in the third step S3, ultrasonic cleaning using pure water and acetone is performed in the fourth step S4. In a fifth step S5, the FIB-irradiated surface of the single crystal silicon substrate is etched by immersion in a KOH aqueous solution to which ultrasonic vibration has been applied. IPA (isopropyl alcohol) is added to this KOH aqueous solution, and its water temperature is about room temperature (24 ° C.). Thereafter, for confirmation, in a sixth step S6, a step formed by an AFM (atomic force microscope) is observed.
[0008]
FIG. 2 shows a cross-sectional view after the completion of the etching process. The meanings of the terms described in relation to this figure are used in common in the following figures. The SiO ₂ mask 2 is selectively formed on the surface of the single crystal silicon substrate 1, and this portion is not etched, and the substrate surface becomes the reference surface 3. The non-irradiated portion is etched by h1. This h1 gives the reference plane height and, based on this, the etch rate of the area is calculated. The FIB irradiating portion is etched by h2, and the etch rate of this region is calculated based on h2. The difference h3 between h1 and h2 is the height of the convex structure of the FIB irradiation part. The height of the convex structure can be controlled by changing the FIB irradiation conditions and the etching processing time.
[0009]
[Dose amount dependence of masking effect]
In order to verify the dose dependency of the masking effect, the height of the convex structure was measured while changing the dose, and the etch rate was calculated. The results are shown in FIGS. 3 (a) and 3 (b). The irradiation ion species is Ga ⁺ , and the acceleration voltage is 30 kV. The concentration of the etchant (KOH) is 20 wt%, and the etching time is 5 minutes.
From FIG. 3, it can be seen that the etch rate decreases linearly with increasing dose up to a dose of 0.5 C / cm ^2, and becomes substantially constant when the dose exceeds 1.0 C / cm ^2. (Saturated).
[0010]
[Dot pitch dependency of masking effect]
In order to verify the dot pitch dependency of the masking effect, the height of the convex structure was measured while changing the dot pitch, and the etch rate was calculated. The results are shown in FIGS. The irradiation ion species is Ga ⁺ , and the acceleration voltage is 30 kV. The etchant concentration is 20 wt%, and the etching time is 5 minutes.
FIG. 4 shows that when the dot pitch is 150 nm or less, the etch rate is high, and when the dot pitch exceeds 250 nm, the etch rate becomes substantially constant (saturates).
FIGS. 5A and 5B are cross-sectional views of the case where the dot pitch is small and the case where the dot pitch is large after the end of the etching process. When the dot pitch is small, the deteriorated layer due to the FIB irradiation spreads uniformly, so that the etching proceeds relatively evenly. On the other hand, when the dot pitch is large, the deteriorated layer due to the FIB irradiation becomes locally strong, so that the etching is also locally suppressed, and a micro pyramid is formed as shown in the figure.
[0011]
[Etching time dependence of masking effect]
In order to verify the dependence of the masking effect on the etching time, samples having different doses were prepared, and the relationship between the etching time, the height of the convex structure, and the etch rate was measured. The results are shown in FIGS. 6 (a) and (b). The height of the reference surface is 45 nm for an etching time of 1 minute, 155 nm for 5 minutes, and 821 nm for 20 minutes. The irradiation ion species is Ga ⁺ , and the acceleration voltage is 30 kV. The etchant concentration is 20% by weight.
As shown in FIG. 6, when the dose is 2.6 × 10 ⁻⁵ / cm ² , the height of the convex structure hardly changes after one minute of the etching time, and the dose is 1.6 × 10 ⁻⁴ / cm. ^In the case of ^2, the height of the convex structure increases until the etching time has elapsed for 5 minutes, and the height does not substantially change thereafter, and when the dose is larger, the etching time has elapsed for 5 minutes or more. Still, the height of the convex structure increases, but the rate of increase decreases. That is, as the etching time increases, the etching rate increases, but the time until the etching rate increases increases as the dose increases. .
[0012]
FIG. 7B is a cross-sectional view for explaining the relationship between the passage of the etching time and the etching state. The FIB-irradiated portion of the single crystal silicon substrate 1 is deteriorated and is formed in the low etch rate region 4. When the etching is started, both the FIB-irradiated portion and the FIB non-irradiated portion are etched, but the etching of the low etch rate region 4 is delayed, and a convex portion is formed with respect to the FIB non-irradiated portion. This state continues until the low etch rate region 4 is completely etched, during which the height of the convex structure continues to increase. When the low etch rate region 4 is completely etched, the difference in etch rate between the FIB-irradiated portion and the FIB non-irradiated portion disappears, and the height of the convex structure remains constant.
As shown in FIG. 6B, the etch rate of the low etch rate region 4 decreases as the dose increases. FIG. 7A is a diagram obtained by additionally writing the reference plane height in FIG. 6A. Regardless of the dose, the low etch rate region has high etching resistance until it is etched by about 35 nm from the reference plane (substrate surface), and the etching rate rises beyond that. From this, it is presumed that under the above-described FIB irradiation conditions, a region having high etching resistance is formed up to a depth of about 35 nm.
[0013]
[Acceleration voltage dependence of masking effect]
In order to verify the acceleration voltage dependence of the masking effect, FIB irradiation was performed while changing the acceleration voltage and the dose, and the height of the convex structure was measured. The results are shown in FIGS. 8 (a) and 8 (b). The irradiation ion species is Si ^{+ 2} , and the acceleration voltage is 20 to 30 kV. The etchant concentration is 20 wt%, and the etching time is 5 minutes.
From FIG. 8, in the range of the acceleration voltage of 20 to 30 kV, the height of the convex structure decreases as the acceleration voltage increases. This phenomenon is presumed to be due to the fact that the region where the masking effect is exhibited becomes deeper as the accelerating voltage increases. In addition, since the masking effect is exhibited by injecting Si ^{+ 2} into single crystal silicon, it is presumed that one of the factors of the masking effect is disordered crystallinity.
As shown in FIG. 9A, an ion-implanted region 5 is formed on a single-crystal silicon substrate 1 by irradiating FIB under the condition that the acceleration voltage is low at the center and the acceleration voltage is high at the periphery, and the bowl is turned down. Is formed and etching is performed, the dome 6 can be formed on the substrate. As shown in FIG. 9B, when the same region is subjected to FIB irradiation a plurality of times while changing the acceleration voltage to form a plurality of ion-implanted regions 5 in the depth direction and perform etching, A convex structure is formed by the masking effect of the ion implantation region 5. If the etching is continued, the uppermost ion-implanted region is eventually etched, but subsequently, the second ion-implanted region functions as a mask, and the convex structure is formed higher. As described above, even if the ion implantation regions 5 are sequentially etched from the top, new ion implantation regions appear one after another, and a masking effect is developed by each of them. As a result, the high aspect ratio convex structure 7 is formed on the single crystal silicon substrate 1. Can be formed.
FIG. 9 (b) shows an example in which one high aspect ratio convex structure 7 is formed. The aspect ratio convex structure 7 may be formed. In addition, for one of the plurality of regions, one or both of the FIB irradiation frequency and the accelerating voltage differ from the other region, so that a workpiece formed between the certain region and the other region is formed. May be made different in height.
[0014]
【Example】
FIG. 10 shows a perspective view before etching and a cross-sectional view after etching, showing one embodiment of the present invention. As shown in FIG. 10A, a dose of 2.7 × 10 ⁻³ C / cm ² Ga ⁺ is applied to a (50) × 50 μm region on the (100) plane of the single crystal silicon substrate 1, and a dose is applied to a 30 μm × 30 μm region. 9.1x10 of ^-3 C / cm ² to Ga ^+, a dose in the region of 10μmx10μm: 69.1x10 of ^-3 C / cm ² to Ga ^+, beam current was irradiated with 10 pA. Etching was performed by immersing in a 20 wt% KOH aqueous solution to which IPA was added in a saturated state and subjected to ultrasonic vibration for 6 minutes. The steps were 10 nm, 20 nm, and 90 nm from the bottom.
By continuously changing the dose, a dome-shaped convex portion could be formed.
[0015]
Although the preferred embodiments and examples have been described above, the present invention is not limited to these embodiments and examples, and appropriate changes can be made without departing from the scope of the present invention. . For example, the substrate to be processed may be a compound semiconductor such as GaAs or InP, or a metal such as Al or Fe, instead of single crystal silicon. Further, the irradiation ion species may be the same material as the base material or another material. For the etchant, for example, hydrazine or NaOH aqueous solution may be used for single crystal silicon, and generally known etchants can be appropriately used for other substrate materials. Also, the spraying method may be used instead of the immersion method for the etching method.
[0016]
【The invention's effect】
As described above, the present invention irradiates the substrate to be processed with FIB under different irradiation conditions and then performs wet etching to form irregularities on the surface of the substrate to be processed. A fine three-dimensional image can be formed by a simple method without requiring a mask or a photolithography step. Therefore, according to the present invention, versatile applications are expected in a wide range of technical fields such as optics requiring microlenses and diffraction gratings, micromachine technology such as MEMS, and semiconductor manufacturing technology.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a processing flow of an etching method according to the present invention.
FIG. 2 is a cross-sectional view of a substrate to be processed for describing an embodiment of the present invention.
FIG. 3 is a graph showing dose dependency of a masking effect for explaining the embodiment of the present invention.
FIG. 4 is a graph illustrating a dot pitch dependency of a masking effect for explaining the embodiment of the present invention.
FIG. 5 is a cross-sectional view illustrating a shape change depending on a dot pitch for describing the embodiment of the present invention.
FIG. 6 is a graph showing the etching processing time dependency of a masking effect for explaining the embodiment of the present invention.
FIGS. 7A and 7B are a graph showing the dependence of the masking effect on the etching processing time and a cross-sectional view showing the progress of etching, for explaining the embodiment of the present invention;
FIG. 8 is a graph showing acceleration voltage dependence of a masking effect for explaining the embodiment of the present invention.
FIG. 9 is a cross-sectional view illustrating an example in which a convex structure is formed by using the acceleration voltage dependence of a masking effect.
FIG. 10 is a perspective view and a cross-sectional view for explaining one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Single crystal silicon substrate 2 SiO ₂ mask 3 Reference plane 4 Low etch rate area 5 Ion implantation area 6 Dome 7 High aspect ratio convex structure

Claims (10)

The process is characterized by irradiating a focused ion beam having different irradiation conditions onto a substrate to be processed, and performing wet etching to form workpieces having different etching depths on the substrate to be processed according to the focused ion beam irradiation conditions. A wet etching method for a processing substrate. A focused ion beam with different irradiation conditions is irradiated on the substrate to be processed, and wet etching is performed to form a workpiece with a different etching depth on the substrate to be processed according to the presence or absence of focused ion beam irradiation and the focused ion beam irradiation conditions. Wet etching method for a substrate to be processed. 3. The wet etching method for a substrate to be processed according to claim 1, wherein the irradiation condition for making the focused ion beam different is one or more of a dose amount, a dot pitch, and an acceleration voltage. The wet etching method for a substrate to be processed according to any one of claims 1 to 3, wherein a difference in etching depth between regions having different focused ion beam irradiation conditions is controlled by controlling an etching time. One or more regions on the substrate to be processed are irradiated with a focused ion beam a plurality of times by different acceleration voltages, and wet etching is performed to form a workpiece having a height corresponding to the number of times of the focused ion beam irradiation on the substrate to be processed. And a wet etching method for a substrate to be processed. For one of the plurality of regions, one or both of the number of focused ion beam irradiations and the acceleration voltage is different from the other regions, and the height of a workpiece formed between the certain region and the other region is different. 6. The wet etching method for a substrate to be processed according to claim 5, wherein The wet etching method for a substrate to be processed according to any one of claims 1 to 6, wherein the substrate to be processed is formed of a semiconductor. The wet etching method for a substrate to be processed according to any one of claims 1 to 6, wherein the substrate to be processed is formed of single crystal silicon. The method according to claim 8, wherein the wet etching is performed using an alkaline etching solution. 9. The method according to claim 8, wherein the wet etching is performed using a KOH aqueous solution.

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