US20040211756A1 - Wet etching apparatus and wet etching method using ultraviolet light - Google Patents

Abstract

A substrate having a film to be etched is held on a rotating stage. While rotating the substrate, a chemical solution containing an etchant is supplied onto the substrate from a nozzle. A lamp house with a drive unit is positioned so that the distance between the substrate and a glass window of the lamp house becomes 2 to 5 mm, the lamp house accommodating a lamp generating ultraviolet light. The ultraviolet light irradiates the film through the chemical solution. The ultraviolet light has a higher energy than the binding energy of constituent molecules of the film.

Description

1. FIELD OF THE INVENTION
• The present invention relates to a semiconductor manufacturing apparatus, and specifically to a wet etching apparatus and a wet etching method.[0001]
2. DESCRIPTION OF THE BACKGROUND ART
• In recent years, a high-dielectric-constant film (hereafter referred to as “high-k dielectric film”) is used as a gate insulating film for an advanced device. The high-k dielectric film is acceleratedly densified by heat treatment (i.e. annealing) performed after film formation, and high-k dielectric film is changed to have properties difficult to etch.[0002]
• Heretofore, for etching of films to be etched, there have been used wet etching wherein a film to be etched is made to contact a chemical solution and etching is performed by an etchant dissociated in the chemical solution; and dry etching wherein radicals and ionic species excited in plasma are drawn in a substrate to forcedly etching a film to be etched.[0003]
• However, there has been the problem of very low etching rate when a dense thin film, such as a high-k dielectric film after annealing, is subjected to wet etching. Therefore, there has been the problem of significantly low throughputs.[0004]
• When a dense thin film is subjected to dry etching in place of wet etching, there has been a problem that although a higher etching rate is obtained than wet etching, the base member that should not be etched is continuously etched. That is to say, there has been a problem that a sufficient etching selectivity to the base member cannot be obtained by dry etching.[0005]
• Heretofore, such difficulty of etching has been a drawback when a high-k dielectric film is applied to advanced devices.[0006]
SUMMARY OF THE INVENTION
• The present invention has been conceived to solve the previously-mentioned problems and a general object of the present invention is to provide a novel and useful wet etching apparatus and is to provide a novel and useful wet etching method.[0007]
• A more specific object of the present invention is to provide a wet etching apparatus and a wet etching method having a high etching selectivity to a base member below a film to be processed, and having a high etching rate.[0008]
• The above object of the present invention is attained by a following wet etching apparatus and a following method for wet etching of a film.[0009]
• According to one aspect of the present invention, the wet etching apparatus comprises a chemical-solution supply component for supplying a chemical solution on a film to be processed on a substrate. An ultraviolet-light radiating component radiates ultraviolet light to the film through the chemical solution.[0010]
• According to another aspect of the present invention, in the method for wet etching of a film, a chemical solution is supplied on a film to be processed on a substrate. Ultraviolet light is radiated to the film through the chemical solution.[0011]
• Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.[0012]
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a schematic sectional view for illustrating a wet etching apparatus according to a first embodiment of the present invention;[0013]
• FIG. 2 is a schematic sectional view for illustrating a wet etching apparatus according to a second embodiment of the present invention;[0014]
• FIG. 3 is a top view showing vicinity of a substrate in the wet etching apparatus shown in FIG. 2; and[0015]
• FIG. 4 is a sectional view for illustrating a substrate to be wet etched.[0016]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• In the following, principles and embodiments of the present invention will be described with reference to the accompanying drawings. The members and steps that are common to some of the drawings are given the same reference numerals and redundant descriptions therefore may be omitted.[0017]
First Embodiment
• FIG. 1 is a schematic sectional view for illustrating an etching apparatus according to a first embodiment of the present invention. Specifically, FIG. 1 is a diagram for illustrating an etching apparatus for wet etching of a film to be etched formed on a substrate.[0018]
• As FIG. 1 shows, a[0019]substrate11 to be wet etched is rotatably held on a rotatingstage5. Specifically, a plurality ofpins4 are installed on therotating stage5, and the end portion (edge portion) of thesubstrate11 is held between thesepins4. Thesubstrate11 may also be held using an electrostatic chuck.
• A rotating[0020]shaft6 is disposed on the center of the rotatingstage5, and when the rotatingstage5 rotates around the rotatingshaft6, thesubstrate11 is also rotates at a desired rotating speed. The rotatingstage5 rotates at a rotating speed of, for example, about 300 to 500 rpm during coating of a chemical solution, and about 2,000 to 3,000 rpm during drying.
• As FIG. 4 shows, a film to be etched (film to be processed)[0021]11ais formed on thesubstrate11 serving as a base member, and amask11bis formed on thefilm11a. Thefilm11ais, for example, a dense thin film such as a high-k dielectric film. The high-k dielectric film is, for example, HfO₂film and HfAlO film formed using an ALD (atomic layer deposition) method and performed an annealing (PDA: post deposition annealing) treatment after film formation.
• A[0022]chemical solution9 is supplied to the surface of the film to be etched on thesubstrate11 through anozzle8 installed on the end of achemical pipe7. The chemical-solution pipe7 is connected to a chemical tank (not shown) for storing the chemical solution, or to a chemical-supply line of an incidental apparatus (not shown)through avalve7aand apump7b.
• A[0023]chemical solution9 containing, for example, a phosphoric-acid-based etchant may also be used. In order to obtain desired properties, a surface active agent or the like may be added to thechemical solution9.
• [0024]Lamp house2 stores a lamp1.Lamp house2 accommodating a lamp1, which radiates ultraviolet light to the film (11a) through thechemical solution9, is disposed above thesubstrate11. The lamp1 serving as a light source is, for example, KrCl (wavelength: 222 nm), Xe₂(172 nm), Kr₂(147 nm), Ar₂(126 nm) excimer lamps or the like. Here, the lamp1 radiates ultraviolet light at energy higher than binding energy of constituent molecules of the film to be etched (11a). Energy of the ultraviolet light can be controlled by a radiating time of the ultraviolet light. The radiating time is, for example, 10 to 200 sec.
• The materials of the[0025]chemical solution9 and the thickness of the film to be etched (11a) are selected so as to attain a high transmissivity for the wavelength of the ultraviolet light radiated from the lamp1.
• On the lower surface of the[0026]lamp house2 is formed an opening having the size same as, or larger than the size thesubstrate11. This opening is covered with a light-transmittingwindow3 formed by a material that transmits ultraviolet light from the lamp1. The light-transmittingwindow3 is, for example, a window formed of quartz glass (hereafter referred to as “quartz glass window”).
• The inside of the[0027]lamp house2 sealed with thequartz glass window3 is filled with an inert gas such as nitrogen. Thereby, a lamp1 having a wavelength absorbed in the presence of oxygen can be used. Illuminance of the ultraviolet light at thequartz glass window3 is preferably 5 to 20 mW/cm².
• On the upper surface of the[0028]lamp house2 is installed adrive unit10 for driving thelamp house2 in the vertical direction. Thedrive unit10 drives thelamp house2 to vicinity of thesubstrate11 when ultraviolet light is radiated, thereby acting the ultraviolet light from the lamp1 to the film (11a) in the close distance. Specifically, thelamp house2 is disposed so that thequartz glass window3 is disposed 2 to 5 mm above the surface of thesubstrate11.
• Next, the operation of the etching apparatus, that is the wet etching of the film to be etched will be described.[0029]
• First, the[0030]substrate11, which has an HfO₂film serving as the film to be etched (11a) and the mask (11b), is held bypins4 on therotating stage5. Thechemical solution9 containing a phosphoric-acid-based is supplied on thesubstrate11 from thenozzle8, while rotating thesubstrate11 at a rotation speed of 300 to 500 rpm by rotating therotating stage5 around the rotatingshaft6. Thereafter, when thechemical solution9 is sufficiently thinly and evenly spread on thesubstrate11, the rotation of thesubstrate11 is stopped. At this time, thechemical solution9 has been applied on the entire surface of thesubstrate11 in a desired thickness without running off thesubstrate11.
• The[0031]lamp house2 is lowered by thedrive unit10 so that thequartz glass window3 locates 2 to 5 mm above the surface of thesubstrate11 without interfering thepins4. Ultraviolet light is radiated from the lamp1 that has previously been turned on to the HfO₂film through thechemical solution9. At this-time, energy of the ultraviolet light breaks the Hf—O bonds of the HfO₂film, and etching reaction proceeds by etchant contained in thechemical solution9 previously applied on thesubstrate11.
• After desired etching has been completed, radiating of the ultraviolet light from the lamp[0032]1 is stopped, thelamp house2 is elevated with by thedrive unit10. Ultra-pure water is supplied from the water-cleaning nozzle (not shown) on thesubstrate11 to wash away thechemical solution9 remaining on thesubstrate11.
• Thereafter, the[0033]substrate11 is rotated at about 2,000 to 3,000 rpm with therotating stage5 to sprinkle the ultra-pure water and to dry thesubstrate11.
• In the first embodiment, as described above, after a[0034]chemical solution9 has been applied to dense film to be etched, ultraviolet light having energy larger than binding energy of constituent molecules of the film to be etched is radiated to the film to be etched through thechemical solution9. Since the ultraviolet light breaks the bonds of the molecules of the film to be etched, the etching rate of the film to be etched contacting thechemical solution9 is significantly increased. In other words, by wet etching performed in the state wherein the most molecular bonds of the film to be etched have been broken, the etching rate can be significantly increased. Therefore, the time of etching process can be shortened, and the throughput can be improved. Also because of a high etching selectivity to the base member (i.e. substrate11), the problem of continuous etching of the base member, as in the use of dry etching, does not arise. Thereby, a dense high-k dielectric film can be used in advanced semiconductor devices.
• The[0035]chemical solution9 used in the first embodiment has a high transmissivity to the wavelength of the lamp1. Therefore, little ultraviolet light radiated from the lamp1 is absorbed by thechemical solution9, and the ultraviolet light having sufficient light energy can reach the film to be etched. Thus, the loss of light energy of ultraviolet light by thechemical solution9 can be decreased as much as possible.
• The etching rate can further be improved by elevating the temperature of the[0036]chemical solution9 and/or thesubstrate11 using a heat exchanger or a hot plate. In this case, however, the quantity of vaporizedchemical solution9 increases, and cloud of the surface of thequartz glass window3 on the bottom of thelamp house2 may occur due to condensation of the vapor. The haze may scatter the ultraviolet radiation, thereby causing insufficiency of the action of the ultraviolet radiation to the film to be etched.
• To cope with this problem, it is preferable to apply a surface-active agent having hydrophobic groups, or the like, to the[0037]quartz glass window3. The film of the surface-active agent prevents the condensation of the vaporizedchemical solution9 on thequartz glass window3, and can prevent the loss of the light energy of ultraviolet light (the same applies to the second embodiment described below).
• It is also considered that the quantity of the etchant in the[0038]chemical solution9 is insufficient by a single application of thechemical solution9, and the etching reaction ceases in the middle. In the case where the supply of the etchant becomes the rate-limiting factor, it is recommended thelamp house2 is once separated (elevated) from the vicinity of thesubstrate11 using thedrive unit10 to supply thechemical solution9 again from thenozzle8, and thelamp house2 is again lowered to the vicinity of thesubstrate11 to radiate ultraviolet light again.
• However, when the supply of the etchant significantly becomes the rate-limiting factor due to the mechanism of the etching, since the supply of the chemical solution and the radiation of the ultraviolet light must be repeated many times, the processing time increases, and the throughput lowers. There also is a case where the[0039]chemical solution9 dries up due to heat given by the light energy of ultraviolet light radiated after the application of thechemical solution9, and an irreversible state may occur during water cleaning after wet etching. The effective means in such a case will be described below as a second embodiment.
• In the first embodiment, the case where the film to be etched was a high-k dielectric film was described. However, the present invention is not limited thereto, but can be applied to a film having a low wet-etching rate, and is particularly preferable to a dense thin film (the same applies to the second embodiment described below).[0040]
• As a comparative example of the first embodiment, the present inventors first radiated ultraviolet light from the lamp[0041]1 to the film to be etched, and then thechemical solution9 was applied on the film to be etched. However, in the comparative example, increase in the etching rate was little compared with the first embodiment, and the desired effect could not be achieved.
Second Embodiment
• FIG. 2 is a schematic sectional view for illustrating an etching apparatus according to a second embodiment of the present invention; and FIG. 3 is a top view showing vicinity of a substrate in the etching apparatus shown in FIG. 2.[0042]
• The etching apparatus according to the second embodiment is particularly suitable in the case where supply of an etchant significantly becomes the rate-limiting factor as described above.[0043]
• As FIG. 2 shows, a[0044]substrate11 to be etched is held on a plate-like stage12 having a wider area than thesubstrate11. On thestage12 are installed a plurality ofpins4 having a height of, for example, 2 to 5 mm, and the end portion (edge portion) of thesubstrate11 is held between thesepins4. As FIG. 4 shows, a film to be etched (film to be processed)11ais formed on thesubstrate11, and amask11bis formed on thefilm11a. Thefilm11ais, for example, a dense thin film such as a high-k dielectric film. The high-k dielectric film is, for example, HfO₂film and HfAlO film formed using an ALD (atomic layer deposition) method, and annealing (PDA: post deposition annealing) treatment.
• As in the first embodiment, the[0045]lamp house2 accommodating a lamp1 is driven by thedrive unit10 in the vertical direction. When ultraviolet light is radiated, thelamp house2 is disposed so that thequartz glass window3 is disposed 2 to 5 mm above the surface of thesubstrate11.
• In the gap between the[0046]quartz glass window3 and thesubstrate11, atip portion13aof a slit-likeflat nozzle13 is inserted.Chemical solution9 is continuously supplied to the gap from theflat nozzle13. Here, as FIG. 3 shows, on thestage12, a pair ofguides16 are formed so as to be parallel to theflat nozzle13 and so as to sandwich thesubstrate11. Thereby, thechemical solution9, supplied to an end of thesubstrate11 from theflat nozzle13, is guided by theguides16 in the direction of the other end of thesubstrate11 facing the end (i.e., the direction opposite from the flat nozzle13), and gradually fills the gap. Furthermore, the excess of thechemical solution9 supplied from theflat nozzle13 runs out in the direction opposite from theflat nozzle13.
• The[0047]flat nozzle13 is connected to an end of apipe15. The other end of thepipe15 is connected, through a switchingvalve14, to apipe15afor chemical solution and apipe15bfor ultra-pure water. Specifically, the switching operation of the switchingvalve14 connects theflat nozzle13 to thepipe15aor thepipe15bthrough thepipe15. That is to say, theflat nozzle13 is connected to a chemical-solution supply line or a ultra-pure-water supply line by switching the switchingvalve14.
• Next, the operation of the above-descried etching apparatus, that is the wet etching of the film to be etched will be described.[0048]
• First, a[0049]substrate11, which has an HfO₂film serving as the film to be etched (11a) and mask (11b), is held bypins4 on thestage12.
• Then, the[0050]lamp house2 is lowered with thedrive unit10 so that thequartz glass window3 locates 2 to 5 mm apart from the surface of thesubstrate11 without interfering thepins4.
• Next, the tip portion of the[0051]flat nozzle13 is inserted in the gap between thequartz glass window3 and thesubstrate11 from the side to continuously supply thechemical solution9 from theflat nozzle13 into the gap. At the same time as the supply of thechemical solution9, ultraviolet radiation is radiated from the lamp1 onto the HfO₂film through thechemical solution9.
• At this time, the light energy of the ultraviolet radiation breaks the Hf—O bonds of the HfO[0052]₂film, and the etchant contained in thechemical solution9 supplied from theflat nozzle13 proceeds the etching reaction. Thechemical solution9 supplied from theflat nozzle13 is led by theguide16 to the opposite side of theflat nozzle13, and gradually enters into the gap, and finally fills the gap. By further continuing the supply of thechemical solution9 at a constant flow rate, theexcessive chemical solution9 runs out of thesubstrate11 at the opposite side of theflat nozzle13. Thereby, thechemical solution9 rich in the etchant is supplied onto the film to be etched.
• After desired etching has been completed, radiation of the ultraviolet light from the lamp[0053]1 is stopped. The location of thelamp house2 is stayed as it is, the switchingvalve14 is switched to supply ultra-pure water from theflat nozzle13 into the gap, and to wash away thechemical solution9 remaining on thesubstrate11. At this time, not only thechemical solution9 remaining on thesubstrate11 is washed away, but also the parts that have contacted thechemical solution9, such as thequartz glass window3, are simultaneously cleaned.
• In the second embodiment, as described above, the supply of the[0054]chemical solution9 from theflat nozzle13 is performed simultaneously with the radiation of the ultraviolet light from the lamp1 for wet etching. Therefore the same effect as in the first embodiment is obtained.
• Furthermore, in the second embodiment, while ultraviolet light is radiated from the lamp[0055]1 (i.e. during wet etching), thechemical solution9 is continuously supplied from theflat nozzle13 into the gap between thequartz glass window3 and thesubstrate11. Thereby, thechemical solution9 rich in the etchant can always been supplied onto the film to be etched. Therefore, the etching rate can be further increased compared with the first embodiment. Thus, even in the etching reaction wherein the supply of the etchant significantly becomes the rate-limiting factor, there is no need to repeat the supply of the chemical solution and radiation of the ultraviolet light, and the elongation of the processing time and the lowering of the throughput can be prevented. The drying up of thechemical solution9 due to the evaporation of thechemical solution9 to change to an irreversible state can also be prevented.
• Also in the second embodiment, ultra-pure water is supplied from the[0056]flat nozzle13 by the switching operation of the switchingvalve14. Thereby, not only thesubstrate11, but also liquid-contacting parts, such as theflat nozzle13 and thequartz window3 can be cleaned. Therefore, the installation of the separate nozzle for ultra-pure water is not required, and the etching apparatus can be simplified, and the costs thereof can be reduced.
• This invention, when practiced illustratively in the manner described above, provides the following major effects:[0057]
• According to the present invention, there can be provided an etching apparatus and an etching method having a high etching selectivity to the base member below the film to be processed, and a high etching rate.[0058]
• Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.[0059]
• The entire disclosure of Japanese Patent Application No. 2003-21556 filed on Jan. 30, 2003 containing specification, claims, drawings and summary are incorporated herein by reference in its entirety.[0060]

Claims (11)

1. A wet etching apparatus comprising:

a chemical-solution supply component for supplying a chemical solution to a film to be processed, the film being supported by a substrate, and

an ultraviolet-light radiating component for irradiating the film with ultraviolet light through the chemical solution.

2. The wet etching apparatus according toclaim 1, wherein the ultraviolet-light radiating component radiates ultraviolet light having an energy higher than binding energy of constituent molecules of the film.

3. The wet etching apparatus according toclaim 1, further comprising a drive unit for moving the ultraviolet-light radiating component, wherein the ultraviolet-light radiating component is moved at a location 2 mm to 5 mm above a surface of the film, when the film is being irradiated with the ultraviolet light.

4. The wet etching apparatus according toclaim 1, wherein the ultraviolet-light radiating component comprises:

a light source generating the ultraviolet light;

a storage component for accommodating the light source and having a light-transmitting window for facing the film; and

a nozzle in the chemical-solution supply component, disposed at a gap between the light-transmitting window and the film, for continuously supplying the chemical solution in the gap.

5. The wet etching apparatus according toclaim 4, further comprising a stage for holding the substrate, the stage including a pair of guides parallel to the nozzle, for sandwiching the substrate.

6. The wet etching apparatus according toclaim 4, including a layer of a surface-active agent located at a surface of the light-transmitting window and contacting the chemical solution.

7. The wet etching apparatus according toclaim 4, wherein the chemical-solution supply component comprises:

a switching valve connected to the nozzle through a pipe and for switching between a supply of the chemical solution and a supply of ultra-pure water;

a pipe for supplying the chemical solution and connected to the switching valve; and

a pipe for supplying the ultra-pure water and connected to the switching valve.

8. A method for wet etching of a film, comprising:

supplying a chemical solution to a film to be processed, the film being disposed on a substrate; and

irradiating the film with ultraviolet light through the chemical solution.

9. The method for wet etching according toclaim 8, including supplying the chemical solution and irradiating the film with ultraviolet light simultaneously.

10. The method for wet etching according toclaim 8, including irradiating the film with ultraviolet light having an energy higher than the binding energy of constituent molecules of the film.

11. The method for wet etching according toclaim 8, wherein the film is a high-k dielectric film that has been annealed.

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