JP2006040969A - Supercritical processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a supercritical processing at a lower pressure. <P>SOLUTION: A surface and patterns 101a of a substrate 101 are immersed in a liquid 103 of fluoride. The liquid 103 of fluoride, where the surface and the patterns 101a of the substrate 101 are immersed is heated and fluoride, is set to a supercritical state in a reaction chamber which is sealed and is kept at a fixed capacity. Thus, the surface and the patterns 101a of the substrate 101 are set, in a state where they are covered by a supercritical fluid 106 of fluoride in a sealed space 105. When the liquid 103 of fluoride is heated to a critical temperature or above in a state of critical pressure, it goes into supercritical state. The liquid 103 of fluoride becomes supercritical, when it is heated higher than the critical temperature under the critical pressure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a supercritical processing method that suppresses deformation such as collapse of a fine pattern due to surface tension of a liquid during drying after processing with the liquid.

  As is well known, in order to manufacture a large-scale and high-performance device such as an LSI, an extremely fine pattern is required. This ultrafine pattern is, for example, a resist pattern that is formed by exposure, development, and rinsing, and that has photosensitivity to light, X-rays, or electron beams. Further, the etching pattern is made of an inorganic material such as an oxide formed through a liquid treatment with water or a chemical solution after selective etching using the resist pattern as a mask. For example, a pattern made of silicon is also used for a fine structure constituting a micro electro mechanical system (MEMS).

  For example, a silicon pattern can be formed by etching a silicon substrate using a resist pattern as a mask. After the pattern is formed, the resist pattern used for the etching mask is generally removed. The resist pattern can be removed by, for example, dissolving the resist pattern with a chemical solution. Then, in order to remove a chemical | medical solution from on a board | substrate, washing processes, such as water washing, are performed, a board | substrate is dried and a series of processes are complete | finished.

  A major problem during drying in the formation of such a fine pattern is the collapse of the pattern. At the time of drying after the treatment with the liquid, a bending force (capillary force) works due to a pressure difference between the liquid remaining between the formed patterns and the external air. As a result, pattern collapse occurs. This falling phenomenon becomes more prominent as the pattern has a higher aspect ratio. It has been reported that the capillary force depends on the surface tension generated at the interface between liquid and gas between patterns (see Non-Patent Document 1).

The surface tension of water is as large as about 72 × 10 ⁻³ N / m, and the above-described capillary force has a force to distort a stronger pattern such as silicon which is an inorganic material. For this reason, the problem of surface tension due to the liquid during the drying process is important.
As a technique for solving this problem, there has been proposed a technique for solving problems such as pattern collapse by using a fluid in a supercritical state and drying after the surface tension does not act (Patent Document 1, Patent Document 1). 2, 3, see Non-Patent Document 2).

  A fluid in a supercritical state (supercritical fluid) is a substance at a temperature and pressure exceeding the critical temperature and pressure, and has a dissolving power close to that of a liquid, but tension and viscosity exhibit properties close to a gas. It can be said that the liquid is kept in a gaseous state. Since the supercritical fluid having such characteristics does not form an interface between the liquid and the gas, the surface tension becomes zero. Therefore, if it is dried in a supercritical state, the concept of surface tension is eliminated, and pattern collapse is eliminated.

  A supercritical fluid has both gas diffusivity and liquid solubility (high density), and can change state from liquid to gas without an equilibrium line. For this reason, if this supercritical fluid is gradually released from the state filled with the supercritical fluid, the interface between the liquid and gas will not be formed, so the surface is dried without applying surface tension to the ultrafine pattern to be dried. be able to.

  In many cases, carbon dioxide, which has a low critical point and is easy to handle, is used as the supercritical fluid. Supercritical drying using a supercritical fluid is started by replacing the liquid adhering to the substrate surface with liquefied carbon dioxide in a sealed container after chemical treatment or the like. Since carbon dioxide liquefies at room temperature when pressurized to about 6 MPa, the above replacement is performed in a state where the pressure in the container is increased to about 6 MPa. After the liquid adhering to the substrate is replaced with liquefied carbon dioxide, the temperature and pressure (critical point of carbon dioxide; 31 ° C., 7.3 MPa) above the critical point of carbon dioxide inside the container Convert to supercritical carbon dioxide.

  Finally, while maintaining the above temperature, a part of the container is opened to release supercritical carbon dioxide to the outside, the inside of the container is reduced to atmospheric pressure, and the supercritical carbon dioxide in the container is vaporized. Finish drying. At the time of this pressure reduction, carbon dioxide is vaporized without being liquefied, so that the interface between the liquid and the gas on which the surface tension acts is not formed on the substrate. For this reason, these can be dried, without producing a fall in the ultra fine pattern currently formed on the board | substrate.

  As an apparatus for the above supercritical drying, for example, as shown in FIG. 3, an apparatus for pumping liquefied carbon dioxide sealed in a cylinder 303 into a reaction chamber 302 in a sealable container 301 by a pump pump 304. There is. In this apparatus, by opening the valve 305 on the liquefied carbon dioxide introduction side, liquefied carbon dioxide is introduced into the container 301, liquefied carbon dioxide is discharged from the tip of the inlet 306 communicating with the valve 305, and the reaction chamber 302. Liquefied carbon dioxide is injected onto the substrate 311 placed on the inner stage 312.

  At this time, for example, the liquefied carbon dioxide in the cylinder 303 is pumped into the reaction chamber 302 by the pump pump 304, and the opening degree of the valve 307 on the discharge side is adjusted in this state, and the liquefied carbon dioxide discharged from the discharge port 309 The pressure in the reaction chamber 302 is controlled by limiting the amount of. If, for example, an automatic pressure valve is used for the valve 307 on the discharge side, the above pressure control is possible.

As described above, in a state where liquefied carbon dioxide is being injected onto the substrate through the inlet 306, the container 301 is heated to, for example, about 31 ° C. by the heater 313, and the pressure in the reaction chamber 302 is set to 7.5 MPa or more. Then, the liquefied carbon dioxide injected onto the substrate 311 in the reaction chamber 302 becomes a supercritical state. The pressure in the reaction chamber 302 can be increased by, for example, increasing the pumping amount by the pumping pump 304 and adjusting the valve 307 to reduce the amount of liquefied carbon dioxide discharged from the reaction chamber 302. .
Thereafter, the valve 305 is closed and the valve 307 is opened, the pressure in the reaction chamber 302 is reduced, and the supercritical carbon dioxide injected into the reaction chamber 302 is vaporized to complete supercritical drying. .

The applicant has not yet found prior art documents related to the present invention by the time of filing other than the prior art documents specified by the prior art document information described in this specification.
Japanese Patent Publication No. 1-220828 JP-A-8-97021 Japanese Patent Publication No. 1-170026 Applied Physics Letters, 66, 2655-2657, 1995 Proceedings of the 44th Joint Conference on Applied Physics, p778, Spring 1997

However, when supercritical drying as described above is performed, problems such as pattern collapse cannot be completely solved unless the rinse liquid is completely replaced with liquefied carbon dioxide.
For example, in the supercritical drying, as shown in FIG. 4A, the liquefied carbon dioxide 404 is put into a state where the pattern 402 on the substrate 401 is immersed in the rinse liquid 403 as shown in FIG. to add. By this addition, as shown in FIG. 4C, most of the rinse liquid 403 that has wetted the surface of the substrate 401 is removed. However, since the liquefied carbon dioxide 404 is difficult to be impregnated up to the minute gap of the pattern 402, the rinse liquid 403 may remain in the gap.

Even if the liquefied carbon dioxide 404 is brought into a supercritical state in this state, as shown in FIG. 4D, the rinsing liquid 403 which is a liquid remains between the patterns 402, and as a result, as shown in FIG. As described above, the pattern 402 falls.
Even between fine patterns, it is possible to replace the rinsing liquid between patterns with liquefied carbon dioxide if the state in which liquefied carbon dioxide is introduced is maintained for a long time. However, in a state that requires a long time for replacement, it is not realistic to apply to an actual process.

  In addition, technology that cleans and removes resist used for processing from a semiconductor substrate on which fine patterns and fine holes are formed by utilizing the high diffusivity of supercritical fluid is being studied. Since the material is difficult to dissolve, the desired cleaning effect is not obtained. Furthermore, in order to realize a supercritical state using carbon dioxide or the like, a very high pressure condition of 7 MPa is required, and thus there is a problem that usable apparatuses are limited. For example, in order to realize the high-pressure environment as described above, a high-pressure vessel that is subject to legal regulations is required.

  The present invention has been made to solve the above problems, and an object of the present invention is to enable supercritical processing at a lower pressure.

The supercritical processing method according to the present invention includes a first step in which a predetermined pattern on the substrate is immersed in a fluoride liquid under atmospheric pressure, and a state in which the pattern is immersed in the liquid, A second step of placing the substrate in a space that is sealed and held at a constant volume, and the liquid in which the pattern is immersed is heated to bring the liquid into a supercritical state, and the pattern is immersed in a fluoride supercritical fluid At least a fourth step for vaporizing the supercritical fluid in which the pattern is immersed, and in the third step, in the space due to an increase in the gas of the fluoride that is heated and vaporized, The pressure is set to the critical pressure of fluoride.
Therefore, in the third step, the supercritical state of the fluoride can be obtained by setting the liquid to a temperature higher than the critical temperature of the fluoride.

In the supercritical processing method, in the second step, a gas may be introduced into the space to be at atmospheric pressure or higher. Alternatively, the liquid may be heated by induction heating using an electric field generation source arranged inside an apparatus constituting the space.
In the supercritical processing method, the fluoride may be at least one of hydrofluoroether and hydrofluoroester.

  As described above, according to the present invention, a fluoride liquid in which a pattern formed on a substrate is immersed in a space that is sealed and held at a constant volume is heated to a supercritical state. Therefore, an excellent effect that supercritical processing can be performed at a lower pressure can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, as shown in FIG. 1A, a cleaning process is performed on a substrate 101 on which a predetermined pattern 101a is formed, so that the surface of the substrate 101 and the pattern 101a are immersed in the cleaning liquid 102. The cleaning liquid 102 is water, for example.

  Then, these are immersed in a fluoride liquid, and as shown in FIG. 1B, the substrate 101 whose surface is wet with the cleaning liquid 102 is immersed in the fluoride liquid 103 in the air atmosphere 104. And For example, a predetermined container in which the fluoride liquid 103 is stored may be prepared, and the substrate 101 may be immersed in the fluoride liquid 103 stored in the container.

  On the surface of the substrate 101 immersed in the fluoride liquid 103, due to the compatibility, a part of the cleaning liquid 102 is replaced with the fluoride liquid 103 as shown in FIG. Further, as shown in FIG. 1D, the surface of the substrate 101 and the pattern 101a are immersed in the fluoride liquid 103.

  Next, the fluoride liquid 103 in which the surface of the substrate 101 and the pattern 101a are immersed is heated in a predetermined sealed and constant reaction chamber to bring the fluoride into a supercritical state. As shown in FIG. 1E, in the sealed space 105, the surface of the substrate 101 and the pattern 101a are covered with a supercritical fluid 106 of fluoride. The pressure in the reaction chamber (sealed space 105), which is sealed and has a constant volume, can be made the critical pressure of fluoride by increasing the gas of the fluoride vaporized by heating. If heated above the critical temperature in a critical pressure state, the fluoride liquid 103 will be in a supercritical state. In this case, the subcritical state is included.

  By the way, in FIG. 1 (e), the sealed space 105 is shown for convenience. However, after the fluoride enters the supercritical state, the sealed space in the reaction chamber is instantaneously filled with the supercritical fluid. It becomes a state. Therefore, at the stage where the fluoride has reached the supercritical state, it is considered that there is substantially no space without the supercritical fluid, and the inside of the reaction chamber is filled with the supercritical fluid.

  Thereafter, in a state where the above-described internal temperature is maintained, for example, the above-described reaction chamber is partially released, the internal fluid is gradually discharged, and the internal pressure of the reaction chamber is reduced, thereby reducing the supercritical fluid of fluoride. As shown in FIG. 1F, the surface of the substrate 101 on which the pattern 101a is formed is in a dry state. According to the present embodiment, in the process of drying, a liquid substance (liquid) is not attached to the pattern 101a. In addition, according to the present embodiment, since the supercritical state of fluoride is used, as will be described later, supercritical processing can be performed at a lower pressure than when carbon dioxide or the like is used. It is said.

  In the state shown in FIG. 1E, the supercritical fluid 106 is very easily diffused compared to the liquid such as the cleaning liquid 102, and easily enters between the fine patterns 101a. Therefore, even if a small amount of the cleaning liquid 102 remains between the patterns 101a, the supercritical state can be quickly replaced with the supercritical fluid 106 and removed.

  By the way, an alcohol such as methanol or ethanol may be added to the fluoride liquid at a ratio of 10% or less and used in the same manner as described above. For example, when the cleaning liquid 102 is water, the compatibility can be improved by adding alcohol to the fluoride liquid. Moreover, if the addition amount of alcohol is about 10% or less, the flame retardancy of the fluoride liquid is maintained.

  In addition, although the case where it applied to the drying after a liquid process was demonstrated above, the supercritical processing method of this invention is not restricted to this. For example, the resist pattern made of an organic material formed on the substrate may be removed. The substrate on which the resist pattern is formed is immersed in the fluoride liquid, and after dissolving the resist in the fluoride liquid, the fluoride liquid is heated to a supercritical state as described above, Thereafter, the supercritical fluoride may be vaporized.

  For example, a pattern is formed on the substrate by etching using a resist pattern as a mask. By the above-described supercritical processing, a dry state without pattern collapse can be obtained in addition to the removal of the resist pattern. Since the fluoride liquid has polarity, the organic resist pattern can be dissolved.

Next, fluoride will be described. The fluoride is, for example, a hydrofluoroether having a COC bond or a hydrofluoroester having a COO group.
Examples of the hydrofluoroether include CF ₃ CF ₂ CH ₂ OCHF ₂ , CF ₃ CF ₂ OCH ₂ CF ₃ , C ₃ F ₇ OCH ₃ , CHF ₂ CF ₂ OCH ₂ CF ₃ , and CF ₃ CHFOCHF ₂ .

These are liquids at a temperature of about 20 ° C. and atmospheric pressure, but when heated to 150 to 200 ° C. in the range of 2 to 4 MPa, they become supercritical. For example, the critical point of CF ₃ CHFOCHF ₂ is 155 ° C. · 3 MPa. The critical point of CF ₃ CF ₂ OCH ₂ CF ₃ is 148 ° C. · 2.3 MPa.
Examples of the hydrofluoroester include CHF ₂ COOCH ₂ CH ₃ and (CF ₃ ) ₂ CHCOOCH ₃ . These are liquids in a state of about 20 ° C./atmospheric pressure, but become supercritical by heating to about 150 to 200 ° C. It goes without saying that the treatment cost can be reduced as the fluoride having a lower critical temperature is used.

Next, a supercritical drying apparatus that performs the above-described supercritical processing method will be described. FIG. 2 is a schematic cross-sectional view illustrating a configuration example of a supercritical drying apparatus 201 that performs the supercritical processing method described above. The supercritical drying apparatus 201 includes a processing chamber 202 whose outer wall is made of a metal material such as SUS and can be sealed inside.
Further, the supercritical drying apparatus 201 includes a dielectric 203 at the bottom of the processing chamber 202. The dielectric 203 is controlled by the control unit 204 and forms a high-frequency AC electric field of several MHz to several tens of MHz on the dielectric 203.

  Further, a discharge port 205 is connected to the processing chamber 202, and the discharge port 205 includes a pressure control valve 206. For example, if the pressure control valve 206 is fully closed, a space that is sealed inside the processing chamber 202 and maintained at a constant volume is obtained. Further, if the opening degree of the pressure control valve 206 is controlled based on the measurement result of the internal pressure of the processing chamber 202 by a pressure gauge (not shown), the amount of fluid discharged from the discharge port 205 and the internal pressure of the processing chamber 202 can be controlled. It becomes.

An operation example of the supercritical drying apparatus 201 will be described. First, a container 211 containing a fluoride liquid 212 in which a substrate 213 to be processed is immersed is carried into the processing chamber 202 and the dielectric 203 Place on top of the.
In this state, the dielectric 203 is operated under the control of the control unit 204, a high-frequency AC electric field of several MHz to several tens of MHz is formed on the dielectric 203, and the fluoride liquid 212 contained in the container 211 is induced. Heat.

  By the induction heating, the fluoride liquid 212 can be heated to a temperature above the critical point to be in a supercritical state. A part of the fluoride liquid 212 is vaporized by induction heating, and the vaporized fluoride gas fills the inside of the sealed processing chamber 202 and raises the pressure inside the processing chamber 202. As a result, the inside of the processing chamber 202 is at or above the critical pressure of fluoride, and the fluoride liquid 212 that is at or above the critical temperature by induction heating enters a supercritical state.

  Note that an inert gas such as nitrogen, carbon dioxide gas, or the like may be introduced into the processing chamber 202 to pressurize the processing chamber 202 to a predetermined pressure in advance. If the inside of the processing chamber 202 is in a state higher than the atmospheric pressure, the fluoride becomes a supercritical state more quickly by the heating described above.

Hereinafter, the supercritical processing method of the present invention will be described in more detail with examples.
First, a substrate having a single crystal silicon layer formed on a silicon oxide layer is prepared, and an opening pattern penetrating to the silicon oxide layer is formed in the single crystal silicon layer by a known electron beam lithography technique and etching technique. For example, a plurality of stripe-shaped opening patterns having a width of 50 nm at intervals of 50 nm are formed in the single crystal silicon layer. Thereafter, the silicon oxide layer in the pattern formation region is removed by wet etching using hydrofluoric acid to obtain a stencil structure.

After the wet etching, the substrate is washed with water, and the substrate is immersed in a CF ₃ CHFOCHF ₂ solution contained in a predetermined container while the substrate is wet with water.
Next, the container containing the CF ₃ CHFOCHF ₂ liquid in which the substrate is immersed is carried into the reaction chamber, the reaction chamber is sealed, and the CF ₃ CHFOCHF ₂ liquid contained in the container is heated. As a result, the CF ₃ CHFOCHF ₂ liquid is brought into a supercritical state.
Thereafter, the supercritical CF ₃ CHFOCHF ₂ is vaporized by lowering the pressure inside the container. When the internal pressure of the reaction chamber reaches about atmospheric pressure, the substrate is unloaded. In the unloaded substrate, a dried state can be obtained in a state where the formed stencil structure pattern is not deformed.

  First, a single crystal silicon substrate is prepared, and a resist pattern is formed on the substrate by a known electron beam lithography technique. For example, a plurality of striped resist patterns having a width of 50 nm at intervals of 50 nm are formed on the substrate. Next, using the formed resist pattern as a mask, the substrate is etched by reactive ion etching to form a silicon pattern on the substrate. The shape of the resist pattern is transferred to the silicon pattern.

Next, the substrate is immersed in a (CF ₃ ) ₂ CHCOOCH ₃ solution contained in a predetermined container. Thus, the resist pattern formed on the silicon pattern or the like is dissolved in the (CF ₃ ) ₂ CHCOOCH ₃ solution.
Next, the container containing the (CF ₃ ) ₂ CHCOOCH ₃ solution in which the substrate is immersed is carried into the reaction chamber, the reaction chamber is sealed, and then contained in the container (CF ₃ ) _2. By heating the CHCOOCH ₃ liquid, the (CF ₃ ) ₂ CHCOOCH ₃ liquid is brought into a supercritical state.

Thereafter, the pressure inside the container is reduced to vaporize (CF ₃ ) ₂ CHCOOCH ₃ in a supercritical state. When the internal pressure of the reaction chamber reaches about atmospheric pressure, the substrate is unloaded. In the unloaded substrate, the resist is removed and dried in a state where the formed silicon pattern is not deformed or collapsed.

It is process drawing explaining the supercritical processing method in embodiment of this invention. It is a block diagram which shows typically the schematic structure of the supercritical processing apparatus in embodiment of this invention. It is typical sectional drawing which shows the structure of the conventional supercritical drying apparatus. It is process drawing for demonstrating the conventional supercritical drying method.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 101 ... Substrate, 101a ... Pattern, 102 ... Cleaning liquid, 103 ... Fluoride liquid, 104 ... Atmosphere, 105 ... Sealed space, 106 ... Supercritical fluid of fluoride.

Claims (4)

A first step in which a predetermined pattern on the substrate is immersed in a fluoride liquid under atmospheric pressure;
A second step of placing the substrate in a space that is sealed and held at a constant volume in a state where the pattern is immersed in the liquid;
A third step in which the liquid in which the pattern is immersed is heated to bring the liquid into a supercritical state, and the pattern is immersed in the fluoride supercritical fluid;
And at least a fourth step of vaporizing the supercritical fluid in which the pattern is immersed,
In the third step, the pressure in the space is made the critical pressure of the fluoride by increasing the gas of the fluoride that is heated and vaporized. The supercritical processing method according to claim 1,
In the second step, a gas is introduced into the space so as to be at or above atmospheric pressure. In the supercritical processing method according to claim 1 or 2,
The liquid is heated by induction heating,
The supercritical processing method, wherein the electric field generation source for the induction heating is arranged inside an apparatus constituting the space. In the supercritical processing method according to any one of claims 1 to 3,
The supercritical processing method, wherein the fluoride is at least one of hydrofluoroether and hydrofluoroester.

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