KR101058980B1 - Silicon Oxide Etching Method Using Supercritical Carbon Dioxide and Cleaning Etch Residue - Google Patents

Abstract

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to etching chemicals using two chamber systems in the manufacture of capacitors constituting a memory cell of a DRAM element and in the fabrication of a structure having a microstructure, such as a micro driver body called MEMS. Etching the sacrificial film using the dissolved supercritical carbon dioxide; And using a supercritical carbon dioxide in which a cleaning chemical is dissolved, to remove the etching residue generated from the reaction of the sacrificial film with the etching chemical.

Supercritical Carbon Dioxide, MEMS, Etching, Sacrificial Layers, Etching Agents, Etch Residues, Cleaning Agents

Description

Method for etching silicon oxide film using supercritical carbon dioxide and cleaning method of etching residues {ETCHING METHOD OF SILICON DIOXIDE FILM AND CLEANING METHOD OF ETCHING RESIDUE USING SUPERCRITICAL CARBON DIOXIDE}

The present invention cleans an etching method and an etching residue for removing a silicon oxide film used as a sacrificial layer in manufacturing a micro electro mechanical system (MEMS) and a dynamic random access memory (DRAM) capacitor using supercritical carbon dioxide. It is about how to.

In general, a wet etching process using hydrofluoric acid (HF) is widely used in the MEMS manufacturing and DRAM capacitor manufacturing processes. MEMS are devices that integrate mechanical and electrical components on a single silicon wafer. Electrical and mechanical components are fabricated using typical integrated circuit (IC) techniques and micromachining processes, respectively. do. MEMS wafers deposit a sacrificial layer and a structural layer on a substrate and form a suspended or freestanding structure such as a beam or lever by selective etching of the sacrificial layer relative to the structural layer. can do. However, a major problem in fabricating MEMS structures is that adhesion may occur in aqueous systems based on the sacrificial layer etching process. The adhesion phenomenon may be due to van der Waals forces, hydrogen bridging or electrostatic attraction between the microstructure and the substrate, surface tension, and precipitation from the solution during the drying step. Due to the etching residue.

Thus drying the structure with an etching method involving hydrofluoric acid with a solvent other than water, a method of increasing surface roughness to minimize surface tension energy, and a liquid with little or no surface tension (e.g. isopropanol (IPA)). Some methods have been proposed to minimize the adhesion phenomenon by removing moisture. However, an etching method using a solvent other than water uses an etching composition including anhydrous hydrofluoric acid gas. In this case, the etching time for forming the microstructure takes 10 hours or more, and water is reduced to reduce the time. Although some are added, this eliminates the advantage of using anhydrous hydrofluoric acid etchant.

Moreover, the rapidly developing semiconductor industry is constantly demanding integration and miniaturization, and therefore, it is essential to manufacture dense structures having high aspect ratios. However, the wet etching process is difficult to penetrate to the lower part of the structure due to the limitation of surface tension, viscosity, and diffusivity of the etching solution, and the pattern poles that collapse and stick to each other due to capillary force during cleaning and drying after etching pattern fall). As described above, in the fabrication of the microstructures (particularly, the etching step of the sacrificial layer), the degree of surface tension of the etchant greatly affects the damage of the microstructures.

Problems such as pattern poles caused by the surface tension can be solved by using a supercritical fluid. As shown in FIG. 1, the material is in a supercritical state that does not liquefy regardless of the change in pressure above a predetermined critical temperature. In the phase diagram, the minimum temperature and pressure at which this supercritical state begins is called the critical point. Unlike the properties of conventional liquid solvents, these supercritical materials (hereinafter, supercritical fluids) have a density, viscosity, diffusion coefficient, and polarity that change with pressure. Physical properties such as polarity may be continuously changed from a gas-like state to a liquid-like state. Such supercritical fluids have high dissolving power, high diffusion coefficient, low viscosity and low surface tension. In particular, carbon dioxide is a material of particular interest in the technical field, such as the manufacture of semiconductor devices, because its critical temperature and pressure are not only 31.1 ° C. and 73.8 atm, but also non-toxic, non-flammable, and inexpensive. Therefore, when the silicon oxide film is etched with a supercritical carbon dioxide having no surface tension as a solvent, the pattern pole can be completely prevented. However, supercritical carbon dioxide fluids have dissolution characteristics similar to nonpolar organic solvents, and therefore have dissolving selectivity when used alone. Therefore, the use of supercritical carbon dioxide fluid alone is insufficient to remove the silicon oxide film as the sacrificial layer and to etch the silicon oxide film which is essential for the removal of the particles. Therefore, a study is performed to etch a silicon oxide film under a supercritical state by adding an additive which is effective for etching a sacrificial film and removing particles, more specifically a fluorinated compound capable of etching the silicon oxide film, to a supercritical carbon dioxide fluid. Has been. For example, a method of removing a silicon oxide film while removing contaminants using a supercritical fluid containing a fluorine compound or an organic solvent as a fluorine compound and a contaminant dissolving aid (JP 64-45125 A, JP 10-135170 A, JP 2003-513342 A and JP2003-224099 A). However, chemicals such as fluorine compounds capable of etching silicon oxide films are generally dissolved in a solvent such as water, but hardly dissolved in a supercritical carbon dioxide fluid and have a low etching rate. In particular, in forming the diaphragm member or the beam member of the sensor component, the silicon oxide film must be completely etched as a sacrificial layer of several tens to hundreds of nm thick, and the single wafer cleaning must be completed within a few seconds to one minute. By the proposed method, a practical etching rate of the silicon oxide film cannot be obtained.

Meanwhile, silicon oxide films such as tetraethoxysilane (TEOS), BPSG (Boron Phosphor Silicate Glass), and BSG (Boron Silicate Glass), which are sacrificial films for manufacturing MEMS and semiconductors, have pyridine (Pyridine) in dry etching using supercritical carbon dioxide. It was investigated that SiF ₄ 2 (CH ₂ ) ₅ NH was generated as an etching residue upon etching by anhydrous hydrofluoric acid added with pyridine, C ₅ H ₅ N). SiF ₄ 2 (CH ₂ ) ₅ NH is easily dissolved by water, but methanol, carbon tetrachloride, benzonitrile, pyridine, benzene, nitrobenzene, monochlorobenzene, chloroform, methyl iodide, thiophene, methylene chloride, methylene bromide, mesitylene, acetonitrile Insoluble properties in most chemicals.

Accordingly, there is a need for a method of etching in a short time without damaging the structure and effectively removing the etching residues generated in the etching.

Therefore, the technical problem to be achieved by the present invention is to etch the sacrificial film using supercritical carbon dioxide in which etching chemical is dissolved in a two chamber system in a short time without damaging the structure having a microstructure. Supercritical carbon dioxide in which a cleaning chemical is dissolved is used to effectively remove the etching residue generated from the reaction between the sacrificial film and the etching chemical.

The present invention includes etching the sacrificial layer using supercritical carbon dioxide in which etching chemical is dissolved using a two chamber system; And using a supercritical carbon dioxide in which a cleaning chemical is dissolved, to remove the etching residue generated from the reaction of the sacrificial film with the etching chemical.

According to the invention, the step of etching the silicon oxide film and the step of removing the etching residues are carried out continuously in the same process chamber (S10), under conditions above the critical point of carbon dioxide. The etching of the silicon oxide film and the conditions for removing the etching residue are a temperature range of 31.1 ° C to 100 ° C and a pressure range of 1085 psi to 5000 psi.

According to the present invention, the sacrificial film is a silicon oxide film used to form a structure in the fabrication of MEMS and DRAM capacitors, such as Tetra Ethyl Ortho Silicate (TEOS), Boro-Phospho Silicate Glass (BPSG), and a thermally oxidized SiO ₂ film ( One of silicon oxide films including Thermal SiO ₂ ), and the etching agent includes both fluoride and co-solvent, and the cleaning agent is nitromethane, bis (2- At least one of methoxyethyl) ether (bis (2-methoxyethyl) ether).

The fluorine compound is hydrofluoric acid (HF), hydrogen fluoride ether (HFE), poly [4-vinylpyridinium poly (hydrogen fluoride), hydrogen fluoride 2,4,6-trimethylpyridine and ammonium fluoride (Ammonium) Fluoride, NH ₄ F) It is characterized in that it comprises at least one.

The cosolvent necessarily includes pyridine (C ₅ H ₅ N) and an alcohol, wherein the alcohol is at least one of methanol, ethanol, Iso Propyl Alcohol (IPA) and propanol.

In the present invention, the etching of the silicon oxide film is characterized in that the mixture of the fluorine compound and the co-solvent in supercritical carbon dioxide is 0.01 to 10 wt%.

The step of removing the etching residue is a result of etching the silicon oxide film using supercritical carbon dioxide in which at least one of the compound is nitromethane, bis (2-methoxyethyl) ether and dissolved at 5 to 20 wt% of one of the compounds And a second cleaning step (C3) for cleaning the resultant of the first cleaning step (C2) by using only the first cleaning step (C2) and the supercritical carbon dioxide. In order to increase the cleaning efficiency in the first cleaning step (C2), alcohols contained in the supercritical carbon dioxide in an amount of 1 to 10 wt% may be used, and the alcohol may be used in methanol, ethanol, isopropyl alcohol (IPA) and propanol. At least one thing.

In order to achieve the above another technical problem, the present invention provides a two-chamber system capable of etching under conditions above the critical point of the solvent. The system includes a process chamber (S10) into which a semiconductor substrate on which a silicon oxide film is formed is loaded, a supply chamber (S7) for providing a mixture of an etching solution and a supercritical fluid to the process chamber, as shown in FIG. Discharge part (S11) for discharging from the chamber Supply unit (S2) for supplying a fluid containing a solvent to the supply chamber (S7) in a supercritical state and the injection unit (S5) for injecting an etching solution into the supply chamber (S7) And, the control unit for controlling the operating temperature and pressure of the supply unit (S2), the supply chamber (S7), the solution injection unit (S5) and the discharge unit (S11). In this case, the control device maintains the supply chamber S7 and the process chamber S10 at a condition above the critical point of the fluid in etching the silicon oxide film and removing the etching residue.

According to the present invention, in the etching of the silicon oxide film, the fluid includes the etching solution and the supercritical carbon dioxide solvent. Also in the step of removing the etch residue, the fluid comprises the cleaning solution and the supercritical carbon dioxide solvent.

The supply chamber S7 and the process chamber S10 may include a temperature control device S9 and a stirring control device S6 for controlling the internal temperature and the fluid agitation, and the supply chamber S7. The operation, temperature, and pressure of the process chamber S10 and the supply unit S2 and the discharge unit S10 may be controlled by a predetermined control device.

3 is a process flowchart illustrating a method of etching the silicon oxide film and a method of removing the etching residue according to embodiments of the present invention.

Referring to FIG. 3, the silicon oxide film etching process and the etching residue removing process may be performed in the following order. First, the semiconductor substrate is supplied to the process chamber S10 from the outside (E0). Subsequently, supercritical carbon dioxide and an etching solution are injected into the supply chamber S7 and stirred (E1). After a certain time, the pressure is applied from the supercritical solvent supply unit S2 to the supply chamber S7, and at the same time, the valve S8 between the supply chamber S7 and the process chamber S10 is opened and closed, thereby etching the solution into the process chamber S10. Is added to proceed with etching (E2). After etching the silicon oxide film, the valve S8 is shielded, the solvent is injected directly into the process chamber S10 from the supercritical solvent supply unit S2, and at the same time, the process chamber S10 is opened by opening and closing the discharge unit S11. To remove the fluid through the discharge (S11) (E3). Likewise, the supercritical solvent supply unit S2 directly injects the solvent into the process chamber S10 for cleaning the supply chamber S7, and simultaneously discharges the fluid in the process chamber through opening and closing the outlet S11. Remove through S11) (E3). Thus, the first cleaning process is performed to complete the etching process of the silicon oxide film and to remove the etching residue. First, the supercritical carbon dioxide and the cleaning solution are injected into the supply chamber S7 and stirred (C1). After a certain time, the pressure is applied from the supercritical solvent supply unit S2 to the supply chamber S7, and at the same time, the valve S8 between the supply chamber S7 and the process chamber S10 is opened and closed to wash the process chamber S10. The washing is carried out by adding (C2). Unlike the etching process, in the cleaning process, the valve S12 between the process chamber S10 and the discharge part S11 is opened and closed to open the process chamber S10 from the supercritical solvent supply part S2 through the supply chamber S7. The cleaning fluid is flowed to the wafer surface at a constant flow rate. After cleaning the etching residue on the wafer surface for a predetermined time, the valve S8 between the process chamber S10 and the supply chamber S7 is shielded and the solvent is directly added to the process chamber S10 at the supercritical solvent supply S2. At the same time, the fluid of the process chamber S10 is removed through the discharge part S11 by opening and closing the discharge part S11 (C3).

The etching rate of the silicon oxide film was indirectly investigated by measuring the thickness of the oxide film through an ellipsometer, and as a result, compared with the conventional wet etching method or using a single chamber without a supply chamber (S7), Improved etch rates have been shown using etch chemicals in two chamber etch systems within critical carbon dioxide.

The results of the etching and cleaning processes were observed under an electron microscope to confirm that the etching residues remaining on the wafer surface were completely removed, and no organic compound peaks appeared in the IR and NMR spectra of the residues. Did.

Etching systems and methods and cleaners for removing etch residues and silicon oxide film etchant in accordance with the present invention are carried out using supercritical carbon dioxide. Because of the high reactivity of the supercritical fluid, the etching process according to the present invention has improved productivity over conventional techniques. In addition, through the low surface tension of the supercritical fluid and the etching residue removal effect of the cleaning solution, the present invention provides the manufacture of capacitors constituting the memory cells of the DRAM device and the fabrication of a structure having a microstructure such as a micro driver body called MEMS. Applicable to

Hereinafter, the configuration and effects of the present invention will be described in more detail with reference to examples, but this is for understanding the configuration and effects of the present invention and is not intended to limit the scope of the present invention.

Example 1

Conventional etching methods using supercritical carbon dioxide have been insufficient in the process of mixing the etching solution and the supercritical carbon dioxide, thus failing to realize a high etching rate.

In the present invention, before the etching reaction in the process chamber (S10) is performed, the alcohol is added to the preparation of the etching solution with the supply chamber (S7) to find a process for making sufficient HF ₂ ^- etching species.

4 is a graph showing the necessity of adding alcohol in preparing the etching solution of the present invention.

In the etching solution used in the present embodiment, a solution in which hydrofluoric acid and pyridine were mixed at a volume ratio of 70:30, methanol, ethanol, IPA, butanol, and pyridine was added at a volume ratio of 1: 5, respectively, to add five types of etching solutions. Prepared. The prepared etching solution is injected into the supply chamber S7 through the solution supply part S5 by 0.5 wt% relative to the supercritical carbon dioxide supply and at a pressure of 4000 psi into the supply chamber S7 fixed at a temperature of 40 ° C. Inject supercritical carbon dioxide. The injected supercritical carbon dioxide and etching solution makes enough HF ₂ ⁻ ions for 10 minutes in the supply chamber S7 (E1). The supply chamber S7 and the process chamber (S7) so that the etching fluid of the supply chamber S7 may be supplied from the supercritical carbon dioxide supply unit S2 to the process chamber S10 containing the wafer on which the TEOS thin film is deposited in advance. It adjusts as valve S8 between S10). After the etching fluid is supplied, the TEOS thin film is etched for 20 minutes (E2), and the body pure supercritical carbon dioxide shielded with the supply chamber (S7) is 20 ml / min directly from the supercritical carbon dioxide supply (S2) for 5 minutes. Flow was completed to complete the etching process (E3).

As a result of performing the above etching process on the five kinds of etching solutions, as shown in FIG. 4, the etching rates were found to be high in the order of methanol, ethanol, IPA, butanol, and pyridine. This seems to be due to the degree of ionization for hydrofluoric acid (HF).

In the present invention, the etching solution is prepared by adding about 5 wt% to 20 wt% of the alcohol in the supercritical carbon dioxide solvent and ionizing hydrofluoric acid for a suitable time using a supply chamber (S7). Performance was obtained.

Example 2

Figure 5 (a) is a SEM image of the result of performing a 900 nm deposited TEOS single thin film on the two-chamber system with the supercritical carbon dioxide containing the etching solution of the present invention through the etching process.

In FIG. 5A, small white particles were observed to remain on the wafer surface, and the etching residue was produced by reacting SiF ₄ generated in the etching process with pyridine present in the etching solution. The resulting etch residue was found to be insoluble in most organic solvents other than water.

The etching process performed in this embodiment was performed in the same manner as in the etching step of Example 1. The etching solution used was prepared by adding a mixture of hydrofluoric acid and pyridine in a 70:30 volume ratio and methanol in a 1: 5 volume ratio, and the etching solution was supplied to the supply chamber S7 through the solution supply part S5. Supercritical carbon dioxide is injected at a pressure of 4000 psi into the supply chamber S7 fixed at a temperature of 40 degrees and injected in an amount of 0.5 wt% relative to the supercritical carbon dioxide supply. The injected supercritical carbon dioxide and the etching solution are sufficiently mixed in the supply chamber (S7) for 10 minutes, and then the supply chamber from the supercritical carbon dioxide supply unit (S2) to the process chamber (S10) containing the wafer on which the TEOS thin film is deposited. It adjusts as the valve S8 between the supply chamber S7 and the process chamber S10 so that the etching fluid of S7 may be supplied by 4000psi. After the etching fluid was supplied for 20 minutes, the TEOS thin film was etched, and the supply chamber S7 and the shielded sieve pure supercritical carbon dioxide were flowed directly from the supercritical carbon dioxide supply unit S2 at 20 ml / min for 5 minutes. .

FIG. 5 (b) shows the result of applying the cleaning process after obtaining the result of FIG. 5 (a). In order to perform the first cleaning process in the cleaning process, a cleaning fluid in which bis (2-methoxyethyl) ether is dissolved by 10wt% with respect to the supercritical carbon dioxide solvent is prepared in the supply chamber S7. The cleaning fluid is pressurized to 4000 psi from the supercritical carbon dioxide supply S2 and has fluidity through opening and closing with the process chamber S10 in which the etching residue is generated on the wafer surface. The cleaning fluid is discharged through the process chamber (S10) to the outlet (S11) for 10 minutes at a rate of 10ml / min to have a cleaning effect. In order to perform the second cleaning process, after the first cleaning process is completed, the pure supercritical carbon dioxide is flowed directly to the process chamber S10 at 20 ml / min for 5 minutes without passing through the supply chamber S7 to complete the process. do.

Through the results of FIG. 5 (b), the cleaning process using the cleaning solution containing the bis (2-methoxyethyl) ether was able to obtain almost 100% of the etching byproducts.

1 is a phase diagram of carbon dioxide.

2 is a conceptual diagram of an etching apparatus for describing two chamber systems according to the present invention.

3 is a process flowchart for explaining an etching method and a cleaning method according to the present invention.

4 is an etching rate graph illustrating the etching performance improvement according to the alcohol co-solvent addition in the two chamber system of the present invention.

5 (a) and 5 (b) are electron micrographs for explaining the cleaning effect of the etching residue of the cleaning chemical of the present invention.

* Explanation of symbols for the main parts of Figure 2 *

S1: carbon dioxide storage tank, S2: ISCO syringe pump (supercritical carbon dioxide supply), S3: non-return valve, S4: 3way valve, S5: etching and cleaning chemical supply, S6: agitator, S7: supply chamber, S8: 3way Valve, S9: temperature control means, S10: process chamber, S11: outlet, S12: hot wire

Claims (13)

A method of fabricating a capacitor constituting a memory cell of a DRAM device and fabricating a structure having a microstructure such as a micro driver body called MEMS, the method comprising: forming a sacrificial film; Etching the sacrificial layer using supercritical carbon dioxide in which an etching chemical is dissolved; And removing the etching residues generated from the reaction of the etching chemicals, and cleaning the resulting product of etching the sacrificial layer by using supercritical carbon dioxide which necessarily includes at least one of nitromethane and bis (2-methoxyethyl) ether. Washing step; And a second cleaning step of cleaning the resultant of the first cleaning step using only supercritical carbon dioxide. The method of claim 1, wherein etching the sacrificial film and removing the etch residue are carried out continuously using two chamber systems, in a same process chamber, under conditions above a critical point of carbon dioxide. Etching method. The etching method of claim 2, wherein the etching of the sacrificial layer is performed at a temperature range of 31.1 ° C. to 100 ° C. and a pressure range of 1085 psi to 5000 psi. The method of claim 2, wherein removing the etch residue is performed at a temperature range of 31.1 ° C. to 100 ° C. and a pressure range of 1085 psi to 5000 psi. 2. The silicon oxide film of claim 1, wherein the sacrificial film is a silicon oxide film used to form a structure in a MEMS fabrication and a DRAM capacitor fabrication, and is formed of Tetra Ethyl Ortho Silicate (TEOS), Boro-Phospho Silicate Glass (BPSG), and a thermally oxidized SiO ₂ film. One of the silicon oxide films containing (Thermal SiO ₂ ), wherein the etching agent comprises both a fluoride and a co-solvent. The method of claim 5, wherein the fluorine compound is hydrofluoric acid (Hydrofluoric Acid (HF), hydrofluoric ether (Hydro Fluoro Ether, HFE), Poly [4-vinylpyridinium poly (hydrogen fluoride), Hydrogen fluoride 2,4,6-trimethylpyridine And ammonium fluoride (Ammonium Fluoride, NH ₄ F). 6. The method of claim 5, wherein the cosolvent necessarily comprises pyridine (C ₅ H ₅ N) and an alcohol, wherein the alcohol is at least one of methanol, ethanol, Iso Propyl Alcohol (IPA) and propanol. . The etching method as claimed in claim 5, wherein the etching of the sacrificial film uses the supercritical carbon dioxide in which one of the mixture of the fluorine compound and the co-solvent is dissolved at 0.01 to 10 wt%. The etching method according to claim 1, wherein the nitromethane or bis (2-methoxyethyl) ether used in the first cleaning step is dissolved at 5 to 20 wt% in supercritical carbon dioxide. The etching method according to claim 1, wherein alcohol is added together with nitromethane or bis (2-methoxyethyl) ether used in the first cleaning step to improve cleaning power. The method of claim 10, wherein the alcohol is at least one of methanol, ethanol, Iso Propyl Alcohol (IPA) and propanol. The etching method according to claim 10, wherein the alcohol is dissolved in supercritical carbon dioxide at 1 to 10 wt%. delete

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