Silicon etching solution and method for manufacturing a silicon device using the etching solution

Abstract

To provide a silicon etchant that makes it possible to suppress the influence of the amount of dissolved oxygen in the chemical solution and enables uniform etching process regardless of the dissolved oxygen concentration.SOLUTION: A silicon etchant consists essentially only of quaternary alkylammonium hydroxide, water, and certain ether compounds.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a silicon etching solution used in surface processing and etching processes when manufacturing various silicon devices. The present invention also relates to a method for manufacturing a silicon device using the etching solution.

Background Art

[0002] In consideration of the selectivity for silicon oxide films and silicon films, alkaline etching may be used in the manufacturing process of semiconductors using silicon. As the alkali, NaOH, KOH, and tetramethylammonium hydroxide (hereinafter also referred to as TMAH), which have low toxicity and are easy to handle, are used alone. Among them, TMAH has an etching rate for silicon oxide films that is approximately one order of magnitude lower than that when using NaOH or KOH. In particular, it is preferably used when using a silicon oxide film that is less expensive than a silicon nitride film as a mask material.

[0003] In semiconductor devices, due to the stacking of memory cells and the densification of logic devices, the requirements for etching are becoming stricter. In the etching of silicon, silicon is oxidized by dissolved oxygen in the silicon etching solution, and accordingly, the etching rate decreases. Since the amount of oxidation of silicon varies depending on the dissolved oxygen concentration, the degree of decrease in the etching rate also varies depending on the dissolved oxygen concentration. Variations in the etching rate due to the dissolved oxygen concentration in the silicon etching solution also occur due to the circumferential direction of the substrate, the depth direction of the pattern, differences in the environment due to device differences and the location of the factory, and the weather, etc., and there is a problem that uniform etching processing may not be possible.

[0004] In recent years, processes using silicon etching have been frequently used in semiconductor manufacturing processes. As an example of such a process, a charge storage type memory will be described. The charge storage type memory includes, for example, a substrate W having a stacked film 91 including a plurality of polysilicon films P1, P2, P3 and a plurality of silicon oxide films O1, O2, O3, and its manufacturing process includes an etching process of the stacked film 91. At the time of etching, an etching solution is supplied to a recess 92 provided in the substrate W to selectively etch the polysilicon films P1, P2, P3. The charge storage type memory operates as a memory by storing charges in the polysilicon film. The amount of charge stored depends on the volume of the polysilicon film. Therefore, in order to achieve the designed capacity, it is necessary to strictly control the volume of the polysilicon film. However, if the etching rate varies depending on the dissolved oxygen concentration as described above, the polysilicon film cannot be etched to the designed volume, making it difficult to manufacture the device. In particular, in recent years, charge storage type memories have been multilayered, and the depth of the pattern reaches several micrometers. Therefore, the dissolved oxygen concentration in the silicon etching solution is different between the layer near the wafer surface and the lower layer, and it is difficult to etch as designed in the depth direction. and the device manufacturing becomes difficult.

[0005] Therefore, in the etching process affected by oxygen, the etching process is carried out in an environment where the oxygen concentration is adjusted by a processing apparatus that controls the processing atmosphere concentration.

[0006] Also, in the process of removing polymer (resist residue), in order to prevent the metal film on the substrate from being oxidized by the dissolved oxygen in the polymer removal solution and the generated metal oxide film from being etched by the polymer removal solution, a treatment is carried out using a chemical solution with a reduced amount of dissolved oxygen using a processing apparatus that adjusts the amount of dissolved oxygen in the chemical solution (Patent Document 1).

[0007] Patent Document 2 discloses an etching solution for a silicon substrate for a solar cell, which contains an alkali hydroxide, water, and a polyalkylene oxide alkyl ether. Patent Document 3 discloses an etching solution for a silicon substrate for a solar cell, which contains an alkali compound, an organic solvent, a surfactant, and water. In Patent Document 3, TMAH is exemplified as an example of the alkali compound, and a polyalkylene oxide alkyl ether is exemplified as the organic solvent, but the alkali compounds actually used are sodium hydroxide and potassium hydroxide.

[0008] Patent Document 4 discloses a developer containing a quaternary alkyl ammonium hydroxide, a nonionic surfactant, and water. Although a polyalkylene oxide alkyl ether is exemplified as the nonionic surfactant, in reality, a nonionic surfactant with high surface activity such as acetylene glycol-based Surfynol (trade name) is used.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, in the processing apparatus of Patent Document 1, it is necessary to precisely control the oxygen concentration in the processing atmosphere and the dissolved oxygen concentration in the chemical solution in order to perform a uniform etching process. Therefore, precise adjustment of the processing apparatus and the technology therefor are required to perform the etching process.

[0011] In addition, in the etching solutions of Patent Document 2 and Patent Document 3, since NaOH and KOH are used as the alkali compounds, the etching rate for the silicon oxide film is high. For this reason, not only the mask material but also the silicon oxide film which is a part of the pattern structure is etched, and it is not possible to selectively etch only the polysilicon film. The developer of Patent Document 4 is not for the purpose of precise etching of silicon, and therefore no consideration is given to the influence of dissolved oxygen on the etching solution. Also, the nonionic surfactant actually used is Surfynol or the like, which has high surface activity performance, covers the surface of the polysilicon film, rather impairs the etching of the polysilicon, and it is not possible to etch the polysilicon film with high precision.

[0012] Therefore, an object of the present invention is to provide a silicon etching solution capable of suppressing the influence of the amount of dissolved oxygen in the chemical solution and enabling uniform etching treatment regardless of the dissolved oxygen concentration. In a preferred aspect of the present invention, it is an object to provide a method for adjusting the degree of influence on the etching rate by the dissolved oxygen concentration of the silicon etching solution by adjusting the composition ratio of the silicon etching solution.

Means for Solving the Problems

[0013] As a result of intensive efforts, the present inventors have found that the above problems can be solved by including the compound represented by the formula (1) in a silicon etching solution containing a quaternary alkylammonium hydroxide and water.

[0014] That is, the first aspect of the present invention is a mixed solution containing a quaternary alkylammonium hydroxide and water, the compound represented by the following formula (1) R 1 O-(C m H 2m O) n -R 2 (1) (In the formula, R 1 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 6, and n is 1 or 2.) is a silicon etching solution containing

[0015] In the first invention, the concentration of the quaternary alkylammonium hydroxide is preferably 0.1 to 25% by mass, and the concentration of the compound represented by the formula (1) is preferably 0.1 to 20% by mass.

[0016] In the first invention, it is more preferable that the concentration of the quaternary alkylammonium hydroxide is 0.5 to 25% by mass, and the concentration of the compound represented by the formula (1) is 0.1 to 20% by mass.

[0017] Further, the silicon etching solution of the first invention preferably has an etching rate ratio of 0.5 to 1.5.

[0018] The second invention is a method for manufacturing a silicon device including a step of etching a silicon wafer, a polysilicon film, and an amorphous silicon film, wherein the etching is performed using the silicon etching solution of the first invention.

[0019] In the present invention, the etching rate ratio is the ratio of the etching rates of the etching solutions having the same component composition of the etching solution but different dissolved oxygen concentrations with respect to polysilicon, and is the ratio of the etching rate of the etching solution with a low dissolved oxygen concentration to the etching rate of the etching solution with a high dissolved oxygen concentration (etching rate at low dissolved oxygen concentration / etching rate at high dissolved oxygen concentration). When the etching rate ratio is close to 1, it means that the etching rate is less affected by the dissolved oxygen concentration.

[0020] According to the studies of the present inventors, when a compound represented by the formula (1) is contained in a conventional silicon etching solution containing a quaternary alkylammonium hydroxide and water, the etching rate of silicon decreases. However, compared with a silicon etching solution not containing the compound represented by the formula (1), it was found that the degree of variation in the etching rate due to the difference in the dissolved oxygen concentration in the silicon etching solution is reduced. When the dissolved oxygen concentration is high, the etching rate is slow, and the etching rate decreases by containing the compound represented by the formula (1). On the other hand, when the dissolved oxygen concentration is low, the etching rate is faster than when the dissolved oxygen concentration is high, but the etching rate significantly decreases by containing the compound represented by the formula (1). The ratio of the decrease in the etching rate when the compound represented by the formula (1) is added to an etching solution with a high dissolved oxygen concentration is smaller compared to the case where the dissolved oxygen concentration is low. That is, the etching rate ratio decreases by the addition of the compound represented by the formula (1).

[0021] Therefore, by adjusting the content of the compound represented by the formula (1), it is possible to reduce the variation in the etching rate (the etching rate ratio is near 1) even when the dissolved oxygen concentration in the silicon etching solution is high or low, and it is possible to suppress the variation in the etching rate due to the variation in the dissolved oxygen concentration in the silicon etching solution.

Advantages of the Invention

[0022] The etching rate of the silicon etching solution of the present invention is hardly affected by the dissolved oxygen concentration, and a uniform etching process is possible regardless of the dissolved oxygen concentration in the silicon etching solution. Therefore, the need for precise adjustment with a processing apparatus that adjusts the oxygen concentration in the processing atmosphere or the dissolved oxygen concentration of the chemical solution is reduced. Furthermore, even if the dissolved oxygen concentration in the silicon etching solution varies due to the circumferential direction of the substrate, the depth direction of the pattern, differences in the apparatus error of the apparatus or the environment due to the location of the factory, the weather, etc., the etching rate does not vary, and a uniform etching process is possible.

[0023] Further, by adjusting the composition ratio of the silicon etching solution, the degree to which the etching rate of the silicon etching solution is affected by the dissolved oxygen concentration can be adjusted, and a silicon etching solution having a desired etching rate ratio can be prepared.

Brief Description of the Drawings

[0024]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0025] The silicon etching solution of the present invention is a mixed solution containing quaternary alkylammonium hydroxide and water, and contains a compound represented by the following formula (1) R 1 O-(C m H 2m O) n -R 2 (1) (In the formula, R 1 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 6, and n is 1 or 2.) and contains.

[0026] As the quaternary alkylammonium hydroxide, tetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), ethyltrimethylammonium hydroxide (ETMAH), tetrapropylammonium hydroxide, or tetrabutylammonium hydroxide, which are used in conventional silicon etching solutions composed of aqueous solutions of quaternary alkylammonium hydroxides, can be used without particular limitation. Among these quaternary alkylammonium hydroxides, those in which the alkyl group has 1 to 4 carbon atoms and all alkyl groups are the same quaternary alkylammonium hydroxide are preferred. In particular, it is most preferred to use TMAH because of the high etching rate of silicon. Also, the concentration of the quaternary alkylammonium hydroxide is not particularly different from that of conventional silicon etching solutions, and a range of 0.1 to 25% by mass is preferred because excellent etching effects can be obtained without crystal precipitation. Furthermore, it is more preferred that the concentration of the quaternary alkylammonium hydroxide is in the range of 0.5 to 25% by mass.

[0027] The silicon etching solution of the present invention is characterized by containing a compound represented by the following formula (1). That is. R 1 O-(C m H 2m O) n -R 2 (1) In the above formula (1), R 1 is a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, R 2 is a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, m is an integer of 2 to 6, and n is 1 or 2.

[0028] R 1 is preferably a hydrogen atom or a methyl group, R 2 is preferably a propyl group or a butyl group, and m is preferably 2 or 3.

[0029] Specific examples of the compound represented by the above formula (1) that are particularly preferably used in the present invention include ethylene glycol monopropyl ether, ethylene glycol dimethyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol dimethyl ether, diethylene glycol methyl ethyl ether, diethylene glycol diethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, propylene glycol dimethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol dimethyl ether. These compounds may be used alone or in combination of two or more different types.

[0030] By including the compound represented by the formula (1), it becomes possible to suppress the influence of the dissolved oxygen concentration in the silicon etching solution, and uniform etching treatment is possible regardless of whether the dissolved oxygen concentration is low or high. Further, by adjusting the content of the compound represented by the formula (1), a silicon etching solution having an influence depending on a desired dissolved oxygen concentration can also be obtained.

[0031] The concentration of the compound represented by the above formula (1) is preferably 20% by mass or less, more preferably less than 15% by mass, still more preferably 12% by mass or less, and particularly preferably 10% by mass or less, based on the mass of the entire etching solution. Also, the concentration of the compound represented by the above formula (1) is preferably 0.1% by mass or more. When the concentration of the compound represented by the above formula (1) is within the above range, the difference in etching rate due to the influence of the dissolved oxygen concentration becomes small, so it becomes difficult to be affected by the circumferential direction of the substrate, the depth direction of the pattern, the difference in the apparatus of the apparatus, the environmental difference due to the location of the factory, the weather, etc., and uniform etching treatment becomes possible.

[0032] The total concentration of the quaternary alkylammonium hydroxide and the compound represented by the formula (1) is preferably 45% by mass or less, more preferably 40% by mass or less, still more preferably 35% by mass or less, and the lower limit is preferably 0.2% by mass or more, and still more preferably 1.0% by mass or more. In the silicon etching solution, within a range not impairing the object of the present invention, in addition to the quaternary alkylammonium hydroxide and the compound represented by the formula (1), a surfactant or the like may be added, but since these may affect the etching property, it is preferably 1% by mass or less, and more preferably not contained. Therefore, it is preferable that the entire remaining amount other than the quaternary alkylammonium hydroxide and the compound represented by the formula (1) in the silicon etching solution is water.

[0033] The mechanism by which the influence of the dissolved oxygen concentration in the silicon etching solution can be reduced by adding the compound represented by the above formula (1) is not necessarily clear. However, the present inventors have considered as follows. The compound represented by the above formula (1) can be considered as a nonionic surfactant having relatively low surface activity. Dissolved oxygen in the silicon etching solution reacts with the polysilicon surface to form an oxide film on the silicon surface. As a result of this oxide film functioning as a mask material, the etching rate for polysilicon decreases. On the other hand, the compound represented by the formula (1) has surface activity and adheres to the polysilicon surface to temporarily protect it. As a result, the contact between the dissolved oxygen and the polysilicon surface is inhibited, and the formation of the oxide film is suppressed. However, since the surface activity of the compound represented by the formula (1) is relatively low, it dissociates from the polysilicon surface. As a result, the silicon etching solution comes into contact with the polysilicon surface and etching is performed. The adhesion and dissociation of the compound represented by the formula (1) to the polysilicon surface are repeated, and etching proceeds gently during this period. As a result, although the etching rate becomes slow, it is considered that the influence of the dissolved oxygen is reduced.

[0034] On the other hand, if a nonionic surfactant with high surface activity is used instead of the compound represented by formula (1), the surfactant strongly adheres to the polysilicon surface, inhibiting the contact between the polysilicon surface and the etching solution and making it difficult for etching to proceed.

[0035] Therefore, the compound represented by formula (1) preferably has appropriate hydrophilicity and hydrophobicity. For example, when m is 4 or more in formula (1), the compound tends to be hydrophobic. In this case, for the balance between hydrophobicity and hydrophilicity, 1 and 2 are both preferably hydrogen.

[0036] Also, the preferred concentration of the compound represented by formula (1) varies depending on the concentration of tetraalkylammonium hydroxide in the silicon etching solution and the temperature of the silicon etching solution. For example, when tetraalkylammonium hydroxide is TMAH, the compound represented by formula (1) is propylene glycol monopropyl ether, the solution temperature is 40 °C, the TMAH concentration is 5% by mass, and the substrate to be etched is an undoped polysilicon substrate, the propylene glycol monopropyl ether is preferably 1 to 5% by mass. When the TMAH concentration is 10% by mass, the propylene glycol monopropyl ether is preferably 4 to 10% by mass.

[0037] The etching rate ratio of the silicon etching solution of the present invention is preferably 0.5 to 1.5, more preferably 0.65 to 1.35, and even more preferably 0.75 to 1.30. When the etching rate ratio is within the above range, it is possible to suppress the influence of the dissolved oxygen concentration in the silicon etching solution on the etching rate. Regardless of fluctuations in the dissolved oxygen concentration caused by the circumferential direction of the substrate, the depth direction of the pattern, differences in the apparatus due to the location of the factory, environmental differences due to the location of the factory, weather, etc., the etching rate of silicon is almost constant, enabling uniform etching.

[0038] The etching rate ratio is the ratio of the etching rate of a silicon etching solution with a low dissolved oxygen concentration to the etching rate of a silicon etching solution with a high dissolved oxygen concentration (etching rate of silicon etching solution with low dissolved oxygen concentration / etching rate of silicon etching solution with high dissolved oxygen concentration) at the liquid temperature during etching of silicon etching solutions having the same component composition and differing only in the dissolved oxygen concentration in the liquid.

[0039] The etching rate ratio is the etching rate (R N ) at the dissolved oxygen concentration (low dissolved oxygen concentration) after deaeration of dissolved oxygen by N2 bubbling and the etching rate (R A ) at the saturated dissolved oxygen concentration (high dissolved oxygen concentration) after air bubbling. It is preferable that the ratio (R N / R A ) is within the above range.

[0040] The preferable conditions for obtaining the ratio (R N ) of the etching rate at the dissolved oxygen concentration after deaeration of dissolved oxygen by N2 bubbling to the etching rate (R A ) at the saturated dissolved oxygen concentration after air bubbling (R N / R A ) are as follows. The temperature during etching is the temperature at the time of actual etching. The N2 bubbling conditions for the silicon etching solution are such that a data table is prepared with the flow rate and bubbling time of N2 determined with respect to the amount of the silicon etching solution so that the dissolved oxygen concentration decreases to a certain concentration value, and adjustment is made by bubbling N2 based on the data table. Thereby, an etching solution substantially free of dissolved oxygen is obtained. The air saturation conditions for the silicon etching solution are such that a data table is prepared with the flow rate and bubbling time of air determined with respect to the amount of the silicon etching solution so that the dissolved oxygen concentration increases to a certain concentration value, and air is bubbled into the silicon etching solution based on the data table. Thereby, an etching solution with a saturated oxygen concentration is obtained. ​Prior to measuring the etching rate, a target substrate from which the native oxide film has been removed is prepared, and this target substrate is immersed in an etching solution to calculate the etching rate calculated from the film thickness difference before and after the treatment. As can be seen from the examples, the etching rate (R N ) at the dissolved oxygen concentration after N2 aeration of the silicon etching solution and the etching rate (R A ) at the saturated dissolved oxygen concentration after air aeration, and the ratio (R N / R A ) are preferably 0.5 to 1.5.

[0041] The silicon etching solution of the present invention can be easily prepared by mixing and dissolving a predetermined amount of the compound represented by the formula (1) in an aqueous solution of quaternary alkylammonium hydroxide at a predetermined concentration. At this time, instead of directly mixing the compound represented by the formula (1), an aqueous solution of the compound represented by the formula (1) at a predetermined concentration may be prepared in advance and mixed.

[0042] The silicon etching solution of the present invention has the characteristics of an aqueous solution-based silicon etching solution of quaternary alkylammonium hydroxide, that is, it has low toxicity and is easy to handle, and has the advantage that a silicon oxide film that is inexpensive as a mask material can be used. In addition, compared with the conventional aqueous solution-based silicon etching solution of quaternary alkylammonium hydroxide, even if the dissolved oxygen concentration in the solution fluctuates, the fluctuation of the etching rate for silicon is small. More specifically, when the etching treatment is carried out under the same conditions, it has the characteristic that it can suppress the influence of the fluctuation of the dissolved oxygen concentration in the etching solution derived from the wafer circumferential direction, the pattern depth direction, the apparatus, the weather, etc. Therefore, the silicon etching solution of the present invention is suitable as an etching solution for manufacturing various silicon devices, such as the processing of valves, nozzles, printer heads, and semiconductor sensors (for example, diaphragms of semiconductor pressure sensors and cantilevers of semiconductor acceleration sensors) for detecting various physical quantities such as flow rate, pressure, and acceleration, and the etching of polysilicon films and amorphous silicon films used as materials for part of metal wiring, gate electrodes, etc.

[0043] When manufacturing a silicon device using the silicon etching solution of the present invention, wet etching of silicon may be performed according to a conventional method. The method at this time is not particularly different from the case of using a conventional silicon etching solution. For example, a "silicon wafer in which a necessary portion of the silicon wafer is masked with a silicon oxide film, a silicon nitride film, etc." is introduced into an etching tank into which the silicon etching solution is introduced as an object to be etched, and the unnecessary portion of the silicon wafer is dissolved by utilizing a chemical reaction with the silicon etching solution, whereby it can be preferably performed.

[0044] In a preferred embodiment of the present invention, the silicon etching solution is used in the manufacture of a silicon device including a step of supplying the silicon etching solution to the recess or through hole and selectively etching the polysilicon film when etching a laminate in which a polysilicon film and a silicon oxide film are alternately laminated and having a recess or through hole penetrating a plurality of films.

[0045] The temperature of the silicon etching solution during etching may be appropriately determined from the range of 20 to 95°C in consideration of a desired etching rate, the shape and surface state of the silicon after etching, productivity, etc., but it is preferably in the range of 30 to 60°C.

[0046] For the wet etching of silicon, it is possible to simply immerse the object to be etched in the silicon etching solution, but it is also possible to adopt an electrochemical etching method in which a certain potential is applied to the object to be etched.

[0047] The objects to be etched in the present invention include single-crystalline silicon, polysilicon, and amorphous silicon, and may contain non-target objects such as silicon oxide films and silicon nitride films that are not targets of the etching process, as well as metals such as aluminum. For example, a structure in which a silicon oxide film, a silicon nitride film, and further a metal film are laminated on a single-crystalline silicon to form a pattern shape, or a structure in which polysilicon or a resist is formed and applied thereon, and a metal portion such as aluminum is covered with a protective film and silicon is patterned.

[0048] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0049] FIG. 3 is a schematic view of a substrate processing apparatus 1 according to an embodiment of the present invention as viewed from above.

[0050] As shown in FIG. 3, the substrate processing apparatus 1 is a single-wafer type apparatus that processes a disk-shaped substrate W such as a semiconductor wafer one by one. The substrate processing apparatus 1 includes a load port LP that holds a carrier C that houses the substrate W, a plurality of processing units 2 that process the substrate W conveyed from the carrier C on the load port LP, a transfer robot that transfers the substrate W between the carrier C on the load port LP and the processing units 2, and a control device 3 that controls the substrate processing apparatus 1.

[0051] The transfer robot includes an indexer robot IR that carries the substrate W into and out of the carrier C on the load port LP, and a center robot CR that carries the substrate W into and out of the plurality of processing units 2. The indexer robot IR transfers the substrate W between the load port LP and the center robot CR, and the center robot CR transfers the substrate W between the indexer robot IR and the processing units 2. The center robot CR includes a hand H1 that supports the substrate W, and the indexer robot IR includes a hand H2 that supports the substrate W.

[0052] The plurality of processing units 2 form a plurality of towers TW arranged around the center robot CR in a plan view. Each tower TW includes a plurality (for example, three) of processing units 2 stacked vertically. FIG. 3 shows an example in which four towers TW are formed. The center robot CR can access any of the towers TW.

[0053] FIG. 4 is a schematic view of the inside of the processing unit 2 provided in the substrate processing apparatus 1 as seen horizontally.

[0054] The processing unit 2 includes a box-shaped chamber 4 having an internal space, a spin chuck 10 that rotates around a vertical axis passing through the central portion of the substrate W while horizontally holding one substrate W in the chamber 4, and a cylindrical processing cup 20 that surrounds the spin chuck 10 around the rotation axis.

[0055] The chamber 4 includes a box-shaped partition wall 5 provided with a carry-in / carry-out port 6 through which the substrate W passes, and a shutter 7 that opens and closes the carry-in / carry-out port 6.

[0056] The spin chuck 10 includes a disk-shaped spin base 12 held in a horizontal posture, a plurality of chuck pins 11 that hold the substrate W in a horizontal posture above the spin base 12, a spin shaft extending downward from the central portion of the spin base 12, and a spin motor 13 that rotates the spin shaft to rotate the spin base 12 and the plurality of chuck pins 11. The spin chuck 10 is not limited to a clamping type chuck that brings the plurality of chuck pins 11 into contact with the outer peripheral surface of the substrate W, and may be a vacuum type chuck that horizontally holds the substrate W by adsorbing the back surface (lower surface) of the substrate W, which is a non-device forming surface, to the upper surface of the spin base 12.

[0057] The processing cup 20 includes a plurality of guards 21 that receive the liquid discharged outward from the substrate W, and a plurality of cups 22 that receive the liquid guided downward by the plurality of guards 21. FIG. 4 shows an example in which two guards 21 and two cups 22 are provided.

[0058] The processing unit 2 includes a guard lifting unit that individually raises and lowers a plurality of guards 21. The guard lifting unit positions the guard 21 at any position from the upper position to the lower position. The guard lifting unit is controlled by the control device 3. The upper position is a position arranged above the holding position where the substrate W held by the spin chuck 10 is arranged. The lower position is a position where the upper end of the guard 21 is arranged below the holding position. The annular upper end of the guard ceiling portion corresponds to the upper end of the guard 21. The upper end of the guard 21 surrounds the substrate W and the spin base 12 in a plan view.

[0059] When the processing liquid is supplied to the substrate W while the spin chuck 10 is rotating the substrate W, the processing liquid supplied to the substrate W is shaken off from the substrate W. When the processing liquid is supplied to the substrate W, the upper end of at least one guard 21 is arranged above the substrate W. Therefore, the processing liquid such as the chemical solution and the rinse solution discharged from the substrate W is received by one of the guards 21 and guided to the cup 22 corresponding to this guard 21.

[0060] The plurality of liquid discharge parts include a first chemical liquid discharge part 41 that discharges a first chemical liquid, a second chemical liquid discharge part 42 that discharges a second chemical liquid, and a rinse liquid discharge part 43 that discharges a rinse liquid. Further, a gas discharge part that discharges a plurality of inert gases may be provided. Each of the plurality of liquid discharge parts has a valve that controls liquid discharge and can start and stop liquid discharge. Each of the plurality of liquid discharge parts has a drive mechanism and can drive between a processing position where liquid is discharged onto the substrate and a standby position outside the substrate. The valve and the drive mechanism are controlled by the control device 3.

[0061] The first chemical liquid is a liquid containing at least one of chemical liquids capable of removing the natural oxide film of the substrate (for example, hydrofluoric acid, buffered hydrofluoric acid, aqueous ammonia, etc.). In FIG. 4, it is denoted as DHF.

[0062] The second chemical solution is the silicon etching solution of the present invention. It is denoted as TMAH COMPOUND in FIG. 4.

[0063] The rinse solution supplied to the rinse solution discharge part 43 is pure water (deionized water). The rinse solution supplied to the rinse solution discharge part 43 may be a rinse solution other than pure water. It is denoted as DIW in FIG. 4.

[0064] FIG. 5 is a schematic diagram showing an example of a cross-section of the substrate W before and after the process shown in FIG. 6 is performed.

[0065] The left side of FIG. 5 shows a cross-section of the substrate W before the process (etching) shown in FIG. 6 is performed, and the right side of FIG. 5 shows a cross-section of the substrate W after the process (etching) shown in FIG. 6 is performed. As shown on the right side of FIG. 5, when the substrate W is etched, a plurality of recesses R1 recessed in the surface direction of the substrate W (a direction orthogonal to the thickness direction Dt of the substrate W) are formed on the side surface 92s of the recess 92.

[0066] As shown in FIG. 5, the substrate W includes a stacked film 91 formed on a base material such as a silicon wafer, and a recess 92 recessed from the outermost surface Ws of the substrate W in the thickness direction Dt of the substrate W (a direction orthogonal to the surface of the base material of the substrate W). The stacked film 91 includes a plurality of polysilicon films P1, P2, P3 and a plurality of silicon oxide films O1, O2, O3. The polysilicon films P1 to P3 are an example of an object to be etched, and the silicon oxide films O1 to O3 are an example of a non-etching object. Silicon oxide is a substance that does not dissolve or hardly dissolves in an alkaline etching solution containing a quaternary ammonium hydroxide.

[0067] The plurality of polysilicon films P1 to P3 and the plurality of silicon oxide films O1 to O3 are stacked in the thickness direction Dt of the substrate W such that the polysilicon film and the silicon oxide film alternate with each other. The polysilicon films P1 to P3 are thin films on which a deposition process of depositing polysilicon on the substrate W and a heat treatment process of heating the deposited polysilicon are performed (see FIG. 6). The polysilicon films P1 to P3 may be thin films on which the heat treatment process has not been performed.

[0068] As shown in FIG. 5, the recess 92 penetrates a plurality of polysilicon films P1 to P3 and a plurality of silicon oxide films O1 to O3 in the thickness direction Dt of the substrate W. The side surfaces of the polysilicon films P1 to P3 and the silicon oxide films O1 to O3 are exposed at the side surface 92s of the recess 92. The recess 92 may be any one of a trench, a via hole, and a contact hole, or may be other than these.

[0069] Before the process (etching) shown in FIG. 6 is started, a native oxide film is formed on the surface layers of the polysilicon films P1 to P3 and the silicon oxide films O1 to O3. The two-dot chain line on the left side of FIG. 5 indicates the contour of the native oxide film. Hereinafter, the native oxide films of the polysilicon films P1 to P3 and the silicon oxide films O1 to O3 are removed by supplying DHF, which is an example of an oxide film removal liquid, and then the process of selectively etching the polysilicon films P1 to P3 by supplying an etching liquid will be described.

[0070] FIG. 6 is a process diagram for explaining an example of the process of the substrate W executed by the substrate processing apparatus 1.

[0071] Hereinafter, an example of the process of the substrate W executed by the substrate processing apparatus 1 will be described with reference to FIGS. 3, 4, and 6. In the substrate processing apparatus 1, the processes after the start in FIG. 6 are executed.

[0072] When the substrate W is processed by the substrate processing apparatus 1, a loading process of loading the substrate W into the chamber 4 is performed (step S1 in FIG. 6).

[0073] Specifically, with all the guards 21 in the lower position, the center robot CR enters the hand H1 into the chamber 4 while supporting the substrate W with the hand H1. Then, with the surface of the substrate W facing upward, the center robot CR places the substrate W on the hand H1 onto the plurality of chuck pins 11. Thereafter, the plurality of chuck pins 11 are pressed against the outer peripheral surface of the substrate W, and the substrate W is gripped. After the center robot CR places the substrate W on the spin chuck 10, the hand H1 is retracted from the inside of the chamber 4.

[0074] Next, the spin motor 13 is driven, and the rotation of the substrate W is started (step S2 in FIG. 6).

[0075] Next, a first chemical solution supply step of supplying DHF, which is an example of the first chemical solution, to the upper surface of the substrate W is performed (step S3 in FIG. 6).

[0076] Specifically, the first chemical solution valve of the first chemical solution discharge unit 41 is opened, and the discharge of DHF is started. The DHF discharged from the first chemical solution discharge unit 41 collides with the central portion of the upper surface of the substrate W and then flows outward along the upper surface of the rotating substrate W. Thereby, a liquid film of DHF covering the entire upper surface of the substrate W is formed, and DHF is supplied to the entire upper surface of the substrate W. When a predetermined time has elapsed since the first chemical solution valve was opened, the first chemical solution valve is closed, and the discharge of DHF is stopped.

[0077] Next, a first rinse solution supply step of supplying pure water, which is an example of the rinse solution, to the upper surface of the substrate W is performed (step S4 in FIG. 6).

[0078] Specifically, the rinse solution valve of the rinse solution discharge unit 43 is opened, and the rinse solution discharge unit 43 starts discharging pure water. The pure water that collides with the central portion of the upper surface of the substrate W flows outward along the upper surface of the rotating substrate W. The DHF on the substrate W is washed away by the pure water discharged from the rinse solution discharge unit 43. Thereby, a liquid film of pure water covering the entire upper surface of the substrate W is formed. When a predetermined time has elapsed since the rinse solution valve was opened, the rinse solution valve is closed, and the discharge of pure water is stopped.

[0079] Next, a second chemical solution supply step of supplying a silicon etching solution as the second chemical solution to the upper surface of the substrate W is performed (step S5 in FIG. 6).

[0080] Specifically, the second chemical solution valve of the second chemical solution discharge unit 42 is opened, and the second chemical solution discharge unit 42 starts discharging the etching solution. Before the discharge of the etching solution starts, the guard lifting unit may vertically move at least one guard 21 to switch the guard 21 that receives the liquid discharged from the substrate W. The etching solution that has collided with the central portion of the upper surface of the substrate W flows outward along the upper surface of the rotating substrate W. The pure water on the substrate W is replaced with the etching solution discharged from the second chemical solution discharge unit 42. Thereby, a liquid film of the etching solution covering the entire upper surface of the substrate W is formed. When a predetermined time has elapsed since the second chemical solution valve was opened, the second chemical solution valve is closed, and the discharge of the etching solution is stopped.

[0081] Next, a second rinse solution supply step of supplying pure water, which is an example of a rinse solution, to the upper surface of the substrate W is performed (step S6 in FIG. 6).

[0082] Specifically, the rinse solution valve of the rinse solution discharge unit 43 is opened, and the rinse solution discharge unit 43 starts discharging pure water. The pure water that has collided with the central portion of the upper surface of the substrate W flows outward along the upper surface of the rotating substrate W. The etching solution on the substrate W is washed away by the pure water discharged from the rinse solution discharge unit 43. Thereby, a liquid film of pure water covering the entire upper surface of the substrate W is formed. When a predetermined time has elapsed since the rinse solution valve was opened, the rinse solution valve is closed, and the discharge of pure water is stopped.

[0083] Next, a drying step of drying the substrate W by rotating the substrate W is performed (step S7 in FIG. 6).

[0084] Specifically, the spin motor 13 accelerates the substrate W in the rotational direction and rotates the substrate W at a high rotational speed (for example, several thousand rpm) that is higher than the rotational speed of the substrate W during the period from the first chemical solution supply step to the second rinse solution supply step. Thereby, the liquid is removed from the substrate W and the substrate W dries. When a predetermined time has elapsed since the high-speed rotation of the substrate W was started, the spin motor 13 stops rotating. Thereby, the rotation of the substrate W is stopped (step S8 in FIG. 6).

[0085] Next, an unloading step of unloading the substrate W from the chamber 4 is performed (step S9 in FIG. 6).

[0086] Specifically, the guard lifting unit lowers all the guards 21 to the lower position. Thereafter, the center robot CR causes the hand H1 to enter the chamber 4. After the plurality of chuck pins 11 of the center robot CR release the gripping of the substrate W, the center robot CR supports the substrate W on the spin chuck 10 with the hand H1. Thereafter, while supporting the substrate W with the hand H1, the center robot CR retracts the hand H1 from the inside of the chamber 4. Thereby, the processed substrate W is unloaded from the chamber 4.

[0087] As described above, in the preferred embodiment of the present invention, the above-described silicon etching solution is supplied to the substrate W on which the polysilicon films P1 to P3 (see FIG. 5) and the silicon oxide films O1 to O3 (see FIG. 5) different from the polysilicon films P1 to P3 are exposed.

[0088] In this embodiment, DHF, which is an example of an oxide film removing solution, is supplied to the substrate W, and the native oxide films of the polysilicon films P1 to P3 are removed from the surface layers of the polysilicon films P1 to P3. Then, an etching solution is supplied to the substrate W, and the polysilicon films P1 to P3, which are the objects to be etched, are selectively etched. The native oxide films of the polysilicon films P1 to P3 are mainly composed of silicon oxide. The etching solution is a liquid that etches the polysilicon films P1 to P3 without etching or hardly etching silicon oxide. This is because although hydroxide ions react with silicon, they do not react or hardly react with silicon oxide. Therefore, by removing the native oxide films of the polysilicon films P1 to P3 in advance, the polysilicon films P1 to P3 can be efficiently etched.

[0089] In this embodiment, the etching rates in the case where the dissolved oxygen concentration in the silicon etching solution is high and the case where it is low can be made substantially equal (the etching rate ratio is near 1), and the variation in the etching rate due to the variation in the dissolved oxygen concentration in the silicon etching solution can be suppressed. Therefore, a uniform etching process can be performed on the substrate without being affected by the variation in the dissolved oxygen concentration caused by the processing environment. On the other hand, when the variation in the etching rate due to the variation in the dissolved oxygen concentration in the silicon etching solution cannot be suppressed, the width of the recess R1 formed by etching the polysilicon film becomes non-uniform, and the volume of the remaining polysilicon film also becomes non-uniform. As a result, the capacity at the time of design cannot be achieved, and a desired device cannot be obtained.

[0090] In this embodiment, the processing unit 2 may include a blocking member disposed above the spin chuck 10. The blocking member includes a disk portion disposed above the spin chuck 10 and a cylindrical portion extending downward from the outer peripheral portion of the disk portion.

[0091] In this embodiment, an example in a single-wafer substrate processing apparatus that processes substrates one by one has been shown, but a batch-type substrate processing apparatus that processes a plurality of substrates at once may also be used.

Example

[0092] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0093] Example 1 As the silicon etching solution, propylene glycol monopropyl ether was used as the compound represented by the formula (1), and a silicon etching solution having the composition shown in Table 1 was prepared.

[0094] Using the prepared silicon etching solution, assuming etching at a liquid temperature of 40°C, the etching rate (R N ) after N2 aeration and the etching rate (R A ) after air aeration at a liquid temperature of 40°C were measured. The ratio (R N / R A ) was measured. In any of the examples and comparative examples, the dissolved oxygen concentration of the silicon etching solution after N2 aeration was 1 ppm or less, and the saturated dissolved oxygen concentration after air aeration was 4 ppm or more. The etching rate (R

[0095] ) after N2 aeration was measured by bubbling N2 gas through the silicon etching solution heated to a liquid temperature of 40°C until the dissolved oxygen concentration decreased to a certain concentration value, then immersing the silicon substrate in the silicon etching solution after aeration for 5 to 60 seconds, and measuring the etching rate of silicon at a liquid temperature of 40°C. The dissolved oxygen concentration of the silicon etching solution was measured with a dissolved oxygen concentration meter. The target silicon substrate was a non-doped polysilicon substrate (PolySi Type A) on which a polysilicon film was formed, and the native oxide film was removed with a chemical solution. The etching rate was determined by measuring the film thickness before and after etching with an ellipsometer and dividing the difference in polysilicon film thickness before and after treatment by the etching time. The etching rate (R N ) after air aeration was measured in the same manner as the measurement of the etching rate (R A ) after N2 aeration, except that air was used instead of N2 gas and bubbling was performed until the dissolved oxygen concentration increased to a certain concentration value. The etching rate (R N ) after N2 aeration and the etching rate (R N ) after air aerationA ) and the ratio (R N / R A ) were calculated. The results under the following evaluation conditions are shown in Table 1 and FIG. 1.

[0096] Example 2 As the silicon etching solution, a silicon etching solution having the composition shown in Table 1 was used, and an etching rate ratio (R N / R A ) was calculated in the same manner as in Example 1, except that a polysilicon substrate (PolySiTypeB) on which a polysilicon film was formed was used as the target silicon substrate. Note that PolySiTypeA and PolySiTypeB are films having different film formation conditions such as film thickness or annealing conditions during film formation. The results are shown in Table 1 and FIG. 1.

[0097] Example 3 An etching rate ratio (R N / R A ) was calculated in the same manner as in Example 1, except that a silicon etching solution having the composition shown in Table 1 was used as the silicon etching solution. The results are shown in Table 1 and FIG. 1.

[0098] Comparative Example 1 An etching rate ratio (R N / R A ) was calculated in the same manner as in Example 1, except that a silicon etching solution not containing the compound represented by the formula (1) was used as the silicon etching solution. The results are shown in Table 1 and FIG. 1.

[0099] Example 4 An etching rate ratio (R N / R A ) was calculated in the same manner as in Example 2, except that a polysilicon substrate (a-SiTypeC) on which an amorphous silicon film was formed was used as the target silicon substrate. The results are shown in Table 1 and FIG. 1.

[0100] Comparative Example 2 An etching rate ratio (R N / R A ) was calculated. The results are shown in Table 1 and Figure 1.

[0101] Examples 5 to 7, Comparative Example 1 As the silicon etching solution, an etching rate ratio (R N / R A ) was calculated in the same manner as in Example 1, except that the silicon etching solution having the composition shown in Table 2 was used.

[0102] The results are shown in Figure 2. The etching rate ratio was Comparative Example 1 > 1.5 > Example 5 > Example 6 > Example 7 > 0.5. In Figure 2, the graphs within the gray area have an etching rate ratio within the range of 0. 5 to 1.5.

[0103] Examples 8 to 68, Comparative Examples 3 to 9 As the silicon etching solution, an etching rate ratio (R N / R A ) was calculated in the same manner as in Example 1, except that the silicon etching solution having the composition shown in Table 3 was used and the silicon substrate described in Table 1 was used as the target silicon substrate. The results are shown in Table 3.

[0104] [Table 1] [Table 2] [Table 3]

[0105] In Tables 1 and 2, X, Y, and Z satisfy 0.1 ≦ X < Y < Z ≦ 20 (mass %), and A, B, and C satisfy 0.1 ≦ A < B < C ≦ 20 (mass %). [Explanation of Reference Signs]

[0106] 1 Substrate processing apparatus 2 Processing unit 3 Control device 4 Chamber 10 Spin chuck 11 Chuck pin 12 Spin base 13 Spin motor 20 Processing cup 21 Guard 22 Cup 41 First chemical liquid discharge part 42 Second chemical liquid discharge part 43 Rinse liquid discharge part 91 Laminated film 92 Concave part R1 Recess P1, P2, P3 Polysilicon film O1, O2, O3 Silicon oxide film LP Load port IR Indexer robot CR Center robot H1(H2) Hand

Claims

1. A silicon etching solution consisting essentially of only at least one ether compound selected from the group consisting of quaternary alkylammonium hydroxide, water, and ethylene glycol monopropyl ether, ethylene glycol dimethyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monopropyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, and dipropylene glycol dimethyl ether.

2. The silicon etching solution according to Claim 1, wherein the concentration of the quaternary alkylammonium hydroxide is 0.1 to 25% by mass and the concentration of the ether compound is 0.1 to 20% by mass.

3. A method for manufacturing a silicon device, comprising a step of etching at least one selected from the group consisting of a silicon wafer, a polysilicon film, and an amorphous silicon film, wherein the etching is performed using the silicon etching solution according to Claim 1 or 2.

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