JP2006202906A - Etching apparatus and etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an etching apparatus for suppressing adhesion of a stain film or suppressing generation of a nitrogen oxide at a low cost, and without contaminating the etching apparatus and a substrate itself. <P>SOLUTION: The etching apparatus for dipping the substrate into a mixed acid etching bath and then transferring the substrate to a water cleaning bath. The inside of the etching apparatus is made into an atmosphere of suppressing the adhesion of the stain film of the substrate or suppressing the generation of the nitrogen oxide. A first thing to do is to maintain the humidity of the inside of the etching apparatus at 90% or more. A second thing to do is to spray pure water to the substrate. A third thing to do is to spray an inert gas the substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an etching apparatus and an etching method for etching a semiconductor substrate or a ceramic substrate. More specifically, the present invention suppresses adhesion of a stain film formed on the surface of a semiconductor substrate or a ceramic substrate after the etching process of the semiconductor substrate or the ceramic substrate. Or the generation of nitrogen oxides.

In a semiconductor element manufacturing process or a ceramic element manufacturing process, etching of a semiconductor substrate or a ceramic substrate is performed with a mixed acid solution of hydrofluoric acid and nitric acid as described in Patent Document 1, for example. That is, etching is performed with a solution made of nitric acid having oxidizing power, hydrofluoric acid or the like that dissolves the oxide film. When a silicon substrate or a ceramic substrate is etched with a mixed acid solution of a high concentration that allows an etching reaction to proceed, and taken out from the mixed acid solution, nitrogen oxide (NOx gas) is generated from the surface of the silicon substrate or the ceramic substrate, or a stain film A black-brown porous silicon film called “A” adheres.
Non-Patent Document 1 discloses that the generation of gas during etching can be reduced by etching at room temperature or lower. Moreover, in order to remove the stain film, it is disclosed that a silicon substrate or a ceramic substrate that has permeated into a strong alkaline aqueous solution such as a NaOH aqueous solution and then permeated with the NaOH aqueous solution is neutralized with an acid aqueous solution. Further, Patent Document 2 discloses a method in which noble metal (platinum) is used for the protective film and etching is performed so that the stain film does not adhere.
Japanese Patent Laid-Open No. 2-1996 Japanese Patent Laid-Open No. 62-13033 A.Hauser and 5 others, “A SIMPLIFIED PROCESS FOR ISOTROPIC TEXTURING OF MC-SI”, 3rd World Conference on Photovoltaic Energy Conversion Proceedings, Osaka, 11-18, MAY 2003, 4PC433

However, as in Non-Patent Document 1, the method for removing the stain film using strong alkali is that NaOH contains an alkali metal such as sodium that adversely affects the characteristics of the semiconductor element, and NaOH is added to the white powder in the etching apparatus. As a residue, the etching apparatus is contaminated. Furthermore, as shown in FIG. 5, the etching process immersed in the mixed acid solution tank 51, the cleaning process immersed in the water tank 52, the stain film removing process immersed in the strong alkaline liquid tank 53, the cleaning process of the water tank 54, the acid neutralization liquid tank Like the neutralization process immersed in 55, and the washing process of the water tank 56, the process becomes longer because it undergoes three stages of processing, and the amount of chemical solution used also increases. Furthermore, the NOx gas generated when the stain film adheres is an air pollutant. If the concentration of NOx gas is high, the NOx gas cannot be sufficiently removed with a normal water scrubber alone. Equipment is required.
Further, in Patent Document 2, the etching method for preventing the stain film from adhering uses a noble metal (platinum) for the protective film, and thus the cost is high.

  In view of the above-described problems, the present invention provides an etching apparatus and an etching method which are low in cost and do not contaminate the etching apparatus and the substrate itself, thereby suppressing adhesion of a stain film or suppressing generation of nitrogen oxides. This is a problem.

The etching apparatus of the present invention is an etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring it to a washing tank, and suppresses adhesion of a stain film on the substrate or generation of nitrogen oxide in the etching apparatus. The invention can be configured by setting the humidity of the atmosphere in the etching apparatus to 90% or more.
The etching apparatus of the present invention is an etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring the substrate to a washing tank so as to suppress adhesion of a stain film or generation of nitrogen oxide in the etching apparatus. A pure water spraying device for spraying pure water onto the substrate is provided between the mixed acid etching tank and the washing tank.
The etching apparatus of the present invention is an etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring the substrate to a washing tank so as to suppress adhesion of a stain film or generation of nitrogen oxide in the etching apparatus. An inert gas spraying device for spraying an inert gas onto the substrate is provided between the mixed acid etching tank and the washing tank.

Moreover, the etching apparatus of this invention is good to provide two or more said etching apparatuses.
The etching apparatus of the present invention is characterized in that the atmosphere in the etching apparatus is lower than room temperature.
Furthermore, the etching method of this invention etches a board | substrate using the said etching apparatus.
The etching method of the present invention is optimal when applied to a semiconductor silicon substrate.

In the etching apparatus of the present invention, the humidity of the atmosphere in the etching apparatus is set to 90% or more so as to suppress the adhesion of the stain film of the substrate or the generation of nitrogen oxide in the etching apparatus. The adhesion of the stain film generated on the substrate during the transfer can be suppressed, or the generation of nitrogen oxides can be suppressed.
According to the present invention, since the generation of the stain film can be suppressed, the removal process of the stain film becomes unnecessary, and a strong alkaline aqueous solution such as an NaOH aqueous solution is not used, so that the substrate may be contaminated with a metal element such as sodium or potassium. There is no. Further, the etching apparatus is not contaminated. Further, since the pure water cleaning process is performed after the etching process, the cleaning process is completed in a short time, and the acid neutralization process process after the stain film removing process is unnecessary, so that the amount of pure water used is small. As a result, the amount of drainage can be reduced, and the processing cost can be reduced.
Further, according to the present invention, since generation of nitrogen oxides (NOx gas) is suppressed, a processing facility for nitrogen oxides (NOx gas) is unnecessary, and the environmental load can be reduced.
In addition, since the present invention is configured by setting the humidity of the atmosphere in the etching apparatus to 90% or more, the effects of the present invention can be obtained with a small capital investment.

The present invention also includes a pure water spraying device that sprays pure water onto the substrate between the mixed acid etching tank and the water washing tank, or an inert gas spraying device that sprays an inert gas onto the substrate. Since generation | occurrence | production of nitrogen oxides or generation | occurrence | production of nitrogen oxides can be suppressed, a board | substrate itself and an etching apparatus are not contaminated, the amount of drainage can be reduced, and processing cost can be reduced. Furthermore, a nitrogen oxide (NOx gas) treatment facility is not required, and the environmental load is reduced.
Further, the present invention is more effective when two or more etching apparatuses are provided. Further, it is more effective to make the inside of the etching apparatus cooler than room temperature.

The present invention has found an atmosphere that suppresses adhesion of a stain film to a substrate after etching or suppresses generation of nitrogen oxides from the substrate.
The present invention relates to a silicon etching process using an acid particularly in the production of crystalline silicon solar cells for residential use, and compared with a conventional process by suppressing the adhesion of a silicon stain film or etching in an atmosphere where nitrogen oxides are not generated. Thus, process shortening and cost reduction at the mass production level are realized.
Examples of the semiconductor substrate in the present invention include crystalline silicon such as single crystal silicon and polycrystalline silicon. The silicon substrate usually has N-type or P-type polarity, but in the present invention, it may have either polarity. In the silicon substrate, the P-type impurity includes Group 3 elements such as boron and aluminum, and the N-type impurity includes Group 5 elements such as phosphorus and arsenic. The impurity concentration of the substrate doped to give P-type or N-type polarity to the silicon substrate is preferably 10 ¹³ to 10 ¹⁸ / cm ³ , although it varies depending on the type of impurity.
In addition to a polycrystalline silicon substrate, a single crystal silicon substrate may be used, and a ceramic substrate such as a PZT piezoelectric ceramic may be used.

  In the present invention, an etching apparatus for etching a semiconductor substrate or a ceramic substrate uses a mixed acid of hydrofluoric acid and nitric acid as the most common mixed acid in mixed acid etching, but hydrofluoric acid, nitric acid, acetic acid or hydrofluoric acid, A combination of sulfuric acid, hydrofluoric acid or hydrogen peroxide water may be used. The etching reaction is performed at a temperature of about 0 ° C. to 30 ° C. Using such a mixed acid, the etching apparatus is configured so that the etching reaction proceeds at a speed of 0.1 μm or more per minute.

The etching apparatus of the present invention arranges a mixed acid tank and a water washing tank in the draft, and after etching a semiconductor substrate or a ceramic substrate in the mixed acid tank, suppresses the adhesion of the stain film inside the draft while being transferred to the water washing tank, Or it is characterized by setting it as the atmosphere which suppresses generation | occurrence | production of nitrogen oxides. That is, in the present invention, the preferable atmosphere is that the first is to maintain the humidity in the draft at 90% or more. The second is to provide water vapor spraying means for spraying mist of water vapor onto the semiconductor substrate or the ceramic substrate between the mixed acid tank and the water washing tank. Thirdly, an inert gas spraying means for spraying an inert gas onto the semiconductor substrate or the ceramic substrate between the mixed acid tank and the water washing tank is provided.
Each of the above three means alone has the effect of suppressing the adhesion of the stain film and the effect of suppressing the generation of nitrogen oxides. However, when all the three means are used or any two of them are used in combination, the respective effects are obtained. Synergistically, higher effects can be obtained. The present invention is effective when the atmosphere in the etching apparatus is lower than room temperature in any etching apparatus.

(Embodiment 1)
FIG. 1 shows a process schematic diagram of the etching processing apparatus of the first embodiment. As shown in FIG. 1, an etching reaction tank 2 containing a mixed acid aqueous solution A and a rinsing tank 3 containing pure water B are arranged in the order of steps in a draft 1. In the etching process, the as-sliced silicon substrate 1-A is put into the etching reaction tank 2 and etched to a predetermined thickness. After completion of the etching, the etched silicon substrate 1-B is taken out from the reaction tank 2 and transferred to the washing tank 3 containing pure water B. Pure water is neither heated nor cooled, is at room temperature, and is 10 ° C to 30 ° C. When the atmosphere around the reaction vessel 2 is at room temperature between the time when the silicon substrate 1-B is taken out from the reaction vessel 2 and before the etching is stopped after entering the water washing vessel 3, the silicon substrate 1-C is being transferred. As the chemical reaction of the etching solution remaining on the silicon substrate surface proceeds, a large amount of nitrogen oxide (NOx gas) is generated, and a product generally called silicon stain film or porous silicon is formed on the silicon substrate surface. Adhere to. In the present text, this is hereinafter referred to as a stain film.

Here, the present invention keeps the area transferred from the etching reaction tank 2 to the washing tank 3 at a humidity of 90% or more so that the stain film does not adhere to the substrate or nitrogen oxides are not generated from the substrate. Thus, when the humidity in the draft is maintained at 90% or more, adhesion of the stain film can be suppressed, or generation of nitrogen oxides (NOx gas) can be suppressed. Alternatively, the adhesion of the stain film can be suppressed, and the generation of nitrogen oxides (NOx gas) can be suppressed. In the present invention, the chemical reaction by the acid on the surface of the silicon substrate 1-D is stopped in the water rinsing tank 3, and after water washing, the water washing is performed in another water washing tank, and then the silicon substrate 1-E. To finish the etching process.
Although the present invention will be described with reference to a silicon substrate, a ceramic substrate such as a PZT piezoelectric ceramic can be similarly processed to obtain the same effect.

Further, the present invention will be described in detail with reference to FIG.
As a substrate used in FIG. 1, for example, a P-type polycrystalline silicon substrate having a size of 126 mm × 126 mm or 155 mm × 155 mm can be used. However, since the substrate size and the cell characteristics are not directly related, a substrate having any shape or size may be used. In the case of a silicon substrate, a single crystal silicon substrate or a thin film silicon substrate can also be used. In the case of single crystal silicon, any substrate manufactured by CZ, MCZ, FZ method or the like may be used. In any case, the thickness of the substrate may be any thickness as long as the mechanical strength is maintained.
The polarity of the silicon substrate may be either P-type or N-type. In the case of P-type, a Group 3 element such as boron or aluminum is doped. In the case of N-type, a Group 5 element such as phosphorus or arsenic is doped. The The resistivity of the silicon substrate is not particularly limited and depends on the application, but is generally in the range of 0.5 to 1000 Ωcm.

As the mixed acid solution A used in FIG. 1, for example, a mixed aqueous solution of hydrofluoric acid and nitric acid is used. Examples of acids having oxidizing power such as nitric acid include sulfuric acid and hydrogen peroxide, and any combination of acid having oxidizing power and hydrofluoric acid that etches an oxide film is not limited to hydrofluoric acid and nitric acid. Any mixed acid may be used, and acetic acid or the like may be added. The concentration of the mixed acid used here is such that the concentration of the acid in the aqueous solution is 5 to 50%. The mixing ratio of hydrofluoric acid and nitric acid is hydrofluoric acid: nitric acid = 3: 1 to 1:20 when a general 50% hydrofluoric acid and 60% nitric acid are used. However, this is not limited as long as chemical etching with acid proceeds.
The temperature of the etching solution must be below room temperature because the hydrofluoric acid that is always included in the mixed acid under any conditions is an aqueous solution in which hydrogen fluoride, which is a gas at room temperature and normal pressure, is dissolved in water. The temperature of the mixed acid solution is preferably 0 to 30 ° C. Furthermore, it is more preferable that the temperature is 15 ° C. or lower and lower than room temperature. The time required for etching depends on the concentration of the mixed acid solution, the temperature, the thickness of the as-sliced silicon substrate and the desired thickness, and is 0.5 to 30 minutes. Here, since the etching amount of the substrate may be more than the extent that the slice damage layer is removed, the etching amount is about 2 microns or more on one side and the thickness that can maintain the strength of the substrate. There is no upper limit.
The pure water to be put into the rinsing tank 3 is preferably perfect pure water. However, it may not be completely pure water depending on the surface state of the silicon substrate and the stage of the process, as long as it does not affect the characteristics of the semiconductor element. Impurities may be mixed.

  The atmosphere in the draft of FIG. 1 is normal air, and it is preferable to feed water vapor into the draft so that the humidity is 90% or more. Although it is desirable that the purity of the water vapor is high, impurities may be mixed in a range that does not affect the characteristics of the semiconductor element. The water vapor outlet 21 may be located anywhere, but is preferably disposed on the ceiling of the draft 1 between the reaction tank 2 and the water washing tank 3 so that the water vapor blows down. When the steam outlet 21 is disposed between the reaction tank 2 and the washing tank 3 in this manner, the humidity can be highest between the reaction tank 2 and the washing tank 3 in the draft, and the effect of the invention is high. . Moreover, water vapor can be applied to the surface of the substrate 1-C immediately after the reaction vessel 2 is pulled up, and the effect of the invention is enhanced. The water vapor generating device may be any device as long as it increases the humidity without increasing the temperature in the draft. For example, a water vapor generator using ultrasonic waves is suitable for the present invention. Alternatively, a simple apparatus in which pure water is atomized and fed into the draft may be used.

  The temperature in the draft is preferably below room temperature. In order to make the inside of the draft below room temperature, coolers 4a, 4b, 4c and 4d are arranged in the draft as shown in FIG. The cooler 4 a is disposed on the front side of the etching reaction tank 2, the cooler 4 b is disposed between the etching reaction tank 2 and the washing tank 3, and the cooler 4 c is disposed on the rear side of the washing tank 3. The cooler 4 d is disposed on the ceiling of the draft 1. Each cooler and the refrigerator installed outside the draft are connected by pipes. The refrigerator cools the refrigerant, and the refrigerant reaches the cooler through the pipe to cool the inside of the draft. As the refrigerant used here, an antifreeze such as ethylene glycol is used, but it is also possible to add pure water and dilute it to about 3 to 50% depending on the temperature in the draft, that is, the set temperature of the refrigerant. Any material may be used for the cooling pipe as long as the refrigerant does not leak, but it is preferable to use a stainless steel pipe whose surface is coated with fluorine in view of thermal conductivity and chemical resistance.

Further, the inside of the draft may be directly cooled by continuously sending cool air into the draft by internal air circulation using a compressor or the like. However, considering the fact that the inside of the draft has a reaction tank containing a mixed acid solution and that there is an atmosphere containing acid, and that the inside of the draft is always exhausted in a certain direction, this internal air circulation is It is more desirable to cool by arranging a cooler in the draft as described above, rather than sending cold air.
The temperature in the draft is preferably 15 ° C. or lower, and the etching reaction on the substrate surface can be suppressed as the temperature is lower. For this reason, although the inside of a draft is made into low temperature, since it needs to be the temperature which water in a mixed acid solution and a washing tank does not freeze, lower temperature is preferable in the range of 0 degreeC-15 degreeC.

(Embodiment 2)
FIG. 3 shows a process schematic diagram of the etching processing apparatus of the second embodiment. Embodiment 2 is characterized in that a mist outlet 31 for spraying mist-like pure water on the substrate surface is provided in the draft 1 while the substrate 1-C is transferred from the reaction tank 2 to the washing tank 3. And As shown in FIG. 3, a plurality of mist outlets 31 are provided on the ceiling of the draft 1 between the reaction tank 2 and the washing tank 3. Other parts are the same as those of the first embodiment.
The nebulized pure water sprayed on the substrate surface is preferably at room temperature or lower, and more preferably at 10 ° C. or lower. The pure water may be the same pure water as the pure water in the washing tank 3. The amount of pure water sprayed on the surface of the substrate is determined according to the temperature of pure water sprayed, the size of the substrate, and the number of substrates filled in the carrier, but it is preferably 0.1 to 5 cc per second per 100 cm ^{2 of the} substrate. . The time during which the mist-like pure water is sprayed is determined by the speed of the transport system until the substrate 1-C enters the washing tank 3 from the reaction tank 2, but is preferably 5 to 40 seconds.
Although the effect of the present invention is recognized even at room temperature in the draft at this time, when the temperature in the draft is 15 ° C. or lower and the humidity in the draft is kept at 90% or more as in Embodiment 1, Each effect is synergistic and a higher effect is obtained.

(Embodiment 3)
FIG. 4 shows a process schematic diagram of the etching processing apparatus according to the third embodiment. Embodiment 3 is characterized in that an inert gas blowing port 41 for blowing an inert gas to the substrate surface is provided while the substrate 1-C is being transferred from the reaction vessel 2 to the rinsing vessel 3 in the draft. To do. As shown in FIG. 4, the inert gas outlet 41 is provided between the reaction tank 2 and the water washing tank 3 on the ceiling of the draft. Here, the inert gas is a stable gas, such as nitrogen or argon gas, which does not cause a chemical reaction under special conditions, that is, at normal temperature and pressure. Other parts are the same as those in the first or second embodiment.
The inert gas sprayed onto the substrate surface is preferably room temperature or lower, and more preferably cooled to 10 ° C. or lower. The amount of the inert gas sprayed on the substrate surface is determined according to the size of the substrate and the number of carriers filled in the substrate, but it is preferably ^{2 to} 200 cc per second per 100 cm ^{2 of the} substrate. The time during which the inert gas is blown is determined by the speed of the transport system until the substrate enters the washing tank 3 from the reaction tank 2, but is preferably 5 to 40 seconds.
Although the effect of the present invention is recognized even at room temperature in the draft at this time, when the temperature in the draft is 15 ° C. or lower and the humidity in the draft is kept at 90% or more as in Embodiment 1, Each effect is synergistic and a higher effect is obtained.

FIG. 3 is a process schematic diagram of the etching processing apparatus of the first embodiment. It is a figure explaining arrangement | positioning of the cooler in a draft. FIG. 6 is a process schematic diagram of the etching processing apparatus of the second embodiment. FIG. 5 is a process schematic diagram of an etching processing apparatus according to a third embodiment. It is the schematic of the conventional stain film removal process.

Explanation of symbols

1-A As-sliced silicon substrate 1-B Etching silicon substrate 1-C Transferring silicon substrate 1-D Washing silicon substrate 1 Draft 2 Etching reaction tank 3 Washing tank 21 Steam outlet 31 Mist outlet 41 Inert gas outlet

Claims (7)

  An etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring it to a water rinsing tank, wherein the humidity of the atmosphere in the etching apparatus is controlled so as to suppress adhesion of a stain film or generation of nitrogen oxide in the etching apparatus. The etching apparatus according to claim 1, wherein the etching rate is 90% or more.   An etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring it to a washing tank, wherein the mixed acid etching tank and the washing tank are used to suppress adhesion of a stain film on the substrate or generation of nitrogen oxides in the etching apparatus. An etching apparatus comprising a pure water spraying device for spraying pure water on the substrate between the two.   An etching apparatus for immersing a substrate in a mixed acid etching tank and then transferring it to a washing tank, wherein the mixed acid etching tank and the washing tank are used to suppress adhesion of a stain film on the substrate or generation of nitrogen oxides in the etching apparatus. An etching apparatus comprising an inert gas spraying device for spraying an inert gas on the substrate. An etching apparatus comprising two or more of the etching apparatuses according to claim 1.   5. An etching apparatus characterized in that the atmosphere in the etching apparatus of the etching apparatus according to claim 1 is lower than room temperature.   An etching method for etching a substrate using the etching apparatus according to claim 1.   The method for etching a semiconductor substrate according to claim 6, wherein the substrate is a semiconductor silicon substrate.

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