JP2012074525A - Etching method and etching device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an etching device for wet-etching a silicon substrate which is arranged to suppress the decrease in the etching rate resulting from the decrease in the oxidation-reduction potential of an etchant, and the deterioration in the in-plane uniformity of the amount of etching owing to the reduction in the circulating flow rate of the etchant.SOLUTION: The etching device comprises: an oxidation-reduction potential measuring device 121 for measuring an oxidation-reduction potential of an etchant; a flowmeter 111 for measuring the amount of circulation of the etchant; a bubbling device 131 which is controlled to bubble the etchant with hydrogen gas based on a measured value of the oxidation-reduction potential; and a circulation pump 110 for circulating the etchant which is driven and controlled based on a value measured by the flowmeter 111 so that the amount of circulation of the etchant is fixed.

Description

  The present invention relates to an etching method and an etching apparatus, and more particularly, to a method and apparatus for performing a wet etching process for etching a silicon substrate with an etching liquid while suppressing a decrease in etching ability of the etching liquid and variation in etching amount.

  As a wet etching technique for a silicon substrate, it is common to immerse a silicon substrate contained in a cassette in an aqueous solution containing an alkali hydroxide and perform a wet etching process on the silicon substrate under bubbling or shaking of the etching solution. Is.

  In an alkaline hydroxide aqueous solution that is an etchant used for wet etching of a silicon substrate, the concentration of hydroxyl groups in the alkaline aqueous solution gradually decreases as the number of processed silicon substrates that are to be etched increases.

  As a result, the etching rate of the silicon substrate with the alkaline aqueous solution gradually decreases, and in the processing under the same conditions, the etching amount of the silicon substrate varies among the processing lots.

  As a countermeasure, in the technique disclosed in Patent Document 1, the processing time for each lot is lengthened according to the number of times of processing since a new solution (new etching solution) is put into the etching tank, that is, the number of processed lots. A method is disclosed.

  This will be specifically described below with reference to the drawings.

  FIG. 5 is a schematic cross-sectional view illustrating the configuration of the etching apparatus disclosed in Patent Document 1 above.

  This etching apparatus 1 is used in an etching process of a silicon substrate in a solar cell manufacturing method.

  Specifically, the etching apparatus 1 includes an etching tank 3 filled with an etching solution 2 that is an aqueous solution containing an alkali hydroxide, supply of the etching solution 2 to the etching tank 3, and etching from the etching tank 3. And an etching solution regulator 4 for adjusting the disposal of the solution. In addition, the etching apparatus 1 includes an etching jig 6 that holds a p-type Si substrate 5 that is a member to be processed, and an etching jig 6 that moves up and down to etch the p-type Si substrate 5 that is contained in the etching tank 3. A vertical slider 7 that is immersed in or lifted from the liquid 2, a transport robot 8 that transports the etching jig 6 and drives the vertical slider 7, and a time control sequencer 9 that controls the etchant regulator 4 and the transport robot 8. Have.

  For example, in a method for manufacturing a solar battery cell, such an etching apparatus is used to mainly remove a portion damaged by mechanical slicing and a contaminated portion in a surface layer portion of a p-type Si (silicon) substrate 5. In order to cope with the liquid fatigue of the aqueous solution used for etching, the etching processing time is increased according to the increase in the number of etching processes after the aqueous solution is replaced with a new liquid. Control to lengthen.

  In this way, in the etching process mainly intended to remove the mechanically damaged part and the contaminated part of the surface layer part of the p-type Si substrate 5, the number of treatments after the new solution is introduced into the aqueous solution The variation in the etching amount can be suppressed by increasing the processing time according to the increase.

JP 2007-220980 A

  However, in addition to the hydroxyl group concentration in the alkali hydroxide aqueous solution, the factors that affect the etching rate of silicon are the effects of the oxidation-reduction potential shown in FIG. 2 and the liquid circulation flow rate shown in FIG. It is insufficient.

  That is, FIG. 2 shows the correlation between the oxidation-reduction potential and the etching rate of silicon with a graph L. From FIG. 2, it can be seen that the etching rate (μm / min) of Si decreases almost linearly as the oxidation-reduction potential (mV) increases.

  FIG. 4 is a bar graph showing the correlation between the circulating flow rate of the etching solution and the in-plane uniformity of silicon etching. As can be seen from FIG. 4, as the liquid circulation flow rate (liter / min) increases, the in-plane uniformity (%), that is, the variation in the etching amount within the wafer surface can be reduced.

  Therefore, in the etching method disclosed in Patent Document 1 in which the processing time is adjusted according to the increase in the number of treatments after the new solution is introduced into the aqueous solution, each lot is treated according to the number of treatments performed so far. Even when the time is set, there is a problem in that the Si etching rate is lowered and the in-plane uniformity is lowered due to fluctuations in the oxidation-reduction potential of the etching solution and the circulation amount.

  For example, the oxidation-reduction potential difference increases or the number of etching treatments increases immediately after a new alkali hydroxide solution is introduced into the etching tank, or when the time interval between the etching treatments of each lot is not constant. The circulating flow rate of the etching solution decreases due to silicon dissolution into the solution, and the decrease in the Si etching rate and in-plane uniformity decreases.

  The present invention has been made in view of the above problems, and the in-plane uniformity of the etching amount due to the decrease in the etching rate due to the decrease in the oxidation-reduction potential of the etching solution and the decrease in the circulating flow rate of the etching solution. An object is to obtain an etching method and an etching apparatus capable of suppressing the decrease.

  An etching method according to the present invention is a method for etching a silicon substrate by immersing a silicon substrate in an etching solution in an etching tank, the step of measuring the oxidation-reduction potential of the etching solution, and the measured oxidation-reduction. And adjusting the oxidation-reduction potential of the etching solution so that it is kept constant based on the potential, thereby achieving the above object.

  According to the present invention, in the above etching method, the oxidation-reduction potential is preferably adjusted by adjusting the amount of dissolved hydrogen in the etching solution.

  In the etching method according to the present invention, it is preferable that the amount of dissolved hydrogen in the etching solution is adjusted by bubbling hydrogen gas in the etching solution.

  In the etching method according to the present invention, it is preferable that the hydrogen gas is bubbled so that the oxidation-reduction potential is equal to or lower than a set potential at which the etching rate of the silicon substrate reaches a maximum value.

  In the etching method according to the present invention, the set potential of the oxidation-reduction potential is preferably −900 mV or less.

  According to the present invention, in the above etching method, the etching solution is circulated between a bubbling portion for bubbling the etching solution and the etching tank, and the amount of the etching solution circulated regardless of the viscosity of the etching solution. It is preferable to keep it constant.

  An etching apparatus according to the present invention is an etching apparatus that has an etching tank filled with an etching solution, and that wet-etches the silicon substrate by immersing the silicon substrate in the etching solution in the etching tank. A potential measurement unit that measures the reduction potential, and a potential adjustment unit that adjusts the oxidation-reduction potential of the etching solution based on the oxidation-reduction potential measured by the potential measurement unit so that the oxidation-reduction potential is maintained at a constant voltage. Yes, and the above objective is achieved.

  According to the present invention, in the etching apparatus, the potential adjusting unit includes a bubbling device that performs bubbling of hydrogen gas to the etching solution, and the bubbling device is turned on / off based on the oxidation-reduction potential measured by the potential measuring unit. It is preferable to have a bubbling control unit.

  In the etching apparatus, the present invention provides a bubbling tank attached to the etching tank for bubbling the etching liquid, a circulation pump for circulating the etching liquid between the bubbling tank and the etching tank, and the circulation An inverter control unit that drives and controls the pump; and a flow meter that measures a circulation amount of the etching solution, the inverter control unit configured to control the etching solution based on the circulation amount of the etching solution measured by the flow meter. It is preferable to control the driving ability of the circulation pump so that the circulation amount is constant regardless of the viscosity of the etching solution.

  In the etching apparatus according to the aspect of the invention, it is preferable that the potential measurement unit includes a measurement electrode provided in the etching tank and an oxidation-reduction potentiometer connected to the measurement electrode.

  In the etching apparatus according to the present invention, it is preferable that the measurement electrode includes an Ag electrode and an AgCl electrode having different polarities.

  According to the present invention, in the etching apparatus, the bubbling control unit collates the measured value of the oxidation-reduction potentiometer with a preset set value, and increases the amount of dissolved hydrogen when the set value is exceeded. It is preferable to have a computer unit that automatically controls the bubbling device so that the oxidation-reduction potential is not more than a set value.

  Next, the operation will be described.

  In the present invention, by controlling the oxidation-reduction potential of the etching solution to be always constant, fluctuations in the etching rate caused by fluctuations in the oxidation-reduction potential that occur when a new solution is introduced can be suppressed.

  In the present invention, the uniformity of the etching amount in the surface of the silicon substrate as the object to be processed can be improved by controlling the liquid circulation flow rate by the inverter control function of the liquid circulation pump.

  As described above, according to the etching apparatus of the present invention, there is an effect that the oxidation-reduction potential is not affected by the introduction of the liquid or the processing interval time by controlling the oxidation-reduction potential.

  Furthermore, by controlling the liquid circulation flow rate, occurrence of fluctuations in the circulation flow rate due to liquid viscosity fluctuations due to silicon dissolution into the alkali hydroxide solution accompanying an increase in the number of processed sheets is suppressed.

  By performing control in such an etching process, a highly accurate etching rate can be made uniform.

FIG. 1 is a diagram showing a schematic configuration of an etching apparatus according to Embodiment 1 of the present invention. FIG. 2 is a graph L showing the correlation between the oxidation-reduction potential and the etching rate of silicon. FIG. 3 shows changes with time of the oxidation-reduction potential in the conventional etching method (solid line graph La) and in the etching method of the present invention (dotted line graph Lb). FIG. 4 is a bar graph showing the correlation between the circulating flow rate of the etchant and the in-plane uniformity of silicon etching. FIG. 5 is a schematic cross-sectional view illustrating the configuration of a conventional etching apparatus disclosed in Patent Document 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a diagram schematically showing a schematic configuration of an etching apparatus according to Embodiment 1 of the present invention.

  The etching apparatus 100 according to the first embodiment of the present invention includes an etching treatment tank 101 filled with an etching solution E, and a silicon substrate (not shown) is immersed in the etching solution in the etching treatment tank 101 to remove the silicon substrate. An etching apparatus for performing wet etching.

  The etching apparatus 100 includes a potential measuring unit 120 that measures the oxidation-reduction potential of the etching solution in the etching treatment tank 101, and the oxidation-reduction potential of the etching solution based on the oxidation-reduction potential measured by the potential measurement unit 120. And a potential adjusting unit 130 that adjusts the voltage so as to be held at a constant voltage.

  Here, the potential measurement unit 120 is connected to the measurement electrode 121a provided in the etching treatment tank 101, and the oxidation-reduction potentiometer 121 connected to the measurement electrode 121a and outputs a measurement signal indicating the measured value of the oxidation-reduction potential. And have. This measurement electrode has an Ag electrode and an AgCl electrode having different polarities.

  The potential adjusting unit 130 controls the supply of hydrogen gas by the bubbling device 131 based on the bubbling device 131 that performs bubbling of hydrogen gas to the etching solution and the oxidation-reduction potential measured by the potential measuring unit 120. And a bubbling control unit 132.

  The bubbling device 131 is attached to the periphery of the etching treatment tank 101 with a hydrogen gas generation source 131 a that generates hydrogen gas, and the etching liquid overflowing from the etching treatment tank 101 by supplying the etching liquid to the etching treatment tank 101. Are attached to a part of the gas supply pipe Gp and a gas supply pipe Gp for supplying hydrogen gas from the hydrogen gas generation source 131a to the etching liquid stored in the bubbling tank 102. And an on-off valve 131b for opening or shutting off the gas supply pipe Gp. The on-off valve 131b is opened and closed by an open / close control signal from the bubbling control unit 132. Here, the bubbling control unit 132 collates the measured value of the oxidation-reduction potentiometer with a preset set value, and increases the amount of dissolved hydrogen if the measured value is equal to or greater than the set value, so that the redox potential becomes the set value. It consists of a microcomputer that automatically controls the following conditions.

  The bubbling control unit 132 compares the measured value indicated by the measurement signal Dv from the oxidation-reduction potentiometer 121 with a preset set value. When the measured value is larger than the set value, the bubbling of hydrogen gas is performed. Then, the on-off valve 131b is opened to perform bubbling, and when the measured value is equal to or lower than the set value, the on-off valve 131b is closed to stop the bubbling of hydrogen gas.

  The etching apparatus 100 is configured to circulate an etching solution E between the etching processing tank 101 and the bubbling processing tank 102. That is, the etching apparatus 100 is provided in the middle of the first and second pipes Lp1 and Lp2 that form the circulation path of the etching solution between the etching treatment tank 101 and the bubbling treatment tank 102, A circulation pump 110 that circulates the etching solution and an inverter control unit 110a that drives and controls the circulation pump 110 are provided. Here, the bubbling treatment tank 102 and the circulation pump 110 are connected by a first pipe Lp1, and the circulation pump 110 and the etching treatment tank 101 are connected by a second pipe Lp2. An etchant flow meter 111 is attached in the middle of the second pipe Lp2, and a measured value Df indicating the circulating amount Fe of the etchant is output from the flow meter 111, and the inverter control unit 110a. Based on this measured value Df, the drive capability of the circulation pump 110 is controlled by the drive signal Vd so that the circulating amount Fe of the etching solution is maintained at a constant set value.

  That is, the viscosity of the etching solution increases as the number of etching processes increases, and the circulation amount of the etching solution decreases when the driving capability of the circulation pump is constant. Therefore, the inverter control unit 110a controls the driving capacity of the circulation pump based on the circulation amount of the etching solution measured by the flow meter so that the circulation amount of the etching solution is constant regardless of the viscosity of the etching solution. It is configured as follows.

  In addition, the etching apparatus 100 detects a state in which the oxidation-reduction potential does not fall below the set value despite the bubbling of hydrogen gas based on the measurement signal Dv of the oxidation-reduction potentiometer 121, or from the flow meter 111. Based on the output measurement value Df and the drive signal Vd of the inverter control unit 110a, an alarm is generated when it is detected that the circulating amount Fe of the etching solution cannot be maintained at a constant set value even if the driving capability of the circulation pump is increased. It has a process management unit 100a configured to emit.

  Next, the operation will be described.

  First, the relationship between the oxidation-reduction potential and the etching rate will be described with reference to FIG.

  As shown in FIG. 2, the oxidation-reduction potential has a correlation with the etching rate of silicon, and when the oxidation-reduction potential shifts in the negative direction, the etching rate increases.

  Next, the relationship between the etching process performed after introducing a new etching solution into the etching tank and the oxidation-reduction potential will be described with reference to FIG.

  As shown by the graph La in FIG. 3, when the etching process is started (the portion of the elapsed time P1 in the figure), the oxidation-reduction potential shows a high value in the positive direction when the new solution is added, and if the silicon etching process is performed, Stable at a low numerical value (the portion of elapsed time P2 to P3 in the figure).

  It can also be seen that the oxidation-reduction potential increases if this etching solution is left without performing the etching treatment (the portion of elapsed time P4 in the figure).

  Thereafter, when the etching process is started again, the oxidation-reduction potential of the etching solution decreases (the portion indicated by the elapsed time P5 in the figure).

  Therefore, in the present embodiment, as the first control of the etching process, the measured value of the oxidation-reduction potentiometer is set between the measured value and the preset value set by the bagling control unit 132 of the potential adjusting unit 130. When the redox potential indicated by the measured value is equal to or higher than the set value, the control for lowering the redox potential is performed by performing hydrogen bubbling.

  Then, when the oxidation-reduction potential becomes equal to or lower than the set value, the etching variation due to the oxidation-reduction potential is suppressed by introducing the silicon substrate as the object to be processed into the etching treatment tank.

  Note that the control value of the oxidation-reduction potential, that is, the optimum value of the set value set in advance in the bubbling control unit 132 of the potential adjustment unit is determined as the measurement electrode from the data shown in FIG. It has been derived that when an electrode composed of an Ag electrode and an AgCl electrode is used, it is −900 mV or less.

  In the present embodiment, as the second control of the etching process, the circulating flow rate is controlled by controlling the driving amount of the circulating pump for circulating the etching solution by the inverter unit.

  That is, when an alkali hydroxide solution as an etchant is repeatedly etched with a silicon substrate, silicon is eluted into the etchant, thereby increasing the viscosity of the etchant. As a result, in a state where the driving ability of the circulation pump is kept constant, the circulating flow rate of the etching solution gradually decreases as the viscosity of the etching solution increases. Such a decrease in the liquid circulation flow rate causes a decrease in the etching amount uniformity in the silicon substrate surface as shown in FIG.

  Therefore, in the present embodiment, the drive capability of the circulation pump is controlled by the inverter drive unit 110a so that the circulating flow rate of the etching solution is kept constant.

  In this embodiment, the circulating amount of the etching solution is selected as 12 L / min as an example of the actual set value as shown in FIG.

  Next, the operation of etching the silicon substrate with the etching apparatus of this embodiment will be specifically described.

  First, when a new etching solution is introduced into the etching treatment tank 101 and the circulation pump 110 is driven by the inverter driving unit 110a, circulation of the etching solution is started between the etching treatment tank 101 and the bubbling treatment tank 102. In this state, the inverter driving unit 110a feedback-controls the circulation pump 110 based on the measurement signal Df from the flow meter 111 so that the circulating amount Fe of the etching solution becomes a set amount.

  Further, before the start of the etching process, the amount of dissolved hydrogen in the etching solution decreases due to the escape of hydrogen gas from the etching solution, and the oxidation-reduction potential increases as shown in the graph La (P1 portion) in FIG. Tend to. For this reason, in the etching apparatus 100 according to the first embodiment, the potential reduction unit 130 adjusts the oxidation-reduction potential to be equal to or lower than the set value.

  Specifically, the hydrogen gas Fh is supplied from the hydrogen gas generation source 131a to the bubbling treatment tank 102 via the gas supply pipe Gp, and the oxidation-reduction potential is represented by the graph Lb (elapsed time P1) by bubbling the hydrogen gas with respect to the etching solution. As shown in (Part)). This minimum potential is a potential lower than the potential at which the etching rate reaches the maximum. At this time, the bubbling control unit 132 determines whether or not the value of the oxidation-reduction potential indicated by the measurement signal Dv from the oxidation-reduction potentiometer 121 is larger than the set value. If it shuts off and becomes larger than the set value, the on-off valve 131b is opened.

  After the oxidation-reduction potential becomes equal to or lower than the set value by adjusting the oxidation-reduction potential by the potential adjustment unit 130, the silicon substrate etching process is started.

  When a silicon substrate (not shown) is immersed and wet etching of the silicon substrate is started, hydrogen gas is generated in the etchant due to the reaction between the etchant and silicon during the etching process. It becomes unnecessary or the frequency of the bubbling process can be reduced.

  Thereafter, when the etching process of the silicon substrate is repeated, silicon is eluted in the etching solution and the viscosity of the etching solution increases. This increase in the viscosity of the etching solution is measured by the inverter control unit 110a from the flow meter 111. Based on the value Df, the driving ability of the circulation pump 110 is substantially avoided by feedback control so that the circulating amount of the etching solution becomes constant.

  In addition, when the etching process is interrupted (the portion of the elapsed time P4), the hydrogen gas dissolved in the etching solution escapes, so that the oxidation-reduction potential tends to increase as shown in the graph La in FIG. However, in the present embodiment, the potential adjustment unit 130 adjusts the oxidation-reduction potential to be equal to or lower than the set value. That is, the bubbling control unit 132 determines whether or not the value of the oxidation-reduction potential indicated by the measurement signal Dv from the oxidation-reduction potentiometer 121 is larger than the set value, and when it becomes smaller than the set value, the on-off valve 131b is shut off. If it becomes larger than the set value, the on-off valve 131b is opened. As a result, the amount of dissolved hydrogen in the etching solution increases, the oxidation-reduction potential is kept low as shown in the graph Lb of FIG. 3, and a decrease in the etching rate is avoided.

  The above-described etching process is generally performed while adding a new solution. However, even if a new solution is added or the bubbling process is performed, the oxidation-reduction potential does not decrease below a set value or a circulation pump. In the state where the circulation amount does not reach the set value even when the driving capacity of the redox potentiometer is maximized, the processing management unit 100a uses the output Dv of the oxidation-reduction potentiometer 121, the output Df of the flow meter 111, and the driving signal of the inverter control unit 110a. Detect based on Vd and issue a warning.

  When this warning is issued, it is necessary to take measures such as replacing the etching solution with a new solution.

  With the etching rate maintained at a constant value in this way, the silicon substrate of the next lot is further immersed in an etching treatment tank to continue wet etching.

  In this way, the etching process can be performed while keeping the oxidation-reduction potential of the etching solution and the circulation amount of the etching solution constant, whereby a highly accurate etching rate can be made uniform.

  As described above, in this embodiment, the measured value of the oxidation-reduction potentiometer 121 is compared and determined by the bagling control unit 132 of the potential adjustment unit 130 with respect to the magnitude relationship between the measured value and the preset setting value. When the redox potential indicated by the measured value is greater than or equal to the set value, control is performed to lower the redox potential by performing hydrogen bubbling, so that the redox potential can always be maintained at the set value and etching is performed. It can be avoided that the rate is lowered at the time of starting the etching process after introducing the new liquid or at the time of starting the etching process after interrupting the etching process.

  In the present embodiment, the inverter control unit feedback-controls the driving capacity of the circulation pump based on the measurement value of the flow meter, so that the circulating flow rate of the etching solution does not depend on the liquid viscosity and is always constant. This makes it possible to realize a silicon etching process that does not depend on the number of processes in the in-plane uniformity of the silicon substrate.

  As described above, by performing the above-described two controls during the etching process, a high-quality process that does not depend on the input interval and the number of processes is realized in the wet etching of the silicon substrate. Accurate silicon substrate wet etching technology can be established.

  In the above embodiment, as an example of the actual set value, the target circulating amount of the etching solution is selected as 12 L / min as shown in FIG. 4 from the result of the experimental apparatus. However, the present invention is not limited to this, and the etching apparatus of the present invention may be any apparatus that maintains a constant liquid circulation flow rate.

  In the above embodiment, an etching apparatus that controls both the oxidation-reduction potential and the circulating flow rate of the etching solution is shown. However, in some cases, the etching apparatus controls the oxidation-reduction potential and performs etching. Only one of the control of the circulation flow rate of the liquid may be performed.

  In addition, as a specific application example using the etching apparatus according to the present invention, texture processing of a solar cell substrate that requires high-precision etching uniformity, that is, unevenness for preventing reflection on the surface is formed. It is also possible to deal with processing.

  As mentioned above, although this invention has been illustrated using preferable embodiment of this invention, this invention should not be limited and limited to this embodiment. It is understood that the scope of the present invention should be construed only by the claims. It is understood that those skilled in the art can implement an equivalent range based on the description of the present invention and the common general technical knowledge from the description of specific preferred embodiments of the present invention. Patents, patent applications, and documents cited herein should be incorporated by reference in their entirety, as if the contents themselves were specifically described herein. Understood.

  In the field of an etching method and an etching apparatus, the present invention can perform a wet etching process for etching a silicon substrate with an etching solution while suppressing a decrease in etching ability of the etching solution and variation in etching amount.

DESCRIPTION OF SYMBOLS 100 Etching apparatus 100a Process management part 101 Etching process tank 102 Bubbling process tank 110 Circulation pump 110a Inverter control part 111 Flowmeter
120 Potential Measurement Unit 121 Oxidation Reduction Electrometer 121a Measurement Electrode 130 Potential Adjustment Unit 131 Bubbling Device 131a Hydrogen Gas Generation Source 131b On-off Valve 132 Bubbling Control Unit Df Measurement Value Dv Measurement Potential E Etching Liquid Fe Circulation Fh Hydrogen Gas Gp Gas Pipe Lp1 , Lp2 First and second piping Vd Drive signal

Claims (12)

A method of etching a silicon substrate by immersing the silicon substrate in an etching solution in an etching bath,
Measuring the oxidation-reduction potential of the etching solution;
Adjusting the oxidation-reduction potential of the etching solution based on the measured oxidation-reduction potential so as to keep it constant. The etching method according to claim 1,
The oxidation / reduction potential is adjusted by adjusting the amount of dissolved hydrogen in the etching solution. The etching method according to claim 2, wherein
An etching method in which the amount of dissolved hydrogen in the etching solution is adjusted by bubbling hydrogen gas in the etching solution. The etching method according to claim 2, wherein
An etching method in which the hydrogen gas is bubbled so that the oxidation-reduction potential is equal to or lower than a set potential at which an etching rate of the silicon substrate reaches a maximum value. The etching method according to claim 4, wherein
The etching method, wherein the set potential of the oxidation-reduction potential is −900 mV or less. The etching method according to claim 1,
Circulating the etching solution between a bubbling portion for bubbling the etching solution and the etching tank,
An etching method in which the circulating amount of the etching solution is kept constant regardless of the viscosity of the etching solution. An etching apparatus having an etching tank filled with an etching solution, and wet etching the silicon substrate by immersing the silicon substrate in the etching solution in the etching tank,
A potential measuring unit for measuring the oxidation-reduction potential of the etching solution;
An etching apparatus comprising: a potential adjusting unit that adjusts the oxidation-reduction potential of the etching solution so as to be maintained at a constant voltage based on the oxidation-reduction potential measured by the potential measurement unit. The etching apparatus according to claim 7, wherein
The potential adjustment unit includes:
A bubbling device for bubbling hydrogen gas with respect to the etching solution;
An etching apparatus comprising: a bubbling control unit that turns on and off the bubbling device based on the oxidation-reduction potential measured by the potential measuring unit. The etching apparatus according to claim 7, wherein
A bubbling tank attached to the etching tank for bubbling the etching solution;
A circulation pump for circulating the etching solution between the bubbling tank and the etching tank;
An inverter control unit for driving and controlling the circulation pump;
A flow meter for measuring the circulating amount of the etching solution,
The inverter control unit controls the driving ability of the circulation pump based on the circulation amount of the etching solution measured by the flowmeter so that the circulation amount of the etching solution is constant regardless of the viscosity of the etching solution. apparatus. The etching apparatus according to claim 9, wherein
The potential measuring unit includes:
A measuring electrode provided in the etching tank;
An etching apparatus having an oxidation-reduction potentiometer connected to the measurement electrode. The etching apparatus according to claim 10, wherein
The measuring electrode includes an Ag electrode and an AgCl electrode having different polarities. The etching apparatus according to claim 8, wherein
The bubbling control unit
The measured value of the oxidation-reduction potentiometer is collated with a set value set in advance.If the measured value is equal to or greater than the set value, the amount of dissolved hydrogen is increased so that the oxidation-reduction potential is equal to or lower than the set value. An etching apparatus having a computer unit for automatically controlling the bubbling apparatus.