JP2008041939A - Silicon anisotropic etching apparatus and silicon anisotropic etching method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To conduct a stable silicon anisotroic etching, while preventing increase in the cost and decrese in the througput. <P>SOLUTION: An Si wafer 2 and a chemical tank 4 for charging a chemical solution 1 for conducting an anisotropic etching of the Si wafer 2 are arranged in the inside of an etching draft 7 with a pipe 6 for emission connected. A heater 5 for heating the chemical solution 1 is provided at the bottom of the chemical tank 4. A hydrogen concentration meter 8 is provided in the etching draft 7 or in the pipe 6 for emission. The Si wafer 2 is etched with the hydrogen concentration value that is measured by the hydrogen concentration meter 8 monitored. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for processing a silicon (Si) wafer, and specifically to an etching apparatus and an etching method for anisotropically etching a Si wafer using a chemical solution.

  In recent years, the fields of LSI (Large Scale Integration) and MEMS (Micro Electro Mechanical Systems) using silicon (Si) semiconductors have advanced, and various microfabrication technologies have been developed and implemented to manufacture these. ing. Further, fine processing is also performed on the Si wafer itself as a substrate, and Si anisotropic etching using an alkaline chemical is performed as one method.

  In Si etching using an alkaline chemical solution, anisotropic etching can be performed because the etching rate varies depending on the crystal plane of Si. Specifically, the etching rate for the Si (111) surface is as small as about 1/50 to 1/200 of the etching rate for the Si (100) surface. For this reason, as a result of the Si (100) surface being etched quickly, an anisotropic shape in which the Si (111) surface having a low etching rate is exposed is obtained. A microfabrication technique of Si wafer is used to obtain a V-shaped groove shape, a pyramidal needle shape, a quadrangular pyramid-shaped hole shape, etc. by exposing only the Si (111) surface using this etching characteristic. .

  Hereinafter, a conventional Si anisotropic etching apparatus and Si anisotropic etching method will be described with reference to the drawings.

  FIG. 7 is a schematic view showing a conventional Si anisotropic etching apparatus. An exhaust pipe 106 for exhausting air is connected to the processing chamber (etching draft) 107 of the etching apparatus 100 shown in FIG. Inside the etching draft 107, a chemical bath 104 for storing a cassette 103 for storing the Si wafer 102 is arranged. In the chemical bath 104, a chemical solution 101 for Si anisotropic etching is stored. A heater 105 for heating the chemical solution 101 is provided at the bottom of the chemical solution tank 104.

  An etching method using the etching apparatus 100 shown in FIG. 7 is as follows. First, the chemical solution 101 is heated to a predetermined temperature by putting the chemical solution 101 into the chemical solution tank 104 and operating the heater 105. As the chemical solution 101, an alkaline aqueous solution, for example, a potassium hydroxide aqueous solution (KOH) or a tetramethylammonium hydroxide (TMAH) aqueous solution is used. After the temperature of the chemical solution 101 reaches a predetermined temperature, the cassette 103 containing the Si wafer 102 is immersed in the chemical solution 101 in the chemical solution tank 104. The Si wafer 102 reacts with the chemical solution 101 while generating bubbles 109, and the Si wafer 102 is etched (dissolved). After a predetermined time has elapsed from the start of etching, the cassette 103 is pulled up from the chemical bath 104, and the etching of the Si wafer 102 is completed. Thereafter, the Si wafer 102 is washed with water and then dried (not shown).

In order to obtain a V-shaped groove shape, a pyramidal needle shape, or a quadrangular pyramidal hole shape by processing a Si wafer by anisotropic etching as described above, the thickness is usually several tens to several hundreds μm. It is necessary to etch a large amount of Si. For this reason, the chemical solution for Si anisotropic etching is used after being heated to a high temperature. However, since the said chemical | medical solution is aqueous solution, it is difficult to make it high temperature of 100 degreeC or more, and the actual use temperature range of the said chemical | medical solution is 70 to 90 degreeC. Further, even when the chemical solution is heated to a high temperature of 70 ° C. to 90 ° C., the etching rate of Si is at most several μm / min (for example, the etching rate for the Si (100) surface is 0.5 to 2 μm / min). In order to obtain the desired shape, etching for a long time of several tens of minutes to several hours is required.
JP 63-240029 A Japanese Patent Laid-Open No. 04-094125 JP 08-274005 A

  However, Si anisotropic etching using the conventional Si anisotropic etching apparatus has a problem that Si dissolved in the chemical solution is precipitated. That is, in the Si anisotropic etching, as described above, since the Si etching with a thickness of several tens to several hundreds of μm is performed, a large amount of Si dissolves in the chemical solution. Further, as the number of processed Si wafers increases, the amount of Si dissolved in the chemical solution also increases. As a result, when the Si concentration in the chemical solution exceeds the saturation solubility, Si in the chemical solution starts to precipitate. In the conventional Si anisotropic etching apparatus as shown in FIG. 7, since it is not known how much Si is dissolved in the chemical solution, the etching process is performed exceeding the saturation solubility of Si, and the chemical solution tank There arises a problem that Si is deposited on the bottom. In particular, in a Si anisotropic etching apparatus having a specification for circulating a chemical solution, there is a risk that Si is deposited and clogged in a circulation line pipe, a pump, a filter, or the like, and the etching apparatus breaks down.

  On the other hand, when chemicals are frequently exchanged to prevent Si precipitation, the cost increases and the throughput decreases.

  In view of the above, an object of the present invention is to enable stable silicon anisotropic etching while preventing an increase in cost and a decrease in throughput.

  In order to achieve the above object, the inventor of the present application has made various studies on a method for measuring the Si concentration in a chemical solution during silicon anisotropic etching, and as a result, has obtained the following knowledge. For example, when a TMAH solution is used as a chemical solution for anisotropic etching of silicon, if the TMAH concentration or Si concentration in the TMAH solution changes, the ultrasonic wave propagation speed (hereinafter referred to as sound velocity) or conductivity in the TMAH solution changes. Therefore, an attempt has been made to obtain the Si concentration in the TMAH solution using this phenomenon. Specifically, using a chemical solution with a known ratio between the TMAH concentration and the Si concentration, the “sound velocity” or “conductivity” in the chemical solution is measured, and the above ratio and the “sound velocity” or “conductivity” are measured. The correlation (calibration curve) is prepared in advance. Next, by measuring “sound speed” or “conductivity” in the chemical solution during silicon anisotropic etching, and applying the measurement result to the calibration curve, the ratio between the TMAH concentration and the Si concentration in the chemical solution is measured. Is obtained by inverse conversion.

  However, the Si concentration measuring method has a problem that the “sound velocity” in the chemical cannot be accurately measured due to the influence of bubbles generated in the chemical during etching. Also, when there is something other than TMAH or Si in the chemical solution, for example, when an additive such as an accelerator for improving the etching rate or a corrosion inhibitor for improving the selection ratio is added to the chemical solution, There is a problem that it becomes difficult to measure “sound speed” or “conductivity” in the chemical solution due to the influence of the additive.

  Therefore, the inventor of the present application paid attention to the following reaction formula between Si constituting the Si wafer and the chemical having alkalinity.

_{^{Si + 2OH - + 2H 2 O}} → Si (OH) 2 (O -) 2 + H 2 ↑
That is, when Si is dissolved in Si anisotropic etching, hydrogen (bubbles 109 in FIG. 7) is always generated. Therefore, if the amount of generated hydrogen can be known, The amount of Si eluted in the chemical solution can be obtained, and the Si concentration in the chemical solution can be obtained using the result.

  The present invention has been made on the basis of the above knowledge. Specifically, the silicon anisotropic etching apparatus according to the present invention includes a processing chamber to which exhaust piping is connected, and an interior of the processing chamber. A silicon wafer and a chemical bath for containing a chemical solution for anisotropic etching of the silicon wafer, a heater disposed in the processing chamber, and for heating the chemical solution, And at least one hydrogen concentration meter installed in at least one of the processing chamber and the exhaust pipe.

  According to the silicon anisotropic etching apparatus of the present invention, since the hydrogen concentration meter is installed in the processing chamber or in the exhaust pipe, the Si etching process is performed while monitoring the hydrogen concentration value measured by the hydrogen concentration meter. Thus, the amount of hydrogen generated during the Si etching process can be known. For this reason, the amount of silicon eluted in the chemical solution can be obtained based on the hydrogen generation amount, and the Si concentration in the chemical solution can be obtained using the result. The state management and exchange of the chemical solution can be performed appropriately. Therefore, since the concentration of silicon dissolved in the chemical solution exceeds the saturation solubility, that is, it is possible to prevent the silicon from being deposited and the etching apparatus from failing, it is possible to prevent the increase in cost and the decrease in throughput, while maintaining stable. Silicon anisotropic etching can be performed.

  In the anisotropic silicon etching apparatus of the present invention, it is preferable that the hydrogen concentration meter is installed at a position above the chemical tank. If it does in this way, since the hydrogen generated in the chemical | medical solution stored in the chemical | medical solution tank can be captured more efficiently, the measurement precision of a hydrogen concentration meter can be improved.

  In the silicon anisotropic etching apparatus of the present invention, an alkaline aqueous solution such as a KOH aqueous solution or a TMAH aqueous solution can be used as a chemical solution for etching.

  The silicon anisotropic etching method according to the present invention is an etching method using the silicon anisotropic etching apparatus of the present invention described above, and the silicon concentration is measured while monitoring the hydrogen concentration value measured by a hydrogen concentration meter. Etching the wafer, more specifically, based on the hydrogen concentration value measured by the hydrogen concentration meter, to calculate the silicon concentration in the chemical solution, based on the calculation result, The state management and exchange of chemicals are performed.

  According to the silicon anisotropic etching method of the present invention, since the silicon anisotropic etching device of the present invention is used, the above effect, that is, a stable silicon anisotropy is prevented by preventing failure of the etching device due to silicon deposition. The effect that reactive etching can be performed can be obtained.

  By the way, in the conventional Si anisotropic etching apparatus shown in FIG. 7, since the Si anisotropic etching chemical solution which is an alkaline aqueous solution is heated to a high temperature and used, the concentration of the chemical solution (for example, TMAH in the TMAH solution) is used. As a result, the etching rate fluctuates. Therefore, when the etching process is performed with the processing time fixed, there is a problem that the Si etching amount changes for each process. Furthermore, since a single etching process takes a long time, there is a problem that the etching rate fluctuates even during the etching process. In response to this, various countermeasures as described below have been attempted.

  (1) As described above, bubbles (hydrogen) are generated as reaction byproducts during etching of Si. Further, when etching of the Si (100) surface proceeds and Si is processed so as to have a desired V-shaped groove or the like and only the Si (111) surface is exposed, the Si etching rate is 1/50. Since it is reduced to about 1/200, the generation of bubbles is remarkably reduced, and it is very difficult to check the bubbles. Using these characteristics, etching is performed by visually confirming the occurrence of the above-mentioned bubbles in response to the problem that etching processing cannot be performed with the processing time fixed due to fluctuations in the etching rate. Attempts have been made to perform end point detection. However, in this method of visually confirming the generation of bubbles, it is impossible to predict when the generation of bubbles will disappear, that is, when the etching should be terminated, so that a person is always on the side of the Si anisotropic etching apparatus. Another problem is that it is necessary to continue to observe the presence or absence of bubbles. In addition, since it is a method for visually judging whether or not bubbles are generated, there is a problem that the operation of the Si anisotropic etching apparatus cannot be automated. Furthermore, since the Si etching process takes a long time (tens of minutes to several hours), the above-described method using the visual judgment misses the etching end point at which bubbles are not observed, or the confirmation of the end point is ambiguous. There is also the problem of becoming.

  (2) Patent Document 1 discloses that “the end point detection of Si etching based on the presence / absence of bubbles is determined by detecting the presence / absence of sound due to bubbles”. However, since the Si anisotropic etching apparatus is installed in a clean room, various noise sounds, for example, air sound due to downflow, driving sound of surrounding apparatuses, air sound of the exhaust duct of the Si anisotropic etching apparatus itself, Alternatively, the driving sound of the circulation pump built in the Si anisotropic etching apparatus for circulating the chemical solution is large. For this reason, the method of Patent Document 1 has a problem in that it is difficult to distinguish between these noise sounds and sounds caused by bubbles.

  (3) Patent Document 2 states that “the end point detection of Si etching based on the presence or absence of bubbles is detected by irradiating light into the chemical bath and detecting whether or not the irradiated light is scattered by bubbles. It is shown that “determine”. However, heaters for heating a chemical solution for anisotropic etching of Si include resistance wire heaters (for example, heating by applying voltage to Kanthal wire resistance) and infrared lamp heaters (for example, infrared radiation by a tungsten filament). In general, it is inevitable that the heater itself generates light. For this reason, the method of Patent Document 2 has a problem that light emitted from the heater becomes noise light, and it is difficult to detect the presence or absence of bubble generation by light.

  On the other hand, the silicon anisotropic etching apparatus of the present invention has a hydrogen concentration meter installed in the processing chamber or the exhaust pipe, and therefore, by monitoring the hydrogen concentration value measured by the hydrogen concentration meter. The presence or absence of hydrogen generation can be known reliably and easily, and the end point detection of etching can be determined based on the result.

  That is, in the silicon anisotropic etching method of the present invention, the end point of etching for the silicon wafer is detected by determining whether or not a silicon etching reaction has occurred based on the hydrogen concentration value measured by the hydrogen concentration meter. It is preferable to carry out. In this way, since the end point detection of Si anisotropic etching can be reliably performed, the Si anisotropic etching process can be performed with good reproducibility and stability.

  In the Si anisotropic etching using an alkaline chemical solution as described above, hydrogen generated as a reaction by-product is a dangerous gas having explosive properties, and there is a risk of explosion fire. However, in the conventional Si anisotropic etching apparatus shown in FIG. 7, since it is impossible to know how much hydrogen is generated, hydrogen, which is a dangerous gas having explosive properties, has an explosion range concentration. Since it is not possible to determine whether or not it remains in the processing chamber up to (4 to 76% by volume), there is a risk of explosion and fire.

  On the other hand, the silicon anisotropic etching apparatus of the present invention has a hydrogen concentration meter installed in the processing chamber or the exhaust pipe, and therefore, by monitoring the hydrogen concentration value measured by the hydrogen concentration meter. Thus, it is possible to know how much hydrogen is generated, and based on the result, it is possible to appropriately implement safety measures for preventing explosion and fire.

  That is, in the silicon anisotropic etching method of the present invention, etching the silicon wafer while confirming that the hydrogen concentration value measured by the hydrogen concentration meter is smaller than a predetermined value, more specifically, Preferably, when the hydrogen concentration value measured by the hydrogen concentration meter becomes equal to or higher than the predetermined value, predetermined safety measures are taken. In this way, even when performing an Si anisotropic etching process in which hydrogen, which is a dangerous gas having an explosive property, is generated, a safe Si etching process without risk of gas explosion can be performed. Further, in this case, if the measured hydrogen concentration value is confirmed to be smaller than the predetermined value by AND processing using at least two hydrogen concentration meters, the erroneous detection of the hydrogen concentration meter is ensured. Can be prevented.

  According to the present invention, by a simple method of measuring the amount of hydrogen generated during Si anisotropic etching with a hydrogen concentration meter, it is possible to safely perform silicon anisotropic etching while preventing an increase in cost and a decrease in throughput. It can be performed stably.

  Hereinafter, an Si anisotropic etching apparatus and an Si anisotropic etching method according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic view showing the Si anisotropic etching apparatus of this embodiment. An exhaust pipe 6 for exhausting the etching draft 7 is connected to the processing chamber (etching draft) 7 of the etching apparatus 20 shown in FIG. Inside the etching draft 7, a chemical tank 4 for placing a cassette 3 for storing the Si wafer 2 is disposed. A chemical solution 1 for Si anisotropic etching is stored in the chemical solution tank 4. A heater 5 for heating the chemical solution 1 is provided at the bottom of the chemical solution tank 4. A chemical solution pipe 11 for circulating the chemical solution is connected to the chemical solution tank 4, and the chemical solution pipe 11 is drawn to the outside of the etching draft 7. A circulation pump 12 and a chemical filter 13 are connected to a portion of the chemical solution pipe 11 that is drawn outside the etching draft 7. A HEPA (High Efficiency Particulate Air) filter 14 is provided on the ceiling portion of the etching draft 7, and an air flow meter for measuring the downflow from the HEPA filter 14 is provided below the HEPA filter 14. . A hydrogen concentration meter 8 is provided in each of the etching draft 7 and the exhaust pipe 6, and the hydrogen concentration value measured by the hydrogen concentration meter is monitored outside the etching draft 7 and the hydrogen concentration is measured. A computer 10 that performs a predetermined calculation using the value is provided.

  The etching method using the etching apparatus 20 of this embodiment shown in FIG. 1 is as follows.

  First, the chemical solution 1 is heated to a predetermined temperature by putting the chemical solution 1 in the chemical solution tank 4 and operating the heater 5. As the chemical solution 1, an alkaline aqueous solution, for example, a KOH aqueous solution or a TMAH aqueous solution is used.

  In order to process the Si wafer 2 to obtain a V-shaped groove shape, a pyramidal needle shape, a quadrangular pyramid hole shape, or the like, a large amount of Si having a thickness of about several tens to several hundreds μm is usually formed. It needs to be etched. For this reason, in order to shorten the etching processing time, it is desirable to heat and use the chemical solution 2 for Si anisotropic etching at a higher temperature. However, since the chemical solution 2 is an aqueous solution, it is difficult to increase the temperature to 100 ° C. or higher, and the actual use temperature range of the chemical solution 2 is about 70 ° C. to 90 ° C. Further, when the TMAH aqueous solution having a concentration of 10% (mass%) is heated to 80 ° C. and used as the chemical solution 2, for example, the etching rate with respect to the Si (100) surface is about 0.5 to 0.6 μm / min. The etching rate for the Si (111) surface is about 0.01 to 0.02 μm / min. Therefore, in this case, about 3 hours are required to etch the Si (100) surface to a thickness of 100 μm.

  Moreover, in this embodiment, in order to make uniform temperature distribution of the chemical | medical solution 2 stored in the chemical | medical solution tank 4, the chemical | medical solution 1 is circulated. Specifically, the chemical solution 1 in the chemical solution tank 4 is sent to the circulation pump 12 through the chemical solution pipe 11 and then returned to the chemical solution tank 4 again through the chemical solution filter 13.

  Next, after the temperature of the chemical solution 1 reaches a predetermined temperature, the cassette 3 containing the Si wafer 2 is immersed in the chemical solution 1 in the chemical solution tank 4. Thereby, the Si wafer 2 reacts with the chemical solution 1 while generating bubbles (hydrogen) 9, and the Si wafer 2 is etched (dissolved). Here, the reaction formula between Si constituting the Si wafer 2 and the chemical solution 1 is expressed as follows.

_{^{Si + 2OH - + 2H 2 O}} → Si (OH) 2 (O -) 2 + H 2 ↑
In the present embodiment, the generated hydrogen gas (bubble 9) is measured by the hydrogen concentration meter 8, and the measured value is monitored by the computing computer 10. FIG. 2 shows an example of the monitoring result of the hydrogen gas concentration value by the computing computer 10.

  As shown in FIG. 2, when the Si wafer 2 is put into the chemical solution 1 and Si etching is started, the hydrogen gas concentration value of the hydrogen concentration meter 8 starts to rise. Specifically, the hydrogen gas concentration value of the hydrogen concentration meter 8 that had been substantially zero before the Si wafer 2 was put is, for example, an 8 inch size Si wafer (Si etching region is about 30% of the wafer surface). By putting 25 sheets in 1, it rises to about 5000 ppm.

  In addition, as shown in FIG. 2, while the Si wafer 2 is being etched while generating bubbles 9, a high hydrogen gas concentration value is maintained, but the Si (100) surface is lost and a V-shaped groove or the like is lost. When the shape is formed and only the Si (111) surface is exposed, the Si etching rate is remarkably reduced to about 1/50 to 1/200 of the Si (100) surface etching. For this reason, the bubbles 9 are hardly seen, and the hydrogen gas concentration value detected by the hydrogen concentration meter 8 also rapidly decreases to 100 ppm or less. In the present embodiment, after performing over-etching for a predetermined time from the hydrogen gas concentration sharply decreasing point, the cassette 3 is pulled up from the chemical bath 4 and the etching of the Si wafer 2 is completed. Thereafter, the Si wafer 2 is washed with water and then dried (not shown).

  As described above, in this embodiment, the end point of the Si anisotropic etching can be accurately detected by detecting the sudden decrease point of the hydrogen gas concentration value using the hydrogen concentration meter 8. Accordingly, even when the Si etching rate changes for each Si etching process due to the concentration change of the chemical solution 1, each Si etching process can be performed stably in the same manner.

  In the present embodiment, the sudden decrease point of the hydrogen gas concentration is set to a point where the hydrogen gas concentration value detected by the hydrogen concentration meter 8 is reduced to about 1/50 to 1/200. Shall be detected. However, since the threshold value of the sharp decrease point varies depending on the ratio of the etching rate with respect to the Si (100) surface and the etching rate with respect to the Si (111) surface, chemical processing such as the concentration and temperature of the chemical solution 1 to be used An appropriate value must be set as the threshold for the sudden decrease point according to the conditions.

  In the present embodiment, as the hydrogen concentration meter 8, for example, a general catalytic combustion type may be used. This type of gas concentration meter detects not only hydrogen but also flammable gases such as methane and ethanol. In this embodiment, the hydrogen concentration meter 8 is placed in the Si anisotropic etching apparatus (specifically, an etching draft 7). Since it is installed and used in the inside and inside the exhaust pipe 6), there is no mixing of the other combustible gas, so that only the concentration of hydrogen gas can be measured.

  In the present embodiment, it is desirable to attach the hydrogen concentration meter 8 to a position above the chemical tank 4. This is because the hydrogen gas generated during etching has the property of rising because its molecular weight is smaller than the molecular weight of air. That is, by installing the hydrogen concentration meter 8 at a position above the chemical tank 4, it is possible to increase the detection amount (capture amount) of hydrogen gas generated in the chemical liquid 1 stored in the chemical tank 4. It becomes possible to measure the hydrogen gas concentration with higher accuracy.

  Further, in the present embodiment, the hydrogen concentration value detected by the hydrogen concentration meter 8 may be affected by the downflow that has passed through the HEPA filter 14, so that the airflow of the downflow does not change and is constant. It is necessary to perform the Si anisotropic etching process after confirming this with the air flow meter 15.

  Next, a method for calculating the Si concentration in the chemical solution in the present embodiment (hereinafter referred to as the Si concentration calculating method of the present invention) will be described.

  In the Si concentration calculation method of the present invention, when performing the Si anisotropic etching process by the same procedure as the above procedure using the Si anisotropic etching apparatus shown in FIG. 1, first, for example, as shown in FIG. Such a “correlation between the Si etching amount and the hydrogen gas concentration in the Si anisotropic etching apparatus” is acquired in advance.

  Specifically, the Si wafer 2 is placed in the chemical bath 4 and Si anisotropic etching is performed, and the hydrogen concentration value detected by the hydrogen concentration meter 8 at that time is acquired. Next, the same Si anisotropic etching process is performed by changing the amount of Si wafers 2 (the number of wafers), and the hydrogen concentration value detected by the hydrogen concentration meter 8 at that time is obtained again. Here, since the Si etching region in each Si wafer 2 is the same, the Si etching amount for one Si wafer 2 is also the same, so the hydrogen concentration value is obtained by changing the amount of the wafer 2 as described above. By repeatedly performing this process, it is possible to obtain the “correlation between the Si etching amount and the hydrogen gas concentration in the Si anisotropic etching apparatus” as shown in FIG.

  Next, using the Si anisotropic etching apparatus shown in FIG. 1, an etching process for providing a V-shaped groove shape or the like on the Si wafer 2 is repeatedly performed. At this time, in the etching draft 7 to which the exhaust pipe 6 is connected (or in the exhaust pipe 6), the hydrogen gas concentration detected by the hydrogen concentration meter 8 increases when the Si wafer 2 is introduced, and the Si wafer Since the change that decreases when 2 is taken out is repeated, for example, time-dependent data of the hydrogen gas concentration as shown in FIG. 4 is obtained. In the present embodiment, the chemical solution is obtained by applying the hydrogen gas concentration detected by the hydrogen concentration meter 8 to the “correlation between the Si etching amount and the hydrogen gas concentration in the Si anisotropic etching apparatus” as shown in FIG. The calculation computer 10 performs processing for obtaining the amount of Si etched by 1, that is, the amount of Si dissolved in the chemical solution 1 as needed. Furthermore, the calculation computer 10 performs a process of calculating the cumulative value of the amount of Si dissolved in the chemical solution 1 and calculating the Si concentration (mass concentration) in the chemical solution 1 based on the cumulative value. When the change in the Si concentration thus obtained (hereinafter referred to as the Si concentration in the liquid) is graphed, for example, as shown in FIG. 5, the temporal change data of the Si concentration in the liquid in the Si anisotropic etching apparatus is obtained. can get.

  In the present embodiment, whether or not the Si concentration value in liquid at the present time (any time point of Si anisotropic etching) exceeds the management set value by setting the management value of Si concentration in liquid in advance. Determine if. Then, when the Si concentration value in the liquid exceeds the management set value, a chemical management process such as replacement of the chemical liquid 1 for Si anisotropic etching is performed.

  As described above, according to the present embodiment, since the hydrogen concentration meter 8 is installed in the etching draft 7 or the exhaust pipe 6, the hydrogen concentration value measured by the hydrogen concentration meter 8 is monitored. By performing the Si etching process, the amount of hydrogen generated during the Si etching process can be known. For this reason, for example, by previously acquiring “a relationship between the Si etching amount and the hydrogen gas concentration”, the hydrogen concentration value measured by the hydrogen concentration meter 8 is dissolved in the chemical solution 1 using the relationship. Since the amount of Si that can be converted can be converted as needed, the cumulative value of the amount of Si dissolved in the chemical solution 1 and the Si concentration in the chemical solution 1 can be accurately obtained. Therefore, since the state management and replacement of the chemical solution 1 can be appropriately performed based on the Si concentration in the liquid, the Si concentration in the liquid exceeds the saturation solubility, that is, Si precipitates and the etching apparatus fails. Therefore, stable Si anisotropic etching can be performed while preventing an increase in cost and a decrease in throughput.

  Further, according to the present embodiment, since the amount of Si dissolved in the chemical solution 1 is obtained based on the actual measurement value of the hydrogen gas concentration, when the etching process is stopped halfway, the number of Si wafers 2 to be etched is determined. Even if each process is different, abnormal etching occurs due to the trouble of the Si wafer 2, or when the chemical processing conditions and the chemical state change to change the Si etching rate, the situation It is possible to accurately obtain the Si concentration in the liquid without being affected by the above.

  Furthermore, according to the present embodiment, the Si etching process is performed while monitoring the hydrogen concentration value of the hydrogen concentration meter 8 installed in the etching draft 7 or the exhaust pipe 6. For this reason, for example, by determining whether an etching reaction has occurred on the Si (100) surface based on the amount of hydrogen generated during the Si etching process, in other words, the change point (rapid decrease point) of the hydrogen gas concentration value is detected. By doing so, the end point detection of Si anisotropic etching can be accurately performed. Therefore, each Si etching process can be performed stably with good reproducibility.

  In this embodiment, when the Si anisotropic etching process is performed by the same procedure as described above using the Si anisotropic etching apparatus shown in FIG. 1, the hydrogen detected by the hydrogen concentration meter 8 is detected. It is preferable to perform the Si anisotropic etching process while confirming that the concentration value does not correspond to the explosion range concentration (4 to 76% by volume). Moreover, when the hydrogen concentration value detected by the hydrogen concentration meter 8 corresponds to the explosion range concentration, it is preferable to implement an emergency shut-off procedure described later as a safety measure. As an emergency shut-off treatment, a treatment that lowers the temperature of the chemical solution 1 by turning off the heater 5 to lower the Si etching reaction is essential. In addition, an alarm is issued, the circulation pump 12 is stopped, the chemical solution 1 is diluted or the temperature is lowered by supplying water to the chemical solution tank 4, the chemical solution 1 is discharged from the chemical solution tank 4, and the chemical solution tank 4 is automatically discharged from the chemical solution tank 4. It is desirable to perform treatment such as removal of the Si wafer 2 alone or in combination. However, when performing these emergency shut-off procedures, care must be taken so that hydrogen gas does not ignite and explode due to these procedures themselves.

  Possible causes of the hydrogen gas concentration abnormality in which the hydrogen concentration value corresponds to the explosion range concentration include exhaust pressure abnormality due to the exhaust pipe 6, disappearance of the mask film on the Si wafer 2, and the like.

  Further, in the present embodiment, the hydrogen gas concentration threshold value (emergency cutoff set value) for determining whether or not to perform the emergency cutoff treatment is set to 4%, which is the lower limit of the explosion range concentration. Is preferably set to a value less than that, for example, 2%. That is, it is desirable from the viewpoint of ensuring safety that the emergency shut-off process is performed before the hydrogen gas concentration value actually corresponds to the explosion range concentration.

  FIGS. 6A and 6B show a state in which a hydrogen concentration value exceeding the set value for emergency cutoff is detected by two hydrogen concentration meters 8 during Si anisotropic etching.

  Incidentally, the hydrogen concentration meter 8 may suddenly detect an abnormal value (error value) due to an external factor. Therefore, for example, as shown in FIGS. 6 (a) and 6 (b), at least two hydrogen concentration meters 8 are installed, and an AND process is performed on the measurement results obtained thereby, so that the hydrogen concentration value is urgently cut off. It is desirable from the viewpoint of preventing erroneous detection of the hydrogen concentration meter to determine whether or not the set value is exceeded.

  As described above, in the present embodiment, the hydrogen concentration value detected by the hydrogen concentration meter 8 at the time of Si anisotropic etching is the explosion range concentration (or a concentration equal to or higher than the emergency cutoff set value in consideration of safety). If the hydrogen concentration value falls within the explosion range concentration (or higher than the emergency cutoff setting value), an emergency shutdown procedure may be implemented as a safety measure. desirable. In this way, even when performing an Si anisotropic etching process in which hydrogen, which is a dangerous gas having an explosive property, is generated, a safe Si etching process without risk of gas explosion can be performed.

  As described above, the present invention is an etching method for anisotropically etching a Si wafer using a chemical solution to provide a V-shaped groove shape, pyramid-shaped needle shape, or a quadrangular pyramid hole shape in the Si wafer. It is very useful as an apparatus and etching method.

FIG. 1 is a schematic view showing a Si anisotropic etching apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of the monitoring result of the hydrogen gas concentration value in the Si anisotropic etching apparatus according to one embodiment of the present invention. FIG. 3 is a diagram showing an example of the correlation between the Si etching amount and the hydrogen gas concentration in the Si anisotropic etching apparatus according to one embodiment of the present invention. FIG. 4 is a diagram showing an example of the temporal change data of the hydrogen gas concentration in the Si anisotropic etching apparatus according to one embodiment of the present invention. FIG. 5 is a diagram showing an example of temporal change data of the Si concentration in the liquid in the Si anisotropic etching apparatus according to one embodiment of the present invention. FIGS. 6A and 6B show how the hydrogen concentration value exceeding the set value for emergency shutdown is detected by two hydrogen concentration meters in the Si anisotropic etching apparatus according to one embodiment of the present invention. FIG. FIG. 7 is a schematic view showing a conventional Si anisotropic etching apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Chemical solution for Si anisotropic etching 2 Si wafer 3 Cassette 4 Chemical solution tank 5 Heater 6 Exhaust piping 7 Etching draft 8 Hydrogen concentration meter 9 Hydrogen (bubble)
DESCRIPTION OF SYMBOLS 10 Computer for calculation 11 Chemical solution piping 12 Circulation pump 13 Chemical solution filter 14 HEPA filter 15 Air flow meter 20 Etching device

Claims (9)

A processing chamber to which exhaust piping is connected;
A chemical bath for placing a chemical solution for anisotropic etching of the silicon wafer and the silicon wafer, which is disposed inside the processing chamber;
A heater disposed inside the processing chamber, for heating the chemical solution;
An anisotropic silicon etching apparatus comprising: at least one hydrogen concentration meter installed in at least one of the processing chamber and the exhaust pipe. The anisotropic silicon etching apparatus according to claim 1,
The silicon anisotropic etching apparatus, wherein the hydrogen concentration meter is installed at a position above the chemical tank. In the silicon anisotropic etching apparatus according to claim 1 or 2,
The silicon anisotropic etching apparatus, wherein the chemical solution is alkaline. A silicon anisotropic etching method using the silicon anisotropic etching apparatus according to claim 1,
An anisotropic silicon etching method, wherein etching is performed on the silicon wafer while monitoring a hydrogen concentration value measured by the hydrogen concentration meter. The silicon anisotropic etching method according to claim 4,
Silicon anisotropy characterized by calculating a silicon concentration in the chemical solution based on a hydrogen concentration value measured by the hydrogen concentration meter, and performing state management and exchange of the chemical solution based on the calculation result Etching method. A silicon anisotropic etching method according to claim 4 or 5,
An anisotropic silicon etching method comprising: detecting an etching end point of the silicon wafer by determining whether or not a silicon etching reaction occurs based on a hydrogen concentration value measured by the hydrogen concentration meter. . A silicon anisotropic etching method according to any one of claims 4 to 6,
An anisotropic silicon etching method, wherein etching is performed on the silicon wafer while confirming that a hydrogen concentration value measured by the hydrogen concentration meter is smaller than a predetermined value. In the silicon anisotropic etching method according to claim 7,
A silicon anisotropic etching method, wherein a predetermined safety measure is taken when a hydrogen concentration value measured by the hydrogen concentration meter exceeds the predetermined value. In the silicon anisotropic etching method according to claim 7 or 8,
A silicon anisotropic etching method characterized in that it is confirmed whether or not a measured hydrogen concentration value is smaller than the predetermined value by an AND process using at least two hydrogen concentration meters.

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