JP2009094455A - Substrate processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a substrate processing apparatus maintaining the etching characteristics of a phosphoric acid solution for a long period of time. <P>SOLUTION: An additive containing a hexafluorosilicic acid solution (H<SB>2</SB>SiF<SB>6</SB>+H<SB>2</SB>O) is sequentially charged into a phosphoric acid solution pooled in an immersion bath 10 from an additive input mechanism 30. Also, a trap agent containing a fluoroboric acid solution (HBF<SB>4</SB>+H<SB>2</SB>O) is charged into the phosphoric acid solution from a trap agent input mechanism 40. F- which accelerates etching of a silicon nitride film is added as appropriate by sequentially charging the additive and siloxane which increases by the sequential input is etched with hydrofluoric acid generated by decomposition of the fluoroboric acid, to thereby suppress a significant increase in the concentration of siloxane. This makes it possible to maintain respective initial etching rates of the silicon nitride film and a silicon oxide film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  In the present invention, a semiconductor wafer on which a silicon oxide film and a silicon nitride film are formed, a glass substrate for a liquid crystal display device, a glass substrate for a photomask, a substrate for an optical disk, etc. (hereinafter simply referred to as “substrate”) in a phosphoric acid aqueous solution. The present invention relates to a substrate processing apparatus for selectively etching a silicon nitride film by being immersed in the substrate.

In the manufacturing process of a semiconductor device, an etching process is an important process for pattern formation. In particular, with the recent high performance and high integration of a semiconductor device, a silicon nitride film (Si ₃ film) formed on a substrate. A process of selectively etching away the silicon nitride film while leaving the silicon oxide film out of the (N ₄ film) and the silicon oxide film (SiO ₂ film) is required. As a technique for performing such a selective etching process of a silicon nitride film, a process using a high temperature (150 ° C. to 160 ° C.) phosphoric acid aqueous solution (H ₃ PO ₄ + H ₂ O) as an etching solution is known. (For example, refer to Patent Document 1). Specifically, as disclosed in Patent Document 1, a plurality of substrates on which a silicon nitride film and a silicon oxide film are formed are immersed in a treatment tank in which a high-temperature phosphoric acid aqueous solution is stored. A selective etching process is performed. However, due to the characteristics of the phosphoric acid aqueous solution, the silicon oxide film is also etched although the amount is small.

  Usually, siloxane is produced when a silicon nitride film is etched using an aqueous phosphoric acid solution. “Siloxane” is a general term for a group of organic or inorganic compounds mainly composed of silicon (Si) and oxygen (O). Siloxane produced during the etching process accumulates in the etching solution as foreign matter. If the siloxane concentration in the etching solution is too low, the etching rate of the silicon oxide film is increased and the etching selectivity with respect to the silicon nitride film is lowered. Conversely, even if the siloxane concentration is too high, there arises a problem that it adheres to the treatment tank or clogs the filter. For this reason, when performing an etching process using a phosphoric acid aqueous solution, it is important to adjust the siloxane concentration in the etching solution within an appropriate range according to the processing purpose.

JP 2003-224106 A

  Immediately after introducing a new phosphoric acid aqueous solution into the treatment tank at the time of liquid exchange etc., the siloxane concentration in the etching solution is naturally low, so in the treatment target with silicon nitride film formed so as to make this within the appropriate range from the past A method (seasoning) for increasing the siloxane concentration by performing an etching process on a non-substrate is performed.

  However, this method has a problem that the downtime of the apparatus becomes too long. For this reason, a method of introducing an additive containing siloxane in the phosphoric acid aqueous solution in advance can be considered, but there is a problem that the etching characteristics of the phosphoric acid aqueous solution cannot be maintained constant due to decomposition or alteration of the additive.

  The present invention has been made in view of the above problems, and an object thereof is to provide a substrate processing apparatus capable of maintaining the etching characteristics of a phosphoric acid aqueous solution constant for a long time.

  In order to solve the above-mentioned problems, a first aspect of the present invention provides a substrate processing apparatus for performing a silicon nitride film etching process by immersing a substrate on which a silicon oxide film and a silicon nitride film are formed in a phosphoric acid aqueous solution. An immersion treatment tank for storing an aqueous solution and immersing the substrate in a phosphoric acid aqueous solution to advance the etching process of the silicon nitride film; and an additive containing hexafluorosilicic acid in the phosphoric acid aqueous solution of the immersion treatment tank And an additive feeding means for feeding a trapping agent containing borofluoric acid into the phosphoric acid aqueous solution in the immersion treatment tank.

  The invention according to claim 2 is the substrate processing apparatus according to claim 1, further comprising charging control means for controlling the additive charging means so as to sequentially add the additive at regular intervals. And

  According to a third aspect of the present invention, there is provided the substrate processing apparatus according to the second aspect of the present invention, wherein the input control unit performs the trap every time a lot consisting of a predetermined number of substrates is etched in the immersion processing tank. The trapping agent feeding means is controlled so as to feed the agent.

  Further, the invention of claim 4 is the substrate processing apparatus according to the invention of claim 2, further comprising a densitometer that measures the concentration of siloxane contained in the phosphoric acid aqueous solution in the immersion treatment tank, The trapping agent feeding means is controlled to feed the trapping agent when the concentration of siloxane measured by the densitometer is equal to or higher than a predetermined threshold value.

  According to a fifth aspect of the present invention, in the substrate processing apparatus according to the fourth aspect of the present invention, the threshold value is set to 80 ppm or more and 120 ppm or less.

According to the present invention, F ⁻ is generated by adding an additive containing hexafluorosilicic acid into an aqueous phosphoric acid solution in an immersion treatment tank, and a siloxane concentration is adjusted by adding a trapping agent containing borohydrofluoric acid. Since the significant increase is suppressed, the etching rate can be maintained for both the silicon nitride film and the silicon oxide film, and the etching characteristics of the phosphoric acid aqueous solution can be maintained constant for a long time.

In particular, according to the second aspect of the present invention, since the additives are sequentially added at regular intervals, F ⁻ can be appropriately supplemented, and the etching rate of the silicon nitride film can be stabilized for a long time.

  In particular, according to the invention of claim 3, since a trapping agent is introduced every time a lot is etched, the siloxane concentration is suppressed from being significantly increased by the etching process, and the etching rate of the silicon oxide film is stabilized for a long time. Can be made.

  In particular, according to the invention of claim 4, since the trapping agent is introduced when the concentration of siloxane contained in the phosphoric acid aqueous solution in the immersion treatment tank is equal to or higher than a predetermined threshold, the siloxane concentration is significantly increased by the etching treatment. And the etching rate of the silicon oxide film can be stabilized for a long time.

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

<1. First Embodiment>
FIG. 1 is a diagram showing an overall schematic configuration of a substrate processing apparatus according to the present invention. The substrate processing apparatus 1 is a wet etching processing apparatus that selectively etches a silicon nitride film by immersing a substrate W on which a silicon oxide film and a silicon nitride film are formed in a phosphoric acid aqueous solution. The substrate processing apparatus 1 includes an immersion treatment tank 10 that stores an aqueous phosphoric acid solution and advances an etching process, a circulation line 20 that circulates the aqueous phosphoric acid solution to the immersion treatment tank 10, and the aqueous phosphoric acid solution in the immersion treatment tank 10. An additive feeding mechanism 30 for feeding the additive and a trapping agent feeding mechanism 40 for feeding the trapping agent into the phosphoric acid aqueous solution in the immersion treatment tank 10 are provided.

  The immersion treatment tank 10 includes an inner tank 11 that stores an aqueous phosphoric acid solution as an etchant, and an outer tank 12 that recovers the overflowed etchant from the upper portion of the inner tank 11. It has a double tank structure. The inner tank 11 is a box-shaped member having a rectangular shape in plan view formed of quartz or a fluororesin material having excellent corrosion resistance against the etching solution. The outer tub 12 is formed of the same material as the inner tub 11 and is provided so as to surround the upper end of the outer periphery of the inner tub 11.

  Further, a lifter 13 for immersing the substrate W in the etching solution stored in the immersion treatment tank 10 is provided. The lifter 13 collectively holds a plurality of (for example, 50) substrates W arranged in parallel with each other in a standing posture (a posture in which the normal line of the substrate main surface is along the horizontal direction) by three holding rods. . The lifter 13 is provided so that it can be moved up and down along the vertical direction by a lifting mechanism (not shown), and a processing position for immersing a plurality of substrates W (lots) to be held in the etching solution in the inner tank 11 (FIG. 1) and the delivery position lifted from the etching solution.

  The circulation line 20 is a piping path for filtering and heating the phosphoric acid aqueous solution discharged from the immersion treatment tank 10 and feeding it back to the immersion treatment tank 10. Specifically, the circulation line 20 is the bottom of the outer tank 12 of the immersion treatment tank 10. And the bottom of the inner tank 11 are connected to each other through a flow path. In the middle of the path of the circulation line 20, a circulation pump 21 and a filter 22 are provided from the upstream side. The circulation pump 21 pumps the aqueous phosphoric acid solution pumped from the outer tank 12 through the circulation line 20 to the inner tank 11. The filter 22 is a filtration filter for removing foreign substances in the phosphoric acid aqueous solution flowing through the circulation line 20.

  The circulation line 20 is provided with a heater 23 downstream of the filter 22. The heater 23 is provided at a position relatively close to the inner tank 11 in the circulation line 20, and reheats the phosphoric acid aqueous solution flowing through the circulation line 20 to a predetermined processing temperature (150 ° C. in this embodiment). . The immersion treatment tank 10 is also provided with a heater (not shown), and the aqueous phosphoric acid solution stored in the immersion treatment tank 10 is also heated to maintain a predetermined treatment temperature.

  Further, in the path of the circulation line 20, a densitometer 24 is inserted upstream of the circulation pump 21 (side closer to the outer tub 12). The densitometer 24 is a type of densitometer that measures the siloxane concentration in the liquid by measuring the absorbance at a specific wavelength, and the concentration of siloxane contained in the phosphoric acid aqueous solution discharged from the outer tank 12 of the immersion treatment tank 10. Measure the concentration.

The additive charging mechanism 30 includes a weighing tank 31 and a charging valve 32 that weigh and store a predetermined amount of additive. The weighing tank 31 is provided with a hexafluorosilicic acid aqueous solution (H ₂ SiF ₆ + H ₂ O) supplied from a hexafluorosilicic acid aqueous solution and a phosphoric acid aqueous solution supplied from a supply source, respectively. Weigh only a fixed amount and store inside. In the weighing tank 31, the hexafluorosilicic acid aqueous solution and the phosphoric acid aqueous solution are mixed to prepare the additive. When the charging valve 32 is opened, a predetermined amount of additive stored in the weighing tank 31 is charged into the outer tank 12 of the immersion treatment tank 10.

The trap agent charging mechanism 40 includes a weighing tank 41 and a charging valve 42 for weighing and storing a predetermined amount of trap agent. The weighing tank 41 has a predetermined amount of each of a borohydrofluoric acid aqueous solution supplied from a borohydrofluoric acid aqueous solution (HBF ₄ + H ₂ O) supply source and a phosphoric acid aqueous solution supplied from a phosphoric acid aqueous solution supply source. Weigh only and store inside. Inside the weighing tank 41, a borohydrofluoric acid aqueous solution and a phosphoric acid aqueous solution are mixed to prepare a trapping agent. When the charging valve 42 is opened, a predetermined amount of trapping agent stored in the weighing tank 41 is charged into the outer tank 12 of the immersion treatment tank 10.

  It should be noted that the additive and trapping agent are charged into the outer tank 12 of the immersion treatment tank 10 from the additive charging mechanism 30 and the trapping agent charging mechanism 40 rather than directly into the inner tank 11. This is because the change and distribution of the concentration of the additive / trapping agent in the inner tank 11 is more stable when it is supplied to the inner tank 11 after passing through the circulation line 20 once.

  Further, the substrate processing apparatus 1 is provided with a supply valve 50 for supplying a phosphoric acid aqueous solution directly to the immersion treatment tank 10. By opening the supply valve 50, the phosphoric acid aqueous solution can be directly supplied from the phosphoric acid aqueous solution supply source to the inner tank 11 of the immersion treatment tank 10. This supply valve 50 is used when supplying a new phosphoric acid aqueous solution to the immersion treatment tank 10 at the time of liquid replacement.

  The substrate processing apparatus 1 is provided with a control unit 60 that manages the entire apparatus. The configuration of the control unit 60 as hardware is the same as that of a general computer. That is, the control unit 60 stores a CPU that performs various arithmetic processes, a ROM that is a read-only memory that stores basic programs, a RAM that is a readable and writable memory that stores various information, and control applications and data. It is equipped with a magnetic disk. When the CPU of the control unit 60 executes predetermined software, the control unit 60 controls the opening and closing of the closing valves 32 and 42. It should be noted that other operation parts of the substrate processing apparatus 1 such as the supply valve 50, the circulation pump 21, the heater 23, and the lift mechanism of the lifter 13 are also controlled by the control unit 60.

  In addition to the above configuration, the substrate processing apparatus 1 includes a temperature sensor that measures the temperature of the phosphoric acid aqueous solution in the immersion treatment tank 10, a regeneration mechanism that discharges and regenerates the used phosphoric acid aqueous solution from the circulation line 20, and the like. Are also not shown).

  Next, the operation content in the substrate processing apparatus 1 having the above configuration will be described. First, regardless of whether or not the substrate W is immersed in the phosphoric acid aqueous solution stored in the immersion treatment tank 10, the circulation pump 21 constantly pumps the phosphoric acid aqueous solution at a constant flow rate. The aqueous phosphoric acid solution refluxed to the immersion treatment tank 10 by the circulation line 20 is supplied from the bottom of the inner tank 11. As a result, an upflow of the phosphoric acid aqueous solution is generated in the inner tank 11 from the bottom upward. The phosphoric acid aqueous solution supplied from the bottom overflows from the upper end of the inner tank 11 and flows into the outer tank 12. The circulation process in which the phosphoric acid aqueous solution that has flowed into the outer tank 12 is collected by the circulation pump 21 via the circulation line 20 and is fed back to the immersion treatment tank 10 again is continued. In the process of refluxing by the circulation line 20, foreign matters mixed in the phosphoric acid aqueous solution are removed by the filter 22. The refluxed phosphoric acid aqueous solution is reheated to a predetermined processing temperature by the heater 23.

  While performing the circulation process of the phosphoric acid aqueous solution by the circulation line 20, the lifter 13 that received a lot consisting of a plurality of substrates W at the delivery position was lowered to the processing position and stored in the inner tank 11. The substrate W is immersed in the phosphoric acid aqueous solution. Thereby, a selective etching process of the silicon nitride film of the silicon oxide film and the silicon nitride film formed on the substrate W proceeds, and the silicon nitride film is gradually removed. After the etching process for a predetermined time is completed, the lifter 13 rises again to the delivery position and pulls up the substrate W from the etching solution. Then, a new lot is again immersed in the phosphoric acid aqueous solution in the inner tank 11 by the lifter 13, and the etching process is repeated.

  By the way, when a silicon nitride film is etched using a phosphoric acid aqueous solution, siloxane is produced. However, the siloxane concentration in the phosphoric acid aqueous solution has an appropriate range depending on the purpose of the treatment, and the siloxane As described above, if the concentration is too low, the etching rate of the silicon oxide film increases and the etching selectivity of the silicon nitride film decreases. On the other hand, in the substrate processing apparatus 1, replacement of the used phosphoric acid aqueous solution with the fresh phosphoric acid aqueous solution is periodically performed, and the siloxane concentration in the phosphoric acid aqueous solution newly supplied to the immersion treatment tank 10 is It is almost 0%.

  For this reason, when a new phosphoric acid aqueous solution is supplied to the immersion treatment tank 10, the etching process of the substrate W to be processed cannot be started immediately, and the additive charging mechanism 30 is added to the new phosphoric acid aqueous solution. The agent is initially charged. The additive added by the additive charging mechanism 30 is a mixed solution of an aqueous hexafluorosilicic acid solution and an aqueous phosphoric acid solution. By adding an additive containing a hexafluorosilicic acid aqueous solution, the following reaction of Formula 1 proceeds in the immersion treatment tank 10.

The generated SiO ₂ is also a kind of siloxane, which increases the initial siloxane concentration. Further, the generated hydrofluoric acid (HF) is decomposed as in the following formula 2.

It has been found that HF ₂ ⁻ decomposed as shown in Equation ₂ increases the etching rate of the silicon oxide film, while F ⁻ increases the etching rate of the silicon nitride film. In this embodiment, the phosphoric acid aqueous solution in the immersion treatment tank 10 is heated to 150 ° C., and in this temperature range, a very large amount of F ⁻ is generated in the decomposition reaction of Formula 2.

  Accordingly, by introducing an additive containing a hexafluorosilicic acid aqueous solution into the phosphoric acid aqueous solution newly supplied to the immersion treatment tank 10, the initial siloxane concentration is increased and the etching rate of the silicon nitride film is increased. Can do. The etching selectivity of the silicon nitride film can be increased by etching the substrate W with an aqueous phosphoric acid solution containing an additive containing such an aqueous hexafluorosilicate solution.

FIG. 2 is a diagram showing changes in the etching rates of the silicon oxide film and the silicon nitride film when etching is performed with a phosphoric acid aqueous solution to which an additive containing a hexafluorosilicic acid aqueous solution is initially added. As shown in the figure, the etching rates of both the silicon oxide film and the silicon nitride film decrease with time. This is because F ⁻ volatilizes and decreases with time, the etching rate of the silicon nitride film decreases, the siloxane concentration in the phosphoric acid aqueous solution increases, and the etching rate of the silicon oxide film also decreases. Is. That is, only by initially adding an additive containing an aqueous hexafluorosilicate solution, good etching characteristics can be obtained initially, but the etching characteristics cannot be maintained for a long time.

For this reason, the control part 60 is controlling the additive injection | throwing-in mechanism 30 so that the additive containing hexafluorosilicic acid aqueous solution may be injected | thrown-in sequentially at fixed intervals. FIG. 3 is a diagram showing changes in the etching rates of the silicon oxide film and the silicon nitride film when etching is performed with a phosphoric acid aqueous solution in which additives are sequentially added. By sequentially adding the additives, F ⁻ is appropriately supplemented in the phosphoric acid aqueous solution in the immersion treatment tank 10, and the initial state of the etching rate of the silicon nitride film can be maintained. However, as the additive is sequentially added, siloxane produced by the reaction shown in Formula 1 is excessively accumulated in the phosphoric acid aqueous solution, and the etching rate of the silicon oxide film rapidly decreases. Then, as shown in FIG. 3, after a predetermined time has elapsed, the excessively accumulated siloxane precipitates on the silicon oxide film and shifts to the Depo mode (etching rate is negative) where the film thickness increases.

  That is, when an additive containing an aqueous hexafluorosilicate solution is sequentially added, the initial good etching rate can be maintained for the etching rate of the silicon nitride film, but the etching rate of the silicon oxide film rapidly decreases. After that, it will turn negative. Therefore, even in this case, the original etching characteristics cannot be maintained.

  Therefore, in the first embodiment, the additive agent mechanism 30 sequentially adds the additive containing the hexafluorosilicic acid aqueous solution at regular intervals, and the trap agent every time the lot consisting of a predetermined number of substrates W is etched. The input mechanism 40 is supplying the trap agent. The trapping agent introduced by the trapping agent introduction mechanism 40 is a mixed solution of a borohydrofluoric acid aqueous solution and a phosphoric acid aqueous solution. The trapping agent containing the borohydrofluoric acid aqueous solution is decomposed in the phosphoric acid aqueous solution in the immersion treatment tank 10 as shown in the following equation (3).

Here, hydrofluoric acid (HF) generated by decomposition of borohydrofluoric acid etches SiO ₂ . For this reason, it is prevented that the siloxane produced by the reaction of Formula 1 is excessively accumulated in the phosphoric acid aqueous solution.

FIG. 4 is a diagram showing changes in the etching rates of the silicon oxide film and the silicon nitride film when etching is performed with a phosphoric acid aqueous solution in which a trapping agent containing a borofluoric acid aqueous solution is added in addition to the sequential addition of additives. It is. As described above, by sequentially adding the additive containing the hexafluorosilicate aqueous solution, the phosphoric acid aqueous solution in the immersion treatment tank 10 is appropriately supplemented with F ^−, and the silicon nitride film in the initial state is etched. The rate can be maintained. In addition, siloxane produced by the sequential addition of additives is etched by hydrofluoric acid generated by decomposition of borofluoric acid contained in the trapping agent. That is, the trapping agent containing the borohydrofluoric acid aqueous solution traps the siloxane produced by the sequential addition of the additive. As a result, an increase in the siloxane concentration in the phosphoric acid aqueous solution is suppressed, and the initial state of the etching rate of the silicon oxide film can be maintained. As a result, as shown in FIG. 4, the initial favorable rate can be maintained for the etching rates of both the silicon nitride film and the silicon oxide film.

  As described above, in the first embodiment, the additive feeding mechanism 30 sequentially feeds the additive containing the hexafluorosilicic acid aqueous solution at regular intervals, and each time a lot of the substrate W is etched. The trap agent charging mechanism 40 is supplying the trap agent. Specifically, the control unit 60 controls the additive charging mechanism 30 and the trapping agent charging mechanism 40 in accordance with preset timings for adding the additive and trapping agent, and throws the additive and trapping agent into the immersion treatment tank 10. Like to do.

FIG. 5 is a timing chart showing an example of the timing of adding the additive and trapping agent. As shown in the figure, after completion of the liquid exchange and temperature control of the phosphoric acid aqueous solution in the immersion treatment tank 10, the initial addition of the additive containing the hexafluorosilicic acid aqueous solution is performed. As a result, the initial siloxane concentration is increased, and the etching rate of the silicon nitride film can be increased by generating a very large amount of F ⁻ . Further, immediately before performing the etching process for a lot consisting of a predetermined number of substrates W, the trap agent injection mechanism 40 inputs a trap agent containing a borohydrofluoric acid aqueous solution. Then, the substrate W of the first lot is immersed in the phosphoric acid aqueous solution in which the additive and the trapping agent are charged, and an etching process is performed.

Thereafter, regardless of whether or not lots are processed, the controller 60 controls the additive charging mechanism 30 to sequentially add the additives at regular intervals. Further, the control unit 60 controls the trapping agent feeding mechanism 40 to feed the trapping agent immediately before performing the etching process for a lot consisting of a predetermined number of substrates W in the immersion treatment tank 10. By doing so, the phosphoric acid aqueous solution in the immersion treatment tank 10 is appropriately supplemented with F ^−, while the siloxane produced by the sequential addition of the additive is etched by the trapping agent, and the phosphoric acid aqueous solution A significant increase in the siloxane concentration in the is also suppressed. As a result, the initial good etching rate as shown in FIG. 4 can be maintained for both the silicon nitride film and the silicon oxide film.

<2. Second Embodiment>
Next, a second embodiment of the present invention will be described. The configuration of the substrate processing apparatus of the second embodiment is exactly the same as that of the substrate processing apparatus 1 of the first embodiment. The second embodiment differs from the first embodiment in the timing at which the trap agent is introduced. In the first embodiment, a trapping agent is introduced every time a lot consisting of a predetermined number of substrates W is etched. In the second embodiment, trapping is performed based on the siloxane concentration measured by the densitometer 24. An agent is added.

Also in the second embodiment, in order to increase the etching selectivity of the silicon nitride film, the control unit 60 sets the additive charging mechanism 30 so that the additive containing the hexafluorosilicic acid aqueous solution is initially charged and sequentially added at regular intervals. I have control. By sequentially adding the additives, F ⁻ is appropriately supplemented in the phosphoric acid aqueous solution in the immersion treatment tank 10, and although the initial state can be maintained with respect to the etching rate of the silicon nitride film, As described above, the etching rate of the silicon oxide film rapidly decreases due to excessive accumulation in the phosphoric acid aqueous solution. After a predetermined time, excessively accumulated siloxane is deposited on the silicon oxide film and the film thickness increases.

  Therefore, in the second embodiment, the additive charging mechanism 30 sequentially adds the additive containing the hexafluorosilicic acid aqueous solution at regular intervals, and the siloxane concentration of the phosphoric acid aqueous solution measured by the densitometer 24 is a predetermined threshold value. At this time, the trapping agent feeding mechanism 40 is feeding the trapping agent. Specifically, while executing the circulation process of the phosphoric acid aqueous solution by the circulation line 20, the siloxane concentration in the phosphoric acid aqueous solution in the immersion treatment tank 10 is constantly monitored by the densitometer 24, and the measurement result is It is transmitted to the control unit 60. A density threshold value is stored in advance in the memory of the control unit 60. Then, the controller 60 controls the trap agent introduction mechanism 40 so that the trap agent is introduced when the siloxane concentration measured by the densitometer 24 is equal to or higher than the threshold value.

  Similar to the first embodiment, the trapping agent introduced by the trapping agent introduction mechanism 40 is a mixed solution of a borohydrofluoric acid aqueous solution and a phosphoric acid aqueous solution. The reaction that occurs when the trap agent is introduced into the phosphoric acid aqueous solution in the immersion treatment tank 10 is also the same as in the first embodiment. That is, siloxane produced by the sequential addition of additives is etched by hydrofluoric acid produced by decomposition of borofluoric acid contained in the trapping agent.

  By sequentially adding an additive containing an aqueous hexafluorosilicate solution, the etching rate of the silicon nitride film in the initial state can be maintained, and siloxane generated by sequentially adding the additive is trapped by the trapping agent, An increase in the siloxane concentration in the phosphoric acid aqueous solution is suppressed, and the initial state of the etching rate of the silicon oxide film can be maintained. As a result, as in the first embodiment, the initial favorable rate can be maintained for the etching rates of both the silicon nitride film and the silicon oxide film.

  By the way, the threshold value is set to an arbitrary concentration value within the range of 80 ppm to 120 ppm. FIG. 6 is a diagram showing the saturation concentration of siloxane in a phosphoric acid aqueous solution. In the figure, the horizontal axis indicates the temperature of the phosphoric acid aqueous solution, and the vertical axis indicates the concentration of siloxane. The higher the temperature of the aqueous phosphoric acid solution, the higher the saturation concentration of siloxane. The selective etching process of the silicon nitride film using the phosphoric acid aqueous solution is performed at a high processing temperature of 150 ° C. to 160 ° C. In this temperature region, as shown in FIG. 6, the concentration range of 80 ppm or more and 120 ppm or less is a relatively high concentration region close to the concentration (saturation concentration) at which siloxane is precipitated. If the threshold value is a concentration value greater than 120 ppm, the trapping agent is introduced after the siloxane is deposited on the silicon oxide film and the film thickness is increased, and the etching rate of the silicon oxide film cannot be kept constant. On the other hand, if the threshold value is less than 80 ppm, the siloxane concentration after adding the trapping agent becomes too low and the etching rate of the silicon oxide film increases, and this cannot be kept constant. For this reason, the threshold value is set to a concentration value within the range of 80 ppm to 120 ppm.

<3. Modification>
While the embodiments of the present invention have been described above, the present invention can be modified in various ways other than those described above without departing from the spirit of the present invention. For example, the addition timing of the additive and the trapping agent is not limited to the examples of the first and second embodiments, and can be changed as appropriate according to the content of the etching process and the required etching rate. .

In addition, the composition of the additive and trapping agent and the amount charged per time can be appropriately set according to the content of the etching process and the required etching rate. That is, an additive containing a hexafluorosilicic acid aqueous solution is sequentially added to a phosphoric acid aqueous solution to appropriately supplement F ⁻ which promotes etching of the silicon nitride film, and a trapping agent containing a borohydrofluoric acid aqueous solution is added. In the form of etching the increasing siloxane, the composition of additive and trapping agent, input amount, input timing, etc. can be appropriately set.

  The amount and timing of trapping agent should be optimized according to the total etching amount of the silicon nitride film on the substrate W, but the total etching amount of the silicon nitride film of the substrate W being processed is calculated. Is extremely difficult. Therefore, a trap agent is introduced every time a lot is etched as in the first embodiment, or a trap agent is introduced when the siloxane concentration of the phosphoric acid aqueous solution is equal to or higher than a predetermined threshold as in the second embodiment. By doing so, it is possible to determine the timing of trap agent introduction relatively easily.

  In the above embodiment, a predetermined amount of additive and trapping agent are weighed and introduced using the weighing tanks 31 and 41. However, a predetermined amount of additive and trapping agent should be accurately introduced. However, other devices such as a mass flow controller may be used.

Further, in the above embodiments, the additive was a mixed solution of hexafluorosilicic acid aqueous solution and phosphoric acid solution, further may be added nitric acid (HNO ₃₎ thereto.

  Moreover, in the said embodiment, the outer tank 12 is not essential, It is the form which connected the piping both ends of the circulation line 20 to the inner tank 11, and circulates the phosphoric acid aqueous solution in the inner tank 11 by the circulation line 20. May be. Further, the lifter 13 is not limited to directly holding the plurality of substrates W, and the lifter 13 may move up and down while holding a carrier containing the plurality of substrates W.

It is a figure which shows the whole schematic structure of the substrate processing apparatus which concerns on this invention. It is a figure which shows the change of the etching rate of a silicon oxide film and a silicon nitride film when performing an etching process with the phosphoric acid aqueous solution which performed the initial addition of the additive containing hexafluorosilicic acid aqueous solution. It is a figure which shows the change of the etching rate of a silicon oxide film and a silicon nitride film when an etching process is performed with the phosphoric acid aqueous solution which added the additive sequentially. It is a figure which shows the change of the etching rate of a silicon oxide film and a silicon nitride film when performing an etching process with the phosphoric acid aqueous solution which supplied the trap agent containing the borohydrofluoric acid aqueous solution in addition to the addition of the additive sequentially. It is a timing chart which shows an example of the injection | throwing-in timing of an additive and a trap agent. It is a figure which shows the saturation density | concentration of the siloxane in phosphoric acid aqueous solution.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate processing apparatus 10 Immersion processing tank 11 Inner tank 12 Outer tank 20 Circulation line 21 Circulation pump 22 Filter 30 Additive introduction mechanism 40 Trap agent introduction mechanism 60 Control part W substrate

Claims (5)

A substrate processing apparatus for performing an etching process on a silicon nitride film by immersing a substrate on which a silicon oxide film and a silicon nitride film are formed in a phosphoric acid aqueous solution,
An immersion treatment tank for storing a phosphoric acid aqueous solution and immersing the substrate in the phosphoric acid aqueous solution to advance the etching treatment of the silicon nitride film;
An additive charging means for charging an additive containing hexafluorosilicic acid into the phosphoric acid aqueous solution in the immersion treatment tank;
Trapping agent charging means for charging a trapping agent containing borohydrofluoric acid into the phosphoric acid aqueous solution in the immersion treatment tank;
A substrate processing apparatus comprising: The substrate processing apparatus according to claim 1,
A substrate processing apparatus, further comprising: a charging control unit that controls the additive charging unit so as to sequentially add the additive at regular intervals. The substrate processing apparatus according to claim 2,
The substrate control method, wherein the input control unit controls the trap agent input unit so as to input the trap agent every time an etching process of a lot consisting of a predetermined number of substrates is performed in the immersion processing tank. apparatus. The substrate processing apparatus according to claim 2,
Further comprising a densitometer for measuring the concentration of siloxane contained in the phosphoric acid aqueous solution of the immersion treatment tank,
The substrate processing apparatus, wherein the input control unit controls the trap agent input unit to input the trap agent when the concentration of siloxane measured by the densitometer is equal to or higher than a predetermined threshold. The substrate processing apparatus according to claim 4, wherein
The substrate processing apparatus, wherein the threshold is set to 80 ppm or more and 120 ppm or less.

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