JP2014072505A - Wet etching device and manufacturing method for semiconductor device - Google Patents

Abstract

Conventionally, when an Si concentration in an etching solution reaches a predetermined concentration, the etching solution in the processing tank is discharged by a discharging unit, while the wet etching of a semiconductor wafer is performed by phosphoric acid that is replenished with a new etching solution by a supplying unit. Although an etching method and a wet etching apparatus are known, there is a problem that the concentration controllability of the etching solution is poor and a stable etching process cannot be performed.
SOLUTION: When the etching process exceeds the set integration (number of processed sheets x processing time), the liquid is drained, draining continues even after the small liquid replacement drain sensor is turned on, and the valve is turned off after a predetermined time. The present invention provides a wet etching apparatus for exchanging a small amount of liquid to stop drainage and a method for manufacturing a semiconductor device for performing wet etching of a semiconductor wafer with the wet etching apparatus.
[Selection] Figure 1

Description

  The present invention relates to an etching apparatus and a method for manufacturing a semiconductor device using the same, and more particularly to a wet etching apparatus and a technique effective when applied to a method for manufacturing a semiconductor device using the same.

  As a semiconductor wafer etching method and etching apparatus, for example, as described in JP-A-2001-23952, when the Si concentration in the etching solution reaches a predetermined concentration, the etching solution in the processing tank is discharged by the discharging means. On the other hand, a semiconductor wafer etching method and an etching apparatus using phosphoric acid in which a new etching solution is replenished by a supply means are known.

JP 2001-23952 A

The above-described conventional etching method has poor concentration controllability and cannot perform stable etching.
Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

  Of the means for solving the problems disclosed in the present application, the outline of typical ones will be briefly described as follows.

  According to one embodiment, if the etching process exceeds the set processing integration (number of processed sheets × processing time), the liquid is discharged, and the liquid is continuously discharged even after the small liquid replacement liquid discharge sensor is turned on. After that, a small amount of liquid is exchanged by turning off the valve and stopping the drainage.

  According to the one embodiment, the amount of increase and decrease of the siloxane concentration can be within an appropriate range, and the concentration controllability of the etching solution is improved.

1 is a schematic view showing an outline of a nitride film wet etching apparatus according to a first embodiment. FIG. 3 is a sequence chart of nitride film wet etching by the nitride film wet etching apparatus shown in FIG. 1. FIG. 3 is a diagram showing the relationship between the concentration of siloxane in liquid and the number of processed sheets × time in Embodiment 1. FIG. 10 is a sequence chart of nitride film wet etching based on the second embodiment. FIG. 10 is a schematic diagram showing an outline of a nitride film wet etching apparatus based on the third embodiment. It is the schematic which shows the outline | summary of the conventional nitride film wet etching apparatus. FIG. 7 is a sequence chart of nitride film wet etching by the nitride film wet etching apparatus of FIG. 6. It is a figure which shows the relationship between the siloxane concentration in a liquid and the number of processed sheets x time in the nitride film wet etching apparatus of FIG. It is sectional drawing of the semiconductor element for demonstrating the conventional problem. It is sectional drawing of the semiconductor element (memory cell part) for demonstrating the conventional problem.

1. First, problems newly found out by the inventor of the present application prior to the present application will be described below.
FIG. 6 shows a wet etching apparatus studied by the present inventors. In the figure, in the etching process, the chemical solution is circulated from the outer tank 2 through the processing liquid circulation line 3 into the processing tank 1, overflowing from the processing tank 1, and returning to the outer tank 2 again.

  In such wet etching, the concentration of siloxane in phosphoric acid, which is an etching solution, increases every time the etching process is repeated. The siloxane concentration is proportional to the product of the number of processed sheets and the processing time. When the siloxane concentration increases, the etching rate decreases, so the siloxane concentration must be controlled within a certain range. For this reason, in wet etching, a small amount of liquid is exchanged such that a part of the chemical is drained at a certain interval and a new liquid is supplied.

  This will be described with reference to FIG. After exceeding the set processing integration (number of processed sheets × processing time), the chemical solution in the outer tub 2 is drained from the drain 6 through the processing solution circulation line 3. At this time, the liquid level of the chemical solution in the outer tub 2 is small. Phosphoric acid is drained until the liquid exchange critical liquid level 14 is reached (the small-volume liquid exchange drainage sensor 11 is OFF). At this time, there is no circulation of the chemical liquid to the treatment tank 1. After the drainage is stopped, new phosphoric acid is supplied from the chemical tank 9 to the outer tank 2 up to the quantitative critical liquid level 15. Thereafter, the circulation of the chemical solution starts, and the next product is batch processed.

  FIG. 7 shows a sequence chart of the wet etching described above. As shown in the figure, (1) During the product etching process, the quantitative sensor 12 is ON, the small amount liquid replacement drain sensor 11 is OFF, the drain 6 valve is OFF, and the chemical tank valve 13 is OFF. (2) The small amount liquid replacement drainage starts when the quantitative sensor 12 is OFF, the small amount liquid replacement drain sensor 11 is OFF, the drain 6 valve is ON, and the chemical tank valve 13 is OFF. Then, (3) the supply of the small amount of liquid begins when the small amount of liquid replacement drain sensor 11 is ON, the quantitative sensor 12 is OFF, the valve of the drain 6 is OFF, and the valve 13 of the chemical tank is ON. During the supply of the small amount liquid, the quantitative sensor 12 OFF, the small amount liquid replacement drain sensor 11 OFF, the drain 6 valve OFF, and the chemical tank valve 13 ON. And it becomes a sequence of liquid supply completion by quantitative sensor 12ON and chemical | medical solution tank valve 13OFF.

  That is, since the small amount of liquid is exchanged after the set processing integration (number of processed sheets × time), depending on the combination of the number of lots and the processing time, the processing integration between the small amount of liquids is changed from 3000 (sheet × min) to 7950 (sheet × Min). (Small liquid exchange frequency: 3000 sheets × min, number of processed sheets: 1 to 50 sheets / batch, processing time: 1 to 100 minutes) For this reason, the siloxane concentration that rises during the small liquid replacement also varies. On the other hand, since the amount of drainage and the amount of liquid supply are constant, the amount of decrease in siloxane concentration due to the small amount liquid exchange is constant. In other words, the siloxane concentration controllability deteriorates due to processing integration variation between small amount liquid exchanges.

  FIG. 8 is a diagram showing the relationship between the conventional siloxane concentration in liquid and the number of processed sheets × time. As shown in the figure, since a small amount of liquid is exchanged at points C, D, E, F, G, and H, the siloxane concentration is lowered. However, as described above, the processing integration varies depending on the combination of the number of processed sheets (number of lots) and the processing time. On the other hand, the amount of liquid discharged and the amount of liquid supplied are constant. Before exchange, the siloxane concentration is very high. An appropriate range of the siloxane concentration that does not cause a decrease in product yield is shown between AB in FIG. At point E, the siloxane concentration exceeds point A before a small amount of liquid exchange. When the siloxane concentration exceeds the point A, the siloxane is deposited on the product pattern, causing a problem of pattern defects, filter clogging, and piping clogging. Further, since the oxide film etching rate is lowered, for example, in the STI 26 of the semiconductor element shown in FIG. 9, the height of the STI 26 becomes higher than the target value, which affects the product characteristics.

  On the other hand, since the amount of drainage and the amount of liquid supply are constant due to variations in processing integration, the siloxane concentration is lower than point B after a small amount of liquid replacement at point H in FIG. It is very low. When the siloxane concentration falls below the point B, the oxide film etching rate increases. For example, in the STI 26 of the semiconductor element shown in FIG. 9, the STI 26 is etched more than necessary, and the height of the STI 26 becomes lower than the target value. Further, there arises a problem that the oxide film 24 is etched and the FG polysilicon layer 23 therebelow is etched. Further, in the semiconductor element (memory cell portion) as shown in FIG. 10, there arises a problem that the oxide film 38 is etched and the underlying impurity-doped polysilicon film 39 is etched. When these problems occur, the product characteristics are affected.

2. Details of Embodiments Hereinafter, embodiments will be described in detail with reference to the drawings.
In the following embodiment, when it is necessary for the sake of convenience, the description will be divided into a plurality of sections or embodiments. However, unless otherwise specified, they are not irrelevant to each other, and one is related to some or all of the other, such as modifications, application examples, detailed explanations, and supplementary explanations. In the following embodiments, when referring to the number of elements (including the number, numerical value, quantity, range, etc.), the number is not limited to the specific number, and may be greater than or equal to the specific number. . However, the case where it is clearly specified and the case where it is clearly limited to a specific number in principle is excluded.

Furthermore, in the following embodiments, the constituent elements (including element steps and the like) are not necessarily indispensable unless otherwise specified and apparently essential in principle. Similarly, in the following embodiments, references to shapes, positional relationships, and the like of components and the like include those that are substantially similar or similar to the shapes and the like. However, this excludes the case where it is clearly indicated and the case where it is not clearly apparent in principle. The same applies to the above numbers and the like (including the number, numerical value, quantity, range, etc.).
Note that components having the same function are denoted by the same or related reference symbols throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted in principle. In the following embodiments, the description of the same or similar parts will not be repeated in principle unless particularly necessary.

<Embodiment 1>
FIG. 1 is a schematic diagram showing an outline of a wet etching apparatus according to the first embodiment. As shown in the figure, a plurality of semiconductor wafers 16 as objects to be processed are stored and installed in a carrier 17 in a processing tank 1. The treatment tank 1 has an outer tank 2, and a chemical liquid tank 9 and a pure water tank 10 are connected to the outer tank 2 via a chemical liquid replenishment line 7 and a pure water replenishment line 8, respectively. Each of the chemical solution replenishment line 7 and the pure water replenishment line 8 has an air operated valve 13.
A processing liquid circulation line 3 is connected to the bottom of the outer tank 2 and the bottom of the processing tank 1 via a pump 4 and a filter unit 5. Further, the filter unit 5 has an air operated valve 52 and a drain 6. Furthermore, a small amount liquid exchange drainage sensor 11 and a quantitative sensor 12 for detecting the liquid level in the outer tub 2 are provided. Further, a control device 51 is provided between the small amount liquid exchange drainage sensor 11 and the air operated valve 52. Such a wet etching apparatus is mainly used for wet etching of a nitride film.

  In such a wet etching apparatus, (1) during the etching process of the semiconductor wafer, the chemical liquid flows from the outer tank 2 through the processing liquid circulation line 3 and flows into the processing tank 1, overflows, and returns to the outer tank 2 again. Perform circulation. (2) After the set processing integration (number of processed sheets × processing time) is exceeded, the chemical solution in the outer tank 2 passes through the processing liquid circulation line 3 and reaches the small liquid replacement critical liquid level 14 in the outer tank 2 from the drain 6. The liquid is drained and drained for the calculated time corresponding to the processing integration between the small liquid exchanges. In that case, after receiving a signal from the small liquid replacement / drainage sensor 11, the control device 51 opens the air operated valve 52 for a period of time calculated corresponding to the integration of the process between the small liquid replacements, and the drainage is continued. And do it. At this time, there is no circulation of the chemical solution to the treatment tank 1. Thereafter, (3) drainage is stopped, and new phosphoric acid is supplied from the chemical tank 9 to the outer tank 2 up to the quantitative critical liquid level 15. Thereafter, the circulation of the chemical solution described in (1) starts, and the next semiconductor wafer etching process is processed in batches (a plurality of semiconductor wafers in a lump). The small amount liquid exchange sequence of the present invention performs small amount liquid exchange after the set processing integration (number of processed sheets × processing time) is exceeded. Perform until “off time” + “calculated drainage time”. In other words, the liquid is drained longer by “calculated drain time” than before. This “calculated drainage time” is calculated in accordance with the processing integration during the small amount liquid exchange. As a result, the drainage time for the small amount liquid exchange is variable according to the processing integration between the small amount liquid exchanges, and can be executed by the wet etching apparatus having the control device 51. Thereby, the siloxane concentration can be controlled within a certain range.

  FIG. 2 is a sequence chart of etching by the wet etching apparatus shown in FIG. As can be seen from the figure, (1) during the batch processing of a plurality of semiconductor wafers, the quantitative sensor 12 is ON, and the small amount liquid replacement drain sensor 11 is OFF. The valve of the drain 6 is OFF and the valve 13 of the chemical solution tank 9 is also OFF. (2) With respect to the drainage liquid for the small amount liquid exchange, the quantitative sensor 12 is OFF, the small amount liquid exchange drainage sensor 11 is also OFF, the drain 6 valve is ON, and the chemical tank 9 valve 13 is OFF. Begins. Even if the small-quantity liquid replacement drain sensor 11 is turned on, the drain 6 is continuously turned on for the time calculated corresponding to the processing integration and the drain is continued. (3) The quantitative sensor 12 remains OFF, the small amount liquid exchange drainage sensor 11 is turned OFF, the valve of the drain 6 is also turned OFF, while the valve 13 of the chemical tank 9 is turned ON to supply the small amount of liquid. The sequence starts when the liquid starts.

FIG. 3 is a diagram showing the relationship between the siloxane concentration in liquid and the number of processed sheets × the processing time in the first embodiment. The horizontal axis indicates the number of processed sheets × processing time, the vertical axis indicates the siloxane concentration, and the range between A and B on the vertical axis indicates the appropriate range of the siloxane concentration.
As shown in the figure, since a small amount of liquid is exchanged at each point of C, D, E, F, G, and H, the siloxane concentration is lowered. As described above, in order to make the small amount liquid exchange drainage amount (drainage time) variable according to the variation in processing integration between small amount liquid exchanges caused by the combination of the number of lots and the processing time, and to make the appropriate amount of drainage. The amount of siloxy acid concentration reduction can be made substantially the same. In addition, this makes it possible to keep the siloxane concentration between A and B in FIG. In other words, the amount of increase and decrease of the siloxy acid concentration can be kept between A and B in FIG.

For example, at point E, the siloxane concentration does not exceed point A before exchanging a small amount of liquid. For example, even at the H point, the siloxane concentration does not fall below the B point after a small amount of liquid replacement. As a result, the siloxane concentration is within the appropriate range shown between A and B in FIG. Therefore, as described above, due to the high siloxane concentration, (a) siloxane precipitates on the product pattern and pattern defects occur, (b) filter clogging and piping clogging, (c) oxide film Since the etching rate is lowered, it is possible to prevent the problem that the STI height becomes higher than the target value and affects the product characteristics.
Further, due to the low siloxane concentration described above, (d) the oxide film etching rate increases, the STI 26 is etched more than necessary, and the STI height becomes lower than the target value, affecting the product characteristics (e The problem that the oxide film is etched and the polysilicon film under the oxide film is etched. (F) In the memory cell portion, the oxide film is etched and the underlying impurity-doped polysilicon film is also solved. can do.
As described above, according to the first embodiment, various excellent effects can be obtained.

<Embodiment 2>
The second embodiment is a method of managing only by time without using a small amount liquid exchange drainage sensor, and FIG. 4 shows a sequence chart thereof.

As can be seen from the figure, (1) During the wet etching process of the semiconductor product, the quantitative sensor 12 is ON, the small-volume liquid exchange drainage sensor 11 is OFF, the drain 6 valve is OFF, and the chemical tank 9 valve is OFF. . (2) When the quantitative sensor 12 is OFF, the small amount liquid replacement drain sensor 11 is also OFF, the drain 6 valve is ON, and the chemical tank 9 valve is OFF, the small amount liquid discharge starts. Without using the small-quantity liquid exchange drainage sensor 11, the valve of the drain 6 is kept on for the time calculated corresponding to the processing integration. When the calculated time corresponding to the processing integration has elapsed, (3) the valve of the drain 6 is turned off, the valve of the chemical tank 9 is turned on, the quantitative sensor 12 is turned off, and the small quantity liquid replacement drain sensor 11 is also turned off. In this state, the supply of a small amount of liquid begins. During the supply of the small amount of liquid, the sequence of the small amount liquid replacement drain sensor 11 OFF, the drain 6 valve OFF, and the chemical tank 9 valve ON is performed with the quantitative sensor 12 OFF.
According to the second embodiment, since the low-volume liquid exchange / drainage sensor 11 is not used, the wet etching apparatus becomes simpler and the operation sequence is simplified.

<Embodiment 3>
FIG. 5 is a schematic diagram showing an outline of a nitride film wet etching apparatus based on the third embodiment. As shown in the figure, the pump flow rate control device 61 is used to control the pump 4 to variably control the pump flow rate. In other words, the longer the time calculated corresponding to the processing integration, the higher the flow rate of the pump 4 for discharging the small amount of liquid. If the calculated time corresponding to the processing integration is short, control is performed to reduce the flow rate of the pump 4 for discharging the small amount of liquid, and the draining time is kept constant.

  Although the invention made by the present inventor has been specifically described based on the embodiments, it is needless to say that the present invention is not limited thereto and can be variously modified without departing from the gist thereof.

1: Treatment tank 2: Outer tank 3: Treatment liquid circulation line 4: Pump 5: Filter unit 6: Drain 7: Chemical liquid replenishment line 8: Pure water replenishment line 9: Chemical liquid tank 10: Pure water tank 11: Small amount liquid exchange drainage Sensor 12: Quantitative sensor 13: Air operated valve 14: Small liquid exchange critical liquid level 15: Quantitative critical liquid level 16: Semiconductor wafer 17: Carrier 21, 31: Si substrate 22, 24, 33, 35, 37, 38: Oxidation Films 23 and 34: Polysilicon film 25 and 36: SiN film 26: STI
32: P-type well region 39: Impurity doped polysilicon film 40: Gate 41: Source 51: Controller 52: Air operated valve 61: Pump flow rate controller

Claims (7)

  In a wet etching device that etches the object to be processed with the chemical stored in the processing tank and circulates this chemical through the outer tank, the amount of liquid discharged from the small amount of liquid is added to the processing integration of the number of processed sheets and the processing time. A wet etching apparatus that drains a small amount of liquid based on a correspondingly calculated drain time.   The small amount liquid replacement drainage performed based on the drainage time calculated corresponding to the processing integration of the number of processed sheets and the processing time is based on a control device provided between the small amount liquid replacement drainage sensor and the air operated valve. The wet etching apparatus according to claim 1, which is performed.   The small amount liquid replacement drainage performed based on the drainage time calculated corresponding to the processing integration of the number of processing sheets and the processing time is performed by using a pump flow rate control device that controls a pump provided in the processing liquid circulation line. The wet etching apparatus according to claim 1, which is performed.   The wet etching apparatus according to claim 1, wherein the object to be processed is a semiconductor wafer.   The wet etching apparatus according to claim 1, wherein the wet etching apparatus includes a quantitative sensor for detecting a liquid level in the outer tank, and drainage starts when the quantitative sensor is turned on.   2. The wet etching apparatus according to claim 1, wherein the wet etching apparatus includes a small amount liquid exchange drainage sensor for detecting the liquid level in the outer tank, and the drainage is continued even when the small amount liquid exchange drainage sensor is turned on. Etching equipment.   A method for manufacturing a semiconductor device, comprising performing wet etching on a semiconductor wafer with the wet etching apparatus according to claim 1.

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