Semiconductor manufacturing apparatus and manufacturing method of semiconductor device

CROSS-REFERANCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent Application No. JP 2003-305605 filed on Aug. 29, 2003, the content of which is hereby incorporated by reference into this application.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a technique for manufacturing a semiconductor device. More particularly, it relates to a technique effectively applied to the wet etching of a deposited film formed on a wafer by using the single-wafer processing.

BACKGROUND OF THE INVENTION

The technique described below has been examined by the inventor of the present invention in the course of developing the present invention, and its outline will be shown below.

In the manufacturing process of a semiconductor device, various kinds of deposited films are formed on a semiconductor wafer and those deposited films are etched appropriately so as to form fine patterns for electrodes, wirings and the like.

Such an etching technique includes the dry etching using reactive gas and the wet etching based on chemical treatment. Of these, the wet etching is an etching technique based on chemical reaction between an object to be etched and the chemical solution, and it has an advantage that it can obtain a higher selectivity to an underlying film more easily than the dry etching.

For this reason, the wet etching has been employed for the selective etching of a silicon nitride film to an underlying silicon oxide film in the shallow-trench device isolation technique when forming the device isolation. “ULSI Technology” by C. Y. Chang & S. M. Sze, McGraw-Hill, 1996, p 365 contains a description about such etching.

In the conventional wet etching, the batch processing is used for the etching. For example, in the case of the wet etching of a silicon nitride film, a plurality of wafers to be processed are dipped at a time in an immersion bath filled with heated phosphoric acid as the etching solution.

In the etching of a silicon nitride film using the batch processing, the heated phosphoric acid at about 150° C. to 170° C. is used and heating means such as an electric heater is employed for heating the phosphoric acid. Such batch processing usually takes about an hour.

FIG. 6A shows an entire configuration of the apparatus for performing the wet etching using the batch processing system. In the configuration adopting the batch processing system, a plurality of wafers are dipped at a time in etching solution and subjected to the wet etching. The apparatus is provided with a station 1 for receiving the wafers and a station 2 for carrying out the processed wafers. Further, it is provided with a buffer section 3 as a temporary waiting place for the received wafers and for the processed wafers.

Also, the apparatus includes a plurality of processing sections 4 for performing the wet etching of the wafers and a drying section 5 for drying the wafers after the wet etching. A wafer received at the station 1 is transferred to a carrying robot (not shown) of a carrying section 6 by means of a carrying robot (not shown) provided in the buffer section 3 and carried to the processing sections 4. A plurality of wafers are wet-etched at a time in the processing sections 4.

The wafers after the wet etching in the processing sections 4 are carried to the drying section 5 by the carrying robot of the carrying section 6 and dried therein, and then, carried further to the buffer section 3 and finally sent to a next step from the station 2.

As shown in FIG. 6B, the wet etching in the processing sections 4 is performed by dipping a plurality of the wafers W at a time in the immersion bath 7 filled with etching solution for a predetermined time. In the immersion bath 7, the etching solution is circulated by an etching solution circulation system provided with a circulating pump 8. More specifically, the etching solution is supplied from a chemical tank 8a containing the etching solution to the immersion bath 7 through a supply pipe 8b by the circulating pump 8. At the same time, the etching solution is returned from the immersion bath 7 to the chemical tank 8a through a return pipe 8c. In this way, the etching solution is always circulated.

Such a circulation system of the etching solution is provided with a heater-type heat exchanger 8d along the supply pipe 8b as shown in FIG. 6B so as to heat the etching solution to a predetermined temperature. For example, if phosphoric acid solution is used as the etching solution for the wet etching of a silicon nitride film, it is heated to 150° C. to 170° C.

Further, the supply pipe 8b is provided with a pulsation prevention damper 8e for stabilizing the amount of supplied etching solution and a filter 8f for removing foreign matters from the etching solution so as to ensure a stabilized supply of the etching solution containing no etching residue to the immersion bath 7.

SUMMARY OF THE INVENTION

However, the inventor of the present invention has found out the following subjects in the wet etching technique based on the above-described batch processing.

That is, although semiconductor device manufacturing line in recent years has gradually adopted a line structure for the single-wafer processing instead of the line structure for the batch processing, even the line structure for the single-wafer processing still adopts the batch processing for the wet etching of a silicon nitride film, and thus, the processing line structure for the single-wafer processing does not operate smoothly. For this reason, the inventor of the present invention has thought that development of single-wafer processing technique for the wet etching of a silicon nitride film is demanded urgently.

Accordingly, an object of the present invention is to provide semiconductor manufacturing apparatus and a manufacturing method of a semiconductor device capable of applying the single-wafer processing to the wet etching of a silicon nitride film.

The above and other objects and novel characteristics of the present invention will be apparent from the description and the accompanying drawings of this specification.

The representative ones of the inventions disclosed in this application will be briefly described as follows.

That is, by heating the etching solution used in the wet etching by electromagnetic wave in a state where it is supplied to the deposited film on a wafer to be etched, the etching solution can be heated to a high temperature in a short time, thereby reducing the time for the etching process.

The effect obtained by the representative one of the inventions disclosed in this application will be briefly described as follows.

That is, by heating the etching solution to a high temperature in a short time, the time for the etching process can be reduced to such an extent that can perform the wet etching by using the single-wafer processing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram schematically showing the concept of the entire configuration of the semiconductor manufacturing apparatus for the wet etching according to an embodiment of the present invention;

FIG. 2A is an explanatory diagram schematically showing an example of the structure of the wafer holding means;

FIG. 2B is an explanatory diagram schematically showing an example of the structure of the wafer holding means;

FIGS. 3A to 3C are explanatory diagrams showing the steps of device isolation forming process;

FIGS. 4A to 4C are explanatory diagrams showing the steps of the device isolation forming process continued from FIG. 3;

FIG. 5 is a graph showing the temperature dependence of the etching rate of phosphoric acid solution; and

FIG. 6A is an explanatory diagram showing the entire configuration of the wet etching apparatus using the batch processing; and

FIG. 6B is an explanatory diagram showing the immersion process into etching solution in the configuration shown in FIG. 6A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference numerals throughout the drawings for describing the embodiments, and the repetitive description thereof will be omitted.

First, the semiconductor manufacturing apparatus that can perform the wet etching by using the single-wafer processing will be described in this embodiment. FIG. 1 is an explanatory diagram schematically showing the entire configuration of the semiconductor manufacturing apparatus. FIGS. 2A and 2B are explanatory diagrams schematically showing the structure of the wafer holding means.

As shown in FIG. 1, the semiconductor manufacturing apparatus formed in the wet etching apparatus comprises wafer holding means 10 for holding a wafer W for wet etching, etching solution supply means 20 for supplying etching solution to the wafer W, electromagnetic wave heating means 30 for heating the etching solution by irradiating the etching solution supplied to the wafer W with electromagnetic wave, and recycle means 40 for recycling the used etching solution after the etching process.

The wafer holding means 10 is formed so as to hold each one wafer W. As shown in FIG. 2A, the wafer holding means 10 is formed as a wafer holding device 10a(10) provided with a base 11 and pawls 11a which are provided on the periphery of the base 11 and capable of opening/closing.

In the case shown in FIG. 2A, the periphery of the wafer W is fastened by the pawls 11a so that it is held substantially horizontally with a surface thereof on which a deposited film (not shown) to be wet-etched is formed facing upward.

The pawls 11a are formed so as to be opened/closed freely as indicated by the double-sided arrows in FIG. 2A. A wafer W carried to a predetermined position by a carrying robot (not shown) is fastened at the side surface thereof by the pawls 11a moved from its open standby position to its closed position shown in FIG. 2A.

The wafer holding device 10a having such a structure is provided in an etching processing chamber 50 as shown in FIG. 1. The etching processing chamber 50 surrounds the wafer holding device 10a to prevent the scattering of the etching solution at the time of etching process. Also, the topside of the chamber 50 is opened so that the etching solution can be supplied to the wafer W held by the wafer holding device 10a through that opening of the chamber 50.

The chamber 50 which contains the wafer holding device 10a is provided within a treatment chamber 60 in which the electromagnetic wave is irradiated. The electromagnetic wave heating means 30 is provided above the chamber 50 in the treatment chamber 60 in order to prevent the leakage of the electromagnetic wave out of the treatment chamber 60. The electromagnetic wave heating means 30 can be formed of, for example, a microwave generating unit composed of magnetron or an infrared generating unit composed of an infrared ray generating tube.

The electromagnetic wave, for example, microwave or infrared generated from the electromagnetic wave heating means 30 goes through the opening of the chamber 50 and reaches the wafer W. A reflecting material is provided inside the chamber 50 to reflect the electromagnetic wave entering the chamber 50 so as to concentrate the electromagnetic wave onto the wafer W.

In a state where the irradiated electromagnetic wave is concentrated onto the wafer W, the etching solution is supplied to the wafer W from above by the etching solution supply means 20. As shown in FIG. 1, the etching solution supply means 20 is provided with a circulating pump 21 to supply the etching solution from a chemical tank 22 storing the etching solution to the wafer W held on the wafer holding device 10a in the chamber 50 of the treatment chamber 60 through a supply pipe 23.

A pulsation preventing damper 24 is provided along the supply pipe 23 in order to stabilize the amount of etching solution supplied to the wafer W.

Further, the supply pipe 23 is provided with a heat exchanger unit 25a as preliminary heating means 25 in order to shorten the heating time by means of electromagnetic wave heating by pre-heating the etching solution to a predetermined temperature before it is supplied to the wafer W. Additionally, a filter 26 is provided along the supply pipe 23 to remove foreign matters contained in the etching solution.

In this way, a predetermined amount of the etching solution is supplied to the wafer W held by the wafer holding device 10a in the chamber 50. As shown in FIG. 2A, a predetermined amount of the supplied etching solution E is kept on the deposited film (not shown) of the wafer W by the surface tension. Before supplying the etching solution, the amount of etching solution necessary for the wafer W to be etched is obtained by using a dummy wafer in advance, and by supplying a slightly larger amount of the etching solution than the necessary amount, the etching solution is appropriately kept on the deposited film of the wafer W by the surface tension.

When a slightly excessive amount of the etching solution is supplied to the wafer W in this way, the excessive etching solution spilt out of the wafer W flows on the base 11 and is discharged through a discharge hole 12 provided in the base 11.

The discharge hole 12 is connected to a return pipe 27 so that the etching solution on the base 11 returns to the chemical tank 22. Consequently, the excessive etching solution when the etching solution is supplied to the wafer W and the used etching solution after the etching process are collected into the chemical tank 22 without being thrown away and then recycled.

When recycling the etching solution, the collected etching solution is mixed with non-used etching solution in the chemical tank 22. Therefore, the recycle means 40 includes concentration adjusting means 41 for adjusting the concentration of supplied etching solution to be constant as shown in FIG. 1.

As the concentration adjusting means 41, at least any one of concentration adjusting means for chemicals composing the etching solution and concentration adjusting means for reaction product produced by etching and contained in the etching solution is provided.

For example, if etching solution containing silicon is assumed as the etching solution, as the concentration adjusting means for chemicals composing the etching solution, concentration adjusting means for phosphoric acid which is a chemical composing the etching solution is equipped, and as the concentration adjusting means for reaction product produced by etching, concentration adjusting means for silicon which is a reaction product produced by the etching is equipped.

As for the concentration adjusting means for phosphoric acid, for example, phosphoric acid concentration in the chemical tank 22 is checked by concentration detecting means based on the absorbance method. The check result is compared with the concentration of the phosphoric acid of supplied etching solution set in advance and if it is higher, purified water is supplied and if it is lower, non-used phosphoric acid solution is supplied.

As for the adjustment of the silicon concentration in the phosphoric acid solution, the silicon concentration in the chemical tank 22 is checked according to the absorption spectrometry, and the check result is compared with the silicon concentration in phosphoric acid solution of the supplied etching solution set in advance. If it is higher, the collected etching solution is not returned to the chemical tank 22 and thrown away, and if it is lower, the collected etching solution is returned to the chemical tank 22 to adjust the concentration.

In the semiconductor manufacturing apparatus for wet etching described above, as shown in FIG. 1, the etching solution is circulated for recycle by the circulating pump 21 from the chemical tank 22 through the supply pipe 23, the wafer W, and the discharge hole 12 to the return pipe 27.

Particularly, in the case where the wet etching of the silicon nitride film is performed with using phosphoric acid solution as the etching solution, the phosphoric acid concentration adjusting means and the silicon concentration adjusting means are provided as the recycle means. By doing so, the selective etching of the silicon nitride film deposited on a silicon oxide film using the phosphoric acid can be performed efficiently.

Since the configuration of the semiconductor manufacturing apparatus described above adopts the means for supplying etching solution to the deposited film to be etched of the wafer W and heating the etching solution by irradiating the supplied etching solution with electromagnetic wave, the etching solution can be heated to a high temperature in an extremely short time.

When the etching solution is heated by electromagnetic wave in a state where it is held on the deposited film of the wafer W by the surface tension as shown in FIG. 2A, the amount of the etching solution to be heated, which is held uniformly and thinly on the deposited film, is extremely smaller than that in the case of the batch processing. In addition, since the electromagnetic wave heating means different from the heater-type heating means is used, the etching solution can be heated up to a high temperature over 200° C. in the unit of seconds. As a result, the etching rate by the phosphoric acid is improved and the process time of the wet etching for a silicon nitride film can be remarkably reduced in comparison to the conventional wet etching using the heated phosphoric acid with a temperature of 150° C. to 170° C.

The wafer holding means 10 with the structure as shown in FIG. 2B can be used as a wafer holding device 10b. The structure shown in FIG. 2B enables the wafer W to be dipped in etching solution one by one. The wafer holding device 10b is provided with a sidewall 13a on the periphery of a base 13 to form the immersion bath 14 as shown in FIG. 2B.

The immersion bath 14 formed to have a volume capable of dipping one wafer W, and a plurality of supporting members 15 which support the wafer W by point contact are provided on the base 13 which corresponds to the bottom of the immersion bath 14. Etching solution is supplied into the immersion bath 14 with the wafer W supported on the supporting members 15 so that the etching solution makes contact with the deposited film to be etched of the wafer W.

By irradiating with electromagnetic wave by means of the electromagnetic wave heating means 30 in a state where the etching solution is supplied to the deposited film, the etching solution in which the wafer W is dipped is heated to a high temperature over 200° C. in a short time because the amount of the etching solution is small and electromagnetic heating is strong heating means. As a result, the etching rate by the phosphoric acid is improved, and the process time of the wet etching for a silicon nitride film can be remarkably shortened in comparison to the conventional wet etching using the heated phosphoric acid with a temperature of 150° C. to 170° C.

In the structure of the wafer holding device 10a shown in FIG. 2A, the deposited film formed on an upper side of the wafer W is the object to be etched, and thus, it can be said that this device is for the etching process of a single side of the wafer W. On the contrary, because the wafer W is dipped in the etching solution in the structure of the wafer holding device 10b shown in FIG. 2B, it can be said that this device is for the etching process of a both sides of the wafer W, which can perform the wet etching of not only a single side but also double sides in parallel depending on the cases.

Also, similar to the wafer holding device 10a as shown in FIG. 2A, the base 13 is provided with a discharge hole 12 so that the used etching solution can be returned through the return pipe 27 to the chemical tank 22 for recycle use after the etching is finished.

Since the wafer W is dipped in the etching solution in the structure of the wafer holding device 10b, the wafer W does not need to maintain a highly precise horizontal posture different from the structure of the wafer holding device 10a shown in FIG. 2A which holds the etching solution by the surface tension. There is no problem if the horizontality is kept to an extent that the surface of the wafer W is not exposed over the etching solution.

Next, the method of manufacturing a semiconductor device with using the semiconductor manufacturing apparatus for wet etching having such a configuration will be described. In the following description, the case where the phosphoric acid solution containing silicon is used as the etching solution and a silicon nitride film formed on a silicon oxide film is selectively wet-etched in order to form device isolation regions for the shallow trench isolation (STI) used in such a semiconductor device as MOS-IC will be described.

As shown in FIG. 3A, a silicon oxide film 100 is formed on a P-type silicon wafer W and a silicon nitride film 200 is sequentially laminated thereon. After that, as shown in FIG. 3B, the device isolation forming areas of the silicon nitride film 200 and silicon oxide film 100 are etched with using a resist film as a mask. Further, as shown in FIG. 3C, the wafer W is etched to a predetermined depth with using the silicon nitride film 200 formed in FIG. 3B as a mask so as to form the STI trench 300.

After that, as shown in FIG. 4A, silicon oxide film 400 is deposited so as to fill the STI trench 300 formed in FIG. 3C with the silicon oxide film 400. Further, the chemical mechanical polishing (CMP) is performed with using the silicon nitride film 200 as a stopper film so as to form a flat surface as shown in FIG. 4B.

In a state where the silicon nitride film 200 is exposed as described above, the silicon nitride film 200 is subjected to wet etching by using the above-described semiconductor manufacturing apparatus having the configuration capable of performing the single-wafer processing.

That is, the wafers W processed to the state shown in FIG. 4B in the previous steps are transported to the semiconductor manufacturing apparatus for wet etching having the configuration shown in FIG. 1 one by one. The transported wafer W is held by the wafer holding device 10a as shown in FIG. 2A one by one.

In a state where the wafer W is held, the etching solution composed of phosphoric acid solution containing silicon is supplied to the wafer W by the etching solution supply means 20. A slightly excessive amount of the etching solution is supplied and then, the etching solution is held on the deposited film formed on the wafer W by the surface tension.

The etching solution composed of phosphoric acid solution containing silicon held on the wafer W by the surface tension is irradiated with microwave, infrared ray, or other electromagnetic wave by the electromagnetic wave heating means 30.

If the phosphoric acid concentration of the phosphoric acid solution containing silicon which composes the etching solution is in a range of 94% and 98%, the phosphoric acid solution containing silicon is heated to a higher temperature of higher than 200° C. and lower than 230° C. in a short time by the above-described electromagnetic wave heating. Although the time required for such heating varies depending on the energy quantity of the irradiated electromagnetic wave, the amount of the phosphoric acid solution containing silicon to be heated and the like, it is heated in the unit of several tens seconds, and thus, the necessary etching is finished in the unit of minutes.

The heating temperature of the phosphoric acid solution is specified by the concentration of phosphoric acid and if the concentration of phosphoric acid is in a range of 94% and 100%, it can be heated to the temperature range of 200° and 250° C. in a short time by the electromagnetic wave heating.

Although the phosphoric acid solution containing silicon can be heated to a temperatures over 250° C., heating up to the temperatures over 250° C. is not preferable because it is necessary to perform the selective etching of the silicon nitride film 200 in contact with the silicon oxide film 100 as shown in FIG. 4B.

FIG. 5 shows the temperature dependence of the etching rate of the phosphoric acid to the silicon nitride film and the silicon oxide film. Etching rates at predetermined temperatures are plotted according to the Arrhenius plot based on the activation energy. FIG. 5 indicates the plotting up to 220° C.

FIG. 5 makes it apparent that a line a indicating the temperature dependence of the etching rate of the silicon nitride film has a smaller gradient than a line b indicating the temperature dependence of the etching rate of the silicon oxide film. That is, if the temperature of the phosphoric acid solution rises, an increment of the etching rate of the silicon oxide film becomes larger than an increment of the etching rate of the silicon nitride film, and the selectivity between the silicon nitride film and the silicon oxide film is decreased.

Thus, as a range of practical selectivity, the temperature upper limit is determined to be 250° C. As is apparent from the graph of FIG. 5, as the temperature drops, the etching rate decreases largely although the selectivity is increased.

Since the present invention aims at the development of the technique for the wet etching using the single-wafer processing, the temperature cannot be reduced more than necessary. To secure the wet etching process time at least in the unit of minutes required for the single-wafer processing, it is judged that the lower limit of the temperature is 200° C. or higher. If the temperature is lower than 200° C., the short wet etching process time necessary for the single-wafer processing cannot be expected.

The selectivity to the silicon oxide film can be improved by adding silicon to the phosphoric acid solution. If the Si concentration in the phosphoric acid solution is kept to be about 100 ppm, an effective selectivity can be obtained in the temperature range of 200° C. and 250° C.

By performing the wet etching under the condition that the solution temperature is in a range of 200° C. to 250° C. and the phosphoric acid solution containing silicon with the Si concentration of 100 ppm is used as the etching solution, the silicon nitride film 200 is removed selectively to the silicon oxide film 100 as shown in FIG. 4C, and the device isolation by the STI can be achieved.

The wet etching of the silicon nitride film 200 shown in FIGS. 4B and 4C can be performed in a short time, for example, in the unit of minutes demanded for the single-wafer processing by using the apparatus shown in FIG. 1.

Although the phosphoric acid solution containing silicon is heated instantaneously to a high temperature by irradiating it with microwave just when it is supplied to the wafer W as described above, it is preferable that the solution is preliminarily heated to about 170° C. by the preliminary heating means 25 so as to further reduce the heating time. However, if this is unnecessary, such preliminary heating can be omitted.

When the wet etching ends, the wafer W is carried from the wafer holding device 10a to a next process by a carrying robot. The used etching solution containing silicon is returned to the chemical tank 22 through the return pipe 27 and recycled after adjusting the phosphoric acid concentration and the silicon concentration by the concentration adjusting means 41 constituting the recycle means 40.

When the apparatus shown in FIG. 1 is operated, by recycling the used etching solution after several dummy wafers are processed, a specified amount of silicon can be dissolved into the phosphoric acid solution. Thus, it is not necessary to prepare any phosphoric acid solution containing silicon from the beginning.

Although the wet etching of the silicon nitride film 200 can be performed by the conventional batch processing, it takes about an hour for the processing and the short time processing demanded for the single-wafer processing cannot be achieved.

The batch processing is superior in the processing capability because a plurality of wafers can be processed at a time in a single apparatus. However, from the viewpoint of the facility, a plurality of apparatus are equipped and one of which is reserved as a backup for a possible accidental trouble. Therefore, in a routine line flow without any trouble, the reserved apparatus is the excessive investment.

Depending on the cases, it is preferable to provide a plurality of the processing apparatus from the viewpoint of stable manufacturing. Further, it is preferable to provide the single-wafer processing apparatus as the reserved apparatus of the batch processing system from the viewpoint of the apparatus cost. Thus, the wet etching using the single-wafer processing has a larger advantage than the batch processing system, and therefore, the present invention in which the single-wafer processing is made technically possible is highly meaningful.

In the foregoing, the invention made by the inventor of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention.

For example, an example in which phosphoric acid solution containing silicon is employed as the etching solution for the wet etching to remove a silicon nitride film has been described. However, there is no problem if other chemical solution is applied to the wet etching and the object to be etched is a deposited film other than the silicon nitride film.

In the case of using the phosphoric acid solution containing silicon, the phosphoric acid is indicated as the chemical whose concentration is to be adjusted by the concentration adjusting means for chemicals composing etching solution. However, it is permissible to adjust the concentration of each of plural chemicals when plural kinds of chemicals are used as the etching solution instead of the phosphoric acid solution containing silicon.

Also, the above-described configuration is formed to achieve the wet etching using the single-wafer processing. However, a part of the configuration can be applied to the batch processing. For example, instead of holding each one wafer by the wafer holding device, the configuration of the batch processing in which plural wafers are held is used and the etching solution is kept on each of the wafers by the surface tension, and in this state, the etching solution is heated to a high temperature by electromagnetic wave heating, thereby reducing the etching process time. It can be said that such a configuration is in the same category as the case where a plurality of the single-wafer processing systems are provided.

The present invention can be effectively applied to the field of the wet etching in the manufacture of the semiconductor device.

Semiconductor manufacturing apparatus and manufacturing method of semiconductor device

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