JP2005150399A - Manufacturing method of semiconductor device - Google Patents

Abstract

A trench sidewall formed in a semiconductor substrate is cleaned simultaneously with an inner wall of an etching chamber.
A gas 12 for etching a semiconductor material is introduced into an etching chamber 10, a plasma 11 is generated in the etching chamber 10 to etch a semiconductor substrate 1, and a total trench volume in the semiconductor substrate 1 is 30 mm. ^Three or more trenches 3 are formed. Subsequently, a gas 14 containing Ar for etching the etching products 4 and 5 generated at the time of trench formation is introduced into the same etching chamber 10 to generate a plasma 13 in the etching chamber 10, and a bias power is set. Without application, both the etching product 4 attached to the side wall of the trench 3 and the etching product 5 attached to the inner wall of the etching chamber 10 are simultaneously etched and removed.
[Selection] Figure 1

Description

  The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device including a step of forming a trench in a semiconductor substrate.

  2. Description of the Related Art Conventionally, a semiconductor device such as a MOSFET (insulated gate field effect transistor) in which a trench is formed in a semiconductor substrate and an insulated gate structure is formed on the side wall of the trench is known. Conventionally, shallow trenches having a depth of 10 μm or less have been the mainstream. However, in recent years, trenches having a deeper ratio of depth to the opening width of the trench, that is, a large aspect ratio, due to demands for higher breakdown voltage of devices. Is needed. In addition, since the region of the device having a trench structure is widened in the wafer surface, the ratio of the area of the opening portion by the trench to the area of the wafer surface, that is, the trench opening ratio is also increased.

  In general, a dry etching method is used to form a trench. When dry etching is performed, etching products adhere to the trench sidewalls. In order to remove this deposit, conventionally, wet cleaning is performed with HF liquid after trench formation. In addition, the etching product adheres not only to the trench sidewall but also to the inner wall of the etching chamber. Etching products adhering to the inner wall of the chamber cause generation of particles and black silicon. Black silicon is an abnormal growth of silicon in a columnar shape in a trench, and it is said that black silicon is generated when an etching product is excessively present in a chamber.

In order to remove deposits on the inner wall of the chamber, conventionally, a dry cleaning process in the chamber is performed periodically using a dummy wafer that is not a product. The reason for using a dummy wafer is that the wafer is damaged because CF ₄ gas and O ₂ gas are introduced into the chamber to generate plasma. As described above, during the dry cleaning process, a product wafer cannot be processed. Therefore, frequent dry cleaning processing increases the cost of product wafers. Therefore, conventionally, a dry cleaning process is performed every time 50 wafers as products are successively etched.

FIG. 7 shows the relationship between the number of black silicon produced on the 20th wafer and the total volume of trenches formed in the wafer when dry etching is performed on 20 wafers in succession. FIG. As is clear from FIG. 7, when the total volume of the trenches in the wafer becomes 30 mm ³ or more, the number of black silicon increases rapidly. Therefore, conventionally, for a product (wafer) having a total trench volume of 30 mm ³ or more in the wafer, dry cleaning processing is performed every time 10 wafers are continuously etched.

By the way, a technique for cleaning reaction products adhering in a trench using a chemical dry etching (CDE) apparatus using an F-based etching gas such as CF ₄ and a carrier gas such as O ₂ has been known. (For example, see Patent Document 1). Further, the damage layer, SiC layer and CF _x Si layer formed on the surface of the semiconductor substrate by etching the semiconductor substrate with a mixed gas containing carbon and fluorine contain fluorine and oxygen with a partial pressure ratio of 70% or more. A method of removing a semiconductor substrate by etching with a mixed gas has been proposed (for example, see Patent Document 2).

  With respect to the cleaning process of the inner wall of the chamber, there has been proposed a method of cleaning the etching residue formed on the inner wall of the chamber after the substrate is taken out of the chamber after completion of the etching process (see, for example, Patent Document 3). . In addition, in order to minimize the accumulation of reaction products on the inner wall of the chamber, the natural oxide film formed on the silicon substrate surface where the trench is to be formed is removed by dry etching in plasma using a fluorine-based etching gas. Next, trenches are formed in the silicon substrate by performing continuous dry etching in plasma using silicon etching gas containing chlorine or bromine gas instead of fluorine etching gas in the same etching chamber. Has been proposed (see, for example, Patent Document 4).

  Furthermore, a method of performing etching so that the product does not adhere to the inner wall of the chamber has been proposed (see, for example, Patent Document 5). In this method, an etchant gas for etching the substrate, which etches the substrate to form an etching residue on the chamber surface, and cleaning for cleaning the etching residue formed on the chamber surface. Process gas including gas is used.

JP-A-8-203863 JP-A-8-250482 JP-T-2001-520463 JP 11-214356 A Special table 2001-523044 gazette

  However, as described above, when the trench becomes deeper and the aspect ratio of the trench becomes higher, in the conventional HF cleaning, it is difficult to reach the depth of the trench sufficiently due to the HF liquid entraining bubbles. Become. Therefore, after the HF cleaning, an etching product partially remains in the trench. This state is shown in FIGS.

  In FIG. 8, a sample having an opening width of 1.2 μm and a depth of 15 μm formed in a semiconductor substrate and then subjected to HF cleaning is cut along the longitudinal direction of the trench, and the state of the cross section is shown as a scanning electron. It is a figure which shows the photograph image | photographed with the microscope. FIG. 9 is a view showing an enlarged photograph of the trench termination portion of FIG. Further, FIG. 10 shows that after forming a trench having an opening width of 1.2 μm and a depth of 50 μm in a semiconductor substrate, a sample subjected to HF cleaning is cut along the longitudinal direction of the trench and the state of the cross section is scanned. It is a figure which shows the photograph image | photographed with the scanning electron microscope. FIG. 11 is a view showing an enlarged photograph of the bottom of the trench in FIG.

As shown in these photographs, the cleaning residue tends to remain at the bottom of the trench centering on the end portion of the trench. If the etching product remains as a cleaning residue in this way, a fatal failure such as a decrease in breakdown voltage may occur in a device such as a trench MOSFET having a gate insulating film on the trench side wall. On the other hand, as described in Patent Document 1, when chemical dry etching is performed using only CF ₄ gas and O ₂ gas, the trench side wall becomes rough. This also causes a fatal failure such as a decrease in breakdown voltage in a device such as a trench MOSFET having a gate insulating film on the trench side wall.

  Further, when the trench is deepened or the trench opening ratio is increased, the amount of silicon removed by etching increases, so that the amount of etching products attached to the inner wall of the chamber increases. For this reason, if the dry cleaning process is performed each time 50 wafers are continuously subjected to the dry etching process, the chamber inner wall is not sufficiently cleaned. Therefore, in practice, the dry cleaning process is performed every time the dry etching process for 10 wafers in succession is completed. In this case, however, the time during which the product wafer is not dry-etched becomes longer, and the cost increases. In addition, since the atmosphere in the chamber changes drastically while 10 wafers are processed, the trench shape is different for all the first to tenth wafers. That is, the lot uniformity is poor.

  In Patent Document 5, an etching product does not adhere to the inner wall of the chamber, so that a dry cleaning process is unnecessary. Therefore, problems such as an increase in cost and deterioration in lot uniformity due to the execution of the dry cleaning process as described above are avoided. However, since an etching product serving as a protective film does not adhere to the trench sidewall during dry etching, the trench sidewall is roughened, the side etching proceeds, and the trench shape is disturbed. This is shown in FIGS. FIG. 12 is a view showing a photograph in which a sample in which a trench is formed in a semiconductor substrate under a condition in which no etching product is generated is cut along the short direction of the trench, and the state of the cross section is photographed with a scanning electron microscope. is there. FIG. 13 is a view showing an enlarged photograph of the trench opening in FIG.

  An object of the present invention is to provide a method of manufacturing a semiconductor device in which the trench sidewall formed in the semiconductor substrate and the etching chamber inner wall are simultaneously cleaned in order to eliminate the above-described problems caused by the prior art. And

  In order to solve the above-described problems and achieve the object, a method of manufacturing a semiconductor device according to claim 1 is for etching a semiconductor material constituting the semiconductor substrate in an etching chamber containing the semiconductor substrate. A step of introducing a gas, generating plasma in the etching chamber, and etching the semiconductor substrate to form a trench in the semiconductor substrate by the etching action of the plasma; and forming the trench in the same etching chamber. A gas for etching the etching product generated during the formation of the plasma is introduced, plasma is generated in the etching chamber, and the etching product attached to the sidewall of the trench during the formation of the trench by the etching action of the plasma And an edge adhering to the inner wall of the etching chamber. Characterized in that it comprises a step of removing by etching both ring product, a.

  According to the first aspect of the present invention, following the formation of the trench, by performing dry etching in the same etching chamber, the etching product adhering to the trench side wall and the etching product adhering to the inner wall of the etching chamber are simultaneously removed. can do.

  According to a second aspect of the present invention, there is provided a method of manufacturing a semiconductor device according to the first aspect of the invention, wherein the etching product is etched without applying a bias power in the step of removing the etching product. .

  According to the second aspect of the present invention, by not applying bias power, etching of the trench sidewall by radicals or ions having directionality is suppressed, so that the trench shape is disturbed or the trench sidewall is roughened. Can be suppressed.

  According to a third aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the first or second aspect of the present invention, wherein in the step of removing the etching product, etching is performed using a gas containing Ar. And

  According to the third aspect of the invention, it is possible to prevent the trench sidewall from being roughened by using the gas containing Ar.

According to a fourth aspect of the present invention, there is provided a semiconductor device manufacturing method according to any one of the first to third aspects, wherein in the step of forming the trench, the total volume in the substrate surface of the trench is 30 mm ^3. The above trench is formed.

According to the invention of claim 4, conventionally, when the total volume of the trench is 30 mm ³ or more, the dry cleaning process of the inner wall of the chamber is performed using the dummy wafer every time 10 wafers are processed continuously. Compared to the above, since the dry cleaning process is unnecessary, the running cost can be reduced by about 20%.

  According to the method for manufacturing a semiconductor device according to the present invention, even if the aspect ratio of the trench is high or the total volume of the trench is large, the etching product attached to the trench sidewall and the etching product attached to the inner wall of the etching chamber Can be removed simultaneously.

  Exemplary embodiments of a method for manufacturing a semiconductor device according to the present invention will be explained below in detail with reference to the accompanying drawings. The gist of the present invention is that, after forming a trench in a semiconductor substrate, the trench sidewall and the chamber inner wall are dry-etched in the same chamber, and the semiconductor element manufacturing process after the trench formation is optional. It is. Therefore, the manufacturing process of the semiconductor element after the trench formation is omitted.

Embodiment 1 FIG.
1 and 2 are explanatory diagrams for explaining the manufacturing method according to the first embodiment of the present invention. As shown in FIG. 1, a mask oxide film 2 having a desired pattern is formed on a semiconductor substrate 1. Then, the semiconductor substrate 1 having the mask oxide film 2 is placed in the etching chamber 10. A gas 12 for etching the semiconductor substrate 1 is introduced into the etching chamber 10, plasma 11 is generated to dry-etch the semiconductor substrate 1, and a trench 3 is formed in the semiconductor substrate 1.

An example of the process conditions for the trench formation step is as follows. The gas species introduced into the etching chamber 10 are HBr, SF ₆ and O ₂ . The gas flow rate of HBr is 60 sccm. The gas flow rate of SF _{6 and} the gas flow rate of O ₂ are both 100 sccm. The bias power Wb is 100 W, and the high frequency output Ws for generating the plasma 11 is 400 W. The pressure in the etching chamber 10 is 25 mTorr. The etching time is 200 seconds.

When etching is performed using the mask oxide film 2 having a trench opening width of 0.5 μm under this process condition, a trench 3 having a depth of, for example, 5 μm and an aspect ratio of 10 is formed. The trench opening ratio of this wafer is 50%, and the total trench volume in a 6-inch wafer is 44 mm ³ . An etching product 4 is attached to the side wall of the formed trench 3. The etching product 5 is also attached to the inner wall of the etching chamber 10. In FIG. 1, an arrow between the plasma 11 and the semiconductor substrate 1 represents a state in which radicals and ions are directed toward the semiconductor substrate 1 by applying bias power (the same applies to FIG. 3).

  Following the trench formation step, as shown in FIG. 2, a gas 14 for etching the etching products 4 and 5 is introduced into the same etching chamber 10. Then, the plasma 13 is generated, and both the etching product 4 attached to the sidewall of the trench 3 and the etching product 5 attached to the inner wall of the etching chamber 10 are simultaneously removed by dry etching.

An example of the process conditions for the etching product removal step is as follows, for example. The gas species introduced into the etching chamber 10 are Ar, CF ₄ and O ₂ . By including Ar in the reaction gas, the side wall of the trench 3 can be prevented from being rough. The Ar gas flow rate is 120 sccm. The gas flow rate of CF ₄ is 90 sccm. The gas flow rate of O ₂ is 10 sccm.

  The bias power Wb is 0W. That is, no bias power is applied in this step. The reason is that when a bias power is applied, the side wall of the trench 3 is etched by radicals and ions having directionality, which may affect the shape of the trench or roughen the side wall of the trench. It is because it is necessary to set it as the conditions which are not etched. The high frequency output Ws for generating the plasma 13 is 1200W. The pressure in the etching chamber 10 is 10 mTorr. The etching time is 30 seconds. By performing the dry etching process under these process conditions, both the etching product 4 attached to the sidewall of the trench 3 and the etching product 5 attached to the inner wall of the etching chamber 10 are removed.

Embodiment 2. FIG.
3 and 4 are explanatory diagrams for explaining the manufacturing method according to the second embodiment of the present invention. As shown in FIG. 3, similarly to the first embodiment, a semiconductor substrate 1 having a mask oxide film 2 having a desired pattern is placed in an etching chamber 10 and a gas 12 for etching the semiconductor substrate 1 is introduced. Then, plasma 11 is generated to dry-etch the semiconductor substrate 1, thereby forming a trench 3 in the semiconductor substrate 1.

An example of the process conditions for the trench formation step is as follows. The gas species introduced into the etching chamber 10 are HBr, SF ₆ and O ₂ . Both the gas flow rate of HBr and the gas flow rate of SF ₆ are ₆₀ sccm. The gas flow rate of O ₂ is 100 sccm. The bias power Wb is 100 W, and the high frequency output Ws for generating the plasma 11 is 400 W. The pressure in the etching chamber 10 is 25 mTorr. The etching time is 1000 seconds.

When etching is performed using the mask oxide film 2 having a trench opening width of 2 μm under this process condition, the trench 3 having a depth of, for example, 25 μm and an aspect ratio of 12.5 is formed. The trench opening ratio of this wafer is 25%, and the total trench volume in a 6-inch wafer is 110 mm ³ . An etching product 4 is attached to the side wall of the formed trench 3. The etching product 5 is also attached to the inner wall of the etching chamber 10.

  Following the trench formation step, as shown in FIG. 4, a gas 14 for etching the etching products 4 and 5 is introduced into the same etching chamber 10. Then, plasma 13 is generated to dry-etch both part or all of the etching product 4 adhering to the sidewall of the trench 3 and the etching product 5 adhering to the inner wall of the etching chamber 10. Remove at the same time.

An example of process conditions for the etching product removal step is as follows, for example. The gas species introduced into the etching chamber 10 are Ar, CF ₄ and O ₂ . The reason why Ar is contained in the reaction gas is to prevent the side wall of the trench 3 from being rough, as in the first embodiment. The Ar gas flow rate is 120 sccm. The gas flow rate of CF ₄ is 90 sccm. The gas flow rate of O ₂ is 10 sccm.

  The bias power Wb is 0W. The reason for not applying the bias power is as described in the first embodiment. The high frequency output Ws for generating the plasma 13 is 1200 W. The pressure in the etching chamber 10 is 10 mTorr. The etching time is 30 seconds. By performing the dry etching process under these process conditions, as shown in FIG. 4, a part of the etching product 4 adhering to the inner wall of the trench 3 (portion near the trench opening) and the inner wall of the etching chamber 10 Both etching products 5 adhering to are removed.

  The photograph which image | photographed the mode of the trench side wall of the sample which performed the etching product removal process for 30 second on the conditions mentioned above with the scanning electron microscope is shown in FIG. For comparison, FIG. 6 shows a photograph taken with a scanning electron microscope of the state of the trench sidewall of a sample that has not been subjected to the etching product removal treatment. In these photographs, the portions that appear white are etching products. As can be seen from FIG. 6, in the sample that has not been subjected to the etching product removal treatment, the etching product adheres to the entire surface of the trench sidewall. On the other hand, as shown in FIG. 5, in the sample subjected to the etching product removal process, the etching product remains in the portion near the bottom of the trench, but the etching product in the portion near the trench opening is removed. I understand.

  In this way, in the case of a deep trench, the amount of etching products generated increases, so that it takes a long time to completely remove the etching products. For example, if the etching product removal process is performed for 60 seconds under the above-described conditions, the etching product can be completely removed. In order to suppress the damage to the trench sidewall due to the extended processing time, the etching product removal process is performed to the extent shown in FIG. 5, and then the remaining etching product is removed by HF cleaning or the like. You may make it do.

Embodiment 3 FIG.
In the third embodiment, when the total trench volume is as large as 110 mm ³ as in the second embodiment, the process conditions of the etching product removal step shown in FIG. 4 are as follows, for example. The gas species introduced into the etching chamber 10 are CF ₄ and O ₂ , the gas flow rate of CF ₄ is 90 sccm, and the gas flow rate of O ₂ is 10 sccm. The bias power Wb is 0W. The high frequency output Ws for generating the plasma 13 is 1200 W. The pressure in the etching chamber 10 is 10 mTorr. The etching time is 60 seconds.

  That is, in Embodiment 3, the gas introduced into the etching chamber 10 does not contain Ar. Therefore, in the third embodiment, the etching products 4 and 5 can be etched more efficiently than in the second embodiment, but on the other hand, a slight roughness may occur on the inner wall of the trench. Therefore, when manufacturing a device in which a gate insulating film is formed on the inner wall of the trench, after the etching product removing step, smoothing processing using sacrificial oxidation or CDE is performed to remove the roughness of the inner wall of the trench. Good.

  As described above, according to the embodiment, even if the aspect ratio of the trench 3 is high or the total volume of the trench 3 is large, the etching product 4 attached to the sidewall of the trench and the inner wall of the etching chamber 10 are formed. The adhered etching product 5 can be removed at the same time. Therefore, since it is not necessary to perform the dry cleaning process on the inner wall of the etching chamber 10 using a dummy wafer every time 10 wafers as products are processed continuously as in the prior art, the running cost of the trench etcher can be reduced. it can. Specifically, compared with the conventional dry cleaning process, the processing time using the dummy wafer becomes zero, so that the running cost can be reduced by 20%.

  In addition, according to the embodiment, the etching product 5 on the inner wall of the etching chamber 10 is removed every time a wafer as a product is processed, so that 50 or more wafers are continuously generated without generating black silicon. Can be processed. Further, since the etching product removing process is performed in the same etching chamber 10 immediately after the trench forming process, the gas or radical reaches the depth of the trench 3 and the etching product 4 in the trench 3 is removed with good uniformity. be able to. Therefore, an effect that the yield rate of devices is improved can be obtained. Moreover, since the etching product 5 attached to the inner wall of the etching chamber 10 is removed every time one wafer is processed, the atmosphere in the etching chamber 10 at the time of trench formation is unified for all wafers. The effect of improving the uniformity of the trench shape in the lot can be obtained.

  As described above, the present invention is not limited to the above-described embodiment, and various modifications can be made. For example, the dimensions such as the above-described trench, the gas type and flow rate during the etching process, the pressure in the chamber, the processing time, the power, and the like are merely examples, and the present invention is not limited thereto.

  As described above, the method for manufacturing a semiconductor device according to the present invention is useful for manufacturing a trench isolation structure or a trench capacitor structure, or for manufacturing a semiconductor element having an insulated gate structure on a trench side wall. It is suitable for a trench formation process of a high voltage MOSFET used for a power device or the like.

It is explanatory drawing for demonstrating the manufacturing method concerning Embodiment 1 of this invention. It is explanatory drawing for demonstrating the manufacturing method concerning Embodiment 1 of this invention. It is explanatory drawing for demonstrating the manufacturing method concerning Embodiment 2 of this invention. It is explanatory drawing for demonstrating the manufacturing method concerning Embodiment 2 of this invention. It is a figure which shows the microscope picture which shows a mode that the etching product in the trench after an etching product removal process was removed. It is a figure which shows the microscope picture which shows a mode that the etching product has adhered in the trench. It is a characteristic view which shows the relationship between the number of black silicon produced | generated on a wafer, and the trench total volume in a wafer. It is a figure which shows the microscope picture which shows a mode that the etching product remains in the trench after the conventional HF washing | cleaning. It is a figure which shows the microscope picture which shows a mode that the etching product remains in the trench after the conventional HF washing | cleaning. It is a figure which shows the microscope picture which shows a mode that the etching product remains in the trench after the conventional HF washing | cleaning. It is a figure which shows the microscope picture which shows a mode that the etching product remains in the trench after the conventional HF washing | cleaning. It is a figure which shows the microscope picture which shows a mode that the shape of the trench formed on the conditions which an etching product does not generate | occur | produce is disordered. It is a figure which shows the microscope picture which shows a mode that the shape of the trench formed on the conditions which an etching product does not generate | occur | produce is disordered.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 3 Trench 4, 5 Etching product 10 Etching chamber 11, 13 Plasma 12, 14 Gas

Claims (4)

A gas for etching a semiconductor material constituting the semiconductor substrate is introduced into an etching chamber containing the semiconductor substrate, plasma is generated in the etching chamber, and the semiconductor substrate is etched by the etching action of the plasma. Forming a trench in the semiconductor substrate;
Into the same etching chamber, a gas for etching the etching product generated during the formation of the trench is introduced, plasma is generated in the etching chamber, and the etching action of the plasma causes the formation of the trench. Etching and removing both the etching product attached to the sidewall of the trench and the etching product attached to the inner wall of the etching chamber;
A method for manufacturing a semiconductor device, comprising:   The method of manufacturing a semiconductor device according to claim 1, wherein in the step of removing the etching product, etching is performed without applying bias power.   The method for manufacturing a semiconductor device according to claim 1, wherein in the step of removing the etching product, etching is performed using a gas containing Ar. The method for manufacturing a semiconductor device according to claim 1, wherein in the step of forming the trench, a trench having a total volume in the substrate surface of the trench of 30 mm ³ or more is formed.

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