JP2007165767A - Semiconductor device and method of manufacturing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device capable of suppressing an increase in the fraction defective of a flash memory, when the flash memory and other semiconductor devices are mounted mixedly. <P>SOLUTION: The method includes a step of preparing a semiconductor substrate 1, having a first region 1a where the flash memory is formed, and a second region 1b where a transistor is formed; a process for introducing impurities to the semiconductor substrate 1 positioned at the second region 1b; a step of forming a protective film 3 on the semiconductor substrate 1 positioned at a first region 1a; a step of forming low-concentration impurity regions 26a, 26b of transistors by thermally diffusing impurities by heat-treating the semiconductor substrate 1 under a nitrogen atmosphere; a step of removing the protective film 3; and a step of forming a tunnel insulating film 11 by thermally oxidizing the semiconductor substrate 1 positioned at the first region 1a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device including a flash memory and a semiconductor device. In particular, the present invention relates to a semiconductor device manufacturing method and a semiconductor device capable of suppressing an increase in the defect rate of the flash memory when the flash memory and other semiconductor elements are mixedly mounted.

FIG. 3 is a cross-sectional view for explaining the configuration of a conventional semiconductor device. The semiconductor device shown in this figure has a flash memory. This flash memory has a structure in which a tunnel insulating film 101, a floating gate 102, an insulating film 103, and a control gate 104 are laminated in this order. The tunnel insulating film 101 is formed by a thermal oxidation method (see, for example, Patent Document 1).
Japanese Patent Laying-Open No. 2003-124359 (FIG. 8)

  In recent years, flash memories and transistors and other semiconductor elements are formed on the same semiconductor substrate. In such a mixed structure, an impurity region of a semiconductor element (for example, a low concentration impurity region of a transistor) may be formed before forming a tunnel insulating film of a flash memory. In order to form the impurity region, it is necessary to apply heat treatment to the semiconductor substrate into which the impurity is introduced. If this heat treatment is performed in a general nitrogen atmosphere, nitrides are formed on the surface of the semiconductor substrate. For the reason, the quality of the tunnel insulating film is lowered, and there is a possibility that the defect rate of the flash memory is increased.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a semiconductor device capable of suppressing an increase in the defect rate of flash memory when the flash memory and other semiconductor elements are mixedly mounted. A manufacturing method and a semiconductor device are provided.

In order to solve the above problems, a method of manufacturing a semiconductor device according to the present invention includes a step of preparing a semiconductor substrate including a first region where a flash memory is formed and a second region where a transistor is formed;
Introducing an impurity into a semiconductor substrate located in the second region;
Forming a protective film on the semiconductor substrate located in the first region;
Forming a low-concentration impurity region of the transistor by thermally diffusing the impurity by heat-treating the semiconductor substrate in a nitrogen atmosphere;
Removing the protective film;
Forming a tunnel insulating film by thermally oxidizing the semiconductor substrate located in the first region.

  According to this method for manufacturing a semiconductor device, since the impurity in the low-concentration impurity region of the transistor is thermally diffused after forming the protective film, a nitride or the like is formed on the surface of the semiconductor substrate located in the first region. Is not formed. Therefore, the occurrence of defects or the like in the tunnel insulating film is suppressed, and the occurrence of defects (for example, a decrease in data retention rate) in the flash memory is suppressed.

  After the step of forming the tunnel insulating film, a step of forming a floating gate positioned on the tunnel insulating film, a step of forming an insulating film positioned on the floating gate, and a control positioned on the insulating film A step of forming a gate; a step of forming a gate insulating film in the second region; a step of forming a gate electrode located on the gate insulating film; and two impurities serving as a source and a drain in the semiconductor substrate Forming a region.

Forming a LOCOS oxide film located on each of the two low-concentration impurity regions before the step of forming the gate insulating film of the transistor;
In the step of forming the gate insulating film, the gate insulating film is formed on the semiconductor substrate located between the two low-concentration impurity regions,
In the step of forming the two impurity regions, the impurity region may be formed in the semiconductor substrate located on the opposite side of the gate insulating film with the low concentration impurity region interposed therebetween. In this case, the withstand voltage of the transistor is, for example, 10V or more.

Another method of manufacturing a semiconductor device according to the present invention includes a step of preparing a semiconductor substrate having a first region and a second region in which a flash memory is formed,
Introducing an impurity into a semiconductor substrate located in the second region;
Forming a protective film on the semiconductor substrate located in the first region;
A step of thermally diffusing the impurity to form an impurity region located in the second region by heat-treating the semiconductor substrate in a nitrogen atmosphere;
Removing the protective film;
Forming a tunnel insulating film by thermally oxidizing the semiconductor substrate located in the first region.

A semiconductor device according to the present invention includes a flash memory formed in a first region of a semiconductor substrate and having a tunnel insulating film formed by thermally oxidizing the semiconductor substrate;
A transistor formed in the second region of the semiconductor substrate and including a gate insulating film, a gate electrode, two low-concentration impurity regions, and two impurity regions serving as a source and a drain;
Comprising
The two low-concentration impurity regions are formed by thermally diffusing impurities in a nitrogen atmosphere after forming a protective film on the semiconductor substrate.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 and 2 are cross-sectional views for explaining a method of manufacturing a semiconductor device according to an embodiment of the present invention. In the semiconductor device manufactured according to the present embodiment, the flash memory and the high breakdown voltage transistor are formed on the same silicon substrate 1. The flash memory is formed in the first region 1a of the silicon substrate 1, and the high breakdown voltage transistor is formed in the second region 1b of the silicon substrate 1.

  First, as shown in FIG. 1A, a photoresist film 50 is applied on the silicon substrate 1, and the photoresist film 50 is exposed and developed. As a result, two openings 50a are formed in the photoresist film 50 located on the second region 1b. Next, impurities are introduced into the silicon substrate 1 using the photoresist film 50 as a mask. Thereby, low-concentration impurity regions 26a and 26b of the high breakdown voltage transistor are formed in the silicon substrate 1 located in the second region 1b.

  Thereafter, the photoresist film 50 is removed as shown in FIG. Next, a protective film 3 is formed on the entire surface including the silicon substrate 1 located in the first region 1a by a CVD method or a sputtering method. The protective film 3 may be any film that does not allow silicon and nitrogen to permeate in an impurity thermal diffusion process described later. Specifically, it is a film formed by laminating one film selected from the group consisting of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, and a silicon film, or a plurality of films selected from the group.

  Next, the silicon substrate 1 is heat-treated in a nitrogen atmosphere. The heat treatment temperature at this time is 1150 ° C., for example. Thereby, the impurities in the low-concentration impurity regions 26a and 26b are thermally diffused. In this step, since the silicon substrate 1 is covered with the protective film 3, no nitride or the like is formed on the surface of the silicon substrate 1 located in the first region 1a.

  Thereafter, as shown in FIG. 1C, the protective film 3 is removed. Next, a silicon oxide film 4 is formed on the silicon substrate 1 by a CVD method, and a silicon nitride film 5 is further formed on the silicon oxide film 4 by a CVD method. Next, a resist pattern (not shown) is formed on the silicon nitride film 5, and the silicon nitride film 5 is selectively etched using the resist pattern as a mask. Thereby, an opening pattern 5 a is formed in the silicon nitride film 5. A part of the opening pattern 5a is located above each of the low-concentration impurity regions 26a and 26b. In this step, part or all of the silicon oxide film 4 located in the opening pattern 5a is removed.

  Next, the silicon substrate 1 is thermally oxidized using the silicon nitride film 5 as a mask. As a result, a LOCOS oxide film 2 that functions as an element isolation film is formed on the silicon substrate 1. Note that the LOCOS oxide film 2 is also formed on the low-concentration impurity regions 26a and 26b.

  Thereafter, as shown in FIG. 2A, the silicon nitride film 5 and the silicon oxide film 4 are removed. Next, a photoresist film 51 is applied on the silicon substrate 1 and the LOCOS oxide film 2, and the photoresist film 51 is exposed and developed. Thereby, the photoresist film 51 located on the first region 1a is removed. Next, impurities are introduced into the silicon substrate 1 using the photoresist film 51 as a mask. Thereby, an impurity region 10 is formed in the silicon substrate 1 located in the first region 1a.

  Thereafter, the photoresist film 51 is removed as shown in FIG. Next, the silicon substrate 1 is thermally oxidized. Thereby, a tunnel insulating film 11 of the flash memory is formed on the silicon substrate 1. As described above, since the impurity thermal diffusion process of the low concentration impurity regions 26a and 26b is performed after the protective film 3 is formed, nitride or the like is formed on the surface of the silicon substrate 1 located in the first region 1a. Not formed. Therefore, it is possible to suppress the occurrence of defects or the like in the tunnel insulating film 11.

Next, a floating gate 12 made of a polysilicon film is formed on the tunnel insulating film 11 by the CVD method. Thereafter, impurities are introduced into the floating gate 12. Next, the floating gate 12 is thermally oxidized. As a result, an insulating film 13 is formed on the floating gate 12. Next, a control gate 14 made of a polysilicon film is formed on the insulating film 13 by a CVD method. Next, a resist pattern (not shown) is formed on the control gate 14, and the control gate 14, the insulating film 13, the floating gate 12, and the tunnel insulating film 11 are selectively etched using the resist pattern as a mask. In this way, the flash memory located in the first area 1a is formed. As described above, since the occurrence of defects or the like in the tunnel insulating film 11 is suppressed, it is possible to suppress the occurrence of defects (for example, a decrease in the data retention rate) in the flash memory.
Thereafter, the resist pattern is removed.

  Next, as shown in FIG. 2C, the silicon substrate 1 is thermally oxidized. Thereby, the gate insulating film 23 of the high breakdown voltage transistor is formed on the silicon substrate 1 located between the low-concentration impurity regions 26a and 26b in the second region 1b. Next, a polysilicon film is formed on the entire surface including the gate insulating film 23 by the CVD method. Next, a resist pattern (not shown) is formed on the polysilicon film, and the polysilicon film is selectively etched using this resist pattern as a mask. As a result, the gate electrode 24 is formed on the gate insulating film 23 and on the LOCOS oxide film 2 located therearound. Thereafter, the resist pattern is removed.

Next, impurities are introduced into the silicon substrate 1 using the LOCOS oxide film 2 and the gate electrode 24 as a mask. As a result, impurity regions 27a and 27b serving as the source and drain of the high breakdown voltage transistor are formed in the silicon substrate 1 located in the second region 1b. The impurity regions 27a and 27b are located on the opposite side of the gate insulating film 23 with the low-concentration impurity regions 26a and 26b interposed therebetween.
In this manner, a high breakdown voltage transistor is formed in the second region 1b.

  As described above, according to the embodiment of the present invention, after the protective film 3 is formed on the silicon substrate 1, the impurities in the low-concentration impurity regions 26a and 26b of the high breakdown voltage transistor are thermally diffused. For this reason, nitride or the like is not formed on the surface of the silicon substrate 1 located in the first region 1a. Therefore, the occurrence of defects or the like in the tunnel insulating film 11 is suppressed, and the occurrence of defects (for example, a decrease in the data retention rate) in the flash memory is suppressed.

  Note that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the structure of the flash memory is not limited to the above-described embodiment as long as the tunnel insulating film is formed by thermally oxidizing the silicon substrate 1. Further, the semiconductor element formed in the second region 1b is not limited to the high breakdown voltage transistor, and the present invention is applied as long as heat treatment (for example, heat treatment for impurity diffusion) is performed before the tunnel insulating film is formed. Is possible.

Each drawing is a sectional view for explaining the method for manufacturing the semiconductor device according to the first embodiment. Each drawing is a cross-sectional view for explaining the next step of FIG. Sectional drawing for demonstrating the structure of the conventional semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate, 1a ... 1st area | region, 1b ... 2nd area | region, 2 ... LOCOS oxide film, 3 ... Protective film, 4 ... Silicon oxide film, 5 ... Silicon nitride film, 5a ... Opening pattern, 10 ... Impurity area | region, DESCRIPTION OF SYMBOLS 11,101 ... Tunnel insulating film, 12, 102 ... Floating gate, 13, 103 ... Insulating film, 14, 104 ... Control gate, 23 ... Gate insulating film, 24 ... Gate electrode, 26a, 26b ... Low concentration impurity region, 27a 27b ... impurity region 50, 51 ... photoresist film 50a ... opening

Claims (7)

Preparing a semiconductor substrate having a first region in which a flash memory is formed and a second region in which a transistor is formed;
Introducing an impurity into a semiconductor substrate located in the second region;
Forming a protective film on the semiconductor substrate located in the first region;
Forming a low-concentration impurity region of the transistor by thermally diffusing the impurity by heat-treating the semiconductor substrate in a nitrogen atmosphere;
Removing the protective film;
Forming a tunnel insulating film by thermally oxidizing the semiconductor substrate located in the first region;
A method for manufacturing a semiconductor device comprising:   2. The protective film is a silicon oxide film or a film selected from the group consisting of a silicon nitride film, a silicon oxynitride film, and a silicon film, or a film in which a plurality of films selected from the group are stacked. The manufacturing method of the semiconductor device of description. After the step of forming the tunnel insulating film,
Forming a floating gate located on the tunnel insulating film;
Forming an insulating film located on the floating gate;
Forming a control gate located on the insulating film;
Forming a gate insulating film in the second region;
Forming a gate electrode located on the gate insulating film;
Forming two impurity regions to be a source and a drain on the semiconductor substrate;
The manufacturing method of the semiconductor device of Claim 1 or 2 which comprises these. Forming a LOCOS oxide film located on each of the two low-concentration impurity regions before the step of forming the gate insulating film of the transistor;
In the step of forming the gate insulating film, the gate insulating film is formed on the semiconductor substrate located between the two low-concentration impurity regions,
The semiconductor device manufacturing method according to claim 3, wherein in the step of forming the two impurity regions, the impurity region is formed in the semiconductor substrate located on the opposite side of the gate insulating film with the low-concentration impurity region interposed therebetween. Method.   The method for manufacturing a semiconductor device according to claim 4, wherein a breakdown voltage of the transistor is 10 V or more. Preparing a semiconductor substrate having a first region and a second region in which a flash memory is formed;
Introducing an impurity into a semiconductor substrate located in the second region;
Forming a protective film on the semiconductor substrate located in the first region;
A step of thermally diffusing the impurity to form an impurity region located in the second region by heat-treating the semiconductor substrate in a nitrogen atmosphere;
Removing the protective film;
Forming a tunnel insulating film by thermally oxidizing the semiconductor substrate located in the first region;
A method for manufacturing a semiconductor device comprising: A flash memory having a tunnel insulating film formed in a first region of a semiconductor substrate and formed by thermally oxidizing the semiconductor substrate;
A transistor having a gate insulating film, a gate electrode, two low-concentration impurity regions, and two second impurity regions to be a source and a drain formed in the second region of the semiconductor substrate;
Comprising
The two low-concentration impurity regions are formed by thermally diffusing impurities in a nitrogen atmosphere after forming a protective film on the semiconductor substrate.

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