JP2013254788A - Semiconductor device and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a two-layer polysilicon capacity element capable of suppressing both an initial defect of a dielectric film and deterioration in an intrinsic breakdown life.SOLUTION: A semiconductor device includes: a lower electrode 3a into which a phosphorus ion is implanted; a dielectric film 6a which is formed on the lower electrode 3a; and an upper electrode 7a which is formed on the dielectric film 6a and into which an impurity is implanted. The dielectric film 6a includes a thermal oxide film 5 formed by oxidizing a part of a polysilicon film 3 which serves as the lower electrode 3a later and a thick film oxide film 6 formed by reoxidizing the thermal oxide flim after a surface layer part of the thermal oxide film is etched out.

Description

  The present invention relates to a semiconductor device and a method for manufacturing the semiconductor device related to a semiconductor capacitor having a low resistance polysilicon and a silicon oxide film as a dielectric.

One of capacitive elements of a semiconductor integrated circuit is a capacitive element made of two-layer polysilicon (hereinafter referred to as a two-layer polysilicon capacitive element). The two-layer polysilicon capacitive element has a configuration in which a silicon oxide film serving as a dielectric is sandwiched between an upper electrode and a lower electrode.
A polysilicon film whose resistance is reduced by doping with impurities such as phosphorus is often used for the upper electrode and the lower electrode of the two-layer polysilicon capacitor. The silicon oxide film between the upper electrode and the lower electrode is generally formed by oxidizing a part of the polysilicon film that has become the lower electrode.

However, in the silicon oxide film formed by directly thermally oxidizing the polysilicon film containing impurities such as phosphorus, impurities remain in the silicon oxide film, resulting in a decrease in breakdown voltage of the two-layer polysilicon capacitor element and an initial defect. There are disadvantages such as occurrence.
The above disadvantages can be suppressed by using a deposited silicon oxide film that does not contain impurities. Generally, however, a deposited silicon oxide film contains more silicon dangling bonds than a thermal silicon oxide film, resulting in leakage current. And has other disadvantages such as deterioration of breakdown voltage and intrinsic fracture life.

As a prior art of the two-layer polysilicon capacitor, for example, there is “insulating film manufacturing method of semiconductor device” described in Patent Document 1. In the semiconductor capacitor device described in Patent Document 1, a laminated structure of a thermal silicon oxide film and a silicon oxide film deposited by a low pressure CVD (Chemical Vapor Deposition) method is used as a dielectric.
However, in the invention described in Patent Document 1, since the dielectric is formed by combining the thermal silicon oxide film and the deposited silicon oxide film, the deposited silicon oxide film contains no impurities, and the impurity concentration of the entire dielectric is reduced. Although suppressed, since the thermal silicon oxide film contains a large amount of impurities, defects cannot be sufficiently suppressed. In addition, the deposited silicon oxide film contains more silicon dangling bonds than the thermal silicon oxide film, and the leakage current is large, and the breakdown voltage and intrinsic breakdown life cannot be avoided. There are limitations.

JP-A-3-280466

  The present invention has been made in view of the above-described point, and in a single layer structure of a thermal silicon oxide film, the thermal silicon oxide film does not contain impurities, and can suppress both degradation of intrinsic fracture life and initial defects. An object of the present invention is to provide a semiconductor device configured as a layer polysilicon capacitor and a method of manufacturing the semiconductor device.

The gist of the present invention is as follows.
(1) A first polysilicon film into which impurities are implanted, a dielectric film formed on the first polysilicon film, and a second polysilicon into which impurities are implanted, formed on the dielectric film. A semiconductor device comprising a polysilicon film of
The dielectric film includes a thermal oxide film in which a surface layer portion of a thermal oxide film formed by oxidizing a part of the first polysilicon film is etched out, and the etched out thermal oxide film is reoxidized. And a thick oxide film formed as described above.
(2) The semiconductor device according to (1), wherein an etch-out amount of a surface layer portion of the thermal oxide film is 1 nm or more.
(3) forming a first polysilicon film on the field oxide film on the substrate;
Injecting impurities into the first polysilicon film;
Oxidizing the first polysilicon film to form a thermal oxide film;
Etching the surface layer portion of the thermal oxide film; reoxidizing the etched thermal oxide film to form a thick oxide film;
Forming a second polysilicon film on the thick oxide film;
Injecting impurities into the second polysilicon film;
A method for manufacturing a semiconductor device comprising:
(4) Further, an upper electrode forming step of patterning the second polysilicon film, the thermal oxide film and the thick film oxide film to form an upper electrode and a dielectric film;
A lower electrode forming step of patterning the first polysilicon film to form a lower electrode;
The method for manufacturing a semiconductor device according to the above (3), characterized by comprising:
(5) The method for manufacturing a semiconductor device according to (3) or (4), wherein an etch-out amount of a surface layer portion of the thermal oxide film is 1 nm or more.

Hereinafter, a semiconductor device and a manufacturing method thereof according to the present invention will be described with reference to the drawings.
The semiconductor device of the present invention includes a lower electrode (for example, the lower electrode 3a shown in FIG. 1) made of a first polysilicon film into which impurities are implanted, and a dielectric film (for example, shown in FIG. 1). A semiconductor device including the dielectric film 6a) and an upper electrode (for example, the upper electrode 7a shown in FIG. 1) formed on the dielectric film and made of a second polysilicon film into which impurities are implanted. The dielectric film 6a includes a thermal oxide film formed by oxidizing a part of the first polysilicon film, a thick oxide film whose surface layer portion is etched out and re-oxidized, It is characterized by including.

  In the method of manufacturing a semiconductor device according to the present invention, the first polysilicon film (for example, the polysilicon film 3 ′ illustrated in FIG. 2A) is formed on the insulating layer (for example, the field oxide film 2 illustrated in FIG. 2A). A first polysilicon film forming step (for example, the step shown in FIG. 2A) for forming a film, and an impurity is implanted into the first polysilicon film to reduce the resistance of the first polysilicon film. 1 impurity implantation step (for example, the step shown in FIG. 2A) and the first polysilicon film 3 whose resistance has been lowered by the first impurity implantation step is oxidized to form a thermal oxide film (for example, FIG. 2C The thermal oxidation step (for example, the step shown in FIG. 2C) for forming the thermal oxide film 5) shown in FIG. 2) and the etching step for wet etching the surface layer portion of the thermal oxide film with a hydrogen fluoride aqueous solution (for example, FIG. 2 (d), and reoxidizing the thermal oxide film. A thermal oxidation process for forming a thick oxide film (for example, the process shown in FIG. 2E), and a second polysilicon film (for example, the polysilicon film 7 shown in FIG. 2F) on the thick oxide film. And a second impurity implantation step (for example, FIG. 2F) for implanting impurities into the second polysilicon film and reducing the resistance of the second polysilicon film 7 ′. And the second polysilicon film 7, the thermal oxide film 5, and the thick oxide film 6 that have been reduced in resistance are patterned to form an upper electrode (for example, the upper electrode 7a shown in FIG. 3G). And the upper electrode forming step for forming the dielectric film 6a (for example, the step shown in FIG. 3G) and the first polysilicon film are patterned to form the lower electrode (for example, shown in FIG. 3H). Lower electrode forming step for forming the lower electrode 3a) (for example, FIG. 3H) And indicated step), characterized in that it comprises a.

In the method for manufacturing a semiconductor device according to the present invention, in the above-described invention, in the thermal oxidation step, a thermal oxide film having a thickness of 10 to 15 nm is formed in an environment having a temperature of 1030 to 1050 ° C. Is desirable. In particular, it is desirable to form a thermal oxide film having a thickness of approximately 12 nm under an environment where the temperature is 1038 ° C.
In the method for manufacturing a semiconductor device according to the present invention, in the above-described invention, the thermal oxide film is heated for 45 to 55 ° C. with ammonia hydrogen peroxide for 800 to 1000 seconds and for 22 to 24 ° C. with hydrogen fluoride aqueous solution for 10 to 30 seconds. It is desirable that the substrate is cleaned and wet etched by 1 to 3 nm. In particular, it is desirable that the thermal oxide film be cleaned with ammonia hydrogen peroxide at 50 ° C. for 900 seconds, with HF: H ₂ O = 1: 99 hydrogen fluoride solution at 23 ° C. for 20 seconds, and wet etched by 2 nm.

  In the method for manufacturing a semiconductor device according to the present invention, in the above-described invention, in the reoxidation step, a thick oxide film having a thickness of 15 to 25 nm is formed in an environment at a temperature of 1030 to 1050 ° C. It is desirable. In particular, it is desirable to form a thermal oxide film having a thickness of approximately 20 nm under an environment where the temperature is 1038 ° C.

  The inventor of the present invention has made extensive studies to solve the above problems, that is, according to the invention of the first embodiment, a polysilicon film is formed and phosphorus is removed by ion implantation. After reducing the resistance by introducing it into the film, the capacitor film is formed with a thermal oxide film by thermal oxidation, and the oxide film surface layer containing phosphorus at a high concentration is wet-etched with an aqueous hydrogen fluoride solution, and further reoxidized. It has been found that by supplementing the film thickness, only the initial defects can be suppressed without impairing the intrinsic fracture life.

Moreover, according to the method for manufacturing a semiconductor device of the invention of the second embodiment, there is provided a method for manufacturing a semiconductor device configured as a two-layer polysilicon capacitor element capable of suppressing both degradation of the intrinsic breakdown life and initial defects. be able to.
In addition, according to the semiconductor device manufacturing method of the invention of the third aspect, it is possible to obtain the optimum film formation condition of the thermal oxide film for the dielectric film.

It is a figure for demonstrating the structure of the semiconductor device of one Embodiment of this invention. It is sectional drawing which shows the process of the manufacturing method of the semiconductor device of one Embodiment of this invention. It is sectional drawing which shows the process of the manufacturing method of the semiconductor device performed following the process of one Embodiment of this invention. It is a graph showing the thermal oxide film wet etch amount and initial stage defect density for showing the effect of this invention.

Hereinafter, embodiments of the present invention will be specifically described.
(Semiconductor device)
FIG. 1 is a diagram for explaining the configuration of the semiconductor device of this embodiment. The illustrated semiconductor device is formed on a lower electrode 3a made of a polysilicon film in which phosphorus ions (P ⁺ ) are implanted as impurities, a dielectric film 6a formed on the lower electrode 3a, and a dielectric film 6a. And a dielectric film 6a is a thermal oxide film 5 made of a thermal oxide film formed by oxidizing a part of the polysilicon film. And a thick oxide film 6 formed by re-oxidizing the thermal oxide film 5.

Here, in the present embodiment, the surface layer portion of the thermal oxide film 5 is etched. The surface layer portion refers to a region of 1 nm or more from the outermost surface of the thermal oxide film 5, for example. That is, when the wet etching amount of the thermal oxide film is less than 1 nm, the initial defect density cannot be sufficiently suppressed.
In the present embodiment, the lower electrode 3a is formed on the field oxide film 2 formed on the silicon substrate 1.

(Semiconductor device manufacturing method)
2A to 2F and FIG. 3G to FIG. 3H are cross-sectional views for explaining the semiconductor device manufacturing method of the present invention in the order of steps.
As shown in FIG. 2A, in the present embodiment, first, a field oxide film 2 for element isolation is formed on a silicon substrate 1. Then, a non-doped polysilicon film 3 ′ is formed on the field oxide film 2. A protective oxide film 4 for impurity implantation (doping) is formed on the non-doped polysilicon film 3 ′ by a low pressure CVD method.

Next, phosphorus ions are doped as impurities from above the protective oxide film 4. By doping with phosphorus ions, the non-doped polysilicon film on the field oxide film 2 becomes a polysilicon film 3 containing a high concentration of phosphorus ions. This polysilicon film 3 will later become the lower electrode 3a.
Next, in the present embodiment, as shown in FIG. 2B, the protective oxide film 4 is removed. The removal of the protective oxide film 4 is performed by washing with a solution such as an aqueous hydrogen fluoride solution, an ammonia perwater solution, or an aqueous hydrogen fluoride solution. Optimization can be achieved by appropriately combining the treatment solution, treatment temperature and treatment time.

  Next, as shown in FIG. 2C, heat treatment is performed in an oxygen atmosphere at 1030 to 1050 ° C. for 7 to 25 seconds to form a thermal oxide film 5 on the polysilicon film 3. As shown in FIG. 2D, the formed thermal oxide film 5 is cleaned with a solution such as ammonia perwater, hydrochloric acid perwater, or aqueous hydrogen fluoride. The cleaning conditions for the thermal oxide film can be optimized by appropriately combining the processing solution, the processing temperature, and the processing time.

After the cleaning, as shown in FIG. 2E, the thermal oxide film 5 is re-oxidized to form a thick oxide film 6. The thick oxide film 6 is formed by heat treatment for 5 to 140 seconds in an oxidizing atmosphere of 1030 to 1050 ° C. For example,
Next, as shown in FIG. 2E, a non-doped polysilicon film 7 ′ (not shown) is formed on the thick oxide film 6. The formed non-doped polysilicon film 7 ′ is also doped with phosphorus ions. By doping, the non-doped polysilicon film becomes a polysilicon film 7 containing a high concentration of phosphorus ions.

Next, as shown in FIG. 3G, the thermal oxide film 5, the thick oxide film 6, and the polysilicon film 7 are patterned by photolithography and etching. By patterning, the upper electrode 7a and the dielectric film 6a are formed. Subsequently, in the present embodiment, as shown in FIG. 3H, the polysilicon film 3 is patterned by photolithography and etching. The patterned polysilicon film 3 becomes the lower electrode 3a.
After the above steps, impurities are doped in a source / drain formation region (not shown). At this time, phosphorus ions doped in the upper electrode 7a are activated.

Next, a method for manufacturing a semiconductor device of the present invention will be described based on examples.
Example 1
As shown in FIG. 2A, in this embodiment, first, a field oxide film 2 for element isolation is formed on a silicon substrate 1. Then, a non-doped polysilicon film 3 ′ is formed on the field oxide film 2 at 365 nm. A protective oxide film 4 for impurity implantation (doping) is formed on the non-doped polysilicon film by a low pressure CVD method. The thickness of the protective oxide film 4 is 10 nm.

  Next, in this embodiment, phosphorus ions are doped as impurities from above the protective oxide film 4. By doping with phosphorus ions, the non-doped polysilicon film on the field oxide film 2 becomes a polysilicon film 3 containing a high concentration of phosphorus ions. This polysilicon film 3 will later become the lower electrode 3a. In the present embodiment, for example, phosphorus ions are doped under the conditions of 20 keV and 1.4 × E16.

Next, in this embodiment, as shown in FIG. 2B, the protective oxide film 4 is removed. The protective oxide film 4 is removed by, for example, cleaning with a hydrogen fluoride aqueous solution of HF: H ₂ O = 1: 19 for 40 seconds, and NH ₃ : H ₂ O: H ₂ O ₂ = 1: 10: 2 at 80 ° C. This is carried out by continuously performing cleaning with ammonia overwater for 600 seconds and cleaning with 23 ° C. HF: H ₂ O = 1: 99 hydrogen fluoride aqueous solution for 50 seconds.

Next, in this embodiment, a heat treatment is performed in an oxygen atmosphere at 1038 ° C. for 14 seconds to form a 12 nm thermal oxide film 5 on the polysilicon film 3. The formed thermal oxide film 5 was formed by using HCl overwater at 50 ° C. with NH ₃ : H ₂ O: H ₂ O ₂ = 1: 10: 2 for 900 seconds at 80 ° C. HCL: H ₂ O: H ₂ O _2. = 1: 5: 1 Hydrochloric acid over water for 600 seconds and 23 ° C. HF: H ₂ O = 1: 99 hydrogen fluoride aqueous solution for 14 seconds. Here, the wet etching amount of the thermal oxide film 5 was 1.7 nm when measured as a capacitance value using an LCR meter.
After cleaning, the thermal oxide film 5 is re-oxidized to form a 20 nm thick oxide film 6. The heat treatment is performed for 64 seconds in an oxygen atmosphere at 1038 ° C.

  Next, as shown in FIG. 3G, in this embodiment, a non-doped polysilicon film 7 'is formed on the thick oxide film 6 at 365 nm. As shown in FIG. 3F, the formed non-doped polysilicon film 7 ′ is also doped with phosphorus ions under the conditions of 50 keV and 7.0 × E15. By doping, the non-doped polysilicon film becomes a polysilicon film 7 containing a high concentration of phosphorus ions.

Next, as shown in FIG. 3G, in this embodiment, the thermal oxide film 5, the thick oxide film 6, and the polysilicon film 7 are patterned by photolithography and etching. By patterning, the upper electrode 7a and the dielectric film 6a are formed. Subsequently, in this embodiment, as shown in FIG. 3H, the polysilicon film 3 is patterned by photolithography and etching. The patterned polysilicon film 3 becomes the lower electrode 3a.
After the above steps, impurities are doped in a source / drain formation region (not shown). At this time, phosphorus ions doped in the upper electrode 7a are activated. Further, when the initial defect density of the semiconductor device manufactured in this example was evaluated using a prober, it was 0.30 cm ⁻² .

(Example 2)
A semiconductor device is manufactured under the same conditions as in Example 1 except that the conditions for etching the thermal oxide film are changed as follows (20 ° C. with an aqueous hydrogen fluoride solution of HF: H ₂ O = 1: 99 at 23 ° C.). did. Here, the wet etching amount of the thermal oxide film 5 was 1.9 nm as measured using an LCR meter. In addition, when the initial defect density of the semiconductor device manufactured in this example was evaluated using a prober, it was 0.12 cm ⁻² .

(Example 3)
A semiconductor device is manufactured under the same conditions as in Example 1 except that the conditions for etching the thermal oxide film are changed as follows (26 ° C. with an aqueous hydrogen fluoride solution of HF: H ₂ O = 1: 99 at 23 ° C.). did. Here, the wet etching amount of the thermal oxide film 5 was 2.3 nm as measured using an LCR meter. In addition, when the initial defect density of the semiconductor device manufactured in this example was evaluated using a prober, it was 0.06 cm ⁻² .

Example 4
A semiconductor device is manufactured under the same conditions as in Example 1 except that the conditions for etching the thermal oxide film are changed as follows (34 ° C. with an aqueous hydrogen fluoride solution of HF: H ₂ O = 1: 99 at 23 ° C.). did. Here, the wet etching amount of the thermal oxide film 5 was 2.7 nm as measured using an LCR meter. In addition, when the initial defect density of the semiconductor device manufactured in this example was evaluated using a prober, it was 0.06 cm ⁻² .

(Comparative example)
As an example, the semiconductor device was manufactured under the same conditions as in the first embodiment except that the thermal oxide film was not etched.
FIG. 4 shows the relationship between the thermal oxidation wet etch amount of the semiconductor device manufactured based on the first to fourth embodiments and the comparative example, and the initial defect density. By etching out the surface layer portion of the thermal oxide film as in the present invention, the initial defect density can be reduced as compared with the case where the surface layer portion is not etched out. For example, by setting the amount of wet etching to 1 nm or more, the initial defect density can be reduced to 1.0 cm ⁻² or less, which is the same as the gate oxide film formed on the silicon substrate.

  According to the semiconductor device and the manufacturing method of the semiconductor device of the present embodiment described above, since the impurity concentration of the entire dielectric film can be suppressed even if the polysilicon film is doped with a high concentration, initial defects are suppressed. it can. In addition, since the entire dielectric can be constituted only by the thermal oxide film, the capacity can be increased by reducing the thickness without deteriorating the intrinsic breakdown life.

  The present invention described above is suitable as a two-layer polysilicon capacitor element having low-resistance polysilicon and a silicon oxide film as a dielectric, and a method for manufacturing the two-layer polysilicon capacitor element.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Field oxide film 3 'Non-doped polysilicon film 3 Doped polysilicon film 3a Lower electrode 4 Protective oxide film 5 Thermal oxide film 5a Thermal oxide film 6 Thick film oxide film 6a Dielectric film 7' Non-doped polysilicon film 7 Doped polysilicon film 7a Upper electrode

Claims (5)

A first polysilicon film implanted with an impurity; a dielectric film formed on the first polysilicon film; and a second polysilicon implanted with an impurity formed on the dielectric film. A semiconductor device comprising a film,
The dielectric film includes a thermal oxide film in which a surface layer portion of a thermal oxide film formed by oxidizing a part of the first polysilicon film is etched out, and the etched out thermal oxide film is reoxidized. And a thick oxide film formed as described above.   The semiconductor device according to claim 1, wherein an etch-out amount of a surface layer portion of the thermal oxide film is 1 nm or more. Forming a first polysilicon film on the field oxide film on the substrate;
Injecting impurities into the first polysilicon film;
Oxidizing the first polysilicon film to form a thermal oxide film;
Etching the surface layer portion of the thermal oxide film; reoxidizing the etched thermal oxide film to form a thick oxide film;
Forming a second polysilicon film on the thick oxide film;
Injecting impurities into the second polysilicon film;
A method for manufacturing a semiconductor device comprising: An upper electrode forming step of patterning the second polysilicon film, the thermal oxide film, and the thick oxide film to form an upper electrode and a dielectric film;
A lower electrode forming step of patterning the first polysilicon film to form a lower electrode;
The method of manufacturing a semiconductor device according to claim 3, wherein: The method for manufacturing a semiconductor device according to claim 3, wherein an etch-out amount of a surface layer portion of the thermal oxide film is 1 nm or more.

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