JP5261911B2 - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device, by which gate destruction due to an inclination angle of a tip part of a field oxide film formed by a LOCOS method can be suppressed. <P>SOLUTION: A pad oxide film is formed on a semiconductor substrate 20, and a SiN film 21 covering an element region is formed. A resist film where a part (short side) of the SiN film 21 is exposed is formed on the substrate 20. The SiN film 21 is etched to the middle of a thickness direction with the resist film as a mask. The resist film is removed, a surface of the substrate 20 is wet-oxidized and the field oxide film 23 is formed. Thus, the inclination angle of a tip of the field oxide film can be controlled. A phenomenon that a surface of the substrate is etched when the pad oxide film and the SiN film 21 are removed by etching is suppressed, and gate destruction is avoided. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device having an element isolation film (field oxide film) formed by a LOCOS (Local Oxidation of Silicon) method.

  When manufacturing a semiconductor device (integrated circuit), it is necessary to form an element isolation film that electrically isolates a plurality of element regions from each other. One element isolation film is a field oxide film formed by a LOCOS (Local Oxidation of Silicon) method.

  1 to 3 are diagrams showing an example of a conventional method for manufacturing a semiconductor device using a LOCOS method. In each of FIGS. 1 to 3, (a) is a plan view when the semiconductor substrate is viewed from above, and (b) is a cross-sectional view taken along the line II in (a).

  First, as shown in FIGS. 1A and 1B, after the surface of the semiconductor substrate 10 is thermally oxidized to form a pad oxide film (not shown), an SiN film (silicon nitride film) covering the element region is formed. ) 11 is formed. That is, a SiN film 11 is formed on the entire upper surface of the semiconductor substrate 10 by a CVD (chemical vapor deposition) method, and this SiN film 11 is patterned by a photolithography method and an etching method, so that the SiN film 11 is formed only on the element region. Leave.

  Next, as shown in FIGS. 2A and 2B, the surface of the semiconductor substrate 10 is wet-oxidized using the SiN film 11 as a mask to form a field oxide film 12. Thereafter, the SiN film 11 and the pad oxide film are removed by etching.

  Next, as shown in FIGS. 3A and 3B, the surface of the element region is thermally oxidized to form a gate insulating film 13. Thereafter, a polysilicon film imparted with conductivity by introducing impurities is formed on the entire upper surface of the semiconductor substrate 10 by CVD. Then, the polysilicon film is patterned by photolithography to form a gate electrode 14 traversing the element region.

  Next, impurities are ion-implanted into the surface of the element region using the gate electrode 14 as a mask to form impurity regions 15 serving as source / drain on both sides of the gate electrode 14. Next, after heat treatment is performed to activate the impurities in the impurity region 15, an interlayer insulating film, contact holes, wirings, and the like are formed on the semiconductor substrate 10. In this way, the semiconductor device is completed.

In addition, there exist some which were described in patent document 1, 2 as a prior art considered to be related to this invention. Patent Document 1 describes an example of a manufacturing method of a semiconductor device in which a field insulating film is formed by a LOCOS method. Patent Document 2 describes that a side wall made of a silicon nitride film is formed in a self-aligned manner around an element isolation film having a trench structure by etching the silicon nitride film using a silicon oxide film as a mask. Yes.
JP 7-183508 A JP-A-11-74526

  In the semiconductor device formed by the above-described method, gate breakdown may occur during a burn-in inspection for driving the semiconductor device in a high-temperature environment, and there is a problem in that the manufacturing yield decreases. From the research by the inventors of the present application, it has been found that gate breakdown is less likely to occur when the element region is a simple rectangle, but gate breakdown is more likely to occur when the element region is not a simple rectangle.

  Although the cause of the gate breakdown related to the shape of the element region is not clear, it can be considered as follows. FIG. 4 is a top view showing the surface of the semiconductor substrate 10 after the SiN film 11 and the pad oxide film are removed. In the semiconductor device manufacturing method described above, as shown in FIG. 4, the lengths of two sides intersecting the gate electrode 14 among the sides that determine the shape of the element region 10a are different from each other. Hereinafter, the shorter side (the side indicated by A in FIG. 4) of these two sides is referred to as the short side, and the longer side (the side indicated by B in FIG. 4) is referred to as the long side. The lengths of the short side and the long side of the element region 10a correspond to the lengths of the two sides of the SiN film 11, respectively. When the field oxide film 12 is formed, the length of the side of the SiN film 11 is related to the tip shape of the field oxide film 12.

  FIG. 5 is a schematic cross-sectional view showing an enlarged front end portion of the field oxide film. As shown in FIG. 5, the inclination angle of the tip of the short-side field oxide film (right-side field oxide film in FIG. 5) 12 is the long-side field oxide film (left-side field oxidation film in FIG. 5). Membrane) 12 is larger than the inclination angle of the tip. As described above, when the inclination angle of the tip of the field oxide film 12 is increased, the surface of the semiconductor substrate near the tip of the field oxide film 12 is etched when the SiN film 11 and the pad oxide film are removed by etching, and a gate is formed at that portion. The polysilicon constituting the electrode 14 enters and conductive projections (portions enclosed by circles in FIG. 5) are formed. As a result, charges are concentrated on the protruding portion during burn-in inspection, and gate breakdown occurs.

  In view of the above, an object of the present invention is to provide a method for manufacturing a semiconductor device capable of suppressing gate breakdown due to the inclination angle of the tip of a field oxide film formed by the LOCOS method.

According to one aspect of the present invention, a plurality of sides including a first side and a second side longer than the first side are arranged on the semiconductor substrate in a plan view from above the semiconductor substrate. A step of forming a SiN film, a step of forming a resist film covering the second side and exposing the first side, and a portion of the SiN film not covered by the resist film in the thickness direction A step of etching halfway, a step of removing the resist film, a surface of the semiconductor substrate is thermally oxidized using the SiN film as a mask, a field oxide film is formed, and a plan view from above the semiconductor substrate And delimiting an element region having a plurality of sides including a third side and a fourth side longer than the third side on the semiconductor substrate, and removing the SiN film. Forming a gate insulating film on the element region; On the gate insulating film, forming a gate electrode that crosses over the element region and intersects the third side and the fourth side; and impurities in the element region on both sides of the gate electrode A method for manufacturing a semiconductor device is provided.

  In the present invention, after forming the SiN film, a resist film in which a part of the SiN film is exposed is formed on the semiconductor substrate. Then, the portion of the SiN film not covered with the resist film is etched to reduce the thickness.

  By reducing the thickness of the SiN film in this way, the inclination angle of the tip of the field oxide film is reduced. When the element region is not rectangular, the inclination angle of the tip of the field oxide film is larger on the short side than on the long side, and therefore, by reducing the thickness of the SiN film on the short side as described above, the short side The inclination angle of the tip on the side can be reduced similarly to the inclination angle of the tip of the field oxide film on the long side. This suppresses etching of the substrate when removing the SiN film and the pad oxide film, avoids the generation of conductive protrusions, and prevents gate breakdown during burn-in inspection.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  6 to 10 are views showing the semiconductor device manufacturing method according to the embodiment of the present invention in the order of steps. 6 to 10, (a) is a plan view of the semiconductor substrate as viewed from above, and (b) is a cross-sectional view taken along the line II-II in (a).

  First, as shown in FIGS. 6A and 6B, the surface of a semiconductor substrate (for example, a silicon wafer) 20 is thermally oxidized to form a pad oxide film (not shown) with a thickness of, for example, 20 nm. A SiN film 21 covering the element region is formed thereon. That is, the SiN film 21 is formed to a thickness of, for example, 120 nm on the entire upper surface of the semiconductor substrate 20 by the CVD method. Thereafter, a photoresist is applied on the SiN film 21 to form a photoresist film, and the photoresist film is exposed through a predetermined exposure mask, followed by development processing to form a resist pattern (FIG. (Not shown). Next, the SiN film 21 is etched by, for example, RIE (reactive ion etching) using the resist pattern as a mask to leave the SiN film 21 only on the element region. Thereafter, the photoresist film is removed.

  Next, a photoresist is applied to the entire upper surface of the semiconductor substrate 20 to form a photoresist film having a thickness of, for example, 0.75 μm. Thereafter, the photoresist film is exposed to a stepper and then developed to form a resist pattern 22 in which a part of the SiN film 21 is exposed as shown in FIGS. 7 (a) and 7 (b). It is important that the resist pattern 22 is formed so as to cover the long side portion of the SiN film 21 and expose the short side portion. In the present embodiment, of the sides of the element region, the longer side of two sides intersecting with a gate electrode described later is called the long side, and the shorter side is called the short side.

Next, as shown in FIGS. 8A and 8B, the SiN film 21 is etched into a rectangular shape halfway in the thickness direction (for example, half) by using the resist pattern 22 as a mask. The film is partially thinned. Etching at this time is performed by dry etching using, for example, CF ₄ gas and O ₂ gas. Next, the resist pattern 22 is removed by ashing.

  Next, the semiconductor substrate 20 is heated to, for example, 900 ° C., and the portion of the surface of the semiconductor substrate 20 that is not covered with the SiN film 21 is wet-oxidized. As a result, as shown in FIGS. 9A and 9B, the portion not covered with the SiN film 21 is thickened, and a field oxide film (LOCOS) 23 is formed. The thickness of this field oxide film 23 is, for example, 500 nm.

  In the present embodiment, as shown in FIG. 9B, since the short side of the SiN film 21 is etched and thinned, the inclination angle of the tip of the field oxide film 23 on the short side becomes small, The inclination angle of the tip of the long-side field oxide film 23 can be made substantially the same.

  Next, the SiN film 21 is removed by etching using, for example, phosphoric acid, and the thermal oxide film therebelow is removed with hydrofluoric acid or the like. Thereafter, the surface of the semiconductor substrate 20 in the element region is thermally oxidized at a temperature of 1000 ° C., for example, to form a gate insulating film 24 with a thickness of 10 nm, for example, as shown in FIGS. Next, a polysilicon film imparted with conductivity by introducing impurities is formed on the entire upper surface of the semiconductor substrate 20 by CVD, for example, to a thickness of 250 nm. Then, the polysilicon film is patterned by using a photolithography method and an etching method to form a gate electrode 25 that traverses the element region. In order to reduce the resistance of the gate electrode 25, it is preferable to form a silicide film (for example, a tungsten silicide film) on the gate electrode 25.

  Next, impurities are ion-implanted into the surface (element region) of the semiconductor substrate using the gate electrode 25 as a mask to form impurity regions 26 that serve as source / drain on both sides of the gate electrode 25, and then heat treatment is performed to remove the impurities. Activate. Thereafter, an interlayer insulating film, contact holes, wirings, and the like are formed on the semiconductor substrate 20. In this way, the semiconductor device is completed.

  In the semiconductor device manufactured by the manufacturing method according to the present embodiment, since the inclination angle of the tip of the field oxide film 23 on both the short side and the long side is small, the SiN film 21 and the pad oxide film are removed. The phenomenon that the substrate surface near the tip of the field oxide film 23 is etched is suppressed. As a result, gate breakdown during burn-in inspection can be avoided, and the manufacturing yield of semiconductor devices can be improved.

  In the above embodiment, the SiN film 21 is etched into a rectangular shape in the steps shown in FIGS. 8A and 8B. However, as shown in FIG. 11, the SiN film 21 is etched into a tapered shape. Also good. The etching shape of the SiN film 21 varies depending on the etching conditions.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1) A step of forming a SiN film covering an element region of a semiconductor substrate;
Forming a resist film exposing a part of the SiN film on the semiconductor substrate;
Etching the part of the SiN film not covered with the resist film to the middle in the thickness direction;
Removing the resist film;
Thermally oxidizing the surface of the semiconductor substrate using the SiN film as a mask to form a field oxide film;
And a step of removing the SiN film.

(Appendix 2) After the step of removing the SiN film,
Forming a gate insulating film on the element region;
Forming a gate electrode across the element region on the gate insulating film;
The method for manufacturing a semiconductor device according to claim 1, further comprising: introducing an impurity into the element region on both sides of the gate electrode.

  (Supplementary Note 3) The element region has two sides intersecting the gate electrode, the resist film covers the longer side of the two sides, and the shorter side is exposed. The method of manufacturing a semiconductor device according to attachment 2, wherein the semiconductor device is formed as described above.

  (Supplementary note 4) The method of manufacturing a semiconductor device according to supplementary note 1, wherein in the step of etching the SiN film, etching is performed so that a cross-section of a portion to be etched is rectangular.

  (Supplementary note 5) The method of manufacturing a semiconductor device according to supplementary note 1, wherein in the step of etching the SiN film, etching is performed so that a cross section of a portion to be etched is tapered.

  (Additional remark 6) The said device area | region is not a rectangle, The manufacturing method of the semiconductor device of Additional remark 1 characterized by the above-mentioned.

FIGS. 1A and 1B are views (part 1) illustrating an example of a conventional method for manufacturing a semiconductor device using a LOCOS method. 2A and 2B are views (part 2) illustrating an example of a conventional method for manufacturing a semiconductor device using a LOCOS method. FIGS. 3A and 3B are views (part 3) illustrating an example of a conventional method for manufacturing a semiconductor device using the LOCOS method. FIG. 4 is a top view showing the surface of the semiconductor substrate after the SiN film and the pad oxide film are removed. FIG. 5 is a schematic cross-sectional view showing an enlarged front end portion of the field oxide film. FIGS. 6A and 6B are views (No. 1) illustrating the method for manufacturing the semiconductor device according to the embodiment of the invention. 7A and 7B are views (No. 2) illustrating the method for manufacturing the semiconductor device according to the embodiment of the invention. 8A and 8B are views (No. 3) illustrating the method for manufacturing the semiconductor device according to the embodiment of the invention. FIGS. 9A and 9B are views (No. 4) illustrating the method for manufacturing the semiconductor device according to the embodiment of the invention. 10A and 10B are views (No. 5) illustrating the method for manufacturing the semiconductor device according to the embodiment of the invention. FIG. 11 is a cross-sectional view showing an example in which a SiN film is etched in a tapered shape.

Explanation of symbols

10, 20 ... Semiconductor substrate,
10a ... element region,
11, 21 ... SiN film,
12, 23 ... Field oxide film,
13, 24 ... gate insulating film,
14, 25 ... gate electrodes,
15, 26 ... impurity region,
22: Resist pattern.

Claims (3)

Forming a SiN film having a plurality of sides including a first side and a second side longer than the first side on the semiconductor substrate in a plan view from above the semiconductor substrate;
Forming a resist film covering the second side and exposing the first side ;
Etching the part of the SiN film not covered with the resist film to the middle in the thickness direction;
Removing the resist film;
Using the SiN film as a mask, the surface of the semiconductor substrate is thermally oxidized to form a field oxide film , and the third side and the third side are formed on the semiconductor substrate in plan view from above the semiconductor substrate. Defining an element region having a plurality of sides including a fourth side longer than the side as an outer periphery ;
Removing the SiN film ;
Forming a gate insulating film on the element region;
Forming a gate electrode on the gate insulating film across the element region and intersecting the third side and the fourth side;
And a step of introducing an impurity into the element region on both sides of the gate electrode . 2. The method of manufacturing a semiconductor device according to claim 1, wherein in the step of etching the SiN film, etching is performed so that a cross section of a portion to be etched has a rectangular shape. 2. The method of manufacturing a semiconductor device according to claim 1, wherein in the step of etching the SiN film, etching is performed so that a cross section of a portion to be etched is tapered.

Images