JP2005045012A - Manufacturing method of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor device having a stable threshold voltage, excellent characteristics and reliability, and an ONO laminated film as a gate insulating film.
After an ONO laminated film 5 made of silicon oxide films 2 and 4 and a silicon nitride film 3 is formed on a semiconductor substrate 1, one of the following charge accumulation suppressing processes is performed on the silicon nitride film 3. After the charge accumulation process, charges are injected into the ONO multilayer film 5 by plasma dry etching or plasma chemical vapor deposition. In the charge accumulation treatment, the silicon nitride film 3 is oxidized by heating to a high temperature in a mixed gas of unreacted hydrogen and oxygen to react with hydrogen and oxygen, or in a high temperature hydrogen atmosphere that is oxidized in an oxidizing atmosphere containing chlorine. And the like that oxidize a silicon nitride film.
[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 having a laminated insulating film.

  Currently, a laminated insulating film typified by a so-called ONO laminated film in which a silicon oxide film, a silicon nitride film, and a silicon oxide film are laminated is widely used as a gate insulating film in a MONOS type semiconductor memory device, a CCD imaging device, or the like.

  Conventionally, a method for manufacturing a semiconductor device having such a laminated insulating film has been as follows.

  3A and 3B are process cross-sectional views illustrating an example of a method for manufacturing a semiconductor device having a conventional ONO stacked film.

  First, as shown in FIG. 3A, a silicon oxide film 102, a silicon nitride film 103, and a silicon oxide film 104 are sequentially stacked on a semiconductor substrate 101 to form an ONO stacked film 105. Next, as shown in FIG. 3B, the semiconductor substrate having the ONO laminated film 105 is then subjected to a plasma processing step such as plasma / dry etching or plasma chemical vapor deposition.

  However, in the conventional method for manufacturing a semiconductor device, as shown in FIG. 4, ultraviolet rays generated in a plasma processing step such as plasma dry etching or plasma chemical vapor deposition reach the silicon substrate 101, and valence electrons The electrons in the band are excited to the conduction band of the silicon oxide film 102 and reach the silicon nitride film 103 to be accumulated therein, or the ONO laminated film in the process of plasma dry etching or plasma chemical vapor deposition An electric field is applied to 105, and as a result, charges are injected into the ONO laminated film 105 and accumulated in the silicon nitride film 103.

  When charges are accumulated in the silicon nitride film 103, the threshold voltage of a transistor having the ONO stacked film 105 as a gate insulating film increases or decreases, and a desired value cannot be obtained. In addition, unnecessary charges are induced in the substrate under the ONO stacked film at portions other than the transistor, which adversely affects the characteristics or reliability of the semiconductor device.

  There has been proposed a semiconductor device that prevents this problem of variation in electrical characteristics due to ultraviolet rays (for example, Patent Document 1).

  FIG. 5 is a cross-sectional view of a semiconductor device that has taken the above-described measures against ultraviolet rays.

As illustrated in FIG. 5, a silicon oxide film 102, a silicon nitride film 103, and a silicon oxide film 104 are sequentially stacked on a silicon substrate 101 to form an ONO stacked film 105, and a gate electrode 106 is formed on the ONO stacked film 105. Is formed. Furthermore, metal light shielding films 110 and 111 are formed on the gate electrode 106 via an insulating film to block ultraviolet rays.
JP 2001-284563 A

  However, in the conventional semiconductor device described above, the metal light shielding films 110 and 111 need to be formed almost seamlessly over a considerable area in order to prevent the ultraviolet rays from being incident on the underlying layer, which is a limitation on the free arrangement of wiring. There is a problem. There is also a problem that it is not effective for ultraviolet rays irradiated in the process before the formation of the metal light-shielding film.

  The present invention solves the above-described problem, can suppress charge accumulation in the laminated insulating film, the threshold voltage of a transistor having the laminated insulating film as a gate insulating film does not deviate from a desired value, It is an object of the present invention to provide a method for manufacturing a semiconductor device in which unnecessary charges are not induced in a semiconductor substrate below a laminated insulating film with respect to a portion other than a transistor.

  In order to solve the above problems, a first method of manufacturing a semiconductor device according to the present invention includes a step of forming a laminated insulating film on a semiconductor substrate, a step of applying a charge accumulation suppressing process to the laminated insulating film, and the laminated insulating film. Injecting charges into the film.

  The second method for manufacturing a semiconductor device of the present invention includes a step of forming a laminated insulating film on a semiconductor substrate, a step of forming a gate electrode on a portion of the laminated insulating film, and a lamination using the gate electrode as a mask. A step of applying a charge accumulation suppressing process to the insulating film; and a step of injecting charges into the laminated insulating film.

  In the first and second methods for manufacturing a semiconductor device of the present invention, the laminated insulating film is preferably composed of a first insulating film, a second insulating film, and a third insulating film from the lower layer.

  In the first and second methods for manufacturing a semiconductor device of the present invention, the charge accumulation suppression process is performed by heating the semiconductor substrate to a high temperature in a mixture gas of unreacted hydrogen and oxygen, and reacting the hydrogen and oxygen with the second. It is preferable to oxidize the insulating film.

  In this way, the silicon nitride film or silicon oxynitride film has a significantly higher oxidation rate than the general thermal oxidation, and the dangling bond density in the film is reduced, so that charge accumulation is suppressed.

  In the first and second semiconductor device manufacturing methods of the present invention, it is preferable that the charge accumulation suppressing process is a process of thermally oxidizing the second insulating film in a high-temperature atmosphere containing chlorine.

  In this way, unreacted material in the silicon nitride film or silicon oxynitride film is discharged, and as a result, the dangling bond density in the film decreases, so that charge accumulation is suppressed.

  In the first and second semiconductor device manufacturing methods of the present invention, it is preferable that the charge accumulation suppressing process is a process of annealing the second insulating film in a high-temperature atmosphere containing hydrogen.

  In this way, dangling bonds in the silicon nitride film or silicon oxynitride film are terminated by hydrogen, and thus charge accumulation is suppressed.

  In the first and second semiconductor device manufacturing methods of the present invention, after the charge accumulation suppression process implants oxygen or hydrogen ions into the second insulating film, the second insulating film is annealed at a high temperature. It is preferable that it is the process to perform.

  In this way, since dangling bonds in the silicon nitride film or silicon oxynitride film are terminated by oxygen or hydrogen, charge accumulation is suppressed.

  In the first and second semiconductor device manufacturing methods of the present invention, it is preferable that the charge injection is caused by generating electron-hole pairs in the semiconductor substrate by ultraviolet irradiation.

  In the first and second semiconductor device manufacturing methods of the present invention, the charge injection is preferably performed by plasma dry etching or plasma chemical vapor deposition.

  In the first and second semiconductor device manufacturing methods of the present invention, it is preferable that the first and third insulating films are silicon oxide films and the second insulating film is a silicon nitride film.

  In the first and second semiconductor device manufacturing methods of the present invention, it is preferable that the first and third insulating films are silicon oxide films and the second insulating film is a silicon oxynitride film.

  As described above in detail, according to the method for manufacturing a semiconductor device of the present invention, since charge accumulation in the stacked insulating film is suppressed, a threshold voltage of a transistor having the stacked insulating film as a gate insulating film is set to a desired value. It will not deviate from the value. In addition, unnecessary charges are not induced in the semiconductor substrate below the laminated insulating film for portions other than the transistors, and as a result, a semiconductor device having excellent reliability can be obtained.

(First embodiment)
FIG. 1A to FIG. 1C are cross-sectional views in order of steps showing the first embodiment of the present invention.

  First, as shown in FIG. 1A, a silicon oxide film 2, a silicon nitride film 3, and a silicon oxide film 4 are sequentially laminated on a semiconductor substrate 1 to form an ONO laminated film 5 that is a laminated insulating film. Next, as shown in FIG. 1B, the charge accumulation suppression process is performed on the ONO multilayer film 5.

  There are several types of processing methods for this charge accumulation suppression processing.

  In the first treatment method, the semiconductor substrate 1 is heated to a high temperature of about 1000 ° C. in a mixed gas of unreacted hydrogen and oxygen by a method such as lamp heating, and hydrogen and oxygen are reacted to form the silicon nitride film 3. It oxidizes. The silicon nitride film 3 is a film that is very difficult to oxidize. However, according to our research, it has been found that the silicon nitride film 3 is oxidized at the same oxidation rate as that of the silicon substrate by such a method. Although the silicon nitride film 3 has a large number of charge trap levels in the film, the number of dangling bonds in the film decreases due to oxidation, and the film composition approaches the stoichiometric composition. The charge trap level density in the medium decreases.

  The second treatment method is to oxidize the silicon nitride film 3 by oxidizing the ONO laminated film 5 at 800 ° C. to 1000 ° C. in an oxidizing atmosphere containing about 1% by weight of chlorine. According to our research, the silicon nitride film 3 is exposed to an oxidizing atmosphere containing chlorine in this oxidation step, whereby the concentration of unreacted NH in the silicon nitride film 3 is reduced, and as a result, the charge trap level density in the film is reduced. Has been found to decrease.

  In the third treatment method, the ONO multilayer film 5 is annealed in a hydrogen atmosphere at about 900 ° C. At this time, hydrogen diffuses into the silicon nitride film 3 and terminates the dangling bonds, thereby reducing the charge trap level density in the silicon nitride film 3.

  In the fourth processing method, oxygen or hydrogen is ion-implanted into the ONO laminated film 5 and then annealed at a temperature of about 900 ° C. Oxygen or hydrogen ion-implanted by this annealing terminates dangling bonds in the silicon nitride film 3, and the charge trap level density in the silicon nitride film decreases.

  By using the above processing method, the silicon nitride film 3 becomes the silicon nitride film 31 in a state where the charge trap level density in the film is reduced, and the ONO laminated film 5 becomes the ONO laminated film 51.

  Next, as shown in FIG. 1C, the semiconductor substrate 1 having the ONO stacked film 51 is irradiated with ultraviolet rays by plasma / dry etching or plasma chemical vapor deposition. The ultraviolet rays generate electron / hole pairs in the semiconductor substrate 1 and the excited electrons are injected into the ONO stacked film 51 on the semiconductor substrate 1, but the silicon nitride film 31 has a very small number of charge trap levels. As a result, only a few electrons are captured.

(Second Embodiment)
FIGS. 2A to 2D are cross-sectional views in order of steps showing a second embodiment of the present invention.

  First, as shown in FIG. 2A, an ONO laminated film 5 is formed by sequentially laminating a silicon oxide film 2, a silicon nitride film 3 and a silicon oxide film 4 on a semiconductor substrate 1. Next, a gate electrode 6 is formed on the ONO multilayer film 5 as shown in FIG. Gate electrode 6 is, for example, n-type polycrystalline silicon. Next, as shown in FIG. 2C, charge accumulation suppression processing is performed on the ONO multilayer film 5 using the gate electrode 6 as a mask.

  There are several types of processing methods for this charge accumulation suppression processing.

  In the first treatment method, the semiconductor substrate 1 is heated to a high temperature of about 1000 ° C. in a mixed gas of unreacted hydrogen and oxygen by a method such as lamp heating, and hydrogen and oxygen are reacted to form the silicon nitride film 3. It oxidizes. The silicon nitride film 3 is a film that is very difficult to oxidize. However, according to our research, it has been found that the silicon nitride film 3 is oxidized at the same oxidation rate as that of the silicon substrate by such a method. Although the silicon nitride film 3 has a large number of charge trap levels in the film, the number of dangling bonds in the film decreases due to oxidation, and the film composition approaches the stoichiometric composition. The charge trap level density in the medium decreases. At this time, the ONO multilayer film 5 located below the gate electrode 6 is not oxidized.

  The second treatment method is to oxidize the silicon nitride film 3 by oxidizing the ONO laminated film 5 at 800 ° C. to 1000 ° C. in an oxidizing atmosphere containing about 1% by weight of chlorine. According to our research, the silicon nitride film 3 is exposed to an oxidizing atmosphere containing chlorine in this oxidation step, whereby the concentration of unreacted NH in the silicon nitride film 3 is reduced, and as a result, the charge trap level density in the film is reduced. Has been found to decrease. At this time, the ONO multilayer film 5 located below the gate electrode 6 is not oxidized.

  In the third treatment method, the ONO multilayer film 5 is annealed in a hydrogen atmosphere at about 900 ° C. At this time, hydrogen diffuses into the silicon nitride film 3 and terminates the dangling bonds, thereby reducing the charge trap level density in the silicon nitride film 3. At this time, hydrogen does not reach the ONO stacked film 5 located below the gate electrode 6.

  In the fourth processing method, oxygen or hydrogen is ion-implanted into the ONO laminated film 5 and then annealed at a temperature of about 900 ° C. Oxygen or hydrogen ion-implanted by this annealing terminates dangling bonds in the silicon nitride film 3, and the charge trap level density in the silicon nitride film decreases. At this time, the ion implantation of oxygen or hydrogen does not reach the ONO stacked film 5 located below the gate electrode 6.

  By using the above processing method, the silicon nitride film 3 not covered with the gate electrode 6 becomes the silicon nitride film 31 in a state where the charge trap level density in the film is reduced, and the ONO laminated film 5 is turned on. A laminated film 51 is formed. On the other hand, in the region covered with the gate electrode 6, the silicon nitride film 3 is not subjected to the charge accumulation suppression process.

  Next, as shown in FIG. 2D, the entire semiconductor substrate is irradiated with ultraviolet rays by plasma / dry etching or plasma chemical vapor deposition. Electrons excited in the semiconductor substrate by the ultraviolet light are injected into the ONO stacked film 51 on the semiconductor substrate, but the silicon nitride film 31 has only a small number of charge trapping levels and is trapped as a result. There are very few electrons. In addition, since the gate electrode 6 is substantially opaque to ultraviolet rays, electrons are not injected into the ONO laminated film 5 located below the gate electrode 6. That is, the ONO laminated film 5 located under the gate electrode 6 has the silicon nitride film 3 in which a certain level of charge trapping order is maintained and no electron injection by ultraviolet irradiation is performed, so that the MONOS type semiconductor It has properties suitable for a gate insulating film such as a memory device or a CCD image pickup device.

  In the first and second embodiments of the present invention, the first, second, and third insulating films are, for example, a silicon oxide film, a silicon nitride film, and a silicon oxide film, respectively. The same effect can be obtained even with this insulating film. In particular, the second insulating film may be a silicon oxynitride film.

  Further, when the silicon nitride film 3 is oxidized, the same effect can be obtained even in a configuration in which the oxidation proceeds into the film to become a silicon oxynitride film or a silicon oxide film.

  In addition, although ultraviolet irradiation by plasma dry etching or plasma chemical vapor deposition is shown, charge injection is also caused by an electric field applied by these plasma processes.

  In the method for manufacturing a semiconductor device of the present invention, charge accumulation in the stacked insulating film is suppressed, so that the threshold voltage of a transistor using the stacked insulating film as a gate insulating film does not deviate from a desired value. For other parts, unnecessary charges are not induced in the semiconductor substrate under the laminated insulating film, and as a result, there is an effect that a highly reliable semiconductor device is obtained, and in particular, the laminated insulating film is provided. This is useful for a method of manufacturing a semiconductor device.

It is process order sectional drawing which shows the 1st Embodiment of this invention. It is process order sectional drawing which shows the 2nd Embodiment of this invention. It is process order sectional drawing which shows an example of the manufacturing method of the conventional semiconductor device. It is a figure which shows the charge accumulation by an ultraviolet-ray. It is sectional drawing which shows an example of the conventional semiconductor device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Silicon oxide film 3 Silicon nitride film 4 Silicon oxide film 5 ONO laminated film 6 Gate electrode 31 Silicon nitride film 51 ONO laminated film

Claims (11)

  A method for manufacturing a semiconductor device, comprising: a step of forming a laminated insulating film on a semiconductor substrate; a step of performing charge accumulation suppression processing on the laminated insulating film; and a step of injecting charges into the laminated insulating film.   Forming a laminated insulating film on a semiconductor substrate; forming a gate electrode on a part of the laminated insulating film; performing a charge accumulation suppressing process on the laminated insulating film using the gate electrode as a mask; And a step of injecting electric charge into the laminated insulating film.   3. The method of manufacturing a semiconductor device according to claim 1, wherein the laminated insulating film is composed of a first insulating film, a second insulating film, and a third insulating film from a lower layer.   4. The semiconductor according to claim 3, wherein the charge accumulation suppressing process is a process of heating the semiconductor substrate to a high temperature in an unreacted mixed gas of hydrogen and oxygen and reacting the hydrogen and oxygen to oxidize the second insulating film. Device manufacturing method.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the charge accumulation suppressing process is a process of thermally oxidizing the second insulating film in a high temperature atmosphere containing chlorine.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the charge accumulation suppressing process is a process of annealing the second insulating film in a high temperature atmosphere containing hydrogen.   4. The method of manufacturing a semiconductor device according to claim 3, wherein the charge accumulation suppressing process is a process of annealing the second insulating film at a high temperature after implanting oxygen or hydrogen ions into the second insulating film.   8. The method of manufacturing a semiconductor device according to claim 1, wherein the charge injection is performed by generating electron-hole pairs in the semiconductor substrate by ultraviolet irradiation.   8. The method of manufacturing a semiconductor device according to claim 1, wherein the charge injection is performed by plasma dry etching or plasma chemical vapor deposition.   The method for manufacturing a semiconductor device according to claim 3, wherein the first and third insulating films are silicon oxide films, and the second insulating film is a silicon nitride film.   8. The method of manufacturing a semiconductor device according to claim 3, wherein the first and third insulating films are silicon oxide films, and the second insulating film is a silicon oxynitride film.

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