JP2006041062A - Manufacturing method of solid-state imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the manufacturing method of a solid-state imaging element capable of suppressing a defective image. <P>SOLUTION: Prior to forming a first insulation film such as an oxide film 8 for preventing impurity diffusion from a second insulation film like a BPSG film 9 on a light shielding film 7 formed of tungsten including fluorine, fluorine is almost removed from a tungsten film at a temperature of 350 °C or over, preferably at 400 °C or over. Thus, no fluorine is stored to the first insulation film at post high temperature heat treatments, and production of a defective image can be suppressed such as white stains due to storage of the fluorine on the border face of the silicon oxide film 8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a solid-state imaging device having an inner lens made of a plasma nitride film.

  In recent years, with the miniaturization of the dimensions of the solid-state imaging device and the pixels constituting the solid-state imaging device, plasma nitridation that can efficiently collect incident light accompanying the image on the pixel onto the light receiving portion formed on the semiconductor substrate A solid-state imaging device having an intralayer lens made of a film has been proposed.

Hereinafter, a conventional configuration of such a solid-state imaging device will be briefly described with reference to FIG.
FIG. 3 is a cross-sectional view of an imaging unit of a solid-state imaging device having an in-layer lens.
In FIG. 3, 1 is an n-type semiconductor substrate on which a solid-state imaging device is formed, 2 is a p-well layer formed on the substrate, 3 is a light receiving unit, 4 is a charge transfer unit that transfers charges generated by incident light, 5 Is an ONO film in which a silicon oxide film and a silicon nitride film (SiN) are combined, and constitutes a gate insulating film of a transfer gate. 6 is a polysilicon electrode of the transfer gate, and 7 is a light shielding film made of a tungsten film formed through an oxide film on the polysilicon electrode 6, which is formed on the step formed by the polysilicon electrode 6. It is deposited by the CVD method with excellent properties. 8 is an oxide film, and 9 is a BPSG film. In order to flatten the surface, reflow by high-temperature heat treatment is generally performed.

  The reason why the BPSG film 9 is formed on the oxide film 8 and the reflow at a high temperature is performed is as follows. That is, in order to increase the condensing rate of the in-layer lens 10 of the solid-state imaging device, the surface flatness of the BPSG film 9 serving as the base of the in-layer lens is required. For this purpose, the boron concentration and phosphorus concentration of the BPSG film 9 must be high, but if the boron concentration and phosphorus concentration are high, boron and phosphorus diffuse downward due to heat treatment, and the solid-state imaging device There is a risk of damaging the characteristics. Therefore, before forming the BPSG film 9, the oxide film 8 is formed on the entire substrate to suppress diffusion of boron and phosphorus into the substrate.

  The intra-layer lens 10 is formed, for example, by applying a resist on the plasma nitride film, heat-treating it into a convex shape, and resist-etching back the plasma nitride film into a convex shape. With this intra-layer lens, incident light can be efficiently collected on the light receiving unit 3. 11 is a semiconductor element surface protective film, 12 is an intermediate transparent film, 13 is a color filter layer, and 14 is an uppermost microlens (see, for example, Patent Document 1).

Due to the configuration including the intra-layer lens as described above and the manufacturing process corresponding to this configuration, the solid-state imaging device is sufficiently focused on the light receiving portion 3 even if the area of the light receiving portion of the pixel is reduced and the miniaturization proceeds. Thus, high sensitivity can be obtained.
Japanese Patent Laid-Open No. 11-11957

However, it has been discovered that the solid-state imaging device formed by the conventional manufacturing method as described above has a problem that a white spot-like image defect occurs in an image.
An object of the present invention is to solve the above-mentioned problems and to provide a method for manufacturing a solid-state imaging device capable of suppressing image defects.

  In order to achieve the above object, a method of manufacturing a solid-state imaging device according to claim 1 of the present invention uses a step of forming a layer serving as a light receiving portion on a semiconductor substrate, and a gas containing fluorine on the semiconductor substrate. Forming a light shielding film containing at least tungsten as a main component; selectively removing the light shielding film on the light receiving portion; and exposing the tungsten film surface constituting the light shielding film from the light shielding film. A step of desorbing fluorine, a step of forming a first insulating film on the light shielding film after desorbing the fluorine, and a step of forming a second insulating film on the first insulating film; And a step of planarizing the second insulating film by heat treatment.

  3. The method of manufacturing a solid-state imaging device according to claim 2, wherein a layer serving as a light receiving portion is formed on a semiconductor substrate, and a light shielding film containing at least tungsten as a main component is formed on the semiconductor substrate using a gas containing fluorine. A step of selectively removing the light shielding film on the light receiving portion, and heating the temperature of the tungsten film constituting the light shielding film to 350 ° C. or higher while exposing the surface of the tungsten film, thereby removing fluorine from the light shielding film. A step of desorbing, a step of forming a first insulating film on the light shielding film after desorbing the fluorine, a step of forming a second insulating film on the first insulating film, And a step of planarizing the second insulating film by heat treatment.

  The solid-state imaging device manufacturing method according to claim 3 is the solid-state imaging device manufacturing method according to claim 1 or 2, wherein the second insulating film is a film containing impurities. And

According to a fourth aspect of the present invention, there is provided a method for manufacturing a solid-state imaging device according to the third aspect, wherein the second insulating film is a BPSG film.
The solid-state imaging device manufacturing method according to claim 5 is the solid-state imaging device manufacturing method according to any one of claims 1, 2, 3, or 4, wherein the second insulating film is heat-treated. The step of performing is a step of reflowing the second insulating film.

  As described above, it is possible to provide a method for manufacturing a solid-state imaging device capable of suppressing image defects.

  As described above, according to the method for manufacturing a solid-state imaging device according to the present invention, the first insulating film for preventing impurity diffusion from the second insulating film such as the BPSG film on the light shielding film made of the tungsten film containing fluorine. Prior to forming the silicon film, the fluorine is hardly separated from the tungsten film at 350 ° C. or higher, preferably 400 ° C. or higher, so that fluorine is not accumulated in the first insulating film in the subsequent high-temperature heat treatment, and the silicon oxide film Generation of image defects such as white spots due to accumulation of fluorine at the interface can be suppressed.

As a result of analyzing the cause of the above-mentioned white spot-like image failure, the present inventors have obtained the following knowledge. That is, fluorine accumulates in the silicon oxide film in the vicinity of the interface between the tungsten light-shielding film and the silicon oxide film on the tungsten film in devices with image defects, and almost no fluorine is detected in devices without image defects. Was not. The tungsten film as the light shielding film 7 in FIG. 3 is formed by a low pressure CVD method using a gas containing fluorine such as WF ₆ in order to ensure the coverage at the level difference of the polysilicon electrode. The formed film contains a fluorine component. For this reason, in the conventional manufacturing method, a large amount of fluorine remains in the tungsten film after the formation of the silicon oxide film 8 after the formation of the tungsten film. For example, the fluorine is subjected to subsequent BPSG film planarization reflow. It was considered that the high temperature heat treatment at about 900 ° C. for accumulation accumulated in the silicon oxide film on the tungsten film, and this caused an image defect. The present invention is thus based on the findings discovered by the present inventors.

Hereinafter, a method for manufacturing a solid-state imaging device according to an embodiment of the present invention will be described with reference to FIGS.
FIG. 1 is a process cross-sectional view illustrating a manufacturing process of an imaging unit pixel of a solid-state imaging device in the present invention. FIG. 2 is a diagram showing the relationship between the temperature of the semiconductor substrate and the desorption amount of the fluorine component from the tungsten film. The desorption amount is a ratio to the initial fluorine content in the film.

In FIG. 1, first, a P-type impurity is implanted into an n-type semiconductor substrate 1 by impurity implantation, a p-well layer 2 is formed using a drive-in furnace, and an N-type impurity implantation method is used for the surface layer portion. A light receiving portion 3 that is a type of photodiode is formed. Next, the N-type charge transfer portion 4 is also formed using ion implantation. Next, a thin SiO ₂ film by pyro-oxidation and a silicon nitride film (SiN) by low pressure CVD are sequentially formed on the substrate surface, and finally the silicon nitride film surface is thermally oxidized to form an ONO film 5. Next, a polysilicon electrode 6 serving as a charge transfer gate electrode is formed on the ONO film 5 by using a low pressure CVD method. Further, a thin SiO film is formed thereon by a CVD method using TEOS as a raw material (FIG. 1A).

Subsequently, tungsten is deposited in the range of 100 nm to 500 nm as the light shielding film 7 so that excessive light does not enter the charge transfer portion 4 and the like on the SiO film, and only the portion above the light receiving portion 3 is removed by etching. Expose. Specifically, a tungsten film is first deposited by sputtering, and then a CVD tungsten film is formed by a CVD method using reduction of a gas containing fluorine such as WF ₆ gas. The sputtered tungsten film ensures good adhesion with the underlying SiO film, and the CVD tungsten film satisfactorily covers the steps of the polysilicon electrode 6 as described above to ensure film continuity. In this embodiment mode, a tungsten film is formed to a thickness of 50 to 200 nm by a sputtering method and a CVD method (FIG. 1B).

The above-described CVD tungsten film using WF ₆ as a material gas contains a fluorine component, and the fluorine component is desorbed from the tungsten film by raising the temperature of the semiconductor substrate.

  As shown in FIG. 2, by raising the temperature of the semiconductor substrate to 400 ° C. or higher, the fluorine component in the tungsten film can be completely desorbed, and most of the fluorine can be desorbed even at 350 ° C. or higher ( It can be seen that the withdrawal amount is 98%. Desirably, it is good to set it as 400 degreeC or more (100% of fluorine detachment | leave amount). In the present embodiment, the atmospheric pressure CVD method is used for the light shielding film 7 and the light receiving portion 3 surface layer, and before the oxide film 8 for preventing impurity diffusion from the BPSG film 9 to be formed thereon is deposited, the semiconductor substrate The temperature is raised to 410 ° C. at a rate of 30 ° C./min to completely desorb the fluorine component in the tungsten film.

  This heat treatment can be performed, for example, using a CVD apparatus for forming the silicon oxide film 8 and flowing a large amount of nitrogen in the film formation preliminary chamber or the preliminary region. In this way, heat treatment can be performed without oxidizing the exposed surface of the tungsten film. Thereafter, an oxide film 8 having a thickness of 100 nm is formed in the same CVD apparatus continuously with this heat treatment (FIG. 1C). Before the silicon oxide film 8 is formed, if the temperature of the semiconductor substrate is much lower than 400 ° C. as in the prior art, the oxide film 8 is deposited with the fluorine component contained in the tungsten film. When the heat treatment such as BPSG film reflow is performed, the fluorine component desorbed from the tungsten film accumulates on the interface side of the light shielding film 7 of the oxide film 8, thereby causing a problem of image defects. However, in the present invention, since fluorine is completely desorbed from the light-shielding film 7, this does not occur, and image defects in the solid-state imaging device can be suppressed.

Next, a BPSG film 9 is deposited on the silicon oxide film 8. The BPSG film 9 has a boron concentration of 4.4 to 5.4 [wt%], a phosphorus concentration of 4.6 to 5.6 [wt%], and a deposited film thickness of 400 to 1000 nm. For example, a typical condition is that the boron concentration is 4.6 [wt%], the phosphorus concentration is 4.9 [wt%], and the film thickness is 600 nm by using the atmospheric pressure CVD method (FIG. 1D). . Thereafter, the BPSG film 9 is planarized by performing heat treatment in a N ₂ atmosphere at 800 ° C. to 900 ° C. in a flow furnace. As an example, heat treatment is performed at 900 ° C. for 60 minutes (FIG. 1 ( e)).

Next, a plasma nitride film 10 ′ is deposited on the BPSG film 9 by a plasma CVD method (FIG. 1 (f)), and an in-layer lens pattern made of a resist film is formed on the BPSG film 9 although not shown in the figure. A heat treatment is performed at a temperature of about 100 ° C. to 160 ° C. to flow the resist pattern so that the cross-sectional shape of the resist pattern is a convex shape. 10 shape is processed (FIG. 1G). Further, at least one film selected from SiO ₂ , SiON, and SiN is formed as the semiconductor element surface protective film 11 on the entire upper surface of the BPSG film 9 and the intralayer lens 10 (FIG. 1H). Finally, a resin material such as an acrylic resin film is applied and planarized on the semiconductor element surface protective film 11 to form the intermediate transparent film 12. The color filter layer 13 is formed in the light receiving portion region inside the intermediate transparent film 12, and the microlens 14 is formed in the region facing the light receiving portion 3 on the surface of the intermediate transparent film 12 (FIG. 1 (i)). In this way, a solid-state image sensor is completed.

  As described above, according to the present invention, by forming the temperature of the semiconductor substrate to about 400 ° C. or higher before forming the silicon oxide film 8 essential for preventing impurity diffusion from the BPSG film 9, By eliminating the fluorine component contained in the CVD tungsten film as the light shielding film, it is possible to suppress the occurrence of image defects such as white spots due to the accumulation of fluorine at the interface of the silicon oxide film 8. .

  In the above embodiment, the silicon oxide film 8 is used, but it goes without saying that other insulating films such as SiON are also effective.

  The manufacturing process of the solid-state imaging device of the present invention can suppress the occurrence of image defects, and is useful for a manufacturing method of a solid-state imaging device including an inner lens made of a plasma nitride film.

Process sectional drawing which shows the manufacturing process of the image pick-up part pixel of the solid-state image sensor in this invention Diagram showing the relationship between the temperature of the semiconductor substrate and the amount of desorption of fluorine components from the tungsten film Cross-sectional view of the imaging unit of a solid-state imaging device with an in-layer lens

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 n-type semiconductor substrate 2 p well layer 3 Light-receiving part 4 Charge transfer part 5 ONO film 6 Polysilicon electrode 7 Light-shielding film 8 Oxide film 9 BPSG film 10 Intralayer lens 10 'Plasma nitride film 11 Semiconductor element surface protective film 12 Intermediate transparent Membrane 13 Color filter layer 14 Micro lens

Claims (5)

Forming a layer to be a light receiving portion on a semiconductor substrate;
Forming a light shielding film mainly containing at least tungsten using a gas containing fluorine on the semiconductor substrate;
Selectively removing the light shielding film on the light receiving portion;
Desorbing fluorine from the light shielding film while exposing the tungsten film surface constituting the light shielding film;
Forming a first insulating film on the light-shielding film after desorbing the fluorine;
Forming a second insulating film on the first insulating film;
And a step of planarizing the second insulating film by heat treatment. Forming a layer to be a light receiving portion on a semiconductor substrate;
Forming a light shielding film mainly containing at least tungsten using a gas containing fluorine on the semiconductor substrate;
Selectively removing the light shielding film on the light receiving portion;
Desorbing fluorine from the light shielding film by raising the temperature to 350 ° C. or higher while exposing the tungsten film surface constituting the light shielding film;
Forming a first insulating film on the light-shielding film after desorbing the fluorine;
Forming a second insulating film on the first insulating film;
And a step of planarizing the second insulating film by heat treatment.   The method for manufacturing a solid-state imaging device according to claim 1, wherein the second insulating film is a film containing an impurity.   4. The method for manufacturing a solid-state imaging device according to claim 3, wherein the second insulating film is a BPSG film.   5. The solid according to claim 1, wherein the step of heat-treating the second insulating film is a step of reflowing the second insulating film. Manufacturing method of imaging device.

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