JP3278917B2 - Method for manufacturing solid-state imaging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a solid-state image pickup device, such as an infrared solid-state image pickup device, which forms a light receiving portion by depositing a substance different from a substrate on a semiconductor substrate.

[0002]

2. Description of the Related Art There is an infrared solid-state imaging device as an example of a solid-state imaging device in which a light receiving portion is formed by depositing a substance different from a semiconductor substrate on a semiconductor substrate. A conventional method for manufacturing this infrared solid-state imaging device will be described with reference to FIGS.

First, FIG. 2 is a plan view for explaining the overall configuration of an infrared solid-state imaging device. In the figure, 1
Reference numeral 09 denotes a light receiving unit for performing photoelectric conversion, which is arranged in a matrix. Here, 3 × 3 = 9 light receiving sections are shown for simplicity. On the other hand, reference numeral 104 denotes a charge transfer unit serving as a path for reading out the charges generated in the light receiving unit 109. To actually read out the charges, the charge transfer unit 10
It is necessary to apply a predetermined clock pulse to the CCD transfer electrode 105 (shown with hatching on the left in the figure) provided on the top of FIG. In FIG. 2, only one CCD transfer electrode 105 is shown, and the others are omitted.

The clock pulse to the CCD transfer electrode 105 is applied to the chip 113 via a bonding pad 112 provided around the semiconductor chip 113 and a metal wiring 111 (both hatched at the upper right in the figure). Provided from outside. In FIG. 2, a part of the bonding pad 112 and the metal wiring 111 is also shown. This bonding pad 112, metal wiring 1
Reference numeral 11 is made of a metal such as Al or an Al alloy.

Next, a method of manufacturing the solid-state imaging device having the structure shown in FIG. 2 will be described with reference to FIG. FIG. 3 shows the second
The structure near the surface of the AA cross section in the figure is shown for each manufacturing process. First, the well-known LO
Si substrate 10 by COS separation method (selective oxidation separation method)
An isolation region 102 made of a thick thermal oxide film is formed on the substrate 1.

Next, BC is added to the charge transfer section (104 in FIG. 2).
A CD diffusion layer 104a is formed, and a CCD transfer electrode 105 made of polysilicon is formed on the diffusion layer 104a. Although not shown in other figures, the MO of the output section of the charge transfer section is
All of the various heat diffusion layers including the source / drain diffusion layers constituting the S transistor and all the polysilicon electrodes are formed. FIG. 3A shows a state in which the formation of the thermal diffusion layer and the polysilicon electrode has been completed. At this time, both the light receiving portion and the polysilicon electrode are thin oxide films 1 respectively.
03,106.

Subsequently, the entire surface of the Si substrate 101 is subjected to CVD.
Thickness of 4000 to 1000 by the chemical vapor deposition method
An oxide film 107 of about 0 ° is deposited. Usually, this oxide film 107 contains impurities such as phosphorus, boron, or arsenic, and when heat-treated at a temperature of about 900 ° C., the surface shape becomes flat. The method of flattening the CVD oxide film 107 containing impurities described above by heat treatment is widely known as "reflow treatment", and is used to form a film in a later step.
This is effective in preventing electrical failure (disconnection, short circuit, etc.) of metal wiring made of l or Al alloy.

After completion of the reflow process, a resist 108 is applied, exposure and development are subsequently performed, and patterning for removing only the oxide film 107 in a portion to be a light receiving portion is performed. The state at this time is shown in FIG.

Next, CV is applied by wet etching.
The D oxide film 107 and the thin thermal oxide film 103 are simultaneously etched away to expose the surface of the Si substrate 101. The state at this time is shown in FIG. Note that FIG.
The steps (b) and (c) will be described later in detail.

After exposing the surface of the Si substrate 101 of the light receiving portion, the resist 108 is peeled off and washed, and then the light receiving portion is formed. In the formation of the light receiving portion, first, Pt is deposited and heat treatment is performed to obtain a PtSi layer 109a. Thus, a light receiving unit (Schottky barrier diode) for performing photoelectric conversion is formed. This state is shown in FIG.

Thereafter, as shown in FIG. 3E, a CVD oxide film 110 is again deposited on the entire surface. After that,
A wiring layer (not shown) made of Al or an Al alloy is formed to complete an infrared solid-state imaging device.

Here, the steps shown in FIGS. 3B and 3C will be described in more detail. In the solid-state imaging device, the light receiving section is the most important element active region and has a damage such as a crystal defect. Not be. For this reason, the above-described CV
In the step of forming a hole in the D oxide film 107 (FIG. 3C), S
A dry etching method that easily damages the i-substrate 101 cannot be applied. In the conventional manufacturing method, holes are formed by a wet etching method after the reflow treatment of the CVD oxide film 107 (FIG. 3B).

At this time, in the wet etching method, the etching proceeds in all directions at a constant speed, and the side etching is large. Further, if the portion indicated by I in FIG. 3C is exposed, electrical failure of the CCD transfer electrode 105 frequently occurs. Therefore, it is necessary to provide the resist 108 to a position where it enters the light receiving unit side. is there. That is, L in FIG.
_It is necessary to make the size of ₁ large enough with a margin,
Usually, it is 1.5 to 2 μm.

Therefore, assuming that the width (W in FIG. 3C) of the element active region where the light receiving portion is to be formed is 10 μm, the region where the light receiving portion is actually formed (L _{2 in} FIG. 3C). Is 6 ~
7 μm.

[0015]

In recent years, however, solid-state imaging devices such as infrared solid-state imaging devices have been used.
1. 1. Chip size is smaller; 2. higher spatial resolution (more pixels); It is required from various fields to simultaneously satisfy the performance such as higher light receiving sensitivity.

In order to satisfy this requirement, it is necessary to increase the area ratio (opening ratio) occupied by the light receiving section in the unit pixel of the solid-state imaging device, and various attempts have been made. As an example, the width of the isolation region 102 shown in FIG. 3 may be reduced, or the width of the BCCD diffusion layer 104a may be reduced. However, this alone cannot sufficiently improve the aperture ratio, and it is difficult to obtain an imaging device with high light receiving sensitivity. Therefore, the aforementioned L
Although it is desirable to reduce as much as possible a value of _1, in the conventional method of manufacturing a solid-state imaging device, it is not possible to reduce the L ₁ for side etching can not be avoided.

The present invention has been made in view of this point,
It is an object of the present invention to provide a solid-state imaging device having a high light-receiving sensitivity by improving an aperture ratio without causing an electrical failure.

[0018]

According to a first aspect of the present invention, there is provided a method for manufacturing a solid-state image forming apparatus, comprising: forming a light receiving portion by applying a material different from the semiconductor substrate on the semiconductor substrate;
Forming a charge readout portion for reading out the charge stored in the light receiving portion; and providing one or more flattening steps of providing an insulating film on a region including the charge readout portion to flatten the surface; Forming a metal wiring for driving the charge readout unit on the planarized insulating film, wherein the charge readout unit is formed.
The step of forming includes a step of forming a charge transfer electrode, and
And before the step of forming the light receiving section,
Forming the semiconductor substrate on which the light receiving section is formed
Remove thermal oxide film that is only placed as an insulating film on the surface
The flattening step, which is performed first among the steps of flattening the surface, is performed after the step of forming the light receiving section.

According to a second aspect of the present invention, the light receiving section is formed by using a Si substrate as the semiconductor substrate and depositing a metal silicide or a compound semiconductor on the Si substrate.

According to a third aspect of the present invention, the flattening step is performed.
From the end of the step of forming the charge transfer electrode
It is performed once before the start of the process of forming the metal wiring.
It is. According to a fourth aspect of the present invention, a silicon substrate is prepared.
Then, a thick silicon film is formed on the silicon substrate by the LOCOS separation method.
A step of forming an isolation region made of a silicon thermal oxide film;
A diffusion layer is formed in the load transfer section, and polysilicon is formed on the diffusion layer.
A step of forming a charge transfer electrode, and a step of forming a light receiving section.
A thin film that is solely placed as an insulating film in the active
The process of removing the thermal oxide film of the silicon and after depositing platinum
Heat treatment to remove the thin silicon thermal oxide film
Process of forming platinum silicide in the active region of
Forming a planarization film by an edge film;
Forming a wiring of a metal thin film on the flattening film.
The above steps are performed in the order described above.

[0021]

According to the present invention, a thick insulating film (usually having a thickness of 4000 to
Before providing the CVD oxide film 107) of about 10000 °, the surface of the semiconductor substrate in the element active region where the light receiving section is formed is exposed. For this reason, in the wet etching step, the thin thermal oxide film 103 growing in the element active region is formed.
(Usually a thickness of about 500-1500 °) only needs to be removed, and the amount of side etching is extremely small (0.1
〜0.3 μm).

Therefore, in the present invention, L ₁ shown in FIG. 3C can be set to about 0.5 μm even with a sufficient margin. When the area (W in FIG. 3 (c)) is 10 μm, the area where the light receiving area is actually formed (L in FIG. 3 (c)).
₂ ) will be 9 μm. Therefore, in the present invention, it is possible to greatly increase the area of the light receiving section in the unit pixel as compared with the related art.

Further, in the present invention, since the light receiving portion is formed before the insulating film is formed as described above, the flattening process of the insulating film is performed after the light receiving portion is formed. By appropriately selecting a flattening method according to the heat resistance temperature of the portion, the surface of the insulating film can be flattened without deteriorating the light receiving portion. Is prevented.

Examples of the insulating film which can be flattened at a low temperature include a polyimide film formed by spin-coating a liquid polyimide resin and heat-treating, a spin-on-glass (SOG) film, or an oxide film formed by a CVD method. , Especially C containing tetraethoxysilane (TEOS) as a main material.
VD oxide film and the like. These insulating films are 500 ° C. lower than the conventional reflow processing temperature (about 900 ° C.).
It can be formed flat at the following temperature, which is preferable in preventing thermal damage to the light receiving section.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an infrared solid-state imaging device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 shows the vicinity of the surface of a unit pixel section of the infrared solid-state imaging device, and is shown on the same scale for comparison with FIG. 3 described above.

First, the well-known L
Si substrate 1 by OCOS separation method (selective oxidation separation method)
An isolation region 2 made of a thick thermal oxide film is formed thereon.

Next, BC is added to the charge transfer section (104 in FIG. 2).
A CD diffusion layer 4a is formed, and a CCD transfer electrode 5 made of polysilicon is formed on the diffusion layer 4a. Although not shown in the figures, all the various heat diffusion layers including the source / drain diffusion layers constituting the MOS transistor of the charge transfer section output section and all the polysilicon electrodes are formed. FIG. 1A shows a state in which the formation of the thermal diffusion layer and the polysilicon electrode has been completed, and the steps up to this point are the same as in the conventional example. At this point, both the light receiving portion and the polysilicon electrode are covered with thin oxide films 3 and 6, respectively.

Next, in this embodiment, a photolithography step for forming a light receiving section is performed. That is, the resist 8 is applied, and subsequently, the resist 8 is patterned by performing exposure and development. The state at this time is shown in FIG.
It is shown in (b).

Subsequently, a hole is formed in the oxide film 3 by wet etching to expose the surface of the Si substrate 1 in the element active region. At this time, in this embodiment, as shown in FIG. 1C, only the thin oxide film 3 (also referred to as a gate oxide film, usually having a thickness of 2000 mm or less) is wet-etched. Is very small. Therefore, L1 shown in FIG.
μm. Therefore, assuming that the width of the element active region where the light receiving portion is formed ( W in FIG. 1C ) is 10 μm, the width of the region where the light receiving region is actually formed (L in FIG. 1C).
2) is 9 .mu.m, and the area of the light receiving section can be greatly increased as compared with the conventional example (L2 = 6 to 7 .mu.m) in FIG.

Thereafter, after the resist 8 is peeled off and washed, a light receiving portion is formed. For the formation of the light receiving portion, first, Pt is deposited and heat treatment is further performed to form a PtSi layer 9a.
Get. Thus, a light receiving unit (Schottky barrier diode) for performing photoelectric conversion is formed. This state is shown in FIG.
(D) .

Next, a flat insulating film 7 obtained at a relatively low temperature of about 500 ° C. is formed. The insulating film 7 is formed by spin-coating a liquid polyimide resin and subjecting it to a heat treatment.
G) A film or an oxide film formed by a CVD method, in particular, a CVD oxide film containing tetraethoxysilane (TEOS) as a main material can be selected from various films.

FIG. 1E shows a state where the insulating film 7 is formed and the surface is flattened. After that, Al or A is formed on the insulating film 7.
A wiring layer (not shown) made of a 1 alloy is formed to complete an infrared solid-state imaging device. In this embodiment, since a flat insulating film is formed after the light receiving region is formed as described above,
End of the process of forming the charge transfer electrode as in the prior art shown in FIG.
For flattening from the time until the start of the process of forming metal wiring
It is not necessary to perform the step of providing the insulating film twice.

In the above embodiment, the infrared solid-state imaging device has been described as an example. However, it is needless to say that the present invention is not limited to the infrared solid-state imaging device. That is, the light receiving section is not limited to PtSi. In addition, other materials (GaAs, CdTe, I
Compound semiconductors such as nSb and InAs, and fluorides such as CaF ₂ may be used. Also, the charge readout section
The invention is not limited to the CD, but may be any of, for example, MOS, CSD, and CPD.

[0034]

As described above, in the present invention, since the light receiving portion is formed, a thick insulating film is provided, and the surface is flattened. Only the film needs to be removed, and the amount of side etching becomes extremely small. Therefore, a light receiving portion having an area substantially equal to the element active region where the light receiving portion is to be formed can be formed, and a solid-state imaging device having a large aperture ratio and excellent light receiving sensitivity can be obtained. Also charge transfer
Forming metal wiring from the end of the electrode forming process
By the start of the process, an insulating film for planarization such as a CVD oxide film
It is also possible to perform the providing step only once. in this case,
The manufacturing process can be simplified and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIGS. 1A to 1E are cross-sectional views illustrating a manufacturing process of a solid-state imaging device according to an embodiment of the present invention.

FIG. 2 is a plan view illustrating an overall configuration of the solid-state imaging device.

FIGS. 3A to 3E are cross-sectional views illustrating a manufacturing process of a conventional solid-state imaging device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Si substrate, 2 ... isolation area, 3,6 ... Thin oxide film, 4
a: BCCD diffusion layer, 5: CCD transfer electrode, 7: insulating film, 8: resist, 9a: PtSi layer.

Claims (4)

(57) [Claims] A step of forming a light receiving portion by depositing a substance different from the semiconductor substrate on the semiconductor substrate;
Forming a charge readout portion for reading out the charge stored in the light receiving portion; and providing one or more flattening steps of providing an insulating film on a region including the charge readout portion to flatten the surface; Forming a metal wiring for driving the charge readout portion on the planarized insulating film, wherein the step of forming the charge readout portion includes forming a charge transfer electrode.
Forming, and forming the light receiving unit
Performing the step of forming the light receiving section, the step of forming the light receiving section is performed.
Thermal oxide film only placed as an insulating film on the surface of the semiconductor substrate
A method of manufacturing a solid-state imaging device, wherein a flattening step performed first of the steps of flattening the surface is performed after a step of forming the light receiving section. 2. An Si substrate is used as the semiconductor substrate,
2. The method according to claim 1, wherein the light receiving section is formed by depositing a metal silicide or a compound semiconductor on the Si substrate. 3. The step of flattening the charge transfer electrode.
Forming the metal wiring from the end of the forming step
2. The process is performed once before the start of the process.
A method of manufacturing the solid-state imaging device according to claim 2.
Law. 4. A method for preparing a silicon substrate, comprising the steps of:
From thick silicon thermal oxide film by LOCOS isolation method
Forming an isolation region, Forming a diffusion layer in the charge transfer portion and forming polysilicon on the diffusion layer;
Forming a charge transfer electrode, Only an insulating film is provided in the active area where the light receiving section is formed.
Removing the placed thin silicon thermal oxide film; After depositing platinum, heat treatment is performed to
Platinum silicide in the active region where the thermal oxide film has been removed
Forming a; A step of forming a planarization film by an insulating film; Forming a wiring made of a thin metal film on the flattening film made of the insulating film
And the step of Wherein each of the steps is performed in the order described above.
A method for manufacturing an image device.