JP2000005693A - Method for forming resist film and preparation of solid imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a resist film with a higher uniformity of film thickness by holding humidity in the neighborhood of a base within a specified range in the same way as a method for forming the resist film. SOLUTION: In a method for forming a resist film wherein a resist soln. 12 is dropped and spread on a rotating substrate 11 and the resist film 13 is formed on the substrate 11, the film thickness of the resist is uniformized by holding humidity in the atmosphere in the neighborhood of the substrate 11 on which the resist film 13 is formed to 35-70% and ununiformity of the area of opening of a sensor opening part caused by ununiformity of the film thickness of the resist is solved by using this method for a method for preparing a solid imaging device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a resist film and a method of manufacturing a solid-state imaging device, and more particularly, to a method of forming a resist film in which humidity around a substrate to which a resist is applied is defined, and the formation of the resist film. The present invention relates to a method for manufacturing a solid-state imaging device using the method.

[0002]

2. Description of the Related Art A solid-state imaging device such as a CCD (Charge c)
oupled device) One of the items affecting the sensitivity output of the imager is the area of the sensor opening. The sensor opening is formed mainly through a resist patterning process including resist application, exposure, development, baking, and the like, and an etching process using the resist film formed in the above process as a mask.

In the above resist patterning step,
If the thickness of the resist film applied on the substrate is not uniform in the substrate surface, exposure is performed with a constant amount of light and individual openings formed in the resist film developed under constant conditions. Becomes uneven. When etching is performed using this resist film as a mask, an opening formed unevenly in the resist film is transferred.
As shown in the layout diagram of the unit cell including the sensor openings, the respective sensor openings 111 after etching have non-uniform areas.

As a result, as shown in the sensitivity output diagram of the 1H line in FIG. 7, the sensitivity output becomes non-uniform corresponding to the non-uniformity of the area of the sensor opening. That is, the sensitivity output does not reach the constant value A, but varies. In this FIG.
The vertical axis indicates the sensitivity output, and the horizontal axis indicates the position on the 1H line. Since the area of the sensor opening becomes non-uniform as described above, the unevenness of the sensor opening causes the sensor characteristics to become unstable. If the degree of the non-uniformity is large, the sensitivity becomes higher than an allowable level, resulting in a defective product.

[0005] The sensitivity output shown in the sensitivity output diagram of the 1H line in FIG. 7 is an example of the 1H line.
Variations also occur in the oblique direction. In FIG. 6, when a normal sensor opening area is a, + α1, + α2,..., + Αn, −β1, −β
When variation occurs like 2,..., −βn,
The sensitivity output also varies in proportion to that. Depending on the tendency and degree of the variation, sensitivity unevenness in a wide range, local sensitivity unevenness, and sensitivity unevenness of various shades may be caused, resulting in deterioration of CCD output characteristics.

Further, at the time of color imaging, uneven sensitivity of each sensor affects a color difference signal and a luminance signal, causing color unevenness.
In terms of sensor characteristics, the level becomes higher than the allowable level, resulting in a defective product.

[0007]

One of the factors that cause a problem in the sensor characteristics of the solid-state imaging device is an etching mask used when the sensor opening is formed by etching. That is, the thickness of the resist film forming the etching mask is not uniform. When the humidity of the coating atmosphere changes during the application of the resist, a slight variation occurs in the resist film thickness. In particular, when the humidity of the coating atmosphere becomes low, the resist is easily dried, so that the viscosity of the resist becomes non-uniform in the substrate surface, and a thick portion and a thin portion are generated.

When the sensor opening is patterned on the resist film in which the resist film thickness varies as described above, a variation occurs in the opening area, which is transferred to the shape of the opening after etching. Will cause non-uniformity. This causes unevenness in sensitivity and color unevenness in color imaging.

[0009] The resist coating apparatus is installed in a clean room, and the humidity in the clean room is usually 30%.
% Or less. Therefore, the conventional resist coating has been performed in an atmosphere where the film thickness tends to vary.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a method of forming a resist film and a method of manufacturing a solid-state imaging device, which have been made to solve the above-mentioned problems. That is, in the method of forming a resist film, a resist solution is dropped and spread on a rotating substrate, and when a resist film is formed on the substrate, the humidity of the atmosphere around the substrate is 35% or more and 70% or less. It is characterized by keeping it.

The method for manufacturing a solid-state imaging device includes a resist coating step of dropping and spreading a resist solution on a rotating substrate and forming a resist film on the substrate.
In the resist coating step, the humidity of the atmosphere around the substrate on which the resist film is formed is maintained at 35% to 70%.

In the method of forming a resist film, since the humidity of the atmosphere around the substrate when forming the resist film is maintained at 35% or more and 70% or less, the volatilization of the solvent in the resist within the substrate surface is moderate and uniform. Then, it becomes possible to form a resist film having high film thickness uniformity. If the humidity is lower than 35%, volatilization of the solvent in the resist spread over the substrate surface is partially facilitated, the viscosity of the resist in that portion is increased, and the resist film has an uneven thickness. Becomes On the other hand, when the humidity is higher than 70%, the solvent in the resist spread over the substrate surface does not evaporate, and the resist is greatly affected by the centrifugal force at the periphery of the rotating substrate. The resist film is formed to be thinner than a predetermined thickness, and the resist film is formed thicker in the central portion of the substrate than in the peripheral portion of the substrate because the influence of centrifugal force is not so large as in the peripheral portion. As a result, the thickness of the resist film becomes non-uniform in the substrate surface. Therefore, it is necessary to keep the humidity between 35% and 70%.

In the method of manufacturing a solid-state imaging device, the humidity of the atmosphere around the substrate is maintained at 35% or more and 70% or less in the step of forming the resist, similarly to the method of forming the resist film. This makes it possible to form a resist film having high film thickness uniformity. As a result, the variation in the area of the sensor opening is reduced, and the opening having excellent opening area uniformity can be formed.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a method for forming a resist film according to the present invention will be described with reference to a resist film forming process diagram in FIG.

As shown in FIG. 1A, the substrate 11 is
For example, it is held by a rotating spin chuck 21. A resist solution 12 (indicated by an arrow) is dropped from, for example, a nozzle 22 near the center of the substrate 11.
Since the substrate 11 is rotating, as shown in FIG. 1 (2), the dropped resist solution 12 is spread over the entire surface of the substrate 11 by the centrifugal force due to the rotation of the substrate 11, Excess resist solution 12e (indicated by an arrow) is blown to the side of the substrate 11 by centrifugal force and removed. At this time, the solvent in the spread resist solution 12 volatilizes appropriately. In FIGS. 1 (2) and (3), the illustration of the nozzle 22 is omitted.

Then, as shown in FIG. 1C, the substrate 1
1. A resist film 13 composed of a resist solution 12 spread on
Is formed, the rotation of the spin chuck 21 is stopped.
During the period from the dropping of the resist solution 12 to the formation of the resist film 13, the humidity of the atmosphere around the substrate 11 should be 35% or more.
Keep below 0%. Although not shown, after that, baking is performed to evaporate the solvent in the resist film 13 and harden the resist film 13 to complete the resist film 13.

In the method of forming a resist film, the humidity of the atmosphere around the substrate 11 when forming the resist film 13 is set to 3
Since it is kept at 5% or more and 70% or less, the volatilization of the solvent in the resist in the plane of the substrate 11 proceeds moderately and uniformly,
This makes it possible to form the resist film 13 having high film thickness uniformity.

If the humidity is lower than 35%, volatilization of the solvent in the resist spread over the surface of the substrate 11 is easily promoted partially, and the resist viscosity in that portion is increased, and the resist film is formed. A non-uniform film thickness results. On the other hand, when the humidity is higher than 70%, the solvent in the resist spread over the surface of the substrate 11 does not evaporate, and the peripheral portion of the rotating substrate 11 is greatly affected by centrifugal force. As a result, the resist is stretched thinner than a predetermined thickness, and the resist film is formed thicker in the central portion of the substrate 11 than in the peripheral portion of the substrate 11 so as to be less affected by centrifugal force than in the peripheral portion. As a result, the thickness of the resist film becomes uneven in the plane of the substrate 11. Therefore, it is necessary to keep the humidity between 35% and 70%.

The method of forming a resist film described with reference to FIG. 1 can be applied to a step of forming a resist film in a method of manufacturing a solid-state imaging device.

That is, the step of forming the resist film comprises:
A step of forming a resist film serving as an etching mask for providing a sensor opening of a solid-state imaging device in a light-shielding film, in which a resist solution 12 is dropped and spread on a rotating substrate 11, and is spread on the substrate 11. A resist film 13 is formed. At this time, the humidity of the atmosphere around the substrate 11 on which the resist film is formed is kept at 35% or more and 70% or less.

In the method of manufacturing a solid-state imaging device, the substrate 1
Since the humidity of the surrounding atmosphere is kept at 35% or more and 70% or less, it is possible to form a highly uniform resist film for the same reason as the resist film forming method described with reference to FIG. Become. As a result, the variation in the area of the sensor opening is reduced, and the opening having excellent opening area uniformity can be formed.

Next, a manufacturing method for forming an opening in a light shielding film of a CCD imager will be described below. First, the CCD imager will be described with reference to the schematic diagram of the CCD imager in FIG. As shown in FIG. 2, the CCD imager 31 is provided with a light receiving section (sensor section) 32 for each pixel (a section indicated by a two-dot chain line). Each light receiving section 32 in the vertical direction
Is connected to the vertical transfer unit 34 via the read gate 33. A horizontal transfer unit 35 is connected to the lowermost stage of each vertical CCD transfer unit 34, and an output unit 36 is provided at an end thereof. Although not shown, the sensor opening is formed in a light-shielding film on each of the light receiving sections 32.

Next, the vicinity of the sensor opening is indicated by X in FIG.
Explanation will be made with reference to an X-ray enlarged sectional view. As shown in FIG. 3, a P-type well 42 is formed on an N-type semiconductor substrate 41,
In the P-type well 42, a P-type read section (read gate) 43, a light receiving section 32 formed of a PN junction, a P-type channel stop 44, and an N-type vertical CCD transfer section 34 are formed in this order. A transfer electrode 46 made of polysilicon is formed on the channel stop 44 and the vertical CCD transfer unit 34 via the insulating film 45. Further, an insulating film 51 is formed on the entire surface, and a light-shielding film 52 is formed on the surface thereof. A sensor opening 53 is provided in the light shielding film 52 on the light receiving section 32. Further, a protective film 54, a flattening film 55, a color filter 56 and the like are laminated.

The CCD imager 31 described above is
The sensitivity output changes depending on the area of the sensor opening 53 on the light receiving section 32. Therefore, if the area of the sensor opening 53 provided on each light receiving section 32 is non-uniform, the sensitivity output varies, which causes uneven sensitivity, uneven color, and the like.

Therefore, in the manufacture of the CCD imager, the sensor opening 53 is formed by the following process. That is, in the same manner as described with reference to FIG. 1, an etching mask is formed on the light shielding film 52 by performing resist patterning, and the light shielding film 52 is etched using the same to form the sensor opening 53. At the time of the resist patterning, the humidity around the substrate is kept at least between 35% and 70%. As a result, extreme progress of drying of the resist during the application of the resist is suppressed, so that variations in the resist film thickness are minimized. As a result, variations in the resist patterning shape are suppressed, and the shape of each sensor opening 53 can be kept uniform.

As a result, as shown in the layout diagram of the unit cell including the sensor openings in FIG. 4, the individual sensor openings 53 are formed with a uniform opening area a. as a result,
As shown in the sensitivity output diagram of the 1H line in FIG. 5, in the CCD imager, the sensitivity output becomes a constant value A between the pixels, and there is no variation. In FIG. 5, the vertical axis indicates the sensitivity output, and the horizontal axis indicates the position on the 1H line.

As described above, in the method of manufacturing a solid-state imaging device according to the present invention, at the time of resist patterning of the sensor opening, the humidity around the substrate is defined, whereby the above-described method shown in FIG.
As shown in (1), it enables uniform sensitivity output characteristics of the CCD imager. CC that is out of the allowable characteristic range of sensitivity unevenness that occurs when the humidity at the time of forming the resist film when forming the sensor opening is lower than 35%
The incidence rate of the D imager and the humidity is 35% or more and 70% or more.
% Of the CCD imager, which is out of the allowable characteristic range of the sensitivity unevenness when the humidity is below 35%, it is possible to suppress the occurrence ratio to less than 1/2 at a humidity of 35% or more and 70% or less. became.

In the method of forming a resist film according to the present invention, in addition to the formation of an etching mask used for etching the sensor opening, it is also possible to perform impurity implantation, processing of a polysilicon electrode, and resist patterning during processing of an insulating film and the like. By defining the humidity as described above, it is possible to improve the processing system. Thereby, fine processing becomes possible. It is also effective when patterning a color filter. That is, the color filter is formed on the protective film, but the thickness variation at the time of patterning tends to be worse due to the influence of the step below the protective film. Therefore, it is effective for improving the film thickness uniformity. as a result,
Since the area of each color filter can be formed to be constant, characteristics such as flicker and horizontal stripes can be improved.

[0029]

As described above, according to the method of forming a resist film according to the present invention, the humidity of the atmosphere around the substrate at the time of forming the resist film is maintained at 35% or more and 70% or less. In this case, volatilization of the solvent in the resist proceeds moderately and uniformly, and a resist film having high uniformity in film thickness can be formed.

According to the method of manufacturing a solid-state imaging device of the present invention, in the step of forming the resist, the humidity of the atmosphere around the substrate is maintained at 35% or more and 70% or less. Properly and uniformly, a resist film with high film thickness uniformity can be formed. Thus, the variation in the area of the sensor opening can be reduced, and the sensor opening having excellent opening area uniformity can be provided in the light shielding film. As a result, the sensitivity output of each sensor becomes constant, and sensitivity unevenness and color unevenness can be reduced. Therefore, the output characteristics of the CCD imager can be stabilized.

[Brief description of the drawings]

FIG. 1 is a process chart of forming a resist film showing an example of an embodiment according to a method of forming a resist film of the present invention.

FIG. 2 is a schematic diagram of a CCD imager.

FIG. 3 is an enlarged sectional view taken along line XX of FIG. 2;

FIG. 4 is a schematic layout diagram of a unit cell including a sensor opening formed by the manufacturing method of the present invention.

FIG. 5 is a sensitivity output diagram of a 1H line of a CCD imager formed by the manufacturing method of the present invention.

FIG. 6 is a schematic layout diagram of a unit cell including a sensor opening formed by a conventional manufacturing method.

FIG. 7 is a sensitivity output diagram of a 1H line of a CCD imager formed by a conventional manufacturing method.

[Explanation of symbols]

 11: substrate, 12: resist solution, 13: resist film

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (reference) H01L 27/14 H01L 27/14 D 5F046 F term (reference) 2H025 AB14 EA05 2H096 AA28 CA14 4D075 AC07 AC64 AC79 BB24Z BB56Y BB91Y CA48 DA06 DC21 DC24 EA45 4F042 AA06 AA10 BA20 BA25 EB09 EB13 EB17 EB29 4M118 AA06 AB01 BA13 CA03 CA40 EA01 FA06 5F046 JA02 JA27

Claims (3)

[Claims] 1. A method for forming a resist film on a rotating substrate by dropping and spreading a resist solution on a rotating substrate, wherein a humidity of an atmosphere around the substrate on which the resist film is formed is provided. Is maintained at 35% or more and 70% or less. 2. A method for manufacturing a solid-state imaging device comprising a step of forming a resist film on a rotating substrate by dropping a resist solution onto a rotating substrate and forming a resist film on the substrate. A method for manufacturing a solid-state imaging device, wherein the humidity of the atmosphere around the substrate is maintained at 35% or more and 70% or less. 3. The method for manufacturing a solid-state imaging device according to claim 2, wherein, in the step of forming the resist film, a resist film serving as an etching mask for providing a sensor opening of the solid-state imaging device in a light-shielding film is formed. A method of manufacturing a solid-state imaging device.