JP2548873B2 - Wet etching method for semiconductor 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 for manufacturing a semiconductor device, and more particularly to a wet etching method.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, an etching operation for removing an unnecessary portion includes dry etching and wet etching. Dry etching utilizes a chemical or physical reaction at the gas-solid phase interface to remove unnecessary portions. Dry etching is performed by placing a semiconductor device between electrodes in a sealed container. There are several methods called plasma etching, ion etching and sputter etching. This etching is easy to give directionality, that is, to make the etching rate in the vertical direction higher than the etching rate in the lateral direction, and it is called anisotropic etching, which is suitable for fine processing, It requires equipment and is not suitable for performing a large amount of etching treatment at one time.

Wet etching uses chemical reactions at the liquid-solid interface to remove unwanted parts. Compared to dry etching which requires special equipment, wet etching has a large capacity to be processed at one time and is low in cost. However, it is difficult for wet etching to have directionality. The etching proceeds not only vertically but also laterally, and the layer under the etching mask is also removed (called side etching).

FIG. 1 shows the state of this side etching. Side etching progresses in the layer to be processed (polyimide) 2 below the mask 1, and the mask 1 overhangs or bends like an eaves. The pattern of the mask 1 cannot be accurately transferred to the processed layer 2. Moreover, the overhanged portion of the mask 1 is likely to drop off, resulting in an obstacle in a subsequent process or a defect of the semiconductor device. For example, when the oxide film or the nitride film 3 exposed under the processed layer 2 is opened in a later dry etching step to expose the wiring layer 4 on the semiconductor substrate 6 thereunder, this overhang occurs. There is a possibility that the portion of the mask 1 will fall off as shown by 5. Therefore, in the conventional wet etching, control of side etching has been a very important problem.

[0005]

SUMMARY OF THE INVENTION
An object of the present invention is to provide a wet etching method which can be applied to fine processing by controlling etching.

A further object of the present invention is to provide a wet etching method which can shorten the steps by integrating the developing step and the etching step of the resist layer used for the etching mask.

A further object of the present invention is to make it possible to perform side etching controlled processing by means of low cost wet etching which enables a relatively large amount of processing.

[0008]

According to the present invention, when a resist layer serving as a mask in wet etching is exposed to form a pattern, a semi-exposure is performed on a boundary between an exposed portion and a non-exposed portion of the resist layer. Provide a part. In the wet etching step, this semi-exposed portion of the resist layer is removed similarly to the layer to be processed.

According to the wet etching method of the present invention, the processed layer under the exposed or unexposed portion of the resist layer developed according to the positive type or the negative type is removed by etching with the etching liquid. At this time, the etching direction of the layer to be processed proceeds not only in the vertical direction but also in the horizontal direction. Therefore, the etching solution also causes side etching on the layer to be processed below the boundary between the exposed and unexposed portions of the resist layer. However, since the resist layer at this boundary portion is a semi-exposed portion, it is attacked and removed by the same etching solution during the etching process. Therefore, the mask layer does not overhang like a canopy at the boundary (semi-exposure) portion. As a result, the exposure pattern of the resist layer including the half-exposed portion of the resist layer can be almost accurately transferred to the layer to be processed by etching. Moreover, the mask layer does not fall off, which does not cause an obstacle in the subsequent steps or a defect in the semiconductor device.

In the method of the present invention, the development of the resist layer and the etching of the layer to be processed may be performed in the same step.
That is, the resist layer is developed with a developing solution for developing the resist layer, and the layer to be processed is etched as it is. According to this method, the whole process can be shortened.

In the method of the present invention, the exposure may be not only irradiation of visible light or ultraviolet light but also irradiation of X-rays or electron beams. The present invention will be described below with reference to an embodiment.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a processed layer 22 of a semiconductor device which is subjected to an etching process by a wet etching process according to an embodiment of the present invention, and a resist layer 21 which serves as an etching mask thereof. The processed layer 22 is made of polyimide (Po
and is applied to be used as a final insulating protective film on the substrate 26 of the semiconductor device for which the wiring process has been completed, and has a thickness of about 5 μm.
Under the processed layer 22, there is an oxide or nitride film 23 and an underlying wiring layer 24. A contact hole for forming a bonding pad communicating with the wiring layer 24 is formed in the final insulating protective film (processed layer) 22 by the etching process of the present invention described below.

The polyimide of the layer to be processed 22 is left in an incomplete imide bond state by being subjected to an appropriate heat treatment after heating, that is, heating to about 120 ° C. When the polyimide is in this imperfect imide bond state, the polyimide is soluble in the alkaline developer of the resist layer 21. Therefore, by utilizing this property, the resist layer 21 is developed and at the same time,
It is possible to wet-etch the processed layer 22 using the developer. However, polyimide is about 35
When heated to 0 ° C., imidization proceeds completely and the resist layer 21 cannot be dissolved in the developing solution. Conventionally, polyimide was completely imidized, and holes were later formed by dry etching.

The resist layer 21 may be a novolac positive resist. The positive resist 21 becomes alkali-soluble depending on the amount of light energy applied. That is, the exposed portion of the resist layer 21 is dissolved by the alkaline developing solution. The degree of solubility depends on the amount of light energy applied. This resist layer 21
Has a thickness of about 3 microns.

In FIG. 3, a contact hole pattern 31 is formed in the resist layer 21 by irradiating it with light (wavelength 436 nm). The pattern 31 is composed of a completely exposed portion 32 of the central portion B and a semi-exposed portion 33 of the peripheral portion. It should be noted here that the size of the contact hole formed in the layer 22 to be processed by etching is the size A including the peripheral portion 33 of the half exposure. Areas other than the pattern 31 of the contact holes are unexposed areas 34 which are not exposed.

In order to form the exposure pattern 31 as shown in FIG. 3, exposure is performed using the photo mask prepared by the method shown in FIGS. 7 to 9. First, as shown in FIG. 7, a light shielding layer 72 of chromium oxide Cr2O3 and chromium Cr is deposited on a glass substrate 71, and a light beam corresponding to a size including the peripheral portion A of the exposure pattern 31 is formed by a conventional method. A window 73 for transmission is formed. The photo mask having the window 73 is manufactured by the same method as that for forming a photo mask which forms the same pattern as the exposure pattern in the conventional method.

To make the photomask used in the method of the present invention, a semitransparent chrome layer 84 is blanket deposited onto the conventional photomask shown in FIG. 7 as shown in FIG. To do. The semitransparent chrome layer 84 transmits approximately half the light (wavelength 436 nm) used for exposure. On the other hand, the light blocking layer 72 blocks almost 100% of light. Next, as shown in FIG. 9, the chromium layer 84 in the central portion B of the window 73 is removed. A semitransparent chrome layer 84 is left outside the central portion B of the window 63. Light (wavelength 436) generated by the photo mask 91 shown in FIG.
(nm) transmittance pattern is shown in FIG. When this photo mask 91 is used, the exposure pattern is formed by an area of 100% of which is completely exposed in the central portion and a semi-exposed area of 50% of which is exposed in the outer peripheral portion. The other parts are not exposed.

Next, the development of the exposure pattern 31 of the resist layer 21 and the subsequent etching of the processed layer 22 will be described with reference to FIG. An alkaline developer such as TMA
H (tetramethyl hydroxide) dissolves the resist portion 32 of the central portion B of the completely exposed pattern 31. This is because the resist portion 32 is completely exposed to light and its components are completely alkali-soluble and immediately react with the developing solution. This developing solution also dissolves the processed layer 22 under the central portion B to remove it by etching. This is because the layer to be processed 22 is a polyimide in a semi-imide state that exhibits alkali solubility.

Etching of the processed layer 22 proceeds as shown by the arrow in FIG. The etching proceeds substantially in the same direction in the vertical direction and the horizontal direction. The etching in the vertical direction proceeds downward in the figure, but the etching in the horizontal direction proceeds in the resist layer 21.
Side etching that penetrates into the bottom of the. The semi-exposed exposed pattern portion 33 has a weaker solubility than the completely exposed portion 32, dissolves in the developing solution relatively slowly, and is dissolved and removed as side etching enters. When the semi-exposed portion 33 is melted in this way, the layer 22 to be processed underneath is further etched in the vertical direction and removed. As a result, in the conventional case, the mask layer 21 at the boundary portion 33 that overhangs like an eave due to side etching is removed by etching, and the processed layer 22 has no side etching. Is formed.

By selecting the size of the semi-exposed portion 33 of the resist layer 21 and its exposure amount, if the etching process is completed when the semi-exposed portion 33 is removed, the pattern 31 as shown in FIG. The contact hole 51 having the same cross-sectional area A from the opening to the bottom is
2 is formed.

Next, as shown in FIG. 6, contact holes 51 are formed.
A hole is formed in the oxide or nitride film 23 exposed underneath by well-known anisotropic dry etching, and the wiring layer 24 underneath is exposed to complete the contact hole 51.

In forming the exposure pattern of the present invention, double exposure is carried out in place of the photo mask shown in FIG. 9 to form a completely exposed portion in the central portion and a semi-exposed portion in the peripheral portion. You can also do it. The layer to be processed is not limited to the final insulating protective film, but may be an interlayer insulating film of a semiconductor device.

[0023]

According to the wet etching method of the present invention, the side etching can be controlled and it can be applied to fine processing. It is possible to prevent the resist layer from overhanging due to side etching, and to prevent the overhanging resist layer from falling off to become an obstacle or a defect in a subsequent process. Therefore, wet etching, which is lower in cost than dry etching, can be applied to the etching process in which size control and quality control are severe. Further, if the layer to be processed is also etched with the resist developing solution, the whole process can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a conventional wet etching method.

FIG. 2 is a sectional view of a step showing a wet etching method according to an embodiment of the present invention.

FIG. 3 is a sectional view of a step showing a wet etching method according to an embodiment of the present invention.

FIG. 4 is a sectional view of a step showing a wet etching method according to an embodiment of the present invention.

FIG. 5 is a sectional view of a step showing a wet etching method according to an embodiment of the present invention.

FIG. 6 is a sectional view of a step of a semiconductor device manufactured by wet etching according to an embodiment of the present invention.

FIG. 7 is a sectional view of a step showing a method of manufacturing a photo mask used for wet etching according to an embodiment of the present invention.

FIG. 8 is a sectional view of a step showing a method of manufacturing a photo mask used for wet etching according to an embodiment of the present invention.

FIG. 9 is a sectional view of a step showing a method of manufacturing a photo mask used for wet etching according to an embodiment of the present invention.

FIG. 10 is a diagram showing the light transmittance of a photo mask used for wet etching according to an embodiment of the present invention.

[Explanation of symbols]

 21 resist layer 22 processed layer 31 exposure pattern 32 fully exposed portion 33 half exposed portion 34 unexposed portion

Claims (2)

(57) [Claims] 1. A provided a resist layer to be processed on the substrate, the resist layer exposed portions, the unexposed parts, and, exposed to a pattern of the said exposed portion at the boundary of the non-exposed portion and a semi-exposed portion and the perform wet etching using the resist layer which is exposed as a mask a wet etching method of processing the processed layer, wherein the layer to be processed and the rate of progression et etching of the semi-exposed portion
At the same time removing the layer to be processed and the semi-exposed portion by aligning the progression rate of the error etching, the processed
Substantially left the protruding portion of the resist layer on the layer
Wet etching method characterized by not performing. 2. The wet etching method according to claim 1, wherein the rate of progress of etching of the semi-exposed portion is adjusted by the exposure amount of the semi-exposed portion.