JPH09279367A - Al taper dry etching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an Al taper dry etching method for Al used as a wiring material of a thin-film device, such as liquid crystal display. SOLUTION: This Al taper dry etching method is based on a resist recessing method for obtaining a small Al taper angle consisting of a stage for forming resist patterns 9 having the small resist taper angle corresponding to the desired small Al taper angle on an Al or Al alloy film 8 and a stage for subjecting the Al or Al alloy film having the resist patterns to anisotropic dry etching.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for processing aluminum (Al) or Al alloy (hereinafter collectively referred to as "Al") used as a wiring material for thin film elements such as LSI and liquid crystal displays. The present invention particularly relates to a taper dry etching method for an Al gate wiring and other Al wiring of an active matrix type liquid crystal display represented by a thin film transistor (TFT).

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display normally has a pattern width of 2
Wide as 10 μm or more. For the gate wiring, Cr, Ta, Mo, W or alloys thereof are generally used because of their ease of processing and chemical resistance. But,
Along with the increase in screen size and definition, signal delay due to an increase in electric resistance of gate wiring has become a problem. Further, in order to reduce the gate line width and increase the aperture ratio of the panel as much as possible, an Al gate electrode having a low electric resistance has been desired.

Further, the processing of Al can be carried out by wet etching of nitric acid, phosphoric acid or acetic acid type, or dry etching using Cl type gas. Currently, when Al is used in liquid crystal displays, wet etching is mainly used. However, when considering fine wiring, ensuring reproducibility, reducing waste and reducing cost, similar to LSI. The processing of Al is considered to proceed from wet etching to dry etching.

FIG. 8 shows a flat panel display '9.
1 is a TFT sectional view of a liquid crystal display described on pages 88 to 99 of 1 (published by Nikkei BP). In the figure,
1 is a substrate made of glass or quartz, and 2 is Al, C
Gate wiring made of r, Ta, Mo or W, 3 is a gate insulating film made of Si ₃ N ₄ , SiO ₂ or Al ₂ O _3, etc., 4 is a channel made of a-Si or poly-Si, and 5 is a A source / drain made of a-Si or poly-Si in which impurities such as P or B are implanted, a source / drain electrode 6 made of Al, Cr, Ta, Mo or W, and 7 Si ₃ N ₄ or SiO _2. It is a protective film composed of. This structure is called a channel-etch bottom gate structure.

A TFT generally has a bottom gate structure as shown in FIG. 8, and it is necessary to form a gate insulating film, a channel and the like on the gate wiring. Coverability of film formed on gate wiring, breakdown voltage of gate insulating film, and TFT
Many experiments have revealed that a small taper angle θ of at least 60 ° or less, preferably 40 ° or less is desirable in consideration of characteristics and the like. However, since the Al dry etching technology used in LSI technology is mainly aimed at miniaturization of 1 μm or less, it is aimed at verticalization opposite to taper, and the taper angle θ is usually 7
0 to 90 °.

As an Al taper dry etching technique, for example, Japanese Patent Application Laid-Open No. 64-15933 discloses a method using two etching steps of vertical etching and over-etching for taper. However, the base (substrate) made of SiO ₂ or Si ₃ N ₄ exposed by over-etching
There was a problem that even the bottom was etched.

As a taper dry etching method, for example, there is a side wall forming method in which a deposit (deposit) is positively formed on a side wall surface of a processed film to be etched to control lateral etching. There is a resist receding method of promoting etching of a resist mask by adding oxygen or the like.

However, the side wall forming method is not preferable because it has a drawback that the surface of the taper portion is likely to be roughened by deposits and dust is increased. Further, the conventional resist receding method has a drawback that oxygen in the resist causes dust generation during Al etching, and there is room for improvement.

Further, the isotropic etching method has a problem that etching residues are likely to occur.

[0010]

SUMMARY OF THE INVENTION In view of the above-mentioned problems, the object of the present invention is to provide an A gate wiring A for a liquid crystal display.
An object of the present invention is to provide an Al taper dry etching technique based on the resist receding method, which can reduce the l taper angle. Another object of the present invention is to provide conditions under which Al taper can be realized by a dry etching process which is as simple as possible with almost no problems of etching the underlying layer.

[0011]

It has been found that an Al taper dry etching method for obtaining a small Al taper angle is effective based on a resist receding method.

The resist receding method of the present invention is characterized in that a small resist taper angle is formed without adding oxygen to the resist and a small Al taper angle is obtained by anisotropic dry etching.

The Al taper dry etching method according to the present invention is as follows.

Based on a resist receding method for obtaining a small Al taper angle, which includes a step of forming a resist pattern having a small resist taper angle corresponding to a desired small Al taper angle and an ionic anisotropic dry etching step. Al taper dry etching method.

In the resist pattern forming step, post-baking may be performed at a resist pre-baking temperature or higher after the resist development.

The resist coating film thickness in the resist pattern forming step is preferably 1.5 μm or less.

In the resist pattern forming step, it is preferable that the focus position at the time of exposure is out of the focus range with respect to the line width of the exposure machine.

In the resist pattern forming step, it is preferable that the amount of exposure at the time of exposure is overexposure, which is larger than the optimum amount of exposure.

The resolution of the exposure device in the resist pattern forming step is preferably larger than the line width of the resist pattern to be formed.

In the resist pattern forming step, the γ value on the resist sensitivity curve is preferably 1.5 or less.

As the dry etching, parallel plate RIE type ionic etching for applying high frequency power to the substrate side or other plasma etching for applying high frequency power to the substrate side can be considered.

The gas pressure in the dry etching process is preferably 30 mTorr or less.

The main reaction gas of the gas in the dry etching process is BCl ₃ , and the BCl ₃ concentration is 80 to 100%.
It is good.

It is preferable that the etching rate ratio of Al to the resist in the dry etching step is 1.0 or less and the etching rate of the resist is fast.

The gas used in the dry etching process is
Fluorine-based gas is preferably added.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention comprises a step of forming a resist pattern having a small resist taper angle and a step of performing anisotropic dry etching.
Al based on resist receding method to obtain taper angle
The present invention relates to a taper dry etching method.

In the present invention, the Al taper angle means the angle θ ₁ formed by the taper portion (tilt portion) of the Al gate wiring and the substrate surface as shown in FIG. 1, and the resist taper angle is the taper portion of the resist. It means the angle θ ₂ formed by the upper surface of the Al processed film (where 1 is the substrate, 8 is Al, and 9 is resist).

There are various methods as follows for reducing the resist taper angle.

(1) Method of forming resist A method of reducing the aspect ratio (film thickness of resist / line width of resist). This is because the resist taper angle can be made smaller because the resist is apt to be pulled in the lateral direction when the resist contracts in volume during post-baking.

(2) At the time of exposure (a) A method in which the focus position is out of the focus range with respect to the resist line width. Here, the focus range means a range in which a substantially vertical resist pattern can be formed, and if deviated from this range, the resist is inevitably tapered.

(B) Overexposure in which the exposure amount is larger than the optimum exposure amount. This is because the resist taper angle can be made small because the resist, which is not originally exposed, is partially exposed by light diffraction and dissolved in the developing solution. The optimum exposure dose means the exposure dose when the reticle (mask) size and the resist size match.

(C) A method of making the resolution of the exposure device lower than the line width of the resist pattern. If the resolution is lower than the resolution that can form a vertical resist pattern (the line width of the resist pattern is smaller than the resolvable line width),
The formed resist is tapered.

(3) During development A method of increasing the solubility of the resist. In this case, it can be achieved by adjusting the temperature and concentration of the developer.

(4) Post-baking A method of causing volume shrinkage of the resist by performing post-baking at a temperature higher than the pre-baking temperature in the resist drying (solvent volatilization) step before exposure. This is to reduce the volume of the resist by removing the volatile components in the resist that could not be sufficiently volatilized during the pre-baking, and as a result, it is possible to reduce the resist taper angle. In particular, post-baking at a temperature equal to or higher than the softening point of the resist is advantageous because the resist taper angle can be reduced by softening and flowing the resist itself.

The above methods may be used alone or in appropriate combination.

The conditions for carrying out the above method will be described in the following examples. Particularly, in order to obtain the small Al taper angle desired in the present invention, 80 ° or less for an Al taper angle of 60 ° or less. 7 for an Al taper angle of 40 ° or less in order to improve the resist taper angle, the TFT characteristics of the bottom gate structure, the covering property of the film formed on the gate wiring, and the breakdown voltage of the gate insulating film.
The resist taper angle is preferably 0 ° or less.

In order to perform the resist receding method in the present invention, it is necessary to form a smaller resist taper angle corresponding to the smaller Al taper angle before etching.

When anisotropic etching is performed on a resist pattern having a small taper angle, the resist itself is also etched. Therefore, the Al layer existing under the resist also has a taper angle corresponding to the taper angle of the resist. Will have. That is, it is possible to transfer an angle corresponding to the resist taper angle to the processed film Al.

When isotropic etching is performed, Al is etched regardless of the shape of the resist and the taper angle, so it is difficult to achieve a small Al taper angle.

As the anisotropic dry etching, anisotropic dry etching using plasmatized ions is preferable, and from the viewpoint that the ions are incident on the substrate side, a parallel plate RIE method is performed by applying high frequency power to the substrate. Ionic anisotropic etching is preferred. For example, E
High density plasma type anisotropic dry etching known to those skilled in the art such as CR, helical, helicon, ICP or SWP type may be performed.

The ionic anisotropic dry etching method for obtaining a small Al taper angle according to the present invention is as follows.

(1) A method of lowering the gas pressure during etching. This is because the lower the gas pressure, the lower the probability of collision between ions, the longer the mean free path of ions, and the greater the anisotropy of etching. Therefore, the Al taper angle can be reduced.

(2) The gas composition during etching is BCl ₃
And a method of containing Cl ₂ . This is because it has a track record in LSI technology as a Cl ₂ -based gas capable of etching Al. In this case,
BC because it enhances anisotropic dry etching
The concentration of l ₃ is preferably 80 to 100%.

(3) A method of reducing the ratio of Al etching rate / resist etching rate (Al / resist selection ratio). In FIG. 1, where θ ₁ is the Al taper angle, θ ₂ is the resist taper angle before etching, M is the Al etching rate, and R is the resist etching rate, M / R is the Al / resist selectivity. , Tan θ
The relational expression ₁ = M / R × tan θ ₂ holds. Therefore, the Al taper angle can be made smaller because the Al taper angle is proportional to the above ratio.

The above methods may be used alone or in appropriate combination.

The conditions for performing the above method are as follows.
This will be described in the following examples.

[0047]

【Example】

[Example 1] The present invention will be described with reference to the following examples.
The present invention is not limited only to these.

The present invention provides two conditions: a process condition for forming a resist pattern (mask) having a small resist taper angle corresponding to a desired Al taper angle and a process condition for performing ionic anisotropic dry etching. It is necessary. First, the resist pattern forming conditions will be described.

FIG. 2 is a diagram showing the post-baking temperature dependency of the resist taper angle according to the present invention. From the figure,
It can be seen that by performing post-baking after development, the resist taper angle decreases as the post-baking temperature increases. This is because by post-baking at a temperature above the pre-baking temperature, the organic solvent remaining in the resist that could not be volatilized by the pre-baking volatilizes and the resist contracts in volume, and at high temperatures above the resist softening point the resist itself By softening and dripping (flowing), the resist is tapered (sometimes called spheroidizing). The post-baking temperature may be a temperature that can reduce the taper angle of the resist to the extent that the accuracy of the resist pattern is not deteriorated, and depends on the softening point of the resist (for example, 140 to 150 ° C.). This is advantageous for tapering the resist.

Next, a small Al taper angle is obtained by performing an ionic anisotropic dry etching process on Al using the resist pattern having the small taper angle.

The film thicknesses of the resist and Al are set to 1.
5 μm and 0.25 μm, the resist line width is 5,
10 and 50 μm (Experiment Nos. 1-1 and 1-2, respectively)
And 1-3) were tested.

The dry etching conditions at this time were as follows: parallel plate type RIE apparatus, gas pressure 30 mTorr, gas composition BCl ₃ / Cl ₂ = 40/10 sccm, power density 1.
It is 4 W / cm ² . As shown in FIG. 2, when a resist pattern having a post-baking temperature of 180 ° C. in Experiment Nos. 1 to 3 was used, the line width was 5, 10 or 5 respectively.
The Al taper angle of the 0 μm Al film was 30 to 60 ° (Experiment Nos. 1-4 to 6).

As can be seen from FIG. 2, the resist taper angle after post-baking has a large difference depending on the line width, and the wider the line width is, the smaller the resist taper angle is. Therefore, it is preferably 10 μm or more. Is good. The reason for this is that the smaller the resist film thickness and the line width aspect ratio, the easier the pattern edge is to be laterally pulled and taper when the resist volume shrinks.

If the aspect ratio of the resist film thickness and the line width is related to the resist taper angle due to the volume contraction during post-baking, the resist taper angle is considered to be related to the resist film thickness as well as the post-baking temperature. . If the smaller the aspect ratio is, the more easily the taper is made, the smaller the resist film thickness is, the smaller the taper angle is when the line width is the same.

FIG. 3 is a graph showing the dependency of the Al taper angle after post-baking according to the present invention on the resist coating film thickness. To obtain a resist taper angle as small as possible,
The post-baking temperature is 180 ° C. Al film thickness is 0.25 μm and resist line width is 5, 10 or 5
It was set to 0 μm (Experiment No. 1-7 to 9). A taper angle of 60 ° or less is obtained for any resist coating film thickness and line width. As described above, the smaller the resist film thickness, the smaller the resist taper angle. Particularly, it is more effective to make the Al taper when the resist coating film thickness is 1.5 μm or less, preferably 0.5 to 1.0 μm.

In the method of promoting resist taper utilizing volume shrinkage by post-baking the resist after development, the line width dependency is large for the above reason. Also, with a small line width, it is difficult to taper. Therefore,
A method of tapering the resist immediately after development without using post bake is preferable.

As another method for obtaining a small resist taper angle, the following can be considered. If the focus position during exposure is out of the focus range for the line width of the exposure machine, the focus will be blurred and a vertical pattern cannot be formed.As a result, the resist will be tapered even immediately after development. It The depth of focus is proportional to wavelength / (lens aperture ratio) ² .

Further, even when overexposure is performed in which the exposure amount at the time of exposure is several tens to several hundreds of% higher than the optimum exposure amount, the portion which is not originally exposed due to light diffraction is slightly exposed and dissolved in the developing solution. Immediately after that, the resist is tapered. In addition, since the line width of the resist pattern becomes thin during overexposure, a mask (reticle) that allows for this thinning
Need to be designed.

If the line width of the resist pattern is narrower than the resolution of the exposure device, a vertical pattern cannot be formed, so that the resist is tapered even immediately after development. Note that resolution is usually defined as the minimum line width that allows formation of a substantially vertical pattern, and therefore an isolated pattern such as a gate wiring cannot form a line width below the resolution. If the line width is fixed, the resolution is wavelength / lens aperture ratio N
Since it is proportional to A, the lens aperture ratio NA is, for example, 0.1.
It should be approximately (NA should be large, so keep it to the minimum necessary). Alternatively, the exposure wavelength is set to g and h of the Hg lamp of the light source used in the liquid crystal display manufacturing.
It is better to make the wavelength longer than the line.

FIG. 4 is a graph conceptually showing the relationship between the exposure dose and the resist residual film rate (resist sensitivity curve). The resist residual film rate on the vertical axis means the resist thickness after development / the resist thickness before development. The tan θ value of the tangent angle θ formed by the resist sensitivity curve and the exposure amount on the horizontal axis (logarithmic axis) is called the γ value. At present, the γ value of a resist generally used in liquid crystal displays (for example, TFR-B (manufactured by Tokyo Ohka Kogyo Co., Ltd.)) is about 1.8. The larger this value, the easier the vertical resist pattern formation becomes. Conventionally, in the case of miniaturization such as LSI, resist material development and process development have been made so that the γ value is 2 or more for pattern verticalization. The ideal (vertical) resist sensitivity curve is shown as A in FIG. The present invention is a method of reducing the Al taper angle θ ₁ to curves B and C. When taper is desired, the photosensitive group of the resist material, the base resin, and the pre-baking temperature (for example, 7) so that the γ value is 1.5 or less, preferably 0.5 to 1.5.
0 to 130 ° C., prebake time (for example, 30 seconds to 1)
The taper is facilitated by selecting conditions such as time), developing solution, developing temperature, and developing time. For example, a resist having a poor resist sensitivity is used, the resist prebaking temperature is lowered or raised from the optimum temperature, and the prebaking time is lengthened to decompose the resist photosensitive group to lower the resist sensitivity. , The temperature of the developing solution is raised or lowered from the normal temperature (for example, 23 ° C.) to increase the solubility of the unexposed portion of the resist, and / or overdeveloped to promote taper formation, which are appropriately combined. It is also possible to carry out.

It should be noted that the above method is not the optimum use condition in the conventional etching process, so that the pattern accuracy and reproducibility are likely to be deteriorated. However, in the case of the gate wiring of the liquid crystal display, since the line width is usually as wide as 5 μm or more, it is not necessary to have the accuracy required in the LSI and the like, and the gate wiring is often designed as a pixel which can be treated as an isolated pattern. Therefore, the above method can be performed.

[Embodiment 2] Next, conditions for promoting Al taper by ionic anisotropic dry etching will be described. In order to realize anisotropic etching, the gas pressure during etching is the most important. The lower the gas pressure, the lower the probability of collision between ions and the longer the mean free path, so that anisotropic etching is easily realized.

FIG. 5 is a diagram showing the gas pressure dependence of the Al taper angle during etching. Experiments were performed with resists having line widths of 5, 10 and 50 μm (Experiment Nos. 2-1 to 3) at gas pressures of 15, 30 and 60 mTorr. The resist post-baking temperature is 180 ° C., the resist film thickness is 1.5 μm, and the gas composition is BCl ₃ / Cl ₂ = 40.
/ 10 sccm, and power density is 1.4 W / cm ² .

From the figure, it can be seen that the smaller the gas pressure is, the easier the taper is, and that the taper angle is preferably 30 mTorr or less (preferably 15 mTorr or less) for any line width of 60 ° or less. The gas pressure is 60 mTo
If it is high with rr, the etching changes from ionic anisotropic etching to radical isotropic etching.
In the case of an Al alloy film such as AlSiCu, the shape of the taper portion is rough at the grain boundary, and the etching residue of an additive having a low vapor pressure such as Cu tends to remain on the substrate.

[Embodiment 3] The gas composition is also very important for promoting anisotropic dry etching.

FIG. 6 is a diagram showing the gas composition dependence of the Al taper angle during etching. The gas pressure during etching was 30 mTorr, and other conditions other than the gas composition were used in Example 2.
Same as (resist line width is 5, 10 and 50 μm
Experiments for the above are designated as experiment numbers 3-1, 2 and 3, respectively. The gas composition is generally BCl ₃ and Cl ₂ because it is a chlorine-based gas capable of etching Al. In this case, the higher the BCl ₃ concentration is, the more the deposition property (deposition property) is added to the dry etching, the effect of protecting the etched Al side wall surface and preventing the lateral etching, and the anisotropic etching is strong. Become. On the other hand, BCl ₃
When the concentration is low, there is no depositing property on the etched Al side wall surface, and the etching in the lateral direction proceeds even if it is contacted with Cl ₂ , so isotropic etching is likely to occur. In addition, the problem that the shape of the taper portion is rough at the grain boundary is likely to occur. In the present embodiment, the Al taper angle when the BCl ₃ concentration is 60% looks small in the figure, but in reality, the shape of the taper portion is rough and uneven (the taper angle is not uniform), and there is no linearity of the pattern. It could not be used. Therefore, B
The Cl ₃ concentration is preferably 80 to 100%.

Similar effects can be expected with SiCl ₄ other than BCl ₃ as a gas having a deposition property (deposition property) for promoting anisotropic etching of Al.

[Embodiment 4] The basic idea of the present invention is based on the resist receding method. Therefore, the mask resist is simultaneously etched during Al etching.

FIG. 7 is a diagram showing the dependence of the Al taper angle on the resist taper angle before etching calculated from the ratio (Al / resist selection ratio) between the resist etching rate and the Al etching rate during anisotropic etching. Al / resist selection ratio is 0.2, 0.5, 0.8, 1.0, 1.5
And 2.0 are 4-1 to 6 respectively. When the Al / resist selection ratio during etching is 1, the Al taper angle and the resist taper angle before etching are the same, but when the Al / resist selection ratio is 1 or less, Al taper is promoted. On the contrary, when the Al / resist selection ratio is 1 or more, Al verticalization is promoted. Therefore, etching conditions that promote the etching rate of the resist are preferable for Al taper so that the Al / resist selection ratio becomes 1 or less.

As a method for promoting the resist etching, the resist is etched in an etching gas.
It is conceivable to add a gas such as O ₂ , CF ₄ or SF ₆ which is not etched for l.

The effect of adding CF ₄ to the etching gas having an Al taper angle was confirmed. Post bake temperature is 180 ° C., resist film thickness is 1.5 μm, line width is 5, 10
And those of 50 μm (Experiment No. 4-
7-9). Here, CF ₄ was added at about 30% with respect to the total flow rate of the reaction gas of BCl ₃ and Cl ₂ . The results are shown in Table 1.

[0072]

[Table 1]

It can be seen that the Al taper is promoted at any line width by promoting the resist etching rate. In a general resist receding method, O ₂ is added to accelerate the resist etching rate.
In l etching, the reaction gases BCl ₃ and O ₂ react with each other to form an oxide of B, which causes dust in the apparatus.
It cannot be used because the number of device defects increases. Therefore, it is effective to add a fluorine-containing gas such as CF ₄ or SF _{6 which} is expected to have the same effect of promoting the resist etching rate.

By the Al taper dry etching method of this example, an AlSiCu alloy gate having a very small Al taper angle of about 20 ° was obtained.

[0075]

According to the present invention, a resist pattern having a small taper angle is transferred to Al by providing a condition for reducing the resist taper angle, a condition for ionic anisotropic etching and a condition for promoting taper formation. A below °
A taper angle of 1 can be obtained. Therefore, it is possible to contribute to the improvement of the covering property of the film formed on the Al gate wiring, the breakdown voltage of the gate insulating film, and the improvement of the TFT characteristics.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an Al taper angle and a resist taper angle.

FIG. 2 is a diagram showing the post-baking temperature dependence of the resist taper angle according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the dependency of the Al taper angle on the resist coating film thickness according to Example 1 of the present invention.

FIG. 4 is a diagram showing a resist sensitivity curve of Example 1 of the present invention.

FIG. 5 is a diagram showing a gas pressure dependency during etching of an Al taper angle according to Example 2 of the present invention.

FIG. 6 is a diagram showing a gas composition dependency of an Al taper angle during etching according to a third embodiment of the present invention.

FIG. 7 is a diagram showing the dependence of the Al taper angle on the resist taper angle in Example 4 of the present invention.

FIG. 8 is a sectional view showing a TFT structure of a liquid crystal display.

[Explanation of symbols]

1 substrate, 2 gate wiring, 3 gate insulating film, 4 channel, 5 source drain, 6 source drain electrode, 7 protective film, 8 Al, 9 resist.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/3065 H01L 21/302 G

Claims (14)

[Claims] 1. A resist pattern having a small resist taper angle corresponding to a desired small Al taper angle is formed by Al.
Or an Al taper dry etching method based on a resist receding method for obtaining a small Al taper angle, which comprises a step of forming on an Al alloy film and a step of performing anisotropic dry etching on an Al or Al alloy film having the resist pattern. . 2. The method according to claim 1, wherein the Al taper angle is 60 ° or less. 3. The method according to claim 1, wherein the resist taper angle is 80 ° or less. 4. The Al taper dry etching method according to claim 1, wherein in the resist pattern forming step, post-baking is performed at a temperature equal to or higher than a resist pre-baking temperature after resist development. 5. The Al taper dry etching method according to claim 1, wherein in the resist pattern forming step, the film thickness of the applied resist after drying is 1.5 μm or less. 6. The A according to claim 1, wherein in the resist pattern forming step, the focal position at the time of exposure is out of the focal range with respect to the resist pattern line width of the exposure machine.
l Tapered dry etching method. 7. The Al taper dry etching method according to claim 1, wherein in the resist pattern forming step, the overexposure is such that the exposure amount during exposure is larger than the optimum exposure amount. 8. The Al taper dry etching method according to claim 1, wherein, in the resist pattern forming step, the resolution of the exposure device is lower than the resist pattern line width to be formed. 9. The Al taper dry etching method according to claim 1, wherein the γ value in the resist sensitivity curve is 1.5 or less in the resist pattern forming step. 10. The Al taper dry etching method according to claim 1, wherein the dry etching step is performed by parallel plate RIE type ionic etching for applying high frequency power to the substrate side or plasma etching for applying high frequency power to the substrate side. 11. The gas pressure during etching in the dry etching step is 30 mTorr or less.
The Al taper dry etching method described in 0. 12. The Al taper dry etching method according to claim 10, wherein the etching gas has a BCl ₃ concentration of 80 to 100% in the dry etching step. 13. The Al taper dry etching method according to claim 10, wherein in the dry etching step, the ratio of the etching rate of Al at the time of etching and the etching rate of the resist is 1.0 or less. 14. The gas of a fluorine-containing compound is added to the etching gas in the dry etching step.
The Al taper dry etching method described in 0.