JPS6273633A - Formation of pattern - Google Patents

Abstract

PURPOSE:To obtain the high-aspect and high-accuracy pattern of organic material film by forming a resist pattern and a metallic film on an organic material film on a substrate and etching the organic material film by using a pattern of the metallic films remaining in recesses after removing the metallic film. CONSTITUTION:Polyamic acid is applied on a substrate 1 by spin-coating and a polyimide film 2 is formed by heat treatment. On this film, a positive resist pattern 4 is formed. On the overall surface of the resist film 4, a metallic film 3 of Cr, Mo or etc. is vapor-deposited. Next, the substrate 1 is immersed in acetone to remove the resist pattern 4 together with the metallic film 3 whereas leaving a pattern of the metallic film 3 formed in openings of the resist pattern 4. By using the metallic film 3 a mask, the polyimide film 2 is removed by etching. After that, the metallic film 3 is removed by a proper method. Consequently, the high-aspect, high-accuracy, and high-reliability pattern can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for stably forming a pattern of a high aspect ratio organic material film using an etching gas.

[Conventional technology]

Figures 1 (al to cl) are cross-sectional views showing the main stages of a conventional method of forming fine patterns using two-stage etching. First, as shown in Figure 2 (a),
Semiconductor substrate f1. Polyamic acid is spin-footed on top of the polyimide film (2), which is converted into polyimide by heating at 250°C or higher, and a titanium (Ti) film (2) is formed on top of this as an intermediate layer.
), a metal film (3) of tantalum (Ta), molybdenum (Mo'), chromium (Cr), etc. is uniformly formed, and a resist pattern (4) is further formed thereon. Next, the same figure (b
), using the resist pattern (4) as a mask, the intermediate layer metal film (3) is dry etched using the first etching gas. At this time, the resist pattern (
41 also becomes thinner as shown. Next, the same figure (C
), the metal pattern (3) formed using the second etching gas in the process shown in FIG.
Using this as a mask, the polyimide film (2) is etched.

If two-step etching is used in this manner, a high selectivity between the intermediate layer metal mask (3) and polyimide film (2) to be etched can be achieved, so that a fine pattern with a high aspect ratio can be formed. However, if the thickness of the polyimide film (2) is increased, the metal film (3) in the intermediate layer must also be made almost proportionally thicker. Sometimes, the film thickness of the resist pattern (41) is insufficient.If the resist (4) is made thicker to compensate for this, it will be disadvantageous in forming a fine pattern.For example, if the pattern width is 0.5 m In this case, a resist film thickness of about 0.5) 1 m (41 mm) is required. is affected by the respective film thicknesses of the first layer polyimide film (2) and the third layer resist pattern (41). 3
Estimation will be made based on the analysis shown in FIG. 4 and FIG.

In FIG. 3, the intermediate layer metal film (3
) is removed by etching. In the figure, the solid line shows the state before etching, and the broken line shows the state after etching.

The rate of decrease in film thickness of resist pattern (4) and gold film (3) is dx, /dt --Vr
[11dxrm/dt; = Vrm[2
] is given by. The subscripts r and rm respectively indicate the resist pattern (4) and the resist and metal film (31) that use this as a mask.The negative sign in the j5 equation indicates a decrease in film thickness. The film thickness change during etching is X r m-Hm 7 for the resist and metal film, respectively.
Vrmd t t> trma C41
rm, Hr and Hn+ are the film thicknesses of the resist mask (41) and the intermediate layer metal film (3), respectively, before being removed by etching.Furthermore, trB and trms are the thicknesses of the resist pattern (41) and the intermediate layer metal film (3), respectively, before etching is started. ) and metal film (3) indicate the time at which etching removal begins.If we assume that the temporal fluctuations in the etching rate are negligible, then vr and vrm can be expressed as (outside the integral). The calculation is straightforward.The time tm required to completely remove the intermediate layer metal film (31) by making the resist pattern 141 a blank.
e and the remaining film jMxr of the resist pattern (4) at the time t - s tme are given by the following equations.

tme-(Hm//vrlTl)+trm8[5]×r
”' ) Ir -Vr ('me - also r9)
[6] Intermediate layer metal film (3
) must be completely etched away, the resist pattern (4) must have a certain residual culm [7]. If the resist pattern (4) disappears before the intermediate layer metal 11Q13+ is removed, the portion of the metal film (3) that should remain will also be etched away, resulting in an insufficient film thickness.As a result, When removing the polyimide film (2) by etching using the pattern of metal H (3) as a mask,
Before the polyimide film (2) is completely removed, the metal film (3+ pattern) disappears, so if you continue etching, the polyimide film (2) will be reduced. Therefore, the resist pattern (4) is masked. Basic conditions for etching without reducing the thickness of the intermediate layer metal film (X r in formula [6]) from Q to V
r Hr > Im+ ("rms - trs)vr
[7] Given by Vrm. For now, trms=trs=O
Then, the film thickness of the resist (4) is the same as that of the intermediate layer metal film (3).
A thickness equal to (vr/vrm) times the positive film thickness Hm is required. , (vr/vrrn) varies depending on many parameters such as the resist (4) and the material of the intermediate layer metal film (31), the Ni91.fE power of the etching gas used, the flow rate, the output, etc. It is preferable that Vr m) be smaller than 1, but it seems that a process that satisfies this condition is very difficult.

Next, (keeping in mind the inequality of Equation 71), a metal film mask (3) with a film thickness of Hm is used to form polyimide III, 'Si' with a film thickness of Hp.
The film thickness conditions under which 2+ can be completely selectively removed using the second etching gas will be discussed.

In Fig. 4, if the speed of thinning of the metal film (3) that serves as a mask for the polyimide film (2) is v1η, and the speed of thinning of the polyimide film (2) is Vmp, then dxrn/dt, =-vmC8J dxmp/dt --vmp [
9] holds true. The subscripts m and mp respectively indicate the permanent metal film [3+] and polyimide film (2) when the metal film pattern (3) is masked and the polyimide film (2) is etched.
). The negative sign in the equation fosters a decrease in film thickness. The film thickness changes during etching are as follows for the metal ff13+ and polyimide film (21).

Xm −HITI −fVmdt [
10) m8 Here, IIm and Hp are the thickness of the metal film (3) and the polyimide film (+1) before being removed by etching, respectively.Furthermore, tII1 day and tmps are the thickness of the gold film (3) and the polyimide film (+1), respectively, after the start of etching. 3) and polyimide film (
2) indicates the time when etching removal actually begins. If we assume that the temporal fluctuation of the etching rate is negligible, then Vm.

Since it can be taken outside the burial mound, calculations become easier. The remaining film thickness xm of the metal film pattern +31 at the time tp6 and the time t+5tpe at which the polyimide film i11 is completely selectively etched away using the gold N film pattern 13 as a mask are given by the following equations.

tpe = (Hp/Vmp) + tmps
[121Xm ” Hm −Vm(tve −
tms) [13] At the time when the polyimide film (2) is completely removed by selective etching, the remaining film thickness of the gold mask (3) must be xm)Q in equation (13). Once upon a time.

In order to completely pattern the polyimide film (21), the thickness of the metal film (31) and the polyimide film (2) must be
The following inequality must hold.

Hm>(Vm/vmp)Hp + (tmpg -t
mll) Vm (14) The second gaseous element (02) used for etching the polyimide film (2) is
It's disgusting. Metal film (depending on the type of 31,
The value of (Vm/Vmp) is distributed around 1/10.

ULh, etching of the intermediate layer metal film (3) using the resist pattern (41 as a mask), etching of the polyimide film (2) using the intermediate layer metal film (3) as a maskffI J
i "F=" has been considered. Then, we will finally consider the film thickness conditions of the intermediate layer metal film 13) from the perspective of the entire two-step etching. [Solving the inequality for T(m in equation 71, [14] By combining K with the expression, 2
The film thickness conditions for the intermediate layer metal film (31) known in the stepwise etching process are expressed by the following equation.

To further simplify the conditions, if the induction time (tmps, tmg, trlTIJ trs) is omitted from the equation [15], the equation [15] becomes -. For example, if the thickness of the polyimide film (2) is H
If p -1.5 μm (vm/Vmp) is l/10 culm degree and the width of resist pattern (4) is 0.5% Il+,
Thickness Hr-Q, 5pm.

When (Vrm/Vr) is set to about 115, equation [16] becomes 0.15. Ilm<Hm<O9l)tm, and the inequality is not satisfied. Therefore, the thickness of the metal film (31 Hm
If 0.15 μm, the IQ thickness of the resist film (41) must be 0.75 μm or more.
, 'y5) For resist lll3in thickness of tm or more, 0.5. It becomes difficult to pattern to a width of xm.

[Problem that the invention seeks to solve]

In the conventional two-step etching method used to form fine patterns with high aspect ratios, as shown in equations [15] or [16], the film thickness of the intermediate layer is equal to that of both the resist cavity and the polyimide film. Limited by thickness.

In order to selectively etch the middle M layer using a resist pattern in the submicron region as a mask, it is necessary to make the middle layer thinner.

Conversely, this is disadvantageous when selectively etching a polyimide film.

The present invention has been made to solve the above-mentioned problems, and it is possible to easily determine the film thickness of the resist film intermediate layer gold film and the organic material film, and also to create a high aspect ratio and highly accurate organic material film pattern. The purpose is to provide a pattern ff4 method that can be obtained.

[Means for solving problems]

The pattern forming method according to the present invention, when patterning an aged organic material film on a semiconductor substrate, forms a resist pattern thereon, and further forms a metal film over the entire surface including the recesses of the resist pattern. Then, in step 1-, the resist pattern is removed, the metal film on it is removed by lift-off method, and the organic material film is etched using the pattern of the metal film remaining in the recessed portion as a mask. .

[Effect]

In the pattern forming method of the present invention, a metal mask for patterning an organic material film is formed by a lift-off method, so it can be made thicker than when it is formed by etching using a conventional resist mask. Etching of the film becomes easy, and it becomes possible to form submicron patterns with high aspect ratios.

〔Example〕

Figure 1 is a cross-sectional view showing the main stages of a pattern forming method according to an example of the present invention, and the same reference numerals as in the above-mentioned conventional example indicate the same parts. First.

As shown in Figure 1 (al), polyamic acid is spin-coated onto the substrate fl+, heat-treated in a lagoon at 250°C or higher to convert it into polyimide, and a polyimide film (2) is formed. (4i wo form 1fi do.

When the pattern width is 0.5 mm, the thickness of the resist film (41) of about 0.5 μm is sufficient.Next, as shown in FIG. Metal film (3) such as Cr or Mo is heated to 2000-300
Vapor deposition is performed on the entire top surface including the openings to a thickness of 0A. next,
In the same figure (c), the substrate fli is immersed in acetone and the resist pattern +41 is removed together with the metal film (3) on it, and the pattern of the metal film (3) formed in the opening of the resist pattern (41) remains. 6 Next, the same figure (di
As shown in the figure, the polyimide film (21) is removed by etching with 02 gas plasma using the K and metal n+31 masks as a mask.Then, as shown in the figure (al), the metal film (3) is removed by an appropriate method to remove the metal film (3) on the substrate full. Polyimide film (2
) A fine pattern with a high aspect ratio can be obtained. In experiments conducted by the inventor, a metal film (31
Using this mask, a polyimide pattern with a thickness of 2.9) tm could be obtained.

In the pattern forming method of the present invention, a polyimide film (2
), the thickness of the metal film (3) and the resist film (41) because there is no step of etching the metal film t3+ using the resist pattern (4) as a mask, as in the conventional method (Vm/Vmp )Hp+Vm(tmpa-tms)<H
m<Hr [ryl inequality holds. That is,
The lI9 thickness of the metal film (3) is the same as that of the resist film (4).
It can be seen that it is better to make the film thinner than the film thickness of the polyimide film (2) that forms the pattern.Furthermore, the etching selectivity of the polyimide film (2) and the metal film (31) becomes clear. The film thickness can be easily estimated.

In the above example, the pattern was formed using a positive resist.
A negative resist may also be used. The metal film formation method is resistance evaporation, i
Any conceivable film forming method such as t-beam evaporation, sputtering evaporation, ion blasting, vapor phase growth, liquid phase growth, etc. may be used.

Although the final pattern material is made of mulberry polyimide, any general organic material such as negative or positive resist may be used. Although materials such as Cr and MO were used as the mask material for polyimide etching, any material may be used as long as it has a high selectivity for polyimide etching and can be formed into a film.

Equation [17] is an inequality derived based on the ninth simplified assumption that will be used to explain the present invention in detail.

Therefore, in carrying out the present invention, it is not strictly limited to formula [17].

〔Effect of the invention〕

Based on the detailed description 1 above, in the present invention, a resist pattern is formed on an organic material film, a metal film is placed on the four parts of the resist pattern, and the resist pattern is removed.

The organic material film is etched using the remaining metal pattern as a mask, resulting in a high aspect ratio.

It has the effect of obtaining a highly accurate and reliable pattern.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the main stages of a pattern forming method according to an example of the present invention; Figure 2 is a cross-sectional view showing the main stages of a conventional pattern forming method; 4 and 4 are cross-sectional views for analyzing each film thickness condition in the conventional method. In the figure, tit is a substrate, (2) is an organic material film, and 13
(4) is probably a resist film; the same reference numerals in the drawings indicate the same or equivalent parts.

Claims (2)

[Claims] (1) A resist is coated on an organic material film formed on a substrate, and this resist film is subjected to exposure and development treatment in a required pattern to form a resist having an exposed portion of the organic material film corresponding to the pattern. a first step of forming a pattern; a second step of forming a metal film over the resist pattern and the exposed portion of the organic material film; and removing the resist pattern together with the metal film thereon. , a third layer that leaves a metal film formed directly on the organic material film.
and a fourth step of selectively etching the organic material film using the remaining metal film as a mask. (2) The pattern according to claim 1, wherein the metal film is thinner than the thickness of the resist pattern and has a thickness such that it can still maintain a mask function even after selective etching of the organic material film is completed. Formation method.