JPH10140377A - Dry etching method and liquid crystal display device - Google Patents

Abstract

(57) [Problem] In a method of patterning a metal chromium thin film by dry etching, a practical method that can be processed quickly without sacrificing patterning accuracy and has little variation in patterning. obtain. SOLUTION: Dry etching is performed by further adding an organic gas to a mixed gas of chlorine gas and oxygen gas. As the organic gas, methyl alcohol, methane and the like are used. This dry etching is performed in a plasma etching mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a dry etching method, and more particularly to an etching gas effective for patterning a chromium metal thin film with high accuracy.

[0002]

2. Description of the Related Art Wet etching is generally used as a method for etching a metal chromium thin film. This is because the etching rate is high, the area can be easily increased, the management is relatively simple, and the mass productivity is high.

On the other hand, the film quality of a metal chromium thin film differs depending on the film forming method and film forming conditions, and the etching rate and patterning characteristics differ depending on the film quality difference. For example, when forming a metal chromium thin film by a method of sputtering in an inert gas atmosphere such as argon with metal chromium as a target, the lower the pressure of the argon gas, the larger the crystal grains of the metal chromium in the thin film grow, The specific resistance of the thin film becomes lower. However, there is a problem that the increase in the crystal grain causes a decrease in the etching rate, a roughening of the patterning shape, and a reduction in the patterning accuracy.

[0004] As described above, the resistivity of the metal chromium thin film and the patterning property are in a contradictory relationship, and there is a problem that the patterning accuracy cannot be obtained if importance is placed on reducing the resistivity.

Further, in the above metal chromium thin film,
Even if the sputtering conditions are the same, the film quality of the chromium metal thin film is very unstable because the film quality may change due to the temporal change of the composition of the target surface.

[0006]

In the formation of the above-mentioned metal chromium thin film, the etching rate is difficult to control because the film formation is often carried out under the condition of giving importance to the specific resistance. In the usual wet etching, the amount of etching is adjusted by controlling the etching time, so that insufficient etching may result in residual etching, or excessive etching may cause side etching and narrow the pattern. Is frequently encountered.

As a solution to this, photolithography,
There is a method of repeating the wet etching process twice. However, this method has a problem that the number of steps is doubled, and mass productivity is impaired.

In the case where a step is formed on the base of the chromium metal thin film, an etching solution permeates between the metal chromium thin film and the base along the step when patterning the chromium metal, and There is a problem that the pattern of the chromium thin film is eroded or, in extreme cases, the pattern is cut.

In order to solve these problems, a dry etching method was studied. For dry etching of the metal chromium thin film, a mixed gas of chlorine gas and oxygen gas is usually used. As an etching method, there are reactive ion etching (hereinafter simply referred to as “RIE”) and plasma etching (hereinafter simply referred to as “PE”). Since the reaction rate of a chromium metal thin film in RIE mode etching is extremely low at 300 ° / min or less, it is realistic to perform the etching in PE mode.

In this dry etching, it is necessary to use oxygen gas in order to convert metal chromium into chromium oxide first, and to react this chromium oxide with chlorine to vaporize it. Has the effect of ashing the resist used as a mask,
There is a problem that the resist pattern is narrowed by the oxygen gas. Therefore, it is difficult to obtain patterning accuracy, and there is a disadvantage that patterning variation occurs.

Accordingly, the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a method for patterning a thin metal chromium film by dry etching, which can be processed quickly without sacrificing patterning accuracy. Moreover, it is an object of the present invention to obtain a practical method with less variation in patterning.

[0012]

Means taken by the present invention to solve the above-mentioned problem is that the metal chromium is formed by dry etching with a mask formed on the surface of the metal chromium in accordance with a predetermined pattern of the mask. A dry etching method in which an etching gas comprising at least a three-component system of chlorine gas, oxygen gas and organic gas is used.

According to this means, the etching rate can be improved without impairing the patterning property by mixing and etching the organic gas in addition to the chlorine gas and the oxygen gas.

Here, the organic gas preferably contains a hydrocarbon.

According to this means, since the hydrocarbon film is formed on the chromium metal mask by mixing the organic gas containing the hydrocarbon, the mask can be prevented from being eroded. Accuracy can be improved.

In this case, the organic gas further comprises:
An organic gas having a CH ₃ group is desirable.

According to this means, by using the organic gas having a methyl group, it is possible to achieve both improvement of the etching rate and securing of the patterning property.

When the organic gas containing hydrocarbon is an organic gas represented by C _n H _{2n + 2} , C _n H
_{When the} organic gas is represented by _{2n + 1} OH, it may be an organic gas represented by CHF ₃ .

Further, the organic gas may be an organic gas represented by CO.

According to this means, in particular, the amount of side etching is reduced, and the patterning accuracy can be improved.

Further, when the organic gas is an organic gas represented by CH ₄ and the flow ratio of the chlorine gas to the etching gas is 7: 4, the organic gas contains at least the organic gas and The flow ratio of the organic gas may be set to a range smaller than 0.75.

Further, when the organic gas is an organic gas represented by CH ₃ OH and a flow ratio of the chlorine gas to the etching gas is 7: 4, the organic gas contains at least the organic gas and is contained in the etching gas. The flow ratio of the organic gas may be set to a range smaller than 0.75.

According to this means, the etching rate can be improved without deteriorating the patterning property.

Further, the liquid crystal display device of the present invention has a metal chromium layer on at least one substrate, and dry-etches the metal chromium in a predetermined pattern of the mask in a state where a mask is formed on the surface of the metal chromium. Wherein the metal chromium is dry-etched with an etching gas comprising at least a three-component system of chlorine gas, oxygen gas and organic gas.

[0025]

Next, an embodiment according to the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a schematic structure of a dry etching apparatus used in the dry etching method according to the present invention. This dry etching apparatus is a parallel plate type apparatus, and can uniformly treat a relatively large area substrate surface.

In this apparatus, an upper electrode 11 and a lower electrode 12 are arranged inside a vacuum vessel 10 so as to face each other in parallel at a predetermined interval. Each of the upper electrode 11 and the lower electrode 12 has a flat plate surface, and the lower electrode 12
The substrate 20 is set on the plate surface of.

The upper electrode 11 is connected to a high-frequency power source 13 arranged outside the vacuum vessel 10, and has a frequency of 13.56M.
It is configured such that a high frequency potential (alternating current potential) of Hz is applied. Note that a ground potential is supplied to the vacuum vessel 10 and the lower electrode 12 via the wiring 14.

A gas introduction pipe 15 connected to a gas supply system (not shown) is connected to the upper electrode 11. The gas supply system is configured to derive a gas at a predetermined flow rate from each of the gas cylinders containing a plurality of types of gases, and to mix and supply the gases, for example, by appropriately adjusting the flow rate of each gas via a mass flow controller. It is configured to be able to supply. The gas introduced into the upper electrode 11 is supplied to the inside of the vacuum vessel 10 from a shower head-shaped bottom portion 11 a having a number of openings in the upper electrode 11. By forming the upper electrode 11 in this manner, the uniformity of etching can be improved.

Further, an exhaust pipe 16 connected to a gas exhaust system (not shown) (for example, a vacuum pump) is connected to the vacuum vessel 10. A known pressure control system is provided so that the pressure in the vacuum vessel 10 during processing can be controlled to be substantially constant by the exhaust from the exhaust pipe 16.

The present embodiment is a method used in a step of patterning a thin metal chromium film formed on a substrate 20. As shown in FIG. 2, a case where a metal chromium thin film is formed on the substrate 20 is a case where one electrode layer is formed of Cr in order to form an MIM element on an element-side substrate of an active matrix type liquid crystal panel. There is.

In this case, the substrate 20 is made of a transparent alkali-free glass, and Ta is deposited on the surface of the substrate 20 by sputtering for about several hundreds of mm, and an underlayer (not shown) made of Ta oxide by thermal oxidation. .) Is formed.
This underlayer is for improving the adhesion between the substrate 20 and an upper layer described below.

Next, Ta is deposited again to a thickness of about 2 to 3000 mm by a sputtering method, and is patterned by a usual photolithography method to form a wiring layer 21. The wiring layer 21 integrally includes a first electrode portion 21a protruding for each pixel region on the substrate 20 which is an element-side substrate. Further, the wiring layer 21 and the first electrode portion 21a
A thin insulating film (not shown) having a thickness of about 500 ° is formed on the surface of the substrate by anodization.

Next, a metal chromium thin film having a thickness of about 800 ° is deposited on the insulating film by sputtering of Cr so as to partially cover the first electrode portion 21. The dry etching apparatus shown in FIG. 1 is used to pattern the metal chromium thin film. The metal chromium thin film is formed by patterning an electrode portion 22a that overlaps on the first electrode portion 21a so as to intersect the electrode portion 22a.
2 having a pixel contact portion 22b extending from FIG.
The second electrode layer 22 formed in a planar pattern as shown in FIG.
Becomes

Finally, the pixel contact portion 22 of the second electrode layer 22
The transparent electrode 23 serving as a pixel electrode is formed of ITO (indium tin oxide) so as to overlap with the pixel electrode b.

In order to form a pattern of the second electrode layer 22 by etching the metal chromium thin film shown in FIG. 2, a resist is applied on the surface of the substrate 20 and exposed, and the portion where the second electrode layer 22 is formed is Then, an etching process is performed using this resist as a mask.

In this case, the portion where the first electrode portion 21a and the second electrode layer 22 are laminated via the insulating film becomes a bonding surface S (shaded portion) shown in FIG. 2, and the area of this bonding surface S is the MIM element. Is the bonding area. Therefore, the area of the joint surface S is M
It is an important factor that determines the characteristics of the IM device. For example, the area of the junction surface S determines the junction capacitance of the MIM element. As a result, the ratio between the liquid crystal capacitance and the MIM capacitance is determined, the ON resistance of the MIM element is determined, and the writing characteristics to the pixel electrode are determined. .

The area of the joint surface S of the MIM element is the first
It is determined by the pattern shape of the electrode portion 21a and the pattern shape of the second electrode layer 22. Therefore, patterning accuracy and pattern variation of the second electrode layer 22 are
It directly affects the accuracy of the characteristics of the M element and the variation in the characteristics.

Next, an etching process in the patterning step of the second electrode layer 22 will be described. This etching process is performed using the dry etching apparatus shown in FIG. In this case, a mixed gas of chlorine gas and oxygen gas for etching metal chromium is usually used as an etching gas introduced into the vacuum vessel 10. Oxygen ions and chlorine ions activated by the introduction of the mixed gas are generated, and a reaction represented by the following equation occurs on the metal chromium thin film, and the etching action proceeds.

[0039] _{^{Cr + XO 2- → CrO X ...}} CrO X + (2-X) O 2- + 2Cl - → CrO 2 Cl 2 ↑ ... That is, the metal chromium as shown in formulas and activated oxygen ions It reacts to chromium oxide, and this chromium oxide reacts with activated oxygen ions and chlorine ions to vaporize as shown in the formula.

Here, as shown in the above formula and the above, oxygen is indispensable for the etching reaction, but this oxygen has a problem that the resist is thinned during the etching by ashing a normal resist layer. . This ashing action on the resist lowers the patterning accuracy of the metal chromium thin film, and causes variations in the pattern of the second electrode layer for each pixel in the liquid crystal panel, and hence variations in the characteristics of the MIM element, thereby causing display unevenness. There is a point.

In this embodiment, in order to solve the above-mentioned problem, etching is performed by further adding an organic gas to the above-mentioned mixed gas. Table 1 below shows etching conditions when dry etching is performed by further adding various organic gases to a mixed gas of chlorine gas and oxygen gas. here,
The mode is the PE mode.

[0042]

[Table 1]

In the above Table 1, the power is 1800 W,
The gap between the electrodes is 100 mm, the temperature of the upper electrode 11 is 20 ° C. except for the sample number 20, and the sample number 20 is 55 ° C. The temperature of the lower electrode 12 was 20 for all sample numbers.
° C. Also, the total flow rate of all gases is approximately 1200 to 16
00 cc / min.

Table 2 below shows the uniformity of the etching rate, the side etch amount and the etching amount in the substrate surface with respect to the samples of Table 1 above.

[0045]

[Table 2]

As described above, it is found that the etching rate can be sometimes improved by adding an organic gas to the chlorine gas and the oxygen gas. Particularly, in methanol (CH ₃ OH) and methane (CH ₄ ), the sample numbers 7 and 2 are adjusted by adjusting the flow rate of the organic gas.
As shown by 0, the etching rate can be increased by about 15 to 33% while maintaining the uniformity of the side etching amount and the etching amount.

Of the above, CO and CHF ₃ are effective in reducing the amount of side etching. Although H ₂₀ has some effect in reducing the amount of side etching, it is not preferable because the etching rate decreases.

In general, when etching is performed using only chlorine gas and oxygen gas, the etching rate can be increased by increasing the oxygen gas. However, when the oxygen gas amount is increased, the resist covering the metal chromium thin film is ashed, And the patterning properties are impaired. Therefore, since it is necessary to suppress the oxygen gas amount to some extent, there is a problem that there is a trade-off between the improvement of the etching rate and the patterning property.

On the other hand, in this embodiment, the etching rate can be increased without increasing the oxygen gas by using an etching gas in which an organic gas is mixed in addition to the chlorine gas and the oxygen gas. I have. As the kind of the organic gas, a molecular gas containing hydrocarbon can improve the etching rate without deteriorating the patterning property. For example, paraffin hydrocarbons (CH ₄ , C ₂ H ₆ , C ₃ H ₈ ,...),
Alcohol (CH ₃ OH, C ₂ H ₅ OH, C ₃ H ₇ O
H, ...). Of these, a methyl group (CH
Organic gas with ₃ ) is effective.

Since the organic gas selectively generates an organic deposition on the surface of the resist, the ashing of the resist is suppressed, and the deterioration of the patterning property is limited. If the ashing of the resist is performed appropriately, the metal chromium thin film is patterned so that the side wall thereof has a forward tapered shape, so that the coatability of the pixel electrode and the like in the upper layer can be enhanced and the pattern can be prevented from being cut. Particularly, an organic gas containing a hydrocarbon forms a hydrocarbon-based thin film on the surface of the resist, so that the ashing action of the resist can be prevented, the patterning accuracy can be increased, and the variation in patterning can be reduced.

The effect of the addition of the organic gas is as follows. When the other etching conditions are almost constant, the etching rate is low when the addition amount is small, and the etching rate peaks when the addition amount is increased. As the amount is increased, the etching rate is reduced. The amount of the organic gas added corresponding to the peak region of the etching rate varies depending on other etching conditions such as the type of the organic gas, the flow rates of chlorine gas and oxygen gas, and the gas pressure.

In the above Table 1, the gas pressure and the chlorine gas flow rate were made substantially constant, and the flow rate ratio between the oxygen gas and the organic gas was changed under the condition that the total flow rate of the oxygen gas and the organic gas was also substantially constant. Etching.

As a result, for example, sample numbers 4 to
When the flow rate of the organic gas is increased under the condition of No. 6, FIG.
As shown in the figure, there is a peak of the etching rate with respect to the flow rate of the organic gas. Similarly, sample number 7 in Table 1 above
When the flow rate of the organic gas is increased under the conditions of 10 to 10,
As shown in FIG. 4, a peak of the etching rate still exists.

As described above, as shown in FIGS. 3 and 4,
In the present embodiment, the etching rate can be improved by adjusting the flow rate of the organic gas without deteriorating the patterning property.

[0055]

As described above, according to the present invention, the following effects can be obtained.

According to the first aspect, by etching by mixing an organic gas in addition to the chlorine gas and the oxygen gas, the etching rate can be improved without impairing the patterning property.

According to the second aspect of the present invention, since the hydrocarbon film is formed on the chromium metal mask by mixing the organic gas containing the hydrocarbon, the mask can be prevented from being eroded. Patterning accuracy can be improved.

According to the third aspect, by using the organic gas having a methyl group, it is possible to achieve both improvement of the etching rate and securing of the patterning property.

According to the seventh aspect, in particular, the amount of side etching is reduced, and the patterning accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic structural view showing an apparatus configuration for performing a dry etching method according to the present invention.

FIG. 2 is a graph showing a planar structure on an element substrate of a liquid crystal panel for performing a dry etching method according to the present invention.

FIG. 3 is a graph showing a relationship between a flow ratio of an organic gas (methyl alcohol) and an etching rate in the dry etching method according to the present invention.

FIG. 4 is a graph showing a relationship between a flow rate ratio of an organic gas (methane) and an etching rate in the dry etching method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Vacuum container 11 Upper electrode 12 Lower electrode 13 High frequency power supply

Claims (10)

[Claims] In a dry etching method for etching a metal chromium according to a predetermined pattern of the mask by dry etching with a mask formed on a surface of the metal chromium, at least one of a chlorine gas, an oxygen gas and an organic gas is used. A dry etching method using a three-component etching gas. 2. The organic gas according to claim 1, wherein
A dry etching method comprising a hydrocarbon. 3. The method according to claim 2, wherein the organic gas is
A dry etching method comprising an organic gas having a CH ₃ group. 4. The method according to claim 2, wherein the organic gas is
The dry etching method which is characterized in that an organic gas shown by C _n H _{2n + 2.} 5. The method according to claim 2, wherein the organic gas is
The dry etching method which is characterized in that an organic gas shown by C _n H _{2n + 1} OH. 6. The organic gas according to claim 2, wherein:
The dry etching method which is characterized in that an organic gas shown by CHF _3. 7. The method according to claim 1, wherein the organic gas is
A dry etching method comprising an organic gas represented by CO. 8. The method according to claim 4, wherein the organic gas is
When an organic gas represented by CH ₄ is used and the flow ratio of the chlorine gas to the etching gas is 7: 4, the organic gas contains at least the organic gas and the flow ratio of the organic gas to the etching gas is less than 0.75. A dry etching method characterized by being in a range. 9. The method according to claim 5, wherein the organic gas is
When an organic gas represented by CH ₃ OH is used and a flow ratio of the chlorine gas to the etching gas is 7: 4,
A dry etching method comprising at least the organic gas and setting a flow ratio of the organic gas to the etching gas in a range of less than 0.75. 10. A liquid crystal display device having a metal chromium layer on at least one substrate, wherein the metal chromium is etched in accordance with a predetermined pattern of the mask by dry etching in a state where a mask is formed on the surface of the metal chromium. 2. The liquid crystal display device according to claim 1, wherein the metal chromium is dry-etched with an etching gas comprising at least a three-component system of chlorine gas, oxygen gas and organic gas.