JPS6214147A - Positive type photoresist composition - Google Patents

Abstract

PURPOSE:To improve an anti-dryetching property of the titled composition by incorporating a novolak resin obtd. by effecting an additional-condensation of specific phenols and formaldehyde to an alkaline soluble resin. CONSTITUTION:The alkaline soluble resin component is the novolak resin obtd. by effecting the additional condensation of the phenolic compd. and the formaldehyde in the presence of an acid catalyst. The phenolic compd. is a mixture of two or more than two compds. shown by the formula and has a substituent having means carbon atoms of 0.5-1.5 per one of a phenol skelton. The formaldehyde comprises for example, a formalin and paraformaldehyde which is an oligomer of formaldehydes. Thus, the titled composition having a good anti- dryetching property is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positive photoresist composition with improved sensitivity, heat resistance and dry etching resistance.

A photosensitive resin composition containing a compound having a quinone diazide group, such as a naphthoquinone diazide group or a benzoquinone diazide group, changes from an alkali-insoluble state by decomposing the quinone diazide group and producing a carboxyl group when irradiated with light at a wavelength of from aOO to 500 nm. It is used in positive photoresists because it is alkali-soluble. In this case, a novolak resin is usually used in combination as the alkali-soluble resin component. Novolac resin is important to obtain a uniform and durable resist film.

This positive photoresist has a feature of significantly superior resolution compared to negative photoresists. Taking advantage of this high resolution, copper clad expansion 1 for printed wiring
It is used as an etching protective film (resist film) in photolithography when manufacturing integrated circuits such as substrates, ICs, and LSIs. Among these, regarding integrated circuits,
With the advancement of miniaturization, pattern formation of 1 μm is now required. Traditionally, a mask contact method has been used to form integrated circuits, but this method requires two
It is said that the limit is μm, and a reduction projection exposure method is attracting attention as an alternative. This method is a method in which the pattern of a master mask (reticle) is reduced and projected using a lens system for exposure, and the resolution is possible up to about 1 μm.

However, one of the problems with this reduction projection exposure method is that
One point is that the throughput is low. That is, unlike the conventional batch exposure method such as the mask contact method, the reduction projection exposure method uses divided and repeated exposure, which results in a longer total exposure time per wafer.

The most important way to solve this problem is to improve the sensitivity of the resist used, as well as improving the equipment. If exposure time can be shortened by increasing sensitivity, throughput and yield can be improved.

What positive photoresists are currently used from this perspective? Looking at it, it can't be said that the sensitivity is necessarily satisfactory. Generally, positive photoresists have lower sensitivity than negative photoresists, and improvements are desired.

The easiest way to achieve higher sensitivity is to lower the molecular weight of the novolac resin used in positive photoresists.

When the molecular weight of the novolak resin is low, its dissolution rate in an alkaline developer increases, and the apparent sensitivity of the resist increases. However, with this method, film burrs in non-exposed areas become large (so-called reduction in residual film rate), pattern shape deteriorates, and the difference in dissolution rate in developer between exposed and non-exposed areas becomes small. In addition to problems such as a decrease in the so-called r (gamma) value, there arises an extremely serious problem of a decrease in the heat resistance of the resist.

The heat resistance of a positive photoresist here means the resistance of a resist pattern to heat after development. More specifically, when heat is applied from the outside world to a resist pattern formed on a substrate, the resist pattern will sag or deform if the temperature exceeds a certain level. The heat resistance of the resist is measured by whether the pattern can maintain its sharp shape without deformation. If the resist pattern is distorted or deformed, the dimensions of the species to be etched after etching may be distorted or the dimensions may vary, and the resist cannot function as an etching protection film required of the resist. In other words, the yield will drop significantly, so it is preferable to
Yes.

Now, what about LSI ffi? With the improvement of 2f BT, the pattern line width is becoming increasingly finer, but dry etching technology is increasingly being used to replace the conventional wet etching as one means of achieving finer Width. ing.

When it comes to dry etching technology, there are various methods. Among them, the method most commonly used these days is called reactive ion etching (RIE). This is an anisotropic etching that combines the sputtering effect of directional ions and chemical etching using highly reactive plasma, and is suitable for obtaining extremely fine patterns. The advantage of this method is that it does not require treatment of waste liquid such as hydrofluoric acid that is required in wet etching, and it also eliminates the side etching (jfl under the resist) that is often seen during wet etching.
Since there is no wraparound to l), it is easy to obtain fine patterns. The conventional drawback that the wafer processing speed is slower than wet etching is being overcome through improvements in equipment, and it can now be said to be an indispensable technology for improving the degree of integration.

However, from the standpoint of cysts, the current situation is that with the spread of dry etching technology, the resist itself is increasingly required to have dry etching resistance. During dry etching, the resist is required to maintain its sharp pattern shape.

Generally, "selectivity" is used as an index of this dry etching resistance. This is defined as the ratio of the etching speed of the base (species to be etched) to the etching speed of the resist, and the larger the value, the better.

The selectivity ratio of currently used positive photoresists is not necessarily satisfactory, although it depends on the underlying material (species to be etched), etching gas, etc. In particular, when the substrate is aluminum, or even more special metals such as molybdenum, tungsten, etc., or their silicides are being used, the dry etching conditions become stricter and the selectivity decreases, making it difficult for current positive photoresists. It cannot be said that it has sufficient dry etching resistance.

On the other hand, according to the results of studies conducted by the present inventors, it has been found that there is an extremely strong correlation between this dry etching resistance and heat resistance. In other words, if the resist has low heat resistance,
It is easily deformed and carbonized during dry etching.

This is thought to be due to the fact that considerable heat is generated during dry etching.

There is also a relationship between dry etching resistance and heat resistance in another sense. That is, in order to improve the dry etching resistance, a method is often used in which the temperature of so-called "post-bake" which is usually carried out after the development of a resist pattern and before etching is increased. Although the detailed reason is unknown, increasing the post-bake temperature tends to improve dry etching resistance. However, if the post-bake temperature is increased when the heat resistance of the resist is low, the resist pattern will already be sagging or deformed at that stage, and this will be exacerbated during dry etching, making it difficult to obtain a desirable etching result. is impossible.

From these facts, it can be said that improving the heat resistance of a resist is nothing but improving its dry etching resistance.

Now, the eight major characteristics required of a resist are "sensitivity" and "
Examples include resolution," and "dry etching resistance." Sensitivity is important for throughput, while resolution and dry etching resistance are important for improving the degree of integration. If any one of these is missing, it can no longer be used as a resist, so all eight must be excellent.

Now, if we look at these eight companies, they tend to be contradictory in some respects in terms of "sensitivity" and "dry etching properties." That is, as mentioned above, in the case of a positive photoresist, if the molecular weight of the novolac resin is lowered in order to increase the sensitivity, the heat resistance becomes poor, and as a result, the dry etching resistance is impaired. Conversely, if the molecular weight is increased in order to improve dry etching resistance, the dissolution rate in the developer decreases and the sensitivity decreases. That is, at present, there is no commercially available positive photoresist that has both sensitivity and dry etch resistance, and the situation is extremely inconvenient in that if an attempt is made to improve one, the other becomes even worse.

In view of the current situation, the present inventors have developed a positive photoresist that improves both "sensitivity" and "dry etching resistance" without impairing the other, and has excellent resolution. As a result of intensive study, it was discovered that this objective could be achieved by using a specific novolak resin, and the present invention was achieved.

That is, the present invention provides a mixture of two or more compounds represented by (A) a photosensitive agent component containing a quinonediazide group and a quinonediazide group, wherein the average number of substituent carbon atoms per phenol skeleton is 0. The present invention relates to a positive photoresist composition containing a novolak resin obtained by addition-condensation reaction of phenols having .5 to 1.5 phenols and formaldehyde in the presence of an acid catalyst.

The present invention will be described in more detail below.

The photosensitizer containing a quinodiazide group (A) is a compound containing a naphthoquinone diazide group or a benzoquinone sialide group, and these are, for example, naphthoquinone diazide sulfonic acid chloride or benzoquinone diazide sulfonic acid chloride and a compound having a hydroxyl group in a weak alkali. It can be obtained by condensation with the presence of . Examples of compounds having a hydroxyl group include hydroquinone resorcinol, phloroglucin, 2,4-dihydroxybenzophenone, 2
, 8.4-trihydroxybenzophenone, gallic acid alkyl ester, 2.2', 4.4'-tetrahydroxybenzophenone, and the like.

Next, the alkali-soluble resin component (B) will be described. The alkali-soluble resin component that can be used in the present invention is a novolak resin obtained by an addition condensation reaction from a phenolic compound and formaldehyde, but the phenols that are the raw materials for the novolak resin mentioned here include any of the H groups. It is necessary that the compound is a mixture of two or more of the compounds shown in ().

More specifically, the following combinations are possible.

■ Phenol and metacresol ■ Phenol and metaethylphenol ■ Metacresol and metaethylphenol ■ Phenol, metacresol, and metaethylphenol Furthermore, in any combination of these, the average number of substituent carbon atoms per side of the phenol skeleton is 0.
The number must be in the range of 5 to 1.5.

Average number of substituent carbon atoms per phenol skeleton is 0.5
If the number of substituent carbon atoms is less than 1.5, the novolac resin dissolves too quickly in the developer (alkaline aqueous solution), resulting in a decrease in the remaining film rate in the unexposed areas, and conversely, if the average number of substituent carbon atoms exceeds 1.5. In this case, the rate at which the novolak resin dissolves in the developer becomes slow, causing a problem that it takes time to develop the exposed areas. Therefore, this average substituent carbon number is 0.5 to 1.5
Choose as many as you like. This condition will be explained using a specific example.

■In the case of phenol and metacresol, phenol,
In metacresol, the average number of substituent carbon atoms is 0 and 1, respectively, so from the above conditions, phenol/metacresol≦1 (molar ratio). Also phenol/
The ratio of metacresol is generally preferably 0.1 or more.

In addition, in the case of ■phenol and metaethylphenol, 1
It may be used within the range of /8≦phenol/metaethylphenol≦8 (molar ratio). Similarly, in the case of metacresol and metaethylphenol in ■, metacresol/
Metaethylphenol≧1 (molar ratio) The ratio of metacresol/metaethylphenol is generally preferably 9 or less. In the case of the eight combinations of phenol, meta-cresol, and meta-ethylphenol (ii), the mixing ratio of each is selected and used in the same manner as in the above specific example.

Next, formaldehyde to be subjected to an addition condensation reaction with phenols will be explained.

As formaldehyde, formaldehyde aqueous solution (
Formaldehyde (formalin) and paraformaldehyde, which is an oligomer of formaldehyde, can be used. Special Iζ37
% formalin is conveniently produced in large quantities industrially.

A novolac resin is obtained by addition condensation of these phenols and formaldehyde in the presence of an acid catalyst.

When an acid catalyst is used, a novolac resin that provides a positive photoresist with good sensitivity and good heat resistance can be obtained.

The acid used as a catalyst may be either an inorganic acid or an organic acid. Specific examples include hydrochloric acid, sulfuric acid, perchloric acid, phosphoric acid, p-toluenesulfonic acid, oxalic acid, trichloroacetic acid, and formic acid.

Further, the reaction can be carried out either in bulk or by using a suitable solvent. The reaction is usually 60-12
Perform at 0°C for 12 to 20 hours.

Next, regarding the molecular weight of the novolak resin, the optimum range varies depending on the type of phenol and the reaction conditions, but the weight average molecular weight Mw determined by GPC is generally 8,000 to ao, ooo, more preferably 5.000
~20,000 is appropriate. Mw shown here is GP
The value calculated from the C chromatogram using a calibration curve obtained using monodisperse polystyrene. The measurement of the GPC chromatogram was carried out using a 635 type liquid chromatography device manufactured by Hitachi Ltd. as a column made by Shimadzu Ltd. H2C of
-15, H2C-40, and H5C-60 each connected in series, tetrahydrofuran was used as a carrier solvent, and the flow rate was 1.0 g//min.

Further, it is preferable that the blending ratio of the quinonediazide compound and the novolak resin is in the range of 1:1 to 1.

The resist solution is prepared by mixing and dissolving a quinonediazide compound and a novolak resin in a solvent. The solvent used here is preferably one that provides a uniform and smooth coating film after the solvent evaporates at an appropriate drying rate. Such are: ethyl cellosolve acetate, methyl cellosolve acetate, ethyl cellosolve, methyl cellosolve,
Examples include butyl acetate, methyl isobutyl ketone, xylene, etc.

The positive photoresist composition described above may further contain small amounts of additional resins, plasticizers, dyes, etc. as additional additives.

According to the present invention, "dry etching resistance" can be improved without reducing "sensitivity", and conversely, a highly sensitive positive photoresist can be obtained without impairing "dry etching resistance", and The performance of each of these is superior to that of conventional positive photoresists, and the resolution is also superior, so that future high integration and miniaturization can be obtained.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

Reference Example 1 [Production example of novolac resin (1) Phenol/metacresol = 1/2 (Mole ratio of charging)] Phenol (purity 99.0%) 1 in a 500 ml separable flask
9. Of, metacresol (purity 994%) 48.5f
I, formalin (37% aqueous solution) 47.5yS oxalic acid dihydrate 1.021 ion-exchanged water 6y1 ethyl cellosolve acetate) 2 (l) was prepared and heated and stirred in an oil bath at 110°C for 3 hours to react, then ethyl cellosolve acetate 40y
and heated for another 3 hours, stirred and reacted, neutralized, washed with water,
After dehydration, a solution of novolac resin in ethyl cellosolve acetate was obtained. The weight average molecular weight determined by GPC chromatography was 12,800.

Reference Example 2 [Production Example of Novolac Resin (2) Phenol/Metacresol = 2/1 (Mole Ratio of Charges) In Reference Example 1, the charge was 38.0g of phenol and 21.78g of metacresol.
The weight average molecular weight was 13 in the same manner as in Reference Example 1.
．． 800 novolak resin was obtained.

Reference Example 8 [Manufacture example of novolac resin (8) Phenol/metaethylphenol = 1/1 (charged molar ratio)] In a 500 ml separate flask, 28.5 g of phenol (purity 99.0%), metaethylphenol ( Purity 99.2%) 36.9f, formalin (37% aqueous solution)
, 45. Of, oxalic acid dihydrate 0.62y, ion exchange water 7
Prepare 51% ethyl cellosolve acetate 60F, 1
Heat and stir in a 10°C oil bath for 26 hours to react, neutralize,
The mixture was washed with water and dehydrated to obtain a solution of novolac resin in ethyl cellosolve acetate.

Weight average molecular weight by GPC chromatography is 1330
Reference Example 4 [Production Example of Novolac Resin (4) Metacresol/Metaethylphenol = 2/1 (Mole ratio of charging)] Metacresol (
Purity 99.4%) 48.5y; metaethylphenol (
Purity 992%) 24.6F, formalin (87% aqueous solution) 47.5F, oxalic acid dihydrate 1.0251. Prepare ion exchange water 6N, ethyl cellosolve acetate 201,
After heating, stirring, and reacting in a 120°C oil bath for 8 hours,
Ethyl cellosolve acetate 401 was charged completely, reacted for further 6 hours, neutralized, washed with water and dehydrated to obtain an ethyl cellosolve acetate solution of novolac resin.

Weight average molecular weight by GPC chromatography is 1200
It was 0.

Reference Example 5 [Production Example of Novolak Resin (5) Metacresol/Nuquethylphenol = 1/2 (Mole Ratio of Charges)] In Reference Example 4, the charge was 21.7 das of metacresol,
Reference example 4 except that metaethylphenol was 49.2 f.
A novolak resin having a weight average molecular weight of 12,900 was obtained in the same manner as above.

Examples 1 to 3, Comparative Examples 1 and 2 As shown in Table 1, the novolac resins shown in Reference Examples 1 to 5 were mixed together with a photosensitizer and a dye in ethyl cellosolve acetate/vinegar p n-butyl/xylene = 8/1 A resist solution was prepared by dissolving it in a solvent with a mixing ratio of /1. (The amount of solvent was adjusted to 1.25 Izm under the coating conditions shown below.) These compositions were filtered through a filter with a pore size of 0.2 μn1. This was coated on a silicon wafer which had been cleaned in a conventional manner using a spin coating machine at 4000 rpm, and then the silicon wafer was placed in a clean oven at 90° C. and baked for 20 minutes. Thereafter, using a contact mask aligner using a 25 QW ultra-high pressure mercury lamp as a light source, exposure was performed for 3 seconds through a step tablet mask whose optical transmittance was changed stepwise. Then the developer solution SOPD (
The film was developed with a tetramethylammonium hydroxide aqueous solution manufactured by Sumitomo Chemical Industries, Ltd. for 70 seconds, rinsed, and dried.

The results are shown in Table 1.

As is clear from Table 1, Examples 1 to 8 are Comparative Examples 1.2 and 2.
It is much superior in sensitivity and heat resistance compared to .

Claims (1)

[Claims] (A) A photosensitizer component containing a quinone diazide group and (B) an alkali-soluble resin component have general formulas ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (R_1 is hydrogen, methyl group, or ethyl group) is a mixture of two or more compounds represented by
A positive photoresist composition containing a novolak resin obtained by subjecting a phenol having an average number of substituent carbon atoms of 0.5 to 1.5 per phenol and formaldehyde to an addition condensation reaction in the presence of an acid catalyst.