RU2524344C1 - Composition for dry etching of silicon dioxide films in photolithographic process - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: disclosed is a composition for chemical etching of silicon dioxide films in a photolithographic process, which contains polyvinyl alcohol as a polymer base and ammonium fluoride as an etching component, and additionally water as a solvent, with the following ratio of components, wt %: polyvinyl alcohol - 10; ammonium fluoride - 0.7-2.0; water - 88.0-89.3.

EFFECT: improved composition.

5 ex

Description

The invention relates to the field of microelectronics, in particular for the production of integrated circuits and other electronic devices using planar technology for their manufacture, based on photolithographic processes. Obtaining the pattern of integrated circuits by traditional methods accepted in modern production is carried out by alternating many production stages with the participation of a large number of diverse aggressive environments, which is a source of large technological losses. Any improvement in technology or a reduction in the number of photolithographic stages can significantly reduce the distortion of the relief of the pattern.

Many compositions for dry etching are known, consisting of a mixture of active gases for plasma-chemical and reactive-ion etching of silicon dioxide films (Moro W. Microlithography. - M .: Mir, 1990. - T.1, 2. - 1990; Ainspruck N., Brown D. Plasma technology in the production of VLSI - translated from English M: Mir, 1987; Hendricks N.N. / Sol. St. Technol. - 2003. - vol. 3; Slovetsky D.N. Chemical mechanisms reactions in non-equilibrium plasma.M .: Nauka, 1980; Nogami Hiroshi, WaniEtsuo, Nakagawa Yukito et al. / NES Res. and Dev. - 1997. - 38.2. - C.150-157; Miyata K., Hori M ., Goto T. / J. Vac. Sci. And Technol. A. - 1997. - 15.3, Pt1. - C.568-572; Pat. 5880037 USA, IPC H01L 21/302 / Arleo Paul; Applid M aterials, Inc. - N948275, 9.3.1999). The disadvantage of the proposed compositions and etching methods are the strong heating of the substrate, radiation damage, erosion of nearby layers, the complexity of the equipment. In addition, the resulting highly fluorinated gases (RFC) during etching significantly pollute the atmosphere (consumption is only from 10 to 40%).

A known composition for dry etching of a SiO ₂ layer in a photolithography process without using a development step that implements a dry transfer of a pattern from resist to SiO ₂ by the reaction of interaction of silicon dioxide with HF vapors at a temperature above 100 ° C. Organic bases and peroxide compounds are used as catalysts for the etching process, which affects the mechanism of the etching process (Study of the etching reaction at the interface of silicon dioxide and the resist film in the process of photolithography without a developmental stage. Studies on the interfacial etching reaction of development-free vapor photolithography / Hong Xiaoyin, Lu Jianping, Duan Shengquan, Chen Qidao, Wang Peiqing // J. Vac. Sci. And Technol. B. - 1999 .-- 17, 5. - C.2090-2095). To carry out the process, the substrate is coated with a film of a cinnamate-based photopolymer containing 5-nitroacenonaphthene as a photosensitive component and an etching catalyst. The known method of lithography allows you to completely exclude the operation of manifestation and killing photoresist.

A disadvantage of the known composition is the use of catalysts in its composition, as well as the use of gaseous HF supplied to the system at elevated temperature during etching.

In modern production of microelectronics products using planar technology, the etching of dielectric layers of SiO _{2 is} carried out in an aggressive environment of hydrofluoric acid with the addition of ammonium fluoride salt (HF + NH ₄ F) (Moro U. Microlithography M .: Mir, 1990, Part 2. C. 854, 858). The optimal composition of the specified buffer mixture for etching consists of 6-7 vol. parts of a 40% aqueous solution of NH ₄ F and 1 vol. parts of 48% HF. Etching is carried out by immersing the plates in the fluoroplastic holders in an etchant placed in an anti-corrosion container. This method of opening the "windows" in the silicon dioxide layer, selected as a prototype, proceeds in 3 stages: preliminary underfading of the photoresist mask, the actual etching and removal of the photoresist. These three processes are extremely time consuming and are the source of marriage. The disadvantage is the need for a preliminary submerging and subsequent removal of the photoresist and the use of concentrated hydrofluoric acid.

So, during underfading, defects can occur - cracking of the film, accumulation of N ₂ in the resist layer, the appearance of thermoelastic stresses, leading to poor adhesion, a decrease in resolution and contrast. The chemical etching process in the compositions (HF + NH ₄ F) is a source of lateral etching (etching wedge) due to the etching isotropy. This marriage is inevitable and always present.

The removal of a zagled photoresist after etching is the final stage of photolithography before the impurity dropper and is extremely responsible since it is carried out at elevated temperatures in solutions containing highly aggressive and toxic reagents. At the same time, compositions for removing stubborn resists, as a rule, are able to corrode many metals used in the technological cycle.

The objective of the invention is to develop a composition for a method of chemical etching of silicon dioxide films in the “windows” of a photolithographic pattern in order to significantly simplify the technology of transferring an image onto a substrate and eliminating aggressive and toxic reagents when using it.

The problem is solved in that the composition includes a polymer base polyvinyl alcohol (PVA), an etching component of ammonium fluoride (NH ₄ F) and water is used as a solvent in the following ratio, wt.%:

Polyvinyl alcohol 10 Ammonium fluoride 0.7-2.0 Water 88.0-89.3

The etching is carried out not by immersion in the etchant solution with pre-tanning of the photoresist layer and its subsequent removal, but by applying a paste-like etching composition to the pattern in the photoresist layer and its subsequent drying at 70 ° C for 5 minutes. When this occurs, etching in the SiO ₂ layer to pure silicon and simultaneous removal of the photoresist layer from unirradiated sites occurs. The products of these reactions can easily be removed with water using a cotton swab. Preliminarily, in the photoresist layer, a pattern is formed by photolithography using a positive photoresist of the industrial brand FP-051ku and a metal photomask with an element size of 10 μm.

The claimed invention is as follows. All work is carried out on silicon wafers with a SiO ₂ layer 0.10 μm thick. The original plate is cleaned from contamination by degreasing in ethanol. Rinsing in acetone, chloroform and other polar solvents is possible. A layer of positive photoresist FP-051ku is applied by centrifugation on a prepared plate with a SiO ₂ layer. The image in the photoresist layer is obtained by the standard photolithography technique. For this, plates coated with photoresist are dried at 70 ° C for 5 min, exposed to a DRL mercury-quartz lamp (200-800 nm) through a metal photomask with an element size of 10 μm for 5 min, then they are shown in 0.4% an aqueous solution of KOH, washed with distilled water and dried in air. A pattern is obtained in a photoresist layer. The control of the resulting figure is carried out using a metallographic microscope MMU-3, with an increase of 80 to 400 times. Observe the completeness of removal of the photoresist from the irradiated areas and the size of the element - it is 10 μm.

For etching SiO ₂ in the "windows" of the photolithographic pattern, an etching composition is prepared. To do this, a portion of polyvinyl alcohol 3.0 g is dissolved by heating in (26.4-26.8) ml of water. To the resulting solution add (0.2-0.6) g of ammonium fluoride NH ₄ F. A viscous, uniform solution is obtained which is stable during storage. An etching composition is applied to the surface of the plate with a pattern in the photoresist layer by the method of watering or by the drop method, and the plate is dried in an oven at 70 ° C for 5 min. After this, the reaction products are removed mechanically with a cotton swab under a stream of water. The plate is dried and observed under a microscope the completeness of removal of SiO ₂ from the "windows" of the picture and the completeness of removal of unirradiated photoresist. Measure the size of the item. It is necessary to note some unique properties of polyvinyl alcohol, which formed the basis of the proposed composition:

- PVA is well soluble in water, which allows to obtain solutions of any viscosity, up to a state of dense mass;

- aqueous solutions of PVA well dissolve many salts and oxides;

- stable in most organic solvents, which allows it to be used in compositions with NH ₄ F for etching SiO ₂ without interacting with the formed pattern in the photoresist layer - there is no interaction of solvents;

- due to the strong polarity, the polymer films have good adhesion to different types of substrates;

- the polymer films are hydrophilic, as a result of which the hydrophilic surface of SiO _{2 is} well wetted. Consequently, the mandatory operation of hydrophobizing the surface of silicon oxide in conventional photolithography, where hydrophobic resistes are used, is no longer necessary. The removal of an undecided photoresist during etching occurs due to the high solvation ability of F ^- ions, as a result of which they are well coordinated by PVA molecules. Due to these processes, the acidic properties of NH ₄ F in the PVA solution weaken and the solution already has a slightly alkaline medium (pH = 8), sufficient to dissolve the undecided photoresist.

The following are examples illustrating the invention.

Example 1

Stage 1. On a silicon wafer with a 0.10 μm thick SiO ₂ layer, previously purified from contaminants in ethanol, a layer of positive photoresist of the industrial grade ФП-051ку is applied by centrifugation (rotation speed 2500 rpm, application time 20 s). The plate is then dried at 70 ° C for 5 minutes. In the photoresist layer according to the standard photolithography technique, a circuit pattern is formed. For this, a plate with a resist layer deposited is irradiated with UV light using a DRL-250 mercury-quartz lamp (emission region 200-800 nm) through a metal photomask with an element width of 10 μm for 5 minutes. The resulting pattern is developed in a 0.4% aqueous KOH solution until a clear pattern is formed in the photoresist layer, washed with distilled water and dried to remove any remaining water.

Next, control the resulting pattern using a metallographic microscope MMU-3 with an increase of 80 to 400 times. Observe the completeness of the removal of the photoresist and the size of the element — it is 10 μm.

Stage 2. On the dry surface of the plate with the formed pattern, an etching composition is applied by watering or brushing. The composition for etching SiO ₂ is prepared as follows. A portion of polyvinyl alcohol 3.00 g is dissolved under heating (70-80 ° C) in 26.4 ml of water, then 0.20 g of NH ₄ F salt is added. The solution is stirred until a thick consistency is obtained. After etching, the plate is dried at 70 ° C for 5 min, after which the etching products are washed off with water. The resulting pattern is monitored under a microscope for completeness of removal of SiO ₂ from the “windows” of the pattern, completeness of removal of unirradiated resist and preservation of the size of the element. The size of the element remains unchanged - 10 microns.

Example 2

Stage 1 - similar to stage 1 of example 1.

Stage 2. On the dry surface of the plate with the formed pattern, an etching composition is applied by watering or brushing. The composition for etching SiO ₂ is prepared as follows. A sample of polyvinyl alcohol 3.00 g is dissolved under heating (70-80 ° C) in 26.8 ml of water, then 0.60 g of NH ₄ F salt is added. The solution is stirred until a thick consistency is obtained. After etching, the plate is dried at 70 ° C for 5 min, after which the etching products are washed off with water. The resulting pattern is monitored under a microscope for completeness of removal of SiO ₂ from the “windows” of the pattern, completeness of removal of unirradiated resist and preservation of the size of the element. The size of the element remains unchanged - 10 microns.

Example 3

Stage 1 - similar to stage 1 of example 1.

Stage 2. On the dry surface of the plate with the formed pattern, an etching composition is applied by watering or brushing. The composition for etching SiO ₂ is prepared as follows. A sample of polyvinyl alcohol 3.00 g is dissolved under heating (70-80 ° C) in 26.6 ml of water, then 0.40 g of NH ₄ F salt is added. The solution is stirred until a thick consistency is obtained. After etching, the plate is dried at 70 ° C for 5 min, after which the etching products are washed off with water. The resulting pattern is monitored under a microscope for completeness of removal of SiO ₂ from the “windows” of the pattern, completeness of removal of unirradiated resist and preservation of the size of the element. The size of the element remains unchanged - 10 microns.

Example 4

Stage 1 - similar to stage 1 of example 1.

Stage 2. On the dry surface of the plate with the formed pattern, an etching composition is applied by watering or brushing. The composition for etching SiO ₂ is prepared as follows. A sample of polyvinyl alcohol 3.00 g is dissolved under heating (70-80 ° C) in 26.8 ml of water, then 0.60 g of NH ₄ F salt is added. The solution is stirred until a thick consistency is obtained. After etching, the plate is dried at 60 ° C for 5 min, after which the etching products are washed off with water. The resulting pattern is monitored under a microscope for completeness of removal of SiO ₂ from the “windows” of the pattern, completeness of removal of unirradiated resist and preservation of the size of the element. The item size remains unchanged. - 10 microns.

Example 5

Stage 1 - similar to stage 1 of example 1.

Stage 2. On the dry surface of the plate with the formed pattern, an etching composition is applied by watering or brushing. The composition for etching SiO ₂ is prepared as follows. A sample of polyvinyl alcohol 3.00 g is dissolved under heating (70-80 ° C) in 26.8 ml of water, then 0.60 g of NH ₄ F salt is added. The solution is stirred until a thick consistency is obtained. After etching, the plate is dried at 80 ° C for 5 min, after which the etching products are washed off with water. The resulting pattern is monitored under a microscope for completeness of removal of SiO ₂ from the “windows” of the pattern, completeness of removal of unirradiated resist and preservation of the size of the element. Under the microscope, etching of the silicon oxide layer under the photoresist layer is observed.

When using the proposed composition for etching thin (0.10 μm) silicon dioxide films, a significant contribution to the improvement of planar technology is possible due to the above advantages due to the reduction in the number of stages, the ease of use of the proposed method and the complete elimination of aggressive media. All sizes of the elements obtained in the layer of positive photoresist FP-051ku are transferred to the silicon dioxide layer without change.

Claims (1)

Composition for chemical etching of silicon dioxide films in a photolithographic process, including polyvinyl alcohol as a polymer base and ammonium fluoride as an etching component, and also an additional solvent - water in the following ratio, wt.%:
Polyvinyl alcohol 10 Ammonium fluoride 0.7-2.0 Water 88.0-89.3