UA34995C2 - A method for preparing negative selective etchant for resist layers of chalcogenide glass Аs2S3 - Google Patents

Abstract

A method for preparing negative selective etchant for resist layers of chalcogenide glass Аs2S3 relates to fields of information recording and can be used in optotechnics, holography, electronics, polygraphy etc. The method consists in that ethyldiamine, acetone and dimethylsulfoxide are mixed at the following ratio of components, % of volume: Ethyldiamine 8-12 Acetone 55-70 Dimethylsulfoxide Rest Thereafter the mixture being kept for at least 24 days at a room temperature. While mixing the reagents a chemical interaction takes place resulting in forming new compounds with a complicated structure which are characterized by high constants of stability. Use of etchant made by this method provides for increase in etching selectivity and quality of surface to be etched.

Description

The invention relates to the fields of information registration by lithographic formation of relief microstructures and can be used in optotechnics, holography, electronic engineering, printing, etc.

It is known that the amorphous layers of some chalcogenide glasses (CS), for example, arsenic trisulfide A525z, change some physical and chemical properties under the influence of photoactive electromagnetic or corpuscular radiation (V.M. Lyubin Photographic processes on the basis of chalcogenid glassy semiconducting semiconductors / V book "Neserebryanye photographic processes!" - L.: Khimiya, 1984. - 376 p.). Thanks to this, CS layers are used as high-resolution inorganic resists. The change in their chemical properties during irradiation is manifested in a decrease or increase in the rate of dissolution of irradiated areas compared to the rate of dissolution of the original non-irradiated layer, depending on the type of solvent. It is believed that in these cases negative and positive selective etching of the XO layer takes place, respectively. An important parameter that characterizes the suitability of using the CS layer as a resist is the etching selectivity y, which is determined by the ratio of the dissolution rates of the unexposed Upe and the exposed me areas of the layer for negative etching and the inverse ratio of me/Upe in the case of positive etching.

High selectivity and good quality of the etched surface are the main criteria when choosing etching agents for resist layers of XO. In general, they are not interrelated, and their priority is set depending on the specific application. So, for example, when using CS layers to form protective masks in the processes of optical microlithography (production of microelectronic devices), the selectivity of the etching agent plays an important role, which depends on the thickness of the resist layer that remains on the substrate after etching. For the technological processes of laser and holographic lithography (production of originals of an optical signal or marking structure, holographic diffraction gratings, elements of integrated optics, etc.), the quality of the surface of the resist layer after etching, which is decisive for the operational characteristics of the products (signal-to-noise ratio and the level of diffused light). An important characteristic of a selective herbalist is also the stability of its functional properties, which ensures the reproducibility of lithographic processes.

For negative etching of A525z resist layers, aqueous solutions of inorganic substances are known (Association of the Czechoslovakian SSR Mo239785

IPC" c0o3s1/76, 1984) and organic reagents-bases (assistant USSR Meo1160483, IPC" NOTI 21/302, 1985). Characteristic disadvantages of these herbicides are low selectivity values (10), inhomogeneity of digestion, as well as rather high concentrations of toxic components (amines, methanol).

As a prototype, a solution for negative etching of chalcogenide glass A525z based on ammonia hydroxide MNAOH and acetone (dimethyl ketone) (СН3)2СО with the following ratio of components, in mass 9о: 2590

MNON - 1.6-2.8; (СНз)»СО - the rest (Pat. of the Russian Federation Me2008285, IPC? Со3С15/00, 1994). This herbizer is characterized by fairly high selectivity indicators (100) and provides a good quality of the etched surface. However, its disadvantage is the instability of functional properties, which is due to the high evaporation rate of acetone, as well as the high volatility of ammonia hydroxide. This leads to a significant dependence of the amount of selectivity on the time of preparation of the herbal medicine, as a result of which repeated use of the selective herbal medicine is impossible.

The task of the invention is to improve the etching characteristics (selectivity and quality of the etched surface) of resist layers of A525z chalcogenide glass, as well as to increase the stability of the properties of the etching agent itself.

To solve the problem, take a mixture of ethylenediamine (CHg)g(MHg)", acetone (CHz)2:CO and dimethyl sulfoxide (CHZz)250 in the ratio in volume percent (vol. 965): (CH)(MH)" d)» 8-12 (Снз»со 55-70 (СНз)»ЗоО the rest, after which the mixture is kept for at least 24 days at room temperature for the final formation of a selective herb as a result of the chemical interaction of the components of the mixture, which leads to the formation of new compounds with a complex structure.

One of the essential features of the proposed invention is the use of ethylenediamine as the main component of the mixture for the preparation of selective herbal medicine. Unlike primary and secondary monoamines, ethylenediamine, which has two amino groups in its composition, can exhibit a chelating effect when interacting with the surface, which consists in a significant increase in the stability constant of the complexes formed by the chelating ligand in comparison with monodentate ligands - organic monoamines. At the same time, the mandatory steric complications that will arise during the interaction of chelating ligands with irradiated areas of the resist surface with a significantly higher degree of structural organization "compared to non-irradiated ones") are an additional factor that increases the selectivity of negative etching.

During the interaction of ethylenediamine with acetone during the preparation of herbal medicine, fragments with a more complex structure can be formed - polychelate and macrocyclic compounds, as well as polymeric ones. Such ligands exhibit polychelate and macrocyclic effects, which consist in increasing the stability constants of complexes compared to those containing chelate ligands, in this case ethylenediamine. The role of dimethylsulfoxide in the process of formation of a selective herbicide, as well as in the etching itself, can be both in the competitive inhibition of some reactions of ethylenediamine with acetone, and in affinity with the 5-fragments of the polymer network of chalcogenide glass.

Thus, the increase in the selectivity of negative etching with the simultaneous provision of high quality of the etched surface of resists based on layers of chalcogenide glass A525z, when using the solution proposed in this invention, occurs, according to the authors, primarily due to the formation of more active components of selective etching during the preparation of the herbarium than starting compounds. In addition, due to the formation of compounds with a relatively high molecular weight (up to polymeric), evaporation of the components, even during long-term storage of the proposed herb, is practically excluded, which ensures the reproducibility of its properties during repeated reuse. The use of organic amines as agents for selective etching also makes it possible to get rid of a number of disadvantages inherent in solutions of inorganic alkalis (precipitation formation, low selectivity, too high dissolution rate of the resist layer) and ammonia (rapid evaporation of the active component and, as a result, irreproducibility of properties herbalist). The above-mentioned advantages of the new selective herbalizer find a concrete expression in the increase in the photosensitivity of the A525z resist layer, which is practically important for the implementation of lithographic processes using this resist.

To prepare a negative selective herbicide for resistance based on A525z, organic components - ethylenediamine (CH)g(MHheg)"2 (7595th solution), acetone (CH3)25СО and dimethyl sulfoxide (CH3)250 are mixed in the ratio selected respectively from the above concentration intervals. When using compositions of the herbalist selected outside these intervals, the characteristics of selective digestion deteriorate. Due to the fact that the rate of formation of macrocyclic and polymer fragments (products of the interaction of ethylenediamine, acetone and dimethylsulfoxide) is very low, the prepared mixture is kept for at least 24 days at room temperature (29325)K, which is necessary for the final formation of a selective herb with stable properties. During this time, the color of the solution undergoes a significant change - it turns from colorless to brown.

After exposure of A525z resist layers in an appropriate manner (contact or projection method), their selective etching is carried out at room temperature until the non-irradiated areas are completely removed. Etched samples with the obtained relief image are thoroughly washed first in propanol, and then in distilled water and dried.

The proposed invention is illustrated by drawings in which:

Fig. 1 depicts the kinetic dependences of the etching of resist layers A529z in different selective etching machines. Curves 1, 2 refer to unexposed, and curves 1, 2! to exposed layers that were processed in the proposed herbarium (1, 2) and in the prototype herbarium (1, 2). The conditions of preparation, exposure, and etching of Ab25z layers are described in detail in example 3.

Fig. 2 shows the characteristic curves (dependence of the reduced thickness after etching on the decimal logarithm of the exposure) of the A525z resist layer for the declared (1) and known (2) etching agents. Modes of preparation, exposure and post-exposure processing of samples with resist layers A525z3 are given in example 4.

Fig. 3 shows the image of the general view and the profilogram of the microrelief of the original optical signalogram of the compact disc, formed as a result of exposure of the A525 layers with sharply focused laser radiation and their processing by the declared (a, b, c) and known (a, b, c) selective herbalists , the modes of which are described in example 5.

The proposed invention is also explained by the following examples of its specific implementation.

Example 1.

For two glass substrates measuring (70740)mm? by thermal evaporation in a vacuum of 2103 Pa, layers of chalcogenide glass A5z25z3 with a thickness of 500 nm were applied. Each of the prepared samples was half covered (lengthwise) with black opaque paper, and the open half was exposed to the collimated integral radiation of a DRSH-250 mercury lamp. At a radiation power density of 0.14W/cm2? exposure was 2J/cm-. Then the samples were cut into 7 equal parts in such a way that each of them contained exposed and unexposed areas of the layer

Av253. After that, solutions were prepared consisting of ethylenediamine, acetone and dimethylsulfoxide, taken in various ratios, including those exceeding the concentration ranges indicated above.

In order to stabilize the properties, the prepared solutions were kept for 28 days at a temperature of 29355K. Selective etching of resist layers was carried out in solutions prepared in this way at a temperature of 207"C

Av253. The selectivity of etching was evaluated by the ratio of the times of complete dissolution of the exposed (ie) and unexposed (tsu) areas of the A529z layer (u z (spe). The quality of its etched surface was assessed visually by its external appearance with the help of a MIY-4 microinterferometer and an atomic force microscope Oitepvsiop 3100. The dependence of the selectivity of etching on the concentration ratio of the components of the initial mixture for the preparation of a selective herbicide is presented in Table 1. The given data indicate that when using herbicides prepared from a mixture with concentrations of ethylenediamine "806.95, although a sufficiently high value of y is achieved, the rate of etching of unexposed layers is very small, as a result of which the productivity of the lithographic process as a whole decreases. The use of mixtures with concentrations of ethylenediamine "1206.95 leads to a significant decrease in the selectivity of the herbarium and the appearance of local defects on the etched surface of the exposed layer A525z3, which is also unacceptable.

Thus, the optimal concentration ratios are in the stated intervals, at which selective etchants are obtained with high y values and controlled etch rates of the A52553 resist layers, as well as a mirror etch surface.

Example 2.

10 samples were prepared on glass substrates measuring (10740)mm:2, each of which contained exposed and unexposed areas of the A5253z layer. The conditions for sputtering and exposure of the A525z layers were similar to those described in example 1. After that, a mixture of ethylenediamine, acetone, and dimethylsulfoxide was prepared, taken in the ratio (vol. 9o): SNz)»ZoO the rest

It was necessary to check the degree of suitability of the selective herbalist depending on the time that passed after the preparation of the mixture of its components. The results of the study of selectivity in relation to the time of exposure of the herb are shown in Table 2.

As can be seen from Table 2, for the formation of stable properties of the selective herb, it is necessary to keep the prepared solution for at least 24 days at room temperature.

Example 3.

To compare the dissolution kinetics of the resistive layers of A5g2Oz chalcogenide glass with different selective solvents, a highly sensitive quartz oscillator technique was used, which is based on the dependence of its resonance frequency on the change in the mass of the substance layer deposited on the quartz element, for example, as a result of its dissolution. The study of the kinetics of etching of XO layers with the help of this technique included measuring the initial frequencies (Ii) of quartz oscillators, applying resistive layers of XC to them with a thickness of Po, measuring the frequencies (Ii) of oscillators with applied layers, exposure, processing of exposed and unexposed XC layers in appropriate selective solutions during time y, measurement of frequencies (r) of quartz oscillators after each treatment. The results of the measurements were presented in the form of a graphical dependence L/АЮю-п/по-(Ю), where Aо-ио-Й-Но; ah-that-

T-p.

Applying A5253 resist layers with a thickness of Zb0Onm was carried out by the method of thermal evaporation in a vacuum of 1.37103Pa at a speed of 1.Onm/s on 4 quartz oscillators with gold electrodes, the initial resonant frequency of which was 3.3 MHz. Two oscillators were exposed to the integral radiation of a DRSH-250 mercury lamp.

At a radiation power density of 0.14 W/cm? exposure was 2J/cm7. Oscillators with applied A525z layers were immersed in pairs (exposed and unexposed) for 10 seconds in solutions of the following compositions: (1) 7595 (СН)Д(МН»г)2 9 vol.o (Снз»со 5806.90 (СНз)»ЗоО the rest

The prepared mixture was kept for 25 days at room temperature (29355K; (2) 2595 MNAOH - 2.5 wt.95; (CH3)25СО - the rest. - (prototype)

After each treatment, which was carried out at a temperature of (2021)"C, the oscillators were thoroughly washed, dried, and their resonance frequencies were measured. Based on the results of the measurements, graphical dependences of p/po- (I) were constructed, which are presented in Fig. 1. Curves 1 ,1" and 2, 2 depict the kinetic dependences of the dissolution of exposed and unexposed layers of A529z in herbariums (1) and (2), respectively.

As can be seen from the comparison of these dependences, the selectivity of negative etching of resist layers A525z in the proposed herbarium is higher than in the prototype herbarium. So, for example, after the complete dissolution of the unexposed layers of Av2z (curves 1 and 2", p/lo--0), the thickness of the exposed layer, which was processed in the proposed herbarium, remains practically unchanged (p/po-1). In that at the same time after treatment with its solution (2), the thickness of the layer decreases by almost 20905.

Example 4.

In order to compare the sensitometric (phototechnical) characteristics of the A525z resist layers when treated with different selective solutions, their characteristic curves are studied. The main sensitometric characteristics of the photoresist are the light sensitivity 5 and the contrast coefficient u, which are determined from the characteristic curve. It represents the experimentally measured graphic dependence of the thickness Пп of the exposed resist layer that remains on the substrate after development, on the logarithm of the exposure value Н: п-П(ИХН) or п/по-Е(ХХН), where По is the initial thickness resistive layer. The photosensitivity of the negative resist 5 is determined by the value of the inverse exposure Н, which corresponds to some selected point of the characteristic curve: 5-1/Н, where Н is the exposure at which a resist layer with a thickness of n remains after development.

The coefficient of contrast of the resist is determined by the value of the tangent of the angle of inclination from the rectilinear section of the characteristic curve to the axis of exposures: sh/-ido. For a negative resist, the value y expresses the increase in the thickness of the resist layer with the growth of the IDN within the rectilinear section of the curve. The value of y shows the ability of the resist to weaken the effect of side effects during exposure, which cause unevenness of illumination along the contour of the image.

Determination of the sensitometric characteristics of the A525z resist layers was carried out using the quartz oscillator technique. At the same time, 24 oscillators were sprayed with A529z layers according to the modes described in example 3. For each herbalist in particular, the recipe of which is given in the previous example, 12 oscillators with applied resist layers were used, which were exposed individually with different exposures (Ni-0, H, НЗз, «, Ниг) by the integral radiation of the Nd-lamp. Then all 12 oscillators were lowered into a selective herbarium, held until the unexposed layer of CS was completely dissolved, washed and dried. For each oscillator, the L/Aio-p/p ratio was determined and the p/p-P(IdH) dependences, which are depicted in Fig. 2, were constructed. From the characteristic curves obtained in this way, the values of light sensitivity 5 and contrast coefficients y were determined. With the determined photosensitivity, the value of exposure No was chosen as its criterion, which ensured that half of the initial thickness of the resist layer was preserved after etching, i.e. 5о5-1/Нов5. For comparison, the values of the sensitometric characteristics of the A525z resist layers treated with different selective herbicides are summarized in Table 3.

As can be seen from Table 3, the light sensitivity of the A525z resist layer when treated with the proposed herbicide (1) is significantly higher than for the prototype herbicide (2). The etching contrast coefficients for both herbalists are practically the same.

Example 5.

To compare the quality of microrelief formation with the help of the resist layer A525z during its treatment with different selective herbicides, a sample was prepared, which was a disk substrate with a diameter of 160 mm, on which, using thermal evaporation in a vacuum of 1.53103 Pa, layers of Cg and Ab25z were successively applied with thicknesses of 5 and 14O0nm. The exposure was carried out on a stand for recording the originals of the optical signalograms of compact discs, in which a sharply focused beam of modulated argon laser radiation (X-488nm) was directed at a disc substrate covered with a resistive layer rotating at a frequency of 10Hz. The step of moving the laser spot along the surface of the resist layer in the radial direction was 1.6 μm. The diameter of the focused beam at the level of 0.5 Io (Io is the radiation intensity at the maximum of its distribution in the cross section of the beam) was equal to 0.8 μm. After exposure of the Azv25z layer, the substrate was cut in half and its development was carried out in various selective herbs, the recipe of which is given in example 1. At the same time, the unexposed areas of the photoresist were completely removed, and the exposed areas remained on the substrate. The topology of the obtained microrelief was studied with the help of an atomic force microscope Oitepviop 3100. Fig. 3 shows the image of the general view (a, a) and the profilogram (B, B", c, c) of the microrelief of the original optical signalogram, formed when the A5z253 layer was exposed to laser radiation with a power of 1.7 mW at the output of the microlens using the herbalist proposed in this application (fig. 3, a, b, c) and the prototype solution (fig. 3, a, b, c).

A comparison of the presented results convincingly indicates the higher quality of the microrelief obtained when using the proposed method of preparing a negative selective herbarium for resist layers of chalcogenide glass A5253.

Table 1

Dependence of the selectivity of the negative etching of the Az525z layer on the ratio of ethylenediamine (CH)ag(MHg)", dimethylsulfoxide (CHz)250 and acetone (CHz)2СО o etching is slow, heterogeneous, the quality of the surface is unsatisfactory 9 | in | the rest | other give le yumovlyu ptn we 2 6 | 60 | -th || 7777777 3 7 | 50 | - |1686|Y - 8 8Dyu 4 8 | 50 | - | 234 |etching is not uniform, the quality of the surface is not satisfactory -Zz" 51 2 shyu.'5Э8e | 55 | - | 286 |etching is uniform, the etched surface of the CS is mirror 6 more | 60 | - | 322 |etching is uniform and polishing//-:/ //.:(КХ? І;Ї/С/ 7| 70 | 65 | - | 345 | engraving uniform polishing//-:/ //77:УК/ 8 11 | в | - | 362 | engraving uniform polishing//-:/ /:/77:Юю local inhomogeneities appear on the etched surface | 5 1 ud il loy ia tel lm lo, 13 | 75 | - | 256 | the number of inhomogeneities increased. 12, 15 | 75 | - Sh|1858| 77777771 13, 15 | 80 | - Sh|156| Eat 14| 15 | 85 | - |yy| 77777771 11111111

Table 2

Dependence of the selectivity in the negative etching of the Av25z layer on the exposure time of the mixture of ethylenediamine, acetone, and dimethylsulfoxide o -

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Table C

Comparison of sensitometric characteristics of resist layers A525z manifested by different selective herbalists" m 7o5 | lov "Solution (1): 7595. rest

The prepared mixture was kept for days at room temperature (29355K;

Solution (2): 2595 MNYA4OH - 2.5 mabs.95; (СНЗ)2СО - the rest. - (prototype)

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Claims (1)

The method of preparing a negative selective herbicide for resist layers of chalcogenide glass Av293, which consists in mixing the base and acetone, which differs in that dimethyl sulfoxide is additionally introduced into the original mixture, and ethylenediamine is used as the base at the following concentration ratio of the components, vol. 90: ethylenediamine 8-12 acetone 55-70 dimethylsulfoxide the rest, after which the mixture is kept for at least 24 days at room temperature.