DE3044434A1 - RESIST STRUCTURE ON A SUBSTRATE AND METHOD FOR DESIGNING A PATTERN IN THIS - Google Patents

Description

description

The invention relates to the machining of components and particularly where high-resolution features are to be produced are.

Accordingly, the invention is directed to a resist build-up on a substrate of the type specified in the preamble and to a method for producing a pattern in such a resist structure.

The manufacture of devices such as semiconductor devices and magnetic bubble devices is largely lithographic Processes. In these lithographic processes, a resist material with radiant energy, for example X-rays, electrons or light, irradiated in a desired pattern. This exposure induces a chemical Reaction in the exposed area of the resist material. The chemical reaction allows development, i. H. the elaboration the pattern, by changing the solubility of the exposed area from that of the unexposed area; it will' hence the removal of the exposed area in the case of a positive resist or the unexposed area in the case of a negative resist. Numerous resist materials

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have been developed. For example, polymethyl methacrylate (PMMA) has been used as a resist material and has led to relatively good resolution, i.e. to a resolution such as that shown by a line width in the range from 1000 to 100 nanometers (10,000 to 1,000 R) on thick substrates (thicker than 10 micrometers) is measured. Although PMMA has a relatively high resolution, its sensitivity is somewhat low where high throughput is required.

PMMA has been modified in a number of ways to be an accompanying one Change in properties such as sensitivity. For example, the basic monomer is from PMMA, d. H. Methyl methacrylate has been copolymerized with methacrylic acid. Although this copolymer does not have the excellent resolution of PMMA, it nevertheless has an increased sensitivity and is therefore recommended wherever high resolution is not essential and where relatively high sensitivity is the more desirable factor. An example of this is the draft of connecting cables for LSI's (highly integrated circuits) .

The lower sensitivity of PMMA is also evident in resist configurations, designed to obtain high resolution have been used. For example, using a two-layer resist structure with an upper layer from the

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Copolymer of methacrylic acid and methyl methacrylate and one PMMA lower layer has been discussed. (See Grobman et. At., Proceedings of IEEE 1978 IEDM, p. 58.) When this resist structure is irradiated with a dose sufficient to expose the upper polymer layer, then in the lower, relatively little chemical change induced in the PMMA layer. (This occurs as a result of the lower sensitivity of PMMA.) The top layer is developed, and after this development step, a solvent is introduced to remove the to remove uncovered PMMA.

With increasingly better resolution, both very high integration and discrete components based on very fine features, much research has been directed towards improving the resolution in a two-layer structure and towards resist compositions which alone have increased resolution. In general, resolutions in the range of 250 to 2,000 nm (2500 to 20,000 R) for two-layer arrangements and in the range of 100 to 3000 nm (1000 to 30,000 R) for single resist compositions are currently achievable on substrates thicker than 10 microns .

According to the invention, very good resolution, ie a resolution of up to 40 nm (400 S) _y , can now be obtained by using a

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carefully selected two-layer resist composition; d. H. of a structure with a lower positive resist material between - and in intimate contact therewith - both a substrate and an upper positive resist material. The fat of the lower resist material is chosen so that the number of backscattered electrons in a given area hit the underside of the upper resist material, reduced will. In addition, the upper resist material should be thinner than the lower resist material and the sensitivity of the lower one Resist material must be sufficiently high to accommodate this difference in thickness to compensate.

An example of the resist structure according to the invention is Two-layer structure with an upper layer made of PMMA and a lower layer made of a copolymer of methyl methacrylate and methacrylic acid (P (MMA / MAS)). With this exemplary composition, lines as narrow as 40 nm (400 8) can be obtained.

The two-layer resist structure according to the invention is characterized in claim 1, and further developments thereof in FIG Claims 2 to 6. A method for designing a pattern in such a resist structure is the subject of claim 7, while further developments of the method are the subject of claims 8 ff.

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The invention is described below with reference to the drawing; show it:

Figures 1 and 2 show a two-layer resist build-up after exposure and development on a substrate in sectional view and

Figures 3 and 4 show two examples of patterns to be designed in the resist.

The use of the two-layer system according to the invention provides higher resolutions than this with a single layer of either one or the other layer material. The explanation for this phenomenon can be seen in the fact that when the exposing radiation, e.g. B. electrons on the substrate carrying the resist material strikes, secondary electrons are generated. The secondary and primary electrons that are backscattered hit the neighboring resist material and cause a chemical reaction there. Since this electron backscatter occurs over a 2if spatial angle, the exposed area of the lower resist material is larger than the area directly hit by the incident radiation. By using a two-layer structure, the backscattered electrons hit the lower resist material first. If this

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Resist material is relatively thick, then these electrons dissipate sufficiently that they are in the upper resist material do not produce any appreciable amount of chemical change. That is, the thicker the lower resist material, the smaller it is becomes the number of backscattered electrons per unit area / that the upper resist material at the interface between Reach upper and lower resist material. The smaller the extent of this exposure as a result of backscattering, the smaller the deterioration in resolution is less. Accordingly, the lower resist material must be thick enough so that it does not precludes receipt of the desired resolution.

The dependence of the resolution on the thickness of the lower resist material is determinable by using a controlled pattern to determine the resolution achieved for a given composition and determine the thickness of the lower resist. In a preferred embodiment, the thickness is sufficient chosen to be large, so that the backscattered electrons cannot improve the resolution achieved; that is, the resolution with higher thicknesses of the lower resist cannot be improved or can no longer be improved. The number of backscattered electrons depends on the composition of the substrate and on the energy of the exposure radiation. In general, for substrate materials, like silicon and for typical electron beam energies of 25 to 30 keV the lower resist material has a thickness

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of at least 100 nm (1000 R), preferably more than 200 nm (2000 S) to meet this requirement.

When the above-described thickness requirement is met, the thickness and composition of the upper resist material determine together with the machining parameters, the available resolution. In general, the thicker the resist, the worse the resolution. Exposure to radiation of a resist increases the rate of dissolution of the exposed resist material in a suitable developer. The greater the exposure dose, the greater the rate of dissolution up to a saturation point. The magnitude of the change in the rate of dissolution with changing exposure depends on the composition of the Materials. When the resist is treated with a developer, the dissolution begins at the top of the upper one Resist material. Development proceeds in all directions, with the going into solution in a given direction advances at a rate dependent on the degree of chemical change induced in that direction; ever the greater the chemical change, the greater the speed. The speed of development is therefore the strongest in the direction of the exposure radiation, but it is also scattered in other directions as a result of exposure to Electrons significant. The thicker the material or the smaller the change in the rate of dissolution, the longer

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is the development time required to create the desired pattern through the resist thickness. The longer the development time, the greater the amount of material dissolved away in areas adjacent to this pattern and consequently the worse the resolution.

The invention is advantageously directed to obtaining resolution of 500 nm (5000 R) or better. To obtain such a resolution, the upper resist material and its thickness must be selected so that the opening in the upper surface of the resist material, as formed after exposure and subsequent development, is 500 nm or smaller in pattern areas which require this drawing fineness. Typically this is achieved by having the top resist material less than 1 micrometer thick for materials such as PMMA. It is possible to measure the opening width on the upper surface and the resulting resolution by electron microscopy. For a given selected material, the thickness required for a desired resolution is determined with the aid of this measuring method in conjunction with a control sample.

The material used for the bottom layer depends on the choice of material for the top layer. As described above, the upper layer is chosen in such a way that a given

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solution is obtained. The top resist material is exposed so that, after development, the entire thickness of the exposed area is removed within a period of time adequate to prevent deterioration in resolution. That The lower resist material is necessarily exposed to substantially the same dose of radiation as that used for exposure of the upper resist material is used. (The number of electrons or other units of exposure energy that the Reaching the upper resist material, but not the lower resist material, is negligible compared to the total incident radiation .)

For the dose used, the lower resist material must also undergo a sufficient reaction as this by the incident radiation and the backscattered electrons on the substrate are generated, so that after development the entire Thickness in the exposed area is removed without any appreciable deterioration in the available resolution. The fulfillment of this Criterion depends on the thickness and. Sensitivity of the material away. To meet the requirement to limit the number of backscattered electrons per unit area that the upper resist material achieve, meet and maintain a resolution better than 500 nm is generally a ratio of Thickness of the lower resist to the thickness of the upper resist in the range of 50: 1 to 1: 1 required.

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Since the developer does not reach the lower resist material until a solution through the entire thickness of the upper Resist material is done, the sensitivity of the lower resist material must be greater than that of the upper to to avoid a deterioration in the resolution. There is a further development of the upper layer during that Time required for adequate lower layer development. Although the more irradiated Areas (those areas that match the desired pattern) are already removed, drive less irradiated areas (the areas adjacent to the pattern) continue to resolve. If that extra development time becomes excessive, so will the deterioration in resolution is significant. The basic criterion is that the sensitivity of the lower resist material must be sufficient such that the development time required for the lower resist material does not preserve it the desired resolution prevented. Accordingly, the sensitivity of the lower resist material must always be significantly greater than that of the upper one. Generally, this goal is achieved by using a lower resist material that is no more than half, preferably no more than a quarter of the development time (for a given exposure dose and one given developer) as it is needed for the top layer.

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In a preferred embodiment, electron beams are used an average electron energy of 25 to 30 keV and a current density in the upper layer of the resist build-up of 10 A / cm ^ to 0.3 A / cm ^ is used. (X-ray exposure is also possible.) However, the use of electrons that are even more energetic is not excluded. Higher current densities are also not ruled out if the coherence of the beam is maintained. Of the Cross section of the beam at the top of the upper resist layer should be set so that it is smaller than that is the smallest feature to be drawn. Excessive or insufficient doses result in poor dissolution. Usual-

doses of 200 to 400 uC / cm are used. Electron beam, which are suitable for the present purposes are, for example, using a conventional Scanning electron microscope apparatus obtained.

The structure of the present resist structure obtainable by exposure is shown in FIG. The lower resist material 5 has an undercut area 4 due to its higher sensitivity after exposure and development on. If the pattern features are close together, it is possible that the two undercut areas concerned overlap in the lower resist material, as shown in Fig. 2 at 6, so that the exposed area

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after development coincides. (The dashed lines shown at 6 indicate the area where the two undercut areas overlap. If the pattern lines are too long for a given degree of overlap, the unsupported area of the resist will coincide.) In general, to avoid any overlap, the thickness of the lower resists must be less than twice the distance between features in the desired pattern. The occurrence of an undercut, which leaves an overhanging portion of the upper resist of limited length, is possible without collapse occurring. In general, to avoid collapse, unsupported spans should be less than five times the width. If this is not possible because of the other criteria discussed above, then the pattern spacing should be increased. As discussed, the sensitivity of the lower resist material should be sufficient so as not to limit the resolution. If this sensitivity prevents drawing of a pattern with a desired distance between pattern lines, then the distance must be increased. Typically, in the present case, patterns with dimensions of, for example, 150 run (1500 Å) length and 50 nm (500 Å) spacing or 500 nm (5000 R) length and 140 nm (1400 S) spacing can be obtained.

Since undercuts are obtained with the present resist build-up 7/8

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are crooked vapor deposition methods (see Dolan, Applied Physics Letters, 31, 337 (1977)) with the use of the present Resist build-up compatible. For example, components that are generated by oblique vapor deposition are, for example those described in E.L. Hu et al., IEEE Transactions on Magnetics, MAG 15, 585 (1979) using the present Layer structure available. In addition, there are common steaming methods with a vapor flow directed perpendicular to the substrate, compatible with the present resist structure.

The two-layer material is produced by customary methods. The lower layer, the layer 5 in FIG. 1, is first applied to the desired substrate 7 by conventional methods such as Centrifugal process applied (see Handbook of Thin Film Technology, L. I. Maissei and R. Glang, McGraw Hill, 1970, Pages 7 - 31). In a preferred embodiment, the upper resist material 8 is then applied to the lower resist material customary methods, such as the centrifugal process, applied. It is desirable that the solvent used for the spin of the upper resist material is used on the lower resist material, the latter does not dissolve. For example, if PMMA are used as the upper resist and P (MMA / MAS) as the lower resist, then the solvents Chlorobenzene and acetic acid are used as the sling vehicle for the top and bottom resist layers, respectively. The thickness of an im

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The layer applied by the centrifugal process is determined by the concentration of the centrifugal solution and the spin speed. The required concentration of a given solution and the selected spin speed with regard to a The given thickness changes with the materials used and can easily be determined in each case on the basis of control samples.

An example of the present resist structure and a device for its further use are given below .

example

A 2.54 cm by 1.27 cm by 0.0508 cm (1 inch by 0.5 inch by 0.020 inch) silicon substrate with one side polished to a local smoothness of better than 10 nm (100 R) was dipped in a hot water / detergent solution cleaned. The solution was stirred with ultrasound for approximately 30 minutes. The substrate was then removed from the detergent solution, rinsed in hot water, followed by a rinse in deionized water. The substrate was then rubbed with a fine sponge in deionized water. The substrate was treated with isopropyl alcohol vapor in a vapor degreaser to remove the water. The substrate was then blown dry with dry nitrogen gas.

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The silicon substrate was ^{immersed in an adhesion accelerator at 70 °} C., mainly hexamethyldisilazane, for 3 minutes. The treated substrate was rinsed in xylene and blown dry again with dry nitrogen. The substrate was "baked" in air at 70 ^{° C.} Shipley AZ-135OJ resist (a product of Shipley Corporation, which is mainly a polymer composition based on cresol-formaldehyde resin) was then spin applied to the polished surface of the substrate for 30 seconds at 6000 revolutions per minute. The spinning apparatus was covered with a beaker during this process in order to prevent the resist from drying too quickly. The resist was then "baked" ^{at 70 ° C. for 30 minutes.}

The resist was exposed to light from a mercury arc lamp in the pattern of the lead frame shown in FIG opening is a 4 5 micron square). A conventional optical mask was used to generate this pattern. The exposed resist was developed in chlorobenzene for 5 minutes and blown dry. The resist was then in a 1: 1 solution of AZ developer in water until full appearance of the pattern. (AZ Developer is a product of Shipley Corporation and is basically an aqueous one Sodium hydroxide solution containing a wetting agent.) The substrate with its developed resist pattern was in the

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The substrate holder of a conventional vapor deposition apparatus with a resistance-heated boat was used, and 100 nm (1000 R) gold were vapor-deposited onto the substrate. The substrate was removed from the vapor deposition apparatus and soaked in acetone until the resist film floated on. (The lead frame pattern thus produced on the silicon is used as a reference frame for the subsequent use of the present resist materials.)

A solution of 2.4 g of a copolymer of methyl methacrylate with methacrylic acid in 20 ml of acetic acid was prepared. The polymer used to obtain this solution contained approximately 8.5 weight percent methacrylic acid and had a relative viscosity of 9.5 when dissolved in a 10 weight percent solution of ethylene glycol monoethyl ether. This solution was applied to the surface of the silicon substrate carrying the lead frame using a centrifugal method. A spin speed of 8,000 per minute was used. As before, a beaker prevented the resist from drying too quickly. The resulting lower resist layer was about 400 nm (4000 R) thick. The sample was baked in air at 160 ° C for 30 minutes. A 1: 1 solution of chlorobenzene and KTI Corporation electron beam resist was prepared. The KTI resist is a 6% by weight solution of polymethyl methacrylate (medium molecular weight

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weight of 950,000). This solution was applied to the lower resist layer using a spin process at a spin speed of about 3000 per minute. The upper resist layer thus obtained was about 120 nm (1200 pages) thick. The sample was then baked ^{at 160 ° C. for 30 minutes.}

For easier focusing of the exposure electron beam created a sharp edge by making a small scratch with a pen through the resist creates the gold film of the lead frame. The sample was placed in a substrate holder of a scanning electron microscope (AEM) attached using silver paste. The substrate holder was then mounted in the AEM. The focusing of the electron beam was done using the detector of the AEM and adjusting the beam so that the previously created scratches was sharply defined. The beam parameters set were an accelerating voltage of 30 kV, an amperage of approximately 11.3 pA and a working distance i.e. H. the distance between the focusing lens and the substrate, of 15 mm. Using these parameters resulted in a Current in the substrate of 10 pA. The beam was adjusted to irradiate an 11 micrometer square area. A transparency having the pattern shown in Fig. 2 was stuck on a cathode ray tube. The banner had

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Side dimensions of approximately 3 inches. A photocell with an active area of approximately 1 cm was placed in a light-tight box together with the cathode ray tube, at a distance of about 15.24 cm (6 inches) from the cathode ray tube. The path of the electron beam in the cathode ray tube was synchronized with that of the electron beam in the AEM.

A 10 KHz oscillator was used to control the AEM electron beam to align the pattern in the desired position used. (This oscillator was used to chop up the electron beam so that it hits the substrate 5% of the "On" time encountered.) The beam was scanned with a Frequency of 1 KHz in the x-direction and a frequency of 10 Hz in the y-direction. The AEM electron beam became complete blanked when the light from the cathode ray tube was obscured by the pattern of the transparency, like this by the Photocell has been detected. Then the pattern appeared on the transparency to the image of the substrate, like this through the AEM is overlaid. The substrate was created using the translational adjustment options of the substrate holder positioned so that the pattern is completely within the confines of the open area of the lead frame lay. (It should be noted that this alignment must be done relatively quickly so that the resist material is negligible is exposed. Negligible exposure occurs

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if the alignment time is limited to one minute under the specified conditions.)

The X sweep frequency and the y sweep frequency were then set to 5 Hz and 0.077 Hz, respectively. The oscillator was made from the Circuit removed so that the electron beam is no longer chopped up became. The photodetector circuit was set so that when light is detected, the electron beam is blanked and no electrons could hit the substrate. The sweep direction was perpendicular to the dark lines (the x-axis was as indicated in Figure 4). The x and y sweep frequencies used and the writing field used determine the Line spacing. The pattern on the cathode ray tube was swept once while exposing the resist became. The exposed resist was removed from the AEM and in a 1: 2 solution of ethylene glycol monoethyl ether for 5 seconds developed in methyl alcohol. The sample was then rinsed in deionized water and with dry nitrogen blown dry.

The substrate was then placed in a conventional vapor deposition apparatus and gold was vapor deposited onto the substrate with perpendicular incidence. The vapor deposition was carried out until a 30 nm (300 R) thick gold layer was obtained. The sample was removed from the vapor deposition apparatus and used to remove the resist

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materials boiled in acetone. The resulting gold pattern had lines 500 ran (5000 R) long and 35 nm (350 8) wide with an edge-to-edge distance of 135 nm (1350 Å).

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Claims (12)

BLUMBACH · WEStR- BERGEN KHAMER ZWIRNER HOFFMANN PATENT LAWYERS IN MUNICH AND WIESBADEN 30 4 443 4 Patentconsult RadeckestraOe 43 8000 Munich 60 Telephone (089) 883603/883604 Telex 05-212313 Telegrams Patentconsult Patentconsull Sonnenberger Straße 43 6200 Wiesbaden Telephone (06121) 562943/561998 Telex 04-186237 Telegrams Patentconsult Western Electric Company, Incorporated New York, N.Y., USA Howard 1 Resist build-up on a substrate and method for designing a pattern therein Claims Qj) Resist build-up on a substrate, in particular for the production of components that require high-resolution features - successively from the substrate - a lower and an upper positive resist material layer, whereby the sensitivity of the resist material of the lower layer is larger than that of the resist material of the upper layer and the lower Layer is thicker than the top, characterized in that - the sensitivity of the resist material of the upper layer and its thickness are such that after exposure of the resist Munich. R. Kramer Dipl.-Ing. . W. Weser Dipl.-Phys. Dr. rer. nat. · E. Hoffmann Dipl.-Ing. Wiosbadon: P G BlumbaJi Dipl.-Ing. . P. Bergen Prof Dr. jur. Dipl.-Ing., Pat.-Ass., Pat.-Anw. until 1979 G. Zwirner Dipl.-Ing. Dipl.-W.-Ing. 130035 / 043t ORIGINAL! MSPECTED construction with an absorbed dose and removal of the exposed
Share the formation of openings with a resolution of
500 nanometers (5000 R) or less in the surface of the
upper layer is enabled, and - the thickness of the lower layer is sufficient to at least avoid harmful effects of exposure on the dissolution to reduce. 2. resist structure according to claim 1, characterized in that that the ratio of the thickness of the lower layer to the thickness of the upper layer is 50: 1 to 1: 1. 3. resist structure according to claim 1, characterized in that that the resist material of the upper layer is polymethyl methacrylate. 4. resist structure according to claim 1, 2 or 3, characterized in that the resist material of the lower Layer is a copolymer of methacrylic acid and methyl methacrylate. 5. resist structure according to any one of claims 1 to 4, characterized in that the lower layer is thicker than
Is 100 nm (1000 R). 130036 / 043t " ³ " 304A434 6. resist structure according to one of claims 1 to 5, characterized in that the lower layer is thicker than 200 nm (2000 R) . 7. Method for designing a pattern in a resist structure on a substrate - one in succession from the substrate lower and an upper positive resist material layer, wherein the sensitivity of the resist material of the lower layer is made larger than that of the resist material of the upper layer and the lower layer is made thicker than that upper and - Areas of the resist build-up exposed to an absorbed dose and the exposed areas of the upper and lower layer be removed, characterized in that the sensitivity of the resist material of the upper layer and the thickness of which is chosen so that, after exposure and removal of the exposed areas, openings in a dissolution of 500 nm (5000 S) or less arise in the surface of the upper layer, and the thickness of the lower layer is chosen to be sufficiently large to avoid adverse effects of exposure on the dissolution at least reduce. 130035/0431 3044A34 8. The method according to claim 7, characterized in that that the ratio of the thickness of the lower layer to the thickness of the upper layer is set to 50 r 1 to 1: 1 will. 9. The method according to claim 7 or 8, characterized in that for the resist material of the upper Layer of polyethyl methacrylate is used. 10. The method according to claim 7 or 8, characterized in that for the resist material of the lower Layer a copolymer of methyl methacrylate and methacrylic acid is used. 11. The method according to any one of claims 7 to 10, characterized in that the lower layer is deposited thicker than 100 nm (1000 R). 12. The method according to any one of claims 7 to 11, characterized α e indicates that the thickness of the lower layer is selected to be greater than 200 nm (2000 R) . 130035/0 43ΐ