Optically patterned filters and production process.

(42) Date of commencement of the patent: 15. 5. 1986 (45) Date of issue: 29.12.1986

<td>(56) Documents:</td><td>(73) Patent owner:</td>

<td>JOURNAL OF VACUUM SCIENCE &amp; TECHNOLOGY, VOL. 16, NO. 6</td><td>STANGL GÜNTHER</td>

<td>NOV / DEC 1979, p.1897-1900: IONBEAM LITHOGRAPHY FOR</td><td>VIENNA (AT).</td>

<td>IC FABRICATION WITH SUBMICROMETER FEATURES ";</td><td>AUSTRIAN RESEARCH CENTER SEIBERSDORF</td>

<td>DE-0S2643811 ELECTRONICS, MARCH 27TH, 1980, p.142-146:</td><td>SOCIETY MBH</td>

<td>IONBEAMS PROMISE PRACTICAL SYSTEMS FOR SUBMICROMETERS</td><td>VIENNA (AT).</td>

<td>WAFER LITHOGRAPHY ";</td><td>MITTERAUER JOHANNES DIPL.ING. Dr.techn.</td>

<td>DE-0S2048915 GB-A-1577479 US-A-4144066 DE-A-2623688</td><td>VIENNA (AT).</td>

<td>US-PS 3682729 GB-A-2079536 GB-A-1583459</td><td>SZALMASSY ZOLTAN DR.</td>

<td>PATENT ABSTRACTS OF JAPAN, BD.7, NO.196 (P-219) (134I), 26.AUG.83; JP-A-5893052;</td><td>VIENNA (AT).</td>

<td>J. ELECTROCHEM SOC. 129, P.827-830, 1982,</td><td>(72) Inventor: STANGL GÜNTHER VIENNA (AT). RÜDENAUER FRIEDRICH VIENNA (AT).</td>

(54) METHOD FOR THE PRODUCTION OF OPTICALLY STRUCTURED FILTERS FOR ELECTROMAGNETIC RADIATION AND OPTICALLY STRUCTURED FILTERS

AT 382 040

INR W78MB

- 2 No. 382040

The invention relates to a method for the production of optically structured filters with substantially smooth surfaces, in particular working masks for the photolithographic production of microelectronic components, with at least one pattern with respect to the filter layer of different transmission for the electromagnetic radiation to be filtered, wherein ions are implanted into the filter layer to form the pattern (s) according to the pattern configuration (s) to be generated.

Processes for the production of structured filters are known in which an optically impermeable layer and thereon a photoresist layer are applied to a radiolucent support, whereupon corresponding desired areas or patterns are exposed to light radiation. During exposure of the photoresist layer, the light distribution within the layer is essentially determined by the light pattern produced by the exposure system - light source and mask - on the layer surface, by the absorption of the light in the photoresist and the reflection at the boundary plane between the different layers , This light distribution determines the structural change of the photoresist, which is made visible by appropriate development. After a further etching or swelling treatment, a pattern corresponding to the exposed regions of the optically opaque layer remains.

The disadvantage of these known photolithographic processes lies above all in the very cumbersome and expensive process control. Moreover, according to these known methods, it is very difficult to produce the very fine structures required in microelectronics with line widths of less than 1 μm. The latter is due to the not fully controllable etching process. It should also be considered that the advancing in microelectronics miniaturization requires ever finer structures of the work masks.

Another possibility of forming structures or patterns in a filter layer for electromagnetic radiation consists in the implantation of particles in the filter layer, for example by ion irradiation. This is eg from Patent Abstracts of Japan, Volume 7, No. 196 (P-219) (1341), August 26, 1983, JA-A-5893052 (SUMA SEIKOSHA KK) 02.06.1983, on a filter layer, a photomask by exposure and washing out the exposed areas of an applied photosensitive layer, whereupon the partially covered filter layer is irradiated with ions. Subsequent to the irradiation, the photomask is chemically removed so that the patterned filter layer remains. This procedure has the disadvantage that the filter layer due to the repeated chemical treatment and the application of the photomask suffers directly on the surface or the formation of a fine pattern is not possible. The lithographic treatment leaves unevenness, in particular in the edge regions of the photomask, whereby the homogeneity of the filter layer is interrupted.

The aim of the invention is to enable a simple production of structured filters, in particular work masks, as they are needed for the production of microelectronic components, preferably with structures with line widths of less than 1 pm.

According to the invention this is achieved in a method of the type mentioned in that the preparation of the filter starting from a homogeneous, unstructured filter layer with continuous uniform transmission, the smooth surface is available in their entirety for ion implantation, in a single process step, namely by the ion implantation takes place in the pattern (s) by means of at least one finely focused ion beam, which is positioned or guided on the filter layer by electromagnetic deflection devices corresponding to the pattern (s) or ion implantation in the pattern (s) with at least one finely focused ion beam by keeping it stationary and exposing the filter layer one or these fine-focused ion beam (s) according to the (s) pattern (s) mechanically positioned or guided or the ion implantation in the pattern (s) by means of an unbundled or a weakly focused ion beam is such that it impinges on a corresponding, in particular scaled-up mask, which is permeable only at the locations corresponding to the patterns for the ion beam and the exiting through the partial beams there by means of a located between the mask and the filter layer ion optical imaging device Accordingly, in particular reduced, is imaged on the filter layer or the ion implan nr.382040

3) by means of an unbundled ion beam passing through a mask in mechanical contact directly with the filter layer, which contains the pattern (s) in a complementary manner, making these patterns scaled (1: 1) conforming to the filter layer is transmitted. In this way it is possible to simplify the manufacturing process considerably, since lithographic steps are eliminated; In particular, the etch processes that are difficult to control in the production of structured filters are eliminated. By this means, in particular, a particularly simple production of structured filters for electromagnetic radiation is possible, which consists of only a single operation.

It is preferred if by spatially different implantation with different types of ions (eg ions of different elements, molecular ions), and / or ions of different energy pattern regions with mutually different transmission for electromagnetic radiation of the same or different wavelength are generated. During ion implantation, the ions penetrate into the layer in which they then remain stationary due to the kinetic energy given to them. By selecting the type and / or density of the implanted ions results in each case the desired transmission characteristic, ie Depending on the type and / or density of the implanted ions, a specific transmission for electromagnetic radiation of a specific wavelength or a specific wavelength range results at those points at which ions are implanted in the filter layer.

In the fabrication of patterned filters, the entirety of the ion implanted regions may provide a pattern of radiation transmissive and opaque regions in the layer.

In the production of structured filters by the method according to the invention, there is yet another important advantage: Due to the small range of ions in solids (less than 10 nanometers), the ions remain localized during implantation in the immediate vicinity of their Einschußortes, so that virtually no line broadening in which the ion-receiving filter layer occurs, as for example in the electron beam lithography by formation of secondary electrons in the penetration of a collimated electron beam in a photoresist layer is the case. For this reason, it is possible in the inventive method to produce structured filters, such as work masks for optical lithography, with a meaningful line width down to 200 nm.

When the pattern is written with a collimated metal ion beam positioned by electromagnetic deflection, this beam of a field emission ion source can be collimated to a diameter of 40 nm. With such a beam, patterns with a line width of 50 nm can be easily produced.

In order to avoid an electrostatic charge of the ion-receiving filter layer through the ion beam, which can lead to a disability during implantation, according to a further feature of the invention provides that depending on the electrical conductivity of the filter layer whose surface before the ion implantation by applying a thin , electrically conductive layer, preferably a gold layer with a thickness of 3 to 20 nm, is made conductive and that this electrically conductive layer after completion of the generation of (s) pattern (s) of different transmission is removed again. This metal layer is vapor-deposited or sputtered by only a few nanometers, and it has been found in practical experiments that a layer thickness of a gold layer of 4 nm, damped on an ion-accepting filter or polymer layer, is very expedient.

In these experiments, it has further proved to be very favorable if the filter layer is a polymer layer having a thickness of up to 0.4 gm, in particular a thickness of 0.1 to 0.2 gm.

In the method according to the invention, metallic ions and also non-metallic

Ions or molecular ions are used for implantation. It is also by appropriate

Choice of the shot dose also makes it possible to make the pattern of the work mask impermeable only for limited areas of the electromagnetic spectrum, whereas in the adjacent spectral regions the radiation is transmitted. This can be work masks

Nr.382040

4, which act in the manner of radiation filters having various transmission characteristics. Basically, it should be noted that working masks prepared according to the invention are suitable for the production of solid-state surfaces for the production of microelectronic components, also for the production of components of integrated optics, for the generation of 1 and 2-dimensional diffraction gratings for electromagnetic radiation and also for the production of zone plates, such as they are used for imaging by means of short-wave electromagnetic radiation.

An optically structured filter, in particular working mask for the photolithographic production of microelectronic components, in which in a homogeneous unstructured substantially smooth filter layer at least one pattern is formed by ion implantation modified transmission for the electromagnetic radiation to be filtered, is according to the invention characterized in that the filter one with regard to a lithographic treatment, in particular etching, has unprocessed or untreated surface or structure. It is preferred if in the filter layer regions or patterns with mutually different transmission for electromagnetic radiation with the same or different wavelength by implantation of ions of different types (eg ions of different elements, molecular ions) and / or formed with different ion dose. It has proven to be expedient if, according to the invention, the filter layer is constructed to be homogeneous from at least selected wavelength ranges of the electromagnetic radiation to be filtered, for example organic or inorganic polymers. To increase the stability, it is advantageous if synthetic quartz glass is used as the material for the filter layer or for the carrier layer.

It is possible to form patterns by respective ion implantation, each with a different transmission characteristic. By a different choice of the type and / or density of the implanted ions for each pattern is achieved that they are different permeable to different areas of the electromagnetic spectrum.

In the following the invention is explained in greater detail with reference to the drawings, in which: FIG. 1 shows a schematic view of patterns in a filter layer, FIG. 2 shows an arrangement for a so-called writing ion implantation, FIG. 3 shows an ion implantation with an unbound ion beam, and FIG a schematic view of the process implementation.

Fig.l shows a filter prepared according to the inventive method. As support -2- for the filter layer -1- was used pure synthetic quartz glass, as required in deep UV lithography, to ensure the transmission of the wavelength required for exposure. A homogeneous 0.3 μm thick, UV-transparent, crystal-clear organic polymer layer was spun on support -2- and sputtered with a gold layer approximately 4 nm thick. Polymethacrylic acid methyl acrylate (PMMA) was used as the polymer. The filter according to the invention was produced by writing ion implantation using as ion source a liquid metal field ionisation source from which a

Beam of indium ions high directivity value was extracted. The ion beam was accelerated to an energy of 10 keV and focused so that an ion current of 10 nA of singly charged indium ions could be concentrated into a 5 pm diameter spot on the polymer layer. By electrostatic deflection of the ion beam, a pattern was written in the polymer or carrier layer -1-, wherein the local ion dose about 4 χ 10¹⁵ Indium ions / cm^z scam. After ion implantation, the remaining gold layer was chemically stripped. The utility of this ion-implanted pattern in the filter layer as Arbeitsbzw. The direct mask for the deep UV exposure was demonstrated by bringing the implanted polymer layer into contact with a substrate coated with positive-working photoresist (Shiplea AZ 1350 J, 06 μm thickness). The exposure was carried out with an ultraviolet light source (high-pressure mercury lamp) with an exposure time of 3.5 s. After development of the thus exposed photoresist (spray development for 60 s at 800 rpm with AZ 350 Developer, dilution 5: 1 with deionized water), a structuring of high edge sharpness resulted in the photoresist layer.

According to Figure 2, the ion implantation can be carried out by one of a Ionenquel5

No.382040 le -11- is focused by known electronic, electromagnetic or magnetostatic ion lenses, or a combination -13- of such lenses to a diameter that is smaller than the diameter of the mask areas, which are made largely radiopaque should. This fine-focused ion beam is controlled by likewise known electric or magnetic deflecting fields -14- in such a way that a pattern corresponding to the mask to be produced is written into the filter layer -1- with the ion beam.

Alternatively, the ion beam may remain stable along its axis and the mask may be formed by moving the filter layer -1- under the fine-focus ion beam so that the ions also enter the filter layer only in the pattern corresponding to the mask to be formed -1- be implanted. Is used as an ion source -11- eg used a liquid metal field emission source, so a particularly high ion current can be focused in areas with very small expansion. As a result, masks of high fineness can be produced in a particularly short time.

According to FIG. 3, a further possibility of carrying out the method according to the invention is that for implanting the pattern, an unbound or an ion beam that is only slightly bundled, an enlarged scale mask, penetrating from an ion source - 11- is used. This mask -16- is projected as an image -18- with the focusing device -17- enlarged or reduced to the polymer layer -1-. In this implementation variant, a primary mask is used, usually made of metal, which is smaller or larger than the mask to be generated for electromagnetic radiation-impermeable mask and which has a pattern complementary to the desired mask pattern. This primary mask -16- is illuminated by a large-size ion beam -12-, which pass through recesses of this mask Elementarionenstrahlen -19- which have the shape of the mask pattern and focused by a known ion optical focusing means -17- and correspondingly reduced or enlarged on the ion-receiving filter layer -1- impact. In this way, the desired pattern can be produced particularly accurately on the work mask, with very thin line widths of the structures can be achieved.

Yet another possibility of carrying out the method according to the invention is shown in FIG. 4, which consists in bringing into contact with the polymer layer -1- a mask 16 which carries the pattern to be inscribed on a scale of 1: 1, and then an unbundled ion beam 12 - is exposed, with which the pattern of the mask -16- is imaged.

The polymer layer -1- may be supported by a substrate -2-.