Researched the parameters of the microstructures, obtained by laser termochemical space recording in films of molybdenum with a thickness of 17, 35 and 70 nm, deposited on a glass and quartz substrates. Graphs of the spatial resolution of the microstructures as a function of the laser power are plotted for different substrate materials. It is shown that a higher spatial resolution of the microstructures can be achieved in the molybdenum films with a 17 nm thickness.
It seems promising to use in various fields of science and technology of diffractive
optical elements (DOE), which are plates formed on their surface microstructure [
At the present time to reduce the dimensions of the microstructures, the widely
used method of formation of topological drawing directly in the source layer of the
material of the contact mask without the use of photoresists. It is based on local
processing of thin films of chromium focused laser radiation [
The disadvantage of this technology is the low resolution of about 0.8 μm.
Therefore urgency to the task of developing techniques that allow to overcome this
barrier. This result is possible through search and application of materials with
contrasting characteristics to selectively use a maximum of activating radiation. In
this respect, a well-known series of works, where instead of chrome offers a variety of
alternative materials, such as silicon, indium phosphide and the oxides of various
metals [
In [
Based on [
The purpose of this work is to study the feature of the contact mask, obtained by laser ablation of films of molybdenum, depending on the thickness of the films, which will produce the optimum conditions of carrying out the process.
The base served as an optically smooth substrate made of glass and fused quartz brand KV of size 50×50 mm, thickness 3 mm. Film of molybdenum with a thickness of 17, 35 and 70 nm were deposited by magnetron sputtering method on the "Caroline D-12A" under the following conditions: the power of the magnetron is 700 W, the temperature of the substrate is 200°C, a pressure of argon to 2.0∙10-1 Pa. The time of deposition was determined by the finite thickness of the films and ranged from 2 to 8 min.
Patterns in the films formed on the laser writing station CLWS-200 [
Recording was conducted under the following conditions: operating wavelength of the laser radiation is 488 nm; maximum power supplied to the recording head 100 mW; record structure – concentric rings with a pitch of 3 μm and an outer radius of 3 mm; the magnitude of the power for each ring decreased from 100 % at the point of greatest radius to 0 in the centre with a step of 0.5 %. The speed of rotation of the sample – about 10 s-1. the Specified parameters of the process corresponded to the maximum power density of laser radiation Emax = 2∙107 W/cm2. The effect of laser radiation led to local evaporation thin film of molybdenum over the entire thickness.
The morphology and elemental composition of the surface of the nanostructures were studied using scanning electron microscope (SEM) Hitachi TM3030 with integrated EDS spectrometer.
In Fig. 1 shows the dependence of the width of the lanes from the laser output
power for a radius record of 3 mm. Dependence obtained for quartz and glass
substrates. The width of the recorded tracks in the first place, depends linearly on the
laser power. When they are the same width for quartz substrates requires
approximately 20% more power, due to the difference in the thermophysical
properties of quartz and glass. Quartz, having a larger thermal conductivity, assigns
laser energy from the field of film. Film thickness of 17 nm show higher spatial
resolution, 2500 mm-1, against 1500 mm-1 for films with a thickness of 35 nm. The
permissions that are close to the maximum was reached in the power density in the
range (0,7...1,2)∙107 W/cm2. Note that this is significantly less than the theoretical
values obtained, for instance, in [
For films with a thickness of 17 nm, the formation of degradation products is not typical (Fig. 3). This can be explained by the fact that the energy of laser radiation is enough for a quick and complete evaporation of the material at the point of impact. For these two cases are well for-markedly boundary of the critical power at which the evaporation of the metal stops. Also around tracks observed subtle trace of a width equal to the diameter of the laser spot. Probably, this area needs to impose restrictions on the minimum recording period. For films with a thickness of 70 nm of the radiation energy is insufficient for the formation of tracks even in areas with a minimum radius of recording (Fig. 4). It is important to note the following. For systems with circular scanning absorbed by the material energy (dose) of laser radiation at a constant power density varies with the radius record, since the radius of the record specifies an effective time of exposure. The decrease of power density from the edge to the center with simultaneous increase of exposure time to have an opposite effect on the magnitude of the radiation energy. However, in our case a decrease in the size of the track as you approach the center, that allows claim about the decrease of the absorbed energy.
The study of microstructures of metallic patterns of the DOE showed that the best spatial resolution and minimum defects in the figure of the mask is achieved at a film thickness of molybdenum 17 nm.
Minimum attainable period of record limit width trace of the laser spot and is in our case 0.8 μm. Spatial resolution will be limited to this value and can be increased by reducing the wavelength and, correspondingly, the diameter of the laser spot.
Given the fact that the selectivity of the plasma etching films of molybdenum
relative to quartz can reach several hundred, the result opens the way for the creation
of structures with submicron resolution, in particular, short-focus of the DOE, and
also allows you to create patterns with a minimum number of manufacturing
operations. In addition, as described in the article, the research is also relevant for the
development of certain laser technology [
The work was supported by RFBR (grant No. 14-07-00177a). The authors Express gratitude to the company "INTERLAB" (Russia, Moscow) for their help in the study of samples on the microscope Hitachi TM.