**3.3. Deposition of large‐size films**

length of the arc of the radius *R* in the sector with an angle *δ*. More accurate values,

156 Applications of Laser Ablation - Thin Film Deposition, Nanomaterial Synthesis and Surface Modification

formed.

uniformity.

obtained if we repeat the calculation using the average values of the film thickness ℎ

slit corrected in the first approximation. After this step, a test of the obtained results is per‐

Both the calculation data and the experiments have shown that the described computation methodology provides the necessary precision for obtaining films with excellent thickness

**Figure 8.** Distortion of sectorial slit. The mask slit curved along the uniform thickness ellipse (dashed line) provides

The method of the mask with a slit in the form of a sector with the curved symmetry axis is realized also with the use of geometry presented in **Figure 4**. This possibility to obtain thickness‐uniform large‐area films is due to the following circumstances. For obtaining a thickness‐uniform film on rotating substrate, the slit in the mask must be a sector with the vertex coinciding with the rotation axis of the substrate. This is valid for the case of uniform flow of deposited substrate. Consider now the realistic pattern shown in **Figure 6**. If we intersect the three‐dimensional surface outlining the thickness of the film, by a plane parallel to the *xy*‐plane, we obtain the line of equal thickness of the film. This line is usually an ellipse. Intersecting the surface above by planes parallel to the *xy*‐plane at different heights, we obtain a set of concentric ellipses. **Figure 8** shows the ellipse passing through point 9 in **Figure 4**. In every point of this ellipse, we have the same thickness of the film. The reason for this is the spatial uniformity of the flow of deposited material along this line. Hence, the slit in the mask in the form of a curved sector having the middle line coinciding with equal thickness ellipse (**Figure 8**) should provide the uniformity of the film thickness. The choice of the ellipse is caused by striving to obtain a uniform film over the entire surface of the substrate. Symmetry of the pattern with respect to the substrate radius causes the possibility to use two slits which doubles the deposition rate. The deposition rate depends as well on the value of angle *α*.

both thickness and composition uniformity of deposited films.

*3.2.3. Slit in the form of a sector with the curved symmetry axis*

 2, may be

2 for the

**Figure 9** shows schematically the deposition geometry for large‐area thin uniform films, whose transverse sizes are limited by only the deposition chamber dimensions [4]. Its distinctive features are as follows:


It can be seen in **Figure 9** that the substrate undergoes translatory motion with respect to the target. Obviously, in this geometry the substrate motion can be replaced by the joint motion of the target and the diaphragm.

To grow a film of uniform thickness over the entire substrate surface, it is necessary to determine the motion law for the substrate. The calculation results for substrate transferred velocity *V* were experimentally checked by depositing thin CuO films on silicon substrates 30 mm long, located over the radius of a disk 300 mm in diameter. The angles between the target plane, laser beam axis, and diaphragm plane were chosen so as to make the diaphragm select a particle beam oriented perpendicular to the target from the plasma plume. At any changes in the deposition parameters during a long‐term process in the chosen geometry, the mass transfer rate of the target material to the substrate will be maximum and the deposition time of a film of specified thickness will be minimum.

**Figure 9.** Schematic of the new technique for depositing thin films of arbitrary sizes.

**Figure 10.** Surface profile of a CuO film deposited on a substrate transferred at a velocity *V* = const/*r*.

The surface profile of a CuO film deposited on a substrate transferred with a velocity *V* = const/ *r* is shown in **Figure 10**. The average film thickness is 85 nm. The thickness deviation from the average value did not exceed ±3% over the entire substrate surface. The method proposed

makes it possible to obtain thin films of uniform thickness on substrates with sizes limited by only the deposition chamber size.
