Production of Mo/si Multilayers At Increased Substrate Temperatures: The Effect On D-Spacing, Interface Roughness and De
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pressure of lx 10- 7 mbar. The deposition rates for the Mo and Si are approximately 0.1 nm/s. In the upper chamber the substrate holder contained three temperature isolated parts heated by three quartz lamps. The temperature was measured with a Chromel-Alumel thermocouple (accuracy ± 2 K). To stabilize the substrate temperature, the holder was heated several hours before the deposition was started. In each run a total of nine samples were deposited at three different substrate temperatures. After deposition the samples were cooled down to room temperature in vacuum. For the production of Mo/Si multilayers, the layer growth was monitored in-situ by measuring the reflectivity of the N-Ka line (X-3.16 nm) at 13.50 with respect to the substrate. The in-situ reflection system installed in our deposition system contains an x-ray source with a boronnitride anode and a channeltron detector. The N-Ka line is separated from the B-Ka and the continuum background which is absorbed in a 1.8 pm Ti-filter. We applied the so-called minimum-maximum criterion, which is deposition of the high-Z or the low-Z material until a maximum, respectively a minimum in the in-situ reflectivity was obtained. This resulted in a multilayer with a d-spacing of 7.9 nm. The in-situ reflections of 310 K, 488 K, 511 K, 538 K are displayed in figure 1. At 300 K and above 550 K the amplitude of the in-situ reflectivity signal diminishes after 12 layer pairs and finally disappears, which makes the in-situ reflection less suitable for Mo/Si multilayers with more than 12 periods below 300 K and above 550 K. The decrease of the amplitude of the in-situ reflection indicates that the interface roughness is still increasing at the last layer. Consequently, the interface roughness of the 12 period multilayers could be lower than a 40 period multilayer. X-RAY MEASUREMENTS Small angle reflection measurements (0-20 scans) with Cu-KoL radiation were used to characterize the multilayer structures. The Si or Ge crystal monochromators used in combination with two slits provide an angular resolution of better than 0.01 degree. The d-spacing of the multilayers were obtained from the position of the Bragg peaks in the 0-20 scan. From the analysis of these measurements the interface roughness, the density and the P-factor (the ratio of Table I: A: d-spacing, arms: interface and Ffactor roughness were obtained from the small angle reflectivity measurements.
Temperature A
Orms
(K)
(nm)
323
(nm) 37.89 7.81
396 414 448 461
0.66
0.410
0.61
0.415
7.74
0.56
0.418
7.67 7.55 7.53
0.422 0.434 0.434
464
7.48
0.55 0.47 0.42
489
7.46
0.34
0.434
498 511
7.49 7.47
0.38 0.44
0.433 0.435
516 529
7.33 7.05
0.44 0.56
0.437 0.428
0.40
1000
P-factor
500T
= 538K
hA T =511
.ilk
T
488K
= 500 0
-
0.433
T 313K
500
0 0.0
500.0
1000.0
1500.0
Time(a.u.l
Figure 1: The in-situ reflection during deposition. 376
the thickness of the high Z-material and the total thickness) were also determined. [6] The near normal incidence reflectivity measurements mul
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