discharge is concentrated on such small circular areas. Owing to an increasing number of uncovered 
es areas the coverage level decreases with sputtering time. At the oxide-free regions the formation of 
N ne cones typical for physical ion etching starts immediately causing a surface roughening. In the case 
o mf of sputtering in a pure Ar atmosphere the formation of some cones with extreme dimension (a few 
© um) should be pointed out. Investigations by EDXS and by cross-sectional TEM (see section 3.2) 
have shown that in contrast to former estimation [1] the coarse cones are of metallic nature and not 
all, at first oxide. The formation of these cones is limited to the primary uncovered areas. Mostly, they are 
© Out (19. ]b), A conglomerates of several neighboured cones and the dimension corresponds to the size of one circu- 
Suma, The lar area. It is assumed, that at the primary areas the strong input of particles and energy causes con- 
HAS a ditions favourably to the growth of aluminium out of the surface. The micrographs in fig. 2 give an 
he Woof 1s impression to the frequency of occurrence. Moreover, scratches caused as artefacts during grinding 
Ri body can will be decorated by a high number of coarse cones. From this, it has been concluded, that the pri- 
ACrostructure are mary etching and the subsequent formation of coarse cones take place at surface steps and edges. 
am and Copper. 
Partally, a pre- The addition of H, to the atmosphere (Ar/H,, 5:1) leads to an improved cleaning behaviour. The 
EINS are pores formation of the oxide coverage is not inhibited, but, compared to the pure Ar atmosphere the speed 
performed at an of oxide removal is nearly twofold, the residual oxygen content is reduced to < 5 at.-% (> 12 at.-% 
ons IS the same, in the case of pure Ar atmosphere) as well as the formation of coarse cones is inhibited. Considering 
£pores has been type, intensity and energy distribution of ions during plasma treatment [4] the following interpreta- 
& ONCE Coverage tion is provided. The addition of H, causes the reduction of intensity and energy of Ar ions as well 
RTE as the formation of ArH ions with high intensity and high energy. Thus, the effect of physical etch- 
in ing will be reduced while the effect of chemical etching is superimposed. 
IS Temoval. Ihe 
itor. Bit by The reason for the formation of the oxide coverage at the beginning of the sputter cleaning process 
tet the glow is not yet clear in detail. Probably, the water partial pressure is to high despite of substrate heating at 
350°C before sputtering. Additionally, the sample surface may contain a lot of artefacts and con- 
tamination after grinding and polishing. 
3.2 Nitriding 
After surface cleaning the input of nitrogen into the metal and the formation of the AIN phase can 
start. The nitride layer thickness increases with time. Thereby, the interface between nitride layer 
and aluminium moves into the depth as well as the height level of the layer surface increases. In 
fig. 3a,b the surface is shown after a short nitriding time (30 min). The topography has been altered 
due to the sputtering effect. Thus, densely arranged cones in the scale of 100 nm or smaller are typi- 
cally. Differences in regard to the micro-roughness as well as to the height level arise from the dif- 
ferent chemical composition of the phases in the material. Therefore, the precipitations protruded 
from the surface before plasma treatment will be recessed during nitriding, compared to the sur- 
rounding nitrided aluminium matrix. The Al-Cu precipitations show a reduced nitriding effect, too. 
In this way, troughs at the surface are generated (fig. 3c). 
The degree of nitriding and the altering of the topography depend on the composition of the atmos- 
phere during both steps of treatment. The best results can be obtained by the admixture of H, during 
sputtering as well as nitriding in regard to the nitriding depth and the nitrogen content inside the 
layer (fig. 4) in connection with a reduced oxygen content (< 5 at.-%). This is consistent with the in- 
situ plasma measurements, which have shown that the admixture of H, during nitriding causes an 
increase of intensity and energy of nitrogen ions as well as the formation of NHy ions and N>H; ions 
[3,4]. The effect of H, admixture on the topography is clearly seen by the comparison of fig. 3c and 
5. In the case of sputter cleaning without H, admixture medium and large sized cones are dominant 
165