This paper describes the control and reduction of agglomeration of the thin copper seed layer deposited on different barrier layers. Higher stress is applied in layers deposited on TaN and Ta barrier layers. This stress greatly affects the agglomeration and adhesion strength. This stress can be reduced markedly with employing a TaSiN barrier layer instead of Ta barrier layer. Correlations have been found between the stress in as-deposited copper seed layer and the agglomeration height formed with this annealing. That is, agglomeration occurs markedly in the layer on tantalum nitride ͑TaN͒ and Ta barrier layers. Although lower stress layer can be accomplished at the Cu seed/TaSiN interface, no agglomerations occur in the TaSiN barrier layer. This barrier layer for copper diffusion can also get promising barrier performance.

Stress of copper seed employing in the copper interconnection layer is studied. Since this stress affects largely the adhesion strength at the Cu/barrier layers and the Cu͑111͒ orientation of copper layer, reduction of stress is important. Higher and high stresses are applied in the layer on TaN and Ta barrier layers. These layers can lead to poor adhesion strength. Much better adhesion strength can be accomplished in the layer on the TaSiN barrier layer. The surface changes to rough surfaces with annealing at 400°C in the layer deposited on TaN. The highly stressed layer changes to a low stress layer as a result of this agglomeration. However, a smooth surface is held in the low stress layer on the TaSiN barrier layer.

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The barrier effect for copper diffusion and the adhesion properties of copper seed layers were studied for sputtered TaSiN layers. The diffusion depth of copper following 400°C annealing is as deep as 25 nm using conventional tantalum nitride ͑TaN͒ barrier layers. With the doping of Si in this layer to form TaSiN, the diffusion depth decreases drastically, reaching 5.0 nm for an optimum Si composition of 0.06-0.09 The stress of thin copper seed layers deposited on TaSiN is much lower than that on conventional Ta barrier layers, decreasing rapidly with increasing Si composition. There appears to be no agglomeration in the low stress copper seed layer. The highest adhesion strength is attained in a copper layer deposited on a TaSiN adhesion layer with a Si composition of 0.16. Note that the optimized Si composition is different between two layers, that is, the barrier and adhesion layers.

Atom and carrier concentration profiles in carbon-ion-implanted GaAs have been measured. Ion implantation of carbon is performed at 300 keV with dose of 1.0×1014 ions/cm2. Carbon concentration profile obtained by secondary ion mass spectrometry measurement is in good agreement with the profile obtained by Monte Carlo simulation. The implanted carbon does not diffuse markedly with annealing at 900° C because the diffusion coefficient is below 4×10-16 cm2/ s for the ion-implanted carbon. Therefore, a shallow carrier concentration profile is formed after annealing. Activation efficiency is 17% at the surface (depth less than 0.47 µ m). However, this efficiency is as low as 4% in deeper regions. The lower activation efficiency in deeper regions is due to the suppression of activation by the precipitation of carbon after the annealing.

This paper describes the properties and adhesion strength of electroplated copper layers deposited onto two different seed layers. In a thin ͑10 nm͒ seed layer, which we term seed layer A, agglomeration occurs across the full thickness of the layer and a stress free or lower stress seed layer is formed with an annealing at 400°C. A highly ͑111͒-oriented copper conductive layer is the result of this electroplating strategy. The adhesion strength is so high ͑40 gf͒ that no peeling occurs during chemical mechanical planarization ͑CMP͒ in this layer. When the layer is electroplated onto a thick ͑100 nm͒ seed layer, which we term seed layer B, agglomeration only occurs at the interface with Ta barrier layer with this annealing. Although a smooth copper layer still remains at the surface, a weakly ͑111͒-orientated copper layer is electroplated. The adhesion strength of this type of copper layer is as low as 10 gf so that peeling can easily occur both during annealing and CMP. Correlation is found between the critical pressure defined by the pressure occurring of the peeling in the copper layers during the CMP with adhesion strength.

Resistivity is observed quantitatively in a thin electroplated copper layer. A resistivity of 2.6 µΩ·cm is observed in a 600-nm-thick as-deposited copper layer by conventional electroplating. This resistivity increases rapidly with decreasing thickness and reaches 7.8 µΩ·cm at a thickness of 75 nm. This rapid increase is mainly due to the increase in the orientation ratio of the copper (111)/(200). The resistivity in the as-deposited layer is maintained at 2.2 µΩ·cm in a 75 nm low resistivity layer with a low orientation ratio. Such a low-resistivity thin layer is electroplated practically by newly developed process. The preparation of a low-stress seed layer is also required in this electroplating process.

This paper describes various parameters affecting to the ͑111͒ orientation in electroplating copper conductive layers. Control of this orientation is important because resistivity, stress, adhesion strength, and electromigration resistance of copper layer are affected largely by this orientation. This orientation cannot be controlled with varying electroplating conditions but can be controlled by the orientation of the copper seed layer used as substrate. That is, the ͑111͒ orientation of electroplating copper layer is closely related with that of the seed layer. Orientation of the seed layer is determined mainly by the barrier layer. Weakly and highly ͑111͒ oriented copper layer is obtained when the seed layer is deposited on tantalum nitride and Ta barrier layers, respectively. Still higher orientation is attained in the depositing of copper layer on a TaSiN barrier layer. Agglomeration does not occur with annealing in the highly oriented copper seed layer.