Filling of though silicon vias (TSV) with ECD copper is an important process step to realize high performance 3D integrated microelectronic devices. Organic additives are used to deposit the copper defect free into the high aspect ratio vias. The decomposition of these organic additives can disturb the TSV filling process. The impact of Accelerator decomposition products to the process stability of a model TSV filling processes was investigated. Copper (I) thiolate was found to be the main contributor to the process fluctuations. Already at very low concentrations the fill performance of a model TSV filling process is disturbed. (Fig. 1) The chemistry of copper (I) thiolate formation and decomposition is discussed and a method for copper (I) thiolate determination in TSV electrolytes is introduced. The increase of process stability by counteracting copper (I) thiolate is discussed and illustrated on hand of examples. Figure 1

Through Silicon Via's (TSV) are one of the key enabling technologies towards 3D packaging. Copper electroplating is frequently mentioned as candidate to fill TSV's besides polySi or ink-jetting conductive inks and attracts high attention. In addition to copper plating solder plating offers the next opportunity. Last but not least the ultimate target of an “all wet TSV” where also barrier and seed layers are electroplated, was demonstrated already. This paper targets to introduce the 3D related plating technologies and will encourage a discussion about targets to be meet in order to enable 3D. Even so copper plating is well introduced to the IC industry for Dual Damascene plating, TSV copper filling challenges the plating technology. One of the reasons why is that TSV dimensions are almost one magnitude larger than dual damascene structures. So in order to meet the industries target of fast and void free copper filling, type and function of organic additives applied in copper plating bathes need to be re investigated. Galvanic copper electrolytes contain three organic additives. Carrier is a mild plating suppressor, Brightener is an accelerator, and Leveler is a strong suppressor and locally deactivates the Brightener. The Leveler component mainly affects the properties of the copper deposits. This paper will give an overview about type and role of organic additives used for TSV application. We will also discuss how namely the Leveler controls the filling mechanism and copper deposit properties. Two different acidic copper systems were used for TSV-filling. System A shows a super-conformal filling behavior and different copper grain structures at the surface compared to the TSV body. System B shows a bottom-up filling with similar copper grain structure at surface and TSV body. Both systems vary further regarding stress of the copper deposits, recrystallization temperature, incorporation of additives, and coefficient of thermal expansion. The paper discusses the influence of organic copper additives to the mechanical, thermal, and electrical properties of the copper deposits. Even so process technology to fill TSV's is still fast progressing we like to give a snapshot of fill times per TSV dimension reached using System B. Other potential plating applications in 3D stacking are eventually plating solder and/or diffusion barriers. This paper intends to introduce the basic principles of electrochemical and electroless plating and give application examples for Tin and Nickel/Palladium electroless plated layers applied for 3D packaging applications. Last but not least the concept of “all wet TSV” appears in the literature, targeting to substitute the barrier and seed layer so fare deposited by vacuum deposition technology by plating technologies. We will shortly review the literature and will introduce work currently under progress in Atotech towards an “all wet TSV”.

For the electrochemical filling of through silicon vias (TSVs) the geometry of these vias as well as their quantity on the wafer have a severe influence on the electrochemical process parameters, in particular on the current process time profile. So the electrochemical deposition (ECD) current was investigated in dependence of the filling progress, the height-to-depth aspect ratio, and the quantity of high aspect ratio vias on the wafer. The same applies to the number of plating steps at constant current, their length, and the total process time. Valuable insights for the design of via filing recipes could be deduce thereof.

Filling through silicon via (TSV) with copper is one important process step in 3D-integration. Void free and reliable galvanic copper deposition is essential for yield and lifetime of microelectronic devices. Different TSV applications, as chip stacking and interposer, require different TSV dimensions. This demands high flexibility and applicability for small and large via sizes in the galvanic filling process. This paper compares two different acidic copper systems in respect of their TSV filling properties. Both systems mainly differ in the leveler compound. System A shows super-conformal filling behavior and System B bottom-up filling. The properties of copper being deposited using System A and B respectively vary further in respect of copper grain size homogeneity, stress of the copper deposits, recrystallization temperature and incorporation of additives. The influence of organic copper additives on the mechanical, thermal, and electrical properties of the copper deposits is discussed. Using the example of System B, filling aspects as well as process optimization will be outlined. For process optimization electrochemical potential characteristics (E vs. t) during the filling process are used to identify important filling steps. Filling examples for small as well as large TSV feature sizes will be discussed.

A new homologous series of alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, prepared by a palladium-catalyzed coupling reaction of stannylated 2-diphenylaminothiophenes with 2-mono- or 2,5-dibromothiophenes and their homologues, was studied by in situ ESR/UV-vis/NIR spectroelectrochemistry. In general, the oxidation potentials of these oligothiophenes were found to be proportional to the inverse number of thiophene units. However, the potential slope of the first oxidation is completely different from that of higher oxidation steps. Trication radicals were identified by electron spin resonance (ESR) for higher thiophene homologues in addition to monocation radicals (polarons). According to the ESR hyperfine structures, the unpaired electron is delocalized in the conjugated system. In contrast to the parent alpha,alpha'-bis(diphenylamino)-capped oligothiophenes, the UV-vis/NIR absorption maxima of the oxidized species strongly depend on the number of thiophene units. Spin-restricted and spin-unrestricted Kohn-Sham density functional calculations were used to explain and to understand these properties. Absorption wavelength and intensities were calculated by the time-dependent density functional response theory. Unrestricted density functional calculations of oligothiophene dications (bipolarons) with five or more thiophene rings result in spin-broken structures which may be considered as two-polaron biradicals (polaron pairs).

The oxidation of several 2-diphenylamino-substituted thiophenes and N,N'-bis(2-diphenylamino-5-thienyl)-substituted phenylene-1,4-diamines with different substitution patterns in the 5-position of their thiophene moieties was studied by ccyclovoltammetric and spectroelectrochemical measurements (ESR, UV/Vis/NIR). These measurements revealed both the structure of the oxidation products obtained and that of their cationic intermediates, as well as the pathway of their formation and follow-up reactions. Thus, the formation of the radical cations in the first electrochemical oxidation step of the target molecules was demonstrated. Depending on the substitution pattern, these radical cations give rise to several consecutive processes to a different extent. Thus radical dimers, dehydrodimers with a 2,2-bithiophene, 3,3'-bithiophene, or benzidine structure, as well as radical monocationic and dicationic products can be formed. For N,N'-bis(2-diphenylamino-5-thienyl)-substituted phenylene-1,4-diamines rather stable radical cations and dications were primarily formed and unambiguously identified. These species were transformed into 2,2'-bithiophene dimers and oligomers when the 5-position of the thiophene moiety was unsubstituted. By in situ spectroelectro-chemistry the influence of the substituents on the type of coupling reactions can be demonstrated and followed in detail.

The adsorption of four beta-dicarbonyl derivatives on highly oriented pyrolytic graphite(HOPG) surface was studied by scanning tunneling microscopy (STM) in an ambient environment. All the molecules include pi-conjugated part and alkyl chains in their chemical structures. The molecules were dissolved in toluene and a drop of the solution was deposited on HOPG to form self-assembled adlayer. The characteristic stripe-like structure in the self-assembled monolayer (SAM) on the high-resolution STM images of the compounds was observed. Different molecular structures led to different SAMs. It was found that noncovalent interactions such as hydrogen bonds and dipole-dipole interactions played an important role in the formation of different SAMs.

The effect of the molecular structure on the self-assembly of specially designed two-core 1,3,2-dioxaborines has been studied with various techniques. It was found that the molecules spontaneously adsorbed on HOPG surfaces and self-organized into well-ordered two-dimensional (2D) monolayers. The structural details of the 2D assemblies were investigated by scanning tunneling microscopy (STM). From X-ray analysis of the corresponding three-dimensional (3D) crystal and from theoretical calculation, we were able to reveal the driving force behind the specific self-assembly. The C-H...F hydrogen bonding between the ortho carbon of the phenyl ring and the fluorine of the BF2 group plays an important role in the formation of the adlayers. The different electron affinities and geometries of the molecules affect the intermolecular interactions which further lead to different properties in the bulk materials.

Novel air-stable n-type organic field-effect transistors based on 4,4′-bis[(6,6′-diphenyl)-2,2-difluoro-1,3,2-dioxaborine] (DOB) have been fabricated. The devices exhibit a filed-effect mobility of 1 × 10−4 cm2 V−1 s−1, an on/off ratio of 104 and a threshold voltage of 8.6 V at room temperature under ambient conditions. Moreover, ambipolar organic field-effect transistors based on DOB and copper phthalocyanine (CuPc) have been fabricated. Two device structures were adopted to investigate their transport properties. When devices were constructed with DOB as the first layer and CuPc as the second layer, they showed typical ambipolar transport properties. However, when the two layers were exchanged, the devices only showed p-channel transport properties. It is probable that CuPc, a bad electron transport material, blocks the electron transport to the DOB layer, leading to the disappearance of electron enhancement.

Lick into shape: Molecular adlayer symmetry can be transformed from lamellar to hexagonal through a thermal-annealing process which causes a trans-to-cis isomerization of the molecules within the adlayer. Different temperatures resulted in the formation of pure trans- and cis-isomer adlayers on the surface.

ESR spectroelectrochemical measurements of 2-diphenylamino-substituted oligothiophenes 8(m) proved the existence of radical cations 8(m)(+.) upon oxidation. Their stability and dimerization depend significantly on the number m of thiophene units. The radical cations 8(1)(+.) and 8(2)(+.) are very reactive and dimerize spontaneously to yield either 2,5-bis(diphenylamino)-2,2'-bithiophene 102 or 2,5-bis(diphenylamino)-5,5'-bis(2-thienyl)-3,3'-bithiopene 11(2), respectively. In contrast, the radical cations 8(3)(+.)-8(5)(+.) are highly stable and do not dimerize at all. (c) 2006 Elsevier Ltd. All rights reserved.

[reaction: see text] A series of new 2-amino-5-thienyl-substituted multicharged methinium compounds have been prepared and characterized spectroscopically and electrochemically by reaction of lithiated species of N,N-disubstituted 2-aminothiophenes with alkyl derivatives of di- and tricarbonic acids and subsequent addition of perchloric acid.

The reaction of 5,5'-dibromo-2,2'-bithiophene with diarylamines in the presence of palladium acetate/tris-(t-butyl)phosphine as catalyst or by a titanium tetrachloride mediated oxidation of 2-(N,N-diarylamino)thiophenes has yielded a series of new N,N'-perarylated 5,5-diamino-2,2'-hithiophenes. These are electron-rich compounds with a low oxidation potential and have a high tendency to form amorphous glasses.

[reaction: see text] A series of alpha,alpha'-bisdiarylamino-capped oligothiophenes C(n) were prepared by the palladium-catalyzed reaction of the dibromo compounds A(i) with diarylamines, N,N-diarylamino-substituted thiophenes or 2,2'-bithiophenes BX(j). These easily oxidizable compounds exhibit a high tendency to form amorphous glasses and characteristic electrochemical and spectroscopic properties that depend significantly on the number of their thiophene moieties.