Planarization Schemes

Planarization rate = polish rate oftiie high features - (2.6) 

However, because the polish rates of the high and low features are functions of step height, the planarization rate decays as the CMP process planarizes. These metrics allow the degree of planarization to be measiu ed, and thus allow a direct comparison of different planarizing schemes. However, each of these sets of metrics, R and 0, SHR, and planarization rate measure a different aspect of the planarizing process, and all are required to sufficiently describe the process. 

A second method of surface smoothing is to deposit a thick layer of SiOj and then a thin the layer by RIE or sputter etching. Because the sputter yield of the SiOj is greatest at an angle of 45°, the corners in the SiOj film etch quicker than the rest of the film and are therefore rounded by the etch process. With some deposition systems, for example, biased electron cyclotron resonance (ECR) plasma deposition, it is possible to deposit and etch concurrently, yielding a one-step process with a reduced deposition rate.  

A second method of local planarization involves spinning photoresist onto the SiOj ILD to obtain local planarity. The resist is then hard baked and etched with an RIE etch tailored to remove SiOz (or ILD) at the same rate as the photoresist. Because the etch rate of the two materials is equal, the planarity of the resist film transfers into the SiOz film. However, a precise match in SiOj and photoresist etch rates is difficult to maintain because the relative ratio of SiOj to photoresist exposed increases as the etch back proceeds. Loading effects then result in a decrease in the Si02 etch rate and increase in the photoresist etch rate. Furthermore, polymer deposits build up on the etch reactor chamber walls over time etching of this polymer depletes the chemicals used to etch the photoresist, which slows the photoresist etch rate. If the etch rates are not matched, the planarity of the photoresist layer will not transfer well to the SiOz. 

Lastly, if the SiOj deposition is highly conformal, the regions between closely spaced metal lines may be filled without the production of gaps. If the film thickness is equal to half the space width, the space will fill completely and the comers of the film will join at the top of the space, thereby leaving a nearly planar film. Examples of CVD SiOj processes capable of the required high degree of conformality are ECR deposition and tetraethyl orthosilicate (TEOS) plasma CVD-enhanced. While this approach yields local planarization above closely spaced lines, the wide spaces between metal lines are not filled, and thus a sharp step is experienced at the edge of such spaces. Therefore, this approach is often coupled with SOG or resist etch-back processes or CMP.  

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The selectivity of glass for alkah metal ions is connected with the presence of oxides of trivalent metals in the glass structure. Zachariasen [450] states that silicate glass has a random cross-linking, where each silicon atom lies in the centre of a tetrahedron formed of oxygen atoms (see planar scheme (6.5.5)). 

By irradiation with visible light (436 nm, 2 h) in an argon matrix at 25 K, 1,2-dithiin was transformed into s-trans-Z-s-fir-2-butenethial 31, which is twisted by ca. 40° away from planarity (Scheme 4) <1996JA4719>. 

Dimeric and higher aggregate lithium amides can generally be classified into the coordination motifs illustrated in Scheme 2.2. The four-membered (LiN)2 ring is ubiquitous in lithium amide chemistry and is observed both in discrete dimeric structures in either planar (Scheme 2.2, A) or non-planar (Scheme 2.2, B) geometries as well as in oligomeric and polymeric (ladder) frameworks (Scheme 2.2, C). Trimeric six-membered (LiN), ring... 

It is of interest to note that the barrier to ring inversion in the 1,8-bridged naphthalene (190) (26.3 kJ moF1) is considerably lower than that for tetrahydropyran. This has been attributed to the fact that only the heteroatom is out of the plane imposed on the system by the naphthalene framework (81JCS(P2)741). The transition state for the inversion process is calculated to be planar (Scheme 29) and the barrier to inversion is considered to arise mainly from bond angle deformation. 

Systems with more than two conjugated double bonds can react by [6 + 2] processes, which in azepines can compete with the [4 + 2] reaction (Scheme 73). Oxepins prefer to react as 4-components, through their oxanorcaradiene isomer, in which the 4-system is nearly planar (Scheme 74). Thiepins behave similarly. Nonaromatic heteronins also react in orbital symmetry-controlled [4 + 2] and [8 + 2] cycloadditions. 

Organosilicon polymers are becoming important in many aspects of device technology. Multilevel metallization schemes require the use of a thin dielectric barrier between successive metal layers (i). Often, these dielectric materials are silicon oxides that are deposited by low-temperature or plasma-enhanced chemical vapor deposition (CVD) techniques. Although conformal in nature, CVD films used as intermetal dielectrics frequently result in defects that arise fi om the high aspect ratios of the metal lines and other device topographies (2). Several planarization schemes have been proposed to alleviate these problems, some of which involve the use of organosilicon polymers (2-4). 

Advanced metallization schemes are required to obtain the performance benefits of scaling device dimensions into the sub-0.5 pm regime. This section discusses the origin of the interconnect delay and impact on IC electrical performance. Methods of reducing interconnect delay will be discussed, including MLM and the use of new metal and ILD materials. As additional metal layers are added, surface planarization requirements increase. This section discusses planarity requirements while subsequent sections discuss planarization schemes, including CMP. 

Triangulo (Bu 2Ge)3 inserts PhNC to give trigermabutanimine (6), and in a similar fashion, the chalcogens sulfur and selenium insert to give the chalcogermetanes (7) and (8), the selenium compound being planar (Scheme 3). ... 

In a detailed study [de Graaf et al/,s], three different planarization schemes were compared, namely, BPSG flow anneal, Spin On Glass (SOG)... 

There is experimental evidence that alkyl radicals are planar, or pyramidal, structures that can become planar through inversion (like ammonia). For example, chlorination of (-l-)-l-chloro-2-methylbutane (10) produced racemic ( )-l,2-dichloro-2-methylbutane (12). The results are most consistent with an intermediate radical 11, which is planar or which has only a small barrier to inversion so that the reaction of 11 can occur equally well from either face of the radical center. The loss of optical activity shows that radical is probably planar (Scheme 4.5). 

Fig. 10.3 Generation of high dynamic pressures with chemical explosives (a) cylindrical scheme, (b) planar direct-contact scheme, (c) planar scheme with explosively accelerated impactor plate. 1 detonator, 2 explosive, 3 ampoule, 4 sample, 5 plane wave generator, 6 layer of inert material, 7 impactor plate...

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