Yield Issues

As discussed previously, CMP is an enabling technology which allows the use of advanced lithography in the sub-0.5 pm 

One of the most important results of Roy et al. is the need to keep the wafer surface wet through all clean steps. If the slurry abrasive is allowed to dry on the wafer surface, a chemical bond apparently forms between the particle and the surface. Once this bond forms, removal of the particle from the surface is virtually impossible. Therefore, the wafer should be sprayed with DI water immediately upon removal from the polishing pad and transported quickly between soluions of the clean sequence to ensure that the wafer remains wet. 

Roy et al. also investigated the use of dilute HF in the clean sequence. Because the solubility of monosilicic acid (Si(OH)4) de- 

Stability of colloidal silica as a function of solution pH. (From Ref. (15).) 

Selection of a pad material must include considerations of scratch density as well as the planarization and conditioning considerations mentioned earlier. Scratching due to the slurry particles is a result of poorly controlled particle size distributions. If agglomeration of the slurry particles occurs during use or storage, the larger slurry particles will result in increased scratching. 

---

Recombinant DNA can be used to overcome a variety of potential problems in the industrial enzyme sector. A schematic outline of the types of problems encountered and the solutions by an rDNA program is shown in Figure 1. Basically, these problems can be divided into strict yield issues (making more of a given protein) and quality issues (making the product more useful). Because of the nature of the enzyme business, the highest return to the enzyme producer will usually come from increasing the value of the enzyme to the user. 

The source material will release excess silicon in the beginning of the growth cycle and be more carbon-rich in the end due to preferential depletion of silicon. This is a known problem and it is a matter of detailed control and an understanding of the dynamic transport mechanisms in combination with thermodynamics. Nevertheless, the result is invariably that SiC boules grown by seeded sublimation growth are Si-rich in the beginning and C-rich near the end, which creates yield issues. Simulation of the process is necessary to improve the situation. 

One of the first and die most widely used CMP process, aside from the final step in the preparation of silicon wafers, is oxide CMP for back-end planarization after the initial oxide ILD deposition and between metal levels. As a result, oxide CMP is the most mature process, with the most fundamental studies having been performed in this area. Indeed, much of our understanding of the CMP of metals and other materials is derived from our understanding of oxide CMP. This chapter first presents the current understanding of the oxide CMP fundamentals. The discussion includes the mechanisms of both mato-ial removal and surface planarization. The second part of the chapter is devoted to the practice of oxide CMP, including reported results on planarization and polish rate performance of oxide CMP processes in industry. In addition, process integration, cost of ownership, manufacturability, and yield issues will be discussed. 

A HE FABRICATION OF INTEGRATED CIRCUITS involves a series of steps that defines insulator, conductor, and semiconductor structures in and on single crystals of silicon or gallium arsenide (I). As practiced today, the circuit elements are as small as 1 micrometer (1 xm) in dimension. Reproducible device performance and yield issues require control of both the dimension and placement of these 1-pm structures to tolerances of fractions of 1 xm. The number of such circuit elements per chip has steadily increased during the past three decades, mainly through a decrease in the size of the elements. This reduction in the feature size and the increase in circuit complexity and integration that it allows is largely responsible for the dramatic improvement in the performance and cost-performance ratio that has occurred and is expected to continue to occur. 

In the Maximum Entropy Method (MEM) which proceeds the maximization of the conditional probability P(fl p ) (6) yielding the most probable solution, the probability P(p) introducing the a priory knowledge is issued from so called ergodic situations in many applications for image restoration [1]. That means, that the a priori probabilities of all microscopic configurations p are all the same. It yields to the well known form of the functional 5(/2 ) [9] ... 

In a more favourable case, the wavefiinction ]i might indeed correspond to an eigenfiinction of one of the operators. If = //, then a measurement of A necessarily yields and this is an unambiguous result. Wliat can be said about the measurement of B in this case It has already been said that the eigenfiinctions of two commuting operators are identical, but here the pertinent issue concerns eigenfunctions of two operators that do not conmuite. Suppose / is an eigenfiinction of A. Then, it must be true that... 

The applicability of the two-parameter equation and the constants devised by Brown to electrophilic aromatic substitutions was tested by plotting values of the partial rate factors for a reaction against the appropriate substituent constants. It was maintained that such comparisons yielded satisfactory linear correlations for the results of many electrophilic substitutions, the slopes of the correlations giving the values of the reaction constants. If the existence of linear free energy relationships in electrophilic aromatic substitutions were not in dispute, the above procedure would suffice, and the precision of the correlation would measure the usefulness of the p+cr+ equation. However, a point at issue was whether the effect of a substituent could be represented by a constant, or whether its nature depended on the specific reaction. To investigate the effect of a particular substituent in different reactions, the values for the various reactions of the logarithms of the partial rate factors for the substituent were plotted against the p+ values of the reactions. This procedure should show more readily whether the effect of a substituent depends on the reaction, in which case deviations from a hnear relationship would occur. It was concluded that any variation in substituent effects was random, and not a function of electron demand by the electrophile. ... 

There are ill-defined limits on EI/CI usage, based mostly on these issues of volatility and thermal stability. Sometimes these limits can be extended by preparation of a suitable chemical derivative. For example, polar carboxylic acids generally give either no or only a poor yield of molecular ions, but their conversion into methyl esters affords less polar, more volatile materials that can be examined easily by EL In the absence of an alternative method of ionization, EI/CI can still be used with clever manipulation of chemical derivatization techniques. 

The issues of faciUtating options such as energy storage and transmission may prove to be important to the success of wind energy technology. Cost-effective storage coupled to wind systems would yield capacity credit benefits. In addition, because sites are often isolated, the value of wind energy would benefit from transmission/distribution access. 

---