Semiconductors diffusion barriers

Electrically Functional. Refractory coatings are used in semiconductor devices, capacitors, resistors, magnetic tape, disk memories, superconductors, solar ceUs, and diffusion barriers to impurity contamination from the substrate to the active layer. 

An imponant component of the complex metallizations for both semiconductor devices and magnetic media is the diffusion barrier, which is included to prevent interdiffiision between layers or diffusion from overlyii layers into the substrate. A good example is placement of a TiN barrier under an Al metallization. Figure 7a illustrates the results of an SNMSd high-resolution depth profile measurement of a TiN diffusion barrier inserted between the Al metallization and the Si substrate. The profile clearly exhibits an uneven distribution of Si in the Al metallization and has provided a clear, accurate measurement of the composition of the underlying TiN layer. Both measurements are difficult to accomplish by other means and dem-... 

Many CVD reactions are being investigated for the deposition of carbides and nitrides, particularly for titanium nitride for semiconductor applications, such as diffusion barrier. The following is a summary of the metallo-organic precursors and deposition condition presently used in development or production of these materials. 

Silicon nitride (Si3N4) is a major industrial material which is produced extensively by CVD for electronic and stmctural applications. It is an excellent electrical insulator and diffusion barrier (to sodium and water vapor) and has replaced CVD oxides in many semiconductor... 

Passivation layers, multilayer resist stacks, diffusion barriers, interlevel dielectrics, side-wall spacers, trench masks, oxidation masks, etc., in semiconductor devices. 

CVD titanium nitride (TiN) is the most important interstitial-nitride coating from an application standpoint. It is used extensively to provide wear resistance and as a diffusion barrier and antireflection coating in semiconductor devices. 1 °]... 

Interconnect. Three-dimensional structures require interconnections between the various levels. This is achieved by small, high aspect-ratio holes that provide electrical contact. These holes include the contact fills which connect the semiconductor silicon area of the device to the first-level metal, and the via holes which connect the first level metal to the second and subsequent metal levels (see Fig. 13.1). The interconnect presents a major fabrication challenge since these high-aspect holes, which may be as small as 0.25 im across, must be completely filled with a diffusion barrier material (such as CVD titanium nitride) and a conductor metal such as CVD tungsten. The ability to fill the interconnects is a major factor in selecting a thin-film deposition process. 

CVD is a maj or process in the production of thin films of all three categories of electronic materials semiconductors, conductors, and insulators. In this chapter, the role of CVD in the fabrication of semiconductors is reviewed. The CVD production of insulators, conductors, and diffusion barriers is reviewed in the following chapter. The major semiconductor materials in production or development are silicon, germanium, ni-V and II-VI compounds, silicon carbide, and diamond. 

Copper is intrinsically a better metal than aluminum for the metallization of IC s. Latest developments in MOCVD show that it can be readily deposited without major changes in existing processing equipment. Diffusion problems are minimized and it appears that present barrier materials, such as titanium nitride or titanium-tungsten alloys, should provide adequate diffusion barriers for the copper-silicon couple, certainly up to the highest temperatures presently used in IC s processing (see Ch. 6). The development of CVD copper for semiconductor metallization is on a considerable scale at this time.Clt ]... 

The geometry of modern semiconductor devices is continuously shrinking and will soon reach the 0.20 im bench mark, with great increase in speed and efficiency. To accomplish this goal requires major advances in materials and fabrication processes. Many obstacles remain and one of the most critical is that of solid-state diffusion and the development of diffusion barriers. OPO]... 

A typical semiconductor device (found in the back-end of the line or the interconnects) consists of a layer of glass followed by a sputtered layer of titanium, which is thermally treated to form a titanium silicide. Next, a layer of titanium nitride is deposited on top of the silicide and on the sidewall of the contacts by sputtering or by MOCVD (see Fig. 13.3 in Ch. 13).P ]P ] This layer of TiN acts as a diffusion barrier and an adhesion promoter. It is followed by the main interconnect, which is an aluminum-copper alloy, in turn followed by another layer of TiN, which acts as adhesion and antireflecting layer. 

Two alternative approaches exist. The first one involves significantly lowering the temperature to values where the diffusion of vacancies can be observed with a technique like STM. At lower temperatures a surface vacancy can then be artificially created by ion bombardment or direct removal of an atom by the tip. This approach has been applied successfully to several semiconductor surfaces [29-31]. For metal surfaces, although vacancy creation at a step by direct tip manipulation of the surface has been demonstrated [32], to our knowledge, no studies have been published where the diffusion of artificially created vacancies in a terrace has successfully been measured. The second approach involves the addition of small amounts of appropriate impurities that serve as tracer atoms in the first layer of the surface [20-24]. The presence and passage of a surface vacancy is indirectly revealed by the motion of these embedded atoms. If one seeks to measure both the formation energy and the diffusion barrier of surface vacancies explicitly, a combination of these two approaches is needed. 

Copper is going to replace aluminum as the material of choice for semiconductor interconnects due to its low electrical resistance and high electromigration resistance (1-4). An inlaid interconnect is used for copper metallization in which the insulating dielectric material is deposited first, trenches and vias are formed by patterning and selective dielectric etching, and then diffusion barrier and copper seed layer are deposited into the trenches and vias (5). 

Amorphous Thin Films Currently, thin amorphous films of silicon nitride for applications as masking layers and as diffusion barriers during semiconductor processing are produced by gas-phase reactions of silicon tetrachloride or silane with ammonia, in the presence of hydrogen as carrier gas. Today, the standard GVD process is augmented by complex molecular excitation methods that include PACVD, laser-excited GVD (LECVD) and photosensitized GVD (PHCVD) enhance-... 

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