Abstract:
Dielectric layers comprising a silicon oxide and having essentially constant thickness across a wafer are produced by a plasma-deposition method; in preferred processing, a wafer is supported on a surface which extends significantly past the edge of the wafer. Resulting layers may be further processed by localized etching of windows or vias, uniform layer thickness being particularly beneficial, when timed etching is used, to ensure uniformity of etched openings.

Description:
This application is a continuation of application Ser. No. 07/401,369, filed on Aug. 31, 1989, now abandoned. 
    
    
     TECHNICAL FIELD 
     The invention is concerned with the deposition of dielectric films or layers on semiconductor wafers in the manufacture of integrated-circuit semiconductor devices. 
     BACKGROUND OF THE INVENTION 
     In the manufacture of integrated-circuit semiconductor devices a number of different material layers are sequentially formed and processed on a substrate which typically takes the form of a wafer several inches in diameter. Among layer materials are conductor, semiconductor, and dielectric materials, and prominent among the latter are materials comprising a silicon oxide such as, e.g., silicon dioxide or a borosilicate, phosphosilicate, or borophosphosilicate glass. Such dielectric layers may be included, e.g., as passivating layers, as electrically insulating layers between conductor layers, or as cap layers on doped semiconductor layers, included to limit dopant migration in the course of layer processing. 
     Highly efficient, for forming silicon oxide layers, is a plasma deposition method in which tetraethylorthosilicate (TEOS, tetraethoxysilane) is used as a reactant with oxygen. This method involves placing a semiconductor wafer on a supporting stage in plasma-deposition apparatus, producing a gas flow including TEOS and oxygen, and applying a suitable radio-frequency voltage between electrodes to both sides of the wafer. Conveniently, the supporting stage also serves as an electrode, with a perforated gas-inlet plate further serving as a facing electrode. 
     Among desiderata with respect to deposited dielectric layers are high density and uniformity of composition, as well as uniformity of thickness. The latter is of particular importance where, for the sake of establishing electrical connections through windows or vias, timed etching will be used to form localized openings across the thickness of a deposited layer. 
     SUMMARY OF THE INVENTION 
     Dielectric layers comprising a silicon oxide and having essentially constant thickness across a wafer are produced by a plasma-deposition method; in preferred processing, a wafer is supported on a surface which extends significantly past the edge of the wafer. Resulting layers may be further processed by localized etching of windows or vias, uniform layer thickness being particularly beneficial, when timed etching is used, to ensure uniformity of etched openings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a schematic cross-sectional view of a portion of plasma deposition apparatus being used in prior-art processing; and 
     FIG. 2 is a schematic cross-sectional view of a portion of exemplary plasma deposition apparatus being used in preferred processing in accordance with the invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 and 2 show support holder 11, wafer support 12 comprising a ceramic portion 121 and an anodized aluminum portion 122 serving as process groundplane, supported silicon wafer 13, deposition plasma 14, gas-inlet plate 15, reagent-gas stream 16, and radio-frequency power source 16. Radiative heat 17 is supplied to the deposition surface of wafer 13 via wafer support 12. Support 12 is essentially circular as viewed in the direction of gas flow; such support may also be termed &#34;susceptor&#34; (suspecting radiative heat 17 as typically provided from below). Among additional features of plasma-deposition apparatus are an hermetic enclosure, and loading, evacuation, and heating means--the latter typically in the form of heat lamps. 
     The preferred arrangement shown in FIG. 2 differs from the prior-art arrangement of FIG. 1 in that the wafer-supporting member has a diameter which is significantly larger than the diameter of the wafer. Preferably, for standard wafers having a diameter in the range from 4 to 8 inches, support diameter exceeds wafer diameter by at least 0.5 inch, and preferably by at least 1 inch. On the other hand, since very much larger diameters do not lead to further significant enhancement of uniformity of layer thickness, and in the interest of minimizing the amount of unproductive deposits on the susceptor, support diameter preferably does not exceed wafer diameter by more than 2 inches. Accordingly, since a wafer is placed essentially centered for plasma-deposition processing, a preferred wafer support extends from 0.25 to 1 inch beyond the edge of thewafer. 
     Dielectric layers of interest in connection with the invention comprise a silicon oxide, SiO x , 0&lt;×&lt;2, in a preferred amount of at least 50 molecular percent. More specifically with respect to reagent gases usedfor deposition, such gases may comprise TEOS and oxygen, as well as, optionally, precursor gases for the inclusion of further layer constituents such as, e.g., boron and/or phosphorus as may be desired in the deposition of glassy layers. For example, for boron, trimethyl borate (TMB) may be used, and trimethyl phosphite (TMP) for phosphorus. Furthermore, the use of silicon-oxide precursors other than TEOS is not precluded; among candidates suitable in this respect are diacetoxyditeriarybutoxysilane (DADBS), diacetoxydiisopropoxysilane (DADIS), and tritertiarybutoxyethoxysilane (TBES). 
     A key benefit of the invention, namely more uniform layer thickness as compared with prior-art processing, may be attributed to one or several factors, including more even temperature distribution across a wafer on account of extended susceptor mass beyond the wafer edge, and attendant reduced wafer-edge heat loss. Also, preferred larger-diameter support may lead to a more uniform, less turbulent flow pattern radially across the wafer, to increased gas residence time, and to a somewhat extended plasma region, resulting in more uniform deposition conditions across a wafer. 
     As a result of uniformity of layer thickness, layers produced in accordancewith the invention are preferred especially where subsequent processing involves timed etching across the thickness of a layer as, e.g., in the formation of electrical contact windows or vias. (As well-understood in the art, such etching is in the presence of a photolithographically patterned mask layer on the dielectric layer.) More generally, wherever subsequent processing benefits from surface uniformity and flatness, the invention reduces or eliminates the need for a planarization step. 
     The preferred method is considered relatively insensitive to changes in thediameter of the reagent flow as determined primarily by the size of the gas-inlet element, and preferred use of a larger susceptor does not necessitate replacement of such element. Indeed, particularly preferred use of a larger-diameter susceptor in combination with a standard gas-inlet (&#34;shower head&#34;) permits essentially unchanged use, as compared with prior-art processing, of other processing-parameter settings, thus permitting realization of preferred, more uniform layer thickness without extensive process modification and recalibration. 
     EXAMPLE 
     On separate 5-inch substrates, layers of silicon oxide were deposited over patterned layers of &#34;metal 1&#34;--by prior-art processing and by exemplary processing in accordance with the invention. Prior-art processing involveduse of commercially available plasma deposition apparatus made by Applied Materials company and known as AMI-5000, comprising an arrangement as schematically depicted in FIG. 1. The reagent flow consisted essentially of TEOS entrained with helium as a carrier gas, together with oxygen. A Prometrix device was used to measure layer thickness across the wafer, anda 1 sigma variation of approximately 2.5 percent was found between a minimum at the center of the wafer, and a maximum which was found to be ata radial distance of approximately 2 inches from the center of the wafer. After replacement of the original 5-inch susceptor with a 6-inch susceptor(namely a part designated as &#34;susceptor, nitride, 125 mm&#34;, Part No. 0010-09134), but without changing any other deposition parameters such as,e.g., flow composition, flow rate, flow diameter, chamber pressure, susceptor temperature, RF-power, and duration of the deposition operation,a silicon oxide layer was obtained with 1 sigma variation not exceeding approximately 0.5 percent across the wafer.