Methods of etching a contact opening over a node location on a semiconductor substrate

A chemical vapor deposition method includes providing a semiconductor substrate within a chemical vapor deposition chamber. At least one liquid deposition precursor is vaporized with a vaporizer to form a flowing vaporized precursor stream. The flowing vaporized precursor stream is initially bypassed from entering the chamber for a first period of time while the substrate is in the deposition chamber. After the first period of time, the flowing vaporized precursor stream is directed to flow into the chamber with the substrate therein under conditions effective to chemical vapor deposit a layer over the substrate. A method of etching a contact opening over a node location on a semiconductor substrate is disclosed.

TECHNICAL FIELD

This invention relates to chemical vapor deposition methods and to methods of etching a contact opening over a node location on a semiconductor substrate.

BACKGROUND OF THE INVENTION

The invention primarily grew out needs for making highly reliable, high density dynamic random access memory (DRAM) contacts, although the invention is in no way so limited. Advanced semiconductor fabrication is employing increasing vertical circuit integration as designers continue to strive for circuit density maximization. Such typically includes multi-level metalization and interconnect schemes.

Electrical interconnect techniques typically require electrical connection between metals or other conductive layers, or regions, which are present at different elevations within the substrate. Such interconnecting is typically conducted, in part, by etching a contact opening through insulating material to the lower elevation of a desired node contact, for example of a conductive layer or conductive region. The significant increase in density of memory cells and vertical integration places very stringent requirements for contact fabrication technology. The increase in circuit density has resulted in narrower and deeper electrical contact openings between layers within the substrate, something commonly referred to as increasing aspect ratio, which is the ratio of maximum opening height to minimum opening width. Increasing aspect ratios make it difficult to complete etches to desired node locations.

For example, one typical contact etch includes the etch to a substrate diffusion region formed within a semiconductive material which is received between a pair of field effect transistor gate lines. The gate lines are typically encapsulated in a silicon nitride and/or undoped silicon dioxide material. A planarized layer of borophosphosilicate glass (BPSG) is typically provided over the field effect transistors and through which a contact opening to the substrate will be etched. Further, a very thin undoped silicon dioxide layer is typically provided intermediate the BPSG layer and the underlying substrate material to shield from diffusion of the boron and phosphorus dopants from the BPSG layer into underlying substrate material. Additionally or alternately, a thin silicon nitride layer might also be provided. An antireflective layer might also be provided over the BPSG. The layers are typically masked, for example with photoresist, and a contact opening is formed through the mask over the underlying layers over the diffusion region to which contact is desired. The antireflective coating is then etched, followed by an etch conducted through the BPSG which is substantially selective to the silicon nitride layer, undoped oxide and underlying silicon substrate such that the etch is typically referred to as a substantially self-aligned contact etch. An example dry anisotropic etching chemistry for the etch includes a combination of CHF3, CF4, CH2F2and Ar. The typical intervening undoped silicon dioxide layer between the underlying substrate and the BPSG will typically also be etched through in spite of a poor etch rate compared to BPSG, principally due to the extreme thinness of this layer. Further, if silicon nitride is used in addition or in place of the undoped silicon dioxide layer, it would typically be separately etched. At the conclusion of the etch or etches, a native oxide might grow, which could be stripped with a dilute HF solution prior to plugging the contact opening with conductive material(s).

When the aspect ratio of the contact opening being etched through the BPSG was sufficiently below 4:1, a single etch chemistry for the BPSG was typically suitable to clear the BPSG and a thin undoped silicon oxide layer all the way to the diffusion region to outwardly expose the same, assuming silicon nitride was not present. However, as the aspect ratio of the contact opening through the BPSG approached and exceeded 4:1, it was discovered in some instances that the subject chemistry, and other attempted chemistries, were not sufficient to enable clearing the doped oxide dielectric material utilizing a single chemistry and a single etching step.

These are the circumstances which motivated the invention, although the results and objectives are in no way to be perceived as claim limitations unless such are specifically provided in the accompanying claims. The invention also has applicability outside of the problems from which it spawned, with the invention only being limited by the accompanying claims as literally worded without writing limitations or interpretations into the claims from the specification or drawings, and as appropriately interpreted in accordance with the doctrine of equivalents.

SUMMARY

The invention comprises chemical vapor deposition methods and methods of etching a contact opening over a node location on a semiconductor substrate. In but one implementation, a chemical vapor deposition method includes providing a semiconductor substrate within a chemical vapor deposition chamber. At least one liquid deposition precursor is vaporized with a vaporizer to form a flowing vaporized precursor stream. The flowing vaporized precursor stream is initially bypassed from entering the chamber for a first period of time while the substrate is in the deposition chamber. After the first period of time, the flowing vaporized precursor stream is directed to flow into the chamber with the substrate therein under conditions effective to chemical vapor deposit a layer over the substrate.

In one implementation, a method of etching a contact opening over a node location on a semiconductor substrate includes forming a dielectric first layer over a node location. An oxide second layer having plural dopants therein is formed over the dielectric first layer. The oxide second layer has an innermost portion and an outer portion. The outer portion has a higher concentration of one of the dopants than any concentration of the one dopant in the innermost portion. Using a single dry etching chemistry, a contact opening is etched into the outer and innermost portions of the oxide second layer to proximate the dielectric first layer over the node location. Etching is conducted into the dielectric first layer through the contact opening to proximate the node location.

In one implementation, a method of etching a contact opening over a node location on a semiconductor substrate includes forming a dielectric first layer over a node location. An oxide second layer having plural dopants therein is formed over the dielectric first layer. The oxide second layer has an innermost portion and an outer portion. The innermost portion has a higher concentration of one of the dopants than any concentration of the one dopant in the outer portion. Using a single dry etching chemistry, a contact opening is etched into the outer and innermost portions of the oxide second layer to proximate the dielectric first layer over the node location. Etching is conducted into the dielectric first layer through the contact opening to proximate the node location.

Other implementations are contemplated.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention comprises a chemical vapor deposition method. The invention also comprises a method of etching a contact opening over a node location on a semiconductor substrate.FIGS. 1-5illustrate but one exemplary semiconductor substrate10for processing in accordance with aspects of the invention. Semiconductor substrate10comprises a bulk monocrystalline silicon substrate12. In the context of this document, the term “semiconductor substrate” or “semiconductive substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.

Substrate12comprises a pair of field effect transistor gate constructions14and16having a diffusion region18formed therebetween in semiconductive material of substrate10/12. In this example, diffusion region18constitutes a node location to which electrical connection is ultimately desired. Various dielectric and conductive layers of constructions14and16are not specifically designated as not being particularly relevant to the invention. In the preferred embodiments, gate constructions14and16include outermost insulative dielectric regions whereby a substantially self aligned contact etch can be made through an overlying insulative layer to region18without exposing conductive material of the gates in the event of some mask misalignment. Exemplary materials are as described above where the overlying layer will be BPSG.

Referring toFIG. 2, a dielectric first layer20is formed over node location18. By way of example only, exemplary materials include silicon nitride, substantially undoped oxide, or combinations thereof. In the context of this document, “substantially undoped” means having essentially no measurable dopants therein, which in this specific example would mean essentially void of either boron or phosphorous. An exemplary preferred deposition thickness for dielectric layer20is from 50 Angstroms to 300 Angstroms. Such is preferably conventionally chemical vapor deposited in equipment which provides adequate conformality. Exemplary equipment includes an ASM A4000 Furnace, available from ASM International N.V. of The Netherlands.

Semiconductor substrate10is provided within a chemical vapor deposition chamber for formation of a first dielectric layer22(FIG.3).FIG. 7diagrammatically illustrates but one exemplary processing schematic usable for processing a semiconductor substrate in accordance with methodical aspects of the invention. Such comprises an exemplary chemical vapor deposition chamber60within which semiconductor substrate10would be received.FIG. 7equipment comprises first, second and third liquid vaporizers61,62and63, which are also designated V1, V2and V3, respectively. Such vaporizers might constitute any existing or yet-to-be developed vaporizers for liquid chemical vapor deposition precursors. Examples include bubblers, liquid flow controllers and other devices which result in vaporization of liquid material for flowing vapor to a chemical vapor deposition reactor. In the illustrated and preferred embodiment, chamber60is preferably a subatmospheric chemical vapor deposition reactor, and preferably not a plasma enhanced chemical vapor deposition reactor. The invention was reduced-to-practice using liquid flow controllers as the vaporizers and a Centura 5200 reactor available from Applied Materials of Santa Clara, Calif. Vaporizers61,62and63include liquid precursor inlets64,65and66, respectively. Such vaporizers also include exiting vapor flowpaths67,68and69, respectively. Exiting streams67,68and69join to form a combined flowpath70. Flowpath70branches into a path72which is directed to chamber60and a path74, which by-passes chamber60. A control valve76is associated with lines70,72, and74. Such controls the flow of vaporized precursors to the chamber and for bypassing the chamber. An additional exemplary vapor input line for chamber60is designated with numeral80. An exit line82extends from chamber60and joins with bypass line74, forming an exhaust line84. Pressure, temperature and other control devices are not shown, as such are not particularly material to the invention disclosed herein.

The description proceeds with that of only an exemplary preferred embodiment of depositing a doped oxide layer over substrate10. In this but one exemplary preferred embodiment, the outermost layer of the preferred dielectric mass being deposited will comprise borophosphosilicate glass. Thereby, feed stream64feeds a first liquid deposition precursor, for example tetraethylorthosilicate (TEOS). Line65feeds an exemplary second liquid deposition precursor of triethylphosphate. The phosphorous in such material constitutes an exemplary first dopant to at some point be provided in the dielectric mass being formed. Line66feeds an exemplary third liquid deposition precursor of triethylborate. The boron in such precursor constitutes an exemplary second precursor different from the first for provision at some point within the dielectric mass being fabricated. In this example, line80constitutes an exemplary input line for a fourth vapor precursor, here in this preferred embodiment to include one or a combination of O2and O3.

In a specific and preferred embodiment, the liquid precursor flowing in stream64to vaporizer V1is vaporized to form a flowing vaporized precursor within stream67and stream70. Valve76is preferably initially totally closed to line72and is preferably initially totally opened to line74. Thereby, the flowing vaporized precursor in stream70is initially bypassed from entering chamber60and allowed to flow out exhaust stream84for some first period of time while substrate10is within deposition chamber60. A preferred reason for initially bypassing flow of the precursor to chamber60is that the flow of the flowing precursor from the vaporizer is typically not initially at a desired steady state. Preferably, the period of time is selected to be effective to achieve steady state flow of the vaporized precursor at the conclusion of the period. Accordingly, in the typical embodiment, flow of the vaporized precursor during the first period of time is not steady state during all of such first period.

In conjunction with the above flowing first vaporized precursor, the second liquid deposition precursor flowing in line65is preferably caused to be vaporized by vaporizer V2to form a flowing second vaporized precursor, in this example comprising the phosphorous dopant, within line68and thereby also within combined flowpath70with the flowing first vaporized precursor from line67. The flowing first and second vaporized precursors are thereby initially bypassed within combined flowpath70from entering chamber60for a period of time while substrate10is within deposition chamber60. The preferred desire and effect is to achieve steady state flow at the desired deposition conditions of the first and second precursors within line70prior to flowing the same to deposition chamber60. The period of time to achieve stabilization is typically less than 10 seconds. Preferably after achieving a steady state flow, the first and second vaporized precursors are directed within combined flowpath70to flow into chamber60with the substrate therein under conditions effective to chemical vapor deposit first dielectric layer22(FIG. 3) comprising the first dopant, in this example phosphorous, over substrate10. Such can be accomplished by reversing the opened/closed relationship of lines72/74with valve76.

Such conditions in the illustrated preferred example also include suitable flow of an oxygen/ozone mixture through line80into chamber60. By way of example only, preferred flow rates from line64to vaporizer V1include a TEOS flow at 600 mg/min and a flow within line80of 12% O3/88% O2by weight at 3 standard liters/min. Such is considered in the context of a single wafer chamber60having a volume of approximately 6 liters. An exemplary pressure during deposition within chamber60is 200 Torr, with the wafer chuck temperature within chamber60preferably being maintained at about 530° C. An exemplary period of time to achieve steady state flow prior to directing the first vaporized precursor to the chamber is 10 seconds or less. A specific exemplary flow for triethylphosphate within line65is at 100 mg/min. A preferred result is to achieve approximately 4% to 12% phosphorous doping within layer22. An exemplary preferred thickness for layer22is from about 50 Angstroms to about 500 Angstroms, with from about 100 Angstroms to about 300 Angstroms being preferred, and from about 200 Angstroms to 275 Angstroms being even more preferred.

At the conclusion of such processing, preferably any flow of ozone within line80is ceased, and a pure oxygen or inert gas caused to flow therethrough. Further preferably, valve76is preferably totally closed to line72and valve76is preferably totally opened to line74, once again causing flowing vaporized precursor from lines67and68into line70, into line74and out exhaust line84.

In this embodiment, layer22is preferably as shown and described directly deposited on underlying dielectric layer20. In this just described embodiment, no vaporized precursor flows from vaporizer V3to chamber60during deposition of layer22. Further, no other source of the second dopant is provided to chamber60in the depicted preferred example. Further, the concentration of the second dopant (in this example, boron) in first dielectric layer22is thereby substantially zero (meaning below detectable levels) at least at this point in the preferred embodiment process. Alternately, some third vaporized precursor might be caused to flow to chamber60during the first dielectric depositing, with the concentration of the second dopant in first dielectric layer22at this point in the process being at some desired measurable level. Typical prior art BPSG layers comprise from 2%-5% boron and from 4%-12% phosphorous, with the remainder constituting SiO2(by weight). In this particular example, where borophosphosilicate glass is being formed either inFIG. 3or ultimately, the preferred concentration of boron within layer22is from 0%-4%. The preferred concentration of phosphorus within layer22is from 6% to 24%. Time for deposition of layer22will typically be from 2-4 seconds.

Preferably essentially simultaneously with the conclusion of layer22formation, the flowing first and second vaporized precursors within combined flowpath70are bypassed from entering chamber60while substrate10is therewithin. Such preferably occurs by switching valve76completely closed to line72and completely opened to line74, all while continuing operation of vaporizers V1and V2. Preferably essentially simultaneously therewith, a third deposition precursor, in this example in the form of triethylborate, flowing in line66is vaporized in vaporizer V3forming a flowing third vaporized precursor comprising a second dopant (here, boron), different from the first dopant, in line69. The flowing third vaporized precursor in line69is combined with the flowing bypassed first and second vaporized precursors in combined flowpath70, with the combined flowing first, second and third vaporized precursors therewithin being bypassed to exhaust84and thereby prevented from entering chamber60for a period of time while substrate10is within chamber60. As with the above-described processing, such period of time is preferably suitable to achieve steady state flow of the combined precursors, and will typically be less than 10 seconds. During the time where deposition does not occur within chamber60, the flow of gasses from line80is preferably again changed to be pure O2or an inert gas. In the preferred described embodiment, flows are preferably as described above, with an exemplary flow of the triethylborate in line66being at 100 mg/min.

Preferably after the steady state has been achieved, the combined flowing first, second and third vaporized precursors within combined flowpath70are directed to flow into chamber60with substrate10therein under conditions effective to chemical vapor deposit a second dielectric layer24(FIG. 4) comprising the first and second dopants over first dielectric layer22, and preferably directly thereon as shown. Second dielectric layer24preferably comprises a greater concentration of the second dopant (here boron) than any concentration of the second dopant in first dielectric layer22. Further preferably, first dielectric layer22preferably comprises a greater concentration of the first dopant (here phosphorus) than any concentration of the first dopant in second dielectric layer24. A preferred thickness for layer24is from 3,000 Angstroms to 15,000 Angstroms, with approximately 10,000 Angstroms being a specific preferred example. In the described example, an exemplary preferred concentration of boron and phosphorous within layer24is 3.8% and 7.6% by weight, respectively.

The illustratedFIG. 4construction can also be considered as constituting an oxide second layer25having plural dopants therein, and which is formed over a dielectric first layer20. Oxide second layer25has an innermost portion22and an outer portion24, with the outer portion having a higher concentration of one of the dopants than any concentration of the one dopant in innermost portion22. Additional portions or layers with respect to oxide layer25might also be provided. Further as outlined above, innermost portion22might be fabricated to contain no measurable quantity of the one dopant (here, boron), which is preferred, or alternately be formed to contain some measurable quantity of the one dopant, which is not as preferred. Further, innermost portion22might also be fabricated to contain no measurable quantity of any dopant.

TheFIG. 4construction can also be considered as innermost portion22having a higher concentration of one of the dopants than any concentration of the one dopant in outer portion24. Further, outer portion24might be fabricated to contain no measurable quantity of the one dopant (here, phosphorus) or alternately and preferred be formed to contain some measurable quantity of the one dopant.

Referring toFIG. 5, substrate10has been removed from chamber60, has been planarized, and an antireflective coating27has been deposited. An exemplary material for layer27is a 400 Angstrom thick silicon rich oxynitride film, for example 54% silicon, 36% oxygen and 10% nitrogen.

Referring toFIG. 6, masking has preferably been conducted over layers25and27, preferably using photolithography and photoresist. An opening is then etched through layer27to expose layer25. An exemplary etch chemistry for the above silicon rich oxynitride coating is 80 sccm CF4, 160 sccm Ar, and 20 sccm O2at 40 mTorr and 1400 Watts. Such is typically fairly non-selective, and preferably also acts as a descum to remove any residual photoresist at the base of the contact hole therein (not shown). Then using a single dry etching chemistry, a contact opening30is etched into outer portion24and innermost portion22to proximate dielectric layer20over node location18. Reduction of boron content within the innermost portion of a BPSG layer, particularly when etching high aspect ratios of at least 4.0 through layer25, has been determined to facilitate achieving adequate removal in etching the exemplary contact opening, preferably at least all the way to dielectric layer20, and depending on the composition of layer20all the way to region18. Further, increase in phosphorus content within the innermost portion of a BPSG layer, particularly when etching high aspect ratios, has been determined to facilitate achieving adequate removal in etching the exemplary contact opening. Preferred is a combination of more phosphorus in the innermost portion as compared to the outer portion, and less boron in the innermost portion as compared to the outer portion. An exemplary preferred chemistry is the CHF3, CF4, CH2F2and Ar chemistry described above in a magnetically enhanced reactive ion plasma reactor.

When layer20comprises nitride or some other material which is not sufficiently etched by the single etching chemistry for layer25, layer20can be suitably dry or wet etched to effectively outwardly expose node location18.