Semiconductor devices with conductive lines that are laterally offset relative to corresponding contacts

A method of electrically linking the contacts of a semiconductor device to their corresponding digit lines. The method includes disposing a quantity of mask material into a trench through which the contact is exposed. The mask also abuts a connect region of a conductive element of a corresponding digit line and, therefore, protrudes somewhat over a surface of the semiconductor device. A layer of insulative material is disposed over the semiconductor device with the mask material being exposed therethrough. The mask material is then removed, leaving open cavities that include the trench and a strap region continuous with the trench and with a connect region of the corresponding digit line. Conductive material is disposed within the cavity and electrically isolated from conductive material disposed in adjacent cavities, which define conductive plugs or studs and conductive straps from the conductive material. These plugs or studs and straps provide an electrically conductive link between each contact of the semiconductor device and its corresponding digit line. Semiconductor devices that include features that have been fabricated in accordance with the method of the present invention are also within the scope of the present invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods of fabricating buried digit lines. Particularly, the present invention relates to a method of fabricating digit lines that are substantially free of stringers. More particularly, the present invention relates to a method of removing stringers from between the straps, plugs and digit lines of semiconductor devices that include digit lines having widths of less than about 0.25 microns. The present invention also relates to semiconductor devices including buried digit lines that are substantially free of stringers and that have widths of less than about 0.25 microns.

2. Background of Related Art

Conventional semiconductor memory devices typically include an array of memory cells, each of which is in communication with a word line and a digit line. Due to the demand for semiconductor devices of ever-increasing density and ever-decreasing size, the semiconductor industry has sought ways to fabricate smaller, more compactly organized features. Thus, in semiconductor memory devices, the sizes of various features, as well as the spacing therebetween, have decreased. For example, the width of state of the art digit lines has decreased to about 0.25 microns or less. The spacing between adjacent digit lines has similarly decreased to about 0.30 microns or less.

Conventionally, photomask techniques, which typically employ visible to near infrared wavelengths of light, have been used to fabricate the digit lines of semiconductor memory devices. The sizes of features of such photomasks are, however, limited by the wavelengths of electromagnetic radiation employed to define these photomasks. As a result, the sizes and spacing of features defined either directly or indirectly by such photomasks are similarly limited.

Semiconductor memory devices that include digit lines having widths of less than about 0.25 microns and pitches of less than about 0.55 microns have been developed. The semiconductor memory devices, however, are relatively inefficient when compared with semiconductor memory devices having wider digit lines and pitches. The inefficiency of these more compact semiconductor memory devices is due, at least in part, to the potential for electrical shorts between adjacent digit lines. Electrical shorts in semiconductor memory devices with densely packed features may be caused by so-called “stringers” that remain following the definition of digit lines or other electrically conductive components, such as the plugs or straps that may be employed to link a contact to its corresponding digit line. The stringers may extend between adjacent structures or from a first structure to a location undesirably close to an adjacent, second structure. Thus, stringers may create an undesirable electrical path between adjacent digit lines.

Since semiconductor memory devices that include digit lines having widths of about 0.25 microns or less and digit line pitches of about 0.55 microns or less may include stringers that would likely cause electrical shorts between adjacent conductive structures, a significant percentage of the semiconductor memory devices will fail quality control testing. Consequently, fabrication costs are undesirably significantly increased.

Accordingly, there is a need for a method by which semiconductor memory devices that include digit lines with widths of less than about 0.25 microns and digit line pitches of less than about 0.55 microns may be more efficiently fabricated. There is a further need for a method of fabricating semiconductor memory devices of increased feature density which employs conventional techniques and equipment.

BRIEF SUMMARY OF THE INVENTION

The present invention includes a method of fabricating semiconductor memory devices that include digit lines having widths of less than about 0.25 microns and, more particularly, to a method of fabricating semiconductor memory devices having digit lines that are, at most, about 0.18 microns wide. Through use of the method of the present invention, a semiconductor memory device may include digit lines that are spaced less than about 0.30 microns apart and, more preferably, at most about 0.22 microns apart. Thus, semiconductor memory devices fabricated in accordance with the method of the present invention may have a digit line pitch of less than about 0.55 microns and, more preferably, a digit line pitch of at most about 0.40 microns. The present invention also includes semiconductor memory devices fabricated in accordance with the method of the present invention.

In accordance with the method of the present invention, a bit contact region of a semiconductor memory device, which is disposed between adjacent word lines of the semiconductor memory device, may be doped as known in the art to define a bit contact. If a bit contact was not formed prior to the fabrication of structures on the substrate, the bit contact region may be exposed by known processes, such as mask and etch techniques, and the bit contact region doped, as known in the art. Alternatively, the exposed bit contact region may be doped following definition of the digit lines. As the conductive elements of the word lines between which the bit contacts are disposed may be exposed during exposure of the bit contact regions of the semiconductor memory device, a layer of insulative material, such as silicon oxide, may be disposed over the semiconductor memory device and adjacent the exposed conductive elements of the word lines. The layer of insulative material may be patterned to fabricate sidewall spacers that electrically isolate the conductive elements of the word lines from the trench within which the bit contact is disposed.

A layer of silicon nitride may be disposed over the semiconductor memory device, including over the bit contacts thereof, by known techniques. Such a layer of silicon nitride may be subsequently employed as an etch stop layer.

Layers of digit line material, such as polysilicon and tungsten silicide (“WSix”), may be fabricated or otherwise disposed over the layer of silicon nitride by known processes. A layer of insulative material may be disposed over the layer of tungsten silicide. A mask, such as a photomask, including a plurality of mutually parallel elongate apertures therethrough, may be defined over the semiconductor memory device. The elongate apertures of the mask are preferably aligned over rows of bit contacts and substantially perpendicular to the underlying word lines of the semiconductor memory device. Preferably, the apertures of the mask have a width that facilitates the definition of digit lines that are spaced less than about 0.30 microns apart and, more preferably, that facilitates the definition of digit lines that are spaced at most about 0.22 microns apart from one another. The distance between adjacent apertures of the mask preferably facilitates the definition of digit lines having a width of less than about 0.25 microns from the digit line material and, more preferably, facilitates the definition of digit lines that have a width of at most about 0.18 microns.

Digit lines may be defined through the mask by known etching processes. The etchants employed to define the digit lines may be selected based on their ability to remove the digit line material or materials. If a layer of insulative material was disposed over one of the layers of digit line material, a first etchant is preferably selected to etch the insulative material. Preferably, an etchant that will remove the silicon nitride etch stop layer is also employed to expose the bit contact regions. Preferably, isotropic wet etch processes are employed to facilitate the removal of electrically conductive stringers from between adjacent digit lines. As the digit lines are defined, digit line materials are removed from above the bit contact regions. If the use of a photomask is desired, two masks may be employed in these patterning processes so as to prevent distortion of the photomasks. A first mask could be employed to define the digit lines and cover the peripheries of the dice. A second mask could be employed to protect the digit lines and to remove any insulative material, digit line material or materials, and silicon nitride from the peripheries of the dice.

One or more layers of insulative material, such as silicon oxide, may be disposed or grown over the digit lines. If the layer or layers of insulative material are deposited onto the semiconductor memory device, such as by tetraethylorthosilicate (“TEOS”) deposition techniques, another mask may be employed to define sidewall spacers adjacent the sides of each of the digit lines. Of course, the mask would be employed in combination with an etchant known to etch the insulative material in order to define the sidewall spacers therefrom. As the layer of insulative material may also cover bit contacts and any adjacent exposed conductive traces of word lines, sidewall spacers for the word lines may also be defined from the layer of insulative material. These sidewall spacers will serve to insulate the word lines from a stud or plug of conductive material to be disposed between the bit contacts and their corresponding digit lines.

Another mask may be employed to shield the bit contacts and the strap regions of the semiconductor memory device, which are disposed between the trenches within which the bit contacts are located and the digit lines that correspond to each of the bit contacts. This mask preferably abuts an exposed portion of a conductive element of a corresponding digit line. As the mask extends across the strap regions of the semiconductor memory device, the mask may protrude from the trenches and, therefore, from a surface of the semiconductor memory device. Preferably, a photomask is employed. Photoresist may be disposed over the surface of the semiconductor memory device and selected regions thereof exposed and developed to define a photomask. Due to the small dimensions of features such as the digit lines of the semiconductor memory device, and due to small dimensional tolerances, proper alignment of the mask is critical to the operability of the semiconductor memory device. Preferably, the photomask is hard-baked so as to facilitate the fabrication of features of desired shapes and dimensions.

A layer of insulative material may be disposed over the surface of the semiconductor memory device, including over regions of the semiconductor memory device that are covered by the photomask. Preferably, this layer of insulative material comprises silicon oxide. Thus, the layer of insulative material may be deposited onto the surface of the semiconductor device by known processes, such as by tetraethylorthosilicate (“TEOS”) wet dip or other TEOS deposition processes. Preferably, the photomask is exposed through the layer of insulative material. If a TEOS wet dip is employed, the surface of the TEOS layer is preferably substantially planar and disposed in a thickness so that the photomask may be exposed through the TEOS layer. Alternatively, regions of a TEOS layer that overlie the photomask may be removed therefrom by known techniques, such as planarization (e.g., chemical-mechanical planarization or chemical-mechanical polishing (“CMP”)) techniques or mask and etch processes. As another alternative, the TEOS deposition process disclosed in U.S. Pat. No. 5,354,715, which issued to Wang et al. on Oct. 11, 1994, the disclosure of which is hereby incorporated in its entirety by this reference, may be employed to fabricate a layer of insulative material through which the photomask may be exposed.

The photomask may then be removed by known techniques. The semiconductor memory device may also be masked or otherwise cleaned.

Another layer of electrically conductive material, such as polysilicon, may be disposed over the semiconductor memory device and within at least the strap regions thereof in contact with at least the bit contacts thereof. A blanket isotropic etch-back of a type known in the art may be employed to reduce the height of the layer of conductive material—preferably to about or just below the height of the digit lines. As electrically conductive studs and straps, which establish electrical communication between the bit contacts and their corresponding digit lines, are to be defined from this layer of electrically conductive material, another mask may be disposed over the semiconductor memory device to facilitate the substantial removal of any remaining conductive material or features from between adjacent conductive structures that are to be isolated from one another, as well as the definition of these features from the electrically conductive layer. Accordingly, the mask preferably shields quantities of electrically conductive material disposed over the bit contacts, which quantities of electrically conductive material are referred to herein as studs or plugs, as well as regions of the electrically conductive material within the strap regions. All other regions of the semiconductor memory device and, thus, the layer of electrically conductive material may be exposed through the mask. Electrically conductive material may be removed through the mask, as known in the art, such as by the use of etchants. Preferably, the electrically conductive material exposed through these apertures is first etched with an anisotropic etchant, then with an isotropic etchant. The anisotropic etchant facilitates the definition of studs and straps of desired dimensions and removes any electrically conductive material between these features. The isotropic etchant further facilitates the substantial removal of any electrically conductive stringers that either may remain from the layer of electrically conductive material from which the studs and straps were defined or may remain from the layer of digit line material from which the digit lines were defined.

A layer of insulative material, such as a silicon oxide, a glass, or silicon nitride, may be disposed over the semiconductor memory device, as known in the art, to insulate the exposed studs and straps. Additional structures may be fabricated over the digit lines of the semiconductor memory device.

Other features and advantages of the present invention will become apparent to those of ordinary skill in the art through a consideration of the ensuing description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

With reference toFIGS. 1A and 1B, a semiconductor memory device10according to the present invention is illustrated. Semiconductor memory device10, which is also referred to herein as a semiconductor device, includes a substrate12including an array of conductively doped regions14therein. Preferably, substrate12comprises a p-type semiconductor material. Doped regions14preferably comprise an n-type semiconductor material and may, therefore, also be referred to herein as n-wells. Word lines16extend across a surface of substrate12in a substantially mutually parallel relationship to one another. The regions of substrate12disposed between adjacent word lines16are referred to as bit contact regions18.

Bit contact regions18that are doped (i.e., comprise doped regions14of substrate12) are referred to as bit contacts20. Bit contact regions18or the bit contacts20thereof are exposed to a surface of semiconductor memory device10by means of a trench22aligned between adjacent word lines16. Sidewall spacers17, which are disposed adjacent word lines16, electrically isolate the conductive elements of word lines16from the adjacent trench22. A plug24of conductive material disposed within trench22and an adjacent strap26of conductive material provide an electrically conductive link between bit contact20and a corresponding digit line28that extends across semiconductor memory device10substantially perpendicularly to word lines16.

Each digit line28preferably includes a conductive element30, an insulative cap32disposed over conductive element30, and a sidewall spacer34disposed laterally adjacent conductive element30and opposite strap26. The conductive element30of each digit line28preferably includes a metal silicide layer36and a conductive layer38disposed over metal silicide layer36. Conductive layer38preferably comprises polysilicon.

Preferably, digit lines28have a width of less than about 0.25 microns and, more preferably, of most about 0.18 microns. Adjacent digit lines28are preferably spaced less than about 0.03 microns apart from one another and, more preferably, at most about 0.22 microns apart from one another. Thus, digit lines28preferably have a pitch of less than about 0.55 microns and, more preferably, of at most about 0.40 microns.

Turning now toFIGS. 2-16, a method is illustrated by which digit lines28(seeFIGS. 1A and 1B) of a desired thickness and pitch may be fabricated upon and in communication with corresponding bit contacts20of a semiconductor memory device10.

With reference toFIG. 2, a semiconductor memory device10, which includes a trench22through which a bit contact region18is exposed, is illustrated. The conductive elements of the word lines16of semiconductor memory device10that are adjacent bit contact region18are exposed to trench22. Trench22may be defined by known processes, such as mask and etch techniques, in order to expose bit contact region18.

As shown inFIG. 3, if bit contact region18of substrate12has not been doped, bit contact region18may be doped by known processes, such as by implanting bit contact region18with arsenic. Alternatively, bit contact region18may be doped after digit lines28(seeFIGS. 1A and 1B) have been fabricated and prior to fabricating plug24or strap26(see FIGS.1A and1B).

As illustrated inFIG. 4, any portions of the conductive elements of word lines16that are exposed to trench22may be electrically isolated from trench22by means of sidewall spacers17. Of course, sidewall spacers17may be fabricated, as known in the art, such as by exposing the conductive material of word lines16to an oxidizing temperature, or by disposing a known oxidizing material in contact therewith, or by disposing an insulative material adjacent the conductive material of word lines16and patterning the insulative material to define sidewall spacers17therefrom.

Referring toFIG. 5, a layer40of silicon nitride may be disposed over a surface of semiconductor memory device10. Preferably layer40of silicon nitride is disposed substantially over the surface of semiconductor memory device10, including the bit contacts20thereof. Layer40may be fabricated, as known in the art, such as by chemical vapor depositing (“CVD”) silicon nitride over the surface on semiconductor memory device10. Such a silicon nitride layer40may subsequently be employed as an etch stop.

Turning toFIG. 6, one or more layers of digit line material or materials may be disposed over the surface of semiconductor memory device10. As illustrated, a first digit line layer42may comprise a metal silicide. Preferably, first digit line layer42comprises a refractory metal silicide, such as titanium silicide, tantalum silicide, cobalt silicide, or tungsten silicide. First digit line layer42may be fabricated, as known in the art, such as by chemical vapor deposition or by fabricating adjacent layers of silicon and metal and annealing these layers to one another.

A second digit line layer44may be disposed over first digit line layer42. Second digit line layer44preferably comprises an electrically conductive material, such as a metal or polysilicon. Second digit line layer44may be fabricated, as known in the art, such as by chemical vapor deposition or physical vapor deposition (“PVD”).

With reference toFIG. 7, an insulative layer46may be disposed over the layer or layers of digit line material. As shown, insulative layer46is disposed over second digit line layer44. Insulative layer46may be fabricated, as known in the art, such as by oxidizing an underlying layer42or44of digit line material or by disposing an electrically insulative material over layer44of digit line material by chemical vapor deposition, spin-on-glass (“SOG”), or other known processes. As digit lines28are defined through the layer or layers of digit line material, insulative layer46may be employed as an insulative cap32(seeFIGS. 1A and 1B) over each of the digit lines28.

Referring now toFIGS. 8-8B, a first mask48may be disposed over the uppermost layer44of digit line material. As shown inFIG. 8A, first mask48includes a plurality of mutually parallel apertures50that are alignable over trenches22and bit contacts20. As illustrated, first mask48shields elongated areas of semiconductor memory device10, over which digit lines28are to be defined. As shown inFIG. 8B, first mask48also preferably shields the periphery6of each die4of a wafer2that includes a plurality of dice4.

Although first mask48may be fabricated by any known process, the use of photomask technology is preferred. When a photomask is employed as first mask48, a photoresist may be disposed over a surface of semiconductor memory device10by known processes, such as by spinning the photoresist onto semiconductor memory device10, and the layer of photoresist exposed and developed, as known in the art.

With reference toFIGS. 9 and 9A, digit lines28may be defined through first mask48. Known patterning processes may be employed to define digit lines28and their overlying insulative caps32. Preferably, one or more isotropic etchants are employed to remove the materials of insulative layer46, second digit line layer44, and first digit line layer42either directly or indirectly (i.e., through apertures formed through an overlying layer) through apertures50of first mask48. With reference toFIG. 10, the underlying layer40of silicon nitride may also be removed by known processes, such as by the use of an isotropic etchant.

With reference toFIG. 9B, if a first mask48that shielded the peripheries of dice4(seeFIG. 8B) was employed, a second mask52may be employed to remove any regions of insulative layer46, second digit line layer44, first digit line layer42, or layer40of silicon nitride that remain at the peripheries6of dice4. Preferably, second mask52substantially shields digit lines28and other features of semiconductor memory device10, which are collectively referred to herein as a central region of the semiconductor memory device, and includes apertures54that expose the peripheries6of dice4. Second mask52may be disposed upon semiconductor memory device10and defined as known in the art, such as by the use of photomask techniques. Any digit line materials, insulative materials, or silicon nitride that remain on the peripheries6of dice4may be removed either directly or indirectly through second mask52by known processes, such as by the use of etchants. The masks48and52may each be removed from semiconductor memory device10by known processes.

Referring toFIG. 10, upon removing layer40of silicon nitride, bit contact regions18are again exposed through trenches22. Portions of sidewall spacers17may also be removed as silicon nitride layer40is removed. Accordingly, it may be necessary to re-isolate the conductive elements of word lines16from their corresponding trench22. Again, known processes may be employed to fabricate sidewall spacers17adjacent the conductive elements of word lines16.

Since bit contact regions18of substrate12are again exposed through their corresponding trench22, bit contact regions18may be conductively doped, as known in the art, to form bit contacts20if such doping was not previously performed.

Referring now toFIG. 11, another mask56may be disposed over semiconductor memory device10. Preferably, mask56comprises a photomask, which may be defined by known processes, such as by disposing a photoresist over semiconductor memory device10and exposing and developing selected regions of the photoresist. Mask56preferably substantially fills each of the trenches22of semiconductor memory device10and, thereby, shields bit contacts20. Mask56also extends laterally over a strap region58of the semiconductor memory device10. Each strap region58is disposed between a trench22and its corresponding digit line28. Thus, mask56may protrude from trench22and somewhat from the surface of semiconductor memory device10. Preferably, mask56contacts an exposed, electrically conductive lateral edge portion of the adjacent digit line28. Mask56is preferably hard-baked, as known in the art, to facilitate the fabrication of structures (i.e., conductive plugs and straps) having the desired dimensions and configurations.

Turning toFIG. 12, another layer60of insulative material may be disposed over semiconductor memory device10. Preferably, mask56is exposed through layer60of insulative material. Insulative material layer60preferably has a substantially planar surface. Accordingly, insulative material layer60may be fabricated by known tetraethylorthosilicate (“TEOS”) wet dip processes. Alternatively, layer60of insulative material may be deposited over semiconductor memory device10by known processes, such as by chemical vapor deposition or spin-on processes. Mask56may then be exposed through insulative material layer60by known processes, such as by planarizing insulative material layer60(e.g., by chemical-mechanical planarization (“CMP”)) or by employing a blanket isotropic etch-back. Insulative material layer60preferably insulates the exposed lateral edges of digit lines28, and may cover digit lines28.

With reference toFIG. 13, mask56may be removed from semiconductor memory device10by known processes, such as by the use of solvents or heat, and semiconductor memory device10washed. Upon removing mask56from semiconductor memory device10, cavities62, which are defined by trenches22, insulative material layer60, and digit lines28, are exposed.

As shown inFIG. 14, upon disposing a layer64of conductive material over semiconductor memory device10, cavities62are preferably substantially filled with the conductive material. Thus, the conductive material of layer64establishes an electrically conductive link between each bit contact20and its corresponding digit line28. Conductive material of layer64may be fabricated by known techniques, such as by physical vapor deposition (e.g., sputtering) or by chemical vapor deposition. Preferably, polysilicon is employed as the conductive material of layer64.

Referring toFIG. 15, the uppermost portions of conductive material layer64are preferably removed so as to substantially expose insulative material layer60through conductive material layer64. Accordingly, the remaining portions of conductive material layer64are substantially confined within cavities62and define conductive plugs24and straps26. The uppermost portions of layer64may be removed by known processes, such as by employing blanket isotropic etch-back techniques. Alternatively, another mask could be disposed over the semiconductor device and the plugs24and straps26defined through apertures thereof.

With reference toFIG. 16, yet another mask66may be disposed over semiconductor memory device10. Mask66preferably shields the portions of layer64of conductive material that are disposed within cavities62. Mask66may also shield digit lines28. The remaining regions of semiconductor memory device10are preferably exposed through mask66. Known processes may be employed to fabricate mask66, such as the use of photomask techniques.

The regions of semiconductor memory device10that are exposed through mask66are preferably exposed to an anisotropic etchant in order to further define plugs24and straps26and to remove any stringers of the conductive materials employed in layers42,44, and64that may remain in these exposed regions. Preferably, an isotropic etchant is then employed to remove any remaining conductive materials that are exposed through mask66. Accordingly, the use of both an anisotropic and an isotropic etchant is useful to substantially remove any stringers that may extend from or between plugs24, straps26, or digit lines28and that may cause electrical shorts in semiconductor memory device10, while facilitating the fabrication of digit lines having a thickness of less than about 0.25 microns and a pitch of less than about 0.55 microns.

An insulative layer may then be disposed over plugs24and straps26by known processes. Other structures may also be fabricated over plugs24, straps26, and their corresponding digit lines28, as known in the art.

Although the foregoing description contains many specifics and examples, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments of the invention may be devised which do not depart from the spirit or scope of the present invention. The scope of this invention is, therefore, indicated and limited only by the appended claims and legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein and which fall within the meaning of the claims are to be embraced within their scope.