RECESSED ACCESS DEVICES AND DRAM CONSTRUCTIONS TECHNICAL FIELD

Embodiments disclosed herein pertain to recessed access devices and to DRAM constructions.

BACKGROUND

A recessed access device is a field effect transistor having its gate construction buried within a trench formed in semiconductive material. The gate construction includes a gate insulator which lines the trench and conductive gate material within the trench laterally inward of the gate insulator. A source/drain region is formed in outermost regions of the semiconductive material on each of opposing sides of the trench. When the two source/drain regions are at different voltages and a suitable voltage is applied to the conductive gate material, current (Ion) flows through the semiconductive material between the source/drain regions along the trench sidewalls and around the base of the trench (i.e. , a conductive channel forms through which current flows between the two source/drain regions) . It is desirable to attain high device on-current (Ion) and low device off-current (e.g. leakage current I ₀ ff) in recessed access devices.

Recessed access devices are typically devoid of non-volatile charge-storage devices (yet may be fabricated to include such), and regardless may be used in memory circuitry, for example DRAM circuitry. Achieving lower I ₀ ff may result in less disturb and longer retention of the information stored in a memory cell incorporating a recessed access device.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a cross-sectional view of a recessed access device and of a DRAM construction in accordance with some embodiments of the invention, and is taken through line 1 - 1 in Fig. 3.

Fig. 2 is a view taken through line 2-2 in Fig. 3.

Fig. 3 is a diagrammatic hybrid schematic and cross-sectional view taken through line 3-3 in Figs. 1 and 2.

Fig. 4 is a diagram of conductivity-modifying dopant concentration and type that may be used in the embodiments of the invention. Fig. 5 is a diagram of drain current I _d as a function of gate voltage V _g that may occur in the embodiments of Figs. 1 -3.

Fig. 6 is a diagram of drain current I _d as a function of drain voltage V _d that may occur in the embodiments of Figs. 1 -3.

Fig. 7 is a cross-sectional view of a recessed access device and of a DRAM construction in accordance with some embodiments of the invention.

Fig. 8 is a diagram of drain current I _d as a function of gate voltage V _g that may occur in the embodiments of Fig. 7.

Fig. 9 is a cross-sectional view of a recessed access device and of a DRAM construction in accordance with some embodiments of the invention.

Fig. 10 is a diagram of drain current I _d as a function of gate voltage V that may occur in the embodiments of Fig. 9.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Embodiments of the invention encompass recessed access devices and DRAM constructions. First example embodiments are initially described with reference to Figs. 1 -3 which show an example fragment of a substrate construction 8 comprising an array or array area 10 that in one embodiment comprises memory cells that have been fabricated relative to a base substrate 1 1. Substrate 1 1 may comprise any one or more of

conductive/conductor/conducting (i.e. , electrically herein),

semiconductive/semiconductor/semiconducting, and

insulative/insulator/insulating (i.e., electrically herein) materials. Various materials are above base substrate 1 1. Materials may be aside, elevationally inward, or elevationally outward of the Figs l -3-depicted materials. For example, other partially or wholly fabricated components of integrated circuitry may be provided somewhere above, about, or within base substrate 11. Control and/or other peripheral circuitry for operating components within a memory array may also be fabricated, and may or may not be wholly or partially within a memory array or sub-array. Further, multiple sub-arrays may also be fabricated and operated independently, in tandem, or otherwise relative one another. As used in this document, a“sub-array” may also be considered as an array.

Base substrate 11 comprises semiconductor material 12

(e.g., appropriately and variously doped monocrystalline silicon and/or other semiconductive material), trench isolation regions 14 (e.g. , silicon nitride and/or doped or undoped silicon dioxide), and active area regions 16 comprising suitably and variously-doped semiconductor material 12. In one embodiment, construction 8 comprises memory cells 75 (Fig. 3), for example DRAM memory cells individually comprising a field effect transistor device 25 and a charge-storage device 85 (e.g. , a capacitor).

However, embodiments of the invention encompass other memory cells and other constructions of integrated circuitry independent of whether

containing memory cells.

Field effect transistors 25 are in the form of recessed access devices (a type of construction of a field effect transistor), with Fig. 3 showing of pair of such transistors/devices 25. Such individually include buried access line constructions 18, for example within trenches 19 in semiconductor material 12. Constructions 18 comprise conductive gate material 22 (e.g., comprising, consisting essentially of, or consisting of conductively-doped semiconductor material and/or metal material) that functions as a conductive gate of individual devices 25. A gate insulator 20 (e.g., comprising, consisting essentially of, or consisting of silicon dioxide and/or silicon nitride) is along sidewalls 21 and a base 23 of individual trenches 19 between conductive gate material 22 and semiconductor material 12.

Individual devices 25 comprise a pair of source/drain regions 24, 26 in upper portions of semiconductor material 12 on opposing sides of individual trenches 19 (e.g., regions 24, 26 being laterally outward of and higher than access line constructions 18) . Each of source/drain regions 24, 26 comprises at least a part thereof having a conductivity-increasing dopant therein that is of maximum concentration of such conductivity-increasing dopant within the respective source/drain region 24, 26, for example to render such part to be conductive (e.g. , having a maximum dopant concentration of at least 10 ¹⁹ atoms/cm ³ ). Accordingly, all or only a part of each source/drain region 24, 26 may have such maximum concentration of conductivity-increasing dopant. Source/drain regions 24 and/or 26 may include other doped regions (not shown), for example halo regions, LDD regions, etc.

One of the source/drain regions (e.g. , region 26) of the pair of source/drain regions is laterally between conductive gate material 22 and is shared by the pair of devices 25. Others of the source/drain regions (e.g. , regions 24) of the pair of source/drain regions are not shared by the pair of devices 25. Thus, in the example embodiment, each active area region 16 comprises two devices 25 with each sharing a central source/drain region 26. A digitline 30 is directly electrically coupled to the one shared source/drain region 26. A pair of capacitors 85 individually are directly electrically coupled to one of the other source/drain regions 24. A conductive via 34 is shown interconnecting shared source/drain region 26 with digitline 30.

Conductive vias 36 are shown interconnecting non-shared source/drain regions 24 with individual capacitors 85. Example insulator material 38 (e.g., comprising, consisting essentially of, or consisting of silicon nitride and/or doped or undoped silicon dioxide) surrounds vias 34, 36.

A channel region 27 is in semiconductor material 12 below pair of source/drain regions 24, 26 along trench sidewalls 21 and around trench base 23. Channel region 27 may be suitably doped with a conductivity- increasing dopant likely of the opposite conductivity-type of the dopant in source/drain regions 24, 26, and for example that is at a maximum

concentration in the channel of no greater than 1 x 10 ¹⁶ atoms/cm ³ . When suitable voltage is applied to gate material 22 of an access line construction 18, a conductive channel forms (e.g., along a channel current-flow line/path 29 [Fig. 3] ) within channel region 27 proximate gate insulator 20 such that current is capable of flowing between a pair of source/drain regions 24 and

26 under the access line construction 18 within an individual active area region 16. Stippling is diagrammatically shown to indicate primary conductivity-modifying dopant concentration (regardless of type) in material 12, with denser stippling indicating greater dopant concentration and lighter stippling indicating lower dopant concentration. Conductivity-modifying dopant may be, and would likely be, un-stippled portions of material 12. Only two different stippling densities are shown for convenience, and additional dopant concentrations may be used and constant dopant

concentration is not required in any region (e.g., see Fig. 4 and the

description thereof below).

At least some of channel region 27 comprises GaP (gallium

phosphide). Figs. 1 -3 show an example embodiment wherein only some of channel region 27 comprises GaP. Specifically, for example, portions 40 (Fig.3 ; e.g., which may be referred to as“those portions”) of channel region

27 that are along all of trench sidewalls 21 below pair of source/drain regions 24, 26 comprise GaP, for example as material designated with numeral 44 (e.g. , and being part of semiconductor material 12). Portion 42 (e.g., which may be referred to as“that portion”) of channel region 27 that is directly below trench base 23 is devoid of GaP, and as material designated with numeral 46 (e.g. , and being part of semiconductor material 12). In this document,“devoid of GaP” means from no molecule of GaP per cubic centimeter (i.e., 0 molecules of GaP per cubic centimeter) to no more than 1 x 10 ¹² molecules of GaP per cubic centimeter. In one embodiment, portion 42 of channel region 27 that is directly below trench base 23 has no detectable GaP therein (i.e., any existing or future-developed technique not able to detect any GaP molecule in material 46). In one embodiment, the portion(s) of the channel region that comprises GaP consist(s) essentially of GaP and conductivity-modifying dopant therein, or consist(s) of GaP and conductivity-modifying dopant therein. In one embodiment, the other portion of the channel region that does not comprise GaP (e.g., portion 42) comprises Si, and in one such embodiment consists essentially of Si and conductivity-modifying dopant therein, or consists of Si and conductivity modifying dopant therein.

In one embodiment, pair of source/drain regions 24, 26 comprises GaP, and in one such embodiment consists essentially of GaP and

conductivity-modifying dopant therein, or consists of GaP and conductivity modifying dopant therein.

Fig. 4 is an example plot of conductivity-modifying dopant

concentration in atoms/molecues per cubic centimeter as a function of depth Z in microns in construction 8, for example at and between depths A, B , and C (Fig. 3), with line-portion 50 showing concentration of one conductivity- impurity type (e.g.,“n”) and line-portion 60 showing concentration of another conductivity-impurity type (e.g. ,“p”).

Fig. 5 are plots of drain current I _d (cell current) as a function of gate voltage V _g (wordline voltage) for channels consisting of Si and

conductivity-modifying dopant therein and for channels consisting of GaP and conductivity-modifying dopant therein. The plots are for cell voltage of 1. 1V, digitline voltage of 0V, body/base substrate 11 voltage of -0.5V, digitline resistance of 10,000 ohms, and cell resistance of 20,000 ohms. The left Si and GaP curves go to the left y-axis logarithmic scale, and the right Si and GaP curves go to the right y-axis linear scale. Such plots show very comparable performance between Si and GaP channel materials, and with much lower off current (I _0ff ; logarithmic scale) at zero wordline voltage for GaP meaning that much lower leakage current may result.

Fig. 6 are plots of drain current I _d as a function of drain voltage V _d (cell voltage) for channels consisting of Si and conductivity-modifying dopant therein and for channels consisting of GaP and conductivity modifying dopant therein. The plots are for wordline voltage of -0.2V, digitline voltage of 0V, and body/base substrate 11 voltage of -0.5V. Such plots essentially show that lower gate induced drain leakage (GIDL) may result for GaP channels.

Any other attribute(s) or aspect(s) as shown and/or described herein with respect to other embodiments may be used in the embodiments of Figs. 1 -3.

An alternate example embodiment DRAM construction 8a comprising a pair of recessed access devices 25a is shown in Fig. 7. Like numerals from the above-described embodiments have been used where appropriate, with some construction differences being indicated with the suffix“a”.

Construction 8a of an array lOa comprises materials 44a and 46a having an interface thereof (e.g. , the horizontal line just above example depth C) that is deeper in construction 8a as compared to construction 8 (e.g., with such interface not being within current path 29 in construction 8a). Those portions 40 of channel region 27 that are along all of trench sidewalls 21 below pair of source/drain regions 24, 26 and that portion 42 of channel region 27 that is around trench base 23 comprises GaP (e.g. , material 44a) . In one such embodiment, those portions 40 and that portion 42 consist essentially of GaP and conductivity-modifying dopant therein, and in one embodiment consist of GaP and conductivity-modifying dopant therein. In one embodiment, GaP is directly below channel region 27 (e.g. , in

un-stippled material 44a below lightly-stippled channel region 27, and un stippled material 44a may include conductivity-modifying dopant therein). Any other attribute(s) or aspect(s) as shown and/or described herein with respect to other embodiments may be used.

Fig. 8 is analogous to Fig. 5, but showing plots of drain current I _d (cell current) as a function of gate voltage V _g for channels consisting of Si and conductivity-modifying dopant therein and for channels consisting of GaP and conductivity-modifying dopant therein that may occur for the construction of Fig. 7. The plots are again for cell voltage of 1. 1V, digitline voltage of 0V, body/base substrate 11 voltage of -0.5V, digitline resistance of 10,000 ohms, and cell resistance of 20,000 ohms.

Another alternate example embodiment DRAM construction 8b comprising a pair of recessed access devices 25b is shown in Fig. 9. Like numerals from the above-described embodiments have been used where appropriate, with some construction differences being indicated with the suffix“b” or with different numerals. Channel region 27 comprises a pair of first portions 70 along upper portions of trench sidewalls 21 that are below pair of source/drain regions 24, 26. First portions 70 comprise GaP (e.g., material 44b). A pair of second portions 80 is along trench sidewalls 21 below pair of first portions 70. Second portions 80 are devoid of GaP (e.g. , material 46b). A third portion 42 is below pair of second portions 80, extends around trench base 23, and is devoid of GaP. In one embodiment, first portions 70 consist essentially of GaP and conductivity-modifying dopant therein, and in one embodiment consist of GaP and conductivity modifying dopant therein. In one embodiment, second portions 80 have no detectable GaP therein. In one embodiment, third portion 42 has no detectable GaP therein. Any other attribute(s) or aspect(s) as shown and/or described herein with respect to other embodiments may be used.

Fig. 10 is analogous to Figs. 5 and 8, but showing plots of drain current I _d (cell current) as a function of gate voltage V _g for channels consisting of Si and conductivity-modifying dopant therein and for channels consisting of GaP and conductivity-modifying dopant therein that may occur for the construction of Fig. 9. The plots are again for cell voltage of 1. 1V, digitline voltage of 0V, body/base substrate 11 voltage of -0.5V, digitline resistance of 10,000 ohms, and cell resistance of 20,000 ohms.

The example embodiments may be manufactured using any existing or future-developed method(s) . For example, trenches 19 including portions thereof in which insulator material 38 is received could be formed in semiconductor material 12. Alternately, by way of example only, GaP- containing material could be formed above Si-containing material and trenches 19 could be formed in the GaP-containing material. Epitaxial growth may be used.

In this document unless otherwise indicated,“elevational”,“higher”, “upper”,“lower”,“top”,“atop”,“bottom”,� �above”,“below”,“under”, “beneath”,“up”, and“down” are generally with reference to the vertical direction. “Horizontal” refers to a general direction (i.e., within 10 degrees) along a primary substrate surface and may be relative to which the substrate is processed during fabrication, and vertical is a direction generally orthogonal thereto. Reference to“exactly horizontal” is the direction along the primary substrate surface (i.e. , no degrees there-from) and may be relative to which the substrate is processed during fabrication. Further, “vertical” and“horizontal” as used herein are generally perpendicular directions relative one another and independent of orientation of the substrate in three-dimensional space. Additionally,“elevationally- extending” and“extend(ing) elevationally” refer to a direction that is angled away by at least 45° from exactly horizontal. Further,“extend(ing) elevationally”,“elevationally-extending”, extend(ing) horizontally, and horizontally-extending with respect to a field effect transistor are with reference to orientation of the transistor’s channel length along which current flows in operation between the source/drain regions. For bipolar junction transistors,“extend(ing) elevationally”“elevationally-extending”, extend(ing) horizontally, and horizontally-extending, are with reference to orientation of the base length along which current flows in operation between the emitter and collector.

Further,“directly above” and“directly under” require at least some lateral overlap (i.e., horizontally) of two stated

regions/materials/components relative one another. Also, use of “above” not preceded by“directly” only requires that some portion of the stated region/material/component that is above the other be elevationally outward of the other (i.e., independent of whether there is any lateral overlap of the two stated regions/materials/components) . Analogously, use of “under” not preceded by“directly” only requires that some portion of the stated region/material/component that is under the other be elevationally inward of the other (i.e. , independent of whether there is any lateral overlap of the two stated regions/materials/components) . Any of the materials, regions, and structures described herein may be homogenous or non-homogenous, and regardless may be continuous or discontinuous over any material which such overlie. Further, unless otherwise stated, each material may be formed using any suitable or yet-to- be-developed technique, with atomic layer deposition, chemical vapor deposition, physical vapor deposition, epitaxial growth, diffusion doping, and ion implanting being examples.

Additionally,“thickness” by itself (no preceding directional adjective) is defined as the mean straight-line distance through a given material or region perpendicularly from a closest surface of an immediately-adjacent material of different composition or of an immediately-adjacent region.

Additionally, the various materials or regions described herein may be of substantially constant thickness or of variable thicknesses. If of variable thickness, thickness refers to average thickness unless otherwise indicated, and such material or region will have some minimum thickness and some maximum thickness due to the thickness being variable. As used herein, “different composition” only requires those portions of two stated materials or regions that may be directly against one another to be chemically and/or physically different, for example if such materials or regions are not homogenous. If the two stated materials or regions are not directly against one another,“different composition” only requires that those portions of the two stated materials or regions that are closest to one another be chemically and/or physically different if such materials or regions are not homogenous. In this document, a material, region, or structure is“directly against” another when there is at least some physical touching contact of the stated materials, regions, or structures relative one another. In contrast,“over”, “on”,“adjacent”,“along”, and“against” not preceded by“directly” encompass“directly against” as well as construction where intervening material(s), region(s), or structure(s) result(s) in no physical touching contact of the stated materials, regions, or structures relative one another.

Herein, regions-materials-components are“electrically coupled” relative one another if in normal operation electric current is capable of continuously flowing from one to the other, and does so predominately by movement of subatomic positive and/or negative charges when such are sufficiently generated. Another electronic component may be between and electrically coupled to the regions-materials-components. In contrast, when regions-materials-components are referred to as being "directly electrically coupled”, no intervening electronic component (e.g. , no diode, transistor, resistor, transducer, switch, fuse, etc.) is between the directly electrically coupled regions-materials-components.

Additionally,“metal material” is any one or combination of an elemental metal, a mixture or an alloy of two or more elemental metals, and any conductive metal compound.

CONCLUSION

In some embodiments, a recessed access device comprises a

conductive gate in a trench in semiconductor material. A gate insulator is along sidewalls and a base of the trench between the conductive gate and the semiconductor material. A pair of source/drain regions is in upper portions of the semiconductor material on opposing sides of the trench. A channel region is in the semiconductor material below the pair of source/drain regions along the trench sidewalls and around the trench base. At least some of the channel region comprises GaP.

In some embodiments, a recessed access device comprises a

conductive gate in a trench in semiconductor material. A gate insulator is along sidewalls and a base of the trench between the conductive gate and the semiconductor material. A pair of source/drain regions is in upper portions of the semiconductor material on opposing sides of the trench. A channel region is in the semiconductor material below the pair of source/drain regions along the trench sidewalls and around the trench base. Those portions of the channel region that are along all of the trench sidewalls below the pair of source/drain regions comprise GaP. That portion of the channel region that is directly below the trench base is devoid of GaP.

In some embodiments, a recessed access device comprises a

conductive gate in a trench in semiconductor material. A gate insulator is along sidewalls and a base of the trench between the conductive gate and the semiconductor material. A pair of source/drain regions is in upper portions of the semiconductor material on opposing sides of the trench. A channel region is in the semiconductor material below the pair of source/drain regions along the trench sidewalls and around the trench base. Those portions of the channel region that are along all of the trench sidewalls below the pair of source/drain regions and that portion of the channel region that is around the trench base comprising GaP.

In some embodiments, a recessed access device comprises a

conductive gate in a trench in semiconductor material. A gate insulator is along sidewalls and a base of the trench between the conductive gate and the semiconductor material. A pair of source/drain regions is in upper portions of the semiconductor material on opposing sides of the trench. A channel region is in the semiconductor material below the pair of source/drain regions along the trench sidewalls and around the trench base. The channel region comprises a pair of first portions along upper portions of the trench sidewalls that are below the pair of source/drain regions. The first portions comprise GaP. A pair of second portions is along the trench sidewalls below the pair of first portions. The second portions are devoid of GaP. A third portion is below the pair of second portions. The third portion extends around the trench base and is devoid of GaP.

In some embodiments, a DRAM construction comprises a pair of recessed access devices individually comprising a conductive gate in a trench in semiconductor material. A gate insulator is along sidewalls and a base of the trench between the conductive gate and the semiconductor material. A pair of source/drain regions is in upper portions of the semiconductor material on opposing sides of the trench. A channel region is in the semiconductor material below the pair of source/drain regions along the trench sidewalls and around the trench base. At least some of the channel region comprises GaP. One of the source/drain regions of the pair of source/drain regions is laterally between the conductive gates and is shared by the pair of recessed access devices. The others of the source/drain regions of the pair of source/drain regions are not shared by the pair of recessed access devices. A digitline is directly electrically coupled to the one shared source/drain region. A pair of capacitors individually are directly electrically coupled to one of the other source/drain regions.