DEVICES AND METHODS INCLUDING AN ETCH STOP PROTECTION MATERIAL
Protective dielectrics are discussed generally herein. In one or more embodiments, a three-dimensional vertical memory may include a protective dielectric material. A device may include an etch stop material, a first control gate (CG) over the etch stop material, a first CG recess adjacent the first CG, a trench adjacent the first CG recess, and an at least partially oxidized polysilicon on at least a portion of the etch stop material. The at least partially oxidized polysilicon may line a sidewall of the trench and may line the first CG recess.
This application is a continuation of U.S. application Ser. No. 15/470,617, filed Mar. 27, 2017, which is a divisional of U.S. application Ser. No. 14/722,824, filed May 27, 2015, all of which are incorporated herein by reference in their entirety.
BACKGROUNDSome memory cells may include a dielectric between a control gate (CG) and a nitride structure. The dielectric may include an oxide. A floating gate (FG) may be separated from the nitride structure by another dielectric. The nitride structure may be wrapped around three sides of the FG. Charges may become undesirably trapped in the nitride structure, particularly in portions of the nitride structure that are not directly between the CG and the FG. The threshold voltage (Vt) of a cell may be altered by the trapped charges in the nitride structure. In a dielectric (e.g., nitride material or other dielectric) removal process, an etch stop material of a memory may be negatively affected.
The following detailed description refers to the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter.
The term “horizontal” as used in this application is defined as a plane parallel to the conventional plane or surface of a wafer, such as a substrate, regardless of the actual orientation of the wafer or substrate. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on”, “side”. “higher”, “lower”, “over” and “under” are defined with respect to the conventional plane or surface being on the top surface of the wafer or substrate, regardless of the actual orientation of the wafer or substrate. The terms “wafer” and “substrate” are used herein to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
A dielectric may be formed by a deposition (e.g., a conformal deposition) of a polysilicon (e.g., a thin film) and a subsequent oxidation that at least partially converts the polysilicon structure into an oxide (i.e. an oxidized polysilicon). The oxidized polysilicon structure may be formed on another material (e.g., a metal oxide, such as aluminum oxide, zirconium oxide, hafnium oxide, silver oxide, iron oxide, chromium oxide, titanium oxide, copper oxide, zinc oxide, or the like). An In Situ Steam Generation (ISSG) oxidation process may selectively oxidize exposed polysilicon. The oxidized polysilicon may be used as an etch barrier for a material covered by the oxidized polysilicon (e.g., a metal oxide). Such an oxidized polysilicon may protect a material that is susceptible to chemical interaction or damage from a downstream process. For example, the oxidized polysilicon may protect a metal oxide etch stop material from a hot phosphoric acid or other chemical, mechanical, or electrical removal process that is used to remove a material (e.g., a nitride material) situated on the oxidized polysilicon.
For a NAND memory, one or more embodiments of the disclosure may help reduce a problem associated with a chemical selectivity between a nitride material and an etch stop material (e.g., a metal oxide). One or more embodiments may provide a method of removing a nitride material from a sidewall of a trench without damaging an etch stop material. The nitride material may otherwise be a source of trapped charge in the channel or control gate recesses and may contribute to a reduced charge density (CD).
Generally, the devices and techniques are applicable to a situation in which a selective etch process may damage a first material, but does not interact with or damage a second material. In such a situation, the second material may be situated on the first material, the selective etch process may be performed, and the second material may help protect the first material from interacting with or being damaged by the selective etch process. The second material may be oxidized prior to performing the second etch process.
One category of devices that may benefit from such a protective material includes a vertical three-dimensional (3D) memory, such as that shown in
A NAND array architecture is an array of memory cells arranged such that the memory cells of the array are coupled in logical rows to access lines (which are coupled to, and in some cases are at least partially formed by, the CGs of the memory cells), which are conventionally referred to as word lines. Some memory cells of the array are coupled together in series between a source and the data line, which is conventionally referred to as a bit line.
Memory cells in NAND array architecture may be programmed to a desired data state. For example, electric charge may be accumulated (e.g., placed) on, or removed from, an FG of a memory cell to program the cell into a desired one of a number of data states. A memory cell conventionally referred to as a single level cell (SLC) may be programmed to a desired one of two data states, e.g., a “1” or a “0” state. Memory cells conventionally referred to as multilevel cells (MLCs) may be programmed to a desired one of more than two data states.
The Vt of the cell may be modified by storing electrons on the FG. Thus, when the cell is “read” by placing a specific voltage on the CG (e.g., by driving the access line coupled to the cell with a read voltage), electrical current will either flow or not flow in the cell's channel depending on the Vt of the cell and the specific voltage placed on the CG. This presence or absence of current may be sensed and translated into 1's and 0's, reproducing the stored data.
Each memory cell may not directly couple to a source and a data line. Instead, the memory cells of an example array may be arranged together in strings, typically of 4, 8, 16, 32, or more cells each, where the memory cells in the string are coupled together in series between a common source and a data line.
A NAND array may be accessed by a row decoder activating a row of memory cells by driving the access line coupled to those cells with a voltage. In addition, the access lines coupled to the unselected memory cells of each string may be driven with a different voltage. For example, the unselected memory cells of each string may be driven with a pass voltage so as to operate them as pass transistors, allowing them to pass current in a manner that is unrestricted by their programmed data states. Current may then flow from the source to the data line through each memory cell of the series coupled string, restricted by the memory cell of each string that is selected to be read. This places the currently encoded, stored data values of the row of selected memory cells on the data lines. A page of data lines is selected and sensed, and then individual data words may be selected from the sensed data words from the page and communicated from the memory apparatus.
The flash memory, such as a NAND array, may be formed as a 3D memory with stacks of more than one memory cells. The CGs for the memory cells may be adjacent to CG recesses.
A polysilicon 308, may be formed on the sidewalls of the trench 328 and on exposed surfaces of the CGs 306A-D in the CG recesses 330, such as shown in the device 300B of
The polysilicon 308 may reduce one or more dimensions of the device 300B as compared to the device 200A. For example, the CG recesses 330 may include a height dimension 352 that is smaller than the height dimension 252 of the CG recesses 230. The width dimension 350 of the trench 328 may be smaller than the width dimension 250 of the trench 228.
The polysilicon 308 may be at least partially oxidized and converted to an oxidized polysilicon 310, such as shown in device 300C of
The trench 328 and the CG recesses 330 may be at least partially filled with a nitride material 332, such as shown in the device 300D of
A dielectric 312 (which may or may not be substantially the same dielectric material as the oxidized polysilicon 310 or the polysilicon 308, as shown in
The trench 328 and the CG recesses 330 may be at least partially filled with a charge storage material 334, such as shown in device 300G of
The portions of charge storage material 334 may be removed using a Certas™ (e.g., a vapor ammonia), an ammonium fluoride and nitric acid mix (NH4F—HNO3), an ozone (O3) or hydrofluoric acid (HF) mix or cycle (e.g., exposed surfaces may be exposed to ozone to create oxide (e.g., oxidize) the surface and the oxidized surface may be exposed to hydrofluoric acid to remove the oxide), hydrofluoric acid and nitric acid mix (HF—HNO3), hydrofluoric acid and hydrogen peroxide mix (HF—H2O2), or a tetra methyl ammonium hydroxide (TMAH) process. The process used to remove portions of charge storage material 334 may be a function of the doping of the charge storage material 334. For example, if the charge storage material 334 is n-type polysilicon, the TMAH process may be used to remove the portions of charge storage material 334.
A dielectric 314, such as a tunnel oxide, may be formed (e.g., grown using an ISSG process) on the FGs 302, such as shown on device 300I of
The CG 306, polysilicon 308, dielectric 312, charge storage material 334, and/or nitride material 332 may be deposited (e.g., conformally deposited) using a Plasma Enhanced Chemical Vapor Deposition (PECVD) process.
The device 400A in
As shown in device 400D of
One or more embodiments discussed herein may provide an alternative to using an expensive chemical process or using a hafnium oxide (HfOx) material. Using an oxidized polysilicon may help provide a physical barrier to protect an etch stop material (e.g., a metal oxide) from a downstream process. One or more embodiments discussed herein may provide a generally planar nitride structure 304, as compared to a nitride structure that surrounds an FG on three sides.
A problem associated with memory cells that include a nitride adjacent to an FG on more than one side may be charges getting trapped in portions of the nitride that do not separate the FG and a CG (e.g., in portions of the nitride that are not directly between the FG and the CG). Also, trapped charge may migrate along the IGD, such as through program, erase, or temperature cycling. Such charge trapping or movement may alter the threshold voltage (Vt) of the memory cell or degrade incremental step pulse programming (ISPP) relative to memory cells that do not have such charge trapping in the nitride.
Such charge trapping or migration on the nitride may be at least partially eliminated by including nitride adjacent to only one surface of the FG (e.g., by including nitride that is substantially rectangular and not “U” shaped). Such a configuration may include charge being trapped on the FG rather than on the nitride.
An advantage of one or more embodiments may include reducing the incidents of erase saturation in memory cells. Another advantage may include improved alignment between the FG and CG due to eliminating a source of variation in manufacturing, such as the nitride wrapping in irregular shapes around corners in a CG recess or a tier oxide. Instead the FG shape and size may be defined by a plasma enhanced chemical vapor deposition (PECVD) process, which may be a substantially uniform stack deposition process.
Program and erase properties of a memory cell are a function of a gate coupling ratio, which is a function of a capacitance between the FG and the CG of a memory cell. With a device 300 or 400 that includes a planar nitride structure 304, such as shown in the
The above description and the drawings illustrate some embodiments of the invention to enable those skilled in the art to practice the embodiments of the invention. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Examples merely typify possible variations. Portions and features of some embodiments may be included in, or substituted for, those of others. Many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description.
Claims
1. (canceled)
2. A method, comprising:
- forming an etch stop material over a substrate;
- forming alternating conductive tiers and dielectric tiers above the etch stop material;
- forming a trench extending through the alternating conductive tiers and dielectric tiers to the etch stop material;
- forming polysilicon extending within the trench and contacting the etch stop material;
- at least partially oxidizing the polysilicon within the trench; and
- removing at least a portion of the oxidized polysilicon contacting the etch stop material.
3. The method of claim 2, further comprising:
- recessing the conductive tiers relative to the dielectric tiers to form recesses in which the remaining material of the conductive tiers forms respective memory cell control gates, wherein the formed polysilicon extends within the recesses as well as in contact with the etch stop material.
4. The method of claim 3, further comprising:
- forming a nitride material on the at least partially oxidized polysilicon; and
- removing at least a portion of the nitride material to form a nitride structure within the recesses.
5. The method of claim 2, wherein the etch stop material comprises a metal oxide.
6. The method of claim 5, where the metal oxide is selected from aluminum oxide, zirconium oxide, hafnium oxide, silver oxide, iron oxide, chromium oxide, titanium oxide, copper oxide, and zinc oxide.
7. The method of claim 2, wherein oxidizing the polysilicon within the trench comprises performing an in-situ steam generation oxidation process to oxidize exposed polysilicon within the trench.
8. The method of claim 2, wherein the remaining oxidized polysilicon forms at least part of an inter-poly dielectric layer of a memory cell and contacts at least a portion of the etch stop material.
9. The method of claim 8, further comprising:
- recessing the conductive tiers relative to the dielectric tiers to form recesses in which the remaining material of the conductive tiers forms respective memory cell control gates;
- wherein the formed polysilicon extends within the recesses as well as in contact with the etch stop material.
10. The method of claim 9, further comprising:
- forming a nitride material on the at least partially oxidized polysilicon; and
- removing at least a portion of the nitride material to form nitride structures within the recesses, wherein the oxidized polysilicon protects the etch stop layer from damage during the removal of the nitride material.
11. The method of claim 10, wherein the etch stop layer is metal oxide and removing at least a portion of the nitride material comprises performing an acid etch.
12. The method of claim 11, where the metal oxide is selected from aluminum oxide, zirconium oxide, hafnium oxide, silver oxide, iron oxide, chromium oxide, titanium oxide, copper oxide, and zinc oxide.
13. The method of claim 10 wherein removing at least a portion of the nitride material comprises performing an acid etch.
14. A method, comprising:
- forming a metal oxide etch stop material over a substrate;
- forming alternating conductive tiers and dielectric tiers above the metal oxide etch stop material;
- forming a trench extending vertically through the alternating conductive tiers and dielectric tiers and at least partially into the etch stop material;
- horizontally recessing the conductive tiers relative to the dielectric tiers to form recesses in which the remaining material of the conductive tiers forms respective memory cell control gates;
- forming a layer of polysilicon extending within the trench and contacting exposed etch stop material within the trench, wherein the formed polysilicon extends within the recesses as well as in contact with the etch stop material;
- at least partially oxidizing the polysilicon within the trench to form a layer of oxidized polysilicon vertically above the exposed etch stop layer;
- forming a nitride material on the at least partially oxidized polysilicon, wherein the formed nitride material extends within the recesses;
- removing at least a portion of the nitride material using acid to form a nitride structures within the recesses, wherein the layer of oxidized polysilicon protects the metal oxide etch stop layer from the acid during the removal of the nitride material; and
- removing at least a portion of the oxidized polysilicon contacting the metal oxide etch stop material and the underlying metal oxide layer to expose the substrate.
15. The method of claim 14 where removing the portion of the nitride material uses a hot phosphoric acid.
16. The method of claim 14, wherein the remaining oxidized polysilicon within the recesses and the nitride structures within the recesses form at least part of an inter-poly dielectric layer of a memory cell, and wherein the remaining oxidized polysilicon extends through the trench to contact at least a portion of the etch stop material.
17. The method of claim 14, where the metal oxide is selected from aluminum oxide, zirconium oxide, hafnium oxide, silver oxide, iron oxide, chromium oxide, titanium oxide, copper oxide, and zinc oxide.
18. The method of claim 14, wherein oxidizing the polysilicon within the trench comprises performing an in-situ steam generation oxidation process to oxidize exposed polysilicon within the trench.
Type: Application
Filed: Feb 24, 2020
Publication Date: Aug 20, 2020
Inventors: John Hopkins (Meridian, ID), Darwin Franseda Fan (Boise, ID)
Application Number: 16/799,517