The present disclosure generally relate to memory devices, and methods of manufacturing the same, and more particularly, to device structures and methods of forming three-dimensional (3D) memory devices.
Memory devices are an essential component in digital electronic devices that are being developed today. With the increase in technology today, there is a need for increased memory capacity in most electronic devices. At the same time there is also a need for smaller memory devices to meet the market place's desire to create smaller electronic devices in which the memory device is positioned within.
In recent years, conventional (2D) NAND memory devices have run into a number of challenges, including voltage drop related issues (e.g., running out of electrons in the current carrying elements due to the ever scaling of the cell size), retention loss and overall reliability. To address challenges encountered in scaling planar 2D NAND memory devices to achieve higher densities at a lower cost per bit, ultra-high density, three-dimensional (3D) stacked memory structures have been introduced. Such 3D memory structures are sometimes referred to as having a Bit Cost Scalable (BiCS) architecture, and include strings of vertically integrated memory cells. Typically, the vertically aligned memory cells are formed from an array of alternating conductor and insulator layers, where the conductive layers correspond to the word lines of the memory structure.
As the number of vertically stacked memory cells in 3D NAND devices increases (e.g., as chip densities increase), the resistivity of the memory cell string (e.g., channel structure) also increases, introducing numerous performance issues. As resistivity increases, more advanced circuits are required for current sensing. Typically, the memory cell string may include a number of word line layers. As the number of vertically stacked layers increase, the overall resistance of the vertically oriented channel region of the 3D NAND memory increases, leading to a drop in the amount of current that can (1) flow in the channel structure and most importantly (2) be detected at by the sense amplifier. Based on the current design rules and pitches, at around 500 stacked word line layers, it may not be possible to detect any current flowing through the channel region which corresponds to the stored state. In turn, the difference between stored states is indistinguishable. Currently, it is common to utilize a polysilicon channel in the channel structure of a 3D NAND device. As a result of the use of a polysilicon channel and its highly granular nature, the 3D NAND device may be suffer from reduced mobility, ON current degradation, increased device variability, as well as retention degradation. In past a macaroni type 3D NAND device were suggested and implemented that comprise off the filler oxide which minimizes the thickness of the polysilicon channel and in turn reduce the number of grain boundaries (GBs) responsible for the electron scattering and improve the ON current. Even though the number of GBs is reduced in this approach, they are still present and cannot overcome the 500 WL stacking limit.
Therefore, there is a need for an improved memory device structure and method of forming the same that solves the problems described above.
Embodiments of the disclosure may provide a three-dimensional memory device, comprising a plurality of alternating layers formed over a surface of a substrate, wherein the alternating layers comprises a word line layer and an inter-word line dielectric layer that are stacked in a first direction and a gate coupled to each of the word line layers of the plurality of alternating layers. The three-dimensional memory device also includes a multi-layer channel having a first end coupled to a source region, a second end coupled to a drain region, and extending in the first direction between the source region and the drain region. The multi-layer channel comprises a first conductive layer extending between the source region and the drain region; and a second conductive layer extending between the source region and the drain region, wherein the first conductive layer is different from the second conductive layer. The three-dimensional memory device also includes an ONO layer stack disposed between the gates and the multi-layer channel, wherein the ONO layer stack extends in the first direction between the source region and the drain region.
Embodiments of the disclosure may provide a three-dimensional memory device, comprising a plurality of alternating layers formed over a surface of a substrate, wherein the alternating layers comprises a word line layer and an inter-word line dielectric layer that are stacked in a first direction and a gate coupled to each of the word line layers of the plurality of alternating layers. The three-dimensional memory device also includes a multi-layer channel having a first end coupled to a source region, a second end coupled to a drain region, and extending in the first direction between the source region and the drain region. The multi-layer channel comprises a first conductive layer extending between the source region and the drain region; and a second conductive layer extending between the source region and the drain region, wherein the first conductive layer is different from the second conductive layer. The multi-layer channel also includes a filler layer extending between the source region and the drain region. The three-dimensional memory device also includes an ONO layer stack disposed between the gates and the multi-layer channel, wherein the ONO layer stack extends in the first direction between the source region and the drain region.
Embodiments of the disclosure can provide a method of forming a three-dimensional memory device, comprising forming a plurality of alternating layers over a surface of a substrate. The method of forming a plurality of alternating layers comprises a dielectric layer (later in process etched and replaced with word line layer) and an inter-word line dielectric layer that are stacked in a first direction over a source region layer that is disposed over the surface of the substrate, wherein each word line layer is coupled to one or more gates. The method of forming a plurality of alternating layers also comprises a plurality of openings (memory holes) extending in the first direction from the source region layer and through the plurality of alternating layers, wherein a portion of a gate of the one or more gates in each word line layer are positioned adjacent to a surface of each opening of the plurality of openings. The method of forming a three-dimensional memory device also comprises forming a memory cell/stack regions and channel region within the plurality of openings. The method of forming the cell region comprises forming an ONO layer stack over the surface of each of the plurality of openings; forming a first conductive layer (channel #1) over a surface of the ONO layer stack; and forming a second conductive layer (channel #2) over a surface of the first conductive layer, wherein the first conductive layer is different from the second conductive layer. The method of forming a three-dimensional memory device also comprises forming a drain region layer over the plurality of alternating layers, wherein at least a portion of the first conductive layer and a portion of the second conductive layer formed within each of the plurality of openings are coupled to a portion of the drain region layer and at least a portion of the first conductive layer and a portion of the second conductive layer are coupled to a portion of the source region layer.
To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the appended drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary embodiments and are therefore not to be considered limiting of its scope, and may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
In the following description, details are set forth by way of example to facilitate an understanding of the disclosed subject matter. It should be apparent to a person of ordinary skill in the field, however, that the disclosed implementations are exemplary and not exhaustive of all possible implementations. Thus, it should be understood that reference to the described examples is not intended to limit the scope of the disclosure. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In particular, it is fully contemplated that the features, components, and/or steps described with respect to one implementation may be combined with the features, components, and/or steps described with respect to other implementations of the present disclosure. As used herein, the term “about” may refer to a +/−10% variation from the nominal value. It is to be understood that such a variation can be included in any value provided herein.
Embodiments of the disclosure provided herein include an apparatus for and method of forming an improved three-dimension (3D) memory structure/cell that includes a multi-layer channel that includes two or more layers that are formed of different materials. In some embodiments, the material of each channel layer may be an amorphous oxide semiconductor material. The formed multi-layer channel described herein can allow for multiple pathways for a current transport and may conduct a higher total current, through the two or more layers of the multi-layer channel during operation. In one embodiment, the two or more layers include a low mobility channel layer and a high mobility channel layer, which are used to increase the speed and reliability of the 3D NAND device due to a higher magnitude of the current that can be conducted through the channel region of the device. The multi-layer channel may include a plurality of layers with differing electron mobilities. For example, the multi-layer channel may include three layers. In this example, the outer layers may act as protection layers for the inner layer. The combination of a low mobility layer and a high mobility layer may result in improved performance for the 3D memory structure, as described herein. For example, the multi-layer channel structure may allow for the utilization of amorphous channel materials, which can decrease and/or eliminate electron scattering created at the grain boundaries of conventional polycrystalline silicon containing channel regions. As a consequence of the decrease in electron scattering at the grain boundaries (amorphous semiconducting oxides are grain-boundary free), the channel structure and whole memory string exhibit a decreased resistance and variability. Additionally, as described above, the mobility of the channel structure and the ON current of the device may also both be improved due to the lack of grain boundaries found in the amorphous structure. As a result, the multi-layer channel in the channel structure may enable a greater number of word lines (e.g., more than 500 word lines) in the 3D memory structure. Transitioning to amorphous multi-channel oxide semiconductor channels and inherent absence of the grain boundaries (typically present in prior-art polysilicon channels) results in reduction of the scattering mechanisms (largest contributor to the variability of the stored bit) which will also allow for an increase in the number of states that can be stored in a multi-level cell, (e.g., more efficient and dense storage density).
Beside the application in the memory devices, this approach can be applied in logic as well to improve the so-called fan-out. The fan-out is the number of gate inputs driven by the output of another single logic gate. Furthermore, as a result of the multi-layer channel in the transistor structure, fan-out may be increased, due to the improved conductivity of the channel structure.
Embodiments disclosed herein can be useful for, but are not limited to, channel structures in two dimensional (2D) and 3D memory including a multi-channel layer with layers having differing mobilities.
The 3D NAND memory structure 100 may also include a source region 212 (e.g., N+ source layer), which may be part of or formed on the CSL 103, and a drain region 214 (e.g., N+ drain layer), which may be part of or formed under the plurality of bit lines 118. The staircase-like structures 110, which are formed on two opposing edges of the 3D NAND memory structure 100, require a two-dimensional area (i.e., X-Z plane) to connect all of the word line layers 115 to external elements outside of the 3D NAND device.
In some embodiments, the first channel 208 material may include indium zinc oxide (IZO), the second channel 210 material may include indium gallium zinc oxide (IGZO), and the second channel 210 may be disposed over the first channel 208. The first channel layer 208 and second channel layer 210 may include any material that allows for the flow of electrons between a source region 212 and a drain region 214, as is provided in more detail below. In some embodiments, the first channel layer 208 may have different electron mobility than the electron mobility of the second channel layer 210. In one example, the first channel layer 208 may be a high electron mobility layer, and the second channel layer 210 may be a lower electron mobility layer. In some embodiments, the first channel layer 208 and the second channel layer 210 may both include a low mobility layer or both include a high mobility layer. In some embodiments, the combination of the first channel layer 208 and the second channel layer 210 results in the multi-layer channel having an effective mobility of from about 1 cm2N s to about 70 cm2N s, such as about 25 cm2N s to about 60 cm2N s, such as about 25 cm2N s to about 35 cm2N s, or from about 35 cm2N s to about 60 cm2N s.
In embodiments where the first channel 208 has a mobility greater than the mobility of the second channel 210, the first channel 208 conducts a large portion of the current through the multi-layer channel, which allows the multi-layer channel to effectively conduct current due to the high mobility of the first channel 208. The combination of the first channel 208 and the second channel 210 results in the multi-layer channel having an effective mobility greater than about 60 cm2N·s. The first channel 208 has a mobility less than about 20 cm2N·s, and the second channel 210 has a mobility greater than about 60 cm2N·s, according to one embodiment.
As discussed above, the 3D NAND memory structure 100 includes a dielectric layer 116 (e.g., inter-word line dielectric layer), a word line layer 115, and a gate region 202, as shown in
The 3D NAND memory structure 100 includes a charge trapping layer structure 206 disposed between the gate regions 202 and the multi-layer channel (e.g., first channel 208 and second channel 210). While not intending to limit the scope of disclosure provided herein the charge trapping layer structure is also referred to herein as an ONO layer stack 206. The ONO layer stack 206 will include a first dielectric layer 206a, a charge trap layer 206b, and a second dielectric layer 206c. In one example, the first dielectric layer 206a includes a silicon oxide material (e.g., SiO2 layer), the charge trap layer 206b includes a silicon nitride (SiN) layer, and the second dielectric layer 206c includes a silicon oxide or an aluminum oxide containing layer.
In some embodiments, the abbreviated ONO stack can be a combination of various thicknesses of materials which form the tunnel oxide, charge-trapping (storage) layer, blocking oxide and/or high-k layer. A tunnel oxide can be formed by a combination of various thicknesses of SiO2/SiN/SiO2, and in some cases the SiN layer includes a completely different stoichiometry and properties compared to the charge-trapping SiN layer. In some embodiments, the tunnel oxide is formed from of a silicon oxide (SiOx), whereas an aluminum oxide (AlxOy) is the most commonly used high-k layer. Other tunnel oxide materials can include, but are not limited to, a hafnium oxide material (HfOx), or a doped hafnium oxide material that contains one or more of Al, Y, Si, N, Sr, or Gd as a dopant. In some cases, the ONO layer stack 206 is referred to herein as an “intermediate layer stack”. In some embodiments, the intermediate layer stack includes the first dielectric layer 206a, the charge trap layer 206b, and the second dielectric layer 206c. However, in some alternate embodiments, the intermediate layer stack includes a ferroelectric material containing layer. In one example, the intermediate layer stack includes HfOx, or a HfOx material that is doped with Si, Al, Y, N, Zr, or Sr. In another example, the intermediate layer stack includes a scandium (Sc) containing material, or scandium material doped aluminum nitride (AlNx).
The 3D NAND memory structure 100 may also include a source region 212, which may be part of a CSL (e.g., 103) and a drain region 214 which may be part of a plurality of bit lines 118. The first channel 208 extends between the source region 212 and the drain region 214 perpendicular (e.g., −Z-direction) to a major surface of the substrate 101. The second channel 210 also extends between the source region 212 and the drain region 214 perpendicular (e.g., −Z-direction) to a major surface of the substrate 101. The ONO layer stack will also extend between the source region and the drain region perpendicular (e.g., −Z-direction) to a major surface of the substrate 101.
The channel structures 117 and ONO layer stack 206 of the 3D NAND memory structure 100 may be symmetrical across the axis of symmetry (AS), as depicted in
The portion 300 also includes a dielectric filler layer 302 that is disposed within the channel structure 117. The filler layer 302 can be used to balance the cross-sectional area ratio (X-Y plane) between the first channel 208 and the second channel 210 and in this way to adjust the voltage/capacitance divider which may be used as a design rule. The filler layer 302 material may include silicon dioxide (SiO2), aluminum oxide (Al2O3), silicon nitride (SiN), silicon oxycarbide (SiOxCy), or another suitable material. The portion 300 may be symmetrical across the axis of symmetry (AS), as depicted in
The method 600 assumes that a memory gate stack and channel structure 117 is ready to be formed in a 3D NAND memory structure 100. The preparation for the formation of a channel structure 117 may include forming a plurality of openings (e.g., memory holes) that extend from a CSL 103 through a plurality of alternating layers 125 perpendicular (e.g., −Z-direction) to a major surface of the substrate 101.
At activity 602 a first dielectric layer 206a (
At activity 604, a charge trap layer 206b (
At activity 606, a second dielectric layer 206c (
At activity 608, as shown in
In some embodiments, the method 600 may optionally include an etching process to remove portions of the deposited dielectric layers in the ONO layer stack 206, such as layers 206a, 206b, 206c, after performing activities 602-604 in order to remove the portions of the layers 206a, 206b, 206c from the bottom of the plurality of openings and allow the subsequently deposited first channel 208 to contact the source region 212 (N+ source layer) after performing activity 608. The etching of the bottom portion of the layers 206a, 206b, 206c will be performed before the deposition of the first channel layer 208 in activity 608, and may involve a sputter etching process, a wet etch, and/or a chemical dry etch.
At activity 610, a second channel layer 210 (
In some embodiments, at least a portion of the first channel layer 208 and a portion of the second channel layer 210 formed within the opening 3D NAND memory structure 100 are coupled to the source region 212 layer and the first channel layer 208 and the second channel layer 210 are coupled to the drain region 214 layer.
In some embodiments, depositing the first channel layer 208 in the plurality of openings in the 3D NAND memory structure 100 may include depositing material on the side walls of the plurality of openings, as well as the bottom of the plurality of openings. In some embodiments, the method 600 may optionally include an etching process to remove a portion of the first channel layer 208 formed at the bottom of the plurality of openings in order to remove the portion of the first channel layer 208 from the bottom plurality of openings and allow a portion of the second channel 210 to contact the source region 212 (N+ source layer) after deposition. The etching of the portion of the bottom of the channel layer 208 can occur before the deposition of the second channel layer (e.g., 210) in activity 610, and may involve a sputter etching process, a wet etch, and/or a chemical dry etch.
Optionally, as shown in
The filler layer 302, such as an oxide layer, can be deposited using any suitable deposition processes and/or apparatus. For example, physical vapor deposition (PVD), atomic layer deposition (ALD) or chemical vapor deposition (CVD) may be used to deposit the first and second channel layers 208, 210, the ONO layer stack 206, and the filler layer 302. Alternatively or additionally, a stand-alone apparatus or a cluster tool can be used to perform an atomic layer deposition (ALD) process. Exemplary apparatus that can be configured for performing the above process include, for example, the OLYMPIA line of ALD apparatus, available from Applied Materials, Inc.
After performing the activities of method 600 on a portion (e.g., 200, 300, 700, 800, 900, 1000) of the 3D NAND memory structure 100, additional conventional processing steps will be performed on the portion of the 3D NAND memory structure 100 to complete the formation of a functioning 3D NAND device. For example, one processing step could include forming the drain region 214 and a plurality of bit lines 118 on top of the plurality of openings in the 3D NAND memory structure 100, as described herein with respect to
In one embodiment, which can be combined with other embodiments described herein, the high mobility channel layer and/or the low or lower mobility channel layer used to form either of the layers within the multi-layer stack, such as the first and second channel layers 208, 210, will include indium (In), zinc (Zn), gallium (Ga), oxygen (O), tin (Sn), aluminum (Al), and/or hafnium (Hf). Examples of the high mobility channel layer include, but are not limited to, InGaZnO, InGaO, InZnO, InGaSnO, InZnSnO, InGaZnSnO, InSnO, HfInZnO, GaZnO, InO, IWO, AlSnZnO, ZnO, ZnSnO, AlZnO, AlZnSnO, HfZnO, SnO, and AlSnZnInO. Examples of the low or lower mobility channel layer include, but are not limited to, InGaZnO, GaO, InGaO, ZnSnO, InSnO, HfInZnO, AlSnZnO, ZnO, AlInZnSnO, and AlSnZnO.
In some embodiments, the material of the high mobility channel layer and the low mobility channel layer includes the same elements, but the stoichiometry of the material differs. For example, InGaZnO is a multi-component amorphous oxide semiconductor (AOS) system. InGaZnO typically shows mobility values of about 10 cm2N·s with 1:1:1 ratios of InO, GaO, and ZnO, but it is also possible to achieve mobility larger than 10 cm2N·s by increasing In and/or reducing Ga compositions from InGaZnO AOS systems. Therefore, mobility is adjustable by changing the compositions of components in AOS systems. ZnO or InO without Ga in AOS systems allow higher mobility (higher carrier concentration), but it can be difficult to obtain an amorphous phase. However, binary components such as ZnInO or ZnGaO can form amorphous phases due to changing composition of ZnO and InO. For high mobility (>20 cm2N·s) AOS, it is possible to increase carrier concentration by increasing the composition of In and/or decreasing the composition of Ga from multi-component AOS systems. Thus, in one embodiment, the low mobility channel layer includes InGaZnO, the high mobility layer includes InGaZnO, and the high mobility channel layer has a higher composition of In than the low mobility channel layer. In another embodiment, the low mobility layer includes InGaZnO, the high mobility channel layer includes InGaZnO, and the high mobility channel layer has a lower composition of Ga than the low mobility channel layer. In yet another embodiment, the low mobility layer includes InGaZnO, the high mobility channel layer includes InGaZnO, the high mobility channel layer has a higher composition of In than the low mobility channel layer, and the high mobility channel layer has a lower composition of Ga than the low mobility channel layer.
It is to be understood that the composition of In, Ga, Zn, and O can easily change electron transport properties (e.g., mobilities). For example, electron transport properties (e.g., mobilities) of In2O3Ga2O3ZnO (InGaZnO) thin films are determined by the composition of In2O3, Ga2O3, and ZnO by changing X, Y, and Z, where X is defined by [(ZnO)x(Ga2O3)1-x] mol %, Y is defined by [(Ga2O3)y(In2O3)1-y] mol %, and Z is defined by (In2O3)z(ZnO)1-z] mol %. In the InGaZnO system, it is generally understood that the In atoms contained therein act as In3+ ions that form electron pathways, which leads to high electron mobility. In addition, it is understood that Zn atoms contained therein act as Zn2+ ions that prefer tetrahedral coordination, which increases stability of an amorphous phase of InGaZnO. Finally, it is understood that Ga atoms contained therein act as Ga3+ ions that suppress carrier generation due to the high ionic field strength of the Ga3+ ions. Ga3+ ions form stronger chemical bonds with oxygen (O) atoms than the Zn and In atoms, due to O vacancy formation. Thus, increasing the Ga percentage leads to low mobility and/or carrier concentration, and thus a layer containing high Ga percentage leads to a low off current and large on/off current ratio. Additionally, in some embodiments, incorporation of tin (Sn) into the mixture can improve the stability and reliability due to the better bonding of oxygen.
If X=Y=Z=0.5, InGaZnO allows a mobility of about 9 cm2/Vs. Higher mobility can be controlled by decreasing Ga and increasing In. For example, if X=1, Y=0, Z=1, the composition is InO. If X=1, Y=0, Z=0, the composition is ZnO. However, InO and ZnO form a crystalline phase. If X=1, Y=0, 0<Z<1, the composition is InZnO. Therefore, InZnO has an amorphous phase and mobility larger than about 50 cm2V-s, which can be the material of the high mobility channel layer. InGaZnO has an amorphous phase and lower mobility less than about 20 cm2V·s, which can be the material of the low mobility channel layer.
The amorphous oxide semiconductor (AOS) systems can include InGaZnO, or other AOS including InZnO, ZnSnO, InGaO, InZnO, InGaSnO, InZnSnO, InGaZnSnO, InSnO, HfInZnO, GaZnO, InO, InWO, AlSnZnO, ZnO, ZnSnO, AlZnO, AlZnSnO, HfZnO, SnO, AlSnZnInO, and the like.
The methods and apparatus described herein can be used to form an improved planar or vertical or even 3D memory device structure. The multi-layer channel comprising two or more layers having differing materials described herein may allow for more area and multiple pathways for the current, and may transport larger total current through both the low mobility and the high mobility channel layers due to higher carrier density in the high mobility channel layer and carrier injection which acts as a positive feedback. Moreover, the use of a multi-layer channel may also allow for the utilization of channel materials other than polysilicon and 3D memory devices, which may decrease the variability of the stored state in 2D and 3D memory devices and those devices in general. The improved planar, vertical or 3D memory device structure may enable an increased memory density through the creation of more memory stacks (3D stacking) or strings (in 3D NAND architectures) and tighter distribution of the stored state, due to the minimization of the main scattering mechanisms which skews/broadens the bit distribution.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims the benefit of and priority to U.S. Provisional Application 63/343,086 filed on May 17, 2022, which is herein incorporated by reference.
Number | Date | Country | |
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63343086 | May 2022 | US |