Selective deposition of SiN on horizontal surfaces

Methods and apparatuses for selectively depositing silicon nitride (SiN) via high-density plasma chemical vapor deposition (HDP CVD) to form a SiN pad on an exposed flat surface of a nitride layer in a 3D NAND staircase structure with alternating oxide and nitride layers are provided. In some embodiments, selective etching is performed to remove undesirable buildup of SiN on sidewalls of the oxide layers of the staircase structure. Nitride layers of the staircase structure are replaced with tungsten (W) to form tungsten wordlines, while the SiN pads are replaced with tungsten to from landing pads, which prevent punchthrough of the tungsten wordlines on the staircase structure by interconnects extending thereto.

BACKGROUND

Semiconductor device fabrication involves fabrication of flash memory. As devices shrink, structures for fabricating efficient and multiple memory cells are used to maximize density of memory cells in a memory device. 3D NAND technology addresses challenges associated with two-dimensional NAND technology by stacking memory cells vertically in layers.

SUMMARY

Methods and apparatuses for processing semiconductor substrates are provided herein. One aspect of the disclosure involves a method of processing a semiconductor substrate for fabricating a 3D NAND structure, the method involving providing a substrate having alternating oxide layers and nitride layers arranged in a staircase pattern. Each of the nitride layers has an exposed horizontal surface. Prior to depositing an oxide filler over the staircase pattern, silicon nitride (SiN) is deposited via high-density plasma chemical vapor deposition (HDP CVD) over both the oxide layers and nitride layers. The SiN is deposited selectively on the exposed horizontal surfaces of the nitride layers relative to oxide sidewall surfaces at each layer to form SiN pads.

The deposition of SiN via HDP CVD may involve simultaneously depositing SiN on the exposed horizontal surfaces of the nitride layers to form the SiN pads, while selectively etching SiN deposited on sidewalls of the oxide layers of the staircase pattern relative to the SiN pads. Further, the exposed horizontal surfaces of the nitride layers may be exposed, at each layer, to deposition chemistry to form the SiN pads. Also, sidewalls of the oxide layers of the staircase pattern may be exposed to an etchant to selectively etch SiN deposited on the sidewalls relative to the SiN pads.

Alternatively, in some embodiments, the exposed horizontal surfaces of the nitride layers may be exposed, at each layer, to deposition chemistry prior to the exposure of the oxide layers of the staircase pattern to the etchant. The etchant may comprise plasma species generated from hydrogen gas (H2) or a fluorine-containing gas. In some embodiments, transitioning from depositing SiN to selectively etching SiN deposited on the sidewalls of the oxide layers may involve lowering a bias applied to a pedestal holding the substrate.

In some embodiments, depositing SiN via HDP CVD may involve flowing a silicon-containing reactant and a nitrogen-containing reactant to a HDP CVD chamber.

In some embodiments, the nitride layers may be replaced with tungsten (W) wordlines. The SiN pads may be replaced with tungsten landing pads. Further, after depositing SiN via HDP CVD over the exposed surfaces of the nitride layers, the oxide filler may be deposited over the staircase pattern. The oxide filler may be etched to form vertical vias in the oxide filler. The vertical vias may extend to the tungsten wordlines. The oxide filler may be etched selectively relative to the tungsten landing pads. Tungsten may be deposited in the vias to form interconnects which extend to the wordlines. The tungsten landing pads may be positioned on the wordlines to protect against punchthrough of one or more of the wordlines by one or more of the vias.

In some embodiments, SiN deposited on sidewalls of the oxide layers of the staircase pattern may be selectively etched while leaving deposition of SiN on horizontal surfaces substantially intact.

Another aspect of the disclosure involves a method for processing a substrate with nitride layers positioned between oxide layers forming a staircase structure. Portions of the nitride layers are exposed. SiN deposited from a silicon-containing reactant and a nitrogen-containing reactant through high-density plasma chemical vapor deposition (HDP CVD) may be deposited on flat surfaces of the exposed portions of the nitride layers while a bias is applied to the substrate. Material deposited on sidewalls of the oxide layers of the staircase structure may be removed by etching the material deposited on the sidewalls selective to material deposited on flat surfaces of the exposed portions of the nitride layers. In some embodiments, depositing of the silicon-containing reactant and a nitrogen-containing reactant may be anisotropic. Further, etching material deposited on the sidewalls may involve exposing the sidewalls to plasma species generated from hydrogen gas or a fluorine-containing gas. Still further, depositing and removing material deposited on the sidewalls may be performed either simultaneously or sequentially.

Another aspect involves an apparatus for processing a substrate. The apparatus may include a reactor containing a process chamber. A plasma source may be in fluid communication with and be coupled with the process chamber. A substrate pedestal may be positioned within the process chamber. The substrate pedestal may receive electrical energy provided by an electrode coupled with the substrate pedestal. One or more gas inlets may open into the process chamber and have flow-control hardware associated with the gas inlets. Process gases may be introduced into the process chamber by the gas inlets. A controller may be configured to control the reactor. The controller has a processor and a memory. The processor and the memory are communicatively connected with one another. The processor is at least operatively connected with the flow-control hardware, and the memory stores computer-executable instructions for controlling the processor to at least control the flow-control hardware by: (a) inletting the process gases to the process chamber, the process gases comprising: a silicon-containing reactant; a nitrogen-containing reactant, and hydrogen gas, wherein the ratio of hydrogen gas to the silicon-containing precursor is at least 1:2, (b) applying a bias to the electrode during (a); (c) after (a), lowering the bias applied to the electrode; and (d) during (c), inletting hydrogen (H2) gas or fluorine-containing gas.

These and other features will be described below with reference to the associated drawings.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide an understanding of the presented embodiments. The disclosed embodiments may be practiced without some or all of these specific details. In other instances, well-known process operations have not been described in detail to not obscure the disclosed embodiments. Further, while the disclosed embodiments will be described in conjunction with specific embodiments, it will be understood that the specific embodiments are not intended to limit the disclosed embodiments.

The implementations disclosed below describe deposition of a material on a substrate such as a wafer, substrate, or other work piece. The work piece may be of various shapes, sizes, and materials. In this application, the terms “wafer” and “substrate,” are used interchangeably.

Semiconductor fabrication often involves fabrication of memory devices. One example is fabrication of a 3D NAND, also referred to as a “vertical NAND” (VNAND), structure. However, existing techniques for forming 3D NAND structures are limited for scaling to smaller devices, and currently available patterning techniques may cause undesirable degradation of various components in the 3D NAND structure.

In current 3D NAND technology, vias may be formed in an oxide filler deposited over alternating oxide and nitride layers that are arranged in a staircase pattern. The vias extend vertically to contact exposed tungsten wordlines, which replace the nitride layers. Metal, such as tungsten, is deposited in the vias to form interconnects which extend to and contact the tungsten wordlines. However, maintaining a sufficient stop distance between various interconnects and their corresponding wordlines may prove difficult, given the variance in height of each layer of wordline relative to the interconnect. Thus, the time required for filling the longest of the interconnects to make to contact with a wordline on a base layer of the staircase pattern may result in inadvertent and undesirable “punchthrough” of shorter interconnects through wordlines positioned higher up on the staircase pattern and into the oxide layers positioned beneath the wordlines. Thus, contact surfaces on wordlines located at higher positions on the staircase may be over-etched relative to wordlines located toward the bottom of the staircase pattern.

Further, increasing the height or number of alternating oxide and nitride layers in a 3D NAND structure may also prove challenging since the height of the alternating layer stack may cause substantial etch and bow issues. To mitigate the impact of etch and bow issues resulting from tall 3D NAND structures, the thickness of each oxide layer or nitride layer may be reduced. However, doing so may further worsen the punchthrough issue described above.

Other remedies to address the above-discussed issues include increasing the contact mask and etch operations, such that over-etch on locations higher on the staircase pattern may be minimized, yet doing so often increases cost and degrades yield.

Alternatively, an etch stop layer may be added over the staircase pattern to address the punchthrough issues described above. However, an etch stop layer that is highly selective may also be selective in the area where the vias are etched, and thus unintentionally block nitride layer removal in the staircase pattern near or within the via area.

Disclosed methods and apparatuses configured to implement the methods provide for the deposition of silicon nitride (SiN) at selected exposed portions of each nitride layer of a staircase pattern to form SiN pads thereon. In some embodiments, the methods include an in situ etch within a high density plasma chemical vapor deposition (HDP CVD) tool. Advantages associated with using HDP CVD to deposit SiN include thin inadvertent sidewall deposition coverage in comparison to other deposition methods. Further, exposure of the SiN pads to etchants, such as etchants generated from hydrogen-containing or fluorine-containing species, delivered isotropically, may remove SiN deposited on sidewalls of the staircase pattern while leaving SiN deposited on horizontal surfaces intact. In some embodiments, SiN deposition may be completed as a single operation, thus minimizing costs and process cycle time. While the methods and tools below are described in the context of forming SiN pads on nitride layers in a 3D NAND structure, they may be employed in any application where selective SiN deposition on horizontal surfaces is sought.

FIG. 1shows a process flow diagram of operations performed in accordance with a method for forming a 3D NAND structure. In operation182, a substrate is provided. In various embodiments, the substrate is a semiconductor substrate. The substrate may be a silicon wafer, e.g., a 200-mm wafer, a 300-mm wafer, or a 450-mm wafer, including wafers having one or more layers of material, such as dielectric, conducting, or semi-conducting material deposited thereon. An example substrate100is provided as a schematic illustration inFIG. 2.

Returning toFIG. 1, in operation184, a film stack of alternating oxide and nitride films is deposited on the substrate. In various embodiments, the oxide layer deposited is a silicon oxide layer. In various embodiments, the nitride layer deposited is a silicon nitride layer.

Each oxide and nitride layer may be deposited to about the same thickness, such as between about 10 nm and about 100 nm, or about 350 nm in some embodiments. The oxide layers may be deposited at a deposition temperature of between about room temperature and about 600° C. It will be understood that “deposition temperature” (or “substrate temperature”) as used herein refers to the temperature that the pedestal holding the substrate is set to during deposition.

Oxide and nitride layers for forming the alternating oxide and nitride film stack may be deposited using any suitable technique, such as atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), or sputtering. In various embodiments, the oxide and nitride layers are deposited by PECVD.

The film stack may include between 48 and 512 layers of alternating oxide and nitride layers. Each oxide or nitride layer constitutes one layer. The film stack including the alternating oxide and nitride layers may be referred to as an oxide-nitride-oxide-nitride (ONON) stack.

FIG. 3shows an example schematic illustration of a substrate100with alternating oxide101and nitride102films deposited on the substrate100. Note that while the structure shown inFIG. 3shows an oxide deposited first, followed by nitride, oxide, nitride, etc., nitride may be deposited first, followed by oxide, nitride, oxide, etc.

Following deposition of the ONON stack, one or more channels (not shown inFIG. 3) may be etched in the substrate. Subsequently, referring toFIG. 1, in operation186, a staircase pattern is formed on the substrate. A “staircase pattern” as referred to herein describes two or more steps, each step including an oxide layer and a nitride layer. It will be understood that the top layer of each set of oxide and nitride layers may be either an oxide layer or a nitride layer for formation of steps in a staircase. In various embodiments, the staircase pattern includes between 24 and 256 steps. The staircase pattern may be formed using a variety of patterning techniques. One technique may include depositing a sacrificial layer over the substrate and masking regions of the substrate to etch each set of oxide and nitride layers to form the staircase.

FIG. 4Aprovides an example of a substrate100including a staircase pattern of oxide layers111and nitride layers112with a hardmask110over the topmost nitride layer. AlthoughFIG. 4Ashows four steps of a staircase pattern, it will be understood that a staircase pattern may have any number of steps, such as between 24 and 256 steps. Each step includes a nitride layer and an oxide layer. The region of each step extending out from the edge of the step above it may be referred to as an “exposed” region of the step or topmost layer of the step, or portion suitable for deposition thereon.

A view199of the staircase pattern shown inFIG. 4Abisected across, for example, a width-wide direction of the staircase, is shown inFIG. 4Bto highlight the tiered structure of the staircase pattern. Oxide layers111are positioned parallel to, and in between, nitride layers112. Each set of one oxide layer111followed by one nitride layer112is longer than the set immediately above it, thus forming the staircase pattern with exposed regions.

In some embodiments, in operation188ofFIG. 1, oxide is deposited over the substrate. The oxide may be of the same or of different composition as the oxide deposited in layers of the ONON stack. In various embodiments, the oxide deposited over the substrate is deposited at the same or a different deposition temperature than the deposition temperature used for depositing the oxide layers in the ONON stack. The deposition temperature may be between room temperature and about 600° C. Vertical slits may be subsequently etched into the substrate after depositing oxide.

FIG. 5Ashows an example substrate100including the ONON staircase, hardmask110, and oxide122deposited over the substrate.FIG. 5Bshows a side view of the substrate100after vertical slits135are etched and the hardmask110is removed.

In operation190, nitride is selectively etched relative to oxide on the substrate. Etching may be performed using a selective dry etch process, such as by exposing the substrate to any one or more of the following gases: chlorine (Cl2), oxygen (O2), nitrous oxide (N2O), tetrafluoromethane (CF4), sulfur tetrafluoride (SF4), carbon dioxide (CO2), fluoromethane (CH3F), nitrogen trifluoride (NF3), nitrogen (N2), hydrogen (H2), ammonia (NH3), methane (CH4), sulfur hexafluoride (SF6), argon (Ar), carbonyl sulfide (COS), carbon disulfide (CS2), hydrogen sulfide (H2S), and nitric oxide (NO). The operation190removes the nitride layers from the ONON stack such that etch species flow into vertical slits formed in the staircase pattern and selectively etches nitride. It will be understood that the selective etching involves etching a first material at a rate faster than etching a second material. For example, selectively etching nitride relative to oxide means nitride is etched at a faster rate than etching of oxide. Nitride can also be selectively etched using a wet etch process, such as by exposing the substrate to phosphoric acid (H3PO4), diluted hydrofluoric acid (“DHF”) or a mixture of these solutions. However, selectively removing nitride poses a risk for degradation and removal of oxide material at various interfaces, such as at the oxide-oxide interface at the end of each staircase. This is described further below with respect toFIG. 6A.

FIG. 6Ashows an example schematic illustration of a substrate100with horizontal gaps132formed from etching the nitride layers112. As shown in the enlarged view depicted in the circle at170, a gap134may form at the oxide-oxide interface due to the etching species flowing into the gaps132and etching away at the oxide during the etching operation.FIG. 6Bshows a side view of a cross-section of the substrate whereby gaps132are formed from selectively etching nitride.

Returning toFIG. 1, in operation192, tungsten is deposited into the gaps of the substrate to form tungsten wordlines. Tungsten may be deposited by any suitable technique, such as ALD, CVD, PEALD, and PECVD. In some embodiments, one or both of a barrier layer or a tungsten nucleation layer is deposited prior to depositing bulk tungsten.FIG. 7Ashows an example of a substrate100including deposited tungsten wordlines140. However, due to the degradation of the oxide at the oxide-oxide interface as shown in the zoomed-in view at170, tungsten fills in the gap at141, thereby connecting two wordlines140, which can cause a short.FIG. 7Bshows a schematic illustration of the substrate in7A at a cross-section from a side view with tungsten140deposited in the gaps where nitride was located previously.

Returning toFIG. 1, in operation194, the oxide is vertically etched to form vias. The oxide may be etched by dry etching using exposure to an etchant such as one or more of the following gases: O2, Ar, C4F6, C4F8, SF6, CHF3, and CF4.FIG. 8shows an example substrate100including the ONON stack in a staircase pattern whereby vias137are etched in the oxide122. However, due to the relative thinness of the tungsten wordline layer, and the lengthy duration of etching used to ensure sufficient vertical etching to etch the deepest vias (e.g.,137b), etching species flows into the vias (e.g.,137a) that are etched for the shallow parts of the oxide, to thus etch through the tungsten layer136and even etching through another oxide layer138. As discussed earlier, such a phenomenon is typically undesirable and referred to as “punchthrough,” or “breakthrough,” to the layers positioned beneath the intended tungsten wordline contact point or layer.

InFIG. 1, in operation196, tungsten is deposited in the vias to form interconnects to the tungsten wordlines. However, as shown inFIG. 9, since the shallow vias caused breakthrough to the layers below due to the duration used to etch the deep vias, tungsten fills the vias (see filled tungsten via142) and causes a short as circled in172ofFIG. 9. Vias vary in depth and may have a depth between about 1 micron and about 12 microns. Shallow vias may be defined as having a depth less than 3.0 microns, such as between about 1.5 microns and 3.0 microns. Deep vias may have a depth greater than 3.0 microns. The critical dimension of vias formed in the oxide may be between about 50 nm and about 500 nm. Vias may be etched using a dry etch process which may involve masking operations to pattern the oxide.

Conventional techniques for forming 3D NAND structures result in degradation at the oxide-oxide interface during selective removal of nitride and punchthrough of tungsten wordlines when etching vias of different depths. Typically, extensive etching techniques performed use a variety of chemistries and patterning processes to mask regions of the substrate to etch vias of different depths using different chemistries and process conditions. Such processes reduce throughput and reduce efficiency of fabrication processes.

Provided herein are methods and apparatuses for forming 3D NAND structures without degrading oxide-oxide interfaces. The methods and apparatuses avoid punchthrough of a tungsten wordline by depositing silicon nitride (SiN) on exposed horizontal portions of nitride layers of the staircase pattern to form SiN pads. Each SiN pad may be formed with a defined height or thickness. The deposition of SiN on exposed horizontal portions of the nitride layers is selective relative to exposed sidewalls of the oxide layers of the staircase pattern. Material deposited inadvertently on exposed sidewall surfaces of the oxide layers may be etched by an isotropic sidewall removal process. Etchants generated from hydrogen-containing or fluorine-containing gases, such as H2(gas) or NF3(gas), respectively, are delivered to a reaction process chamber housing the 3D NAND structure. Selective deposition of SiN and anisotropic etching of SiN may be performed as sequential processes with deposition occurring prior to etching, or performed as concurrent processes. The nitride layers of the staircase pattern, along with the SiN pads formed on each nitride layer, are etched selective to the oxide layers to form horizontal gaps and vacant regions corresponding to the locations of the SiN pads. Tungsten fills the horizontal gaps and vacant regions to form tungsten wordlines and landing pads on the wordlines. Each of the landing pads has a sufficient thickness to function as an etch stop layer or a protective barrier to prevent an interconnect from punching through the tungsten wordline.

FIG. 10is a process flow diagram of operations for a method performed in accordance with some embodiments. That shown inFIG. 10results in the formation of landing pads at operation1092. The thickness of each of the landing pads provides ongoing protection against punchthrough of interconnects through wordlines that are also formed with the landing pads at operation1092. In some embodiments, operations1002and1004may be the same as, or similar to, operations182and184presented earlier inFIG. 1, respectively. In operation1006, a staircase pattern is formed on the substrate. Operation1006may be the same as or similar to operation186ofFIG. 1as described above.

In operation1008a, prior to depositing oxide over the staircase pattern in operation1010, SiN is directionally deposited on exposed horizontal surfaces of the nitride layers, at each nitride layer, of the staircase pattern by high-density plasma chemical vapor deposition (HDP CVD). The deposition is conducted selectively relative to exposed sidewall surfaces of the oxide layers. Under optimal operational conditions, selective deposition will result in no SiN being deposited on the exposed sidewall surfaces of the oxide layers. Thus, SiN material is deposited on exposed horizontal surfaces of each of the nitride layers to form SiN pads thereon, where each of the SiN pads may have a defined height.

The selective deposition of SiN inFIG. 10is performed by HDP CVD using silicon-containing reactants and nitrogen-containing co-reactants. Examples of silicon-containing reactants include silane (SiH4) and disilane (Si2H6). Examples of nitrogen-containing co-reactants include molecular nitrogen (N2) and ammonia (NH3).

The silicon-containing reactants and nitrogen-containing co-reactants may be flowed into a reaction process chamber in a HDP CVD process apparatus to react to form SiN for deposition as needed at operation1008a. SiN may be deposited at a suitable deposition temperature between about 100° C. and about 700° C., or between about 150° C. and about 400° C., such as at about 400° C. Example chamber pressures may be between about 1 Torr and about 10 Torr, or between about 1.5 Torr and about 7 Torr. Although directional in nature to target exposed horizontal surfaces of the nitride layers, the deposition conducted in operation1008amay, in some embodiments, result in some SiN material being deposited on exposed, vertically oriented, sidewall surfaces of the oxide layers. Etchant species may be flowed into the deposition chamber, either concurrently with the deposition described in operation1008a, or sequentially after the completion of the deposition, to isotropically etch SiN deposited on the exposed sidewalls surfaces as described at operation1008b, and as shown inFIGS. 12 through 14B. Process conditions for etching may include, in some embodiments, any of those described earlier with respect to operation190ofFIG. 1, or as that described above for deposition as conducted in operation1008a. In some embodiments, SiN deposited on the exposed sidewall surfaces of the oxide layers is removed entirely, or in sufficient amount, that it does not form a continuous film to prevent an electrical short between tungsten wordlines layers upon a tungsten gap-fill at operation1092, to be described in further detail below.

After operations1008aand1008b, oxide, also referred to as oxide filler, is deposited over the staircase pattern, including the SiN pads formed on the nitride layers at operation1010. At operation1012the nitride layers with SiN pads extending from each nitride layer are selectively etched relative to the oxide layers and oxide filler to create horizontal gaps between the oxide layers in the staircase pattern, similar to that shown inFIGS. 6A and 6B. The horizontal gaps are later filled with tungsten at operation1014through a gap-fill operation to form tungsten wordlines and to replace the SiN pads with landing pads comprising tungsten. The landing pads are formed on the wordlines as shown inFIG. 14B, e.g., landing pads182formed on wordlines140. This operation may be performed using any technique or process condition as described above with respect to operation192ofFIG. 1. The vacant regions created from etching the SiN pads are filled with tungsten during operation1092during the formation of the tungsten wordlines to form landing pads on the tungsten wordlines.

The oxide122is then etched to form vias in operation1016. For example, a via is etched vertically through the oxide, e.g. similar to that shown inFIG. 8, to contact and end at a landing pad extending from a wordlines. Accordingly, multiple vias extend to each of the landing pads formed on the staircase pattern. Formation of longer vias to contact wordlines near the bottom of the staircase pattern may require a relatively longer etch duration compared to the time needed to form shorter vias to contact wordlines near the top of the staircase pattern. Accordingly, an extended etch duration needed to form long vias that extend to wordlines near the bottom of the staircase pattern may result in vias intended to contact wordlines at the top of the staircase pattern punching through such wordlines. The process shown inFIG. 10protects against such punchthrough of vias through wordlines, e.g., wordlines located near the upper layers of the staircase pattern, by forming a landing pads on each wordline. Each landing pad provides additional material through which a given via must penetrate prior to punching through the wordline upon which the landing pad is formed.

At operation1018, tungsten is deposited into the vias to form interconnects that extend through the oxide filler to contact the landing pads. In addition to providing protection against punchthrough of vias through wordlines, the landing pads also protect against punchthrough of interconnects through the wordlines as well at operation1020.

The method described with reference toFIG. 10is further illustrated and described in connection withFIGS. 11 through 15. First, turning toFIG. 11, undesirable SiN accumulations172are shown. The accumulations172can result from conformal or non-directional nitride-on-nitride deposition at regions124on the alternating nitride layers112of the staircase pattern. As shown in the enlarged circular region170ofFIG. 11, the accumulations172may be irregular in shape or size due to imperfections in the deposition process and extend over a given nitride layer112toward another accumulation172on the nitride layer beneath as shown beneath region124. These irregular deposition patterns may crowd area126located between the alternating nitride layers112, making filling area126with oxide122more difficult. Further, in some embodiments, irregularities in deposition of nitride at accumulations172may lead to contact (not shown in the enlarged region170) of an accumulation172formed on a given nitride layer112to another accumulation172deposited on the nitride layer112, which may lead to a short when the nitride layers112are later replaced with tungsten wordlines140, potentially rendering the 3D NAND device unusable. Further, possible deposition of nitride on exposed oxide layer sidewalls may also contribute to a short between the alternating wordlines140(not shown inFIG. 11).

To avoid potential contact of accumulations172on nitride layers112as shown inFIG. 11and discussed above, and to achieve a desirable nitride deposition pattern, HDP CVD is conducted to deposit SiN at exposed regions174on the alternating nitride layers112to form SiN pads182as shown inFIG. 12.

HDP CVD as used herein is distinct from plasma-enhanced chemical vapor deposition (PECVD) processes. Inductively coupled HDP CVD process conditions and resulting films are different from capacitively-coupled PECVD processes. For example, various HDP reactors as described herein operate at a pressure less than about 100 mTorr, with a plasma density greater than 1011ions/cm3. HDP reactors may ignite plasma at a plasma frequency of 400 kHz for coils and a frequency of 13.56 MHz for the pedestal where the wafer is placed. In a capacitively-coupled plasma reactor, a plasma frequency of 13.56 MHz is used to generate plasma as applied to either a showerhead or the pedestal, and 400 kHz is applied to either the showerhead or the pedestal. Ion energies in HDP reactors may be greater than in PECVD reactors. As a result, film composition and characteristics of films deposited in HDP CVD reactors are different than those deposited in PECVD reactors.

As introduced and discussed in operations1008aand1008binFIG. 10, SiN to be deposited to form SiN pads182on exposed horizontal nitride surfaces174, as shown inFIG. 12, may be formed by flowing a silicon-containing precursor and a nitrogen source into an HDP CVD chamber. An example of a silicon-containing precursor is silane (SiH4). Examples of nitrogen sources are nitrogen gas (N2) and ammonia (NH3).

In some embodiments, HDP CVD may be conducted to target exposed horizontal surfaces174on nitride layers112of the staircase pattern to deposit SiN thereon. Thus, one SiN pad182is formed on each exposed horizontal surface174of the staircase pattern as shown inFIG. 12. In some embodiments, HDP CVD is conducted to deposit SiN such that the depth of the SiN pads is approximately half of each nitride layer of the alternating nitride layers112, each nitride layer being approximately 25 nm to 35 nm thick. Thus, in some embodiments, the SiN pads182will have a height176ranging from 13 nm to 18 nm. However, deposition processes conducted via HDP CVD still may result in some potential undesirable SiN deposition, on exposed oxide layer sidewalls128, as shown inFIG. 12, potentially leading to a short between alternating wordlines140.

To address SiN deposition on oxide layer sidewalls128, an isotropic etch is performed to etch SiN deposited on the sidewalls128at regions130, as shown inFIGS. 12 and 13. In some embodiments, various gases may be flowed to a plasma generator responsible for forming etchant species, including radicals, such as atomic fluorine, fluorine (F) ions, or molecular fluorine (F2). Such gases may include one or both of a hydrogen-containing gas, e.g., H2or NH3, and a fluorine-containing gas, e.g., F2or NF3, which form etchant species that are delivered to a reaction chamber to selectively etch SiN deposited on sidewalls128of oxide layers111at regions130. Etch is performed relative to the SiN pads182formed on exposed horizontal surfaces174of nitride layers112to remove some or all SiN buildup on sidewalls128, as shown inFIGS. 14A, 14B, and 15, to thus reduce or eliminate the possibility of a short between wordlines140, e.g. when the nitride layers112are replaced with tungsten (W) to form wordlines140.

Fluorine-containing plasmas etch nitrides selectively relative to oxides and may be used in some embodiments to etch SiN nitride deposited on sidewalls128. In some embodiments, sidewalls128may be removed via an isotropic hydrogen (H2) gas etch to retain SiN deposited on surfaces174to form SiN pads182, as shown inFIG. 13. However, inclusion of oxygen O2gas during any etch process (e.g., fluorine (F)-based or hydrogen (H)-based) is undesirable as application of O2may convert exposed nitride surfaces174to oxide surfaces to thus potentially reduce the etch rate.

Variance in temperature within the reaction chamber used to conduct etch processes may influence the etch rate. Etch processes may be conducted at, or very close to, deposition temperature, namely from approximately 80° C. to 150° C., where substantial variance in process chamber temperature may influence etch results. Moreover, bias may be applied to the substrate100to attract etchant species to deposited SiN material.

Operations1008aand1008bas shown inFIG. 10, namely the selective deposition of SiN to form SiN pads182and the isotropic etch of SiN deposited on sidewalls128, may be performed sequentially, with deposition at operation1008aoccurring before etch at operation1008b, or concurrently as shown inFIG. 10. For concurrent applications, deposition chemistry and etch chemistry may be concurrently flowed into a reaction process chamber to deposit SiN on exposed surfaces of nitride layers112to form one SiN pad182on each nitride layer112, while concurrently selectively etching SiN deposited on sidewalls128of the oxide layers111. Also, in some embodiments, deposition and etch processes may occur only once, that is, such processes are not intended to be cyclical.

Deposition of SiN on exposed horizontal surfaces174to form SiN pads182with concurrent isotropic etch of SiN deposited on the sidewalls128, has various advantages. For instance, total process completion time may be reduced. In some embodiments, gases used to generate suitable etchant species include hydrogen or ammonia. Flourine-containing gases are generally not used during deposition. Also, in some embodiments, the ratio of the amount of silicon-containing precursor and hydrogen-containing etchant may be controlled to conduct deposition concurrently with etch of SiN deposited on the sidewalls128. NH3may be used to supply nitrogen, for SiN formation, as well as hydrogen, for the concurrent etching of SiN deposited on the sidewalls128. Alternatively, in some embodiments, fluorine-containing gases may be flowed into a reaction chamber along with H2NH3. Process conditions for the reaction chamber may be tuned to successfully conduct SiN deposition on exposed surfaces of the nitride layers112concurrently with etch of SiN deposited on the sidewalls128.

Next, referring toFIGS. 14A and 14B, the nitride layers112and the SiN pads182deposited thereon, respectively, are etched relative to oxide on the substrate. Etching is conducted substantially as described for operation190, as shown inFIG. 1, to remove nitride layers112by flowing etchant species vertically through a slit in the ONON stack such that etchant species flow into the vertical slit and selectively etches nitride. Nitride may be selectively etched using a wet etch process, such as by exposing the substrate to phosphoric acid (H3PO4), or diluted hydrofluoric acid (“DHF”), or a mixture of these solutions. For example,FIG. 6Ashows an example schematic illustration of a substrate100with horizontal gaps132formed from etching nitride.

Following the selective etching of nitride found in nitride layers112and SiN pads182, tungsten is deposited into the gaps of the substrate to form tungsten wordlines140and landing pads180, respectively, as shown inFIG. 14B. Horizontal gaps, similar to gaps132shown inFIG. 6A, are filled with tungsten to form tungsten wordlines. Similarly, voids resultant from etch of the SiN pads182are filled with tungsten to form landing pads180. Tungsten may be deposited by any suitable technique, such as ALD, CVD, PEALD, or PECVD, to create wordlines140or landing pads182which may provide a sufficient stop, also referred to as an “etch stop layer,” to prevent punchthrough by interconnects to a subsequent nitride layer positioned beneath the nitride layer to which contact is made, shown inFIG. 15.

Returning toFIG. 13, a situation where SiN is deposited on sidewalls128of oxide layers111at regions130is shown. Thus, upon replacement of the nitride layers112with wordlines140as described above, the SiN on sidewalls128may also be replaced with tungsten, thus potentially leading to a short between the alternating wordlines140. Thus, the etch processes as described above may remove SiN on sidewalls128, as shown inFIGS. 14A and 14B, or remove enough SiN such that there is no continuous SiN layer between steps on the staircase pattern as shown inFIG. 13, to prevent against such a short.

FIGS. 14A and 14Billustrate situations where isotropic etch processes have removed all SiN deposition upon regions130of sidewalls128. Thus, risk of a short between alternating wordlines140through replacement of SiN deposited on sidewalls of the oxide layers111with tungsten is substantially reduced or eliminated entirely.

Similar to that generally shown and discussed with reference toFIGS. 8 and 9, oxide122is vertically etched to form vias, later filled with tungsten to form interconnects142, as shown inFIG. 15. As described for operation194forFIG. 1, oxide122may be etched by dry etching conducted by exposure to any one or more of the following gases: O2, Ar, C4F6, C4F8, SF6, CHF3, and CF4.

Formation of the landing pads182, as described above and shown inFIG. 15, protects against punchthrough that is shown inFIG. 9. The depth of each landing pad182on each wordline140provides additional tungsten through which an interconnect142must penetrate prior to punching through to below wordlines140, as shown inFIG. 15.

Accordingly, the possibility of a punchthrough condition is greatly minimized with usage of landing pads182. A scenario is shown inFIG. 15, where isotropic etch processes etch SiN deposited on sidewalls128of the oxide layers111, thus minimizing risk of a short, and the landing pad182prevents etching of a via through an upper wordline140, thus preventing against punchthrough. Accordingly, the overall structural integrity of the ONON stack is preserved as needed for successful operation.

Apparatus

As semiconductor device dimensions shrink, methods of fabricating semiconductor devices become increasingly sensitive to contamination. For example, semiconductor devices are often fabricated in reactors or chambers including chamber components and chamber walls made of metallic material, such as aluminum. While some semiconductor device fabrication processes do not involve plasma, in some processes that do implement a plasma, chamber components exposed to an in-situ plasma during deposition may flake and peel, thereby increasing the risk of incorporating metallic particles into the films deposited on a wafer. For example, “high density plasma chemical vapor deposition” (HDP CVD) systems generate high density plasma used for integrated circuit applications, such as dielectric film deposition and gap filling. Some systems implement inductively-coupled plasma powered by low frequency radio frequency (LFRF) power on a top dome and capacitively-coupled plasma powered by high frequency (HF) power at an electrostatic chuck (ESC). Gases are flowed ionized and accelerated towards a wafer on the ESC during processing. HDP CVD processing may implement simultaneous sputtering etch during deposition to allow gap filling of high aspect ratio trenches. Components of an HDP CVD system may be susceptible to flaking and peeling when exposed to plasma used during processing.

As noted above, HDP CVD as used herein is distinct from PECVD. HDP CVD process conditions and resulting films are different from capacitively-coupled PECVD processes. For example, various HDP reactors as described herein operate at a pressure less than about 100 mTorr, with a plasma density greater than 1011ions/cm3. HDP reactors may ignite plasma at a plasma frequency of 400 kHz for coils and a frequency of 13.56 MHz for the pedestal where the wafer is placed. In a capacitively-coupled plasma reactor, a plasma frequency of 13.56 MHz is used to generate plasma as applied to either a showerhead or the pedestal, and 400 kHz is applied to either the showerhead or the pedestal. Ion energies in HDP reactors may be greater than in PECVD reactors. As a result, film composition and characteristics of films deposited in HDP CVD reactors are different than those deposited in PECVD reactors.

Disclosed embodiments may be performed in a chamber such as the chamber shown inFIG. 16as described above. Although a high density plasma chemical vapor deposition (HDP CVD) chamber is depicted inFIG. 18, other reactors or tools for depositing films may be used in various embodiments described herein.

FIG. 16is a schematic illustration of an example of a HDP CVD reactor suitable for performing disclosed embodiments. Reactor1601includes a process chamber1603, which encloses other components of the reactor and serves to contain the plasma. In some implementations, the process chamber walls are made from aluminum, aluminum oxide, or other suitable material. The embodiment shown inFIG. 16has two plasma sources: top radio frequency (RF) coil1605and side RF coil1607. Top RF coil1605is a medium frequency or MFRF coil and side RF coil1607is a low frequency or LFRF coil. In the embodiment shown inFIG. 16, MFRF frequency may be from 430-470 kHz and LFRF frequency from 340-370 kHz. However, disclosed embodiments are not limited to operation in reaction chambers with dual sources, nor RF plasma sources. Any suitable plasma source or sources may be used.

Within the reactor, a wafer pedestal1609supports a workpiece1611. The workpiece1611may be a PEC or a wafer. The wafer pedestal1609includes a chuck (sometimes referred to as a clamp) to hold (or clamp) the wafer in place. The chuck may be used to clamp an object on the pedestal during various processes. The chuck may be an ESC, a mechanical chuck, or various other types of chuck as are available for use. A gas delivery subsystem including a line1613for supplying gas or heat transfer liquid to the wafer pedestal1609controls the temperature of workpiece1611. The wafer pedestal1609and gas delivery subsystem can facilitate maintaining appropriate wafer temperatures.

A high frequency RF of HFRF source1615serves to electrically bias the workpiece1611and draw charged gas species onto the workpiece1611during various processes. Electrical energy from source1615is coupled to the workpiece1611via an electrode or capacitive coupling, for example. Note that the bias applied to the workpiece1611may not be an RF bias. Other frequencies and DC bias may be used as well.

The process gases are introduced via one or more inlets1617. The gases may be premixed or not. The process gases may be introduced through a gas supply inlet mechanism including orifices. In some embodiments, at least some of the orifices orient the process gas along an axis of injection intersecting an exposed surface of the workpiece1611at an acute angle. Further, the process gases may be introduced from a primary gas ring1621, which may or may not direct the gases toward the pedestal. In some embodiments, process gases may be introduced from one or more gas rings (not shown) in addition to primary gas ring1621. Injectors may be connected to the primary gas ring1621to direct at least some of the gases or gas mixtures into the chamber and toward the pedestal. Note that injectors, gas rings or other mechanisms for directing process gas toward the wafer may not be used in some embodiments. The sonic front caused by a process gas entering the chamber will itself cause the gas to rapidly disperse in all directions—including toward the workpiece1611. Process gases exit chamber1603via an outlet1622. A vacuum pump (e.g., a turbomolecular pump) typically draws process gases out and maintains a suitably low pressure within the reactor. Reactor1601may be controlled using controller1690. Controller1690may include machine-readable instructions for performing various operations disclosed herein. Further description regarding the controller1690is provided below.

As shown inFIG. 16, reactor1601includes a controller1690for controlling operations in accordance with disclosed embodiments. The controller1690may be used to control various parameters, such as flow rate and pressure for gas flow to the pedestal1609via inlet1613, movement of the pedestal1609, bias power for an electrostatic chuck (ESC), plasma power for the MFRF coils1605and MFRF coils1607, pedestal temperature, chamber pressure, gas flow to the process chamber1603, transfer of the workpiece1611in and out of the chamber1603, and other operations.

In some embodiments, reactor1601shown inFIG. 16is part of a tool for processing one or more wafers. An example of a tool including one or more reactors is provided inFIG. 17.FIG. 17is a block diagram of a plasma processing system suitable for conducting a multi-step deposition process in accordance with disclosed embodiments. The system1700includes a transfer module1703, such as the wafer transfer system (WTS) used on the SPEED™ platform available from Lam Research Corporation of Fremont, Calif. The transfer module1703provides a clean, pressurized environment to minimize the risk of contamination of workpieces, such as wafers, being processed as they are moved between the various processing stages. Mounted on the transfer module1703are one or more HDP CVD modules or process chambers1705, such as Lam SPEED™ reactors, available from Lam Research Corporation of Fremont, Calif. The etch modules1707may be a Lam atomic layer removal (ALR) reactor or Kiyo™ reactor. These etch reactors may be mounted on the same or separate platforms as the deposition reactors.

The system may optionally include a chamber1709capable of performing PECVD or atomic layer deposition (ALD) process. Chamber1709may include multiple stations1711,1713,1715, and1717that may sequentially perform deposition or removal operations or protective electrostatic chuck cover (PEC) cleaning operations. The system1700also includes one or more (in this case two) wafer source modules1701where wafers are stored before and after processing. A device (generally a robot arm unit) in the transfer module1703moves the wafers among the modules mounted on the transfer module1703.

Wafers are transferred by the robot arm between the HDP CVD reactors1705and/or the plasma etch reactor1707for deposition and etch back processing, respectively. The robot arm may also transfer wafers between the conditioning layer deposition module1709and the other chambers. In one embodiment, a single etch reactor can support two SPEED deposition modules1705in this application with a high throughput of about 15-16 wafers per hour (wph). In other embodiments, two etch reactors1707may support one or more SPEED deposition modules1705.

Disclosed embodiments may also be practiced without a plasma etch chamber. For example, a single chamber may be configured for both HDP CVD deposition and reactive plasma etch. For example, the Lam SPEED HDP-CVD reactors are capable of conditioning, deposition, and plasma etch with a throughput similar to that of using separate reactors. Given the details and parameters provided herein, a single chamber may be configured, for example, a plasma reactor, with equipment, for example the various plasma sources described herein, for deposition (HDP CVD) and reactive plasma etch (e.g., in-situ or downstream plasma source).

FIG. 17also depicts an embodiment of a system controller1750employed to control process conditions and hardware states of process tool1700. System controller1750may provide program instructions for implementing the above-described processes. The program instructions may control a variety of process parameters, such as DC power level, RF bias power level, pressure, temperature, etc. The instructions may control the parameters to condition a chamber and perform deposition operations on a PEC prior to processing wafers in a batch according to various embodiments described herein.

In some embodiments, system controller1750controls all of the activities of process tool1700. System controller1750may include one or more memory devices1756, one or more mass storage devices1754, and one or more processors1752. Processor1752may include a CPU or computer, analog and/or digital input/output connections, stepper motor controller boards, etc. System controller1750executes system control software1758stored in mass storage device1754, loaded into memory device1756, and executed on processor1752. Alternatively, the control logic may be hard coded in the controller1750. Applications Specific Integrated Circuits, Programmable Logic Devices (e.g., field-programmable gate arrays, or FPGAs) and the like may be used for these purposes. In the following discussion, wherever “software” or “code” is used, functionally comparable hard coded logic may be used in its place. System control software1758may include instructions for controlling the transfer of PEC into and out of a process chamber, transfer of wafers into and out of a process chamber, timing of gases, mixture of gases, amount of gas flow, chamber and/or station pressure, backside gas flow pressure, chamber and/or reactor temperature, wafer temperature, bias power, target power levels, RF power levels, pedestal, chuck and/or susceptor position, and other parameters of a particular process performed by process tool1700. System control software1758may be configured in any suitable way. For example, various process tool component subroutines or control objects may be written to control operation of the process tool components necessary to carry out various process tool processes. System control software1758may be coded in any suitable computer readable programming language.

In some embodiments, system control software1758may include input/output control (IOC) sequencing instructions for controlling the various parameters described above. Other computer software and/or programs stored on mass storage device1754and/or memory device1756associated with system controller1750may be employed in some embodiments. Examples of programs or sections of programs for this purpose include a wafer positioning program, a process gas control program, a pressure control program, a heater control program, and a plasma control program.

A wafer positioning program may include program code for process tool components that are used to load a wafer or PEC onto pedestal1718and to control the spacing between the wafer or PEC and other parts of process tool1700. A process gas control program may include code for controlling gas composition (e.g., conditioning process gases, deposition gases, helium gas or other gas for backside flow, carrier gases, etc., as described herein) and flow rates and optionally for flowing gas into one or more process stations prior to deposition in order to stabilize the pressure in the process station. A pressure control program may include code for controlling the pressure in the process station by regulating, for example, a throttle valve in the exhaust system of the process station, a gas flow into the process station, pressure of gas introduced to backside of PEC during conditioning operations, etc.

A heater control program may include code for controlling the current to a heating unit that is used to heat the workpiece. Alternatively, the heater control program may control delivery of a heat transfer gas (such as helium) to the wafer. A plasma control program may include code for setting RF power levels applied to the process electrodes and the bias in one or more process stations in accordance with the embodiments herein. A pressure control program may include code for maintaining the pressure in the reaction chamber in accordance with the embodiments herein.

In some embodiments, there may be a user interface associated with system controller1750. The user interface may include a display screen, graphical software displays of the apparatus and/or process conditions, and user input devices such as pointing devices, keyboards, touch screens, microphones, etc.

In some embodiments, parameters adjusted by system controller1750may relate to process conditions. Non-limiting examples include process gas composition and flow rates, temperature, pressure, plasma conditions (such as RF bias power levels), pressure, temperature, etc. These parameters may be provided to the user in the form of a recipe, which may be entered utilizing the user interface.

Signals for monitoring the process may be provided by analog and/or digital input connections of system controller1750from various process tool sensors. The signals for controlling the process may be output on the analog and digital output connections of process tool300. Non-limiting examples of process tool sensors that may be monitored include mass flow controllers, pressure sensors (such as manometers), thermocouples, etc. Appropriately programmed feedback and control algorithms may be used with data from these sensors to maintain process conditions.

CONCLUSION