Patent Publication Number: US-2022238372-A1

Title: Method for forming barrier layer in semiconductor structure

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is continuation of International Application No. PCT/CN2021/074005, filed on Jan. 27, 2021, entitled “METHOD FOR FORMING BARRIER LAYER IN SEMICONDUCTOR STRUCTURE,” which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates to a semiconductor process for forming a semiconductor structure. 
     Thin conductive films are used in the fabrication of integrated circuits to route signals through and between many of the device elements of an integrated circuit, including interconnect lines, capacitor and gate electrodes, and contacts to the source and drain transistor regions. Generally, interconnect lines are fabricated from metal materials, such as tungsten (W), aluminum (Al), or copper (Cu), and are embedded in dielectric insulation layers. For improving the device performance, low dielectric constant (low-K) materials are also used in the semiconductor process to lower the signal propagation time delay. 
     A barrier layer is employed to prevent the diffusion of impurities, such as hydrogen and fluorine, from metal lines into memory stack structures. The barrier material and deposition method need to be carefully designed to avoid compromising the resistivity and reliability of the interconnect system. 
     SUMMARY 
     In one aspect, a method for forming a barrier layer in a semiconductor structure is disclosed. A substrate having a dielectric layer is provided. The dielectric layer is exposed to a precursor having a first metal, and a pulse-type nitridation operation is performed. The pulse-type nitridation operation includes performing a first ammonia treatment. A first purge operation is performed, a second ammonia treatment is performed after the first purge operation, and a second purge operation is performed after the second ammonia treatment to form the barrier layer on the dielectric layer. 
     In another aspect, a method for manufacturing a three-dimensional (3D) memory device is disclosed. A dielectric stack is formed on a substrate, the dielectric stack includes a plurality of first dielectric layers and a plurality of second dielectric layers, and the first dielectric layers and the second dielectric layers are alternately formed on the substrate. A slit is formed in the dielectric stack to vertically separate the dielectric stack to a plurality of arrays. The second dielectric layers in the dielectric stack are removed, and a first deposition process is performed to form a barrier layer on the first dielectric layers. The first deposition process includes an atomic layer deposition (ALD) process having the dielectric stack exposed to a precursor having a first metal, and a plurality of pulse-type nitridation operations performed to form the barrier layer on the first dielectric layers. 
     In still another aspect, a method for forming a semiconductor device is disclosed. A substrate is provided. A barrier layer is formed on the substrate using an ALD process with a plurality of pulse-type nitridation operations. 
     In yet another aspect, a semiconductor manufacturing device is disclosed. The semiconductor manufacturing device includes a reaction chamber, a substrate holder located in the reaction chamber to hold a substrate, a precursor source connected to the reaction chamber through a gas line, an ammonia source with a pressure above 200 Torrs connected to the reaction chamber through the gas line, and a dinitrogen source connected to the reaction chamber through the gas line. The precursor source, the ammonia source, and the dinitrogen source are configured to perform an ALD process to form a barrier layer on the substrate, and the ammonia source and the dinitrogen source are configured to perform a plurality of pulse-type nitridation operations in the ALD process. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate implementations of the present disclosure and, together with the description, further serve to explain the present disclosure and to enable a person skilled in the pertinent art to make and use the present disclosure. 
         FIG. 1  illustrates an exemplary barrier layer deposition process, according to some aspects of the present disclosure. 
         FIGS. 2A-2F  illustrate cross-sections of an exemplary semiconductor structure, according to some aspects of the present disclosure. 
         FIGS. 3A-3B  are flowcharts of an exemplary method for forming a barrier layer in a semiconductor structure, according to some aspects of the present disclosure. 
         FIG. 4  illustrates another exemplary barrier layer deposition process, according to some aspects of the present disclosure. 
         FIG. 5  illustrates another exemplary barrier layer deposition process, according to some aspects of the present disclosure. 
         FIGS. 6A-6B  are flowcharts of an exemplary method for performing an atomic layer deposition process to form a barrier layer, according to some aspects of the present disclosure. 
         FIGS. 7A-7H  illustrate cross-sections of an exemplary semiconductor structure, according to some aspects of the present disclosure. 
         FIGS. 8A-8B  are flowcharts of an exemplary method for manufacturing a semiconductor device, according to some aspects of the present disclosure. 
         FIGS. 9A-9B  are flowcharts of an exemplary method for forming a semiconductor device, according to some aspects of the present disclosure. 
         FIG. 10  illustrates an exemplary semiconductor manufacturing device according to some aspects of the present disclosure. 
     
    
    
     Aspects of the present disclosure will be described with reference to the accompanying drawings. 
     DETAILED DESCRIPTION 
     Although specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. As such, other configurations and arrangements can be used without departing from the scope of the present disclosure. Also, the present disclosure can also be employed in a variety of other applications. Functional and structural features as described in the present disclosures can be combined, adjusted, and modified with one another and in ways not specifically depicted in the drawings, such that these combinations, adjustments, and modifications are within the scope of the present discloses. 
     In general, terminology may be understood at least in part from usage in context. For example, the term “one or more” as used herein, depending at least in part upon context, may be used to describe any feature, structure, or characteristic in a singular sense or may be used to describe combinations of features, structures or characteristics in a plural sense. Similarly, terms, such as “a,” “an,” or “the,” again, may be understood to convey a singular usage or to convey a plural usage, depending at least in part upon context. In addition, the term “based on” may be understood as not necessarily intended to convey an exclusive set of factors and may, instead, allow for existence of additional factors not necessarily expressly described, again, depending at least in part on context. 
     It should be readily understood that the meaning of “on,” “above,” and “over” in the present disclosure should be interpreted in the broadest manner such that “on” not only means “directly on” something but also includes the meaning of “on” something with an intermediate feature or a layer therebetween, and that “above” or “over” not only means the meaning of “above” or “over” something but can also include the meaning it is “above” or “over” something with no intermediate feature or layer therebetween (i.e., directly on something). 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     As used herein, the term “layer” refers to a material portion including a region with a thickness. A layer can extend over the entirety of an underlying or overlying structure or may have an extent less than the extent of an underlying or overlying structure. Further, a layer can be a region of a homogeneous or inhomogeneous continuous structure that has a thickness less than the thickness of the continuous structure. For example, a layer can be located between any pair of horizontal planes between, or at, a top surface and a bottom surface of the continuous structure. A layer can extend horizontally, vertically, and/or along a tapered surface. A substrate can be a layer, can include one or more layers therein, and/or can have one or more layer thereupon, thereabove, and/or therebelow. A layer can include multiple layers. For example, an interconnect layer can include one or more conductor and contact layers (in which interconnect lines and/or via contacts are formed) and one or more dielectric layers. 
     As used herein, the term “substrate” refers to a material onto which subsequent material layers are added. The substrate itself can be patterned. Materials added on top of the substrate can be patterned or can remain unpatterned. Furthermore, the substrate can include a wide array of semiconductor materials, such as silicon, germanium, gallium arsenide, indium phosphide, etc. Alternatively, the substrate can be made from an electrically non-conductive material, such as a glass, a plastic, or a sapphire wafer. 
     As used herein, the term “3D memory device” refers to a semiconductor device with vertically oriented strings of memory cell transistors (referred to herein as “memory strings,” such as NAND memory strings) on a laterally-oriented substrate so that the memory strings extend in the vertical direction with respect to the substrate. As used herein, the term “vertical/vertically” means perpendicular to the lateral surface of a substrate. 
     One important aspect of 3D memory development is the increase in the number of memory cells, requiring an increase in integration level at all. An application to memory production is a multiplication of the number of metal lines, such as word lines or bit lines, resulting in a higher stair structure and increased thickness. Therefore, it is particularly important to reduce the thickness of the whole memory structure when increasing the number of layers of metal lines. 
     The height reduction cannot be at the expense of the resistivity of the metal lines. In other words, the thickness of the metal electrodes or metal lines (such as tungsten) should be kept unchanged. Therefore, reducing the thickness of the metal barrier layers becomes one of the choices. Furthermore, the continuity and the compactness of the barrier layers is another important factor to prevent the fluorine impurities in the metal lines causing leakage through the barrier layer in a subsequent high-temperature process. 
     To address the aforementioned issues, the present disclosure introduces a solution in which the thickness reduction and leakage prevention can be balanced in forming a barrier layer in a semiconductor structure. 
       FIG. 1  illustrates an exemplary barrier layer deposition process, according to some aspects of the present disclosure. In  FIG. 1 , TiCl 4  is used as the precursor, and NH 3  is used as the ammonia source to explain the present disclosure; however, the precursor and the ammonia source are not limited to these materials. For example, the precursor may be TaCl 5 , TaF 5 , TaBr 5 , TiCl 4 , TiBr 4 , TiI 4 , or TiF 4 , and the ammonia source may be NH 3 , N 2 H 4 , N 2 H 2 , or other suitable ammonia gas. 
     As the number of operations in the stair memory structure increases, the TiCl 4  flow rate for forming the barrier layer might be increased to improve the operation coverage. The high TiCl 4  flow rate might also have more Cl atoms hidden in the barrier layer and cause the defects in the barrier layer. Furthermore, the crystal structure and barrier properties of the barrier layer might be further worsened if the thickness of the barrier layer is reduced. When the TiCl 4  flow rate is increased, the increased Cl atoms might be removed by extending the nitridation time. However, when extending the nitridation time, the operation coverage might be affected because the extended nitridation time might convert the atomic layer deposition (ALD) process into the chemical vapor deposition (CVD) process. In the present disclosure, as shown in  FIG. 1 , a wafer is placed on a heater in the reaction chamber. The heater is used to heat and maintain the temperature of the wafer to a preset process temperature. TiCl 4  absorption operation  102  includes high flow TiCl 4  operation  106 . During the TiCl 4  absorption operation  102 , a high flow TiCl 4  is provided in the reaction chamber and TiCl 4  is absorbed or deposited on the wafer. During the nitridation operation  104 , NH 3  is provided in the reaction chamber. Nitridation operation  104 , including the ammonia treatments and the purge operations, utilizes the NH 3  flow of multiple pulse-type nitridation operation  108  to react with TiCl 4 . The multiple pulse-type nitridation operation  108  includes repeating high NH 3  pressure and short process time ammonia treatments followed by the purge operations. TiCl 4  absorption operation  102  and pulse-type nitridation operation  108  may be repeated several times to form a sufficient thickness of the barrier layer. Details of pulse-type nitridation operation  108  are described thoroughly below in  FIGS. 2A-2F . As shown in  FIG. 1 , pulse-type nitridation operation  108  is repeated twice; however, the repeating times of pulse-type nitridation operation  108  is not limited to twice and could be modified or increased according to actual requirements. 
     Hence, the Cl atoms in the barrier layer could be gradually removed and scrubbed in the multiple pulse-type nitridation operation  108 . The impurity content in the barrier layer is lowered, and the barrier properties are therefore ensured and improved. In some implementations, pulse-type nitridation operation  108  includes using high ammonia pressure above 200 Torrs. In some implementations, the ammonia pressure may be between 200 Torrs and 250 Torrs. In some implementations, the ammonia pressure may be between 210 Torrs and 230 Torrs. In some implementations, the processing time of the ammonia treatment may be less than 0.4 seconds. In some implementations, the processing time of the ammonia treatment may be between 0.1-0.4 seconds. In some implementations, the processing time of the ammonia treatment may be between 0.2-0.4 seconds. 
       FIGS. 2A-2F  illustrate cross-sections of an exemplary semiconductor structure  200 , according to some aspects of the present disclosure, and  FIGS. 3A-3B  are flowcharts of an exemplary method  300  for forming a barrier layer in the semiconductor structure  200 , according to some aspects of the present disclosure. For the purpose of better explaining the present disclosure,  FIGS. 2A-2F  and the flowcharts in  FIGS. 3A-3B  could be referred to together. In  FIG. 2A  and operation  302  of  FIG. 3A , the semiconductor structure  200  having a dielectric layer  202  is provided. Dielectric layer  202  may be an insulating layer including, but not limited to, silicon oxide (including doped or undoped silicate glass), silicon nitride, silicon oxynitride, organosilicate glass (OSG), spin-on dielectric materials, dielectric metal oxides that are commonly known as high dielectric constant (high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectric metal oxynitrides and silicates thereof, and organic insulating materials. In some implementations, dielectric layer  202  may be silicon oxide. 
     In  FIG. 2A  and operation  304  of  FIG. 3A , dielectric layer  202  is placed in a reaction chamber and is exposed to a precursor  204  having a first metal. Precursor  204  may be TaCl 5 , TaF 5 , TaBr 5 , TiCl 4 , TiBr 4 , TiI 4  or TiF 4 . In some implementations, precursor  204  may be TiCl 4 , and the first metal may be Ti. In some implementations, precursor  204  may be TaCl 5 , and the first metal may be Ta. As shown in  FIG. 2A , precursor  204  is deposited on dielectric layer  202 . In some implementations, the substrate and dielectric layer  202  are placed on a heater in the reaction chamber, and a furnace-based process is used to deposit precursor  204  onto dielectric layer  202 . In some implementations, in operation  304 , the reaction chamber may be provided only precursor  204 . In some implementations, in operation  304 , when supplying precursor  204  into the reaction chamber, the inert gas, such as dinitrogen (N 2 ), could also be provided in the reaction chamber simultaneously. 
     As shown in  FIG. 2B , after exposing dielectric layer  202  to precursor  204 , the gas supply of precursor  204  is stopped, and a precursor purge operation is performed thereafter. During the precursor purge operation, the gas supply of precursor  204  is stopped, and the inert gas supply, such as dinitrogen, is provided in the reaction chamber to bring residual precursor  204  away. 
     After the precursor purge operation, as shown in  FIGS. 2C-2F  and operation  306  of  FIG. 3A , a pulse-type nitridation operation is performed.  FIG. 3B  further shows details of the pulse-type nitridation operation. As shown in  FIG. 2C  and operation  3062  of  FIG. 3B , a first ammonia treatment is performed. An ammonia gas  206  is provided in the reaction chamber to react with precursor  204  to form a barrier layer  208 . In some implementations, ammonia gas  206  may be NH 3 , N 2 H 4 , N 2 H 2 , or other suitable ammonia gas. In some implementations, the substrate and dielectric layer  202  are placed on a heater in the reaction chamber, and a furnace-based process is used to form barrier layer  208 . By using TiCl 4  as precursor  204  and using NH 3  as ammonia gas  206  as an example, the chlorine in TiCl 4  is replaced by the nitrogen of NH 3  and the barrier layer TiN is therefore formed on the dielectric layer. In some implementations, in operation  3062 , the reaction chamber may be provided only ammonia gas  206 . In some implementations, in operation  3062 , when performing the first ammonia treatment by supplying ammonia gas  206  into the reaction chamber, the inert gas, such as dinitrogen, could also be provided and pre-mixed with ammonia gas  206  in a gas line before being supplied to the reaction chamber. 
     Before supplying ammonia gas  206  into the reaction chamber, an ammonia source, such as an ammonia tank, may be used to store ammonia gas  206 . In some implementations, the gas pressure of ammonia gas  206  in the ammonia source may be above 200 Torrs. In some implementations, the gas pressure of ammonia gas  206  may be between 200 Torrs and 250 Torrs. In some implementations, the gas pressure of ammonia gas  206  may be between 210 Torrs and 230 Torrs. In operation  3062 , the ammonia source is connected to the reaction chamber by opening a valve between the ammonia source and the reaction chamber, and ammonia gas  206  could be supplied to the reaction chamber. In some implementations, the ammonia source may be pre-mixed with the inert gas in a gas line before the valve, and then be supplied to the reaction chamber by opening the valve. Then, precursor  204  on dielectric layer  202  could react with ammonia gas  206 . In some implementations, the processing time of the first ammonia treatment may be less than 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.1 and 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.2 and 0.4 seconds. 
     As shown in  FIG. 2D  and operation  3064  of  FIG. 3B , straightly after performing the first ammonia treatment, a first purge operation may be performed. The first purge operation includes disconnecting the ammonia source from the reaction chamber to stop the gas supply of ammonia gas  206 , and, at the same time, the inert gas, such as dinitrogen, is still provided to the reaction chamber. It is understood that straightly performing an operation means the operation is performed directly after a previous operation without any intermediate interposition. For example, when performing the first purge operation straightly after performing the first ammonia treatment, no intermediate operation should be inserted in between the first ammonia treatment and the first purge operation. 
     The first purge operation is used to bring the unnecessary product of operation  3062  away. For example, when using TiCl 4  as precursor  204  and using NH 3  as ammonia gas  206 , the barrier layer TiN could be formed on dielectric layer  202 , and a byproduct  210  could be HCl. In the first purge operation, byproduct  210  could be brought away by the inert gas, and barrier layer  208  could be deposited and kept on dielectric layer  202 . 
     Referring to  FIG. 2E , after the first purge operation, part of precursor  204  has reacted with ammonia gas  206  and forms barrier layer  208  on dielectric layer  202 . However, the remainder of precursor  204  is still on dielectric layer  202  without reacting with ammonia gas  206 . As shown in  FIG. 2E  and operation  3066  of  FIG. 3B , straightly after performing the first purge operation, a second ammonia treatment is performed to have ammonia gas  206  reacting with the remainder of precursor  204  on dielectric layer  202 . In some implementations, the process of the second ammonia treatment may be similar to the process of the first ammonia treatment, such as the process pressure or the processing time. In some implementations, the process of the second ammonia treatment may be different from the process of the first ammonia treatment. 
     As shown in  FIG. 2F  and operation  3068  of  FIG. 3B , straightly after performing the second ammonia treatment, a second purge operation may be performed to remove byproduct  210  from semiconductor structure  200  and the reaction chamber. In some implementations, the process of the second purge operation may be similar to the process of the first purge operation, such as the process pressure or the processing time. In some implementations, the process of the second purge operation may be different from the process of the first purge operation. 
     It is understood that although  FIG. 2F  shows dielectric layer  202  is fully covered by barrier layer  208  after the second purge operation; however, the actual situation might be different from the ideal one. Therefore, after the second purge operation, more ammonia treatments and purge operations could be added according to the actual requirements. In some implementations, the ammonia treatments and purge operations are repeated three times. In some implementations, the ammonia treatments and purge operations are repeated six times. In some implementations, the ammonia treatments and purge operations are repeated ten times. It should be further noted that, in some implementations, the process including operations  302 - 306  may be further repeated several times to form a sufficient thickness of barrier layer  208 . 
     In the present disclosure, the pulse-type nitridation process, including the ammonia treatments and the purge operations, is repeated more than once. The repeated pulse-type nitridation operation could gradually remove and scrub the byproduct formed in the ammonia treatments. By repeating the pulse-type nitridation operation, the impurity in the barrier layer is lowered, and the barrier properties are improved. 
       FIG. 4  illustrates another exemplary barrier layer deposition process, according to some aspects of the present disclosure. Operation  402  shows the process does not use high flow TiCl 4  and pulse-type nitridation operation. Under this situation, the TiCl 4  absorption and the removal of the byproduct formed in the ammonia treatments are related low. Operation  404  shows the process using high flow TiCl 4  and pulse-type nitridation. According to Langmuir&#39;s theory of adsorption (a.k.a. Langmuir adsorption model), when the reaction temperature is fixed, the adsorption and desorption rate of the same gas on the substrate surface will reach an equilibrium status. Therefore, when increasing the TiCl 4  flow rate, the overall structure surface of the dielectric layer, including the corners, could be covered by TiCl 4 , and the adsorption amount is the same. In some implementations, the TiCl 4  flow rate in operation  404  may be above 7 cc/cycle. In some implementations, the TiCl 4  flow rate in operation  404  may be above 6 cc/cycle. In some implementations, the TiCl 4  flow rate in operation  404  may be above 5 cc/cycle. 
     In the case of adsorbing the same amount of TiCl 4 , the barrier layer could grow without chlorine when applying the multiple pulse-type nitridation operation of NH 3 . As shown in operation  404 , the chlorine atom removal is increased by applying the multiple pulse-type nitridation operation. Hence the continuity and the barrier properties of the barrier layer are enhanced, and the resistivity is also reduced.  FIG. 4  further shows, by increasing times of the pulse-type nitridation operation, the continuity of barrier layer  406 A can be improved to barrier layer  406 A and then to barrier layer  406 C. Therefore, as shown in  FIG. 4 , barrier layer  406 C, such as TiN layer, may have an improved continuity by using high flow TiCl 4  and pulse-type nitridation operation. 
       FIG. 5  illustrates another exemplary barrier layer deposition process, according to some aspects of the present disclosure. In some implementations, the metal layers or metal lines  502 , such as tungsten (W), formed consequent to the barrier layer  504 , may use fluorine-containing precursors, such as WF 6 . The barrier layer is effective as fluorine barriers in the following process. In the present disclosure, using the fresh NH 3  gas with multiple flush purges could reduce secondary contamination of the Cl atoms (such as the byproduct HCl  506  shown in  FIG. 5 ) to the barrier layer thin film. In addition, by using multiple high-flow NH 3  flushes, the film defects could be reduced or even avoided, because the repeated pulse-type nitridation operation could gradually remove and scrub the byproduct formed in the ammonia treatments and therefore enhance the blocking capability to fluorine. 
       FIGS. 6A-6B  are flowcharts of an exemplary method  600  for performing an ALD process to form a barrier layer, according to some aspects of the present disclosure. In operation  602  of  FIG. 6A , a substrate having a stack of spaced dielectric layers is provided in a reaction chamber. The stack of spaced dielectric layers may have gaps between the dielectric layers. In some implementations, each gap may be formed a metal line in a later process. In some implementations, the dielectric layers may be silicon oxide. In operation  604 , the stack of dielectric layers is exposed to a precursor having a first metal. The precursor may be TaCl 5 , TaF 5 , TaBr 5 , TiCl 4 , TiBr 4 , TiI 4 , or TiF 4 . In some implementations, the precursor may be TiCl 4 , and the first metal may be Ti. In some implementations, the precursor may be TaCl 5 , and the first metal may be Ta. When supplying the precursor into the reaction chamber, the inert gas, such as dinitrogen (N 2 ), could also be provided in the reaction chamber simultaneously. In operation  606 , a precursor purge operation is performed. During the precursor purge operation, the gas supply of the precursor is stopped, and the inert gas supply, such as dinitrogen, is still provided in the reaction chamber to bring the residual precursor away. In operation  608 , a pulse-type nitridation operation is performed, and  FIG. 6B  further explains the detailed procedures of the pulse-type nitridation operation of operation  608 . 
     In operation  6082  of  FIG. 6B , a first ammonia treatment is performed. In some implementations, during the first ammonia treatment, an ammonia source filling an ammonia gas is provided, and the gas pressure of the ammonia gas may be above 200 Torrs. In some implementations, the gas pressure of the ammonia gas may be between 200 Torrs and 250 Torrs. In some implementations, the gas pressure of the ammonia gas may be between 210 Torrs and 230 Torrs. The ammonia source is connected to the reaction chamber to provide the ammonia gas in the first ammonia treatment when the dielectric layer is exposed to the ammonia gas. In some implementations, the processing time of the first ammonia treatment may be less than 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.1 and 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.2 and 0.4 seconds. 
     In operation  6084 , straightly after performing the first ammonia treatment, a first purge operation is performed. In some implementations, during the first purge operation, the ammonia source is disconnected from the reaction chamber, and dinitrogen is still provided to the reaction chamber. In operation  6086 , straightly after performing the first purge operation, a second ammonia treatment is performed. In some implementations, the process of the second ammonia treatment may be similar to the process of the first ammonia treatment, such as the process pressure or the processing time. In some implementations, the process of the second ammonia treatment may be different from the process of the first ammonia treatment. In operation  6088 , straightly after performing the second ammonia treatment, a second purge operation is performed. In some implementations, the process of the second purge operation may be similar to the process of the first purge operation, such as the process pressure or the processing time. In some implementations, the process of the second purge operation may be different from the process of the first purge operation. In some implementations, after performing the second purge operation, more ammonia treatments and purge operations could be added according to the actual requirements. In some implementations, the process including operations  602 - 608  may be further repeated several times to form a sufficient thickness of the barrier layer. 
     The semiconductor devices, such as memory cells, are scaled to smaller sizes by improving process technology, circuit design, programming algorithm, and fabrication process. However, as feature sizes of the semiconductor devices approach a lower limit, planar process and fabrication techniques become challenging and costly. As a result, memory density for planar memory cells approaches an upper limit. The three-dimensional (3D) memory device is a device architecture in which memory cells are arranged vertically (three-dimensional), rather than horizontally (planar) to increase memory bit density. 
     To achieve the goal of increasing memory density, increasing the number of layers of metal lines in a specific thickness plays an important role. When increasing the number of layers of metal lines, the performance of the barrier layers between the metal line and the insulation layer has become an important indicator. 
       FIGS. 7A-7H  illustrate cross-sections of an exemplary semiconductor structure  700 , according to some aspects of the present disclosure, and  FIGS. 8A-8B  are flowcharts of an exemplary method  800  for manufacturing the semiconductor structure  700 , according to some aspects of the present disclosure. For the purpose of better explaining the present disclosure,  FIGS. 7A-7F  and the flowchart in  FIGS. 8A and 8B  could be referred to together. In  FIGS. 7A and 7B  and operation  802  of  FIG. 8A , a dielectric stack is formed on a substrate  702 .  FIG. 7B  shows a cross-section of semiconductor structure  700  in  FIG. 7A  along the line AA. The dielectric stack includes a plurality of first dielectric layers  706  and a plurality of second dielectric layers  704 , and first dielectric layers  706  and second dielectric layers  704  are alternately formed on substrate  702 . Furthermore, at least one channel structure  708  is formed in semiconductor structure  700 . Each channel structure  708  can extend vertically through the dielectric stack having interleaved first dielectric layers  706  and second dielectric layers  704 . 
     It is understood that for ease of illustration, the detailed structure of channel structure  708  is not shown in  FIGS. 7A-7H . In some implementation, channel structure  708  includes a channel hole filled with a semiconductor layer (e.g., as a semiconductor channel) and a composite dielectric layer (e.g., as a memory film) including a tunneling layer, a storage layer (a.k.a. a charge trap layer), and a blocking layer. First dielectric layers  706  and second dielectric layers  704  may be insulating layers including, but not limited to, silicon oxide (including doped or undoped silicate glass), silicon nitride, silicon oxynitride, organosilicate glass (OSG), spin-on dielectric materials, dielectric metal oxides that are commonly known as high dielectric constant (high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectric metal oxynitrides and silicates thereof, and organic insulating materials. In some implementations, the first dielectric layers  706  may be silicon oxide, and the second dielectric layers  704  may be silicon nitride. 
     As shown in  FIG. 7C  and operation  804  of  FIG. 8A , a slit  710  is formed in the dielectric stack to vertically separate the dielectric stack to a plurality of arrays. Slit  710  may be formed by any suitable process including, but not limited to, dry etching (e.g., deep reactive ion etch (DRIE)) or wet etching. In  FIG. 7D  and operation  806  of  FIG. 8A , second dielectric layers  704  are removed from the dielectric stack, and first dielectric layers  706  are kept. For example, second dielectric layers  704  may be selectively etched using a wet chemical etchant that has a relatively high selectivity (e.g., above 5) with respect to first dielectric layers  706 . In some implementations, the first dielectric layers  706  kept are silicon oxide. After operation  806 , the stack of spaced first dielectric layers  706  is formed and has gaps between first dielectric layers  706 . In some implementations, each gap may be formed a metal layer  716  in a later process. 
       FIG. 7E  shows a gate dielectric layer  712  formed on the first dielectric layer  706 . Gate dielectric layer  712  may be a dielectric material that functions as a control gate dielectric for the control gates that may be subsequently formed. In some implementations, gate dielectric layer  712  may be silicon dioxide, silicon nitride, silicon oxynitride, other suitable dielectric materials, and/or combinations thereof. In some implementations, gate dielectric layer  712  may be formed by chemical vapor deposition (CVD), atomic layer deposition (ALD), plasma-enhanced CVD (PECVD), plasma-enhanced ALD (PEALD), other suitable processes, and/or combinations thereof. 
     It should be noted that the gate dielectric layer  712  is optional and may be formed or omitted according to actual requirements. Referring to  FIG. 7F  and operation  808  of  FIG. 8A , a first deposition process is performed to form a barrier layer  714  on the first dielectric layers  706  using an atomic layer deposition (ALD) process. Barrier layer  714  is effective as fluorine barriers in the consequent process of forming the metal layers. In case gate dielectric layer  712  is present, barrier layer  714  may be formed directly on gate dielectric layer  712 . In case gate dielectric layer  712  is not present, barrier layer  714  may be formed directly on the exposed surfaces of first dielectric layers  706 . 
       FIG. 8B  shows the detailed procedures of operation  808  of performing the first deposition process. In operation  8082 , the dielectric stack is exposed to a precursor having a first metal. The precursor may be TaCl 5 , TaF 5 , TaBr 5 , TiCl 4 , TiBr 4 , TiI 4 , or TiF 4 . In some implementations, the precursor may be TiCl 4 , and the first metal may be Ti. In some implementations, the precursor may be TaCl 5 , and the first metal may be Ta. In operation  8084 , a plurality of pulse-type nitridation operations are performed to form the barrier layer on the first dielectric layers. Each of the plurality of pulse-type nitridation operations includes performing a first ammonia treatment and performing a first purge operation. In some implementations, during the first ammonia treatment, an ammonia source filling an ammonia gas is provided, and the gas pressure of the ammonia gas may be above 200 Torrs. In some implementations, the gas pressure of the ammonia gas may be between 200 Torrs and 250 Torrs. In some implementations, the gas pressure of the ammonia gas may be between 210 Torrs and 230 Torrs. The ammonia source is connected to the reaction chamber to provide the ammonia gas in the first ammonia treatment when first dielectric layers  706  are exposed to the ammonia gas. In some implementations, the processing time of the first ammonia treatment may be less than 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.1 and 0.4 seconds. In some implementations, the processing time of the first ammonia treatment may be between 0.2 and 0.4 seconds. Straightly after performing the first ammonia treatment, a first purge operation is performed. In some implementations, during the first purge operation, the ammonia source is disconnected from the reaction chamber, and dinitrogen is provided to the reaction chamber. In some implementations, the process including operations  8082 - 8084  may be further repeated several times to form a sufficient thickness of barrier layer  714 . 
     As shown in  FIG. 7G , after performing the first deposition process to form barrier layer  714 , a metal layer  716  may be formed on barrier layer  714 . In  FIG. 7H , an etching back process may be performed to remove partials of gate dielectric layer  712 , barrier layer  714 , and metal layer  716  to form the metal lines in between first dielectric layers  706 . 
       FIGS. 9A-9B  are flowcharts of an exemplary method  900  for forming a semiconductor device, according to some aspects of the present disclosure. In operation  902 , a substrate having an oxide layer is provided. In some implementations, the semiconductor device is a 3D memory device, and the substrate has a stack of spaced oxide layers with gaps between the oxide layers. In some implementations, each gap is capable of forming a word line in a later process. In operation  904 , a barrier layer is formed on the oxide layer using an atomic layer deposition (ALD) process with a plurality of pulse-type nitridation operations using an ammonia source having a pressure above 200 Torrs. Furthermore, operations  9042 - 9046  of  FIG. 9B  show the detailed procedures of operation  904 . 
     In operation  9042 , the oxide layers are exposed to a precursor source. In some implementations, the precursor source may be titanium tetrachloride (TiCl 4 ). Then, in operation  9044 , a first purge process is performed to bring the residual TiCl 4  away. It should be noted that TiCl 4  functions as a precursor having a first metal used by the process. In some implementations, TiCl 4  could be replaced by other precursors, such as TaCl 5 , TaF 5 , TaBr 5 , TiBr 4 , TiI 4 , or TiF 4 . In operation  9046 , a plurality of pulse-type nitridation operations are performed. Each of the plurality of pulse-type nitridation operations includes performing an ammonia treatment and a second purge operation. The ammonia treatment is performed by providing an ammonia gas on the oxide layer to react with TiCl 4  on the oxide layer. The ammonia treatment is a pulse-type process including providing high-pressure ammonia gas to the reaction chamber in a short reaction time. In some implementations, the pulse type process includes using high-pressure NH 3  higher than 200 Torr, and the processing time of the first ammonia treatment may be less than 0.4 seconds. The second purge operation is performed to remove the product after the ammonia treatment. In some implementations, the process including operations  9042 - 9046  may be further repeated several times to form a sufficient thickness of the barrier layer. Then, after forming the barrier layer, as shown in operation  906  of  FIG. 9A , a metal layer is formed on the barrier layer. The metal layer could be further formed a metal line of the 3D memory device in a later process. 
       FIG. 10  illustrates a semiconductor manufacturing device  1000  according to some aspects of the present disclosure. Semiconductor manufacturing device  1000  includes a reaction chamber  1002  having a substrate holder  1006  therein to hold a substrate  1004 . In some implementations, substrate holder  1006  may be a heater to maintain the reaction temperature of substrate  1004 . In some implementations, substrate  1004  may be a wafer and some semiconductor devices may be formed on substrate  1004 . Semiconductor manufacturing device  1000  also includes an evacuation unit  1008  to maintain the reaction pressure in reaction chamber  1002 . In some implementations, evacuation unit  1008  may be a vacuum pump including a pressure control valve. Semiconductor manufacturing device  1000  further includes a reaction gas supplying system including a precursor source, an ammonia source  1010 , and a dinitrogen source connecting to reaction chamber  1002  through a gas line  1012 .  FIG. 10  illustrates that the precursor source, ammonia source  1010 , and the dinitrogen source are connected to reaction chamber  1002  through the same gas line  1012 . However, it is understood that the precursor source and the dinitrogen source may be connected to one gas line and ammonia source  1010 , and the dinitrogen source may be connected to another gas line. The amount of the gas lines is not limited here. 
     Ammonia source  1010  is filled with ammonia gas having a pressure above 200 Torrs. In some implementations, the gas pressure of ammonia gas may be between 200 Torrs and 250 Torrs. In some implementations, the gas pressure of ammonia gas may be between 210 Torrs and 230 Torrs. 
     In some implementations, the precursor source, ammonia source  1010 , and the dinitrogen source are the reaction gases of an ALD process to form a dielectric layer on substrate  1004 . In some implementations, the precursor source may be titanium tetrachloride (TiCl 4 ), and the barrier layer may be titanium nitride (TiN). In some implementations, ammonia source  1010  and the dinitrogen source are used to perform a plurality of pulse-type nitridation operations in the ALD process. 
     The pulse-type nitridation operation includes an ammonia treatment and a purge operation. In the ammonia treatment, ammonia source  1010  and the dinitrogen source are provided to the reaction chamber to react with the precursor deposited on substrate  1002 . In some implementations, ammonia source  1010  may be a tank filled with ammonia gas with the pressure above 200 Torrs. In some implementations, the processing time of the ammonia treatment may be between 0.1 and 0.4 seconds. In some implementations, the processing time of the ammonia treatment may be between 0.2 and 0.4 seconds. In some implementations, ammonia source  1010  is filled with an ammonia gas with the pressure above 200 Torrs, and the dinitrogen is mix with the ammonia gas in gas line  1012  in the ammonia treatment. 
     After the ammonia treatment, a purge operation may be performed by disconnecting ammonia source  1010  to stop the gas supply of ammonia gas, and, at the same time, the dinitrogen source is still provided to reaction chamber  1002 . The pulse-type nitridation operation includes repeating the ammonia treatment and the purge operation several times to bring away the byproduct and keep the barrier layer on substrate  1004 .  FIG. 10  illustrates TiCl 4  as the precursor source and NH 3  as the ammonia gas. However, it is understood that TiCl 4  and NH 3  could be replaced by other precursor sources and ammonia gas, as explained above and are not limited here. 
     According to one aspect of the present disclosure, a method for forming a barrier layer in a semiconductor structure is provided. A substrate having a dielectric layer is provided. The dielectric layer is exposed to a precursor having a first metal, and a pulse-type nitridation operation is performed. During the pulse-type nitridation operation, a first ammonia treatment is performed. A first purge operation is performed, a second ammonia treatment is performed after the first purge operation, and a second purge operation is performed after the second ammonia treatment to form the barrier layer on the dielectric layer. 
     In some implementations, after performing the second purge operation, a third ammonia treatment is performed. In some implementations, after performing the third ammonia treatment, a third purge operation is performed. In some implementations, exposing the dielectric layer to the precursor having the first metal and performing the pulse-type operation are repeated to increase the thickness of the barrier layer. In some implementations, after exposing the dielectric layer to the precursor having the first metal, a precursor purge operation is performed. 
     In some implementations, when performing the first ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, the ammonia source is connected to a reaction chamber containing the dielectric layer, and the dielectric layer is exposed to the ammonia gas. In some implementations, when performing the first ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, dinitrogen (N 2 ) is provided to mix with the ammonia source in a gas line, the mixed ammonia source and dinitrogen is connected to a reaction chamber containing the dielectric layer, and the dielectric layer is exposed to the mixed ammonia source and dinitrogen. In some implementations, when performing the first purge operation, the ammonia source is disconnected from the reaction chamber, and dinitrogen (N 2 ) is provided to the reaction chamber. 
     In some implementations, when performing the second ammonia treatment, the ammonia source filling an ammonia gas with the pressure above 200 Torrs is provided, the ammonia source is connected to the reaction chamber, and the dielectric layer is exposed to the ammonia gas. 
     In some implementations, the precursor is titanium tetrachloride (TiCl 4 ), the first metal is titanium (Ti), and the barrier layer is titanium nitride (TiN). In some implementations, the precursor is tantalum penta-chloride (TaCl 5 ), the first metal is tantalum (Ta), and the barrier layer is tantalum nitride (TaN). 
     According to another aspect of the present disclosure, a method for manufacturing a three-dimensional (3D) memory device is disclosed. A dielectric stack is formed on a substrate, the dielectric stack includes a plurality of first dielectric layers and a plurality of second dielectric layers, and the first dielectric layers and the second dielectric layers are alternately formed on the substrate. A slit is formed in the dielectric stack to vertically separate the dielectric stack to a plurality of arrays. The second dielectric layers in the dielectric stack are removed, and a first deposition process is performed to form a barrier layer on the first dielectric layers using an atomic layer deposition (ALD) process. The ALD process includes the dielectric stack exposed to a precursor having a first metal, and a plurality of pulse-type nitridation operations performed to form the barrier layer on the first dielectric layers. 
     In some implementations, the ALD process includes exposing the dielectric stack to a precursor having a first metal and performing a plurality of pulse-type nitridation operations to form the barrier layer on the first dielectric layers. In some implementations, each of the plurality of pulse-type nitridation operations includes performing an ammonia treatment using the ammonia source with the pressure above 200 Torrs and, straightly after performing the ammonia treatment, performing a purge operation. 
     In some implementations, after exposing the dielectric stack to the precursor having the first metal, a precursor purge operation is performed. In some implementations, after performing the first deposition process, the first deposition process is repeated to increase the thickness of the barrier layer. In some implementations, the first dielectric layers are silicon oxide layers, and the second dielectric layers are silicon nitride layers. 
     In some implementations, the precursor is titanium tetrachloride (TiCl 4 ), the first metal is titanium (Ti), and the barrier layer is titanium nitride (TiN). In some implementations, the precursor is tantalum penta-chloride (TaCl 5 ), the first metal is tantalum (Ta), and the barrier layer is tantalum nitride (TaN). 
     In some implementations, when performing the ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, the ammonia source is connected to a reaction chamber containing the dielectric layer, and the dielectric layer is exposed to the ammonia gas for less than 0.4 seconds. In some implementations, the reaction chamber is further filled with dinitrogen (N 2 ). In some implementations, when performing the first ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, dinitrogen (N 2 ) is provided to mix with the ammonia source in a gas line, the mixed ammonia source and dinitrogen is connected to a reaction chamber containing the dielectric layer, and the dielectric layer is exposed to the mixed ammonia source and dinitrogen. In some implementations, when performing the purge operation, the ammonia source is disconnected from the reaction chamber, and dinitrogen is provided to the reaction chamber. 
     According to still another aspect of the present disclosure, a method for forming a semiconductor device is disclosed. A substrate is provided. A barrier layer is formed on the substrate using an atomic layer deposition (ALD) process with a plurality of pulse-type nitridation operations. 
     In some implementations, during the ALD process, the substrate is exposed to a precursor source, a first purge process is performed, and a plurality of pulse-type nitridation operations are performed. In some implementations, the method repeats exposing the substrate to the precursor source, performing the first purge process, and performing the plurality of pulse-type nitridation operations to increase the thickness of the barrier layer. 
     In some implementations, each of the plurality of pulse-type nitridation operations includes performing an ammonia treatment by providing the ammonia source having the pressure above 200 Torrs to the oxide layers and performing a second purge process. 
     In some implementations, when exposing the substrate to the precursor source, the precursor source and dinitrogen are provided to a reaction chamber containing the substrate. In some implementations, when exposing the substrate to the precursor source, titanium tetrachloride (TiCl 4 ) is provided to a reaction chamber containing the substrate. In some implementations, when performing the first purge process, the precursor source supply is stopped, and dinitrogen is provided to the reaction chamber. 
     In some implementations, when performing the ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, the ammonia source is connected to the reaction chamber containing the substrate and dinitrogen, and the substrate is exposed to the ammonia gas. In some implementations, when performing the first ammonia treatment, an ammonia source filling an ammonia gas with a pressure above 200 Torrs is provided, dinitrogen (N 2 ) is provided to mix with the ammonia source in a gas line, the mixed ammonia source and dinitrogen is connected to a reaction chamber containing the substrate, and the substrate is exposed to the mixed ammonia source and dinitrogen. In some implementations, the barrier layer is titanium nitride (TiN), and the substrate includes an oxide layer. In some implementations, the semiconductor device is a 3D memory device, and the substrate has a stack of spaced oxide layers with gaps between the oxide layers. 
     According to still another aspect of the present disclosure, a semiconductor manufacturing device is disclosed. The semiconductor manufacturing device includes a reaction chamber, a substrate holder located in the reaction chamber to hold a substrate, a precursor source connected to the reaction chamber through a gas line, an ammonia source with a pressure above 200 Torrs connected to the reaction chamber through the gas line, and a dinitrogen source connected to the reaction chamber through the gas line. The precursor source, the ammonia source, and the dinitrogen source are configured to implement an atomic layer deposition (ALD) process to form a barrier layer on the substrate, and the ammonia source and the dinitrogen source are configured to implement a plurality of pulse-type nitridation operations in the ALD process. 
     In some implementations, the ammonia source and the dinitrogen source are provided to the reaction chamber and are configured to perform an ammonia treatment on the substrate, and the dinitrogen source is provided to the reaction chamber and is configured to perform a purge operation. The ammonia source and the dinitrogen source are configured to perform the ammonia treatment and the purge operation more than once. 
     In some implementations, the ammonia source is filled with an ammonia gas with the pressure above 200 Torrs, and the dinitrogen is mix with the ammonia gas in the gas line in the pulse-type nitridation operation. In some implementations, the precursor source is titanium tetrachloride (TiCl 4 ), and the barrier layer is titanium nitride (TiN). 
     The foregoing description of the specific implementations can be readily modified and/or adapted for various applications. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed implementations, based on the teaching and guidance presented herein. 
     The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary implementations, but should be defined only in accordance with the following claims and their equivalents.