CN107481926A - A kind of filling method of metal tungsten - Google Patents

Abstract

The present invention provides a kind of fill method of tungsten, filling applied to the control gate of 3D NAND devices, silicon nitride layer in stack layer of the fill process in 3D NAND devices is carried out after being removed, in fill process, reacting gas is hydrogen and tungsten hexafluoride, and pressure is 5 30torr, and temperature is 250 430 DEG C, the flow of hydrogen is 7500 20000sccm, and the flow of tungsten hexafluoride is 60 500sccm.This method is particularly suitable for use in the filling of more deep hole and more high-aspect-ratio, and deposition during filling is low, can effectively reduce the filling defect in the gap and cavity in filling, improve filling quality.

Description

A kind of filling method of metal tungsten

technical field

The invention relates to the field of 3D NAND storage devices and its manufacture, in particular to a method for filling metal tungsten.

Background technique

NAND flash memory is a better storage device than hard disk drives, and it has been widely used in electronic products as people pursue non-volatile storage products with low power consumption, light weight and high performance. At present, the planar NAND flash memory is close to the limit of practical expansion. In order to further increase the storage capacity and reduce the storage cost per bit, a 3D NAND memory is proposed.

In the 3D NAND memory structure, a stacked 3D NAND memory structure is realized by vertically stacking multiple layers of data storage units. When forming a 3D NAND memory, first, a stacked layer of silicon nitride (Si ₃ N ₄ ) layer and silicon oxide (SiO ₂ ) layer is formed on the substrate, and the sidewall of the stacked layer has a stepped shape; A channel hole (Channelhole) is formed in the layer, and the channel hole is used to form a storage area; after the storage area is formed in the channel hole, the silicon nitride layer in the stack layer is removed, and then the metal material is filled, so that the stack The silicon nitride layer in each layer is replaced by a metal layer, the metal layer of each layer is the control gate of each layer of memory cells, and each step of the stacked layers is used to form a contact plug of each layer of control gate.

Currently, a chemical vapor deposition (CVD) process is usually used to fill metal tungsten (W) to form a metal layer. With the continuous improvement of integration, the number of stacked layers is also increasing, and the size of the gate lines is also decreasing. During the filling process, defects such as seams or voids will appear, which will lead to leakage. And problems such as abnormal heating affect the yield and reliability of the device.

Contents of the invention

In view of this, the object of the present invention is to provide a filling method for metal tungsten, which can reduce filling defects and improve filling quality.

To achieve the above object, the present invention has the following technical solutions:

A method for filling metal tungsten, forming a stacked layer with a 3D NAND device on a substrate, and after the silicon nitride layer in the stacked layer is removed; filling with metal tungsten, the filling process of metal tungsten includes :

The reaction gas is hydrogen and tungsten hexafluoride, the pressure is 5-30torr, the temperature is 250-430°C, the flow rate of hydrogen gas is 7500-20000sccm, and the flow rate of tungsten hexafluoride is 60-500sccm.

Optionally, before the metal tungsten is filled, the deposition of a tungsten seed layer is also included.

Optionally, the deposition process of the tungsten seed layer includes: the reaction gas is diborane and tungsten hexafluoride, and the pressure, temperature and flow rate of tungsten hexafluoride are respectively related to the pressure and temperature in the filling process of the metal tungsten The flow rate of tungsten hexafluoride is the same, and the flow rate of diborane is 300-750 sccm.

Optionally, the flow rate of diborane is 400-500 sccm.

Optionally, the number of removed silicon nitride layers in the stacked layers is 32 or 64 layers.

Optionally, in the filling process of metal tungsten, the pressure is 5-15 torr.

Optionally, in the filling process of metal tungsten, the temperature is 250-300°C, the flow rate of tungsten hexafluoride is 100-300 sccm, and the flow rate of hydrogen gas is 9000-19000.

Optionally, in the filling process of metal tungsten, the pressure is 30 torr, the temperature is 250° C., the flow rate of tungsten hexafluoride is 60 sccm, and the flow rate of hydrogen gas is 9500 sccm.

The filling method of metal tungsten provided by the embodiment of the present invention is applied to the filling of the control gate of the 3D NAND device, and is performed after the silicon nitride layer in the stacked layer of the 3D NAND device is removed in the filling process. In the filling process, the reaction gas It is hydrogen and tungsten hexafluoride, the pressure is 5-30torr, the temperature is 250-430°C, the flow rate of hydrogen gas is 7500-20000sccm, and the flow rate of tungsten hexafluoride is 60-500sccm. This method is especially suitable for the filling of deeper holes and higher aspect ratios. The deposition rate during filling is low, which can effectively reduce the gaps and filling defects in filling, and improve the filling quality.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are For some embodiments of the present invention, those skilled in the art can also obtain other drawings based on these drawings without creative work.

1 to 5 show schematic cross-sectional structures during the manufacturing process of 3D NAND devices.

detailed description

In order to make the above objects, features and advantages of the present invention more comprehensible, specific implementations of the present invention will be described in detail below in conjunction with the accompanying drawings.

In the following description, a lot of specific details are set forth in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described here, and those skilled in the art can do it without departing from the meaning of the present invention. By analogy, the present invention is therefore not limited to the specific examples disclosed below.

Secondly, the present invention is described in detail in combination with schematic diagrams. When describing the embodiments of the present invention in detail, for the convenience of explanation, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic diagram is only an example, and it should not be limited here. The protection scope of the present invention. In addition, the three-dimensional space dimensions of length, width and depth should be included in actual production.

As described in the background technology, in the manufacturing process of 3D NAND memory, the stacked 3D NAND memory structure is realized by vertically stacking multi-layer data storage cells. When forming the control gate, the nitride in the stacked layer is After the silicon layer is removed, it is filled with metal tungsten to form a control gate. The filling position is located between two silicon oxide layers. Seam or void defects are prone to appear during filling, especially when the integration level continues to increase. Afterwards, the number of stacked layers continued to increase, the size of the gate lines also continued to decrease, and the defects became more obvious. During the use of the device, there will be problems such as leakage and abnormal heating, which will affect the yield and reliability of the device.

For this reason, the present invention proposes a method for filling metal tungsten, forming a stacked layer with a 3D NAND device on the substrate, and after the silicon nitride layer in the stacked layer is removed; filling with metal tungsten, so The filling process of metal tungsten includes:

The reaction gas is hydrogen and tungsten hexafluoride, the pressure is 5-30torr, the temperature is 250-430°C, the flow rate of hydrogen gas is 7500-20000sccm, and the flow rate of tungsten hexafluoride is 60-500sccm.

This method is the filling of metal tungsten when forming the control gate in the manufacture of 3D NAND devices. This method is especially suitable for filling deeper holes and higher aspect ratios. The deposition rate during filling is low, which can effectively reduce gaps and voids in filling. Fill defects and improve filling quality.

In order to better understand the technical solutions and technical effects of the present invention, the following will be described in detail in conjunction with specific embodiments.

Referring to FIG. 1 , the method is performed after forming a stack layer 110 with 3D NAND devices on a substrate 100 and removing the silicon nitride layer 1102 in the stack layer 110 .

In order to better understand the technical solution of the present invention, the manufacturing process before metal tungsten filling will be described in detail in combination with specific examples.

Firstly, a substrate 100 is provided, and a stacked layer 110 is formed on the substrate 100. The stacked layer 110 is formed by alternately stacking nitride layers 1102 and oxide layers 1101, as shown in FIG. 1 .

The substrate 100 is a semiconductor substrate, such as a Si substrate, a Ge substrate, a SiGe substrate, SOI (Silicon On Insulator, Silicon On Insulator) or GOI (Germanium On Insulator, Germanium On Insulator) and the like. In other embodiments, the semiconductor substrate may also be a substrate including other elemental semiconductors or compound semiconductors, such as GaAs, InP or SiC, etc., or a stacked structure, such as Si/SiGe, etc., or other epitaxial Structures, such as SGOI (silicon germanium on insulator), etc. Typically, the substrate is a bulk silicon substrate.

The stacked layer 110 is formed by alternately stacking silicon nitride layers and oxide layers, and the number of layers of the stacked layer 110 is determined according to the number of memory cells required to be formed in the vertical direction. The number of layers of the stacked layer 110 can be, for example, 32 layers, 64 layers, etc. The number of stacked layers here refers to the number of layers of the silicon nitride layer. The silicon nitride layer is a sacrificial layer, which will be replaced by a metal layer in subsequent steps, and is the control gate of the storage device. The number of layers determines the number of storage units in the vertical direction. Therefore, the more layers there are in the stack, the more integration can be improved.

The stacked layer 110 can be formed by alternately depositing silicon nitride and silicon oxide sequentially by using chemical vapor deposition, atomic layer deposition or other suitable deposition methods; The structure is used to subsequently form a contact on the control gate, and the central area of the stacked layer is used to form a channel hole and a storage area in the channel hole.

Next, channel holes 120 are formed in the stacked layers.

The channel hole 120 is a through hole in the stack layer 110, and an etching technique, such as RIE (Reactive Ion Etching) method, may be used to etch the stack layer until the substrate surface is exposed, or a part of the substrate may be over-etched. , thereby forming the channel hole 120 . After the channel hole 120 is formed, usually, by selective epitaxial growth (Selective Epitaxial Growth), an epitaxial structure 122 is grown in situ at the bottom of the channel hole 110, and the epitaxial structure 122 plays a role of connecting the storage area in the channel hole , and to support the stacked layers while removing the silicon nitride layer.

Then, a memory region is formed in the channel hole.

The storage area of the NAND storage device includes a charge trapping layer and a channel layer. In this step, the charge trapping layer is first formed in the channel hole. In a specific embodiment, the charge trapping layer is a stack of ONO, ONO (Oxide-Ntride- Oxide) is oxide, nitride and oxide. The charge trapping layer of the ONO can be formed by atomic layer deposition (ALD). After deposition, the sidewalls as well as the bottom of the channel hole are covered with the charge trapping layer. Then, a channel layer is formed. In a specific embodiment, polysilicon is used to form the channel layer. Finally, oxide is filled in the channel hole, thereby completing the fabrication of the storage area in the channel hole.

Then, referring to FIG. 2 , the stacked layer 110 is etched to form a gate line seam (Gate Line Seam) 130 , and the silicon nitride layer 1102 in the stacked layer 110 is removed through the gate line seam 130 , as shown in FIG. 3 .

When removing the silicon nitride layer 1102 in the stacked layer, an acid solution with a high selectivity ratio to silicon nitride and silicon oxide is selected to realize the removal of silicon nitride while avoiding the removal of silicon oxide. In the actual process, usually adopt Phosphoric acid (H ₃ PO ₄ ) performs the removal of the silicon nitride layer.

After the removal of the silicon nitride layer, as shown in FIG. 3 , the stacked layer 110 is a hollow structure, and between the oxide layers 1101 is a vacant layer 1103 , which is filled with metal to form a gate line, which is the control gate of the memory cell. The metal tungsten filling method of the present invention is to fill the metal tungsten after the removal of the silicon nitride layer. Compared with the formation of tungsten in other semiconductor processes, filling the metal tungsten in the hollow structure requires a lower filling rate. , to improve filling quality and avoid filling defects.

When chemical vapor deposition (CVD) deposits tungsten, the reaction gases used are hydrogen (H ₂ ) and tungsten hexafluoride (WF ₆ ), and the reaction rate, that is, the deposition rate formula is as follows:

DepRate＝R ₀ e ^-E/kT [H ₂ ] ^0.5 [WF ₆ ] ⁰

Among them: K, R ₀ , E are relative deposition coefficients; [H ₂ ] is partial pressure of hydrogen; [WF ₆ ] is partial pressure of WF ₆ ; T is temperature.

It can be seen that the deposition rate is mainly reduced by the temperature of the reaction and the partial pressure of the reaction gas, while for the filling of the hollow structure in the 3D NAND device, the deposition rate is reduced only by the reduction of the gas partial pressure and temperature. It will bring the problems of high resistivity and increased stress of metal tungsten. At this time, metal tungsten is used as the control gate of the memory, and the high resistivity and increased stress will cause performance problems, which cannot meet the filling quality and performance requirements at the same time. Require.

For this reason, the inventor, through research, proposed the problem of filling the gate lines in the above-mentioned 3D NAND device, and proposed a filling method of metal tungsten. At this time, the stacked layer 110 on the substrate 100 is a hollow structure, Referring to Figure 3, the filling process includes:

The reaction gas is hydrogen and tungsten hexafluoride, the pressure is 5-30torr, the temperature is 250-430°C, the flow rate of hydrogen gas is 7500-20000sccm, and the flow rate of tungsten hexafluoride is 60-500sccm.

In this filling, the pressure during deposition is further reduced, combined with appropriate temperature and flow rate, better filling quality can be obtained, and at the same time, properties such as resistivity and stress can also meet the requirements.

Before the tungsten filling, preferably, the tungsten seed layer is deposited first.

In the deposition process of the tungsten seed layer, the reaction gases are diborane (B ₂ H ₆ ) and tungsten hexafluoride, the tungsten seed layer and the tungsten filling are usually performed in the same equipment, and the pressure, temperature and The setting of tungsten hexafluoride gas flow rate in the whole process can be the same. During the specific deposition, firstly, select the process temperature from the temperature range of 250-430°C, select the process pressure from the pressure range of 5-30torr, B ₂ H ₆ The flow range of WF ₆ is 300-750sccm, and the flow rate of WF 6 is 60-500sccm. Under these process conditions, tungsten is deposited to form a tungsten seed layer; after that, the supply of B ₂ H ₆ is stopped, and hydrogen gas is introduced. The flow rate is 7500-20000 sccm, other process conditions remain unchanged, the temperature, pressure and flow rate of WF ₆ during the previous deposition are maintained, and a thicker layer of tungsten is filled. After filling, the gap between the oxide layers 1101 is filled with tungsten metal layer, so that the gate line 1104 is formed in the vacant layer of the stack layer, as shown in FIG. The wet etching process removes the part of the metal tungsten layer 140 , as shown in FIG. 5 .

In a more preferred embodiment, the range of pressure is 5-15 torr, the range of temperature is 250-300°C, the flow rate of B ₂ H ₆ is in the range of 750-1500 sccm, the flow rate of WF ₆ is in the range of 100-300 sccm, H ₂ The flow range is 9000-19000sccm. It should be noted that the above ranges of parameters such as temperature, pressure, and flow rate mean that in the deposition process, these parameters are selected from the ranges.

In a more preferred embodiment, in the filling process of metal tungsten, the pressure is 30 torr, the temperature is 250°C, the flow rate of tungsten hexafluoride is ₆₀ sccm, the flow rate of _B2H6 is 450 sccm, and the flow rate of hydrogen gas is 9500 sccm , under this process condition, the deposition rate is

In a specific embodiment, the pressure is 40torr, the temperature is 300°C, the flow of WF ₆ is 400sccm, and the flow of H ₂ is 19000sccm. At this time, the deposition rate of tungsten is

In a specific embodiment, the pressure is 30torr, the temperature is 300°C, the flow of WF ₆ is 400sccm, and the flow of H ₂ is 19000sccm. At this time, the deposition rate of tungsten is

In a specific embodiment, the pressure is 40torr, the temperature is 250°C, the flow of WF ₆ is 400sccm, and the flow of H ₂ is 19000sccm. At this time, the deposition rate of tungsten is

In a specific embodiment, the pressure is 30 torr, the temperature is 250°C, the flow of WF ₆ is 400 sccm, and the flow of H ₂ is 19000 sccm. At this time, the deposition rate of tungsten is

The above metal tungsten deposition is especially suitable for the filling of deeper holes and higher aspect ratios. It is applied in the gate line filling process of 32-layer and 64-layer 3D memory devices. The deposition rate during filling is low, which can effectively reduce the filling process. Filling defects in gaps and cavities improves the quality of filling, while ensuring that the resistivity and stress of the grid line meet the requirements.

The above descriptions are only preferred implementations of the present invention. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person familiar with the art, without departing from the scope of the technical solution of the present invention, can use the methods and technical content disclosed above to make many possible changes and modifications to the technical solution of the present invention, or modify it into an equivalent of equivalent change Example. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments according to the technical essence of the present invention, which do not deviate from the technical solution of the present invention, still fall within the protection scope of the technical solution of the present invention.

Claims (8)

1. A method for filling metal tungsten, characterized in that, on a substrate, a stacked layer with a 3D NAND device is formed, and after the silicon nitride layer in the stacked layer is removed; the filling of metal tungsten is carried out, the The filling process of metal tungsten includes: The reaction gas is hydrogen and tungsten hexafluoride, the pressure is 5-30torr, the temperature is 250-430°C, the flow rate of hydrogen gas is 7500-20000sccm, and the flow rate of tungsten hexafluoride is 60-500sccm. 2 . The method according to claim 1 , further comprising depositing a tungsten seed layer before filling the metal tungsten. 3 . 3. method according to claim 2, is characterized in that, the deposition process of described tungsten seed layer comprises: reaction gas is diborane and tungsten hexafluoride, and the flow rate of pressure, temperature and tungsten hexafluoride are respectively with the described tungsten hexafluoride The pressure, temperature and flow rate of tungsten hexafluoride in the filling process of metal tungsten are the same, and the flow rate of diborane is 300-750 sccm. 4. The method according to claim 3, characterized in that the flow of diborane is 400-500 sccm. 5 . The method according to claim 1 , wherein the number of removed silicon nitride layers in the stacked layers is 32 layers or 64 layers. 6. The method according to any one of claims 1-5, characterized in that, in the filling process of the metal tungsten, the pressure is 5-15 torr. 7. The method according to claim 6, characterized in that, in the filling process of metal tungsten, the temperature is 250-300°C, the flow rate of tungsten hexafluoride is 100-300 sccm, and the flow rate of hydrogen gas is 9000-19000. 8. The method according to any one of claims 1-5, characterized in that, in the filling process of metal tungsten, the pressure is 30 torr, the temperature is 250°C, the flow rate of tungsten hexafluoride is 60 sccm, and the flow rate of hydrogen The flow rate is 9500sccm.