Forming method and processing device of high aspect ratio structure

Abstract

The invention discloses a forming method and a processing device of a high aspect ratio structure. The forming method comprises the steps that a substrate is provided and comprises a to-be-etched material layer, the upper surface of the substrate is provided with a carbon-based mask layer, and the carbon-based mask layer is provided with a plurality of openings to expose the to-be-etched material layer; etching: introducing etching gas, and selectively etching the exposed to-be-etched material layer to form an etching hole; in the etching process, a polymer is formed on the side wall of the opening; a finishing step: introducing a finishing gas, and etching the polymer; the finishing gas comprises rare gas, nitrogen-containing gas and oxygen-containing gas; and alternately and repeatedly executing the etching step and the finishing step until the etching hole reaches the preset depth. According to the forming method provided by the invention, the etching step is switched into the finishing step at a proper time, and the finishing step is limited to be carried out on the mask layer by selecting proper finishing gas and controlling process conditions, so that the etching efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of semiconductor device processing, and in particular relates to a method for forming a high aspect ratio structure and a processing device. Background Art

[0002] With the advent of the big data era, the demand for storage has increased exponentially. To meet this demand, the technology of storage chips has transformed from 2D NAND to 3D NAND, which has higher storage density but more complex structure.

[0003] One of the challenges in plasma etching is the ever-increasing aspect ratios required to meet design requirements for high-density or ultra-high-density structures.

[0004] In traditional processes, in order to form holes or groove structures with high aspect ratios, methods such as increasing power or extending processing time are usually used, that is, by using very high RF power (including high-frequency source RF and low-frequency bias RF) for a long time, deep hole etching is achieved and a sufficiently thick polymer protective layer is formed on the etch stop layer or conductor layer at the bottom of the deep hole to reduce damage to the etch stop layer or conductor layer. However, this long-term high-power bombardment is not only inefficient and energy-intensive, but also easily damages other components in the processing chamber, reducing its service life. Summary of the invention

[0005] The purpose of the present invention is to improve the forming efficiency of a structure with a high aspect ratio and to improve the yield rate of the structure with a high aspect ratio.

[0006] In order to achieve the above object, the present invention provides a method for forming a high aspect ratio structure, comprising the following steps:

[0007] A substrate is provided, comprising a material layer to be etched, wherein a carbon-based mask layer is disposed on the upper surface of the material layer to be etched, and the carbon-based mask layer is provided with a plurality of openings to expose the material layer to be etched;

[0008] Etching step: introducing etching gas to selectively etch the exposed material layer to be etched to form an etching hole; during the etching process, a polymer is also formed on the side wall of the opening;

[0009] Trimming step: introducing a trimming gas to etch the polymer; the trimming gas includes a rare gas, a nitrogen-containing gas and an oxygen-containing gas, wherein the flow rate of the nitrogen-containing gas is not less than the flow rate of the rare gas; the nitrogen-containing gas can dissociate into nitrogen positive ions;

[0010] The etching step and the trimming step are performed alternately and repeatedly until the etched hole reaches a predetermined depth.

[0011] Optionally, the flow ratio of the rare gas to the nitrogen-containing gas is 0.6:1 to 1:1.

[0012] Optionally, the nitrogen-containing gas includes at least one of N2 (nitrogen) and nitrogen oxides.

[0013] Optionally, the rare gas includes at least Ar (argon).

[0014] Optionally, the nitrogen-containing gas does not contain oxygen, and the proportion of the oxygen-containing gas in the total flow of the trimming gas is 0.5% to 1%.

[0015] Optionally, the oxygen-containing gas is O2 (oxygen) or O3 (ozone).

[0016] Optionally, the rare gas flow rate is 400 sccm to 800 sccm, and the nitrogen-containing gas flow rate is 400 sccm to 800 sccm.

[0017] Optionally, the process gas pressure in the trimming step is higher than the process gas pressure in the etching step.

[0018] Optionally, in the trimming step, the process gas pressure is 100mT to 180mT.

[0019] Optionally, in the trimming step, the power of the bias radio frequency in the trimming step is lower than the power of the bias radio frequency in the etching step.

[0020] Optionally, in the trimming step, the source RF is turned on, the RF frequency is 60 MHz, and the power is 1800 W to 2200 W; the bias RF is also turned on, the RF frequency is not higher than 2 MHz, and the power is 100 W to 500 W.

[0021] Optionally, in the trimming step, the frequency of the bias radio frequency is 400KHz and the power is 300W to 500W.

[0022] Optionally, the time ratio of the etching step to the trimming step is 12:1 to 7:1.

[0023] Optionally, the material layer to be etched is a silicon oxide layer, or a structure in which silicon oxide layers and silicon nitride layers are alternately stacked, or a structure in which silicon oxide layers and polysilicon layers are alternately stacked.

[0024] Optionally, the etching selectivity ratio of the etching gas to the material layer to be etched and the mask layer is not less than 10:1.

[0025] Optionally, the etching gas includes at least one of O 2 and CO (carbon monoxide) and at least one of CF gas and CHF gas.

[0026] Optionally, the forming method is used to etch and form contact holes on each level of the stepped structure in the stepped region of a 3D NAND.

[0027] Optionally, a stepped etch stop layer is formed on each level of the stepped structure.

[0028] Optionally, an etching selectivity ratio of the etching gas to the material layer to be etched and the etching stop layer is not less than 150:1.

[0029] The present invention also provides a processing device for a high aspect ratio structure, characterized by comprising:

[0030] Processing chamber;

[0031] Source RF;

[0032] Bias RF; and

[0033] Control Department;

[0034] The control unit controls the processing device to execute the method for forming a high aspect ratio structure as described above.

[0035] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0036] During the etching process of the present invention, when the polymer on the side wall of the opening of the carbon-based mask layer accumulates to a certain extent and is still relatively loose and not dense enough, the step is switched to a trimming step to specifically trim and remove the polymer on the side wall of the opening of the carbon-based mask layer, thereby avoiding the aperture of the opening of the mask layer from gradually shrinking as the etching proceeds, greatly improving the etching efficiency, reducing production costs, and improving the morphology of the etched holes.

[0037] In the trimming step, a specific trimming gas is introduced, wherein the rare gas and the nitrogen-containing gas have different ion scattering radii, and the opening side walls of the mask layer can be fully covered. The polymer is loosened and then sputtered away by ion bombardment; the oxygen-active particles dissociated from the oxygen-containing gas react chemically with the polymer, and the polymer can also be effectively removed.

[0038] Furthermore, the present invention also limits the trimming step mainly to the mask layer on the surface of the substrate by controlling the process gas pressure, source RF and bias RF power in the processing chamber, without affecting the deposited layer in the etched hole, which not only improves the trimming efficiency but also avoids the loss of the deposited layer.

[0039] In addition, the present invention also optimizes the time ratio between the etching step and the trimming step, ensures the overall process efficiency by controlling the start timing of the trimming step, and improves the etching efficiency of the high-power etching step. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1The present invention is a flow chart of a method for forming a high aspect ratio structure in the prior art.

[0041] Figure 2 for Figure 1 Schematic diagram of the morphology of the substrate corresponding to each step in the formation method, wherein a represents the morphology of the substrate before treatment, b represents the morphology of the substrate after treatment in high-power etching step 1 (S1.1), c represents the morphology of the substrate after treatment in high-power etching step 2 (S1.2), and d represents the morphology of the substrate after treatment in high-power etching step 3 (S1.3).

[0042] Figure 3 The present invention is a flowchart of a method for forming a high aspect ratio structure.

[0043] Figure 4 It is a schematic diagram of the morphology of the substrate corresponding to each step in the formation method of the present invention, wherein a represents the morphology of the substrate provided in step S1, b represents the morphology of the substrate after being processed in the etching step (S2), c represents the morphology of the substrate after being processed in the trimming step (S3), and d represents the morphology of the substrate after being processed by alternating and repeating the etching step and the trimming step (S4).

[0044] Figure 5 It is a schematic diagram of the principle of the trimming step of the present invention, wherein a shows the scattering state of Ar ions and nitrogen ions in the trimming step, and b shows the morphology of the opening of the mask layer after the trimming step is completed.

[0045] Figure 6 A schematic diagram of a partial semiconductor structure of a three-dimensional storage device.

[0046] Figure 7 It is a structural schematic diagram of a processing device for a high aspect ratio structure of the present invention.

[0047] Figure 8 This is a comparison diagram of the opening morphology of the mask layer in the etching method of the embodiment of the present invention and the opening morphology of the carbon-based mask layer in the etching method of the comparative example, wherein a represents a scanning electron microscope image of the opening of the mask layer after the etching of the embodiment is completed, and b represents a scanning electron microscope image of the opening of the mask layer after the etching of the comparative example is completed.

[0048] Figure ID:

[0049] Plasma 1

[0050] Base layer 10

[0051] Layer 11

[0052] Conductor layer 111

[0053] Insulation layer 112

[0054] Extension 113

[0055] Dielectric layer 20

[0056] Etching hole 21

[0057] Sedimentary layer 211

[0058] Contact hole 21'

[0059] Mask layer 30

[0060] Opening 31

[0061] Polymer 311

[0062] Etch stop layer 40

[0063] Processing chamber 71

[0064] Source RF 72

[0065] The first radio frequency matching network 721

[0066] Bias RF 73

[0067] The second RF matching network 731

[0068] Control unit 74

[0069] Transmission port 701

[0070] Gas sprinkler head 702

[0071] Base 703

[0072] Gas supply device 704

[0073] Electrostatic chuck 705

[0074] Electrostatic electrode 706

[0075] Vacuum pump 707. DETAILED DESCRIPTION

[0076] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0077] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0078] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0079] In the 3D NAND process with higher storage density and more complex structure, the preparation of stacked structures often exists. Whether it is the oxide / nitride overlapping process or the oxide / polysilicon overlapping process, a very critical process is involved, namely etching step holes. This process usually requires a carbon-based mask layer of several microns (such as amorphous carbon) as a protective etching to form contact holes of several microns to more than ten microns, and finally stops on a conductor layer of tens of nanometers (such as tungsten, etc.) or an etching stop layer (such as SiN (silicon nitride), etc.), and the damage caused by plasma to the conductor layer or the etching stop layer needs to be controlled within a very small range. This process has several major characteristics such as high aspect ratio, high selectivity, and long process time.

[0080] like Figure 1 As shown, the conventional process usually adopts steps S1.1, S1.2, S1.3 and other multiple etchings under very high RF power (combination of high frequency and low frequency) conditions to complete the etching of the deeper contact holes, and to form a sufficiently thick polymer protective layer on the conductor layer or the etch stop layer at the bottom of the contact hole to reduce damage to the conductor layer or the etch stop layer.

[0081] like Figure 2As shown in the figure, a is the morphology of the substrate before etching, b shows the morphology of the substrate after etching in step S1.1, c shows the morphology of the substrate after etching in step S1.2, and d shows the morphology of the substrate after etching in step S1.3 or even more times. It can be seen that under such a process window, polymers can easily accumulate on the side walls of the carbon-based mask layer. As etching continues, more and more polymers will accumulate on the side walls of the carbon-based mask layer, making the opening aperture of the mask layer smaller and smaller. In addition, the problem of polymer accumulation on the side walls of the mask layer will also exist in the etching process of other high aspect ratio structures. This will lead to the following consequences: 1) It will deflect the angle of ion incidence, causing the contour deformation and side wall bowing of the etching hole bottom, resulting in a decrease in yield; 2) It will block the flux of precursors and ions entering the etching hole, causing a decrease in the etching rate; 3) When the accumulation reaches a certain level, it will cause blockage of the etching hole, making etching difficult; 4) Since the etching rate is reduced, the etching time will be extended, resulting in increased high-power RF bombardment and consumption of other components in the chamber.

[0082] In view of the above-mentioned problems of traditional etching methods, the present invention proposes a new etching method, which can timely trim and remove the accumulation of polymer on the side wall of the carbon-based mask layer, thereby improving the etching efficiency, obtaining better etching hole morphology, and at the same time reducing the wear rate of vulnerable parts in the chamber and extending the service life.

[0083] like Figure 3 As shown, the present invention provides a method for forming a high aspect ratio structure, comprising:

[0084] Step S1, providing a substrate, which includes a material layer to be etched, wherein the material layer to be etched includes a dielectric layer, a carbon-based mask layer is disposed on the upper surface of the dielectric layer, and the carbon-based mask layer is provided with a plurality of openings to expose the dielectric layer.

[0085] like Figure 4 As shown in a, it is a partial example of a substrate, including: a base layer 10. In one embodiment, the base layer 10 has a slope structure formed by a horizontal cross section of the side portion extending horizontally step by step from top to bottom. A dielectric layer 20 is formed on the slope structure, and the length of the horizontal cross section of the dielectric layer 20 gradually shortens from top to bottom. The base layer 10 is flush with the upper surface of the dielectric layer 20 and is in the same horizontal plane. A mask layer 30 is also provided on the upper surface of the base layer 10 and the dielectric layer 20. The mask layer 30 covering the upper surface of the dielectric layer 20 is formed with an opening 31 of a certain pattern to expose the dielectric layer 20 to be etched. By selective etching, the pattern can be transferred to the dielectric layer 20 to form an etching hole 21, see Figure 4 b, c, d.

[0086] In this embodiment, the slope structure is stepped, and the etched hole 21 is a step through hole. The base layer 10 is formed by stacking a plurality of stacked layers 11, wherein each stacked layer at least comprises a conductor layer 111 and an insulating layer 112. The material of the conductor layer 111 may be polysilicon or a conductive metal, such as tungsten. The material of the insulating layer 112 may be an oxide, such as silicon oxide. The material layer to be etched is a dielectric layer 20. The material of the dielectric layer 20 is silicon oxide.

[0087] In another embodiment, the material layer to be etched is a planar structure formed by stacking multiple layers, for example, each stack 11 includes a silicon oxide layer and a silicon nitride layer, or includes a silicon oxide layer and a polysilicon layer. In yet another embodiment, the material layer to be etched is a planar structure formed by a single material, such as silicon oxide.

[0088] The material of the carbon-based mask layer includes at least one of amorphous carbon, silicon carbide (SiC), boron-doped carbon (BDC), spin-on-carbon hard mask (SOC) and diamond-like carbon (DLC).

[0089] Step S2, etching step: introducing etching gas to selectively etch the exposed dielectric layer to form etching holes; during the etching process, polymer is also formed on the sidewalls of the openings.

[0090] In order to achieve selective etching of the dielectric layer, the etching selectivity ratio of the etching gas to the dielectric layer and the mask layer is not less than 10:1. In order to improve the selectivity of the etching gas, the etching gas can select at least one of O2 and CO and CF gas, wherein CF gas refers to a compound composed of fluorine atoms and carbon atoms. When etching SiN, the CF gas can be replaced with CHF gas, or CF gas and CHF gas can be added at the same time, wherein CHF gas refers to a compound composed of fluorine atoms, carbon atoms and hydrogen atoms. Using the above-mentioned etching gas, a deposition layer 211 of a certain thickness can be formed at the bottom of the etching hole while forming the etching hole, avoiding damage to the etching stop layer or conductive layer in contact with the bottom of the dielectric layer. The CF gas can select C4F6, C4F8, C3F8 and other gases known in the art. The CHF gas can select CH2F2, CHF3, C4H2F6 and other gases known in the art.

[0091] However, during the etching process, when the deposition layer 211 is formed at the bottom of the etching hole, the polymer 311 is inevitably formed on the sidewall of the mask layer opening, thereby causing the aperture of the opening to gradually become smaller. Figure 4 b. Figure 5As shown in a, the etching rate and the morphology of the etched hole are affected. Therefore, measures need to be taken to remove the polymer 311, and it is best not to affect the deposited layer 211. The polymer 311 is usually C x F y (x, y are positive numbers) polymer.

[0092] Step S3, a trimming step: introducing a trimming gas to etch the polymer; the trimming gas includes a rare gas, a nitrogen-containing gas and an oxygen-containing gas, and the nitrogen-containing gas can dissociate into nitrogen positive ions. Preferably, the flow rate of the nitrogen-containing gas is not less than the flow rate of the rare gas.

[0093] The trimming step is to specifically remove the polymer 311 on the sidewalls of the mask layer opening, and to concentrate the etching reaction on the sidewalls of the mask layer 30, without involving the etching of the deposition layer 211 at the bottom of the etching hole. To this end, the present invention adopts the following measures:

[0094] 1) Start time of the trimming step: The present invention switches to the trimming step when the polymer 311 has just accumulated to a certain extent on the side wall of the mask layer 30 and is not yet dense. The advantage of this is that the polymer 311 is relatively loose and can be easily removed through the trimming step without damaging the deposition layer 211 at the bottom of the etched hole. If trimming is performed when the etching time of step S2 is too short, frequent process switching will affect process efficiency. If trimming is performed when the etching time of step S2 is too long, the polymer 311 accumulates on the side wall of the mask layer 30 and becomes increasingly dense, making it more difficult to remove, especially considering that the deposition layer 211 at the bottom of the etched hole 21 must not be damaged.

[0095] 2) The trimming gas contains rare gases, which dissociate into heavier positive ions under high pressure and high frequency, and can provide stronger vertical downward physical bombardment, such as Figure 5 As shown in a, it plays the role of loosening the polymer 311 on the side wall of the mask layer 30 and sputtering it away. The rare gas can be at least one of argon (Ar), krypton (Kr) and xenon (Xe). Preferably, the rare gas includes at least argon (Ar).

[0096] 3) The trimming gas contains nitrogen-containing gas. The ion scattering radius of the nitrogen positive ions dissociated under high pressure and high frequency is large, which is particularly conducive to lateral etching, that is, it is easier to bombard the side wall of the opening 31 of the mask layer 30, and it is not easy to enter the etching hole 21 to etch the deposition layer 211 at the bottom of the etching hole. After the trimming step of the present invention, the morphology of the opening 31 of the mask layer is as follows: Figure 4 c. Figure 5 As shown in b, the polymer 311 is basically removed, the opening profile of the mask layer is restored to the initial state, and the etching step can be continued.

[0097] It is found in the experiment that when the flow rate of the nitrogen-containing gas is greater than or equal to the flow rate of the rare gas, it is easier to cover the mask layer and it is not easy to damage the deposited layer 211 in the etched hole. In some embodiments, the flow rate ratio of the rare gas to the nitrogen-containing gas is 0.6:1 to 1:1. The flow rate of the rare gas is 400 sccm to 800 sccm, and the flow rate of the nitrogen-containing gas is 400 sccm to 800 sccm.

[0098] The nitrogen-containing gas is capable of dissociating into nitrogen cations (such as N + 、N2 + The gas may be N2 or nitrogen oxides, such as N2O and NO.

[0099] 4) The trimming gas includes an oxygen-containing gas, and the active oxygen ions or free radicals dissociated from the oxygen-containing gas can easily react with the polymer on the sidewall to remove the polymer 311 .

[0100] In some embodiments, when the nitrogen-containing gas also contains oxygen, for example, N2O or NO, oxygen or other oxygen-containing gas may not be added.

[0101] In some embodiments, in order to prevent the mask layer from being over-consumed, the nitrogen-containing gas without oxygen is used, and the oxygen-containing gas accounts for 0.5% to 1% of the total flow of the trimming gas. As an example, the oxygen-containing gas may be O2 or O3.

[0102] 5) Because the number of collisions increases under higher gas pressure, the average free path of ions is shorter, and it is easier to bombard and sputter the polymer 311 on the mask layer closer to the plasma. In addition, higher gas pressure can also prevent the deposition layer 211 at the bottom of the etching hole from being extracted. Therefore, in order to further limit the trimming step to the mask layer 30 and less involve the etching hole 21, and prevent the deposition layer 211 from being extracted, the process gas pressure in the trimming step is higher than the process gas pressure in the etching step. Preferably, in the trimming step, the process gas pressure is 100mT to 180mT.

[0103] 6) Since the bias RF is used to physically bombard the substrate, the power of the bias RF in the trimming step is lower than the power of the bias RF in the etching step, so as to appropriately physically bombard the mask layer closer to the plasma, loosen and remove the polymer 311, and avoid damaging the deposited layer 211 in the etched hole.

[0104] In the trimming step, the source radio frequency is turned on, the radio frequency frequency is 60MHz, and the power is 1800W~2200W, so as to activate the trimming gas and dissociate it into plasma. Furthermore, the bias radio frequency is also turned on, and its radio frequency frequency is not higher than 2MHz, and the power is 100W~500W, so as to bombard the polymer with ions. The power of low-frequency radio frequency is low, which is conducive to the bombardment of heavy ions on the side walls of the mask layer closer to the plasma, while the bombardment of the deposition layer at the bottom of the etched hole farther from the plasma is very small. In some embodiments, in the trimming step, the frequency of the bias radio frequency is 400KHz, and the power is 300W~500W.

[0105] Step S4, alternately and repeatedly performing the etching step and the trimming step until the etched hole reaches a predetermined depth.

[0106] Generally speaking, when the polymer 311 is formed on the sidewall of the opening of the mask layer, the trimming step can be switched to remove the polymer 311. However, if the switching is too frequent, not only the process is complicated, but also it is easy to cause redundancy and waste of trimming gas. The present invention switches to the trimming step when a certain amount of polymer 311 accumulates on the sidewall of the opening of the mask layer but is still relatively loose. The time ratio of the etching step to the trimming step can be 12:1 to 7:1, and the time of the etching step can be 140s-200s.

[0107] like Figure 4 As shown in FIG. d , by alternately repeating the etching step and the trimming step, after the etching is completed, the aperture of the opening 31 of the mask layer is substantially maintained to be the same as that before the etching begins.

[0108] The method of the present invention can efficiently form etching holes of different depths, and can be used to etch contact holes on the stepped structures of various levels in the stepped region of 3D NAND. In order to form etching protection for the base layer (for example, the conductive layer is polysilicon) during the process of etching the dielectric layer to form etching holes, a stepped etching stop layer can be formed on the stepped structures at various levels. The etching selectivity ratio of the etching gas to the dielectric layer and the etching stop layer is not less than 150:1. The etching stop layer can be SiN or a metal material.

[0109] like Figure 6As shown, a partial semiconductor structure of a three-dimensional memory device includes a base layer 10, a dielectric layer 20, and an etch stop layer 40. The base layer 10 is a stacked structure, which is formed by stacking a plurality of stacks 11, each stack 11 including a conductor layer 111 and an insulating layer 112. The edge of one side of each stack 11 extends outward relative to the edge of the side of the stack 11 above it, and the upper surface of the extension portion 113 formed by each stack 11 is longer than the upper surface of the extension portion 113 formed by the stack 11 above it. The vertical distance from the top of the dielectric layer 20 is longer, and the plurality of extension portions 113 form steps, so that one side of the base layer 10 has a stepped slope structure. The etch stop layer 40 covers the slope structure. The dielectric layer 20 is formed on the etch stop layer 40, and the upper surface of the dielectric layer 20 is flush with the upper surface of the base layer 10. By adopting the processing method of the present invention, the dielectric layer 20 is etched to form a plurality of etching holes 21 of different depths, and then the etching stop layer is penetrated to form a contact hole 21', the bottom of the contact hole 21' is the conductor layer 111, and the contact hole 21' can be filled with a conductor material, such as a metal material, so that the contact hole 21' can independently connect the conductor layer 111 of different depths to the outside, and adjacent contact holes 21' are isolated by the dielectric layer 20. This structure can electrically connect the storage cells of different layers to the peripheral circuit through the mutually insulated contact holes 21', so as to independently perform read and write operations on the storage cells of different layers.

[0110] In order to implement the above processing method, the present invention also provides a processing device for a high aspect ratio structure, which is a dual-frequency plasma system, such as Figure 7 As shown, it includes: a processing chamber 71, a source RF 72, a bias RF 73 and a control unit 74.

[0111] A film transfer port 701 is provided on the side wall of the processing chamber 71 for accommodating the substrate W in and out. A gas shower head 702 and a base 703 arranged opposite to the gas shower head 702 are provided in the reaction chamber. The gas shower head 702 is connected to a gas supply device 704 for delivering reaction gas to the processing chamber 71 and serving as the upper electrode of the processing chamber 71. An electrostatic chuck 705 is provided above the base 703 and serves as the lower electrode of the processing chamber 71. A reaction area is formed between the upper electrode and the lower electrode. An electrostatic electrode 706 is provided inside the electrostatic chuck 705 for generating electrostatic suction to support and fix the substrate W to be processed during the process.

[0112] A source RF power source (usually at 40 MHz-200 MHz) is connected to the lower electrode to excite the reaction gas between the upper electrode and the lower electrode into plasma 1, which is usually composed of a source RF 72 and a first RF matching network 721. A bias power source (usually at 100 kHz-10 MHz) is connected to the lower electrode or the upper electrode to control the distribution of the energy of the plasma 1, i.e., the thickness of the plasma sheath and the DC bias, which is usually composed of a bias RF 73 and a second RF matching network 731.

[0113] The etching gas or trimming gas is injected into the processing chamber 71 through the gas shower head 702, and the source RF 72 generates a high-frequency RF electric field between the upper electrode and the lower electrode, so that the etching gas or trimming gas in the processing chamber 71 is ionized to generate plasma 1. The plasma contains a large number of active particles such as electrons, ions, excited atoms, molecules and free radicals. The above active particles can undergo various physical and chemical reactions with the surface of the substrate to be processed, so that the morphology of the substrate surface changes, that is, the etching or trimming process is completed. The bias RF 73 applies the bias RF voltage to the base 703 through the second RF matching network 731 to control the bombardment direction of the charged particles in the plasma. A vacuum pump 707 is also provided below the processing chamber 71 to extract the reaction by-products out of the vacuum processing chamber 71 and control the process gas pressure.

[0114] The control unit 74 controls the following steps:

[0115] A substrate W is transferred onto the electrostatic chuck 705 , wherein the substrate W includes a material layer to be etched, and a carbon-based mask layer 30 is disposed on the upper surface of the material layer to be etched. The carbon-based mask layer 30 is provided with a plurality of openings 31 to expose the material layer to be etched.

[0116] Etching step: introducing etching gas to selectively etch the exposed material layer to be etched to form an etching hole 31; during the etching process, a polymer 311 is also formed on the side wall of the opening.

[0117] Trimming step: introducing trimming gas to etch the polymer 311; the trimming gas includes a rare gas, a nitrogen-containing gas and an oxygen-containing gas, wherein the flow rate of the nitrogen-containing gas is not less than the flow rate of the rare gas, and the nitrogen-containing gas can dissociate into nitrogen positive ions.

[0118] The etching step and the trimming step are performed alternately and repeatedly until the etched hole reaches a predetermined depth.

[0119] The above processing device is only an example and is not limiting. Other processing devices such as an inductively coupled plasma (ICP) processing device or an electron cyclotron resonance (ECR) plasma processing device can also be used to form the high aspect ratio structure of the present invention.

[0120] Example

[0121] A substrate W is provided, which includes a dielectric layer 20. A carbon-based mask layer 30 is provided on the upper surface of the dielectric layer 20. The carbon-based mask layer 30 is provided with a plurality of openings 31 to expose the dielectric layer 20. The substrate W is transferred to a Figure 7 The high aspect ratio structure processing device is shown on an electrostatic chuck 707. The frequency of the source RF 72 is 60 MHz, and the frequency of the bias RF 73 is 400 KHz.

[0122] Etching step: introducing etching gas through the gas injection port 705, the etching gas contains 40sccm of O2, 500sccm of CO, 40sccm of C4F6 and 40sccm of C4F8; the power of the source RF is 3000W, the power of the bias RF is 10000W, the process pressure is controlled to be 35mT, and the exposed dielectric layer 20 is selectively etched for 200s to form an etching hole 21; during the etching process, a deposition layer is formed at the bottom of the etching hole 21, and a polymer 311 is formed on the side wall of the opening of the mask layer.

[0123] Trimming step: introducing a trimming gas, wherein the trimming gas comprises 450 sccm of Ar, 650 sccm of N2 and 8 sccm of O2, and etching the polymer for 20 seconds; the power of the source RF is 2000 W, the power of the bias RF is 500 W, and the process gas pressure is 150 mT.

[0124] The etching step and the trimming step are repeated alternately, with the time ratio of the etching step to the trimming step being 10:1, until the etched hole reaches a predetermined depth. Figure 8 As shown in a, it is a scanning electron microscope image of an opening part of the mask layer after etching is completed. It can be seen that there is very little polymer deposition at the opening of the mask layer, and the pore size is equivalent to that at the beginning of substrate processing.

[0125] Comparative Example

[0126] Use Figure 1 The conventional process shown in the figure is used for etching. After the etching is completed, the scanning electron microscope image of an opening portion of the mask layer is as follows Figure 8 As shown in b, there is obvious polymer accumulation at the opening of the mask layer, and the aperture is greatly reduced.

[0127] Compared with the comparative example, the method for forming a high aspect ratio structure provided by the present invention has almost no polymer accumulation at the opening of the mask layer, and ultimately, while achieving the same etching amount, the time of the high-power etching step is reduced by about 5% relative to the comparative example, thereby significantly improving the etching efficiency of the high-power etching step.

[0128] In summary, the method for forming a high aspect ratio structure provided by the present invention switches the etching step to the trimming step at an appropriate time, and by selecting a suitable trimming gas and controlling the process conditions, the trimming step is limited to the side wall of the mask layer, thereby achieving the purpose of trimming the polymer on the side wall of the mask layer opening without damaging the polymer at the bottom of the etched hole, thereby improving the etching efficiency and the morphology of the etched hole.

[0129] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.

Claims

1. A method for forming a high aspect ratio structure, characterized in that: The following steps are involved: A substrate is provided, comprising a material layer to be etched, wherein a carbon-based mask layer is disposed on the upper surface of the material layer to be etched, and the carbon-based mask layer is provided with a plurality of openings to expose the material layer to be etched; Etching step: introducing etching gas to selectively etch the exposed material layer to be etched to form etching holes; During the etching process, a polymer is also formed on the sidewalls of the opening; A trimming step: introducing a trimming gas to etch the polymer; the trimming gas includes a rare gas, a nitrogen-containing gas and an oxygen-containing gas, wherein the flow rate of the nitrogen-containing gas is not less than the flow rate of the rare gas, and the nitrogen-containing gas can dissociate into nitrogen positive ions; The etching step and the trimming step are performed alternately and repeatedly until the etched hole reaches a predetermined depth.

2. The method for forming a high aspect ratio structure according to claim 1, wherein: The flow ratio of the rare gas to the nitrogen-containing gas is 0.6:1 to 1:

1.

3. The method for forming a high aspect ratio structure according to claim 1 or 2, characterized in that: The nitrogen-containing gas includes at least one of N2 and nitrogen oxides.

4. The method for forming a high aspect ratio structure according to claim 1 or 2, characterized in that: The rare gas includes at least Ar.

5. The method for forming a high aspect ratio structure according to claim 1 or 2, characterized in that: The nitrogen-containing gas does not contain oxygen, and the proportion of the oxygen-containing gas to the total flow of the trimming gas is 0.5% to 1%.

6. The method for forming a high aspect ratio structure according to claim 5, wherein: The oxygen-containing gas is O2 or O3.

7. The method for forming a high aspect ratio structure according to claim 1 or 2, characterized in that: The flow rate of the rare gas is 400 sccm to 800 sccm, and the flow rate of the nitrogen-containing gas is 400 sccm to 800 sccm.

8. The method for forming a high aspect ratio structure according to claim 1, wherein: The process gas pressure in the trimming step is higher than the process gas pressure in the etching step.

9. The method for forming a high aspect ratio structure according to claim 8, wherein: In the trimming step, the process gas pressure is 100mT to 180mT.

10. The method for forming a high aspect ratio structure according to claim 1, wherein: In the trimming step, the power of the bias radio frequency in the trimming step is lower than the power of the bias radio frequency in the etching step.

11. The method for forming a high aspect ratio structure according to claim 10, wherein: In the trimming step, the source radio frequency is turned on, the radio frequency frequency is 60 MHz, and the power is 1800 W to 2200 W; the bias radio frequency is also turned on, the radio frequency frequency is not higher than 2 MHz, and the power is 100 W to 500 W.

12. The method for forming a high aspect ratio structure according to claim 11, wherein: In the trimming step, the frequency of the bias radio frequency is 400KHz, and the power is 300W to 500W.

13. The method for forming a high aspect ratio structure as claimed in claim 1, characterized in that: The time ratio of the etching step to the trimming step is 12:1 to 7:

1.

14. The method for forming a high aspect ratio structure according to claim 1, wherein: The material layer to be etched is a silicon oxide layer, or a structure in which silicon oxide layers and silicon nitride layers are alternately stacked, or a structure in which silicon oxide layers and polysilicon layers are alternately stacked.

15. The method for forming a high aspect ratio structure according to claim 1, wherein: The etching selectivity ratio of the etching gas to the material layer to be etched and the mask layer is not less than 10:

1.

16. The method for forming a semiconductor structure according to claim 1, wherein: The etching gas includes at least one of O 2 and CO and at least one of CF gas and CHF gas.

17. The method for forming a high aspect ratio structure according to claim 1, wherein: The forming method is used to etch and form contact holes on each level of the stepped structure in the stepped region of a 3D NAND.

18. The method for forming a high aspect ratio structure according to claim 17, wherein: A stepped etching stop layer is formed on each level of the stepped structure.

19. The method for forming a high aspect ratio structure according to claim 18, wherein: The etching selectivity ratio of the etching gas to the material layer to be etched and the etching stop layer is not less than 150:

1.

20. A processing device for a high aspect ratio structure, characterized in that: include: Processing chamber; Source RF; Bias RF; and Control Department; The control unit controls the processing device to execute the method for forming a high aspect ratio structure as described in any one of claims 1-19.

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