Method of depositing a pre-etch protection layer

Abstract

A method of cyclic etching includes: (A) conformally depositing a pre-etch protective layer (120) over the mask (104), the sidewall (116) of the mask (104) defining the mask opening (108), and the exposed portion of the substrate (100) exposed through the mask opening (108) before cyclically etching the substrate (100) through the mask opening (108), the pre-etch protective layer (120) being deposited to a first thickness; and (B) cyclically etching the substrate (100) by the following steps: (i) depositing a protective layer (132) in the opening (108) of the mask (104), the protective layer (132) being deposited to a second thickness less than half of the first thickness; (ii) etching through a portion of the protective layer (132) disposed on the substrate (100) and etching the substrate (100); and (iii) repeating (i) and (ii) until an end point is reached.

Description

Technical Field

[0001] The examples described in this article are generally about methods for depositing a protective film on a substrate before etching it. Background Technology

[0002] The fabrication of microelectronic devices involves many different stages, each comprising various processes. During one stage, a specific process may involve applying plasma to the surface of a substrate to alter its physical and material properties. This process, known as etching, involves removing material to create holes, vias, and / or other openings in the substrate.

[0003] Methods for etching high aspect ratio (depth-to-width) features (such as trenches or holes) often utilize a cyclic process of etching and depositing protective material on a substrate in a single etching reactor. During the etching process, as the trenches form, material is deposited on the sidewalls of the trenches. When forming high aspect ratio features such as trenches in a substrate, the roughness of the trench sidewalls can lead to defects in the microelectronic device if the sidewall roughness is not properly controlled. A pattern of stripes with a series of "peaks" and "valleys" can develop along the sidewalls of the trenches. A particular challenge is controlling the amount of undercutting below the etching mask, which can result in very large valleys directly beneath the mask. Large peaks and valleys increase the roughness of the trench sidewalls. The frequency and amplitude of peaks and valleys can jeopardize the integrity of the microelectronic device, thereby shortening its lifespan.

[0004] Therefore, there is a need in the art for improved methods for etching high aspect ratio features. Summary of the Invention

[0005] This document discloses a cyclic etching method for forming high aspect ratio features in a substrate. In one example, the cyclic etching method includes conformally depositing a pre-etch protective layer over the mask and the sidewalls of the mask defining the mask opening before cyclically etching the substrate through a mask opening. The pre-etch protective layer is deposited over the exposed portion of the substrate exposed through the mask opening. The pre-etch protective layer is deposited to a first thickness. The method further continues to cyclically etch the substrate by the steps of: (i) depositing the protective layer in the mask opening; and (ii) etching through a portion of the protective layer disposed on the substrate, and etching the substrate. The protective layer is deposited to a second thickness less than half the first thickness. Additionally, the method continues (iii) by repeating (i) and (ii) until an endpoint is reached.

[0006] In another example, a semiconductor processing system is provided. This semiconductor processing system includes an etching chamber and a non-transitory computer-readable medium configured to store instructions. When the instructions are executed by a processor, a cyclic etching method is performed in the etching chamber. This method includes conformally depositing a pre-etch protective layer over a mask and the sidewalls of the mask defining the mask opening before cyclically etching the substrate through a mask opening. The pre-etch protective layer is deposited over the exposed portion of the substrate exposed through the mask opening. The pre-etch protective layer is deposited to a first thickness. This method further continues to cyclically etch the substrate by the steps of: (i) depositing the protective layer in the mask opening; and (ii) etching through a portion of the protective layer disposed on the substrate, and etching the substrate. The protective layer is deposited to a second thickness less than half the first thickness. Additionally, this method continues (iii) by repeating (i) and (ii) until an endpoint is reached.

[0007] In another example, a semiconductor processing system is provided. The semiconductor processing system includes an etching chamber and a non-transitory computer-readable medium configured to store instructions. When the instructions are executed by a processor, a cyclic etching method is performed in the etching chamber. This method includes (A) conformally depositing a pre-etch protective layer over a mask, specifically over a sidewall defining the mask opening, prior to cyclically etching a substrate through a mask opening. The pre-etch protective layer is conformally formed over an exposed portion of the substrate exposed through the mask opening. The pre-etch protective layer is deposited to a first thickness. A first bias power is applied to the substrate. The method includes (B) cyclically etching the substrate by the steps of: (i) depositing the protective layer in the mask opening; (ii) etching through a portion of the protective layer disposed on the substrate and etching the substrate; and (iii) applying a second bias power to the substrate. The protective layer is deposited to a second thickness. The first thickness is between about 100 nm and about 300 nm. The second thickness is between about 10 nm and about 30 nm. The first bias power is less than 0.5 W. The second bias power is greater than the first bias power. In addition, this method involves repeating (i), (ii) and (iii) until the endpoint is reached. Attached Figure Description

[0008] To gain a more detailed understanding of the aforementioned features of this disclosure, a more specific description of the disclosure, which has been briefly summarized above, can be obtained by referring to the examples herein, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings are merely illustrative and should not be construed as limiting the scope of this disclosure. Therefore, the drawings allow for other equivalent examples.

[0009] Figures 1A to 1E This is a schematic cross-sectional view of the substrate during different stages of the high aspect ratio etching process.

[0010] Figure 2 For corresponding Figures 1A to 1E A flowchart illustrating an example of a high aspect ratio etching process in the indicated sequence.

[0011] Figure 3 The diagram illustrates the execution within it. Figure 2 The method shown is used to process the chamber.

[0012] To facilitate understanding, the same reference numerals are used where possible to indicate the same elements with common features. It is contemplated that elements and features of one example may be beneficially incorporated into other examples without further description. Detailed Implementation

[0013] The examples disclosed herein relate to methods for etching high aspect ratio features (e.g., holes or trenches) in a substrate. The etching method utilizes cyclic etching and deposition processes. The methods disclosed below are illustrated with reference to their use in a system configured to etch a substrate. While the methods described herein are particularly useful in forming high aspect ratio features, i.e., features having a depth 10 times or more than the cross-sectional profile (e.g., width or diameter), this method can be used alternatively in other etching applications.

[0014] High aspect ratio etching methods utilize an initial deposition process followed by cyclic etching and deposition processes to form trenches or vias in a substrate. The initial deposition process differs from the deposition process used in the cyclic etching and deposition processes. The initial deposition process, performed before the cyclic etching and deposition processes, forms an initial polymer film on the surface of the substrate exposed through openings in an etching mask. This initial polymer film is opened during the etching portion of the cyclic etching and deposition processes, thereby exposing the top surface of the substrate through openings in the etching mask used for cyclic etching. A second polymer layer is deposited during the deposition portion of the cyclic etching and deposition processes. This second polymer layer covers the sidewalls of the trenches and protects them from lateral etching, thus making the etching process highly anisotropic.

[0015] Repeated etch and deposition processes are employed to gradually deepen the feature to the desired depth. After etching, the mask is removed by ashing or other suitable methods.

[0016] The initial polymer layer substantially reduces the undercut of the substrate directly beneath the mask. Specifically, the initial (e.g., pre-etched) protective layer deposited on top of the substrate prior to cyclic etching and deposition processes not only reduces the undercut of the sidewalls formed in the substrate but also additionally enables tighter critical dimension (CD) tolerances.

[0017] Figure 2This is a flowchart of a method 200 for etching a substrate 100 to form high aspect ratio etched features (e.g., trenches, holes, etc.). The different stages of the method 200 for etching the substrate 100 are shown in... Figures 1A to 1E The figures are drawn sequentially.

[0018] The method 200 for etching substrate 100 begins at operation 204, as follows: Figure 1A The illustration shows an etch mask 104 disposed on a substrate 100. The mask 104 is patterned to form at least one opening 108. As disclosed above, suitable methods for forming the opening 108 include photolithography, etching, and other known methods. The mask 104 may be formed from photoresist, hard mask material, or other suitable materials.

[0019] A substrate 100 and a mask 104 are disposed in an environment 101 in which plasma etching and deposition can be performed. The mask 104 has an opening 108 formed through its top surface 110. The opening 108 in the mask 104 exposes a top portion 112 of the substrate 100. Additionally, sidewalls 116 of the mask 104 are exposed through the opening 108. In one example, the substrate 100 is formed of silicon (Si) or a Si-containing material. Exemplary silicon-containing materials include silicon nitride or silicon oxynitride. Alternatively, the substrate 100 may be formed of other materials.

[0020] An environment 101 is adapted to process substrate 100 with plasma. The environment 101 may be disposed within a processing chamber (not shown) having sidewalls surrounding it. The processing chamber may include a source power source (not shown) (e.g., RF source power) and a substrate support (not shown), on which substrate 100 may be disposed. The substrate support may have electrostatic chucks (not shown) for holding or biasing substrate 100 to the substrate support. A gas suitable for plasma formation is supplied to the environment 101. The gas may be supplied via a conduit coupled to one or more gas sources and a pump (not shown), the pump providing the gas supply pressure to the environment 101. A valve is disposed within the conduit to control the gas flow rate to the environment 101. The processing chamber may also include a matching network (not shown) to achieve impedance matching between the source power and the load. Additionally, one or more control systems control the RF power, bias power, gas flow, and plasma formation rate in the environment 101. Sensors may be disposed in the environment 101, the processing chamber, the conduit, the pump, or the valve to monitor control parameters.

[0021] As described above, the openings 108 in the mask 104 can be formed by methods including etching, photolithography, or other known techniques. In one example, the mask is a photoresist. The photoresist can be a positive-tone photoresist and / or a negative-tone photoresist, each capable of chemically amplified reactions. In one example, the mask 104 is made of a polymeric photoresist material. In one example, the mask 104 is an organic polymer material. Other suitable materials can be used for the mask 104, including other fluoropolymers.

[0022] In operation 208, such as Figure 1B As illustrated, a pre-etched protective layer 120 is deposited on substrate 100. The pre-etched protective layer 120 is deposited conformally with mask 104 and substrate 100 such that the pre-etched protective layer 120 covers top surface 110, top portion 112 and sidewall 116 of mask 104.

[0023] A pre-etched protective layer 120 is deposited to a first thickness 124. The pre-etched protective layer 120 conformally covers the top surface 110, the top portion 112, and the sidewalls 116 of the mask 104. The first thickness 124 of the pre-etched protective layer 120 is between about 100 nm and about 300 nm, for example, about 100 nm. In another example, the first thickness 124 is between about 150 nm and about 200 nm. In another example, the first thickness is between about 175 nm and about 185 nm. In yet another example, the first thickness 124 may be between about 200 nm and 300 nm, for example, about 225 nm or about 250 nm.

[0024] The deposition gas 128 reacts with the plasma above the mask 104 in the environment 101 to form a pre-etched protective layer 120. In one example, the deposition gas 128 is a carbon- and fluorine-containing gas. The carbon- and fluorine-containing gas can be C x F y In one example, it may be C4F8. However, the deposited gas 128 is not limited to C4F8 and may be other gases containing carbon and fluorine.

[0025] During the deposition of the pre-etched protective layer 120, the pressure of the environment 101 can be adjusted during the cyclic etching process to further improve the trench profile. The deposition gas 128 can be supplied to the environment 101 at a rate between about 35 sccm and about 250 sccm, for example, a rate between about 50 sccm and about 150 sccm. In one example, the rate at which the deposition gas 128 flows into the environment 101 can be between 65 sccm and about 115 sccm, for example, about 75 sccm. In another example, this rate can be about 85 sccm or about 90 sccm. The pressure of the environment 101 is maintained between about 25 millitors (mT) and about 65 mT, for example, about 60 mT. In one example, the pressure is maintained at about 30 mT. The pressure can also be maintained at about 40 mT. In another example, the pressure is maintained at about 45 mT; in yet another example, the pressure is maintained at about 55 mT.

[0026] In one example, RF source power is applied to a capacitor plate or inductor coil to excite and decompose the deposited gas above substrate 100 at a range of approximately 100 watts (W) to approximately 600 W. For example, RF source power may be applied between approximately 150 W and 400 W. In yet another example, RF source power may be applied between approximately 250 W and 350 W, for example, approximately 300 W.

[0027] RF bias power can be applied to substrate 100 via a substrate support on which the substrate is placed to facilitate deposition in a direction perpendicular to the surface of substrate 100. The RF bias power can be applied in an RF range from about 100 kHz to about 13.56 MHz, from about 100 kHz to about 2 MHz, or from about 400 kHz to about 2 MHz. In one example, the RF bias power provided to the electrodes of the electrostatic chuck by a bias source power (not shown) is about 0.5 W to about 200 W. For example, the RF bias power can be between about 25 W and about 150 W, such as about 100 W. In another example, the applied RF bias power is substantially equal to 0 W (i.e., not applied). In another example, the RF bias power can be between about 45 W and about 75 W, such as about 55 W. The RF bias power can be pulsed or applied as a continuous duty. The duration of the pulse is from about 1.0 second to about 5.0 seconds. In one example, the duration of the pulse is between about 1.0 second and about 3.0 seconds. In one example, a pre-etched protective layer 120 is deposited at least until a thickness of at least about 100 nm is obtained.

[0028] The RF bias power applied to substrate 100 by the bias source power can be pulsed, for example, repeatedly storing or harvesting energy over a period of time and then rapidly releasing energy over another period of time to deliver an increased instantaneous power amount. The RF source power can be applied continuously while the RF bias power is being applied. Specifically, the RF bias power can be pulsed using a generator pulse capability set by a control system (not shown) to provide a percentage of power on time, referred to as the "duty cycle." In one example, the on and off times of the pulsed bias power can be consistent throughout the entire etching cycle. For example, if the power is on for approximately 3 milliseconds and then off for approximately 15 milliseconds, the duty cycle is approximately 16.67%. The pulse frequency, expressed in cycles per second or Hertz (Hz), is equal to 1.0 divided by the sum of the on and off time periods in seconds. For example, when the bias power is on for approximately 3 milliseconds and off for approximately 15 milliseconds, totaling approximately 18 milliseconds, the pulse frequency, expressed in cycles per second, is approximately 55.55 Hz.

[0029] After the pre-etched protective layer 120 is deposited on the substrate 100 in operation 208, as Figures 1C to 1E The illustration shows a cyclic etching and deposition process. In one example, the cyclic etching and deposition process is performed without depositing an additional pre-etched protective layer 120 before the end of the cyclic etching and deposition process. The cyclic etching and deposition process includes operations 212, 216, 220, and 224.

[0030] In operation 212, such as Figure 1C As illustrated, a protective layer 132 is deposited through an opening 108 formed in mask 104. In the first iteration of the cyclic etching and deposition process, the protective layer 132 is deposited on top of and in contact with the pre-etched protective layer 120. In subsequent iterations of the cyclic etching and deposition process, the protective layer 132 is deposited on top of and in contact with the portion of substrate 100 exposed through the opening 108 in mask 104.

[0031] During operation 212, a protective layer 132 is deposited on substrate 100 to a second thickness 136. The thickness of the protective layer 132 is less than the thickness of the pre-etched protective layer 120. In one example, the thickness of the protective layer 132 is less than half the thickness of the pre-etched protective layer 120. In one example, the second thickness 136 is between about 10 nm and 45 nm, for example, about 30 nm. Another example of the second thickness 136 is between about 20 nm and about 25 nm, for example, about 20 nm. In yet another example, the second thickness 136 is between about 20 nm and about 30 nm. In yet another example, the second thickness 136 is about 40 nm.

[0032] The protective layer 132 is formed by the deposition gas 128. That is, in one example, the protective layer 132 is formed by the same deposition gas 128 used to form the pre-etched protective layer 120. However, the protective layer 132 is deposited using different processing parameters than those used for the deposition of the pre-etched protective layer 120. Alternatively, the protective layer 132 and the pre-etched protective layer 120 may be formed by deposition gases with different chemical compositions.

[0033] During the deposition of the protective layer 132, the etching pressure of the environment 101 can be between about 20 mT and about 75 mT, for example, between about 35 mT and about 65 mT. In one example, the pressure is about 45 mT. In another example, the pressure is about 50 mT; and in yet another example, the pressure is about 60 mT. The deposition gas 128 can be supplied to the environment 101 at a rate between about 75 sccm and about 165 sccm, for example, at a rate of about 115 sccm. In another example, the rate is between about 120 sccm and about 145 sccm, for example, about 130 sccm. In yet another example, the rate is about 135 sccm. Exemplary rates include about 85 sccm, about 100 sccm, and about 125 sccm.

[0034] The source RF power applied during the deposition of the protective layer 132 is between approximately 200 W and approximately 1000 W. The RF bias power applied during the deposition of the protective layer 132 is between 0.1 W and approximately 100 W, for example, approximately 35 W. In one example, the RF bias power is essentially 0 W. In yet another example, the RF bias power is between approximately 10 W and approximately 25 W, for example, approximately 15 W or approximately 20 W.

[0035] In operation 212, the protective layer 132 can be deposited using any of the above-described processing parameters for any variation of the pre-etched protective layer 120. For example, the pre-etched protective layer 120 may have already been deposited using any of the various processing parameters described above, and then any variation of the protective layer 132 deposition is performed in operation 212.

[0036] In operation 216, such as Figure 1D As illustrated, substrate 100 is etched through opening 108 in mask 104. Etching agent 140 is used to etch substrate 100. Etching agent 140 removes portions of protective layer 132 and pre-etched protective layer 120 exposed at the bottom of opening 108, and then etches the now exposed portions of substrate 100.

[0037] During operation 216, etchant 140 is introduced into environment 101. Ions 144 are generated when etchant 140 decomposes within the plasma formed in environment 101 by the applied RF source power. Ions 144 are driven toward substrate 100 and enter opening 108. Ions bombard and react with protective layer 132, removing molecules from it. Ions 144 remove a portion of protective layer 132 covering the bottom of the opening, thereby exposing pre-etched protective layer 120. Pre-etched protective layer 120 is then removed by etchant 140 to expose the substrate through the opening. The exposed portion of the substrate is then etched by etchant 140.

[0038] In one example, etchant 140 is an oxygen-containing gas, such as O2. Other examples of oxygen-containing gases include CO2, CO, N2O, NO2, O3, and H2O. In another example, etchant 140 is a fluorine-containing gas, such as SF6. Examples of suitable fluorine-containing wet or dry etchants include NF3, CF4, C2F, C4F6, C3F8, C5F8, CHF3, ClF3, BrF3, IF3, NF3, or other suitable gases.

[0039] The first etching of the top portion 112 of substrate 100 may include isotropic etching to remove pre-etched protective layer 120 and / or protective layer 132 from the top portion 112 of substrate 100 through opening 108. The first etching includes providing a mixture of fluorinated gas and oxygen to environment 101. Etching agent 140 may contain a fluorinated gas, such as SF6. The flow rate of the fluorinated gas is between about 50 sccm and about 100 sccm, for example, about 75 sccm. In one example, the flow rate is between about 55 sccm and about 70 sccm, for example, about 65 sccm. Etching agent 140 may also contain an oxygen-containing gas, such as O2. The flow rate of the oxygen-containing gas is between about 2 sccm and about 15 sccm, for example, about 10 sccm. In another example, the oxygen-containing gas is provided to environment 101 at a rate between about 3.5 sccm and about 7.5 sccm, for example, at a rate of about 5 sccm or about 5 sccm. The first etch may have a duration of about 0.5 seconds to about 4 seconds, for example, about 1.0 second. In another example, the first etch has a duration of between about 1.5 seconds and about 2.5 seconds, for example, about 2.0 seconds. The RF source power is between about 200W and about 550W, for example, about 250W or about 300W. The RF bias power provided to the substrate 100 is between about 5W and about 125W, for example, about 85W. In another example, the RF bias power is between about 25W and about 75W, for example, about 65W. In yet another example, the RF bias power is between about 40W and about 55W, for example, about 45W. Additional parameters, including but not limited to pressure, may be adjusted according to the disclosure herein.

[0040] Following the first etching, anisotropic etching of the substrate 100 occurs during a second etching. The second etching involves providing an etchant 140 containing a mixture of fluorinated gases (e.g., SF6) to the environment 101. The flow rate of the fluorinated gas is between about 50 sccm and about 100 sccm, for example, about 75 sccm. In one example, the flow rate is between about 55 sccm and about 70 sccm, for example, about 65 sccm. The second etching may have a duration of about 1 second to about 5 seconds, for example, about 4 seconds. In another example, the duration of the second etching is about 1.5 seconds to about 3.5 seconds, for example, about 2.5 seconds or about 3.0 seconds. The RF source power is between about 200 W and about 550 W, for example, about 250 W or about 300 W. The RF bias power provided to the substrate 100 is between about 0 W and about 3 W. In one example, the RF bias power provided to the substrate 100 is substantially 0. In at least one example, the first etching has a longer duration than the second etching. For example, the first etching may be about 0.2 seconds to about 0.5 seconds longer than the second etching.

[0041] As described above, in one example, when the pre-etched protective layer 120 is deposited on the substrate 100, the pressure of the environment 101 is maintained at approximately 25 mT to approximately 65 mT. The RF source power is applied at less than 500 W, for example, between approximately 150 W and 400 W. The RF bias power can be between approximately 25 W and approximately 150 W, for example, approximately 100 W. The applied RF bias power is substantially equal to 0 W (i.e., not applied). The pulse duration is approximately 1.0 second to approximately 5.0 seconds. The deposition gas 128 is supplied to the environment 101 at a rate of approximately 35 sccm to approximately 250 sccm, for example, at a rate of approximately 50 sccm to approximately 150 sccm.

[0042] The etching of the substrate 100 through the opening can occur using any of the above-described processing parameters, with any variation of the etching process described for operation 216. For example, the substrate 100 may have been etched using any of the various processing parameters described above after any variation of the deposition of the protective layer 132 was performed in operation 212 and any variation of the deposition of the pre-etched protective layer 120 was performed in operation 208.

[0043] In operation 220, determine whether the endpoint has been reached. The endpoint can be determined by measuring etching depth, etching time, number of cycles, or other suitable techniques. If the endpoint is determined to have been reached, such as... Figure 1EAs shown, the process is complete once the trenches or other high aspect ratio features have been formed to the desired depth. If the endpoint is not reached, the process proceeds to operation 224, iteratively executing operations 212, 216, and 220 until the endpoint is reached. In one example of operation 220, the substrate 100 is etched to a predetermined depth within a predetermined time period.

[0044] In operation 224, a new protective layer 132 is formed in the trench 156 (i.e., a high aspect ratio feature) that has been iteratively etched in the substrate 100 by repeating operation 212. For example, the protective layer 132 is deposited in the opening 108 and adheres to the remaining pre-etched protective layer 120 and the sidewalls of the trench 156. In the subsequent operation 216, an additional etching process is performed to remove the portion of the protective layer 132 disposed at the bottom of the trench 156, allowing additional substrate material to be isotropically etched and the trench 156 to be iteratively deepened. Operations 212, 216, 220, and 224 are repeated until the trench 156 is determined to have reached the desired depth by the endpoint determination at operation 220.

[0045] like Figure 1E As illustrated, a trench 156 is formed therethrough after exposure to etchant 140. Etching 140 removes a protective layer 132 from the bottom of the trench 156, causing material 148 from the substrate 100 to be removed to deepen the trench 156. In one example, a pre-etched protective layer 120 is retained until the desired depth of the trench 156 is reached. After the desired depth of the trench 156 is reached, the pre-etched protective layer 120 can be removed.

[0046] Figure 3 The executable is shown in the diagram. Figure 2The illustrated method 200 is a non-limiting example of a processing chamber 300. The processing chamber 300 includes a chamber body 304 having a plurality of walls surrounding a chamber volume 308. The chamber volume 308 provides an environment 101 in which the method 200 is performed. In one example, as described above, the processing chamber 300 is an etching chamber configured to etch a substrate 100. A substrate support 312 configured to support the substrate 100 thereon is disposed within the chamber volume 308. The substrate support 312 has a bias power electrode 320 embedded therein, the bias power electrode 320 being coupled to a bias power source 324. As described above, the bias power source 324 is configured to supply bias power to the bias power electrode 320. A gas source 328 is fluidly coupled to a nozzle 332, which is disposed within the chamber volume 308 and attached to the chamber body 304. Gas source 328 is configured to supply one or more gases disclosed above into chamber volume 308 via nozzle 332 according to method 200. Plasma power source 336 is coupled to inductive plasma power applicator 344 via matching circuit 340. As described above, plasma power source 336 supplies RF power to inductive plasma power applicator 344 to excite and decompose etchant 140 above substrate 100. Exhaust port 348 is fluidly coupled to pumping system 352, which removes gas from chamber volume 308.

[0047] Controller 360 is coupled to processing chamber 300. Controller 360 provides signals to at least one of bias power electrode 320, bias power source 324, gas source 328, plasma power source 336, matching circuit 340, induced plasma power applicator 344, and pumping system 352. Controller 360 includes a processor 362, memory 364, and support circuitry 366 coupled to each other. Processor 362 can be any form of general-purpose microprocessor or general-purpose central processing unit (CPU), each of which can be used in industrial environments, such as programmable logic controllers (PLCs), supervisory control and data acquisition (SCADA) systems, or other suitable industrial controllers. Memory 364 is non-transitory and can be one or more readily available memories, such as random access memory (RAM), read-only memory (ROM), or any other form of local or remote digital storage device. Memory 364 contains instructions that facilitate the execution of method 200 when executed by processor 362. The instructions in memory 364 exist in the form of a program product, such as a program that implements the methods of this disclosure. The program code of the program product may conform to any of a variety of different programming languages. Exemplary computer-readable storage media include, but are not limited to: (i) non-writable storage media that permanently stores information thereon (e.g., a read-only memory device within a computer, such as a CD-ROM disc readable by an optical disc drive, flash memory, ROM chip, or any type of solid-state non-volatile semiconductor memory); and (ii) writable storage media that store changeable information thereon (e.g., a floppy disk in a floppy disk drive or a hard disk drive, or any type of solid-state random access semiconductor memory). Such computer-readable storage media are examples of this disclosure when they carry computer-readable instructions instructing the functions of the methods described herein.

[0048] Therefore, the foregoing discloses a method for high aspect ratio etching of a substrate using a combination of pre-etch deposition and cyclic etching and deposition processes. Advantageously, this method significantly reduces the undercut of the substrate directly beneath the etch mask compared to known Bosch processes. Although the foregoing refers to specific examples, other examples may be designed without departing from the basic scope of this disclosure, and the scope of this disclosure is determined by the appended claims.

Claims

1. A method for cyclic etching, comprising the following steps: (A) Before cyclically etching the substrate through the mask opening of the mask, a pre-etch protective layer is conformally deposited over the mask, the sidewall of the mask defining the mask opening, and the exposed portion of the substrate exposed through the mask opening, the pre-etch protective layer being deposited to a first thickness; and (B) The substrate is etched cyclically by the following steps: (i) A protective layer is deposited in the mask opening, the protective layer being deposited to a second thickness, the second thickness being less than half of the first thickness; (ii) Etching through a portion of the protective layer disposed on the substrate, and etching the substrate, wherein the etching includes exposing the substrate to a plasma formed by fluorine-containing gas and oxygen for a first time period in the presence of a bias power applied to the substrate, and exposing the substrate to a plasma essentially formed by the fluorine-containing gas for a second time period, wherein the bias power applied during the first time period is greater than the bias power applied during the second time period. as well as (iii) Repeat steps (i) and (ii) until the endpoint is reached.

2. The method of claim 1, wherein the step of depositing the pre-etched protective layer further comprises the following steps: The pre-etched protective layer is formed by carbon-containing gas.

3. The method of claim 2, wherein the step of depositing the protective layer further comprises the following steps: The protective layer is formed from the same carbon-containing gas as the pre-etched protective layer.

4. The method of claim 2, wherein the step of depositing the pre-etched protective layer further comprises the following steps: A bias power is applied to the substrate.

5. The method of claim 4, wherein the step of depositing the protective layer further comprises the following steps: The protective layer is formed from the same carbon-containing gas as the pre-etched protective layer without applying bias power to the substrate.

6. The method of claim 5, wherein the step of forming the protective layer with the same carbon-containing gas as the pre-etched protective layer further comprises the following steps: The pre-etched protective layer and the protective layer are formed from CF4.

7. The method of claim 1, wherein the step of depositing the pre-etched protective layer further comprises the following steps: The pre-etched protective layer is formed to a thickness of at least 100 nm.

8. The method of claim 1, wherein the step of depositing the pre-etched protective layer further comprises the following steps: The pre-etched protective layer is formed to a thickness between 100 nm and 300 nm.

9. The method of claim 1, wherein the step of depositing the protective layer further comprises the following steps: The protective layer is formed to a thickness of less than 40 nm.

10. A semiconductor processing system, comprising: Etching chamber; and A non-transitory computer-readable medium storing instructions that, when executed by a processor, cause a cyclic etching method to be performed in the etching chamber, the method comprising the following steps: (A) Before cyclically etching the substrate through the mask opening of the mask, a pre-etch protective layer is conformally deposited over the mask, the sidewalls of the mask defining the mask opening, and the exposed portion of the substrate exposed through the mask opening, the pre-etch protective layer being deposited to a first thickness; and (B) The substrate is etched cyclically by the following steps: (i) A protective layer is deposited in the mask opening, the protective layer being deposited to a second thickness, the second thickness being less than half of the first thickness; (ii) Etching through a portion of the protective layer disposed on the substrate, and etching the substrate, wherein the etching includes exposing the substrate to a plasma formed by a fluorine-containing gas and oxygen for a first time period in the presence of a bias power applied to the substrate, and exposing the substrate to a plasma essentially formed by the fluorine-containing gas for a second time period, wherein the bias power applied during the first time period is greater than the bias power applied during the second time period; and (iii) Repeat steps (i) and (ii) until the endpoint is reached.

11. The semiconductor processing system of claim 10, further comprising: A gas source coupled to the internal volume of the etching chamber, the gas source being configured to flow a carbon-containing gas to form the pre-etched protective layer when the carbon-containing gas reacts with the plasma.

12. The semiconductor processing system of claim 11, wherein the carbon-containing gas is further configured to form the protective layer.

13. The semiconductor processing system of claim 11, further comprising: A bias power source configured to supply bias power, wherein the protective layer is formed when the bias power is 0 watts.

14. The semiconductor processing system of claim 13, wherein the pre-etched protective layer and the protective layer are formed of CF4.

15. The semiconductor processing system of claim 10, further comprising: A bias power source configured to apply bias power to the substrate; and A plasma power source configured to generate plasma within the internal volume of the etching chamber.

16. The semiconductor processing system of claim 10, further comprising: A bias power source configured to apply a first bias power, the first bias power being configured to form the pre-etched protective layer to the first thickness; and A second bias power is applied to the substrate, the second bias power being configured to form the protective layer to a second thickness, wherein the first bias power is less than the second bias power, and the second thickness is less than the first thickness.

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