Plasma etching method and apparatus

Abstract

The present application relates to a method and apparatus for plasma etching. A method for plasma etching a structure including a substrate and a component forming a non-volatile metal etching product comprises the following steps: providing a structure including a substrate and a component forming a non-volatile metal etching product; positioning the structure on a support in a chamber having a first gas inlet arrangement including one or more gas inlets and a second gas inlet arrangement including one or more gas inlets; etching the structure by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being introduced into the chamber only through the first gas inlet arrangement; and further etching the structure by performing a second plasma etching step using a second etching process gas mixture, the second etching process gas mixture being introduced into the chamber only through the second gas inlet arrangement.

Description

Technical Field

[0001] The present invention relates to a plasma etching method, and more particularly, to a method for plasma etching a structure including a substrate and a component forming a non-volatile metal etching product. The present invention also relates to an apparatus for plasma etching. Background Art

[0002] Plasma etching is a common technique in the field of semiconductor device manufacturing. An undesirable side effect of the etching process is the buildup of material inside the chamber where the etching occurs. Once the material reaches a certain thickness, the chamber must be cleaned regularly to prevent material from flaking off the chamber walls and contaminating the system. This period is called the mean time between cleans (MTBC). A longer MTBC is desirable because it increases the productivity of the plasma tool.

[0003] Substantial problems may be encountered when etching certain structures including a substrate and another component that forms non-volatile metal etch products when etching. Special problems are encountered when etching PZT (lead zirconate titanate), which is typically used with noble metal electrodes such as Pt. PZT is a piezoelectric material commonly used in sensor / actuator applications such as ultrasonic transducers, AFM actuators, and in microelectronic devices for manufacturing non-volatile memory devices. Dry etching of PZT layers presents specific problems, especially in the case of large wafer diameters (>150mm) and high open areas (>80%). Etching byproducts are largely non-volatile, resulting in the interior of the process chamber being coated with Pb, Zr and Ti-rich films, PZT and Pt from the electrodes, and process gas byproducts such as carbon, fluorine and oxygen used in the etching process. Although the use of O2 batch cleaning and O2 wafer-to-wafer cleaning can minimize carbon-based byproduct deposition, the remaining byproducts are non-volatile and are therefore difficult to remove by dry etching. Beyond a certain thickness, changes in the film stress in the deposited material can cause the deposited material to peel off. This situation is worse due to the presence of thermal gradients in the chamber and / or thermal cycles during idle time and / or poor adhesion points. Peeling off can lead to an increase in the number of particles and defects on the processed wafer. It is then necessary to open the vacuum chamber to the atmosphere and use a wet / mechanical method to clean the interior of the chamber. This will result in an MTBC lower than the desired value. In addition, peeling the material onto the electrostatic chuck (ESC) may interfere with the integrity of the clamping force applied by the ESC. This affects the heat transfer between the structure containing PZT and the ESC, resulting in uneven cooling of the wafer and poor process performance. This ultimately leads to product defects. Therefore, there are significant economic consequences associated with peeling off because tool productivity is reduced, and unexpected particle generation may also adversely affect the yield of the device. However, with the growth of demand for PZT-based devices, in order to improve the yield of the device and improve the productivity of the etching system, higher and higher requirements are placed on the plasma etching process of improved materials.

[0004] The present invention, in at least some of its embodiments, addresses one or more of the problems and desires disclosed above. Summary of the invention

[0005] According to aspects of the present invention, there is provided a method for plasma etching a structure including a substrate and a component forming a non-volatile metal etching product, the method comprising the following steps:

[0006] Providing a structure including a substrate and an assembly for forming a non-volatile metal etch product;

[0007] positioning the structure on a support within a chamber having a first gas inlet arrangement including one or more gas inlets and a second gas inlet arrangement including one or more gas inlets;

[0008] etching the structure by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being supplied to the chamber only through the first gas inlet arrangement; and

[0009] The structure is further etched by performing a second plasma etching step using a second etching process gas mixture which is supplied to the chamber only through the second gas inlet arrangement.

[0010] According to another aspect of the present invention, there is provided a plasma etching apparatus for plasma etching a structure including a substrate and a component forming a non-volatile metal etching product, the apparatus comprising:

[0011] a chamber having a first gas inlet arrangement including one or more gas inlets and a second gas inlet arrangement including one or more gas inlets;

[0012] a support member located within the chamber on which the structure is positionable;

[0013] a plasma generating device; and

[0014] a controller configured to control the first gas inlet arrangement and the second gas inlet arrangement so that the structure is etched by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being supplied to the chamber only through the first gas inlet arrangement, and the structure is further etched by performing a second plasma etching step using a second etching process gas mixture, the second etching process gas mixture being supplied to the chamber only through the second gas inlet arrangement.

[0015] The present invention uses a two-step etching process with gas inlet switching to extend the mean time between chamber cleanings. It is believed that higher concentrations of precursor gas near the gas inlet lead to increased deposition around the gas inlet. By using a two-step etching process with gas inlet switching, the present invention provides greater uniformity in chamber deposition, thereby extending MTBC.

[0016] The gas inlet of the first gas inlet arrangement may be located radially inwardly of the gas inlet of the second gas inlet arrangement, and vice versa. The chamber may further comprise a plasma generating device. The plasma generating device may separate the gas inlet of the first gas inlet arrangement from the gas inlet of the second gas inlet arrangement.

[0017] The plasma generating device may comprise an annular housing and a plasma generating element disposed within the annular housing. The gas inlet of the first gas inlet arrangement may be located radially inside the annular housing, and the gas inlet of the second gas inlet arrangement may be located radially outside the annular housing, or vice versa. The plasma generating element may be an RF antenna. The annular housing may be formed of a ceramic material.

[0018] The structure may be positioned on a support and RF bias power is applied to the support during the first plasma etching step and the second plasma etching step. Thus, the plasma etching apparatus may include a power application arrangement for applying RF bias power to the support. The RF bias power in the first plasma etching step may be greater than the RF bias power in the second plasma etching step.

[0019] The first plasma etching step and the second plasma etching step may use different etching process gas mixtures. The second etching process gas mixture may contain a fluorocarbon. The fluorocarbon may not be present in the first etching process gas mixture. Alternatively, the first plasma etching step and the second plasma etching step may use the same etching process gas mixture.

[0020] The structure may be plasma etched using a single first plasma etching step and a single second plasma etching step. Alternatively, the structure may be etched in a cyclic manner by alternatingly repeating the first plasma etching step and the second plasma etching step a desired number of times. When a cyclic etching process is used, it is possible to exchange the order of the first gas inlet arrangement and the second gas inlet arrangement between etching cycles, i.e., in some etching cycles, the first etching process gas mixture may be supplied to the chamber only through the second gas inlet arrangement, and the second etching process gas mixture may be supplied to the chamber only through the first gas inlet arrangement. Therefore, the method may further include the steps of: further etching the structure by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being supplied to the chamber only through the second gas inlet arrangement; and further etching the structure by performing a second plasma etching step using a second etching process gas mixture, the second etching process gas mixture being supplied to the chamber only through the first gas inlet arrangement.

[0021] The components of the structure that form the non-volatile metal etching product can be a piezoelectric layer and / or a metal electrode. The components of the structure that form the non-volatile metal etching product can be a layer of PZT (lead zirconate titanate) and / or a noble metal electrode such as a Pt electrode. The PZT layer can be separated from the semiconductor substrate by one or more other material layers. The PZT layer can include a lower surface. The lower surface can be separated from the semiconductor substrate by an electrode layer such as a Pt layer. Additionally or alternatively, the PZT layer can be separated from the semiconductor substrate by a barrier layer such as SiO2. The PZT layer can include an upper surface. An electrode layer such as a Pt layer can be present on the upper surface. The structure can further include a photoresist layer or other mask material.

[0022] When etching PZT and / or precious metal electrodes, the first etching process gas mixture may be mainly composed of CF4, H2 and optionally one or more inert diluents such as Ar, and the second etching process gas mixture may be mainly composed of C4F8, CF4, H2 and optionally one or more inert diluents such as Ar.

[0023] The substrate may be a semiconductor substrate.

[0024] The semiconductor substrate may be a silicon substrate. In some embodiments, the semiconductor substrate is a silicon substrate, and the component forming the non-volatile metal etching product is a layer of PZT.

[0025] The semiconductor substrate may be a SiC substrate, and the component forming the non-volatile metal etching product may be a metal mask. The plasma etching may include back-etching the SiC substrate through the metal mask.

[0026] The first gas inlet arrangement and the second gas inlet arrangement may each comprise any suitable number of gas inlets. In principle, the first gas inlet arrangement and / or the second gas inlet arrangement may have a single gas inlet, but in practice it is more likely that each gas arrangement will have multiple gas inlets.

[0027] The substrate may be in the form of a wafer. Semiconductor substrates such as Si will typically be in the form of a wafer.

[0028] Different types of plasma generating devices suitable for plasma etching are well known to the skilled person. The present invention can be used in conjunction with a variety of these plasma generating devices.

[0029] Although the present invention has been described above, the present invention will extend to any inventive combination set forth in the above or following description. For example, a feature described with respect to one aspect of the present invention is disclosed with respect to another aspect of the present invention. Although illustrative embodiments of the present invention are described in detail herein with reference to the accompanying drawings, it should be understood that the present invention is not limited to these precise embodiments. In addition, it is contemplated that specific features described separately or as part of an embodiment may be combined with other separately described features or parts of other embodiments, even if the other features and embodiments do not mention the specific features. Therefore, the present invention extends to such specific combinations not yet described. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0031] Figure 1 and 2 is a schematic diagram of a plasma etching apparatus of the present invention;

[0032] Figure 3 shows the deposition on the RF source window and indicates the Figure 4 and 5 The corresponding area;

[0033] Figure 4 yes Figure 3 SEM micrograph of well-adhered material as indicated in;

[0034] Figure 5 yes Figure 3 SEM micrograph of poorly adhered material as indicated in;

[0035] Figure 6 An EDX composition analysis of the deposited material layers is shown. DETAILED DESCRIPTION

[0036] The present invention uses a two-step etching method and corresponding plasma etching equipment to extend the mean time between chamber cleanings.

[0037] Figure 1 and 2 The plasma processing device according to the present invention is shown. Synapse TM The invention is implemented in an adapted version of an etching process module that has been configured to perform a two-step etching process with gas inlet switching. Well-known features such as an exhaust gas pumping system are not included in the present invention. Figure 1 and 2 However, it will be well understood by those skilled in the art.

[0038] The apparatus comprises a plasma etching chamber 11 having a plurality of inner surfaces. The apparatus comprises a first gas inlet arrangement 10, a second gas inlet arrangement 12, a ceramic annular housing 18, an RF antenna 14, a planar RF electrode 16, and a support 20 for supporting a structure 28 undergoing etching. Figure 1 and 2 In the embodiment shown in , the support 20 is an electrostatic chuck, and the flat plate RF electrode 16 is used to control the directionality of the etching ions. This in turn controls the degree of physical etching achieved during the process. Higher flat plate power will increase the substrate etch rate.

[0039] The plasma etching chamber 11 has an upper wall or roof. An annular housing 18 is immersed in the chamber 11 and depends downwardly from the upper wall. The annular housing 18 defines a circular area on the interior of the upper wall.

[0040] exist Figure 1 and 2 In the embodiment shown in , the first gas inlet arrangement 10 is an inner gas plenum and the second gas inlet arrangement 12 is an outer gas plenum. Each gas inlet arrangement includes a plurality of gas inlets, each gas inlet terminating in an opening through which a process gas enters the interior of the chamber 11. The inner plenum 10 is located within a circular area defined by an annular housing 18. The gas inlet of the inner gas plenum 10 is located inside the annular housing 18 as a plurality of openings arranged in a circular pattern. The outer plenum 12 is located outside the circular area defined by the annular housing 18. The gas inlet of the outer gas plenum 10 is located outside the annular housing 18 as a plurality of openings arranged in a circular pattern. The inner gas plenum may have eight gas inlets, while the outer gas plenum may have about 10 times more gas inlets. However, it should be understood that the first gas inlet arrangement and the second gas inlet arrangement may have any suitable number of gas inlets.

[0041] exist Figure 2 The etching chamber is further shown in Figure 2 The treatment of a structure 28 present in a chamber is shown. The chamber includes a chamber wall 24 within which the structure 28 is placed on a support 20. The plasma 26 is ignited and maintained by RF power coupled into the chamber from an RF power supply (not shown) via an RF antenna 14 contained within an annular housing 18. The annular housing 18 acts as a window to allow RF power to be coupled into the chamber. The etching process gas enters the chamber through a gas inlet of either the inner gas plenum 10 or the outer gas plenum 12. A controller 30 is used to switch the gas entry point from the first gas plenum to the second gas plenum.

[0042] The present invention can be used to etch structures containing PZT (lead zirconate titanate). The typical wafer structure is a silicon substrate base layer, followed by a SiO2 layer, a platinum layer, a PZT layer, a second platinum layer, and finally a photoresist mask on the upper surface of the wafer. The photoresist mask protects the wafer from plasma etching. The mask is patterned according to the desired etching product. Typically, the platinum electrode layer will have a thickness of 50-250nm, and the PZT layer will have a thickness of 500-2500nm.

[0043] The wafer to be etched is electrostatically clamped to the support 20. Helium gas is used to cool the wafer.

[0044] During the first etch step, a higher plate power is used to etch the PZT to the stop layer at a higher rate with low selectivity (PZT / Pt). The stop layer is typically a platinum electrode. The plate power is reduced in the second step and can be completely turned off. The reduced plate power results in a reduced etch rate for the PZT and an increase in the PZT / PT selectivity. This means that during the second step, the plasma will continue to etch any remaining PZT, but will not etch the stop layer or remove Pt at a significantly reduced rate.

[0045] The inner surface of the chamber was textured to improve adhesion of the first layer of deposited material. The metal shield in the chamber was coated with arc sprayed Al to achieve a surface roughness of about 20-35 μm, while the ceramic window 18 was coated with yttrium oxide coating to achieve a surface roughness of about 6 μm. Experiments were conducted by etching high open area (80% OA) patterned wafers with photoresist mask (4.5 μm thickness) / Pt (100 nm thickness) / PZT (2 μm thickness) / Pt (100 nm thickness) layers formed thereon, using the process conditions shown in Table 1, using either internal or external gas booster chambers to deliver the etching process gases.

[0046] Typical process parameters for each step are shown in Table 1. PZT etching is typically performed at a chamber temperature of 55°C and a pressure of 5-50 mTorr.

[0047] Step 1 Step 2 <![CDATA[C4F8 flow rate (sccm)]]> 0 5-10 <![CDATA[CF4:H2 ratio]]> >1.5:1 <1:1 Antenna RF power (W) 1000-1500 1500-1900 Panel RF power (W) 500-1000 0-500 Time (min) 5-10 10-15

[0048] Table 1

[0049] It was found that when an outer gas plenum was used to perform the etching step, there was significant deposition on the chamber surfaces near the outer gas plenum. When an inner gas plenum was used to perform the etching step, there was significant deposition on the annular housing and near the inner gas plenum. Over 214 microns of PZT were successfully etched using the inner plenum before delaminating the material from the ceramic window of the annular housing.

[0050] Figure 3There is shown material deposited on the annular housing 18. It can be seen that the material adheres well in some areas, while in other areas it is flaking off.

[0051] Figure 4 The SEM micrographs shown in correspond to Figure 3 The area with good adhesion is indicated in . There is a thick layer of fluorocarbon polymer between each layer of metal etch product. As the number of wafers processed in the chamber increases, the layered structure of etch products and fluorocarbon polymer accumulates on the inside of the chamber.

[0052] In contrast, Figure 5 The SEM micrographs in Figure 3 The poor adhesion area indicated in . In this area, there is a thin or no fluorocarbon layer between the etch product layers. The SEM image indicates that the area where there is a thick fluorocarbon polymer layer between each redeposited etch product layer has better adhesion than the area where there is a thin or no fluorocarbon layer.

[0053] Figure 6 Figure 2 shows the EDX composition analysis of the redeposited material taken from the area with good adhesion. Figure 4 This is consistent with the thick fluorocarbon layer sandwiched between metal etch product layers seen in .

[0054] Without wishing to be bound by any particular theory or conjecture, it is believed that there are two main deposition mechanisms inside the chamber. The first mechanism is the deposition of process gases directly inside the chamber. The second mechanism is the redeposition of etch products from the wafer during etching. It is believed that since the precursor gas concentration varies locally with the distance from the gas inlet, the material deposited from the etching process gas mixture varies throughout the chamber. This produces a higher deposition near the gas inlet. By using a two-step etching method and switching the position of the gas inlet between the two etching steps, a more uniform deposition can be achieved and the time between chamber cleanings can be extended accordingly. It is believed that the deposition of wafer etch products acts in a manner visible from the wafer and is therefore not affected by the gas inlet.

[0055] Although the present invention has been demonstrated to be particularly effective for etching of PZT, the present invention may be applied to etching of other structures including components that form non-volatile metal etching products. For example, the present invention may be applied to backside etching of SiC using a metal mask.

Claims

1. A method for plasma etching a structure comprising a substrate and an assembly forming a non-volatile metal etch product, the method comprising the steps of: Providing a structure including a substrate and an assembly for forming a non-volatile metal etch product; positioning the structure on a support within a chamber having a first gas inlet arrangement comprising one or more gas inlets and a second gas inlet arrangement comprising one or more gas inlets, wherein the gas inlets of the first gas inlet arrangement are radially inward of the gas inlets of the second gas inlet arrangement; etching the component by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being supplied to the chamber only through the first gas inlet arrangement; as well as further etching the component by performing a second plasma etching step using a second etching process gas mixture, which is supplied to the chamber only through the second gas inlet arrangement, The chamber further comprises a plasma generating device, the plasma generating device separating the gas inlet of the first gas inlet arrangement from the gas inlet of the second gas inlet arrangement, the plasma generating device comprising an annular housing and a plasma generating element disposed within the annular housing, wherein the gas inlet of the first gas inlet arrangement is radially located on the inner side of the annular housing, and the gas inlet of the second gas inlet arrangement is radially located on the outer side of the annular housing.

2. The method of claim 1, wherein the plasma generating element is an RF antenna.

3. The method of claim 1 or 2, wherein the structure is positioned on a support and RF bias power is applied to the support during the first plasma etching step and the second plasma etching step.

4. The method according to claim 1 or 2, wherein the first plasma etching step and the second plasma etching step use different etching process gas mixtures.

5. The method of claim 4, wherein the second etch process gas mixture comprises a fluorocarbon, the fluorocarbon being absent from the first etch process gas mixture.

6. The method of claim 1 or 2, wherein the component of the structure that forms the non-volatile metal etch product is a layer of lead zirconate titanate PZT and / or a noble metal electrode. The method according to claim 1 , wherein the substrate is a semiconductor substrate. The method according to claim 7 , wherein the semiconductor substrate is a silicon substrate. 9 . The method according to claim 7 , wherein the semiconductor substrate is a SiC substrate, and the component forming the non-volatile metal etching product is a metal mask.

10. A plasma etching apparatus for plasma etching a structure including a substrate and an assembly forming a non-volatile metal etching product, the apparatus comprising: a chamber having a first gas inlet arrangement comprising one or more gas inlets and a second gas inlet arrangement comprising one or more gas inlets, wherein the gas inlets of the first gas inlet arrangement are radially inwardly of the gas inlets of the second gas inlet arrangement; a support member located within the chamber on which the structure is positionable; a plasma generating device, the plasma generating device separating the gas inlet of the first gas inlet arrangement from the gas inlet of the second gas inlet arrangement, the plasma generating device comprising an annular housing and a plasma generating element disposed within the annular housing, wherein the gas inlet of the first gas inlet arrangement is located radially inwardly of the annular housing and the gas inlet of the second gas inlet arrangement is located radially outwardly of the annular housing; as well as a controller configured to control the first gas inlet arrangement and the second gas inlet arrangement so that the component is etched by performing a first plasma etching step using a first etching process gas mixture, the first etching process gas mixture being supplied to the chamber only through the first gas inlet arrangement, and the component is further etched by performing a second plasma etching step using a second etching process gas mixture, the second etching process gas mixture being supplied to the chamber only through the second gas inlet arrangement.

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