Metal etching method

Abstract

The present invention provides a metal etching method, characterized by comprising the following steps: S1, depositing a metal layer on a dielectric layer on a wafer substrate; S2, performing a first photolithography on the metal layer using an original metal photomask; S3, performing a first dry etching on the metal layer, followed by removal of the photoresist; S4, providing a protective metal photomask, and performing a second photolithography on the metal layer; S5, performing a second dry etching to remove metal residue on the sidewalls, followed by removal of the photoresist. This method provides a metal etching process employing two dry etching steps, eliminating metal residue on the sidewalls and meeting metal-related parameter requirements for small-sized devices.

Description

Technical Field

[0001] The present invention relates to the technical field of metal etching, and in particular to a metal etching method. Background Art

[0002] In the production of integrated circuits, processes such as photolithography, etching, deposition, ion implantation, and oxidation are performed on silicon wafers using different masks one by one. These processes are mainly divided into front-end and back-end processes. The front-end process mainly involves the production of devices (such as transistors and capacitors) in the active area, while the back-end process is metal wiring, which usually uses metal materials with relatively high conductivity for wiring, interconnecting various devices to form functional circuits, mainly involving the production of metal wires and metal vias.

[0003] The traditional method of manufacturing metal wiring (or metal routing) generally uses wet etching of the metal layer when the device size is large. When wet etching the metal, the lateral etching distance of the metal is large. When the device size is small, wet etching cannot meet the requirements of narrow line width. The solution is to use dry etching of the metal layer, which is suitable for small device sizes and small height differences on the wafer surface.

[0004] Metal dry etching process, the general process flow is:

[0005] 1) depositing a metal layer on a dielectric layer on a wafer substrate;

[0006] 2) performing photolithography on the metal layer (including photoresist coating, exposure, and development);

[0007] 3) Dry etching of metal layer;

[0008] 4) Remove the photoresist.

[0009] However, in the thick silicon process of silicon photonics, there are cases where ridge waveguides with large height differences (generally greater than 1 micron, or even greater than 9 microns) are etched, and also cases where modulators or receivers with sizes less than 1 micron are etched. Figure 1 As shown, the above metal etching process is prone to either metal residue on the ridge waveguide or step sidewall, or it may cause process problems such as the metal failing to reach the width target and the metal being etched and unable to completely cover the hole.

[0010] Therefore, in order to avoid the above two situations, it is necessary to improve the existing metal etching process. Summary of the Invention

[0011] Technical problems solved

[0012] In response to the above-mentioned shortcomings of the prior art, the present invention provides a metal etching method, which provides a metal etching process using two dry etching steps, so that there is no metal residue on the sidewall and the metal-related parameter requirements of small-sized devices can be met.

[0013] Technical Solution

[0014] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0015] The present invention provides a metal etching method, comprising the following steps:

[0016] S1. depositing a metal layer on the dielectric layer on the wafer substrate;

[0017] S2, performing a first photolithography on the metal layer using an original metal photomask;

[0018] S3, performing a first dry etching on the metal layer, and then removing the photoresist;

[0019] S4, setting a protective metal photoresist, and performing a second photolithography on the metal layer;

[0020] S5. Perform a second dry etching to remove the metal residue on the sidewall and then remove the photoresist.

[0021] Furthermore, the protective metal photomask extends with a positive deviation value relative to the original metal photomask along a first direction, and the first direction is perpendicular to the sidewall.

[0022] Furthermore, the positive deviation value is not less than the etching length of the second photolithography along the first direction.

[0023] Furthermore, the first dry etching adopts metal dry etching that is biased towards electrons; and the second dry etching adopts metal dry etching that is biased towards chemical substances.

[0024] Furthermore, the etching machine adopts the method of reducing the chlorine gas flow and increasing the pressure to achieve metal dry etching that deviates from the electron property; the etching machine adopts the method of increasing the chlorine gas flow and reducing the pressure to achieve metal dry etching that deviates from the chemical property.

[0025] Furthermore, the metal etching method is used for ridge waveguides or devices or terrains with large step heights.

[0026] Furthermore, the devices or terrains with large step heights at least include silicon photon detection devices, silicon photon modulation devices, and stepped terrains of MESA structures.

[0027] Furthermore, the positive deviation value ranges from 1.0 to 5.0 microns.

[0028] Furthermore, step S1 further includes: forming at least active devices, ridge waveguides, and junction and hole devices on the wafer substrate.

[0029] Furthermore, the active devices include at least a detector, a modulator, an amplifier, a heater and a temperature sensor, and the deposited metal layer includes a metal material that is conductive and suitable for semiconductor process steps.

[0030] Beneficial effects

[0031] The method provided by the present invention adopts a metal etching process of two dry etchings, so that no metal residue is left on the sidewalls, and the metal-related parameter requirements of small-sized devices can be met: for example, maintaining a stable metal line width, ensuring good metal morphology, preventing metal from being undercut, and being able to completely cover the holes. The protective metal photomask provided by the present invention utilizes the original metal photomask and adds an appropriate positive bias value, so that the photoresist formed by the second metal photolithography can completely and effectively protect the metal pattern formed after the first metal photolithography. In addition, the phenomenon of partial metal undercutting can be avoided when crossing terrain with large height differences such as ridge waveguides or steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0033] Figure 1 A schematic diagram of the background technology problem of the present invention;

[0034] Figure 2 A schematic diagram of the steps of a metal etching method provided by one embodiment of the present invention;

[0035] Figure 3 A schematic cross-sectional view of a metal layer deposited in a metal etching method according to an embodiment of the present invention;

[0036] Figure 4 A schematic cross-sectional view of the first photolithography step in a metal etching method according to an embodiment of the present invention;

[0037] Figure 5 A schematic cross-sectional view of the first dry etching step in the metal etching method provided in one embodiment of the present invention;

[0038] Figure 6 A schematic diagram of removing the photoresist after the first dry etching in the metal etching method provided by one embodiment of the present invention;

[0039] Figure 7 A schematic cross-sectional view of the second dry etching step in the metal etching method provided in one embodiment of the present invention;

[0040] Figure 8 A schematic diagram of removing the photoresist after the second dry etching in the metal etching method provided by one embodiment of the present invention;

[0041] Figure 9 Schematic diagram of metal residue on the sidewall;

[0042] Figure 10 This is a schematic diagram of performing a second dry etching without using an extended positive bias value according to an embodiment of the present invention;

[0043] Figure 11 This is a three-dimensional schematic diagram of removing the photoresist after performing the second dry etching without using an extended positive bias value according to an embodiment of the present invention;

[0044] Figure 12 A schematic cross-sectional view of removing the photoresist after performing the second dry etching without using an extended positive bias value according to an embodiment of the present invention;

[0045] Figure 13 A schematic diagram of the one-time layout for protecting the metal photomask;

[0046] Figure 14 Schematic diagram of the segmented layout for protecting the metal photomask;

[0047] Figure 15 A schematic diagram of a second dry etching process using an extended positive bias value according to an embodiment of the present invention;

[0048] Figure 16 This is a schematic diagram of a second dry etching process using an extended positive bias value according to an embodiment of the present invention;

[0049] Figure 17 Another schematic diagram of a second dry etching process performed with an extended positive bias value according to an embodiment of the present invention. DETAILED DESCRIPTION

[0050] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. 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 making any creative efforts shall fall within the scope of protection of the present invention.

[0051] In the description of the following specific embodiments, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying 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 are therefore not to be understood as limiting the present invention.

[0052] In addition, the terms "first" and "second" are used for descriptive purposes only and do not refer to limitations on time sequence, quantity, or importance. They should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Instead, they are used only to distinguish one technical feature from another in the technical solution. Therefore, features defined as "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly specified. Similarly, qualifiers similar to "one" appearing in this article do not refer to limitations on quantity, but rather describe technical features that have not appeared in the previous text. Similarly, unless a noun is modified by a specific quantitative quantifier, it should be regarded in this article as including both singular and plural forms. In this technical solution, the technical feature can be included in both the singular and plural. Similarly, modifiers similar to "approximately" and "approximately" that appear before a numeral in this article generally include the number itself, and their specific meaning should be understood in conjunction with the context.

[0053] See Figure 2 One embodiment of the present invention provides a metal etching method, comprising the following steps:

[0054] S1, depositing a metal layer 103 on a dielectric layer 102 on a wafer substrate 101;

[0055] S2, performing a first photolithography 104 on the metal layer using an original metal photomask;

[0056] S3, performing a first dry etching on the metal layer, and then removing the photoresist;

[0057] S4, setting a protective metal photoresist, and performing a second photolithography 105 on the metal layer;

[0058] S5. Perform a second dry etching to remove the metal residue 107 on the sidewall, and then remove the photoresist.

[0059] For step S1, see Figure 3On wafer substrate 101, devices including active devices, ridge waveguides, junctions and vias (the junctions of active devices contact metal via vias), and other underlying metal wiring have already been formed. Wafer substrates include both single-crystal silicon wafers and SOI (Silicon on Insulator) wafers. Active devices are electronic components that require power to achieve their specific functions, primarily including electron tubes, transistors, integrated circuits, and the like, and are generally used for signal amplification and conversion. If an electronic component operates with an internal power source, it is called an active device. This device requires an energy source to achieve its specific function. Based on its physical structure, circuit function, and engineering parameters, active devices can be divided into two categories: discrete devices and integrated circuits. The active devices provided by the present invention generally include detectors, modulators, amplifiers, heaters, and temperature sensors. Finally, the deposited metal layer 103 generally comprises conductive metal materials such as aluminum or titanium that are suitable for semiconductor processing steps.

[0060] For step S2, in this embodiment, see Figure 4 A first photolithography 104 is performed on the metal layer using an original photolithographic metal plate. This first photolithography 104 includes photoresist coating, exposure, and development. Photoresist, also known as photoresist, refers to a thin film material whose solubility changes when exposed to ultraviolet light, electron beams, ion beams, X-rays, or the like. It is a light-sensitive liquid mixture composed of three main components: a photosensitive resin, a sensitizer, and a solvent. During the photolithography process, it serves as an anti-corrosion coating material. When surface processing semiconductor materials, using an appropriate selective photoresist can produce the desired image on the surface. Photoresists are classified into two main categories: positive and negative, depending on the image they form. During the photoresist process, after exposure and development, the exposed portions of the coating are dissolved, leaving the unexposed portions. This coating material is considered a positive photoresist. If the exposed portions remain while the unexposed portions are dissolved, the coating material is considered a negative photoresist. Depending on the exposure light source and radiation source, photoresists are classified into UV (including positive and negative UV photoresists), deep UV photoresists, X-ray photoresists, electron beam photoresists, and ion beam photoresists. Photoresists are primarily used in fine-grained processing applications such as display panels, integrated circuits, and discrete semiconductor devices. Photoresist production technology is complex, with a wide variety of specifications. Stringent requirements are imposed on the photoresists used in the manufacture of integrated circuits in the electronics industry.

[0061] For step S3, in this embodiment, see Figure 5 The first dry etching in this step is a metal dry etching that deviates from the electron property. The purpose is to form the metal line width required by the design and minimize the length of the metal lateral etching to ensure that the metal can completely cover the hole, but allow the metal 107 to remain on the side wall. Then remove the photoresist. Figure 6shown.

[0062] In this embodiment, the etching machine can adopt methods such as reducing the chlorine gas flow rate and increasing the pressure to achieve a dry etching process that deviates from the ionization and produces anisotropic etching. Ideal etching must have the following characteristics: anisotropic etching, that is, only vertical etching without lateral undercutting; good selectivity, that is, the etching rate of the mask and the next layer of material is much lower than that of the film being etched. It is easy to control, low cost, low environmental pollution, good uniformity, high efficiency, and suitable for industrial production.

[0063] For step S4, in this embodiment, see Figure 7 , covering the protective metal photomask, and performing a second photolithography 105 on the metal layer. This second photolithography 105 also includes photoresist coating, exposure, and development. The original metal photomask used in the present invention is designed based on the metal wiring requirements of the active device. In the present invention, the original metal photomask is used with an appropriate positive offset value to produce the protective metal photomask suitable for the present invention. Regarding the positive offset value, a smaller positive offset value is generally used for flatter locations. In this invention, this is referred to as the basic offset value, which generally takes into account the process window and device design limitations. The minimum basic offset value is determined by ensuring that, even when errors due to accumulated errors such as photolithography alignment and exposure energy occur, the photoresist formed by the second photolithography can still fully and effectively cover the metal pattern formed by the first photolithography. The maximum positive offset value is determined by ensuring that the photoresist formed by the second photolithography does not cover the sidewall area, otherwise the purpose of removing the sidewall metal residue cannot be achieved.

[0064] For step S5, in this embodiment, see Figure 8 The second dry etching in this step is a metal dry etching with a partial chemical property, and its purpose is to remove the metal 107 remaining on the sidewall.

[0065] Among them, dry etching processes can generally be divided into two types: ionic etching and chemical etching. Ionic etching uses glow discharge to ionize a gas (such as argon) into positively charged ions, and then uses bias to accelerate the ions, which splash onto the surface of the etched material and knock out the atoms of the etched material. This process is completely a physical energy transfer, so it is also called physical etching. Its characteristic is that it has very good directionality and can obtain a nearly vertical etching profile. However, because the ions are sputtered uniformly on the chip, the photoresist and the etched material are etched at the same time, resulting in low etching selectivity. At the same time, the substances knocked out are not volatile substances, and these substances are easily deposited on the surface and sidewalls of the etched film. Therefore, in the ultra-large-scale integrated manufacturing process, completely physical dry etching methods are rarely used.

[0066] Chemical etching, also known as plasma etching (PE), utilizes plasma to ionize the etching gas and form charged ions, molecules, and highly reactive atomic groups. These diffuse onto the surface of the film being etched, reacting with the surface atoms of the film to produce volatile reaction products, which are then extracted from the reaction chamber by vacuum equipment. Because this reaction is entirely chemical, it is called chemical etching. This etching method is similar to the wet etching described above, except that the state of the reactants and products is changed from liquid to gaseous, and plasma is used to accelerate the reaction rate. Therefore, chemical dry etching has similar advantages and disadvantages to wet etching, namely, higher selectivity to the mask or underlying layer and isotropy. Due to the disadvantage of chemical etching's isotropy, pure chemical etching methods are only used in semiconductor processing steps where etching does not require pattern transfer, such as photoresist removal.

[0067] In this embodiment, the etching machine can increase the chlorine gas flow rate and reduce the pressure to achieve a chemically biased dry etching process, producing an isotropic etching effect. Dry etching can also use the metal wet etchant used in traditional processes to remove residual metal on the sidewalls, achieving the same purpose as dry etching.

[0068] In this embodiment, see Figure 9 and Figure 10 When there is metal residue 107 on the sidewall, at the position 108 where the metal wiring crosses the sidewall, the photoresist 105 formed by the second photolithography cannot completely cover the metal pattern formed after the first metal etching. The second metal etching adopts a partial chemical etching to remove the metal residue 107 on the sidewall. The lateral metal etching causes undercutting at the position 108 where the metal wiring crosses the sidewall. Figure 11 As shown, the metal pattern finally formed has a void 109 due to etching at the position crossing the sidewall. Therefore, the protective metal photomask extends a positive deviation value along the first direction relative to the original metal photomask, and the first direction is perpendicular to the sidewall. Furthermore, the positive deviation value is not less than the etching length of the second photolithography along the first direction. Figure 15-17 As shown, the protective metal photoresist with the positive deviation value not less than the etching length of the second photolithography along the first direction is used for the second metal etching. The second metal etching adopts a biased chemical etching to remove the metal residue on the side wall. Although there is also lateral metal etching, the etching starting point is far away from the metal pattern, so the metal pattern formed after the first metal etching does not cause undercutting.

[0069] In this embodiment, the positive deviation value ranges from 1.0 to 5.0 microns.

[0070] In this embodiment, the metal etching method is used for ridge waveguides or devices or terrains with large step heights, and the devices or terrains with large step heights include at least silicon photonic detection devices, silicon photonic modulation devices, and stepped terrains of MESA structures.

[0071] In this embodiment, the present invention adopts an extended positive deviation value when the metal wiring crosses the side wall. The positive deviation value is at least greater than the lateral etching length of the second metal etching. The setting method of the positive deviation value can be a one-time layout or a segmented layout. Among them, the one-time layout is as follows: Figure 13 As shown, the segment layout is as follows Figure 14 shown.

[0072] The advantages of the present invention are that the provided method adopts a metal etching process of two dry etchings, so that no metal residue is left on the sidewalls, and the metal-related parameter requirements of small-sized devices can be met: for example, maintaining a stable metal line width, ensuring good metal morphology, preventing metal from being undercut, and being able to completely cover the holes, etc.; the protective metal photomask provided by the present invention utilizes the original metal photomask, and adds an appropriate positive deviation value, so that the photoresist formed by the second metal photolithography can completely and effectively protect the metal pattern formed after the first metal photolithography, and can avoid the phenomenon of partial metal undercutting when crossing terrain with a large height difference, such as ridge waveguides or steps.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements will not cause the essence of the corresponding technical solutions to deviate from the protection scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A metal etching method, characterized in that: The steps include: S1. Depositing a metal layer on a dielectric layer on a wafer substrate, wherein the wafer substrate is previously formed with a device or terrain having a large step height; S2, performing a first photolithography on the metal layer using an original metal photomask; S3, performing a first dry etching on the metal layer, and then removing the photoresist; S4. Setting a protective metal photomask and performing a second photolithography on the metal layer; wherein the protective metal photomask extends by a positive deviation value relative to the original metal photomask along a first direction, the first direction being perpendicular to the step sidewall, and the positive deviation value is not less than the etching length of the second photolithography along the first direction; S5. Perform a second dry etching to remove the metal residue on the sidewall of the step, and then remove the photoresist.

2. The metal etching method according to claim 1, characterized in that: The first dry etching adopts metal dry etching that is biased towards electrons; and the second dry etching adopts metal dry etching that is biased towards chemical substances.

3. The metal etching method according to claim 2, characterized in that: The etching machine adopts the method of reducing the chlorine gas flow and increasing the pressure to achieve non-ionic metal dry etching; The etching machine adopts the method of increasing the chlorine gas flow and reducing the pressure to achieve chemical-biased metal dry etching.

4. The metal etching method according to claim 1, wherein: The devices or terrains with large step heights at least include silicon photon detection devices, silicon photon modulation devices and step terrains of MESA structures.

5. The metal etching method according to claim 1, characterized in that: The positive deviation value ranges from 1.0 to 5.0 microns.

6. The metal etching method according to claim 1, characterized in that: Step S1 also includes: forming at least active devices, ridge waveguides, and junction and hole devices on the wafer substrate.

7. The metal etching method according to claim 6, characterized in that: The active devices at least include a detector, a modulator, an amplifier, a heater and a temperature sensor, and the deposited metal layer includes a metal material that is conductive and suitable for semiconductor process steps.

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