Chemical-assisted ion beam dicing

Abstract

The present disclosure relates to a wafer singulation process utilizing chemical-assisted ion beam dicing (CAIBD) and a dicing equipment configured for the CAIBD. The disclosed process starts with providing a wafer covered with a patterned mask. The wafer includes a first region and a second region over the first region. Horizontally, the wafer is divided into multiple product sections, with street sections provided between adjacent product sections. The patterned mask exposes each street section, where the first region and the second region consist of different materials. The second region within each street section is etched first using first collimated ion beams and first radicals that perform vertically. After the second region within each street section is fully removed, the first region within each street section is etched using a second set of collimated ion beams and radicals, which also perform vertically. The CAIBD technique enables accurate and material-specific wafer singulation.

Description

CHEMICAL-ASSISTED ION BEAM DICINGRelated Applications

[0001] This application claims the benefit of provisional patent application serial number 63 / 762,724, filed February 25, 2025, and provisional patent application serial number 63 / 844,968, filed July 16, 2025, the disclosures of which are hereby incorporated herein by reference in their entireties.Field of the Disclosure

[0002] The present disclosure relates to a wafer singulation process utilizing chemical-assisted ion beam dicing (CAIBD) and dicing equipment configured to provide the CAIBD.Background

[0003] Dielectric materials, especially low-K dielectric materials, are widely used in complementary metal-oxide-semiconductor (CMOS) technology for improved performance. The low-K dielectric materials enable higher operating speed, lower power consumption, and better signal integrity by reducing parasitic capacitance.

[0004] However, due to their high brittleness, the low-K dielectric materials impose significant challenges during wafer singulation. Conventional techniques such as saw dicing or laser grooving, which are commonly employed for separating individual dies from a processed wafer, often cause peeling, cracking, or delamination in structures incorporating low-k materials. The issue is severely worsened in cases of stacked wafers for three-dimensional (3D) applications. In addition, there is a growing need for narrowing street areas, where the dicing operations are typically performed, to enhance the device volume across the wafer. These mechanical limitations hinder manufacturing yield and reliability, particularly in advanced CMOS processes where the low-K materials are prevalent.

[0005] Plasma dicing has been introduced as an alternative solution to the wafer singulation. However, plasma dicing exhibits a relatively low etching rate when applied to dielectric materials due to their chemical stability. Moreover, for a thick dielectric stack (e.g., greater than 20 pm), the etching rate of plasma dicing further decreases significantly with increasing depth, rendering it impractical to completely etch through such a thick dielectric stack.

[0006] Accordingly, there is an object of the present disclosure to provide an improved dicing solution for singulating wafers, which are capable of including thick dielectric stacks and providing narrow street widths, without causing any chipping and / or cracking issues.

[0007] The present disclosure relates to a wafer singulation process utilizing chemical-assisted ion beam dicing (CAIBD) and a dicing equipment configured to provide the CAIBD. The disclosed process starts with providing a wafer covered with a patterned mask. Herein, the wafer includes a first region and a second region over the first region. On a horizontal plane, the wafer is divided into product sections and street sections, with each street section located between two adjacent ones of the product sections. The first region confined within each street section is only composed of a first type of material, while the second region confined within each street section is only composed of a second type of material, which is different from the first type of material. The patterned mask is formed over a top surface of the second region to expose each of the street sections. Next, the second region within each street section is etched utilizing first collimated ion beams and first radicals. The first collimated ion beams bombard exposed portions of the second region through the patterned mask solely in a vertical direction, and reactive ions from the first collimated ion beams and the first radicals chemically react with the exposed portions of the second region solely along the vertical direction. The first region within each street section is then etched after the second region within each street section is completely removed, utilizing second collimated ion beams and second radicals.The second collimated ion beams bombard exposed portions of the first region through the patterned mask solely in the vertical direction, and reactive ions from the second collimated ion beams and the second radicals chemically react with the exposed portions of the first region solely along the vertical direction.

[0008] In one embodiment of the process, each street section has a width of 20 pm or less.

[0009] In one embodiment of the process, the first collimated ion beams and the first radicals are generated from a first group of reactive gases, while the second collimated ion beams and the second radicals are generated from a second group of reactive gases, which are different from the first reactive gases.

[0010] In one embodiment of the process, the first type of material includes silicon, while the second type of material includes dielectric materials. The first collimated ion beams and the first radicals are generated at least from fluorocarbon gases, while the second collimated ion beams and the second radicals are generated from fluorocarbon gases and / or chlorine (CI2).

[0011] In one embodiment of the process, the dielectric materials include one or more low-K dielectric materials, which exhibit a dielectric constant of no greater than 3.

[0012] In one embodiment of the process, a total thickness of the dielectric materials is greater than 20 pm.

[0013] In one embodiment of the process, both the first radicals and the second radicals are produced from more than one source.

[0014] In one embodiment of the process, the first collimated ion beams and the second collimated ion beams are produced from a primary plasma source at different times. The first radicals and the second radicals are produced from both the primary plasma source and a secondary plasma source at different times.

[0015] In one embodiment of the process, an average-density of the first radicals produced from the secondary plasma source is higher than an averagedensity of the first radicals produced from the primary plasma source, and an average-density of the second radicals produced from the secondary plasmasource is higher than an average-density of the second radicals produced from the primary plasma source.

[0016] In one embodiment of the process, the first radicals are further produced by the first collimated ion beams dissociating the first group of reactive gases, while the second radicals are further produced by the second collimated ion beams dissociating the second group of reactive gases.

[0017] According to one embodiment, a dicing equipment configured to provide CAIBD includes a discharge chamber, a grid assembly, a wafer holder, and a secondary plasma source. Herein, the discharge chamber is equipped with a primary plasma source and configured to provide at least reactive ions based on a first group of reactive gases introduced into the discharge chamber. The grid assembly is positioned downstream of the discharge chamber and configured to create and accelerate collimated ion beams composed of the reactive ions supplied from the discharge chamber. The wafer holder is positioned downstream of the grid assembly and faces the discharge chamber. The wafer holder is configured to hold a target wafer such that the collimated ion beams from the grid assembly are capable of completely covering and being orthogonal to an exposed surface of the target wafer. The secondary plasma source is configured to provide at least radicals based on a second group of reactive gases. The collimated ion beams are configured to bombard and chemically react with the target wafer at the exposed surface to perform selective etching, and are capable of propelling any intervening radicals from the first set of radicals that lie along their bombarding path toward the target wafer. The first set of radicals are configured to chemically react with the target wafer at the exposed surface to further perform selective etching.

[0018] According to one embodiment, the dicing equipment further includes a processing chamber, where the discharge chamber, the grid assembly, the wafer holder, and the secondary plasma source are positioned within the processing chamber. The second group of reactive gases are introduced into the processing chamber.

[0019] According to one embodiment, the dicing equipment further includes a neutralizer, which is disposed between the discharge chamber and the grid assembly, and inside the processing chamber. The neutralizer is configured to balance a charge on the reactive ions provided by the discharge chamber, so as to prevent charge buildup on the target wafer.

[0020] According to one embodiment, the dicing equipment further includes a gas-flow system. Herein, the gas-flow system is configured to introduce a third group of reactive gases into the processing chamber, and is positioned close to the wafer holder, such that the third group of reactive gases can surround the exposed surface of the target wafer. The collimated ion beams are capable of dissociating the third group of reactive gases introduced near the exposed surface of the target wafer, thereby generating extra radicals in that localized area.

[0021] In one embodiment of the dicing equipment, the gas-flow system includes a gas release pipe-ring, which is positioned between the grid assembly and the wafer holder. A ring structure of the gas release pipe-ring is configured to allow the collimated ion beams to pass through the third group of reactive gases without physical obstruction.

[0022] In one embodiment of the dicing equipment, the second group of reactive gases and the third group of reactive gases are identical and are different from the first group of reactive gases.

[0023] In one embodiment of the dicing equipment, the first group of reactive gases and the second group of reactive gases are not identical but share at least one common reactive gas.

[0024] According to one embodiment, an alternative dicing equipment configured to provide CAIBD includes a discharge chamber, a grid assembly, a wafer holder, and a gas-flow system. Herein, the discharge chamber is equipped with a plasma source and configured to provide at least reactive ions and radicals based on a first group of reactive gases introduced into the discharge chamber. The grid assembly is positioned downstream of the discharge chamber and configured to create and accelerate collimated ion beams composed of thereactive ions supplied from the discharge chamber. The wafer holder is positioned downstream of the grid assembly and faces the discharge chamber. The wafer holder is configured to hold a target wafer such that the collimated ion beams from the grid assembly are capable of completely covering and being orthogonal to an exposed surface of the target wafer. The gas-flow system is configured to introduce a second group of reactive gases and is positioned between the grid assembly and the wafer holder, close to the wafer holder, such that the second group of reactive gases can surround the exposed surface of the target wafer. The collimated ion beams are configured to bombard and chemically react with the target wafer at the exposed surface to perform selective etching. The collimated ion beams are capable of dissociating the second group of reactive gases introduced near the exposed surface of the target wafer, thereby generating extra radicals in that localized area. The collimated ion beams are capable of propelling any intervening radicals that lie along their bombarding path toward the target wafer. The intervening radicals originate either from the radicals provided by the discharge chamber or from the extra radicals generated by the dissociation. The radicals and the extra radicals are configured to chemically react with the target wafer at the exposed surface to further perform selective etching.

[0025] According to one embodiment, the alternative dicing equipment further includes a processing chamber, where the discharge chamber, the grid assembly, the wafer holder, and the gas-flow system are positioned within the processing chamber. The second group of reactive gases are introduced by the gas-flow system into the processing chamber.

[0026] According to one embodiment, the alternative dicing equipment further includes a neutralizer, which is disposed between the discharge chamber and the grid assembly, and inside the processing chamber. The neutralizer is configured to balance a charge on the reactive ions provided by the discharge chamber, so as to prevent charge buildup on the target wafer.

[0027] In one embodiment of the alternative dicing equipment, the gas-flow system includes a gas release pipe-ring. A ring structure of the gas release pipe-ring is configured to allow the collimated ion beams to pass through the third group of reactive gases without physical obstruction.

[0028] In one embodiment of the alternative dicing equipment, the first group of reactive gases and the second group of reactive gases are not identical but share at least one common reactive gas.

[0029] In another aspect, any of the foregoing aspects individually or together, and / or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various features and elements as disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein.

[0030] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.Brief Description of the Drawing Figures

[0031] The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

[0032] Figure 1 illustrates typical defects that occur in dielectric layers due to traditional wafer singulation approaches.

[0033] Figure 2 illustrates a partial schematic diagram of a three-dimensional (3D) wafer.

[0034] Figures 3A-3B illustrate ion trajectories within a trench caused by different dicing techniques.

[0035] Figure 4 provides an exemplary dicing equipment for a chemical-assisted ion beam dicing (CAIBD) process according to according to some embodiments of the present disclosure.

[0036] Figure 5 provides a flow diagram that illustrates the CAIBD process according to one embodiment of the present disclosure.

[0037] Figures 6-9 illustrate the steps associated with the fabricating procedure provided in Figure 5.

[0038] Figures 10A-1 OC show comparisons of singulation results caused by different dicing techniques.

[0039] It will be understood that for clear illustrations, Figures 1 -1 OC may not be drawn to scale.Detailed Description

[0040] The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

[0041] It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0042] It will be understood that when an element such as a layer, region, or substrate is referred to as being "on" or extending "onto" another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly onto" another element, there are no intervening elements present. Likewise, it will be understood that when an element such as a layer, region, or substrate is referred to as being "over" or extending "over" another element, it can be directly over or extend directly overthe other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly over" or extending "directly over" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

[0043] Relative terms such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe a relationship of one element, layer, or region to another element, layer, or region as illustrated in the Figures. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures.

[0044] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises," "comprising," "includes," and / or "including" when used herein specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0045] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0046] Embodiments are described herein with reference to schematic illustrations of embodiments of the disclosure. As such, the actual dimensions of the layers and elements can be different, and variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and / or tolerances, are expected. For example, a region illustrated or described as square or rectangular can have rounded or curved features, and regions shown as straight lines may have some irregularity. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the disclosure. Additionally, sizes of structures or regions may be exaggerated relative to other structures or regions for illustrative purposes and, thus, are provided to illustrate the general structures of the present subject matter and may or may not be drawn to scale. Common elements between figures may be shown herein with common element numbers and may not be subsequently redescribed.

[0047] In modern complementary metal-oxide-semiconductor (CMOS) fabrication, multiple dielectric layers are deposited along with various metal layers, where the metal layers are configured to establish electrical interconnections, while the dielectric layers are configured to provide electrical insulation between the metal layers, thereby preventing undesired current flow and ensuring proper signal transmission. For certain applications, especially for radio frequency (RF) applications, low-K dielectric materials are utilized in these dielectric layers to reduce parasitic capacitance between the various metal layers and enhance overall device RF performance (e.g., higher operating speed, lower power consumption, and / or better signal integrity). Herein and hereafter, a dielectric material having a dielectric constant of no greater than 3 is referred to as a low-K dielectric material, such as a material formed from silicon (Si), carbon (C), oxygen (O), and hydrogen (H) atoms (SiCOH), a material formed from Si, C, nitrogen (N) and H atoms (SiCHN), carbon-doped oxides, porous dielectrics, etc.

[0048] However, due to high brittleness of low-K dielectric materials, conventional wafer singulation techniques such as saw dicing or laser groovingoften result in defects when applied to wafers incorporating the low-K dielectric materials. These defects may include peeling, cracking, or delamination of the dielectric layers, and may cause major concern with upstream packaging flow. Figure 1 shows defects that occur in dielectric layers of a singulated die as a result of traditional wafer singulation approaches, including laser grooving and saw dicing. Therefore, although low-K dielectric materials are very crucial for high performing CMOS devices, they impose a critical challenge for a wafer singulation / dicing process. This issue is severely worsened in cases of stacked wafers for three-dimensional (3D) applications (see PCT Patent Application No. PCT / US2023 / 071309, entitled “WAFER-LEVEL HYBRID BONDED RADIO FREQUENCY CIRCUIT” the disclosure of which is incorporated herein by reference in its entirety), since the thickness of the dielectric layers will be much higher (e.g., the thickness will be doubled).

[0049] Figure 2 shows a partial schematic diagram of a 3D (i.e., stacked) wafer 100, which includes a top wafer 102 with a number of top dies 102D and a bottom wafer 104 with a number of bottom dies 104D. Each of the top dies 102D and the bottom dies 104D is configured to provide one or more active components (e.g., field-effect transistors, FETs) and optionally one or more passive components (e.g., resistors). The top wafer 102 is carefully bonded to the bottom wafer 104 through top and bottom hybrid bonding (HB) vias, such that each top die 102D in the top wafer 102 is electrically connected to and aligned with a corresponding bottom die 104D in the bottom wafer 104 to provide a 3D die within one die section 106. From a top view, the 3D wafer 100 is composed of a number of die sections 106 and street sections 108. The street sections 108 serve as sacrificial portions for wafer singulation (i.e., areas for separating the die sections 106 from each other), and each street section 108 is located between two adjacent die sections 106.

[0050] For the purpose of this illustration, each of the top wafer 102 and the bottom wafer 104 includes three metal layers (e.g., M1 T, M2T, M3T, and M1 B, M2B, M3B, respectively) and multiple vias VV (only a few vias are labeled for clarity) for connecting the active and passive devices. Additionally, each of thetop wafer 102 and the bottom wafer 104 includes a number of dielectric layers DL, some of which are interleaved with the metal layers, while others are positioned between or over the active and passive devices to provide electrical isolation, surface passivation, and / or a contamination barrier. The dielectric layers DL might be formed from one or more dielectric materials, including materials with normal dielectric constant materials (e.g., K>3, such as silicon oxide, silicon nitride) as well as low-K dielectric materials (e.g., K<=3, such as SiCOH, SiCHN, carbon-doped oxides, porous dielectrics). Herein, the low-K dielectric materials can help reduce parasitic capacitance between the metal layers, so as to enhance overall RF performance of the final product. Moreover, the bottom wafer 104 further includes a handle substrate 110 used as a fabrication base during wafer processing, which might be formed of silicon.

[0051] It is noted that each street section 108 contains only a dielectric stack 112, which is composed of portions of the dielectric layers DL from both the top wafer 102 and the bottom wafer 104, as well as a portion of the handle substrate 110 of the bottom wafer 104. There is no metal portion present within any street section 108. For the 3D wafer 100, a total thickness of the dielectric stack 112 (including the low-K and normal dielectric constant materials) within each street section 108 might be more than 20 pm, while a thickness of the handle substrate 110 is about 100-150 pm. Thus, in order to completely separate the die sections 106 from each other, more than 20 pm of dielectric materials and about 100-150 pm of silicon material (from the portion of the handle substrate 110) need to be removed. In different applications, either the top wafer 102 or the bottom wafer 104 might exist independently. The street sections within one single wafer 102 / 104 might include a dielectric stack of reduced thickness (e.g., >10 pm), while still containing no metal portions.

[0052] Typically, each street section 108 may have a width between 60 pm and 80 pm. To improve the overall die volume per wafer, thereby leading to significant cost reduction, there is a constant push to reduce the areas of the street sections 108, such as narrower than 20 pm. Therefore, there is need for an improved approach to singulate / dice a wafer (e.g., the 3D wafer 100) withoutcausing any damage, where the wafer is capable of including a thick dielectric stack incorporating low-K dielectric materials (e.g., greater than 20 pm total thickness) and providing narrow street widths (e.g., limited to 20 pm width, between 5 pm and 20 pm).

[0053] Apart from the traditional saw dicing and laser grooving approaches, a typical plasma dicing technique is also explored for wafer singulation (i.e., to remove materials in street sections of a wafer). In general, the plasma dicing technique (e.g., the Bosch process) can work effectively to etch silicon material, however, serious challenges arise when attempting to implement this technique on wafers featuring a thick dielectric stack (e.g., >10 pm). Plasma dicing exhibits a relatively low etching rate when applied to dielectric materials primarily due to their inherent chemical stability, which makes them less reactive with plasma species (ions, radicals). As etching progresses and trench depths increase, the etching rate of the plasma dicing further decreases significantly. This is attributed to the low mean free path of ions and the accumulation of space-charge potential at the bottom of the trench. In fact, during the plasma dicing process, energetic ions are used to bombard material-to-be-removed, which causes material sputtering and simultaneously initiates chemical reactions between the radicals and the material-to-be-removed to produce volatile products, thereby achieving etching. However, in the case of deep trenches, the ions lose energy during collisions with sidewalls of the trenches and other particles (e.g., other ions, radicals, etc.) inside the trenches, as shown in Figure 3A. Accordingly, when the ions arrive at the bottom of the trenches beyond a certain depth (>10 pm), the ions are not energetic enough to initiate the reactions. Furthermore, the spacecharge accumulated at the bottom of the trenches may prevent the low-energy ions from reaching the bottom. Hence, the etching of the dielectric materials does not continue after a certain depth.

[0054] Herein, a chemical-assisted ion beam dicing (CAIBD) process is proposed for wafer singulation, which effectively addresses all aforementioned issues. Figure 4 illustrates a simplified exemplary dicing equipment 200 for the proposed CAIBD process. The dicing equipment 200 includes a dischargechamber 202, a neutralizer 204, a grid assembly 206, a gas-flow system 208, and a wafer holder 210, each of which is positioned within a processing chamber 212.

[0055] In detail, reactive gases are introduced (through a gas inlet) into the discharge chamber 202 equipped with a radio frequency (RF) and / or inductively coupled plasma (ICP) source 213 to generate plasma species (including reactive ions, radicals, and electrons). The reactive gases might be sulfur hexafluoride (SFe), trifluoromethane (CHFs), carbon tetrafluoride (CF4), hexafluoroethane (C2F6), octafluorocyclobutane (C FS), oxygen (O2), chlorine (CI2), or any other proper reactive gases.

[0056] The grid assembly 206 is configured to create and accelerate collimated ion beams CIB composed of the reactive ions supplied from the discharge chamber 202. The grid assembly 206 is positioned between the discharge chamber 202 and the wafer holder 210 used to hold a target wafer (e.g., a target wafer 220 as shown in Figure 6), such that the collimated ion beams CIB can completely cover and be orthogonal to an exposed surface (e.g., a top surface) of the target wafer. Since the reactive ions in the collimated ion beams CIB possess enhanced energy (e.g., a few eV to a few KeV), velocity, and directional collimation, they are capable of penetrating deep into trenches formed in the target wafer during the singulation / dicing process, and bombarding the bottoms of the trenches to facilitate effective etching. As shown in Figure 3B, the reactive ions from the collimated ion beams CIB can traverse the trench vertically without colliding with sidewalls of the trenches and reduce collisions with the particles within the trench (owing to their highly collimated trajectories). Therefore, the collimated ion beams CIB will not bombard the sidewalls and will not cause damage to the sidewalls. Moreover, the increased energy and velocity of the reactive ions, combined with reduced collisions, significantly enhance their ability to reach the bottom of the trench. Upon arrival, these high-energy reactive ions can not only directly participate in the reaction with the material at the trench bottom but also initiate or facilitate reactions between the radicals and the material at the trench bottom. The presence of high-energy ions enables thebreaking of chemical bonds in the material at the trench bottom, thereby enhancing overall etching efficiency and anisotropy. In one embodiment, the grid assembly 206 may be implemented by three grids 214 (see Figure 4) with three specific voltages: a screen grid 214S to extract reactive ions from the plasma species, an accelerator grid 214A to accelerate the reactive ions to a desired energy level, and a decelerator grid 214D to reduce beam divergence and finetune the ion energy before it reaches the target wafer. Each individual grid 214 has a hole pattern 216 to allow the reactive ions to pass through.

[0057] The neutralizer 204, disposed between the discharge chamber 202 and the grid assembly 206, is configured to balance the charge on the reactive ions to reduce the space-charge, thereby preventing beam divergence and charge buildup on the target wafer. Additionally, the gas-flow system 208, which is configured to provide additional reactive gases, is positioned close to the wafer holder 210 / the target wafer, such that the additional reactive gases can surround the exposed / top surface of the target wafer. In one embodiment, the gas-flow system 208 comprises a gas release pipe-ring, which is positioned between the grid assembly 206 and the wafer holder 210. The ring structure of the gas-flow system 208 is configured to allow the collimated ion beams CIB to pass through the additional reactive gases without physical obstruction (i.e., the ring structure of the gas-flow system 208 does not physically interfere with the path of the collimated ion beams CIB). Herein, the collimated ion beams CIB are capable of dissociating the additional reactive gases introduced near the exposed surface of the target wafer, thereby generating more radicals in that localized area. By increasing the concentration of the radicals near the wafer surface, this mechanism helps improve an etching rate and uniformity, thereby enhancing the overall process efficiency, particularly in high aspect ratio structures (e.g., deep trenches).

[0058] In order to further enhance the radical density, a secondary plasma source 218 (e.g., RF source and / or ICP source) might be added into the processing chamber 212. The secondary plasma source 218 might be positioned anywhere in the processing chamber 212, provided that it does not physicallyobstruct the path of the collimated ion beams GIB. For instance, the secondary plasma source 218 is positioned with an offset downstream of the grid assembly 206.

[0059] Herein, the plasma source 213 in the discharge chamber 202 is primarily configured to provide reactive ions, which are used to form the collimated ion beams GIB for physical bombardment and chemical reaction. The secondary plasma source 218 is primarily configured to generate high averagedensity radicals, which are transported mainly through thermal diffusion, exhibit high chemical reactivity, and serve as the primary reactants in chemical reactions. In fact, reactive gases have varying tendencies to generate radicals and ions, depending on their molecular structures and ionization energy. Gases that are more easily ionized and contributing heavily to the ion density in the plasma will be good gas candidates introduced to the discharge chamber 202, such as Argon (Ar), CF4, CHF3, a mixture thereof, or the like. Gases that readily dissociate in the plasma to form a large amount of neutral radicals will be good gas candidates used for the secondary plasma source 218, such as CF4, CHF3, CI2, a mixture thereof, or the like. Therefore, reactive gases activated by the secondary plasma source 218 to provide radicals and those introduced into the discharge chamber 202 might be different. The reactive gases activated by the secondary plasma source 218 may be introduced through an additional gas inlet (not shown, different from the gas inlet for the discharge chamber 202) or through the gas-flow system 208 into the processing chamber 212. When the reactive gases activated by the secondary plasma source 218 are introduced by the additional gas inlet, since the secondary plasma source 218 can provide much higher average-density radicals than those produced by dissociating the additional reactive gases introduced via the gas-flow system 208, the gas-flow system 208 might be omitted in some embodiments.

[0060] Additionally, the high average-density radicals provided by the secondary plasma source 218 will not affect the formation of the collimated ion beams GIB. Instead, the collimated ion beams GIB tend to propel any intervening radicals that lie along their bombarding path toward the target wafer. Herein, thecollimated ion beams CIB can bombard the material-to-be-removed, not only causing sputtering but also disrupting crystal structures of the material-to-be-removed. This damage to the material’s structural integrity enhances its chemical reactivity, making it more susceptible to interaction with radicals and reactive ions, thereby facilitating more efficient etching. On the other hand, the high average-density of the radicals leads to more frequent chemical reactions, thereby enhancing the overall etching rate. Since radicals diffuse isotropically (i.e., in all directions), the high average-density helps achieve more uniform distribution across the wafer surface, thereby improving etching consistency. Moreover, the high average-density of the radicals enhances the probability that the radicals will diffuse into and be pushed by the collimated ion beams CIB into the trench.

[0061] Figure 5 illustrates a flowchart of the proposed CAIBD process for wafer singulation according to some embodiments of the present disclosure. Although the process steps are illustrated in a series, the process steps are not necessarily order dependent. Some steps may be taken in a different order than that presented. Further, processes within the scope of this disclosure may include fewer or more steps than those illustrated in Figure 5.

[0062] Initially, a wafer 220 is provided (step 302) as illustrated in Figure 6. The wafer 220 includes a first region 222 (e.g., the handle substrate 110) and a second region 224 (e.g., the top wafer 102 and / or the bottom wafer 104 excluding the handle substrate 110) formed over the first region 222. For simplicity and clarity, elements, such as metal layers, vias, and active / passive components, within the second region 224 are not depicted. Herein, the wafer 220 might have a 3D structure (e.g., the 3D wafer structure 100) or a 2D structure (e.g., the top wafer 102 or the bottom wafer 104).

[0063] On a horizontal plane, the wafer 220 can be divided into product sections 226 and street sections 228. Each product section 226 might be similar to one die section 106 described above, which includes metal layers, vias, and active / passive components. Each street section 228 is similar to the street section 108 described above, which is located between two adjacent productsections 226 and serves as a dicing area to separate the product sections 226. The first region 224 confined within each street section 228 is only composed of a first type of material (e.g., silicon, silicon carbide, glass, or other suitable materials), while the second region 224 confined within each street section 228 is only composed of a second type of material (e.g., dielectric materials including low-K dielectric materials, like the dielectric stack 112), which is totally different from the first type of material. Accordingly, within each street section 228, only the first type of material from the first region 222 and the second type of material from the second region 224 are present.

[0064] Next, a patterned mask 230 is formed over a top surface of the wafer 220 / the second region 224 (step 304), as illustrated in Figure 7. Each product section 226 is completely covered by the patterned mask 230, while each street section 228 is exposed through the pattern mask 230. Herein, the patterned mask 230 might be formed from an organic layer or a photoresist layer. After the top surface of the wafer 220 / the second region 224 is covered with the patterned mask 230, the wafer 220 with the patterned mask 230 is placed at the wafer holder 210 inside the processing chamber 212 of the dicing equipment 200 (step 306, not illustrated).

[0065] When the discharge chamber 202 includes only the plasma source 213 within the dicing equipment 200 (i.e., the secondary plasma source 218 is omitted), the wafer 220 is placed so that the partially covered (by the patterned mask 230) top surface of the wafer 220 is near the gas-flow system 208 and faces toward the discharge chamber 202. Accordingly, through the patterned mask 230, the street sections 228 of the wafer 220 are exposed to reactive gases supplied by the gas-flow system 208, and can receive both radicals and collimated ion beams CIB generated from reactive gases introduced into the discharge chamber 202.

[0066] Alternatively, when the dicing equipment 200 includes both the plasma source 213 in the discharge chamber 202 and the secondary plasma source 218, the wafer 220 is placed so that the partially covered (by the patterned mask 230) top surface of the wafer 220 faces toward the discharge chamber 202. If the gas-flow system 208 also exists, the wafer 220 is placed so that the partially covered top surface of the wafer 220 is also adjacent to the gas-flow system 208. As such, through the patterned mask 230, the street sections 228 of the wafer 220 are optionally exposed to the reactive gases supplied by the gas-flow system 208, can receive both the radicals and the collimated ion beams CIB generated from the reactive gases introduced into the discharge chamber 202, and can receive radicals generated from reactive gases activated by the secondary plasma source 218.

[0067] Once the wafer 220 with the patterned mask 230 is mounted properly at the wafer holder 210, etching the second region 224 within each street section 228 is then performed (step 308), as illustrated in Figure 8. During this etching step, the second region 224 within each street section 228 is bombarded by first collimated ion beams CIB1 through the patterned mask 230. These first collimated ion beams CIB1 are composed of reactive ions that are generated from reactive gas introduced into the charge chamber 202, subsequently balanced by the neutralizer 204, and then accelerated, energized, and collimated by the grind assembly 206. As such, structural integrity of the second region 224 within each street section 228, which is exposed through the patterned mask 230, is damaged, thereby enhancing chemical reactivity of the exposed portions of the second region 224. The reactive ions in the first collimated ion beams CIB1 may also chemically react with the exposed portions of the second region 224. As etching proceeds, trenches 232 are individually formed within the street sections 228, with an exposed surface in each street section 228 becoming a bottom surface of its corresponding trench 232. Since the first collimated ion beams CIB1 exhibit a focused direction, the first collimated ion beams CIB1 traverse the trenches 232 vertically to bombard the bottom surfaces of the trenches 232 without colliding with the sidewalls of the trenches 232. Therefore, the first collimated ion beam CIB1 will not bombard the sidewalls, thereby preventing any associated damage on the sidewalls of each trench 232.

[0068] On the other hand, first radicals, diffusing or being pushed through the patterned mask 230, only chemically react with the exposed portions of thesecond region 224 within the street sections 228. Herein, since the sidewalls of the trenches 232 remain undamaged, the first radicals inside the trenches 232 tend not to react with the sidewalls, but instead preferentially react with the damaged bottom surfaces of the trenches 232. The first radicals may be provided from different sources. The first radicals might be generated from the reactive gases introduced into the discharge chamber 202. Additionally, if the dicing equipment 200 includes the gas-flow system 208, the first radicals may also be provided by the first collimated ion beams CIB1 dissociating the reactive gases supplied by the gas-flow system 208. If the dicing equipment 200 includes the secondary plasma source 218 (with the additional gas inlet) but not the gas-flow system 208, the first radicals may be generated from the reactive gases introduced through the additional gas inlet and activated by the secondary plasma source 218. If the dicing equipment 200 includes the secondary plasma source 218 as well as the gas-flow system 208, the first radicals may further be generated through two mechanisms: by the first collimated ion beams CIB1 dissociating the reactive gases supplied by the gas-flow system 208, and by the secondary plasma source 218 activating the reactive gas introduced through the additional gas inlet.

[0069] Note that the reactive gases activated within the discharge chamber 202 are primarily used to generate reactive ions for the first collimated ion beams CIB1 , which are used for physical bombardment as well as chemical reactions. Therefore, the reactive gases introduced into the discharge chamber 202 are preferably those that are easily ionized and contribute significantly to the ion density in the plasma, such as Ar, CF4, CHF3, a mixture thereof, or the like. In contrast, the reactive gases activated by the secondary plasma source 218 are primarily used to generate first radicals for chemical reactions with the second region 224 within the street sections 228. Therefore, the reactive gases selected for the secondary plasma source 218 are preferably those that are readily dissociating in the plasma to form a large amount of radicals, such as CF4, CHF3, Cl, a mixture thereof, or the like. Furthermore, the reactive gases supplied by the gas-flow system 208 are primarily used to increase radical density bydissociation through the first collimated ion beams CIB1. Therefore, the reactive gases supplied by the gas-flow system 208 are preferably those that are highly susceptible to dissociation when bombarded by the first collimated ion beams CIB1 , such as CF4, CHF3, Cl, a mixture thereof, or the like. For the purpose of etching the second region 224 within the street sections 228, the reactive gases activated within the discharge chamber 202, activated by the secondary plasma source 218, and supplied through the gas-flow system 208 may be identical, may partially share one or more common gases, or may be completely different. For a non-limiting example, when the second region 224 within the street sections 228 is a dielectric stack, to remove such dielectric stack, the same fluorocarbon gases (e.g., CF4, C2F6, and / or C4F8) might be introduced into the discharge chamber 202, supplied through the gas-flow system 208, and activated by the secondary plasma source 218. Additionally, extra oxygen might be supplied through the gas-flow system 208 and activated by the secondary plasma source 218 to enhance etching performance. This etching step can be used to remove dielectric materials (including low-K dielectric materials) with a thickness more than 20 pm.

[0070] After the completion of the removal of the second region 224 within the street sections 228, etching the first region 222 within each street section 228 is performed (step 310), as illustrated in Figure 9. Since the first type of material from the first region 222 is different from the second type of material from the second region 224 within each street section 228, the first type of material might react with different ions / radicals to produce volatile products than those selected for etching the second region within each street section 228. Additionally, the first type of material might require different energy beams to effectively damage its structural integrity. Therefore, reactive gases employed for removing the first region 222 within each street section 228 might be adjusted according to an enhanced etching performance.

[0071] Herein, the reactive gases employed for removing the first region 222 within each street section 228 are configured to provide second collimated ion beams CIB2 and second radicals, using mechanisms similar to those describedfor the first collimated ion beams CIB1 and the first radicals. During this etching step, the first region 222 within each street section 228 is bombarded by the second collimated ion beams CIB2 through the patterned mask 230 within the trenches 232. As such, the structural integrity of the first region 224 within each street section 228, which is exposed at the bottom of the trenches 232, is damaged, thereby enhancing chemical reactivity of the exposed portions of the first region 222. The reactive ions in the second collimated ion beams CIB2 may also chemically react with the exposed portions of the first region 222. As etching proceeds, each trench 232 deepens within a corresponding street section 228. Since the second collimated ion beams CIB2 exhibit a focused direction, the second collimated ion beams CIB2 traverse the trenches 232 vertically to bombard the bottom surfaces of the trenches 232 without colliding with the sidewalls of the trenches 232. Therefore, the second collimated ion beam CIB2 will not bombard the sidewalls, thereby preventing any associated damage on the sidewalls of each trench 232.

[0072] On the other hand, the second radicals, diffusing or being pushed into the trenches 232, only chemically react with the exposed portions of the first region 222 within the street sections 228. Herein, since the sidewalls of the trenches 232 remain undamaged, the second radicals inside the trenches 232 tend not to react with the sidewalls, but instead preferentially react with the damaged bottom surfaces of the trenches 232. The second radicals may also be provided from various sources, as described above for the first radicals. For a non-limiting example, the first region 222 is a handle substrate formed of silicon, to remove the first region 222 within each street section 228, fluorocarbon gases, CI2 gases, and / or other proper reactive gases are introduced into the discharge chamber 202. Optionally, CF4, CHF3, and / or CI2 gases might be activated by the secondary plasma source 218 and / or supplied through the gas-flow system 208. This etching step can be used to remove silicon with a thickness ranging from 100 pm to 150 pm.

[0073] Regardless of the reactive gases activated in the discharge chamber 202, the collimated ion beams CIB1 / CIB2 directed toward the wafer 220 areinvariably accelerated, energized, and collimated. Therefore, the collimated ion beams CIB1 / CIB2 enable anisotropic removal of the second / first region 224 / 222 within each street section 228, resulting in etching occurring effectively and only in the vertical direction. Consequently, sidewalls of each trench formed during this etching step within a corresponding street section 228 are well protected, and higher dicing throughput can be achieved. Moreover, each street section 228 can be narrowed to a width of less than 20 pm (e.g., between 5 pm and 20 pm) without causing sidewall damage, while maintaining an effective etching rate. After the removal of all the materials from the street sections 228 is completed, optional substrate grinding, die pick-up, and / or die packaging will be followed (not shown).

[0074] Figures 10A-10C show comparisons of singulation results caused by different dicing techniques. Figure 10A illustrates sidewalls of a singulated die formed by laser grooving, which exhibit very rough surfaces with visible cracks. Figure 10B illustrates sidewalls of a singulated die formed by a BOSCH plasma process for silicon etching, which exhibit rough surfaces. Figure 10C illustrates sidewalls of a singulated die formed by the proposed CAIBD process, which exhibit vertical and smooth mirror-like finishing surfaces. In traditional techniques, severe sidewall damage is commonly observed. In contrast, the proposed CAIBD technique, using the collimated ion beams associated in combination with high average-density radicals, enables the formation of mirror-like vertical sidewalls. The prevention of sidewall damage, along with the ability to use very narrow street areas, contributes to increased die yield and overall cost reduction.

[0075] It is contemplated that any of the foregoing aspects, and / or various separate aspects and features as described herein, may be combined for additional advantage. Any of the various embodiments as disclosed herein may be combined with one or more other disclosed embodiments unless indicated to the contrary herein.

[0076] Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. All such improvementsand modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Claims

ClaimsWhat is claimed is:

1. A dicing equipment comprising:a discharge chamber, equipped with a primary plasma source and configured to provide at least reactive ions based on a first group of reactive gases introduced into the discharge chamber;a grid assembly, positioned downstream of the discharge chamber, configured to create and accelerate collimated ion beams composed of the reactive ions supplied from the discharge chamber;a wafer holder, positioned downstream of the grid assembly and facing the discharge chamber, configured to hold a target wafer such that the collimated ion beams from the grid assembly are capable of completely covering and being orthogonal to an exposed surface of the target wafer; anda secondary plasma source, configured to provide at least radicals based on a second group of reactive gases, wherein:the collimated ion beams are configured to bombard and chemically react with the target wafer at the exposed surface to perform selective etching, and are capable of propelling any intervening radicals from the first set of radicals that lie along their bombarding path toward the target wafer; andthe first set of radicals are configured to chemically react with the target wafer at the exposed surface to further perform selective etching.

2. The dicing equipment of claim 1 further comprising a processing chamber, wherein:the discharge chamber, the grid assembly, the wafer holder, and the secondary plasma source are positioned within the processing chamber; and the second group of reactive gases are introduced into the processing chamber.

3. The dicing equipment of claim 2 further comprising a neutralizer, which is disposed between the discharge chamber and the grid assembly, and inside the processing chamber, wherein the neutralizer is configured to balance a charge on the reactive ions provided by the discharge chamber, so as to prevent charge buildup on the target wafer.

4. The dicing equipment of claim 2 further comprising a gas-flow system, wherein:the gas-flow system is configured to introduce a third group of reactive gases into the processing chamber, and positioned close to the wafer holder, such that the third group of reactive gases can surround the exposed surface of the target wafer; andthe collimated ion beams are capable of dissociating the third group of reactive gases introduced near the exposed surface of the target wafer, thereby generating extra radicals in that localized area.

5. The dicing equipment of claim 4 wherein:the gas-flow system comprises a gas release pipe-ring, which is positioned between the grid assembly and the wafer holder; anda ring structure of the gas release pipe-ring is configured to allow the collimated ion beams to pass through the third group of reactive gases without physical obstruction.

6. The dicing equipment of claim 5 wherein the second group of reactive gases and the third group of reactive gases are identical and are different from the first group of reactive gases.

7. The dicing equipment of claim 1 wherein the first group of reactive gases and the second group of reactive gases are not identical but share at least one common reactive gas.

8. A dicing equipment comprising:a discharge chamber, equipped with a plasma source and configured to provide at least reactive ions and radicals based on a first group of reactive gases introduced into the discharge chamber;a grid assembly, positioned downstream of the discharge chamber, configured to create and accelerate collimated ion beams composed of the reactive ions supplied from the discharge chamber;a wafer holder, positioned downstream of the grid assembly and facing the discharge chamber, configured to hold a target wafer such that the collimated ion beams from the grid assembly are capable of completely covering and being orthogonal to an exposed surface of the target wafer; anda gas-flow system, configured to introduce a second group of reactive gases, and positioned between the grid assembly and the wafer holder, close to the wafer holder, such that the second group of reactive gases can surround the exposed surface of the target wafer, wherein:the collimated ion beams are configured to bombard and chemically react with the target wafer at the exposed surface to perform selective etching;the collimated ion beams are capable of dissociating the second group of reactive gases introduced near the exposed surface of the target wafer, thereby generating extra radicals in that localized area;the collimated ion beams are capable of propelling any intervening radicals that lie along their bombarding path toward the target wafer, wherein the intervening radicals originate either from the radicals provided by the discharge chamber or from the extra radicals generated by the dissociation; andthe radicals and the extra radicals are configured to chemically react with the target wafer at the exposed surface to further perform selective etching.

9. The dicing equipment of claim 8 further comprising a processing chamber, wherein:the discharge chamber, the grid assembly, the wafer holder, and the gasflow system are positioned within the processing chamber; andthe second group of reactive gases are introduced by the gas-flow system into the processing chamber.

10. The dicing equipment of claim 9 further comprising a neutralizer, which is disposed between the discharge chamber and the grid assembly, and inside the processing chamber, wherein the neutralizer is configured to balance a charge on the reactive ions provided by the discharge chamber, so as to prevent charge buildup on the target wafer.

11. The dicing equipment of claim 8 wherein:the gas-flow system comprises a gas release pipe-ring; anda ring structure of the gas release pipe-ring is configured to allow the collimated ion beams to pass through the third group of reactive gases without physical obstruction.

12. The dicing equipment of claim 1 wherein the first group of reactive gases and the second group of reactive gases are not identical but share at least one common reactive gas.

13. A method of dicing a wafer comprising:providing a wafer covered with a patterned mask, wherein:the wafer includes a first region and a second region over the first region;on a horizontal plane, the wafer is divided into product sections and street sections, each street section located between two adjacent ones of the product sections;the first region confined within each street section is only composed of a first type of material, while the second region confined within each street section is only composed of a second type of material, which is different from the first type of material; andthe patterned mask is formed over a top surface of the second region to expose each of the street sections;etching the second region within each street section utilizing first collimated ion beams and first radicals, wherein the first collimated ion beams bombard exposed portions of the second region through the patterned mask solely in a vertical direction, and reactive ions from the first collimated ion beams and the first radicals chemically react with the exposed portions of the second region solely along the vertical direction; andetching the first region within each street section after the second region within each street section is completely removed, utilizing second collimated ion beams and second radicals, wherein the second collimated ion beams bombard exposed portions of the first region through the patterned mask solely in the vertical direction, and reactive ions from the second collimated ion beams and the second radicals chemically react with the exposed portions of the first region solely along the vertical direction.

14. The method of claim 13 wherein each street section has a width of 20 pm or less.

15. The method of claim 13 wherein the first collimated ion beams and the first radicals are generated from a first group of reactive gases, while the second collimated ion beams and the second radicals are generated from a second group of reactive gases, which are different from the first reactive gases.

16. The method of claim 15 wherein:the first type of material comprises silicon, while the second type of material comprises dielectric materials; andthe first collimated ion beams and the first radicals are generated at least from fluorocarbon gases, while the second collimated ion beams and the second radicals are generated from fluorocarbon gases and / or chlorine (CI2).

17. The method of claim 16 wherein the dielectric materials include one or more low-K dielectric materials, which exhibit a dielectric constant of no greater than 3.

18. The method of claim 17 wherein a total thickness of the dielectric materials is greater than 20 pm.

19. The method of claim 15 wherein both the first radicals and the second radicals are produced from more than one source.

20. The method of claim 19 wherein:the first collimated ion beams and the second collimated ion beams are produced from a primary plasma source at different times; andthe first radicals and the second radicals are produced from both the primary plasma source and a secondary plasma source at different times.

21. The method of claim 20 wherein an average-density of the first radicals produced from the secondary plasma source is higher than an average-density of the first radicals produced from the primary plasma source, and an averagedensity of the second radicals produced from the secondary plasma source is higher than an average-density of the second radicals produced from the primary plasma source.

22. The method of claim 20 wherein the first radicals are further produced by the first collimated ion beams dissociating the first group of reactive gases, while the second radicals are further produced by the second collimated ion beams dissociating the second group of reactive gases.

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