Copper metallization for through-glass vias on thin glass

Abstract

A method for metallizing through-glass vias in a glass substrate includes functionalizing a surface of the glass substrate with a silane. The glass substrate has an average thickness t and comprises a plurality of vias extending through the thickness t. The method further includes applying an electroless plating solution comprising a copper ion to deposit a copper seed layer on the functionalized surface, disposing an electrolyte within the plurality of vias, wherein the electrolyte comprises copper ions to be deposited on the copper seed layer within the plurality of vias; positioning an electrode within the electrolyte; and applying a current between the electrode and the glass substrate, thereby reducing the copper ions into copper within the plurality of vias such that each of the plurality of vias is filled with copper and the copper has a void volume fraction of less than 5%.

Description

BACKGROUND

Field

The present specification generally relates to the manufacture of through-glass vias and, more specifically, to copper metallization of through-glass vias.

Technical Background

Through-substrate vias provide electrical connections between layers in a physical electronic circuit or chip. For example, in a three-dimensional stacked integrated circuit, the through-substrate vias enable integration of electronic components both vertically and horizontally. Conventionally, through-substrate vias are used in silicon substrates. However, because glass is less expensive than silicon, glass substrates are becoming more prevalent in electronic devices. Glass substrates may also provide improved electromagnetic loss properties, improved dielectric properties, tailorable coefficients of thermal expansion, and the ability to come in scalable form factors, including roll-to-roll forms.

Conventional processes for metallizing vias include dry processes and wet processes. Dry processes, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), are carried out in an environment under vacuum, which limits throughput and adds to manufacturing costs. Additionally, such dry processes may be limited in terms of their ability to produce a continuous metal layer within vias of glass substrates with aspect ratios greater than 5, wherein the aspect ratio is the ratio of the average thickness of the glass substrate to the average diameter of the vias, particularly where the via diameter is small (e.g., less than 50 μm). Wet processes, such as electroless plating, are cost effective compared to dry processes, but have been conventionally limited to use on vias with large diameters (e.g., greater than 75 μm).

Accordingly, a need exists for alternative methods for metallizing through-glass vias having small diameters and high aspect ratios.

SUMMARY

According to various aspects disclosed herein, a method for metallizing through-glass vias in a glass substrate includes functionalizing a surface of the glass substrate with a silane. The glass substrate has an average thickness t and comprises a plurality of vias extending through the thickness t. The method further includes applying an electroless plating solution comprising a copper ion to deposit a copper seed layer on the functionalized surface, disposing an electrolyte within the plurality of vias, wherein the electrolyte comprises copper ions to be deposited on the copper seed layer within the plurality of vias; positioning an electrode within the electrolyte; and applying a current between the electrode and the glass substrate, thereby reducing the copper ions into copper within the plurality of vias such that each of the plurality of vias is filled with copper and the copper has a void volume fraction of less than 5%.

Another aspect includes the method of the previous aspect, wherein the average thickness t of the glass substrate is greater than or equal to 50 μm and less than or equal to 150 μm.

Another aspect includes the method of any of the previous aspects, wherein the average thickness t of the glass substrate is greater than or equal to 90 μm and less than or equal to 110 μm.

Another aspect includes the method of any of the previous aspects, wherein each of the plurality of vias has an average diameter of greater than or equal to 8 μm and less than or equal to 20 μm; and an aspect ratio of the average thickness t of the glass substrate to the average diameter of the plurality of vias is greater than or equal to 5:1 and less than or equal to 12:1.

Another aspect includes the method of any of the previous aspects, wherein the electrolyte further comprises chloride ions and an additive.

Another aspect includes the method of the previous aspect, wherein the additive consists of nitrotetrazolium blue chloride.

Another aspect includes the method of any of the previous aspects, wherein the additive is present in the electrolyte in a concentration of greater than or equal to 20 ppm and less than or equal to 60 ppm.

Another aspect includes the method of any of the previous aspects, wherein the chloride ions are present in the electrolyte in a concentration of greater than or equal to 20 ppm and less than or equal to 140 ppm.

Another aspect includes the method of any of the previous aspects, wherein applying the current comprises applying the current at a current density of greater than or equal to 0.05 amp s/dm² and less than or equal to 2 amp s/dm².

Another aspect includes the method of any of the previous aspects, wherein applying the current comprises applying a first current at a first current density for a first period of time and applying a second current at a second current density for a second period of time, wherein the second current density is greater than the first current density.

Another aspect includes the method of any of the previous aspects, further comprising wetting the glass substrate including the copper seed layer prior to disposing the electrolyte within the plurality of vias.

Another aspect includes the method of any of the previous aspects, wherein the copper in each of the plurality of vias has a void volume fraction of less than 1%.

Another aspect includes the method of any of the previous aspects, wherein the copper in each of the plurality of vias is free of voids.

Another aspect includes the method of any of the previous aspects, further comprising cleaning the glass substrate prior to functionalizing the surface, wherein the glass substrate has a water contact angle of less than or equal to 5 degrees after the cleaning.

Another aspect includes the method of any of the previous aspects, wherein functionalizing the surface of the glass substrate comprises functionalizing sidewalls of the plurality of vias.

Another aspect includes the method of any of the previous aspects, further comprising annealing the glass substrate comprising the copper seed layer prior to disposing the electrolyte within the plurality of vias.

According to another aspect, a glass article includes a glass substrate having a first major surface and a second major surface opposite the first major surface and separated from the first major surface by an average thickness of greater than or equal to 50 μm and less than or equal to 150 μm and a plurality of vias extending through the glass substrate from the first major surface to the second major surface. Each of the plurality of vias has an average diameter of greater than or equal to 8 μm and less than or equal to 20 μm. Additionally, an aspect ratio of the average thickness of the glass substrate to the average diameter of the plurality of vias is greater than or equal to 5:1 and less than or equal to 12:1 and each of the plurality of vias is filled with copper such that the copper in each of the plurality of vias has a void volume fraction of less than 5%.

Another aspect includes the glass article of the previous aspect, wherein the void volume fraction of the copper in each of the plurality of vias is less than 1%.

Another aspect includes the glass article of any of the previous aspects, wherein the copper in each of the plurality of vias is free of voids.

Another aspect includes the glass article of any of the previous aspects, wherein the average thickness of the glass substrate is greater than or equal to 90 μm and less than or equal to 110 μm.

Another aspect includes the glass article of any of the previous aspects, wherein the copper is deposited by electroless on sidewalls of the plurality of vias followed by electroplating.

Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description which follows, the claims, as well as the appended drawings.

It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate the various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts a cross-section of a glass substrate including a plurality of vias in accordance with one or more embodiments shown and described herein;

FIG. 2 schematically depicts a method for metallizing the plurality of vias in accordance with one or more embodiments shown and described herein;

FIG. 3 schematically depicts a cross-section of a glass substrate having a seed layer deposited thereon in accordance with one or more embodiments shown and described herein;

FIG. 4 schematically depicts a cross-section of a glass substrate in which the electroplated electrically conductive material forms “butterflies” within each of the plurality of vias in accordance with one or more embodiments shown and described herein;

FIG. 5 schematically depicts a cross-section of a glass substrate in which the plurality of vias are filled with electrically conductive material in accordance with one or more embodiments shown and described herein;

FIG. 6A is a scanning electron microscope (SEM) image showing the uniform and continuous copper seed layer deposited on the sidewall of a 10 μm diameter via in the glass substrate having an aspect ratio of 10 in accordance with one or more embodiments shown and described herein;

FIG. 6B is a scanning electron microscope (SEM) image showing the uniform and continuous copper seed layer deposited on the sidewall of a 20 μm diameter via in the glass substrate having an aspect ratio of 5 in accordance with one or more embodiments shown and described herein;

FIG. 7A is an SEM image showing the formation of a plug formed from the copper within the 10 μm vias in accordance with one or more embodiments shown and described herein;

FIG. 7B is a CT scan image further evidencing the formation of the plug formed from the copper within the 10 μm vias in accordance with one or more embodiments shown and described herein;

FIG. 7C is an SEM image showing the formation of a plug formed from the copper within the 20 μm vias in accordance with one or more embodiments shown and described herein;

FIG. 7D is a CT scan image further evidencing the formation of the plug formed from the copper within the 20 μm vias in accordance with one or more embodiments shown and described herein;

FIG. 8A is an SEM image showing the complete and void-free filling of the 10 μm vias with the copper in accordance with one or more embodiments shown and described herein;

FIG. 8B is a CT scan image further evidencing the complete and void-free filling of the 10 μm vias in accordance with one or more embodiments shown and described herein;

FIG. 8C is an SEM image showing the complete and void-free filling of the 20 μm vias with the copper in accordance with one or more embodiments shown and described herein;

FIG. 9A is an SEM image showing voids created within the vias as a result of the electroplating at a current density of 0.16 amps/dm² through the entirety of the process; and

FIGS. 9B and 9C are SEM images further evidencing the voids within the vias as a result of the electroplating at a current density of 0.16 amps/dm² through the entirety of the process.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of components used in the methods of the present disclosure is shown in FIG. 1, and is designated generally throughout by the reference numeral 100. The components generally include a glass substrate including a plurality of vias having an aspect ratio greater than or equal to 5:1, wherein the aspect ratio is equal to the average thickness t of the glass substrate to the average diameter of the vias, that are filled with an electrically conductive material such that the electrically conductive material has a void volume fraction of less than or equal to 5%.

Unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is in no way intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and; the number or type of embodiments described in the specification.

As used herein, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a” component includes aspects having two or more such components, unless the context clearly indicates otherwise. Also, the word “or” when used without a preceding “either” (or other similar language indicating that “or” is unequivocally meant to be exclusive—e.g., only one of x or y, etc.) shall be interpreted to be inclusive (e.g., “x or y” means one or both x or y).

The term “and/or” shall also be interpreted to be inclusive (e.g., “x and/or y” means one or both x or y). In situations where “and/or” or “or” are used as a conjunction for a group of three or more items, the group should be interpreted to include one item alone, all the items together, or any combination or number of the items. Moreover, terms used in the specification and claims such as have, having, include, and including should be construed to be synonymous with the terms comprise and comprising.

Unless otherwise indicated, all numbers or expressions, such as those expressing dimensions, physical characteristics, and the like, used in the specification (other than the claims) are understood to be modified in all instances by the term “approximately.” At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the claims, each numerical parameter recited in the specification or claims which is modified by the term “approximately” should be construed in light of the number of recited significant digits and by applying ordinary rounding techniques.

All disclosed ranges are to be understood to encompass and provide support for claims that recite any and all subranges or any and all individual values subsumed by each range. For example, a stated range of 1 to 10 should be considered to include and provide support for claims that recite any and all subranges or individual values that are between and/or inclusive of the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less (e.g., 5.5 to 10, 2.34 to 3.56, and so forth) or any values from 1 to 10 (e.g., 3, 5.8, 9.9994, and so forth).

All disclosed numerical values are to be understood as being variable from 0-100% in either direction and thus provide support for claims that recite such values or any and all ranges or subranges that can be formed by such values. For example, a stated numerical value of 8 should be understood to vary from 0 to 16 (100% in either direction) and provide support for claims that recite the range itself (e.g., 0 to 16), any subrange within the range (e.g., 2 to 12.5) or any individual value within that range (e.g., 15.2).

The drawings shall be interpreted as illustrating one or more embodiments that are drawn to scale and/or one or more embodiments that are not drawn to scale. This means the drawings can be interpreted, for example, as showing: (a) everything drawn to scale, (b) nothing drawn to scale, or (c) one or more features drawn to scale and one or more features not drawn to scale. Accordingly, the drawings can serve to provide support to recite the sizes, proportions, and/or other dimensions of any of the illustrated features either alone or relative to each other. Furthermore, all such sizes, proportions, and/or other dimensions are to be understood as being variable from 0-100% in either direction and thus provide support for claims that recite such values or any and all ranges or subranges that can be formed by such values.

The terms recited in the claims should be given their ordinary and customary meaning as determined by reference to relevant entries in widely used general dictionaries and/or relevant technical dictionaries, commonly understood meanings by those in the art, etc., with the understanding that the broadest meaning imparted by any one or combination of these sources should be given to the claim terms (e.g., two or more relevant dictionary entries should be combined to provide the broadest meaning of the combination of entries, etc.) subject only to the following exceptions: (a) if a term is used in a manner that is more expansive than its ordinary and customary meaning, the term should be given its ordinary and customary meaning plus the additional expansive meaning, or (b) if a term has been explicitly defined to have a different meaning by reciting the term followed by the phrase “as used in this document shall mean” or similar language (e.g., “this term means,” “this term is defined as,” “for the purposes of this disclosure this term shall mean,” etc.). References to specific examples, use of “i.e.,” use of the word “invention,” etc., are not meant to invoke exception (b) or otherwise restrict the scope of the recited claim terms. Other than situations where exception (b) applies, nothing contained in this document should be considered a disclaimer or disavowal of claim scope.

In the three-dimensional integrated circuit (3D-IC) industry, stacking devices is a technique being used to increase device performance in a limited space. The performance of the integrated circuit may be further enhanced through the use of thinner substrates and smaller vias, which leads to higher aspect ratios (e.g., aspect ratios the average thickness of the glass substrate to the average diameter of the via of greater than or equal to 4:1), thereby reducing packaging size and stress effects. However, the higher the aspect ratio, the more difficult it is to metallize the sidewalls of the vias, particularly when the vias have small (e.g., less than or equal to 50 μm) diameters, which may lead to voids within the electrically conductive material within the vias after filling.

The methods of the present disclosure enable through-glass vias to be filled with an electrically conductive material, such as copper or another metal, despite the challenges associated with the glass substrate having an aspect ratio of greater than 5:1. As used herein, the term “aspect ratio” refers to the ratio of the average thickness t of the glass substrate to the average diameter of the plurality of vias. For example, by utilizing a method that includes a wet electroless plating step in conjunction with a wet electroplating step, the challenges associated with metallizing vias with a high aspect ratio in a thin glass substrate may be mitigated.

In the embodiment shown in FIG. 1, the glass article is in the form of a glass substrate 102 that includes a plurality of vias 104, or precision holes, defined by one or more sidewalls 105. For example, in the embodiments described herein, the vias 104 are circular in cross section and, as such, the vias 104 have a single sidewall 105. However, it should be understood that vias with other cross-sectional geometries are contemplated include, for example vias which have more than one sidewall. The glass substrate 102 may be used, for example, as an interposer to provide vertical electrical connections within a three-dimensional integrated circuit. The glass substrate 102 comprises a first face 110 and a second face 112 opposite the first face 110. The first face 110 of the glass substrate 102 is separated from the second face 112 of the glass substrate 102 by a thickness t of the glass substrate.

The composition of the glass substrate 102 is not particularly limited, and may be selected based on the desired end use of the glass substrate 102. In some embodiments, the glass substrate 102 may be a flexible glass substrate. The glass substrate 102 may be formed from glasses suitable for electronics applications including, for example, WILLOW® glass, Eagle XG™ glass, or Code 2318 glass, manufactured by Corning, Inc. However, it should be understood that other glasses are contemplated and possible. For example, other types of ion-exchangeable glasses or fused silica may be used to form the glass substrate 102. Additionally, the glass substrate 102 may be in the shape of a wafer having a 10 cm, 15 cm, 20 cm, or 30 cm diameter, for example. However, it should be understood that glass substrates 102 of other dimensions are contemplated and possible. The thickness of the glass substrate 102 may also vary depending on its end use, although in various embodiments, the average thickness t of the glass substrate is greater than or equal to 50 μm and less than or equal to 150 μm. For example, the glass substrate 102 may have a thickness of from greater than or equal to 90 μm and less than or equal to 110 μm. In various embodiments, the glass substrate 102 has a thickness of less than or equal to about 100 μm. In some embodiments, the glass substrate 102 has a thickness of less than 100 μm. However, it should be understood that glass substrates of any suitable thickness may be utilized. In embodiments, the thickness of the glass substrate may be measured through interferometric methods at locations within the area of the substrate. Additionally or alternatively, mechanical means (e.g., calipers) may be used to measure the thickness of the glass substrate. Unless otherwise specified, thickness of the glass substrate is measured by interferometric methods.

The plurality of vias 104 can be formed in the glass substrate 102 by any suitable method. For example, in embodiments, the plurality of vias 104 may be drilled in the glass substrate 102 using a pulsed laser. The laser may be any laser having suitable optical properties for drilling through the glass substrate 102 as well as a sacrificial cover layer positioned on a surface of the glass substrate 102. Suitable lasers include, without limitation, ultra-violet (UV) lasers, such as frequency tripled neodymium doped yttrium orthovanadate (Nd:YVO₄) lasers, which emit a beam of coherent light having a wavelength of about 355 nm. The beam of the laser may be directed onto a predetermined location on the surface of the glass substrate and pulsed to form each of the plurality of vias 104 in the glass substrate 102. Alternatively, the plurality of vias may be mechanically machined.

In some embodiments, a diameter of an opening of a via in face 110 of the glass substrate 102 and a diameter of an opening of the via in face 112 of the glass substrate 102 may be the same such that the via is cylindrical. Alternatively, a diameter of an opening of a via in face 110 of the glass substrate 102 and a diameter of an opening of the via in face 112 of the glass substrate 102 may differ by 2 μm or less, such that the via is substantially cylindrical. In other embodiments, a diameter of the vias may decrease from one face of the glass substrate 102 to the other face of the glass substrate 102 such that the vias have a cone shape. In various embodiments, each of the plurality of vias has an average diameter of greater than or equal to 8 μm and less than or equal to 20 μm, or greater than or equal to 8 μm and less than or equal to 12 μm. For example, each of the plurality of vias may have an average diameter of about 20 μm, about 15 μm, about 12 μm, or about 10 μm. As used herein, the term “average diameter” refers to the diameter of the via normal to the axis of the via through the thickness of the glass, averaged along the axis of the via. In embodiments, the average diameter is measured using an SEM cross-section or visual metrology from the top/bottom side (e.g., averaging the top, waist (or some location within the via within the thickness of the glass), and the bottom). Unless otherwise specified, the average diameter is measured using an SEM cross-section.

According to various embodiments, the aspect ratio is greater than or equal to 3:1, or greater than or equal to 5:1. For example, the aspect ratio may be greater than or equal to 3:1 and less than or equal to 16:1, greater than or equal to 5:1 and less than or equal to 12:1, or greater than or equal to 5:1 and less than or equal to 10:1.

In the embodiments described herein, the plurality of vias 104 are filled with an electrically conductive material 500 (shown in FIG. 5). The electrically conductive material may be, by way of example and not limitation, copper, silver, aluminum, nickel, alloys thereof, and combinations thereof. In some embodiments, the plurality of vias 104 are filled with a copper-containing material, such as a copper alloy. In various embodiments, the electrically conductive material in each of the plurality of filled vias has a void volume fraction of less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, or even less than or equal to 1% by volume. In some embodiments, the electrically conductive material in each of the plurality of filled vias has a void volume fraction of less than or equal to 1%. In some embodiments, the electrically conductive material in each of the plurality of filled vias is free of voids (i.e., the electrically conductive material in each of the plurality of filled vias has a void volume fraction of 0%). In embodiments herein, the void volume is measured based on analysis of a scanning electron microscope (SEM) cross-section image or an X-ray CT scan. Unless otherwise specified, the void volume fraction is measured based on analysis of an SEM cross-section. Accordingly, “free of voids” means that there are no voids visible according to the resolution of the imaging equipment.

FIG. 2 depicts one embodiment of a method 200 for filling, or metallizing, the vias with the electrically conductive material. In particular, as shown in FIG. 2, the method generally includes functionalizing a surface of the glass substrate (step 202), applying an electroless plating solution to deposit a seed layer on the functionalized surface (step 204), wetting the glass substrate including the seed layer (step 206) and employing an electroplating process to reduce a conductive material within the vias on the seed layer (step 208). In embodiments, the method 200 is performed as a wet process that enables the electrically conductive material to be substantially void-free manner without the use of a temporary carrier, thereby enabling the method 200 to be employed in roll-to-roll manufacturing processes. As used herein, the term “substantially void-free” means that the electrically conductive material has a void volume fraction of less than or equal to 5%, less than or equal to 1%, less than or equal to 0.5%, less than or equal to 0.1%, less than or equal to 0.05%, or even 0%.

In some embodiments, prior to functionalizing the surface of the glass substrate, the glass substrate may be optionally cleaned (optional step 201). Cleaning may be performed according to any conventional cleaning process known and used in the art to remove organic residues and enrich hydroxyl groups on the surface of the glass substrate. For example, the glass substrate may be cleaned by a process such as O₂ plasma, UV-ozone, or RCA cleaning to remove organics and other impurities (metals, for example) that would interfere with the silane reacting with the surface silanol groups. Washes based on other chemistries may also be used, for example, HF or H₂SO₄ wash chemistries. In some embodiments, the glass substrate may be cleaned with a detergent in an ultrasonic bath and rinsed with deionized water. In various embodiments, the glass substrate has a water contact angle of less than or equal to 7 degrees, less than or equal to 6 degrees, less than or equal to 5 degrees after cleaning, less than or equal to 4 degrees, or less than or equal to 2 degrees as measured using an goniometer, such as DSA100 available from Kruss GmbH (Germany).

At step 202, the surface of the glass substrate 102 is functionalized with a silane. In embodiments, the surface of the glass substrate 102 that is functionalized includes one or more of the sidewall(s) 105 of the plurality of vias 104, the first surface 110 of the glass substrate 102, and the second surface 112 of the glass substrate 102. Silanes are chosen so as to produce a suitable surface energy on the functionalized surfaces, and so as to have sufficient thermal stability upon exposure to elevated temperatures experienced by the glass substrate 102 in downstream processing. Suitable silanes may include, by way of example and not limitation, cationic silanes or polymers, such as 3-(2-amino ethylamino)propyldimethoxy-methylsilane. Moreover, in various embodiments, silane modification of the surface of the glass substrate modifies the glass surface to have a positive charge and enables binding of the palladium (Pd) used in the electroless plating to the surface of the glass substrate, as will be described in greater detail below.

In embodiments, the surface functionalization is performed by diluting a silane in isopropanol to form a silane solution and submerging the glass substrate in the silane solution. Optionally, ultrasonic energy is applied to the silane solution with the submerged glass substrate and the glass substrate to enhance wetting and bubble removal. In embodiments, the glass substrate is soaked in the silane solution for a predetermined period of time. For example, the glass substrate may be submerged in the silane solution for a period of time of greater than or equal to 15 minutes, greater than or equal to 20 minutes, or greater than or equal to 30 minutes. After soaking in the silane solution, the glass substrate may be dried, for example, in an oven. While one example of a functionalization process is described herein, it should be understood that other functionalization processes are contemplated, provided that such processes are effective to adsorb the silane to the surface of the glass substrate. In embodiments, the glass substrate may be heated to control the surface hydroxyl concentration prior to functionalization, and/or may be heated after silane application to complete silane condensation with the hydroxyl groups on the surface of the glass substrate.

After functionalization, in step 204, electroless plating is used to deposit a seed layer 300 of a conductive material (e.g., a copper seed layer) on the surface of the glass substrate, as depicted in FIG. 3. In the embodiments described herein, the deposition of the seed layer renders the surfaces of the glass substrate electrically conductive, enabling an electroplating technique to be used to fill the vias with electrically conductive material. In particular, the seed layer 300 is deposited on the silane-modified surface 305 of the glass substrate 102. In embodiments, commercially available kits and/or electroless plating solutions may be employed to deposit the seed layer 300. For example, in some embodiments, the glass substrate may be dipped into a catalyst mixture, such as a Pd/Sn colloid, and then rinsed. A coating of the catalyst mixture remains on the surfaces of the glass substrate after the rinsing. The catalyst on the surfaces of the glass substrate may then be activated, such as through removal of the Sn shell from the Pd. The activation may include, for example, dipping the glass substrate into an activation solution including fluoroboric acid and boric acid. Commercially available activation solutions include those available from Uyremura. After the catalyst is activated, the glass substrate may be dipped into an electroless plating bath to form the seed layer on the surface of the glass substrate. In embodiments, the seed layer 300 is formed on at least the sidewalls 105 of each of the plurality of vias 104, although it is contemplated that the seed layer 300 may be additionally be formed on the first surface 110, the second surface 112 of the glass substrate 102, as shown in FIG. 3.

In embodiments, the glass substrate may be thermally annealed (not shown in FIG. 2) after the seed layer is deposited thereon to relieve stresses in the glass substrate and thereby reduce the impact of any downstream thermal processing steps which may otherwise effect the dimensional stability of the glass substrate materials, such as electrically conductive materials, deposited on the glass substrate. In embodiments, the glass substrate may be heated to a temperature of greater than or equal to 400° C. for a time period sufficient to relieve the stresses in the glass substrate.

Returning to FIG. 2, the glass substrate is wetted (step 206) following deposition of the seed layer. In embodiments, the glass substrate is wetted by submerging the glass substrate including the seed layer in water to ensure that each of the vias is wetted. For example, the glass substrate may be dipped into deionized water for a period of greater than or equal to 2 minutes. In embodiments, ultrasonic energy may be applied to the glass substrate while the glass substrate is submerged in the water to enhance wetting and bubble removal. Without being bound by theory, it is believed that wetting the glass substrate prior to electroplating ensures that the vias are pre-wetted thereby preventing bubbles from being trapped within the vias, which bubbles may create voids in the conductive material subsequently filled within the vias.

After the glass substrate is wetted at step 206, electroplating (step 208) is carried out. In particular, an electrolyte is disposed within the plurality of vias. For example, the glass substrate may be submerged in an electrolyte solution such that the electrolyte enters the vias. The electrolyte includes ions of the electrically conductive material, for example, copper ions, to be deposited on the seed layer.

In embodiments, the electrolyte comprises ions of the electrically conductive material (e.g., copper ions) in addition to chloride ions and an additive. The chloride ions combine with the organic species in the solution to form a complex that slows down the plating rate. The chloride ions may be present in a concentration of greater than or equal to 20 ppm and less than or equal to 140 ppm in the electrolyte or greater than or equal to 20 ppm and less than or equal to 120 ppm. For example, the chloride ions may be present in a concentration of 20 ppm, 80 ppm, 100 ppm, 120 ppm, or even 140 ppm.

In embodiments, the additive is a leveler, such as nitrotetrazolium blue chloride (NTB). The leveler may enhance current density in the center of the via and help control surface morphology of the deposited electrically conductive material. In addition, the leveler may possess several physiochemical characteristics, such as a potential-dependent electrochemical desorption or breakdown and a mass-transfer controlled electrochemical adsorption. The mass-transfer controlled electrochemical adsorption may create a concentration gradient of the leveler from the opening to the center of the via during plating. Without being bound by theory, it is believed that the physiochemical characteristics of the leveler, and in particular, the NTB, enable the leveler to adsorb to the via sidewalls and suppress deposition of the electrically conductive material near the opening of the vias at a greater rate than near the center of the vias.

The additive may be present in a concentration of greater than or equal to 20 ppm and less than or equal to 60 ppm in the electrolyte. For example, the additive may be present in a concentration of 20 ppm, 40 ppm, or even 60 ppm. The electrolyte may have a ratio of chloride ions to additive of greater than or equal to 0.5 and less than or equal to 7. In some embodiments, the electrolyte is free of accelerators which form electroactive species responsible for enhanced plating rate, suppressors which combine with chloride ions to inhibit plating on areas where a reduced plating rate is desired, and additional levelers that are conventionally found in electrolyte solutions for electroplating. Such single-additive electrolytes may reduce the number of degrees of freedom and simplify optimization of the electroplating process. In other words, the use of single-additive electrolytes may result in fewer variables within the electroplating process to be modified for optimization, thereby simplifying the optimization of the electroplating process.

In some particular embodiments, the electrolyte is an electrolyte bath consisting of CuSO₄, H₂SO₄, chloride ions, and NTB. In such embodiments, the CuSO₄ provides a source of copper ions, while the H₂SO₄ makes the bath conductive and acts as a charge carrier.

Electroplating is carried out by positioning one or more electrodes within the electrolyte. In various embodiments, two electrodes, three electrodes, or more can be positioned within the electrolyte. For example, in some embodiments, three electrodes are employed. In these embodiments, the glass substrate including the seed layer is the working electrode, or cathode, and the other two electrodes are anodes. In such embodiments, the anodes may be positioned on opposite sides of the glass substrate such that plating of the electrically conductive material may be conducted symmetrically from both sides of the glass substrate. The anodes may be, by way of example and not limitation, copper plates. While a specific configuration of the electrodes is described herein, it should be understood that other configurations are contemplated and possible.

Thereafter, a current is supplied through the electrodes, the electrolyte, and the glass substrate, thereby reducing the electrically conductive ions in the electrolyte into electrically conductive material within the plurality of vias. For example, in embodiments in which the electrolyte includes copper ions, the copper ions are reduced into copper within the plurality of vias such that each of the plurality of vias is filled with copper. In embodiments, the current is applied at a current density of greater than or equal to 0.05 amps/dm² and less than or equal to 2 amps/dm². The current density is a measure of the total current passed over a time period divided by the total surface area over which the deposition took place. In various embodiments, the total surface are is a summation of the first and second surfaces of the glass substrate and the interior surface areas of the vias. The current density, in various embodiments, is constant. However, the current density may be varied during the electroplating process. For example, in embodiments, the current may be changed in a step-wise fashion during the electroplating process.

In embodiments, the current is applied at a first current density for a first period of time and then at a second current density for a second period of time. In embodiments, the second current density is greater than the first current density. For example, the current may be applied at a current density of about 0.05 amps/dm² (ampere per square decimeter or “ASD”) for a time sufficient to generate a “butterfly” merged shape within the vias, as shown in FIG. 4. In particular, as shown in FIG. 4, when vias are being filled with copper, the copper tends to begin to deposit on the walls at the center of the via where it plugs at the center forming a “butterfly” or two vias. The two vias fill to complete the deposition of the through-glass vias. Without being bound by theory, the initial use of a low current density results in greater copper particle diffusion distance, enabling the copper particles to deposit and build up along the center of the via sidewall as opposed to along the entrance to the via, which can seal up the via and result in voids within the copper material, particularly when coupled with the effects of the leveler in the electrolyte, which suppresses copper deposition near the entrance to the via, as described above.

After formation of the plug, or butterfly 400, the current may be applied at a second density for a second period of time to continue filling the conductive material toward the open ends of the vias. In particular, the current density may be increased following the formation of the butterfly 400 to fill the vias to improve throughput efficiency, since the diffusion limitation has decreased significantly. For example, the current may be applied at a current density of about 0.1 amps/dm² to about 1.6 amps/dm² for a time sufficient to fill the vias with the conductive material 500, as shown in FIG. 5. In some particular embodiments, the current may be applied at a current density of 0.1 amps/dm² for a period of about 5 minutes, and then at a current density of 1.6 amps/dm² until the vias are filled. It is contemplated that the current may be applied at any number of current densities to fill the vias.

In embodiments, the electroplated glass substrate may be thermally annealed (not shown in FIG. 2) after the electrically conductive material is deposited thereon to relieve the stress in the glass substrate and reduce the impact of any downstream thermal processing steps. For example, the glass substrate may be heated to a temperature of greater than or equal to 400° C. for a time period sufficient to release the stresses. In various embodiments, after being filled with the electrically conductive material, the electrically conductive material in each of the plurality of vias has a void volume fraction of less than or equal to 5% or less than or equal to 1%. In particular embodiments, the electrically conductive material in each of the plurality of vias is free of voids after being filled with the electrically conductive material.

EXAMPLES

The following examples illustrate one or more features of the embodiments described herein.

Glass substrates (WILLOW™ glass available from Corning, Incorporated) having an average thickness t of 100 μm and including 20 μm or 10 μm diameter vias were cleaned using a standard cleaning process. In particular, the substrates were cleaned with 2.5 vol % of PK-LCG225X-1 detergent at 70° C. for 8 minutes in an ultrasonic bath. The substrates were then rinsed with deionized water to remove organic residues and enrich hydroxyl groups on the substrate surfaces. After cleaning, the glass substrates showed good wettability with a water contact angle of less than 5° as measured using a DSA100 from Kruss GmbH (Germany).

Next, 1 vol % of 3-(2-aminoethylamino)propyldimethoxy-methylsilane (AEA-PDMMS) diluted in ispopropanol was used to functionalize the glass surfaces. In particular, the cleaned glass substrates were submerged into the AEA-PDMMS solution with applied ultra sonic energy at 23° C. for 30 minutes. The glass substrates were then dried in an oven at 120° C. for 1 hour.

The AEA-PDMMS-modified glass substrates were then processed using a copper electroless plating kit available from Uyemura, Taiwan. Specifically, the glass substrates were dipped into a Pd/Sn colloid at room temperature for 8 minutes, then gently rinsed with deionized water. Next, the glass substrates were dipped into an activation solution at room temperature for 3 minutes to remove the Sn shell from the Pd catalyst. Finally, the glass substrates were dipped into an electroless plating bath at 35° C. for 5 minutes to form a uniform copper layer having a thickness of greater than or equal to 130 nm and less than or equal to 200 nm on the surface of the glass substrates and on the via sidewalls. The glass substrates including the seed layer were annealed by rapid thermal process (RTA) at 400° C. for 8 minutes with a 10° C./s ramping rate to release the stress.

FIG. 6 is a scanning electron microscope (SEM) image showing the uniform and continuous copper seed layer deposited on the sidewall of a via in the glass substrate having an aspect ratio of 10 (e.g., via diameter of 10 μm).

The glass substrates were then pre-wetted by dipping the glass substrate into DI water in an ultrasonic bath for 2 minutes. Next, the wetted glass substrates were plated in a 2 L electrolyte bath including 0.88 M CuSO₄.5H₂O and 0.54 M H₂SO₄. The electrolyte bath included 20 ppm of chloride ions and 40 ppm of nitrotetrazolium blue chloride. The glass substrates were positioned between two copper plates (anodes), and a constant current density of 0.05 amps/dm² was applied using an Auto-Lab PGSTAT 302N to plug the vias, forming the butterfly shape within the vias, as shown in FIGS. 7A and 7B.

FIG. 7A is an SEM image showing the plug in the shape of a butterfly within the 10 μm vias. FIG. 7B is a CT scan image further evidencing the formation of the plug within the 10 μm vias. FIG. 7C is an SEM image showing the plug in the shape of a butterfly within the 20 μm vias. FIG. 7D is a CT scan image further evidencing the formation of the plug within the 20 μm vias

Following formation of the plug within the through-glass vias, the current density was increased to 0.1 amps/dm² for 5 minutes, and then increased to 1.6 amps/dm² to completely fill the vias with the copper. FIG. 8A is an SEM image showing the complete and void-free filling of the 10 μm vias with the copper. FIG. 8B is a CT scan image further evidencing the complete and void-free filling of the 10 μm vias. FIG. 8C is an SEM image showing the complete and void-free filling of the 20 μm vias with the copper.

As a comparative example, a glass substrate (WILLOW™ glass available from Corning, Incorporated) having an average thickness t of 100 μm and including 10 μm diameter vias was cleaned, processed using the copper electroless plating kit, and pre-wetted as described for the samples above. However, following pre-wetting, the wetted glass substrate was plated at a constant current density of 0.16 amps/dm² was applied using an Auto-Lab PGSTAT 302N. The electrolyte solution was the same as described for the samples above. FIG. 9A-9C show the results. In particular, FIG. 9A is an SEM image showing voids created within the vias as a result of the electroplating at the current density of 0.16 amps/dm² through the entirety of the process. FIGS. 9B and 9C are additional SEM images further evidencing the voids within the vias.

Accordingly, FIGS. 6-8B demonstrate that the methods described herein may be used to produce a thin (<150 μm thick) glass substrate including vias at an aspect ratio of greater than 5:1 that are filled with copper such that the electrically conductive material in the filled vias have a void volume fraction of less than 5%. Specifically, the examples show that the methods may be used to produce a 100 μm thick glass substrate including vias at an aspect ratio of 12:1 that are filled with copper such that the electrically conductive material in the vias is free of voids.

It should now be understood that embodiments of the present disclosure enable through-glass vias to be formed in a thin glass substrate at an aspect ratio of greater than or equal to 5:1 and metallized such that the electrically conductive material in the filled vias has a void volume fraction of less than or equal to 5%. In particular, various embodiments enable a glass substrate including through-glass vias to be metallized without the use of a carrier. Accordingly, such processes may be used in roll-to-roll processes to fill through holes in thin, flexible glass substrates without the creation of voids.

It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

1. A method for metallizing through-glass vias in a glass substrate, the method comprising: functionalizing a surface of the glass substrate with a silane, wherein the glass substrate has an average thickness t and comprises a plurality of vias extending through the thickness t;applying an electroless plating solution comprising a copper ion to deposit a copper seed layer on the functionalized surface;disposing an electrolyte within the plurality of vias, wherein the electrolyte comprises copper ions to be deposited on the copper seed layer within the plurality of vias;positioning an electrode within the electrolyte; andapplying a current between the electrode and the glass substrate, thereby reducing the copper ions into copper within the plurality of vias such that each of the plurality of vias is filled with copper and the copper has a void volume fraction of less than 5%, wherein the second current density is greater than or equal to 0.75 amps/dm2 and less than or equal to 2 amps/dm2.

2. The method according to claim 1, wherein the average thickness t of the glass substrate is greater than or equal to 50 μm and less than or equal to 150 μm.

3. The method according to claim 1, wherein the average thickness t of the glass substrate is greater than or equal to 90 μm and less than or equal to 110 μm.

4. The method according to claim 1, wherein each of the plurality of vias has an average diameter of greater than or equal to 8 μm and less than or equal to 20 μm; and an aspect ratio of the average thickness t of the glass substrate to the average diameter of the plurality of vias is greater than or equal to 5:1 and less than or equal to 12:1.

5. The method according to claim 1, wherein the electrolyte further comprises chloride ions and an additive.

6. The method according to claim 5, wherein the additive consists of nitrotetrazolium blue chloride.

7. The method according to claim 6, wherein the additive is present in the electrolyte in a concentration of greater than or equal to 20 ppm and less than or equal to 60 ppm.

8. The method according to claim 5, wherein the chloride ions are present in the electrolyte in a concentration of greater than or equal to 20 ppm and less than or equal to 140 ppm.

9. The method according to claim 1, wherein applying the current comprises applying the current at a current density of greater than or equal to 0.05 amps/dm2 and less than or equal to 2 amps/dm2.

10. The method according to claim 1, further comprising wetting the glass substrate including the copper seed layer prior to disposing the electrolyte within the plurality of vias.

11. The method according to claim 1, wherein the copper in each of the plurality of vias has a void volume fraction of less than 1%.

12. The method according to claim 1, wherein the copper in each of the plurality of vias is free of voids.

13. The method according to claim 1, further comprising cleaning the glass substrate prior to functionalizing the surface, wherein the glass substrate has a water contact angle of less than or equal to 5 degrees after the cleaning.

14. The method according to claim 1, wherein functionalizing the surface of the glass substrate comprises functionalizing sidewalls of the plurality of vias.

15. The method according to claim 1, further comprising annealing the glass substrate comprising the copper seed layer prior to disposing the electrolyte within the plurality of vias.