Wide lip seal for electroplating

Abstract

To provide a lipseal for use in a lipseal assembly of an electroplating clamshell which engages with a semiconductor substrate and supplies electrical current to the semiconductor substrate during electroplating, and a method of electroplating the semiconductor substrate using the lipseal.SOLUTION: A lipseal 212 includes an elastomeric body having an outer portion configured to engage with a cup 201 of the lipseal assembly and an inner portion configured to engage with a peripheral region of the semiconductor substrate. The inner portion includes a protrusion having a width in a radial direction sufficient to provide a contact area with the semiconductor substrate which inhibits diffusion of acid in an electroplating solution used during the electroplating. The protrusion is located at an inner periphery of the lipseal.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to the formation of damascene interconnects for integrated circuits and to electroplating equipment used during integrated circuit processing. [Background technology]

[0002] Electroplating is a common technique used in integrated circuit (IC) fabrication to deposit one or more layers of conductive metal. In some processes, it is used to deposit single or multi-level copper interconnects between various substrate features. Apparatus for electroplating typically includes an electroplating cell having a pool / bath of electrolyte and a clamshell designed to hold the semiconductor substrate during electroplating.

[0003] During operation of an electroplating apparatus, a semiconductor substrate is immersed in a pool of electrolyte so that one surface of the substrate is exposed to the electrolyte. One or more electrical contacts established with the substrate surface are used to drive current through the electroplating cell and deposit metal on the substrate surface from metal ions available in the electrolyte. Typically, electrical contact elements are used to form an electrical connection between the substrate and a bus bar, which acts as a current source. However, in some configurations, the conductive seed layer on the substrate that the electrical connection contacts may thin toward the edge of the substrate, making it more difficult to establish an optimal electrical connection with the substrate.

[0004] Another problem that arises in electroplating is the potentially corrosive nature of the electroplating solution. Therefore, in many electroplating apparatus, a lip seal is used at the clamshell and substrate interface to prevent electrolyte leakage and contact with elements of the electroplating apparatus other than the interior of the electroplating cell and the surface of the substrate designated for electroplating. Summary of the Invention

[0005] Disclosed herein is a lip seal for use in a lip seal assembly of an electroplating clamshell that engages with a semiconductor substrate to supply electrical current to the semiconductor substrate during electroplating. The lip seal includes an elastomeric body having an outer portion configured to engage a cup of the lip seal assembly and an inner portion configured to engage a peripheral region of the semiconductor substrate. The inner portion includes a protrusion having a radial width sufficient to inhibit diffusion of acid in an electroplating solution used during electroplating. The protrusion includes an annular rim that extends completely around the inner circumference of the lip seal. [Brief explanation of the drawings]

[0006] [Figure 1] 1 illustrates an electroplating apparatus that may utilize the lip seals described herein to prevent acid from reaching the contact elements.

[0007] [Figure 2] FIG. 2 is a detailed view of a lip seal assembly that can be used in the device shown in FIG. 1;

[0008] [Figure 3] FIG. 3 is a detail view of the lip seal assembly shown in FIG. 2.

[0009] [Figure 4] FIG. 4 is a detail view of the lip seal assembly shown in FIG. 3.

[0010] [Figure 5] 2 is a graph showing acid concentration in the lip seal area versus lip seal width.

[0011] [Figure 6a] Photograph of the copper seed layer after electroplating showing the copper seed layer after electroplating a dried wafer. [Figure 6b] Photograph of the copper seed layer after electroplating showing severe corrosion after electroplating a wet wafer using a 0.028 inch (1 inch = 25.4 mm, same below) wide lip seal. [Figure 6c]Photograph of the copper seed layer after electroplating showing minor corrosion of the copper seed layer after electroplating a wet wafer with a 0.034 inch wide lip seal. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following description, numerous specific details are set forth to facilitate a thorough understanding of the presented concepts. The presented concepts may be practiced without some or all of these specific details. Additionally, detailed descriptions of well-known processing operations have been omitted to avoid unnecessarily obscuring the described concepts. While some concepts are described in connection with specific embodiments, it should be understood that these embodiments are not intended to be limiting.

[0013] To provide context for the various lip seals and contact elements disclosed herein, an example of an electroplating apparatus is shown in FIG. 1. Specifically, FIG. 1 is a perspective view of a wafer holding / positioning apparatus 100 for electrochemically processing semiconductor wafers. The apparatus 100 includes wafer-engaging components, also referred to as "clamshell components," "clamshell assemblies," or simply "clamshells." The clamshell assembly includes a cup 101 and a cone 103. As shown in subsequent figures, the cup 101 holds the wafer, and the cone 103 securely clamps the wafer within the cup. Other cup and cone designs than those specifically illustrated herein may be used. A common feature is that the cup has an interior area for the wafer to fit within, and the cone presses the wafer against the cup to hold it in place.

[0014] In the illustrated embodiment, the clamshell assembly (comprising cup 101 and cone 103) is supported by posts 104, which are coupled to a top plate 105. This assembly (101, 103, 104, and 105) is driven by a motor 107 via a spindle 106 connected to the top plate 105. The motor 107 is attached to a mounting bracket (not shown). The spindle 106 transmits torque (from the motor 107) to the clamshell assembly to rotate a wafer (not shown in this view) held therein during plating. An air cylinder (not shown) within the spindle 106 also provides a normal force to engage the cup 101 with the cone 103. When the clamshell is disengaged (not shown), a robot with an end effector arm can insert a wafer between the cup 101 and the cone 103. After the wafer is inserted, the cone 103 engages the cup 101 to secure the wafer within the apparatus 100 and expose one working surface of the wafer for contact with the electroplating solution (but not the other side).

[0015] In certain embodiments, the clamshell assembly includes a spray skirt 109 that protects the cone 103 from electrolyte splashes. In the illustrated embodiment, the spray skirt 109 includes a vertical peripheral sleeve and a circular cap portion. A spacer member 110 maintains separation between the spray skirt 109 and the cone 103.

[0016] For purposes of this discussion, the assembly comprising components 101-110 will be collectively referred to as a "wafer holder" (or "substrate holder") 111. However, it should be noted that the concept of "wafer holder" / "substrate holder" generally extends to various combinations and sub-combinations of components that engage with and enable movement and positioning of a wafer / substrate.

[0017] A tilt assembly (not shown) may be connected to the wafer holder to allow the wafer to be immersed in the plating solution at an angle (as opposed to flat horizontal immersion). A drive mechanism and arrangement of plates and pivot joints is used in some embodiments to move the wafer holder 111 along an arcuate path (not shown), thereby tilting the proximal end (i.e., cup and cone assembly) of the wafer holder 111.

[0018] Additionally, the entire wafer holder 111 is lifted vertically, either up or down, by an actuator (not shown) to immerse the proximal end of the wafer holder in the plating solution. Thus, the two-component positioning mechanism provides the wafer with both vertical movement along a trajectory perpendicular to the electrolyte surface and tilt movement that allows deviation from a horizontal orientation (i.e., an orientation parallel to the electrolyte surface) (tilt wafer immersion function).

[0019] Note that the wafer holder 111 is used with a plating cell 115 having an anode chamber 157 and a plating chamber 117 containing the plating solution. Chamber 157 holds an anode 119 (e.g., a copper anode) and may include a membrane or other separator designed to maintain different electrolyte chemistries in the anode and cathode compartments. In the illustrated embodiment, a diffuser 153 is used to direct the electrolyte solution upward toward the rotating wafer with a uniform front surface. In a specific embodiment, the flow diffuser is a high-resistance virtual anode (HRVA) plate, formed from a solid piece of insulating material (e.g., plastic) with a large number (e.g., 4,000-15,000) of small, one-dimensional holes (0.01-0.050 inches in diameter) connected to the cathode chamber above the plate. The total cross-sectional area of ​​the holes is less than about 5 percent of the total projected area, thus introducing substantial flow resistance within the plating cell and helping to improve plating uniformity in the system. Further description of high-resistivity virtual anode plates and corresponding apparatus for electrochemically processing semiconductor wafers is provided in U.S. Patent Application Publication No. 2010 / 0032310, which is incorporated herein by reference in its entirety for all purposes. The plating cell may include a separate membrane for controlling and generating a separate electrolyte flow pattern. In another embodiment, the membrane is used to define an anode chamber, which contains an electrolyte that is substantially free of suppressors, accelerators, or other organic plating additives.

[0020] The plating cell 115 may also include piping or piping connections for circulating the electrolyte through the plating cell and, therefore, to the workpiece being plated. For example, the plating cell 115 includes an electrolyte inlet pipe 131 that extends vertically through a central hole in the anode 119 to the center of the anode chamber 157. In another embodiment, the cell includes an electrolyte inlet manifold (not shown) that introduces fluid into the cathode chamber below the diffuser / HRVA plate in the peripheral wall of the chamber. In some examples, the inlet pipe 131 includes outlet nozzles on both sides (anode and cathode sides) of the membrane 153. This configuration supplies electrolyte to both the anode and cathode chambers. In another embodiment, the anode and cathode chambers are separated by a flow-resistant membrane 153, and each chamber has a separate flow cycle of the separated electrolyte. As shown in the embodiment of FIG. 1, the inlet nozzle 155 supplies electrolyte to the anode side of the membrane 153.

[0021] Additionally, plating cell 115 includes a rinse drain line 159 and a plating solution return line 161, each connected directly to plating chamber 117. Rinse nozzles 163 also provide deionized rinse water for cleaning wafers and / or cups during normal operation. The plating solution typically fills most of the chamber 117. To mitigate bubble splashing and generation, chamber 117 includes an inner weir 165 for plating solution return and an outer weir 167 for rinse water return. In the illustrated embodiment, these weirs are peripheral vertical slots in the wall of plating chamber 117.

[0022] As described above, electroplating clamshells typically include a lip seal and one or more contact elements to provide sealing and electrical connection functions. The lip seal may be formed of an elastomeric material. The lip seal forms a seal with the surface of the semiconductor substrate and excludes electrolyte from the perimeter region of the substrate. This perimeter region does not undergo deposition and is not used for IC device formation; i.e., the perimeter region is not part of the work surface. This region is sometimes referred to as the edge exclusion region because electrolyte is excluded from the region. The perimeter region is used to support and seal the substrate during processing and to make electrical connections with the contact elements. Because a large work surface is generally desirable, the perimeter region should be as small as possible while maintaining the above-mentioned functions. In certain embodiments, the perimeter region is between about 0.5 millimeters and 3 millimeters from the edge of the substrate.

[0023] During installation, the lip seal and contact elements are assembled with the other components of the clamshell. Those skilled in the art will appreciate this difficulty, especially when the peripheral area is small. The overall opening provided by the clamshell corresponds to the size of the substrate (e.g., an opening for accommodating a 200 mm wafer, a 300 mm wafer, a 450 mm wafer, etc.). Furthermore, the substrate has its own dimensional tolerances (e.g., + / - 0.2 millimeters for a typical 300 mm wafer according to SEMI specifications). A particularly challenging task is the alignment of the elastomeric lip seal and the contact elements, since both are fabricated from relatively flexible materials. These two components must have very precise relative positions. If the sealing edge of the lip seal and the contact elements are positioned too far from each other, poor or no electrical connection between the contacts and the substrate may occur during operation of the clamshell. At the same time, if the sealing edge is positioned too close to the contacts, the contacts may interfere with the seal and cause leakage into the peripheral area. For example, conventional contact rings are often formed with multiple flexible "fingers" that press with a spring-like action onto a substrate to establish an electrical connection as shown in the clamshell assembly (cup 201, cone 203, and lip seal 212) of Figure 2. Not only are these flexible fingers 208 very difficult to align with the lip seal 212, they are easily damaged during installation and difficult to clean if electrolyte gets into the surrounding area.

[0024] As described above, in an electroplating cell, electrical contact is made to the wafer around the wafer edge, and electroplating is performed on the remainder of the wafer. However, when the plating solution reaches the contact point, the acid in the plating solution can corrode the metal seed layer on the wafer in the contact area, resulting in an unevenly distributed increase in resistance around the wafer and a corresponding decrease in plating performance and increase in within-wafer non-uniformity. Metal ions in the solution can also deposit on the contact point, reducing plating efficiency. To prevent seed corrosion and plating at the contact point, the area where contact is made is isolated from the plating solution by a lip seal. Previously, it was believed that total damage to the lip seal (e.g., cracks, tears, etc.) was sufficient to completely isolate the contact point from the plating solution. However, recent research has shown that when a wet wafer is placed on the lip seal (e.g., as in Sabre 3D's advanced pretreatment process), a thin layer of water remains between the lip seal and the wafer, allowing the acid in the plating solution to diffuse through it and reach the contact area. At high temperatures and / or long plating times, this diffusion can occur to the extent that enough acid reaches the contact area to cause corrosion of the metal seed layer (seed corrosion). To address this issue, wide lip seals have been designed to increase the distance the acid must diffuse and correspondingly slow the rate at which the acid reaches the contact area. In this way, seed corrosion at the wafer edge is reduced and plating uniformity is improved.

[0025] In an electroplating cell, the wafer to be plated is held in a cup that makes electrical contact with the edge of the wafer in an area surrounded by a lip seal while exposing the remainder of the wafer to the plating solution. The cup is partially immersed in the plating solution within the plating cell during plating. However, as explained above, acid can diffuse across the liquid film between the wafer and the lip seal quickly enough to damage the metal seed layer on the wafer at the contact area.

[0026] In one embodiment, a hardware design change was implemented to increase the width of the lip seal (the width of the protrusion on the lip seal that seals the wafer) to reduce the rate at which acid diffuses through the liquid layer between the wafer and the lip seal. Increasing the lip seal width increases the diffusion distance, resulting in less acid reaching the contact area, thereby reducing etching of the metal seed layer.

[0027] The lip seal width can be increased by increasing the outer diameter of the lip seal projection or by decreasing the inner diameter of the projection, with the preferred embodiment being to increase the outer diameter of the projection as this does not reduce the area available for plating.

[0028] The shape of the protrusions on the lip seal may be enlarged to form a lip seal with a cross-section similar in shape to previous designs, where the protrusions are simply extended in the radial dimension. This is the preferred embodiment. The lip seal may have a single contact surface in the form of an annular rim with a cylindrical wall and a flat or angled surface that contacts the wafer.

[0029] Previously, the lip seal design for the Sabre 3D did not prevent significant acid diffusion into the contact area at higher temperatures or higher plating solution acid concentrations than existed during standard operating conditions in the past (below 35°C, below 140 grams per liter of acid). The advantage of the wider lip seal is that it can provide adequate sealing at more demanding operating conditions, such as temperatures above 35°C and / or acid concentrations above 140 grams per liter of acid.

[0030] During wafer processing, when a wet wafer is placed on the lip seal, a thin layer of water remains, and acid can diffuse through this layer, reach the contact area, and damage the metal seed layer on the wafer. To avoid this problem, the lip seal is configured to provide a longer diffusion path for the acid, thus substantially increasing the time required for etching to occur at the contact area. A longer diffusion path can be achieved by a wider lip seal (longer linear length).

[0031] Diffusion across the lip seal can be modeled as one-dimensional diffusion with a constant source, which has the following equation: C / C s =erfc(z / 2√Dt), where z is the width of the lip seal, D is the diffusion constant of the acid, t is time, and C s is the concentration of acid at the source, C is the concentration of acid at z, and erfc is the complementary error function. Therefore, 2√Dt (diffusion length) is the function of C, C for given conditions. s , and can be estimated by knowing z and C s We can find C as a function of , and predict that 2√Dt will remain roughly constant as long as time, temperature, and diffusing species remain the same.

[0032] For example, z=0.020 inches and "C s = 180 g / L sulfuric acid: Under these conditions, C is estimated to be approximately 8-9 g / L after 1.5 hours of plating time, with 2√Dt ≈ 0.014, and 2√Dt can be used to estimate the sulfuric acid concentration after plating for other lip seal widths, as shown in the graph in Figure 5. C reaches 1 g / L (approximately the level at which negligible corrosion occurs at 1.5 hours) at a lip seal width of approximately 0.028 inches and then drops off rapidly thereafter. A preferred lip seal width is at least 0.032 inches, and more preferably at least 0.034 inches.

[0033] FIG. 3 illustrates one embodiment of a lip seal 212 mounted to a cup 201, with an electrical contact 208 engaging the underside of a semiconductor substrate (e.g., wafer W). As shown in FIG. 4, the lip seal 212 includes an inner portion 218 having a protrusion 220 with an upper surface 220a that contacts the underside of the wafer W, and an outer portion 230 having a rim 232 that engages the recess 201a of the cup 201. The protrusion 220 extends axially upward and has a width (measured radially between the inner and outer cylindrical walls of the protrusion) sufficient to prevent diffusion of acid in the plating solution from reaching the contact point between the electrical contact 208 and the wafer W. For processing 300 mm diameter wafers, the width of the protrusion 220 may be at least about 0.032 inches, and preferably at least about 0.034 inches. The lip seal 212 is preferably a unitary, fully elastomeric component configured to mate with the cup 201. Thus, the lip seal 212 is a separate consumable part that can be easily replaced when necessary.

[0034] Figures 6a-c are photographs of the outer edges of wafers processed under different conditions. Figure 6a shows a wafer plated without prewetting; the copper seed layer at the wafer's edge is not corroded because the lip seal provided an adequate seal to prevent acid diffusion beyond it. Scratches are visible on the copper seed layer due to the electrical contacts used during electroplating. Figure 6b shows a wafer plated with prewetting but using a 0.028-inch-wide lip seal that does not provide an adequate seal. Prewetting forms a water film between the wafer and the lip seal, beyond which the acid can diffuse and corrode the copper seed layer at the wafer's edge. In Figure 6b, the copper seed layer is severely corroded; only a thin copper oxide (black) and tantalum barrier layer (silver) are visible. Figure 6c shows a wafer plated with prewetting but using a 0.034-inch-wide lip seal that provides an adequate seal. In the image, the copper seed layer is visible and has only suffered minor corrosion due to the wider lip seal which created a longer diffusion path as a very thin layer of copper oxide on the surface of the copper seed layer creates small stains.

[0035] The term "about" is often used herein in conjunction with a numerical value to indicate that mathematical precision of such value is not intended. Thus, when the term "about" is used in conjunction with a numerical value, a tolerance of ±10% is assumed for that numerical value.

[0036] While embodiments and applications of the present invention have been shown and described herein, many modifications and variations are possible that are within the concept, scope, and spirit of the invention, and these modifications will become apparent to those skilled in the art upon perusal of this application. Accordingly, the embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may vary within the scope of the appended claims and their equivalents. For example, the following application examples are possible. [Application Example 1] A lip seal for use in a lip seal assembly of an electroplating clamshell that engages with a semiconductor substrate during electroplating to supply current to the semiconductor substrate, comprising: an elastomer body having an outer portion configured to engage a cup of the lip seal assembly and an inner portion configured to engage a peripheral region of the semiconductor substrate; The lip seal of claim 1, wherein the inner portion includes a protrusion having a radial width sufficient to inhibit diffusion of acid in an electroplating solution used during the electroplating, the protrusion including an annular rim extending completely around an inner circumference of the lip seal. [Application Example 2] A lip seal according to Application Example 1, wherein the width is the width between the inner wall and the outer wall of the protrusion, and the width is at least about 0.8128 mm (0.032 inches). [Application Example 3] The lip seal according to Application Example 2, wherein the width is approximately 0.8636 mm (0.034 inches). [Application Example 4] The lip seal according to Application Example 1, wherein the outer portion includes a downwardly extending rim configured to be received in a recess of the cup. [Application Example 5] The lip seal according to Application Example 1, wherein the inner surface of the protrusion defines the inner diameter of the lip seal. [Application Example 6] A method for electroplating a semiconductor substrate using the lip seal of Application Example 1, comprising the steps of supporting a pre-wetted semiconductor substrate in an electroplating clamshell so that the protrusions of the lip seal contact the outer periphery of the semiconductor substrate, and contacting the exposed surface of the semiconductor substrate inside the protrusions with an electroplating solution. [Application Example 7] The method described in Application Example 6, wherein the protrusion has a width of approximately 0.8636 mm (0.034 inches).

Claims

1. 1. A lip seal for use in a lip seal assembly of an electroplating clamshell that engages a semiconductor substrate during electroplating to provide electrical current to the semiconductor substrate, comprising: a body made of a single, unitary piece of elastomeric material, the body having an outer portion configured to engage a cup of the lip seal assembly and an inner portion configured to engage a peripheral region of the semiconductor substrate; the inner portion includes an upwardly projecting protrusion having a radial width sufficient to inhibit diffusion of acid in an electroplating solution used during the electroplating, the upper surface of the upwardly projecting protrusion having an angled surface for contacting the semiconductor substrate, the upwardly projecting protrusion defining an annular rim extending completely around an inner circumference of the lip seal; the width being the width between the inner and outer walls of the upwardly projecting protrusion, the width being about 0.8128 millimeters (0.032 inches), with "about" defining ±10%, so as to slow the rate of chemical diffusion by increasing the diffusion distance when the operating conditions of the lip seal are temperatures above 35° C. or acid concentrations above 140 grams per liter of acid; the outer portion of the body has a downwardly projecting rim that engages a recess in the cup and assists in aligning the lip seal with the cup, the downwardly projecting rim extending completely around the peripheral area of ​​the lip seal of the outer portion; Lip seal.

2. 1. A lip seal for use in a lip seal assembly of an electroplating clamshell that engages a semiconductor substrate during electroplating to provide electrical current to the semiconductor substrate, comprising: a body made of a single, unitary piece of elastomeric material, the body having an outer portion configured to engage a cup of the lip seal assembly and an inner portion configured to engage a peripheral region of the semiconductor substrate; the inner portion includes an upwardly projecting protrusion having a radial width sufficient to inhibit diffusion of acid in an electroplating solution used during the electroplating, the upper surface of the upwardly projecting protrusion having an angled surface for contacting the semiconductor substrate, the upwardly projecting protrusion defining an annular rim extending completely around an inner circumference of the lip seal; the width being the width between the inner and outer walls of the upwardly projecting protrusion, the width being about 0.8636 millimeters (0.034 inches), with "about" defining ±10%, to slow the rate of chemical diffusion by increasing the diffusion distance when the operating conditions of the lip seal are temperatures above 35° C. or acid concentrations above 140 grams per liter of acid; A lip seal, wherein the outer portion of the body has a downwardly projecting rim that engages a recess in the cup and assists in aligning the lip seal with the cup, the downwardly projecting rim extending completely around the peripheral region of the lip seal on the outer portion.

3. 3. The lip seal of claim 1 or claim 2, wherein an inner surface of the upwardly projecting projection defines an inner diameter of the lip seal.

4. A method for electroplating a semiconductor substrate using the lip seal of claim 1 or 2, comprising: supporting a pre-wetted semiconductor substrate within an electroplating clamshell such that the upwardly projecting protrusion of the lip seal contacts the outer periphery of the semiconductor substrate; contacting the exposed surface of the semiconductor substrate inside the upwardly projecting protrusions with an electroplating solution; A method for providing the above.

Images