Ar / O₂ Loop Formation Method and Apparatus

Abstract

To clean exposed metallic features on a substrate so as to remove residues such as fluorine-containing contaminants.SOLUTION: In cleaning a metallic feature on a substrate, the substrate is carried by a carrier sheet included in a workpiece and attached to a frame member while the workpiece is provided onto a workpiece support disposed within a chamber of an inductively coupled plasma apparatus. A sputter etch step is performed which comprises introducing a sputter gas or gas mixture into the chamber and sustaining inductively coupled plasma of the sputter gas or gas mixture so as to sputter-etch the substrate. A chemical etch step also is performed which comprises introducing O2 gas and / or O3 gas into the chamber and sustaining inductively coupled plasma of the O2 and / or O3 gas so as to chemically etch the substrate. These steps are repeated.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for cleaning metal features (outer features) on a substrate, such as metal bonding pads and / or bumps. More specifically, the present invention relates to a method for removing fluorine-containing contaminants from the surfaces of metal features, such as metal bonding pads and / or bumps, on a substrate. The present invention also relates to related apparatuses for cleaning metal features on a substrate.

Background Art

[0002] Typically, a semiconductor substrate, such as a silicon wafer, is singulated into dice by dicing. Dicing techniques can include mechanical cutting, laser grooving, plasma etching, and the like. In plasma etching techniques, typically, a semiconductor substrate is placed on a carrier sheet, such as a tape carrier, and surrounded by a frame member. The semiconductor substrate 11, the carrier sheet 12, and the frame member 13 together form a workpiece 10 as shown in FIG. 1. According to plasma dicing, dice can be singulated in an efficient manner, thereby increasing the throughput for small-size dice, reducing the street width to better utilize the wafer surface and increase the yield, and reducing the damage to the edges or sides of the dice to improve the strength and quality of the dice.

[0003] In plasma dicing applications, the "Bosch process" is widely used to etch streets in a semiconductor substrate and singulate the dice on that semiconductor substrate. The Bosch process is described in Patent Document 1 and generally constitutes a cyclic method of forming an anisotropic etching profile by an etching process and a deposition process. Usually, a fluorine-containing compound is used in those etching and / or deposition processes, whereby fluorine-containing residues or contaminants may be formed on the surface of the substrate that has undergone a plasma etching process. If there are fluorine-containing contaminants on the exposed metal features, such as the surfaces of bonding pads or bumps, it may lead to corrosion problems and long-term reliability problems. Although most of the die surface is protected by a dielectric passivation layer, the bonding pads and metal bumps need to be exposed to enable wire or flip-chip bonding to an external circuit. Further, when those metal features are made of aluminum, AlF3 may be formed by reaction with a fluorine-based process gas, and it may further react to form AlFO3 in air (or other oxidizing atmospheres). Contaminants such as AlFO3 increase the resistivity of the bonding pad surface and lead to the formation of non-optimal wire bonds.

[0004] Regardless of what they are, to remove residues, such as fluorine-containing residues, a post-etch cleaning process is usually required. Known cleaning processes capable of removing fluorine-containing contaminants, such as AlFO3, from the surface of the bonding pad include sputtering the substrate with Ar or an Ar / O2 mixture. However, known methods may be incompatible for cleaning diced substrates placed on a temperature-sensitive carrier sheet. It is desirable to develop an improved method capable of cleaning the metal features on the substrate while keeping the workpiece maintained below strict temperature constraints.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] An improved version of a method for removing fluorine-containing contaminants from exposed metal features on a substrate, especially those that have undergone a plasma dicing process, is desired to be developed. It is desired to more efficiently remove fluorine-containing contaminants such as AlFO3, and to keep the workpiece within a strict thermal budget.

[0007] At least some of the embodiments of the present invention are aimed at addressing at least some of the above problems, desires, and needs. In particular, the embodiments of the present invention aim to provide an improved version of a method for cleaning metal features such as bonding pads and / or bumps. The embodiments of the present invention aim to remove fluorine-containing residues or contaminants from metal features while keeping the thermal budget low for the workpiece. Further, according to the embodiments of the present invention, throughput can be improved, and yet an effective cleaning treatment can be achieved.

Means for Solving the Problems

[0008] Provided in accordance with a first aspect of the present invention is a method for cleaning metal features on a substrate of a type that is a portion of a workpiece subjected to a plasma dicing process, the workpiece further comprising a carrier sheet mounted to a frame member and transporting the substrate, the method comprising the steps of supplying the workpiece onto a workpiece support disposed within a chamber of an inductively coupled plasma apparatus, a sub-step of introducing a sputter gas or gas mixture into the chamber, and a sub-step of maintaining an inductively coupled plasma of the sputter gas or gas mixture such that the substrate is sputter etched, to perform a sputter etching step; a sub-step of introducing O2 gas and / or O3 gas into the chamber, and a sub-step of maintaining an inductively coupled plasma of the O2 and / or O3 gas such that the substrate is chemically etched, to perform a chemical etching step; and repeating the steps of performing the sputter etching step and the steps of performing the chemical etching step.

[0009] According to this cleaning method, contaminants such as fluorine-containing contaminants (e.g., AlFO3) can be removed from the surface of the substrate, for example, the surface of the metal features on the substrate. By alternately performing a physical sputter etching process and a chemical etching process, according to the knowledge, the fluorine-containing contaminants existing on the surface of the metal features on the substrate can be reduced. According to the consideration without being restricted by any theory or speculation, the oxygen-containing chemical etching process helps to remove carbonaceous substances from the surface of the substrate (including the surface of the metal features), and thus helps to better prepare the substrate surface for the subsequent physical sputter etching process. As a result, the physical sputter etching process can be made more effective and more selective when removing contaminants such as fluorine-containing contaminants from the surface of the metal features. Generally, according to the method of the present invention, it is possible to reduce surface contaminants such as fluorine-containing contaminants with a shorter sputter etching duration. Thereby, problems related to the high resistivity and corrosion of those metal features can be reduced. Thereby, it becomes possible to produce a device with better reliability and higher quality with a more excellent throughput.

[0010] Since the level of contaminants can be reduced using a shorter treatment duration, it is possible to keep the workpiece at a lower temperature, i.e., a temperature that helps to avoid damage to the carrier sheet sensitive to temperature. Further, the reduction in the heat load applied to the substrate in the chemical etching process can also be used to keep the workpiece at a correspondingly low temperature, and thus help to avoid damage to the carrier sheet sensitive to temperature.

[0011] The sputter etching process and the chemical etching process can be executed in any order. For example, the first sputter etching process may be executed after the first chemical etching process. Instead of this, the first chemical etching process may be executed after the first sputter etching process.

[0012] The sputter etching process can further include a sub-process of applying bias power, for example RF bias power, to the workpiece support while maintaining the plasma. The frequency of the RF bias can be 2 to 20 MHz, and typically is 13.56 MHz.

[0013] By applying bias power, for example RF bias power, to the workpiece support, it is possible to impart directionality to the species in the plasma (i.e., make the plasma anisotropic). Using the bias power applied to the workpiece support, the scale of ion collisions on the substrate surface can be controlled, and thus the physical sputtering rate in the sputter etching process can be controlled.

[0014] The magnitude of the bias power applied to the workpiece support in the sputter etching process can be 500 W or more, optionally 600 W or more, optionally 700 W or more, and also optionally about 800 W. The magnitude of the bias power applied to the workpiece support in the sputter etching process can be 1000 W or less, optionally 900 W or less, optionally 850 W or less, and also optionally about 800 W.

[0015] The chemical etching process can further include a sub-process of applying bias power, for example RF bias power, to the workpiece support while maintaining the plasma. The frequency of the RF bias can be 2 to 20 MHz, and typically is 13.56 MHz.

[0016] The bias power applied to the workpiece support in the chemical etching process is usually less than the bias power applied to the workpiece support in the sputter etching process.

[0017] The magnitude of the bias power applied to the workpiece support in the chemical etching process can be 250 W or less, optionally 200 W or less, optionally 150 W or less, optionally 100 W or less, optionally 75 W or less, and optionally about 50 W. The magnitude of the bias power applied to the workpiece support in the chemical etching process can be 0 W or more, optionally 10 W or more, optionally 20 W or more, optionally 30 W or more, optionally 40 W or more, and optionally about 50 W. Reducing the bias power applied to the workpiece support in the chemical etching process can help reduce the scale of the resulting physical sputtering and favor chemical etching. By reducing or setting to 0 the bias power applied to the workpiece support, the heat load applied to the workpiece in the chemical etching process is reduced. Therefore, the chemical etching process can also serve as a heat removal (cooling) process, and this can be further utilized to keep the temperature of the workpiece within the allowable heat limit.

[0018] The flow rate when the sputtering gas or gas mixture is introduced into the chamber can be in the range of 50 - 500 sccm (standard cubic centimeters per minute), optionally 100 - 400 sccm, and optionally 200 - 300 sccm.

[0019] The sputtering gas or gas mixture can consist entirely or essentially of an inert sputtering gas. Physical sputtering of the workpiece by the inert sputtering gas does not involve a chemical reaction with the workpiece. The sputtering gas or gas mixture can consist entirely or essentially of a noble gas. The noble gas can be argon, krypton, or xenon. Preferably, the sputtering gas or gas mixture consists entirely or essentially of argon gas. A small amount, for example, a trace amount of auxiliary gas can be contained in the sputtering gas. The auxiliary gas can be O2 gas. The abundance of the auxiliary gas (percentage of the total flow rate of the sputtering gas mixture) can be less than 10%, optionally less than 5%, and optionally less than 1%. The content of the inert sputtering gas, for example, argon, in the sputtering gas, in terms of the percentage of the total flow rate of the sputtering gas or gas mixture, can be 90% or more, optionally 95% or more, and optionally 99% or more.

[0020] When introducing O2 and / or O3 gas into the chamber, the flow rate can be in the range of 50 - 500 sccm, optionally 100 - 400 sccm, and optionally 200 - 300 sccm. The flow rate of O2 and / or O3 gas can be made substantially the same as the flow rate of the sputtering gas or gas mixture.

[0021] The O2 and / or O3 gas can consist entirely or essentially of O2 gas. A small amount, for example, a trace amount of diluent gas can be contained in the O2 and / or O3 gas. The diluent gas can be a noble gas, for example, argon gas. The abundance of the diluent gas (percentage of the total flow rate in sccm of the O2 and / or O3 gas) can be less than 10%, optionally less than 5%, and optionally less than 1%.

[0022] The chamber pressure in the sputter etching process can be in the range of 10 to 80 mTorr, optionally in the range of 15 to 50 mTorr, and optionally about 20 mTorr. The chamber pressure in the chemical etching process can be in the range of 10 to 80 mTorr, optionally in the range of 15 to 50 mTorr, and optionally about 20 mTorr.

[0023] The workpiece support can be an electrostatic chuck. Using an electrostatic chuck (ESC) can help remove heat from the workpiece during the plasma etching process. The method can further have a heat removal step to lower the temperature of the workpiece, optionally without plasma. The chemical etching process can be the heat removal step.

[0024] The sputter etching process and the chemical etching process can be repeated any number of times, for example, at least 3 times, optionally at least 4 times, optionally at least 5 times, and optionally 6 times. The repetitions of the sputter etching process and the chemical etching process can be a predetermined number of times or until the level of contaminants drops below a predetermined level. The number of repetitions can be determined based on the initial level of contaminants (e.g., fluorine), the duration of the sputter etching process and the chemical etching process, and the etching rate.

[0025] The plasma maintained in the sputter etching process and the chemical etching process is inductively coupled plasma. The inductively coupled plasma is maintained using a plasma generator. The plasma generator can be provided with a coil. Usually, the inductively coupled plasma is maintained by applying RF power to the plasma generator (e.g., the coil). The frequency of the RF bias can be in the range of 2 to 20 MHz, and typically is 13.56 MHz. The RF power applied to the coil in the sputter etching process can be in the range of 0 to 500 W, optionally 100 to 400 W, and optionally 200 to 300 W. The RF power applied to the coil in the chemical etching process can be in the range of 1000 to 2000 W, optionally in the range of 1250 to 1750 W, and optionally about 1500 W. By using inductively coupled plasma (ICP), it is possible to maintain a high-density plasma in the chamber in the sputter etching process and the chemical etching process. Further, by using ICP plasma, the collision between the species in the plasma and the substrate can be quickly controlled by controlling the bias power applied to the workpiece support. Therefore, by using ICP plasma, better cleaning process control can be achieved compared to other types of plasma.

[0026] The metal feature can be made of a metal or a metal alloy. The metal or metal alloy can be selected from aluminum, aluminum alloy, copper, nickel, tin, silver, and SnAg alloy. When the metal feature is made of aluminum or an aluminum alloy, the present method can remove fluorine-containing contaminants such as AlFO3 from the surface of the metal feature. The metal feature can be a metal bonding pad or a metal bump. For example, the metal feature can be an aluminum bonding pad or a copper bump.

[0027] The carrier sheet can be made of a polymer material. The polymer material can be polyolefin (PO), polyvinyl chloride (PVC), or polyethylene terephthalate (PET). The carrier sheet can have a softening point of about 90°C. Preferably, the temperature of the carrier sheet is maintained at about 60°C or lower. In the process provided by this method, heat transfer to the workpiece is reduced compared to known methods. Therefore, the temperature of the carrier sheet can be kept much lower than its softening point, and it can be used to avoid thermal damage to the carrier sheet.

[0028] The workpiece includes a substrate, a carrier sheet, and a frame member. The carrier sheet is attached to the frame member. The substrate is conveyed by the carrier sheet.

[0029] The substrate can be a semiconductor substrate. The substrate can be a silicon wafer. The substrate can be a compound semiconductor wafer, such as a GaAs wafer. The substrate can have a diameter of about 200 mm or 300 mm.

[0030] The workpiece is subjected to a plasma dicing process prior to the step of supplying the workpiece onto the workpiece support. The plasma dicing process can be a Bosch etching process. In the plasma dicing process, an etching step and a deposition step can be repeatedly cycled. In the plasma dicing process, a fluorine-containing etchant (e.g., SF6) and / or a fluorine-containing deposition species (e.g., C4F8) can be used. The method of the present invention is particularly useful when executed after a plasma dicing process, such as a Bosch etching process. This is because fluorine-containing contaminants can be formed on the surface of the substrate, for example, on the surface of a metal feature, by the fluorine-containing process gas used in the plasma dicing process. For example, when the metal feature is made of aluminum, the fluorine-containing process gas may react with the surface of the aluminum to form AlF3, which may further react in air (or another oxidizing atmosphere) to form AlFO3. The presence of such fluorine-containing contaminants may inadvertently lead to corrosion and an increase in surface resistivity. The method of the present invention is particularly suitable for removing fluorine-containing contaminants from the surface of the substrate (e.g., from the surface of a metal feature) after the plasma dicing process.

[0031] The plasma dicing process can be performed in a plasma dicing chamber. The method can include a step of transferring the workpiece from the plasma dicing chamber to a cleaning chamber (i.e., a chamber in which a sputter etching step and a chemical etching step are performed). The plasma dicing chamber and the cleaning chamber can be part of the same cluster tool. By performing the plasma dicing treatment and the subsequent cleaning treatment in separate processing chambers, the substrate throughput can be improved. Alternatively, the plasma dicing process, the sputter etching step, and the chemical etching step can also be performed in the same chamber.

[0032] Provided in accordance with a second aspect of the present invention is an inductively coupled plasma apparatus for cleaning metal features on a substrate of a type that is a part of a workpiece, the workpiece further comprising a carrier sheet mounted to a frame member and for transporting the substrate, the apparatus comprising: a chamber; a workpiece support disposed within the chamber; at least one gas inlet for introducing a gas or gas mixture into the chamber; a plasma generator for maintaining an inductively coupled plasma within the chamber; and a controller configured to control sputter etching and chemical etching processes and alternate between them, the sputter etching process including a sub-step of introducing a sputter gas or gas mixture into the chamber and a sub-step of maintaining an inductively coupled plasma of the sputter gas or gas mixture such that the substrate is sputter etched, the chemical etching process including a sub-step of introducing O2 gas and / or O3 gas into the chamber and a sub-step of maintaining an inductively coupled plasma of the O2 and / or O3 gas such that the substrate is chemically etched.

[0033] The plasma generator can be provided with a coil. Usually, an inductively coupled plasma is maintained in the chamber by supplying RF power from an RF power source to the coil.

[0034] The apparatus can further comprise a power source, such as an RF power source, for supplying bias power to the workpiece support. The workpiece support can be configured to receive bias power, such as RF bias power, from the power source. The controller can be further configured to control the bias power supplied to the workpiece support.

[0035] The matters described above with respect to the present invention extend to any inventive combination of the features in the above-listed columns or the following description, drawings or claims. For example, any feature disclosed in connection with one aspect of the present invention can be combined with any feature disclosed in connection with any other aspect of the present invention.

[0036] With reference to the accompanying drawings as follows, embodiments of the present invention will be described by way of example only.

Brief Description of the Drawings

[0037]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0038] Apparatuses suitable for performing the method of the present invention include the SPTS (registered trademark) Mosaic 200 or 300 mm system (trade name), which is commercially available from SPTS Technologies Limited, Newport, South Wales, UK. All of the exemplary embodiments and comparative examples described hereinafter were performed using this apparatus. The apparatus includes a chamber and a plasma generating device, such as a coil, designed to maintain a plasma within the chamber. A typical example of the plasma is an inductively coupled plasma. A workpiece support, such as a platen, is disposed within the chamber, thereby supporting the workpiece thereon. Bias power, such as RF bias power, can be applied to the workpiece support. The workpiece support can be provided with an electrostatic chuck (ESC). The ESC includes a cooperating gas and fluid heat removal channel, thereby enabling heat removal from the workpiece. The apparatus further includes a controller configured to control and alternate various processing conditions during the steps of the method. For example, the controller can control the process gas flow rate and the bias power applied to the workpiece support.

[0039] FIG. 1 shows a workpiece 10 suitable for use in a plasma etching process. The workpiece 10 includes a semiconductor substrate 11, such as a silicon wafer, with the substrate 11 disposed on a carrier sheet 12. The carrier sheet 12 is attached to and surrounded by a frame member 13. The frame member 13 can be made of a metal material or a polymer material.

[0040] The frame member 13 is sized to accommodate the semiconductor substrate. For example, when using a 300 mm diameter semiconductor substrate, the diameter of the frame member can be about 400 mm. Smaller or larger substrates (e.g., 200 mm diameter substrates) can also be used.

[0041] The carrier sheet 12 (also known as a tape or tape carrier) can be made of a polymer material, such as polyolefin (PO), polyvinyl chloride (PVC), or polyethylene terephthalate (PET). The softening point of a typical carrier sheet is about 90°C. It is highly desirable to keep the temperature of the carrier sheet 12 in the plasma etching process below about 60°C to avoid damage to the carrier sheet 12 and any adhesives, such as acrylic adhesives, on the carrier sheet 12. The workpiece 10 can be heat-removed during the plasma etching process using techniques known in the art, such as an electrostatic chuck (ESC).

[0042] In a plasma dicing or plasma etching process, such as a Bosch etching process, fluorine-containing etching and / or deposition species can typically be used. For example, SF6 can be used in the etching step, while a fluorine-containing polymer gas, such as C4F8, can be used in the deposition step. With the use of such fluorine-containing process gases, the substrate is exposed to fluorine chemistry. Metal features on the substrate 11, such as bonding pads and bumps, are particularly likely to react with fluorine and fluorine-based process gases to form fluorine-containing residues. Those metal features, such as bonding pads and / or bumps, can be made of Al, an alloy of Al, other metals, such as copper or nickel, or SnAg.

[0043] Figure 2 shows a schematic cross-section of a substrate 20 including a silicon wafer 21, an exposed metal bonding pad 22, an interconnect layer 23, and an open scribe line 24. The bonding pad 22 can be made of Al, an alloy of Al, Cu, Ni, or other metals or metal alloys. A fluorine-based process gas used in an etching process may react with the bonding pad 22, and fluorine-containing residues or contaminants may be formed. As a result, it may lead to corrosion of the bonding pad 22 and further to reliability problems. For example, when the bonding pad is made of aluminum, AlF3 may be formed by the reaction of the fluorine-containing process gas with the bonding pad, and it may further react in air (or an oxidizing atmosphere) to form AlFO3. The presence of AlFO3 inadvertently increases the resistivity of the bonding pad surface, resulting in non-optimal wire bonding.

[0044] Figure 3 shows a cross-section of a substrate 30 including a silicon wafer 31, an exposed metal bump 32, an interconnect layer 33, and an open scribe line 34. The metal bump 32 can be made of, for example, SnAg, Cu, or Ni. A fluorine-based process gas may react with the metal bump 32 to form a hydrophobic surface. As a result, it may lead to packaging problems, such as poor surface wetting or underfill or contact problems.

[0045] To help reduce fluorine-containing contaminants, prior to the plasma dicing process, those metal features (e.g., bonding pads and bumps) can be covered with a coating. Figure 4 shows a cross-section of a substrate 40 where bumps 42 and scribe lines 44 are covered with a coating 46. By using a laser grooving process, the coating 46 (and interconnect layer 43) above the scribe lines 44 can be removed to open through to the surface of the substrate (e.g., expose the underlying silicon wafer or GaAs substrate 41). Thereafter, by performing a plasma dicing process, the die can be singulated. After the plasma dicing process, the coating 46 can be removed. Using the coating 46 can help reduce the spread of fluorine-containing residues, but contamination problems may still remain, albeit on a smaller scale.

[0046] If fluorine-containing contaminants are present after the plasma dicing process, it is necessary to perform a post-plasma dicing cleaning process (or defluorination process) to remove those fluorine-containing contaminants from the surface of the substrate. The post-plasma dicing cleaning process can be performed in the same chamber as the plasma dicing process, or alternatively in a separate chamber dedicated to that task, e.g., within a defluorination module, and that separate chamber can be made part of the same cluster tool or part of a separate system. It is desirable to perform the post-plasma dicing cleaning process in a separate chamber for productivity reasons. It is desirable to make that separate defluorination chamber part of the same cluster tool as the plasma dicing chamber.

[0047] Figures 5 and 6 show an overview of embodiments of the method of the present invention. The cleaning method of the present invention is usually carried out after a plasma dicing process 50, for example, a Bosch etching process. The cleaning method has steps of removing fluorine-containing contaminants from metal features on a semiconductor substrate 11, which is a part of a workpiece 10 of a type that also includes a carrier sheet 12 and a frame member 13. The cleaning method has a sputter etching step 52 and a chemical etching step 54, which are alternately repeated a predetermined number of times (i.e., n times, where n is a predetermined value or a variable determined during use by monitoring a desired condition to be achieved). In the embodiment shown in FIG. 5, the sputter etching step 52 is carried out before the chemical etching step 54. However, the sputter etching step 52 and the chemical etching step 54 can be carried out in any order. In another embodiment shown in FIG. 6, the chemical etching 54 is carried out before the sputter etching step 52.

[0048] In certain embodiments, the sputter etching step 52 is an inert gas sputter etching step, and the chemical plasma etching step 54 is an oxygen-containing plasma etching step.

[0049] In the inert gas sputter etching step 52, an inert gas is introduced into the chamber, and a plasma, for example, an inductively coupled plasma, is maintained so that substances are physically sputtered from the surface of the substrate. Contaminants can be removed from the substrate surface by this physical sputtering. The inert gas is usually a noble gas (i.e., a gas belonging to Group 18 of the Periodic Table of the Elements). Preferably, the inert gas is composed entirely or essentially of argon. However, a gas phase mixture can also be employed. For example, the gas phase mixture used in the sputter etching step can contain an inert gas (e.g., argon) and oxygen gas (i.e., O2), and the gas flow rate of the inert gas can be 90% or more of the total flow rate. In this inert gas etching step, an electrical bias, preferably an RF electrical bias, is applied to the workpiece support. Usually, the bias power is in the range of 500 to 1000 W, for example, the value is 800 W. Applying an electrical bias to the workpiece support can be used to impart directionality to the species in the plasma (i.e., to form an anisotropic plasma).

[0050] In the chemical plasma etching step, an oxygen-containing gas is introduced into the chamber, and a plasma, for example, an inductively coupled plasma, is maintained so that the substrate is exposed to the oxygen-containing plasma. The oxygen-containing gas can be O2, O3, or a mixture thereof. Preferably, the oxygen-containing gas is composed entirely or essentially of O2. However, a small amount of a diluting gas, for example, argon gas, can also be further added to the oxygen-containing gas.

[0051] According to what the inventors have found, by alternating with a sputter etching process (e.g., that using argon) and exposing the substrate to an oxygen-containing plasma (e.g., O2 plasma), beneficially, the rate of removal of fluorine-containing contaminants from the surface of the metal feature is increased, and furthermore, the heat load acting on the workpiece is reduced. Without being bound by any theory or speculation, according to what has been considered, as a result of physical sputtering (i.e., during the sputter etching process), the fluorine-containing contaminants are first removed uniformly. On the other hand, exposing the substrate to an oxygen-containing plasma during the chemical plasma etching process helps to chemically remove carbonaceous residues from the surface of the substrate. Again, without being bound by any theory or speculation, according to what has been considered, those carbonaceous residues may be residual organics left from the plasma dicing process by the action of the plasma on the carrier sheet, or those generated by the interaction between the plasma and the carrier sheet in the sputter etching process. By removing such carbonaceous residues, a better-prepared surface, i.e., a surface that is more easily sputtered in a subsequent sputter etching process (e.g., that using argon), is provided. This results in a shortened sputter etching time and a more efficient sputter etching process. Furthermore, while still achieving excellent removal of fluorine-containing contaminants, the amount of substances to be removed can be reduced.

[0052] An electrical bias, preferably an RF electrical bias, can be applied to the workpiece support in the chemical plasma etching step 54. The bias power used in the chemical plasma etching step 54 is usually less than the bias power used in the sputter etching step 52. Usually, the bias power used in the chemical etching step 54 is 2.5 to 250 times, optionally 5 to 50 times, optionally 10 to 20 times, and optionally about 16 times less than the bias power used in the sputter etching step 52. In certain embodiments, the bias power is not applied in the chemical plasma etching step 54. For example, the bias power is in the range of 0 to 200 W, for example, the value is 50 W. The bias power in the chemical plasma etching step 54 is desirably less than about 200 W so that an oxygen-containing plasma (e.g., O2 plasma) reacts chemically with the substrate. By doing so, carbonaceous residues can be removed from the workpiece while avoiding an additional heat load on the workpiece. This can be useful for keeping the workpiece 10 at a sufficiently low temperature to avoid damage to the carrier sheet 12 and / or the adhesive on the carrier sheet.

[0053] An additional heat removal step can be performed between the sputter etching step 52 and the chemical etching step 54. Heat removal can be performed through the use of an electrostatic chuck (ESC) as the workpiece support. The additional heat removal step can also be useful for keeping the temperature of the workpiece, especially the carrier sheet, within an operable range where damage to the carrier sheet may occur if exceeded. For example, during the cleaning process, the temperature of the workpiece can be kept below about 60°C.

[0054] Typical process parameters according to the present invention are shown in Table 1.

Table 1

[0055] In the first example (Example 1), a workpiece 10 provided with an aluminum bonding pad and an exposed scribe line (that shown in FIG. 2) on a semiconductor substrate 11 was subjected to a plasma dicing process using Bosch etching. Thereafter, the workpiece 10 was transferred to another inductively coupled plasma chamber and subjected to a post-plasma dicing cleaning treatment to remove fluorine-containing contaminants (e.g., AlFO3) according to the method of the present invention. The first plasma etching process was an argon sputter etching process 52. The second plasma etching process was an O2 plasma etching process 54. Each of the argon sputter etching process and the O2 plasma etching process was repeated alternately 6 times using the process parameters shown in Table 2. Each etching process was performed in an inductively coupled plasma (ICP) mode while applying RF bias power to the workpiece support (i.e., driving the ICP coil). The duration of each argon sputter etching process and each O2 plasma etching was 20 s. The total processing time was 240 s, and no additional heat removal process was required.

[0056] In the first comparative example (Comparative Example 1), after the workpiece was subjected to a plasma dicing process, it was transferred to another chamber and subjected to a post-plasma dicing cleaning treatment in the same manner as in Example 1. However, the post-plasma dicing cleaning treatment was composed solely of an argon single sputter etching process using the parameters shown in Table 2. The argon sputter etching process was performed in a reactive ion etching (RIE) mode (i.e., the ICP coil was not driven). The duration of the argon sputter etching process was 180 s.

[0057] In the second comparative example (Comparative Example 2), the workpiece was subjected to a plasma dicing process and then transferred to another chamber, where it was subjected to post-plasma dicing cleaning treatment in the same manner as in the first example. However, the post-plasma dicing cleaning treatment was constituted by a sputter etching process, and the feed gas was a mixture of argon and O2 with a mixing ratio of 90:10 based on the individual sccm unit flow rates (hereinafter referred to as "Ar+O2(90:10)"). The processing parameters are shown in Table 2. This Ar+O2(90:10) etching process was performed in ICP mode while applying an RF bias to the workpiece support (i.e., driving the ICP coil). The duration of the Ar+O2(90:10) sputter etching was set to 240 s.

Table 2

[0058] The fluorine contamination level on the bonding pad surface was determined using energy-dispersive X-ray (EDX) measurement based on the F:O signal ratio when a beam voltage of 1.5 kV was used. A workpiece not subjected to the plasma dicing treatment was used as the first comparison standard. A workpiece subjected to the plasma dicing process but not subjected to any post-plasma dicing cleaning treatment was used as the second comparison standard.

[0059] Also, the selectivity of the etching process in the cleaning treatment was recorded by measuring the etching rates of SiO2 and SiN.

[0060] Table 3 shows the results of Example 1, Comparative Example 1, and Comparative Example 2.

Table 3

[0061] When considered without any theoretical or speculative constraints, fluorine-containing contaminants such as AlFO3 formed on aluminum bonding pads are first removed by physical sputtering, for example, in an argon sputter etching process. Therefore, it would be expected that the fluorine-containing contaminants would be removed more efficiently at a higher etching rate, and the resulting F:O ratio would follow the etching rate trends for SiO2 and SiN. That is, since the etching rates of SiO2 and SiN are high, a low F:O ratio would be expected. However, surprisingly, this has not been observed.

[0062] Comparative Example 1 (i.e., Ar single sputter etching in RIE mode) had the highest etching rate and was thus the most aggressive etching treatment. However, despite the high etching rate, in Comparative Example 1, the F:O ratio only decreased to a value of 0.15 (the value was determined by EDX).

[0063] In Comparative Example 2 (i.e., sputter etching using an Ar+O2 mixture (90:10)), the etching rate was lower than that of Comparative Example 1. However, the resulting F:O ratio was 0.15, the same as that of Comparative Example 1 (the value was determined by EDX).

[0064] Example 1 had the lowest etching rates for both SiO2 and SiN and was thus the least aggressive etching. As a result, hardly any material was etched during the cleaning treatment. However, despite the low etching rate, this method unexpectedly resulted in the greatest reduction in the F:O ratio (a reduction to a value of 0.12 as determined by EDX). Clearly, with the method of Example 1, the reduction of fluorine-containing contaminants from the metal features of the substrate was maximized while the amount of material etched was minimized. Therefore, this method provides an improved version of the process for removing fluorine-containing contaminants from the metal features on the substrate.

[0065] In the O2 plasma etching process of Example 1, relatively low platen power (e.g., less than 200 W) was used. According to considerations without any theoretical or speculative constraints, by making the platen power used in the O2 plasma etching process relatively low, the O2 plasma etching process mainly proceeds as chemical etching. Further considering, carbonaceous residues are removed from the workpiece surface by this low-bias O2 plasma etching process. By using a chemical etching process (instead of a sputter etching process), the thermal load on the workpiece is reduced. Reducing the platen power used in the O2 plasma etching process helps reduce heat transfer to the workpiece. Therefore, by keeping the temperature of the workpiece within the framework of thermal budget constraints (e.g., about 60 °C or less), damage to the carrier sheet can be avoided while achieving a significant reduction in fluorine-containing contaminants.

[0066] By making the chemical etching process 54 function as a heat removal process during the cleaning treatment, the need for any additional heat removal process can be eliminated (although they can also be executed if desired). Therefore, the total processing time of the cleaning treatment can be shortened compared to known methods. Generally, this can increase the substrate throughput.

[0067] Table 4 shows the total duration of the Ar sputter etching process for Example 1, Comparative Example 1, and Comparative Example 2.

Table 4

[0068] According to a consideration without any theoretical or speculative constraints, the sputter etching process is a major factor that increases the heat load acting on the workpiece 10 during the cleaning treatment. Therefore, in order to keep the workpiece within the appropriate heat budget constraint, it is desirable to keep the duration of the sputter etching process short. As is obvious, in the method of the present invention, the sputter etching duration is shortened, which not only helps to reduce the heat load transmitted to the workpiece but also improves the removal of fluorine-containing contaminants.

Explanation of Signs

[0069] 10 Workpiece, 11 Semiconductor substrate, 12 Carrier sheet 13 Frame member.

Claims

1. A method for cleaning metal features on a substrate of a type that is part of a workpiece subjected to a plasma dicing process, the workpiece further comprising a carrier sheet mounted to a frame member and transporting the substrate, the method comprising: supplying the workpiece onto a workpiece support disposed within a chamber of an inductively coupled plasma apparatus; performing a sputter etching process including a sub-step of introducing a sputter gas or gas mixture into the chamber and a sub-step of maintaining an inductively coupled plasma of the sputter gas or gas mixture such that the substrate is sputter etched; Introducing O ２ gas and / or O ３ gas in the chamber, and maintaining inductively coupled plasma of the O ２ and / or O ３ gas so that the substrate is chemically etched, and performing a chemical etching process including these sub-processes repeating the step of performing the sputter etching process and the step of performing the chemical etching process; A method having the above steps.

2. The method according to claim 1, wherein the sputter etching process further includes a sub-step of applying a bias power to the workpiece support while maintaining the plasma.

3. The method according to claim 2, wherein the magnitude of the bias power applied to the workpiece support during the sputter etching process is 500 W or more.

4. The method according to claim 3, wherein the magnitude of the bias power applied to the workpiece support during the sputter etching process is 1000 W or less.

5. The method according to any one of claims 1 to 4, wherein the chemical etching process further includes a sub-step of applying a bias power to the workpiece support while maintaining the plasma.

6. The method according to claim 5, wherein the magnitude of the bias power applied to the workpiece support during the chemical etching process is 250 W or less.

7. The method according to claim 6, wherein the magnitude of the bias power applied to the workpiece support during the chemical etching process is 0 W or more.

8. The method according to any one of claims 1 to 7, wherein the sputter gas or gas mixture is introduced into the chamber at a flow rate in the range of 50 to 500 sccm.

9. The method according to any one of claims 1 to 8, wherein the sputter gas or gas mixture contains an inert sputter gas.

10. The method according to claim 9, wherein the sputter gas or gas mixture is composed of argon gas.

11. A method according to any one of claims 1 to 10, wherein the O ２ and / or O ３ gas is introduced into the chamber at a flow rate in the range of 50 to 500 sccm.

12. A method according to any one of claims 1 to 11, wherein the O ２ and / or O ３ gas is composed of O ２ gas.

13. A method according to any one of claims 1 to 12, wherein the workpiece support is an electrostatic chuck.

14. A method according to any one of claims 1 to 13, wherein the sputter etching step and the chemical etching step are each repeated at least three times.

15. A method according to any one of claims 1 to 14, wherein the metal feature is made of a metal or metal alloy selected from aluminum, aluminum alloy, copper, nickel, tin, silver, and SnAg alloy.

16. A method according to any one of claims 1 to 15, wherein the metal feature is a metal bonding pad or a metal bump.

17. A method according to any one of claims 1 to 16, wherein the carrier sheet is made of a polymer material, polyvinyl chloride, or polyethylene terephthalate.

18. A method according to any one of claims 1 to 17, wherein the substrate is a semiconductor substrate or a compound semiconductor substrate.

19. An inductively coupled plasma apparatus for cleaning metal features on a substrate of a type that is a part of a workpiece, using the method of claim 1, the workpiece further comprising a carrier sheet mounted on a frame member for transporting the substrate, the apparatus comprising: a chamber; a workpiece support disposed within the chamber; at least one gas inlet for introducing a gas or gas mixture into the chamber; a plasma generating device for maintaining an inductively coupled plasma within the chamber; A controller configured to control a sputter etching process and a chemical etching process and to alternate between them, wherein the sputter etching process includes a sub-process of introducing a sputter gas or a gas mixture into the chamber, and a sub-process of maintaining an inductively coupled plasma of the sputter gas or the gas mixture so that the substrate is sputter etched, and the chemical etching process includes a sub-process of introducing O ２ gas and / or O ３ gas into the chamber, and a sub-process of maintaining an inductively coupled plasma of the O ２ and / or O ３ gas so that the substrate is chemically etched.

Images