Method of manufacturing a semiconductor device having aluminum contacts or vias

Abstract: A semiconductor device and a method of manufacture therefor. The semiconductor device includes: (1) a substrate having a recess therein, (2) an aluminum-alloy layer (20) located over at least a portion of the substrate and filling at least a portion of the recess and (3) a protective metal layer (22) at least partially diffused in the aluminum-alloy layer, the metal protective layer having a high affinity for oxygen and acting as a sacrificial target for oxygen during a reflow of the aluminum-alloy layer.

Description: TECHNICAL FIELD OF THE INVENTION The present invention is directed, in general, to semiconductors and fabrication techniques and, more specifically, to a method of manufacturing a semiconductor device having a conductive layer with a metal protective layer at least partially diffused into the conductive layer and a method of manufacture therefor. BACKGROUND OF THE INVENTION In semiconductor integrated circuits, the formation of metal interconnect layers is important to the proper operation of such devices. Metal interconnect signal lines make contact to lower conductive layers of the integrated circuit through vias or through contact windows to "active" device regions of the semiconductor in an insulating layer. For best operation of the device, the metal used to form the interconnect layer should completely fill the via or contact window (hereinafter referred to as opening(s)). Because of its physical properties, aluminum-alloys (e.g., aluminum-copper, aluminum-silicon, aluminum-copper-silicon) are especially suited for fabrication of metal interconnect lines in integrated circuits. However, the sputtering process used to apply aluminum-alloy thin film layers to an integrated circuit generally results in less than ideal filling of openings. Since the aluminum-alloy is deposited at an elevated temperature to obtain large grains for improved electromigration reliability, these large aluminum-alloy grains tend to form on the upper surface of the insulating layer. The grains that form at the edges of the opening tend to block the opening before the aluminum-alloy has a chance to completely fill it. This results in voids and uneven structures within the via. This problem is especially acute as integrated circuit devices are fabricated using smaller geometries. The smaller openings used in these devices tend to have a larger aspect ratio (opening height to width ratio) than larger geometry devices, which exacerbates the aluminum-alloy filling problem. The uneven thickness of the aluminum-alloy layer going into the opening has an adverse impact on device functionality. If the voids in the opening(s) are large enough, contact resistance can be significantly higher than desired. In addition, the thinner regions of the aluminum-alloy layer will be subject to the well known electromigration problem. This can cause eventual open circuits at the contacts and failure of the device. To solve the problems associated with sputtering techniques, many approaches have been used to ensure good metal contact to lower interconnect levels. For example, one technique involves depositing the aluminum-alloy interconnect by sputtering in a physical vapor deposition tool ("PVD")and then reflowing it in a separate reflow module at temperatures that range between 500°C to 575°C. At these temperatures, the surface mobility and diffusion kinetics of the aluminum-alloy are enhanced, allowing it to deposit into the openings and fill them. However, at these high temperatures, the reflow module is very sensitive to impurities. As is well known, aluminum-alloy easily oxidizes and any presence of oxygen or moisture in the tool, particularly while processing in the reflow module will negate the reflow process. In other words, the aluminum-alloy will not reflow and properly fill the opening if the aluminum-alloy oxidizes or moisture forms on it. Thus, the deposition, transfer and subsequent reflow is carried out in an ultra high vacuum environment, preferably in a multi-chamber cluster tool having very low partial pressures of water vapor and oxygen. These environmental conditions require extensive pre-conditioning times, such as tool chamber pump-down and bakes, to bring the modules up to the required pristine operating conditions. Further, metal vacuum seals must be used instead of conventional "O"-ring seals to reduce module pump-down times. These metal seals must be used in the transfer chamber as well as in the deposition and reflow chambers. Consequently, these pre-conditioning steps increase the overall cost of the machine and the production time, which also increase the overall cost of the semiconductor devices. EP-A-0 042 096 discloses a semiconductor device with a substrate having a recess, over which is deposited a single layer of conductive material to fill at least a portion of the recess to form a plug. Although EP-A-0 042 096 discloses depositing a single layer of conductive material over a portion of a substrate to fill at least a portion of a recess to form a plug, it does not disclose depositing a metal protective layer to serve as a sacrificial target for oxygen when the conductive layer is re-flowed to fill more than at least a portion of the recess. Thus EP-A-0 042 096 does not solve the problem of producing a uniformly filled recess without oxygen contamination. In the article "Roles of Ti-Intermetallic Compound Layers on the Electromigration Resistance of Al-Cu Interconnecting Stripes" by C.C. Lee, et al., published in Volume 71, no. 12, of the Journal of Applied Physics (15 June 1992), the authors describe the advantages of using alloying to decrease grain-boundary self-diffusivity. However, this articles does not discuss or describe the uniform filling of a via-hole by locating a metal protective layer alloyed with an aluminium alloy over a conductive layer so that it can serve as a sacrificial target for oxygen during a re-flow process and reduce oxidation. Accordingly, what is needed in the art is a method of manufacturing a semiconductor device such that the conductive layers connecting the openings are not subject to substantial oxidation during the manufacturing process. The method of the present invention addresses these needs. According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of depositing a conductive layer over at least a portion of a substrate, said conductive layer filling at least a portion of a recess located in said substrate, said conductive layer susceptible to oxidation; depositing a metal protective layer consisting of a metal alloyed with in alumium alloy over said conductive layer, said metal protective layer having a higher affinity for oxygen than said conductive layer; and reflowing said conductive layer, said metal protective layer oxidizing and at least partially diffusing into said conductive layer, said metal protective layer acting as a sacrificial target for oxygen during said reflowing. The step of depositing said aluminium-alloy lay can comprise the step of depositing said conductive layer with a physical vapour deposition (PVD) process. The step of depositing said metal protective layer can comprise the step of depositing said metal layer with a physical vapour deposition (PVD) process. The step of reflowing can comprise the step of reflowing said conductive layer at a pressure ranging between 2 to 10 milliTorr. The step of reflowing can comprise the step of reflowing said conductive layer with a rapid thermal anneal (RTA) process. The step of reflowing can comprise the step of heating said conductive layer to a temperature of at least 350°C. According to a further aspect of the invention, there is provided a method of manufacturing a semiconductor device, comprising the steps of: depositing, via a physical vapour deposition (PVD) process, an aluminium-alloy layer over at least a portion of a silicon substrate, said aluminium-alloy layer filling at least a portion of a recess located in said silicon substrate; depositing, via said PVD process, a metal protective layer consisting of a metal alloyed with an aluminum alloy over said aluminium-alloy layer, said metal protective layer having a higher affinity for oxygen than said aluminum-alloy; and reflowing said aluminum-alloy layer at a temperature of at least 350°C and at a pressure of at least between 2 to 10 milliTorr, said metal protective layer oxidizing and at least partially diffusing into said aluminum-alloy layer, said metal protective layer acting as a sacrificial target for oxygen during said reflowing. The metal can be selected from titanium, vanadium, magnesium, yttrium, hafnium, cerium, scandium, and zirconium, and is alloyed with an aluminum alloy. The step of reflowing can comprise the step of reflowing said aluminum-alloy layer with a rapid thermal anneal (RTA) process. To address the above-discussed deficiencies of the prior art, the present invention provides a method of manufacturing a semiconductor device. The semiconductor device includes: (1) a substrate having a recess therein, (2) a conductive layer located over at least a portion of the substrate and filling at least a portion of the recess and (3) a metal protective layer consisting of a metal alloyed with an aluminum alloy at least partially diffused in the conductive layer. The metal protective layer has a higher affinity for oxygen than the conductive layer and thereby may be capable of gettering the oxygen from either the environment or from the conductive layer. The present invention thereby introduces the broad concept of reducing or eliminating the oxidation that occurs in the conductive layer by providing a barrier or cap, in the form of at least a partially oxidized metal layer that traps oxygen before it reaches the conductive layer or removes it from the conductive layer, or in other embodiments, removes it from the conductive layer in the event that the conductive layer oxidizes prior to deposition of the metal protective layer. The present invention therefore allows a conductive plug to be formed reliably without requiring the exotic low pressure environment of the prior art. In one embodiment of the present invention, the substrate comprises silicon and the conductive layer may be aluminum, aluminum-alloy or other conventional or later-discovered conductive metals used for forming a circuit pattern on the semiconductor device. Alternatively, the substrate may be gallium arsenide or any other conventional or later-discovered substrate suitable for providing a foundation for a solid state device. In one preferred embodiment of the semiconductor device, the metal protective layer decreases the rate of electromigration damage accumulation in the conductive layer when it partially diffuses into the conductive layer. In an alternative embodiment of the present invention, the aluminum or aluminum-alloy layer fills at least the portion of the recess and forms a contact for the semiconductor device. The recess thus may be a via that provides inter-layer connectivity in a multi-layer substrate or a contact for a terminal (such as a source, gate, drain, base, emitter or collector) of a semiconductor device. In one embodiment of the present invention, the metal protective layer is a metal alloyed with an alumium alloy, which metal is selected from the group of titanium, vanadium, magnesium, yttrium, hafnium, cerium, scandium, and zirconium. Those skilled in the art are familiar with other metals and alloys that may be advantageous, depending on the application. In another embodiment of the present invention, the metal protective layer is able to at least partially reduce any oxide on the conductive layer. Moreover, the elements of the metal protective layer may be at least partially diffused into the conductive layer without substantially altering the intended purposes of the conductive layer. Furthermore, the metal protective layer may be fully sacrificed during the reflow process, or alternatively, some of the original metal protective layer may remain intact. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which: FIGURE 1 illustrates a cross-sectional view of a semiconductor device that has a contact window or via formed therein; FIGURE 2 illustrates a schematic diagram of a conventional physical vapor deposition tool with the various deposition chambers therein. FIGURE 3 illustrates a cross-sectional view of the semiconductor device of FIGURE 1 with a conductive layer partially deposited in the via; FIGURE 4 illustrates a cross-sectional view of the semiconductor device of FIGURE 3 with a metal protective layer deposited over the conductive layer prior to its diffusion in the conductive layer; FIGURE 5 illustrates a cross-sectional view of the semiconductor device of FIGURE 4 after the device has been subjected to a reflow process, where the metal layer has been oxidized and diffused into the conductive layer. DETAILED DESCRIPTION Referring initially to FIGURE 1, an integrated circuit device is formed on a semiconductor substrate 10, which may be comprised of materials known to those skilled in the art such as silicon or gallium arsenide. Although a substrate 10 is described, it will be apparent to those skilled in the art that the described technique may be used with a contact formed to any underlying conductive layer. Thus, the substrate 10 may include multiple layers of polycrystalline silicon or metallic interconnect, as well as being an active region in a monocrystalline silicon substrate. An insulating layer 12 that has a thickness, which varies from device to device, depending on the application, such as a silicon oxide (SiO 2 ), is formed over the substrate 10, and an opening 14 (via or contact window) is formed therethrough using a mask and an isotropic etching technique as known in the art. The semiconductor device is placed in a conventional deposition tool 16, such as a physical vapor deposition tool ("PVD") schematically illustrated in FIGURE 2, or a chemical vapor deposition tool, not shown. A barrier layer 18, such as a refractory metal, refractory metal nitride, refractory metal silicide, or combination thereof, is uniformly deposited over the insulating layer 12 and in the opening 14 using conventional deposition techniques. The barrier layer 18 is preferably deposited to a thickness of approximately 20 nm to 200 nm and is preferably comprised of titanium and titanium nitride. A "wetting layer" to improve the aluminum-alloy deposition characteristics may also be included as part of barrier layer 18. Because of the innate advantages associated with the present invention as discussed herein, the deposition tool 16 is preferably of conventional design. As such, the deposition tool 16 preferably has a deposition chamber 16a in which the barrier layer 18 is deposited, a deposition chamber 16c in which the conductive layer 20 is deposited, a transfer chamber 16b through which the semiconductor device is transferred from one chamber to another, a chamber 16e and a reflow chamber 16d. The metal protective layer 22 (FIGURE 3) is subsequently deposited in chamber 16e and the substrate 10 is heated in a reflow chamber 16d in which the conductive layer 20 is reflowed after deposition. However, it should be understood that in some embodiments, all depositions steps may be conducted in a single chamber. Alternatively, the semiconductor device may be transferred to a rapid thermal anneal ("RTA") device 24 as schematically illustrated in FIGURE 2. Because the PVD tool 16 is of conventional design, special metallic seals and preparation techniques for the PVD tool, which are required by conventional processes to maintain extremely low vacuums, are not necessary. Turning now to FIGURE 3, the semiconductor device with a conductive layer 20 deposited thereon is illustrated. The deposition of the conductive layer 20 is conducted in the PVD tool 16, and is deposited over the substrate 10 and the barrier layer 18 using conventional PVD techniques at a pressure of ranging from about 1 milliTorr to about 10 milliTorr and temperatures that ranges from about 25°C to about 400°C. In preferred embodiments, the thickness of the conductive layer ranges from about 400 nm to about 700 nm. The conductive layer 20 is susceptible to oxidation and may be comprised of any type of such conductive material, such as aluminum or aluminum-alloy, known to those skilled in the art. The purpose and function of the conductive layer 20 is well known in the art and serves as an interconnect layer that electrically connects devices on the semiconductor device. The conductive layer 20 is not a barrier layer, such as titanium nitride. For reasons previously discussed with respect to conventional processes, the conductive layer 20 is not uniformly deposited within the opening 14 and must, therefore, be reflowed so that it can uniformly fill and contact the sides of the opening 14 to form a reliable contact point for the integrated circuit device. Upon deposition of the barrier layer 18 and the conductive layer 20, the metal protective layer 22, as illustrated in FIGURE 4, is deposited over the conductive layer 20. In a preferred embodiment, the metal layer 22 is deposited using conventional PVD techniques under a pressure that ranges from about 2 milliTorr to about 10 milliTorr and a temperature that ranges from about 25°C to about 400°C and deposition is conducted to achieve a metal layer that has a thickness that ranges from about 5 nm to about 20 nm . It should be particularly noted that the pressure at which the semiconductor is fabricated is substantially higher than the 10 -8 torr associated with conventional techniques. Thus, the special metal seals and time consuming preparation steps for the PVD tool are not required in the present invention. In one embodiment, the metal protective layer 22 may be capable of gettering the oxygen from either the environment or from the conductive layer 20. In such embodiments, the metal protective layer 22 is comprised of a metal selected from the group consisting of a combination of metals previously discussed above and alloyed with aluminum alloys such as aluminum-copper, aluminum-silicon, or aluminum-copper-silicon. For example, the metal protective layer 22 may be comprised of either titanium or vanadium or magnesium, yttrium, hafnium, cerium, scandium and zirconium, which may be alloyed with an aluminum alloy. After deposition of the metal protective layer 22, the semiconductor device is then transferred to either a reflow chamber 16d or a rapid thermal anneal device 24 to be subjected to temperatures ranging between 350°C to 550°C, which are sufficient to reflow the conductive layer 20 such that it uniformly fills the opening 14. As previously stated, the deposition tool may be of such a design that has only one chamber in which all phases of the deposition and annealing may be conducted. After deposition and during the reflow process, it is believed that the metal protective layer 22 oxidizes and forms an oxidized metal that at least partially diffuses into the conductive layer 20 (FIGURE 5). In such instances, research has shown that diffusion of titanium into aluminum-alloy acts to decrease the rate of electromigration damage accumulation in an aluminum-alloy-copper conductive layer as discussed in the article entitled "Roles of Ti-intermetallic compound layers on the electromigration resistance of Al-Cu interconnecting stripes", J. Appl. Phys. 71, June 1992, pages 5877-5887, which is incorporated herein by reference. In some embodiments, the metal layer 22 may completely diffuse into the conductive layer 20 or remain substantially on top of the conductive layer 20. In either embodiment, however, the metal layer 22 serves as a target to which oxygen may bond, thereby preventing substantial oxidation of the conductive layer 20 such that it reflows uniformly into the opening 14 and forms a reliable electrical contact point within the integrated circuit. From the foregoing it is apparent that the present invention provides a semiconductor device that includes: (1) a substrate having a recess therein, (2) a conductive layer located over at least a portion of the substrate and filling at least a portion of the recess and (3) a metal protective layer at least partially diffused in the conductive layer. The metal protective layer has a higher affinity for oxygen than the conductive layer and thereby acts as a sacrificial target for oxygen during a reflow of the conductive layer to reduce oxidation in the conductive layer. The present invention thereby introduces the broad concept of reducing the oxidation that occurs in the conductive layer by providing a barrier or cap, in the form of the oxidized metal, that traps oxygen before it reaches the conductive layer or removes it from the conductive layer in the event that the conductive layer partially oxidizes prior to deposition of the protective oxidizable metal layer. The present invention therefore allows a conductive plug to be formed reliably without requiring the exotic low pressure environment of the prior art. The foregoing has outlined, rather broadly, preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the scope of the invention as claimed.

Claims: A method of manufacturing a semiconductor device, by forming a conductive layer over at least a portion of a substrate by depositing said conductive layer with a physical vapor deposition process, said conductive layer filling at least a portion of a recess located in said substrate, said conductive layer susceptible to oxidation, said method comprising: depositing a metal protective layer on said conductive layer, said deposited metal protective layer consisting of a metal alloyed with an aluminum alloy and having a higher affinity for oxygen than said conductive layer; and reflowing said conductive layer, said metal protective layer oxidizing and at least partially diffusing into said conductive layer, said metal protective layer acting as a sacrificial target for oxygen during said reflowing. The method of claim 1, wherein said substrate comprises silicon. The method of claim 1, wherein said metal is selected from the group consisting of titanium, vanadium, magnesium, yttrium, hafnium, cerium, scandium, and zirconium. The method of claim 1, wherein said step of reflowing comprises the step of fully diffusing said metal protective layer in said conductive layer. The method of claim 1, wherein said conductive layer is an aluminium-alloy layer. The method of claim 1, wherein said conductive layer fills at least said portion of said recess and forms a contact for said semiconductor device.

Inventors: MERCHANT SAILESH M, NGUYENPHU BINH, MERCHANT, SAILESH M., NGUYENPHU, BINH
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 1998
Main classification: H01L21
IPC codes: H01L23, H01L21