A PROCESS FOR IN-SITU DEPOSITION OF A Ti/TiN BARRIER METAL STACK

Abstract: A single chamber of a vapor deposition system is used to deposit both Ti and TiN. A Ti layer is deposited on the sample using a noncollimated process. N2 gas in then introduced in the chamber. A TiN layer is then deposited over the Ti layer, and afterwards, the chamber is evacuated. This process requires one less handling step that the conventional process, thereby increasing throughput. Further, Ti pasting of a TiN chamber is eliminated, thereby further increasing throughput. Still further, an Al layer deposited on the TiN layer produced by the present process can have impoved texture and grain size relative to an Al layer deposited on the TiN layer of the conventional process.

Description: A PROCESS FOR IN-SITU DEPOSITION OF A Ti/TiN BARRIER METAL STACK FIELD OF THE INVENTION This invention relates to deposition methods for manufacturing integrated circuits, and particularly, to methods for depositing Titanium (Ti) and Titanium Nitride (TiN) stacks. BACKGROUND The results of recent electromigration studies suggest that a leading candidate for the next generation metal stack is Ti/TiN/Al/TiN. However, manufacturing such a metal stack presents some throughput problems. A typical vapor deposition system for forming metal stacks has four physical vapor deposition chambers. Thus, using a conventional process (where a separate deposition chamber is used for each layer) , all four chambers would be used to deposit the stack. Figure 1 illustrates this conventional process. In step i, a wafer (also referred to as a "sample") 100 is moved into chamber 110 for Ti deposition. In step ii, wafer 100 is moved into chamber 120 for TiN deposition. In step iii, wafer 100 is moved into chamber 130 for Al deposition. In step iv, wafer 100 is moved into chamber 140 for a second TiN deposition. As a result of this conventional process, the system's throughput is limited because each wafer must be moved in and out of a chamber at least four times to form the Ti/TiN/Al/TiN stack. Additionally, because all four chambers are utilized for the metallization scheme, the flexibility of the system is greatly reduced. The supported metallization scheme can only involve Ti, Al, and TiN. Moreover, because the TiN deposited in chamber 120 has a special clamp that leaves large areas on wafer 100 uncovered with TiN, the system of Figure 1 cannot accommodate TiN/Tungsten barrier depositions because typical barrier depositions must cover most (if not all) of the wafer surface (typically within 2 mm of the edge of wafer 100) . As a result, the subsequently deposited tungsten will only deposit on TiN and, thus, will adhere to wafer 100. However, because all the chambers used to deposit the Ti/TiN/Al/TiN stack have special clamps, the system cannot be used for these barrier depositions. Further, in a conventional process, the TiN chamber requires Ti pasting to prevent TiN from flaking off the interior surface of the chamber. Consequently, Ti pasting further decreases throughput. Figure 2 illustrates an alternative conventional process. In step 1, wafer 100 is moved into chamber 110 for Ti deposition. In step 2, wafer 100 is moved into chamber 120 for TiN deposition. In step 3, wafer 100 is moved into chamber 130 for Al deposition. In step 4, wafer 100 is moved back into chamber 120 for another TiN deposition. This process has limited throughput not only because there are four handling steps (i.e., moving the sample into and out of a chamber) , but also because the chambers cannot be used concurrently due to the requirement that chamber 120 be available for the second TiN deposition of step 4. SUMMARY According to one embodiment of the present invention, a single chamber of a vapor deposition system is used to deposit both Ti and TiN. A Ti layer is deposited on the sample using a noncollimated process. N 2 gas is then introduced in the chamber. A TiN layer iβ then deposited over the Ti layer, and afterwards, the chamber is evacuated. Because both Ti and TiN are deposited in the same chamber, the process requires one less handling step than the conventional process, thereby increasing throughput. Further, the need for Ti pasting of a TiN chamber is eliminated, thereby further increasing throughput. Still further, an Al layer deposited on the TiN layer produced by the present process can have improved texture and grain size relative to an Al layer deposited on the TiN layer of the conventional process. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates a process flow of a conventional Ti/TiN/Al/TiN process using a separate vapor deposition chamber for each layer. Figure 2 illustrates a process flow for an alternative conventional Ti/TiN/Al/TiN process. Figure 3 illustrates the process flow for Ti/TiN/Al/TiN deposition using one embodiment of the present invention in a deposition system having four physical vapor deposition chambers. Figure 4 shows a Ti/TiN vapor deposition system according to one embodiment of the present invention. Figure 5 shows a cross-sectional view of a Ti/TiN/Al/TiN stack. DETAILED DESCRIPTION Figure 3 illustrates the process flow for Ti/TiN/Al/TiN deposition using one embodiment of the present invention in a deposition system having four physical vapor deposition chambers. In step A, wafer 100 is moved into a chamber 310 for Ti/TiN deposition. A robot arm (not shown) is used to move wafer 100 into and out of the chambers. In step B, wafer 100 is moved into chamber 130 for Al deposition. In step C, wafer 100 is moved into chamber 120 for TiN deposition. Throughput is increased in the process of Figure 3 as compared to the processes of Figures l and 2 because the system of Figure 3 requires one fewer handling step. Further, the Ti/TiN step A is self-pasting because the chamber 310 is pasted by the Ti deposition of the next wafer moved into chamber 310 for Ti/TiN deposition. Still further, a fourth chamber is left available for barrier depositions without disrupting concurrent use of the remaining three chambers. Figure 4 shows a vapor deposition system 400 according to one embodiment of the present invention. In vapor deposition system 400, wafer or sample 100 is held approximately 52 mm from Ti target 430 by a heater clamp 420. For this embodiment, the steps for "same chamber" Ti/TiN deposition are summarized in Table 1 below. TABLE 1 Step BSP Preheat Pep Gas Dep_ BSP Time 2 15 9.3 5.0 34 4.0 (sec) Power 0 0 3000 0 6500 0 (W) Power 0 0 3000 0 6500 0 Rate (W/s) Gas Flow Heated -2 PV 15 15 15 15 ■2 PV Ar Ar 34 34 •2 PV N, 90 90 ■ 2 PV In the first BSP step, the gas lines for providing various gases to the chamber are closed and the heated Ar gas line is evacuated to the final valve of the gas line to a pressure of approximately 10"* Torr (-2 PV) . As a result, the chamber is evacuated to a base pressure of approximately 10"* Torr. This step takes approximately 2 seconds to complete. In the Preheat step, sample 100 is placed against the heater clamp 420, and 15 SCCM (standard cubic centimeters per minute) of heated Ar gas is supplied into the chamber below sample 100 to preheat sample 100 and maintain a pressure differential to keep sample 100 in contact with heater clamp 420. In this embodiment, sample 100 is heated to approximately 250 °C, but any temperature may be used depending on the coverage and film quality desired. Typically, a temperature in the range of 25-450 °C is suitable. A target-to-sample spacing of 52 mm is maintained. This spacing is the optimized spacing for TiN deposition for the power and magnet (not shown) in this process. Ar gas is introduced into the chamber above the sample for generating a plasma. In this embodiment, 50 SCCM of Ar gas is used, although any flow of Ar gas can be used so long as enough Ar gas is provided to create a suitable plasma. Typically, an Ar gas flow in the range of 40- 100 SCCM is suitable. This step takes approximately 15 seconds. In the first Dep step, Ti is deposited on sample 100. A plasma is created in the chamber by applying a voltage across the Ti target 430 and sample 100. In this embodiment, a 3000 W plasma is used, although any power level can be used depending on the sputtering rate and coverage desired. Typically, a power level greater than 1000 W is suitable. A suitable plasma pressure can be anywhere from a few to several hundred mTorr. No collimator is necessary, which if used, would slow down the deposition process thereby reducing throughput. The Ar and heated Ar gas flows are maintained and a 250A thick layer of Ti is deposited on sample 100 after approximately 9.3 seconds. In the Gas step, the plasma is terminated by terminating the power, and N 2 gas is introduced into the chamber. As a result, Ti target 430 is placed in a "Nitrided" mode for TiN deposition. In this embodiment, 90 SCCM of N 2 flow is used, although any gas flow can be used that provides sufficient N under the existing conditions to place Ti target 430 into nitrided mode. Typically, a N 2 gas flow in the range of 60 and 200 SCCM is suitable. The Ar flow is reduced to a lower value (34 SCCM) . In the second Dep step, TiN is deposited on sample 100. A plasma is created by applying a voltage across the nitrided Ti target 430 and sample 100. In this embodiment, a 6500 W plasma is used because of the lower sputtering rate of TiN (compared to Ti) . Again, any power level can be used depending on the sputtering rate and coverage desired. Typically, a power level greater than 5000 W is used to achieve a suitable sputtering rate. The N 2 , Ar and heated Ar gas flows are maintained and after approximately 34 seconds, 800A of TiN is deposited on sample 100. In the second BSP step, the plasma is terminated and the gas lines closed. The Ar and N 2 gas lines are evacuated to the final valve of the gas line, and consequently, the chamber is no longer flooded with N 2 gas. Thus, Ti target 430 is left in a semi-nitrided mode. This step takes approximately 4 seconds to complete. Figure 5 shows a cross-sectional view of a Ti/TiN/Al/TiN stack produced by the above-described embodiment. First, Ti layer 510 is deposited on the sample to a thickness of approximately 250A. Then, in the same chamber, TiN layer 520 is deposited on top of Ti layer 510 to a thickness of approximately 800A. The sample is moved to another chamber where Al layer 530 is deposited on top of TiN layer 520 to a thickness of approximately 4000A. The sample is then moved to a third chamber where TiN ARC layer 540 is deposited on Al layer 530. The same chamber Ti/TiN deposition process is observed to have a "first wafer" effect (i.e., the Ti film of the first wafer is thicker) when the layer deposited prior to the Ti layer was also Ti. When the Ti layer for the first wafer is deposited from a metallic Ti target, the Ti layer is relatively thick. In contrast, the Ti layer for the second wafer in this process will be deposited from a nitrided Ti target. Consequently, the Ti layer for the second wafer will be relatively thin because the sputtering rate for TiN (in the surface of the nitrided Ti target) is lower than the sputtering rate of Ti from a metallic Ti target. Also observed for the same chamber Ti/TiN deposition process is that the Ti/TiN layer formed thereby is slightly different than a Ti/TiN layer formed by depositions in separate chambers. The main differences are that the Ti layer from the same chamber Ti/TiN deposition has degraded uniformity (i.e., the variation in the layer's thickness is increased) and incorporation of approximately 3 to 5 at% N. The degradation in uniformity is attributable at least in part to the 52 mm TiN target-to-sample spacing (rather than the optimal 43 mm Ti target-to-sample spacing) used in the same chamber Ti/TiN deposition process. Separate chamber Ti/TiN deposition has an observed sheet resistance uniformity of approximately 1.5% lσ as compared to approximately 3.1% lσ for same chamber Ti/TiN deposition. A uniformity of 3.1% lσ is acceptable for many applications. Moreover, when Al is included in the stack, the observed sheet resistance uniformity is approximately 1.4% lσ, which is excellent under current standards. Further, studies show that the degraded uniformity of the Ti/TiN layer does not substantially compromise (and in some aspects improves) the quality (e.g., grain size, texture, and electromigration properties) of the Al layer in the Ti/TiN/Al/TiN stack. For example, the Al layer's observed crystallographic texture as determined using x-ray diffraction is slightly stronger for Al deposited on "same chamber" Ti/TiN (volume fraction <111> « 0.92) than for separate chamber Ti/TiN (volume fraction <.111> • = 0.89). Also, the observed average grain size of the Al layer (Al-l%Cu) as determined using transmission electron microscopy was 0.85 μm ±0.35 μm for Al deposited on same chamber Ti/TiN and 0.77 μm ±0.35 μm for Al deposited on separate chamber Ti/TiN. The foregoing has described the principles and preferred embodiments of the present invention. However, the invention should not be construed as being limited to the particular embodiments described. For example, the deposition time, temperature, plasma power, gas flows and spacing can be varied to produce Ti or TiN films of different thickness and/or quality at different rates and/or efficiency. Thus, above- described embodiments should be regarded as illustrative rather than restrictive. Variations can be made to those embodiments by workers skilled in the art without departing from the scope of the present invention as defined by the following claims.

Claims: CLAIM? We claim: 1. A method for depositing Ti and TiN on a sample in a single physical vapor deposition chamber, said chamber containing a Ti target, said method comprising the steps of: depositing Ti on said sample; introducing a gas into said chamber to form TiN on said target; and depositing TiN on said sample. 2. The method of Claim 1, further comprising the step of removing said gas from said chamber thereby placing said target in a semi-nitrided mode. 3. The method of Claim 1, wherein said step of introducing a gas comprises the step of introducing N 2 gas into said chamber. 4. The method of Claim 3, wherein said step of introducing N 2 gas comprises the step of introducing 70 to 90 SCCM of N 2 gas into said chamber. 5. The method of Claim 1, wherein said step of depositing Ti comprises the step of creating a plasma in said chamber between said target and said sample. 6. The method of Claim 5, wherein said step of creating a plasma comprises the steps of: introducing Ar gas into said chamber; and creating a plasma using at least 1000 W of power. 7. The method of Claim 1, wherein said step of depositing TiN comprises the steps of: introducing N 2 gas into said chamber; and creating a plasma in said chamber between said target and said sample. 8. The method of Claim 7, wherein said step of introducing N 2 gas comprises the step of introducing 70 to 110 SCCM of N 2 gas into said chamber, and said step of creating a plasma comprises the step of creating a plasma using at least 5000 W of power. 9. The method of Claim 1, further comprising the step of preheating said sample. 10. The method of Claim 9, wherein said step of preheating said sample comprises the step of heating said sample to a temperature of 25 to 450 °C at least in part by using heated Ar gas. 11. An apparatus for depositing Ti and TiN on a sample in a single physical vapor deposition chamber, said chamber containing a Ti target, said apparatus comprising: means for depositing Ti on said sample; means for introducing a gas into said chamber to form TiN on said target; and means for depositing TiN on said sample. 12. The apparatus of Claim 11, further comprising means for removing said gas from said chamber, whereby said target is placed in a semi-nitrided mode. 13. The apparatus of Claim 11, wherein said means for introducing a gas comprises means for introducing N 2 gas into said chamber. 14. The apparatus of Claim 11, wherein said means for depositing Ti comprises: means for introducing Ar gas into said chamber; and means for creating a plasma in said chamber between said target and said sample. 15. The apparatus of Claim 11, wherein said means for depositing TiN comprises the steps of: means for introducing N 2 gas into said chamber; and means for creating a plasma in said chamber between said target and said sample. 16. The apparatus of Claim 11, further comprising means for preheating said sample with heated Ar gas. 17. A method for improving the texture and grain size of an Al layer deposited on a sample, said method comprising the steps of: depositing a layer of Ti on said sample in a physical vapor deposition chamber; depositing a layer of TiN on said Ti layer deposited in said Ti depositing step, said TiN deposition occurring in said physical vapor deposition chamber; and depositing a layer of Al on said TiN layer deposited in said TiN depositing step, whereby the grain size of said Al layer is increased and the volume fraction is increased. 18. The method of Claim 17, further comprising the step of depositing a layer of TiN on said Al layer deposited in said Al depositing step, said TiN layer deposited on said Al layer for serving as an anti- reflective coating. 19. An apparatus for improving the texture and grain size of an Al layer deposited on a sample, said apparatus comprising the steps of: means for depositing a layer of Ti on said sample in a physical vapor deposition chamber,* means for depositing a layer of TiN on said Ti layer deposited in said Ti depositing step, said TiN deposition occurring in said physical vapor deposition chamber; and means for depositing a layer of Al on said TiN layer deposited in said TiN depositing step, whereby the grain size of said Al layer is increased and the volume fraction is increased. 20. The apparatus of Claim 19, further comprising means for depositing a layer of TiN on said Al layer deposited by said Al depositing means, wherein said TiN layer deposited on said Al layer serves as an anti- reflective coating.

Inventors: ALVIS ROGER L, BESSER PAUL R, IACOPONI JOHN A, TRAN KHANH Q, ALVIS, ROGER, L., BESSER, PAUL, R., IACOPONI, JOHN, A., TRAN, KHANH, Q
Applicants: ADVANCED MICRO DEVICES INC, ADVANCED MICRO DEVICES, INC.
Application year: 1995
Main classification: C23C14
IPC codes: C23C14