PULSED MODE DEPOSITION FOR LOW RATE FILM DEPOSITION

Abstract: A pulsed mode sputtering method and system for sputtering a material from a target onto a substrate in a sputtering deposition process to create thin films. The thin films are created by generating pulsed power from a power supply operated in pulsed mode. The power supply can be either a DC or RF power supply. The pulsed power is applied at full load during the power on portion and at a significantly reduced power (e.g., at 5 % of the full load power) during the power off portion. The pulsed power is applied to the target to sputter the target material onto the substrate at a reduced deposition rate to create a thin film on the substrate. Uniform films having thicknesses of less than 50 angstroms can be created using this pulsed mode deposition technique.

Description: PULSED MODE DEPOSITION FOR LOW RATE FILM DEPOSITION TECHNICAL FIELD OF THE INVENTION The present invention relates generally to electronic systems and methods, and more particularly, to a system and method for achieving a low rate film deposition using pulsed mode RF and DC deposition. BACKGROUND OF THE INVENTION Newer semiconductor applications, such as metal layers for spin valve GMR structures, thin film resistors, thin barriers/liners, and masks, have arisen that require the deposition of thin films of less than fifty angstroms (< 50 A) height. Optimally, these thin films would be formed using a sputtering or similar process that can ensure a uniform thin film using a process that is controllable and repeatable. Conventional sputtering deposition methods typically employ continuously operated power sources, including DC magnetron sputtering and RF diode sputtering methods. A typical deposition rate for DC magnetron sputtering is 1000 A/min/kW. For repeatable deposition, the deposition process time should be at least 20 to 30 seconds so that the accuracy of process timing does not limit the repeatability that can be achieved. Furthermore, there are inherent delays in the electronic systems used for sputtering deposition. Also, a minimum amount of time is required in order to provide uniform and continuous films, especially when using a rotating DC magentron. Given a minimum amount of processing time, one way to reduce the deposition rate in order to achieve a thin film would be to reduce the power. However, these various power sources have limitations when attempting to lower the power. For example, operating a DC magnetron source for 20 to 30 seconds to create a 20 A film requires a reduction in target power to a range of 40 to 60 W. For a 12" diameter target, this target power range translates to a power density that is too low to sustain a stable plasma, especially in a more optimal low pressure processing environment. In addition, the target voltage may not be adequate to impart sufficient energy to the sputtered atoms. Lowering the deposition power also has other undesirable effects such as increased contamination. Thus, the approach of simply decreasing the target power is not feasible for depositing thin films using DC magnetron sputtering. While the deposition rates for RF diode sputtering are typically lower (200 - 400 A/min/kW) than for DC magnetron sputtering, similar problems arise. Even this 3-5 times reduction in deposition rate is often too high for thin films, especially those less than 30 A in height . The deposition rate can also be reduced by increasing the pressure so that a smaller fraction of the sputtered atoms actually reach the substrate. However, higher pressures also reduce the sputtered atom energy and result in porous, non-continuous films. Reduction of deposition rates can also be achieved through the use of shields, physical/long throw collimators, and mechanical choppers. However, these options are not attractive due to mechanical complexity, particulate generation and increased likelihood of plasma instability. Using a mixture of sputtering gases (e.g. Ne and Ar) instead of pure Ar can reduce the sputter yield, increase the target voltage and decrease the plasma density for a given target power. However, this solution introduces additional complexity because it is more difficult to sustain a plasma in Ne than in Ar and a secondary hollow cathode source may be necessary. Furthermore, since a cryopump does not pump Ne effectively, a turbo pump is necessary which requires a change in system configuration. Ultra-low pressure sputtering can also be effective in reducing the deposition rate because of the decrease in plasma density as the pressure is reduced below 1 Torr. However, for conventional DC magnetrons, operation below 1 mTorr is tenuous and a secondary electron source such as a hollow cathode emitter must be used. An additional drawback to conventional ultra-low pressure sputtering is larger in- film contamination and a relatively modest reduction in deposition rate (a factor of 2 - 3) . Furthermore, this mode sputtering is not feasible for RF diode deposition. Another widely discussed approach is ion beam deposition. Ion beam deposition enables low deposition rates and improved film crystallinity because of the higher adatom mobility. However, GMR spin valve structures fabricated using ion beam deposition exhibit a lower GMR response compared to spin valves fabricated via sputtering. Ion beam deposition generally also requires scanning of the substrate which complicates the equipment design especially for larger diameter substrates. Pulsed mode power sources have been used for reactive applications to deposit insulating films, for example pulsed mode reactive deposition of substances like tantalum dioxide, titanium dioxide, aluminum oxide, and aluminum nitride. However, pulsed mode reactive deposition has typically been used for high rate deposition of thick films. Thus, pulsed mode reactive deposition has not been used to effectively reduce the rate of deposition, but rather to deposit insulating films that are significantly thicker than 50 A. Furthermore, these pulsed mode reactive deposition processes use pulsing frequencies that are high, typically in the range of 50 kHz to 100 kHz with duty cycles of 40% to 60%, for thin film sputtering applications . SUMMARY OF THE INVENTION A need exists for a sputtering deposition process and system that can produce highly uniform thin films (<50 A) using a process that is controllable and repeatable. The present invention provides a pulsed mode system and method for sputtering of thin films that substantially eliminates or reduces disadvantages and problems associated with previously developed thin film sputtering systems and methods . More specifically, the present invention provides a method for controlling the deposition rate from a target to a substrate to create a relatively thin film on the substrate. The pulsed power mode method includes the steps of generating pulsed power at a pulsing frequency from a power supply and applying the pulsed power to the target in order to sputter the material onto the substrate to create the thin film. The present invention can incorporate both RF and DC pulsed power supplies having a range of pulsing frequencies. The pulsed power has both a power on and a power off portion during the pulse where the power off portion can either be completely powered off (zero power) or some small portion of the power on (e.g., the "power off" power can be equal to approximately 5% of the "power on" power) . The method of the present invention can produce a deposition rate of less than 1 angstrom/second to create films have a thickness of less than 50 angstroms. The present invention provides an important technical advantage by providing the ability to deposit thin films of less than 50 A while maintaining acceptable film quality and uniformity requirements in a repeatable process. The present invention provides another technical advantage by incorporating the pulsed mode power source into existing processing equipment without requiring significant modification. The present invention provides an additional technical advantage by effectively increasing the deposition time to enable thin film deposition while maintaining film uniformity and quality. BRIEF DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying drawings in which like reference numerals indicate like features and wherein: FIGURE 1 shows a sputtering process chamber in which the sputtering process can be accomplished according to the present invention; FIGURE 2 shows an exemplary pulsed mode power waveform that can be used with a power supply according to the present invention; FIGURE 3A is a graph showing the deposition rate as a function of power for an RF pulsed power deposition of a FeTa film on a substrate; FIGURE 3B is a graph showing film resistivity as a function of the deposition rate for an RF pulsed power deposition of a FeTa film on a substrate; FIGURE 4A is graph showing deposition rate and film stress as a function of power for RF pulsed power deposition of a NiFe film; FIGURE 4B is graph showing deposition rate and film stress as a function of power for DC pulsed power deposition of a Ta film; and FIGURES 5A and 5B are graphs showing process repeatability from wafer to wafer (variability in sheet resistance) and film thickness control for spin valve stacks and FeMn/Cu/FeMn stacks. DETAILED DESCRIPTION OF THE INVENTION Preferred embodiments of the present invention are illustrated in the FIGURES, like numerals being used to refer to like and corresponding parts of the various drawings . The present invention reduces the sputtering deposition rate in a sputtering process by applying pulsed power, such as pulsed RF or DC power from a power supply operated in pulsed mode, to a target in order to form uniform thin films in a repeatable process. Each pulse results in deposition of a small portion of the material from the target onto a substrate. A series of pulses will successively increase the amount of material deposited, and therefore, the thickness of the film on the substrate. By operating using a series of pulses instead of continuos power, the present invention reduces the deposition rate. For example, pulsing the power source at a duty cycle of 25% will increase the overall deposition time by a factor of four. This will allow for a controllable and uniform deposition process, while enabling thin film deposition. Deposition rates of less than 0.5 A/second can be achieved, with a range from 0.5 A/second to 1.5 A/second being typical for deposition of thin films of less than 50 A height. Thus, for a 5 A film, using the pulsed mode deposition at a rate of 0.5 A/second, the deposition time will be 10 seconds. Pulsed mode deposition improves deposition repeatability because of reduction in deposition rate (and noncomitant increase in deposition time) as well as the effect of averaging over the numerous pulses that are used to deposit thin films of less than 50 A. The time added to the process due to pulsed mode operation of the power supply allows the operator the options of 1) increasing the deposition time by the added time due to pulsing; 2) increasing the operating power while maintaining the original deposition time; or 3) increasing the power and increasing the deposition time. FIGURE 1 shows a DC power magnetron sputtering process chamber 10 incorporating the pulsed mode deposition process of the present invention. The types of processing that the present invention is applicable to are those processes requiring uniform thin films, including but not limited to metal layers for GMR and MRAM structures, thin film resistors, thin barriers and liners, and masks. A power source 20, shown in FIGURE 1 as a DC power supply, is connected to the process chamber 10 to provide a source to apply power to target 12 in order to sputter material from target 12 through process environment 14 that deposits on wafer 16. Target 12 materials can include both nonmagnetic materials (such as tantalum and copper) and magnetic materials (such as cobalt and nickel-iron) . The present invention is potentially applicable to any type of power source that can be pulsed, including power sources capable of generating pulsed mode DC and RF power. Examples of DC power supplies that can be used as power source 20 to create pulsed DC power include the ENI RPG50 using either the pulsed or sequence modes of operation and the ENI DCG10 using the sequence mode of operation. Examples of RF power supplies that can be used as power source 20 to create pulsed RF power include the ENI OEM- 2000 2 kilowatt RF power supply and the ENI OEM-12B 1.2 kilowatt RF power supply. FIGURE 2 shows an example of the pulsed power output 22 that can be used during a sputtering operation in order to create a uniform thin film according to the present invention. The pulsed output power 22 is the result of a square wave pulse input to the power source. FIGURE 2 shows the resulting square wave pulsed power 22 plotted on an x axis representing time and a y axis representing power. The pulsed output power 22 is at its maximum power output P max between time t 0 and t (otherwise defined as the "power on" portion of the cycle) and the pulsed output power 22 is at its minimum power output P min between time t and t 2 (otherwise known as the "power off" portion of the cycle) . As shown in FIGURE 2, this pattern repeats itself. The power off portion of the cycle could be a zero power level, but as shown in FIGURE 2, the power level can be greater than zero during the power off portion of the pulse. It should be understood that it is not essential to have a square wave output. For example, in a square wave output is often difficult to achieve for RF power supplies that cannot be turned on/off instantaneously due to the presence of reactive loads parasitics. Thus, other wave forms could be used. The pulsing frequency, defined as the duration from t 0 to t 2 , is dependent on the specific deposition application and thickness of the film required. Furthermore, it should be understood that during a particular film application sequence, the pulsing frequency could change. For example, referencing FIGURE 2, the pulsing frequency t 0 to t 2 could potentially be different than the pulsing frequency t 2 to t 4 during a single thin film deposition process. Similarly, the pulse width t 0 — t λ and t 2 —1 3 could be changed during the deposition sequence. Likewise, PMAX and PMIN can change over time as well. In the present invention, the power supply pulsing frequencies are typically in the range of 5 Hz to 50 Hz for DC power supplies and 0.25 kHz to 10 kHz for RF power supplies. For both RF and DC power supplies the lower limit on the pulsing frequency is defined by the limitation on ignition of the plasma during the pulse. Thus, at an RF pulsing frequency significantly less than 250 Hz or a DC pulsing frequency significantly less than 5 Hz, if the power is completely turned off during the "power off" portion of the pulse, the plasma simply cannot be sustained. However, lower pulsing frequencies can be used if during the "power off" portion of the pulse the pulse power is maintained at some small percentage (for example, 5%) of the "power on" power value. Thus, the power is never entirely off during operation. This concept can improve the stability of the pulsing during operation. The upper limit on the both the DC and RF pulsing frequency is simply a function of the power supply and could be increased significantly above the upper limits discussed herein using improved power supplies. In operation, the conventional sputtering process power supply is replaced with a pulsed mode (RF or DC) power supply and the pulsed mode power supply is programmed to the power and pulsing frequency desired (or alternatively the pulsing frequency can be supplied to the power supply) . The power supplied to the target 12 by the power source 20 is pulsed (either pulsed DC or pulsed RF) to electronically chop the sputtered flux. The pulsing can be accomplished in a variety of ways, including pulsing the analog input of the power supply with a square wave pulse generator or by providing a pulsed input signal from a signal generator. Some power supplies have internal pulsing capabilities to allow for pulsed power output. The pulsing must be done at adequately high frequencies so the plasma does not extinguish during the power off portion of the cycle. Duty cycles as low as 10% may be used, which means that a factor of 10 reduction in deposition rate is possible without compromising the process. It should be understood that the present invention can apply the same total energy/power to the target as an equivalent continuous wave process, only over a longer period of time. For lower pressure plasma generation processing, especially at low duty cycles, a secondary electron source (e.g. hollow cathode or inductively-coupled-plasma assist) may be needed for effective operation. The pulsed power is supplied to the target 12 to cause the sputtering of some of the target material through the process chamber 14, and deposition onto wafer 16 to build a film on the wafer 16. Each repeated pulse of power to target 12 will cause additional material to be deposited onto wafer 16. However, the pulsing of the power will cause a reduction in the rate of material deposition (and thus slow down rate at which the film builds up) as compared to continuously applying power to the target. This reduced deposition rate allows for the deposition of a thinner film over the same period of time using the same maximum power output as compared to continuous power processes. Thus, even thin films (< 50 angstroms) can meet the uniformity requirements of these sputtering applications. The present invention has demonstrated the capability to produce uniform films as thin as 4-5 angstroms and even thinner film capability can be expected. The deposition rate of the present invention tends to increase/decrease linearly as a function of target power. In an alternative embodiment, a P max even higher than the typical operating power for a particular sputtering operation for producing the films could be used by decreasing the pulsing duty cycle. By effectively increasing the deposition time of the process, the maximum power output in a pulsed mode sputtering process could potentially be increased while still allowing enough time between pulses to accomplish deposition of thin films. Pulsed power can be generated in a variety of ways. A technical advantage of the present invention is the ability to use commercially available power supplies with no or minimal modification to the power supply which can be used in existing deposition processes with little or no modification to the other process equipment. Examples of the approaches for generating pulsed RF power from commercially available power supplies include: 1. Pulsed RF power generated by an ENI OEM-2000 2 kW RF power supply by pulsing the analog input of the power supply with a square wave pulse generator. The maximum pulsing frequency on this model power supply is limited to 300 Hz. 2. Pulsed RF power generated by an ENI OEM-12B 1.2 kW RF power supply by pulsing the analog input of the power supply with a square wave pulse generator. The maximum pulsing frequency on this model power supply is limited to 3000 Hz. 3. Pulsed RF power generated by an ENI 0.5 kW A-500 wide band amplifier by providing a pulsed RF input signal from a signal generator. 4. Pulsed RF power generated by an RFPP RF10S-PWT 1 kW power supply with internal RF pulsing capability. 5. Continuous wave RF power generated by a lower frequency (2 - 4 MHz) ENI power supply with a matching network designed for lower frequency operation. Examples for generating pulsed DC power include using the ENI RPG50 in the pulsed and sequence modes of operation and the ENI DCG10 using the sequence mode of operation. Specific embodiments of the thin film deposition process of the present invention have been demonstrated. Pulsed RF power feasibility was determined using FeTa and NiFe, while pulsed DC power feasibility was determined using Ta . Pulsed RF FeTa Deposition A ENI OEM-2000 2 kW RF power supply was installed on the RF diode module of a cluster tool . This power supply can be pulsed through an analog input at rates up to 300 Hz with a variable duty cycle (10 - 100 %) . The necessary hardware (a test fixture, a pulse generator and a directional coupler) was installed on the power supply and the power supply was configured for pulsed RF operation. The RF power supply was operated in a manual mode (i.e., the set-point power and the power on/off were controlled through the test fixture) . A directional coupler was installed between the output of the power supply and the matching network and was used to monitor the output of the power supply. An FeTa target was installed on the RF diode module. The process conditions for these tests are shown in Table 1. The plasma was ignited by raising the pressure to 15 mTorr and then decreasing it to the set- point value as listed in Table 1. Table 1 : Process conditions The demonstration was conducted in two phases. In the first phase, the stability of the plasma was analyzed as a function of the pulsing frequency and the duty cycle, and the maximum pulsing frequency/minimum duty cycle was determined. In the second phase, wafers were processed using 100% duty cycle, then 50% duty cycle, and finally 25% duty cycle at the maximum pulsing frequency. For comparison, wafers were also processed at 50% and 25% power levels; i.e., 300 W and 150 W respectively. The resistivity and deposition uniformity of the films were measured. The output pulse width, mean power and target bias voltage as a function of the pulsing frequency and the duty cycle are shown in Table 2. Note that the output pulse width (measured as PW 50 ) is longer than the input pulse width. This is because even though the rise time on the pulse is very short (< 0.2 ms) , the decay time on the pulse is fairly long. These rise and fall times limit the maximum pulsing frequency to ~ 300 Hz. Table 2: Plasma parameters as a function of pulsing frequency and duty cycle Pulsing frequencies below 100 Hz resulted in some plasma instability, especially at low pressures (< 5 mTorr) , since the plasma tends to extinguish between pulses. The average power and bias are consistent with the duty cycle and increase with increasing duty cycle as expected. The process results are summarized in Table 3 for the process conditions shown in Table 1 and a pulsing frequency of 250 Hz. No bias or orienting field was used so that the film properties could be compared easily. Table 3: Process results The deposition rate drops from 2.5 A/s for 100% duty cycle to 0.5 A/s for 25% duty cycle, but the film resistivity is similar for the films deposited at duty cycles of 25 - 100% (as shown in FIGURES 3A and 3B) . The film resistivity is slightly higher for the low duty cycle, film compared to the 100% duty cycle film. This could be because the output power was not completely turned off at the end of the pulse. Hence there is some deposition even during the 'off' period of the pulse. The resistivity is lower for the low power deposition. This may be due to a possible change in film composition (i.e. Fe:Ta ratio) at lower power levels. However, the variation in resistivity is within the measurement error (~ 10 %) and thus may not be significant. The deposition uniformity is also not significantly affected by pulsing, indicating that the plasma is stable (i.e. not flickering) . These results are somewhat surprising because one might expect that for low pulsing frequency, the plasma would extinguish between the pulses resulting in a flickering of the plasma. The characteristic extinction time for a low pressure plasma is given by L /D a where L is the characteristic diffusion length (i.e. half the target to substrate spacing; ~ 4 cm) and D a is the ambipolar diffusion coefficient (~ 1.5 x 10 cm /s for Ar plasmas at 5 mTorr) . This implies that the plasma should extinguish since the pulsing period (- 4 ms) exceeds the plasma extinction time of 10 μs . However, the plasma does not extinguish. This may be attributed to the presence of Ar metastables which return energy to the plasma during the afterglow through super-elastic collisions. The corresponding diffusion coefficient for Ar metastables is much lower (D Ar = 10000 cm /s) and the characteristic time for loss of Ar metastables via diffusion is 1 - 2 ms . This is comparable to the pulsing frequency and thus the plasma is operating just within the stable domain. Since the power was not completely turned off during the "power off" period this helps sustain the plasma as well. To ensure plasma stability over a wide processing domain (power, pressure and orienting currents) , the pulsing frequency must be increased so that the period of the pulsing is 5 10X shorter than the characteristic time for plasma extinction. This implies a pulsing frequency of 5 - 10 kHz. The upper limit on the pulsing frequency is set by the time required by the plasma to reach steady state. The period of the pulse must be at least 5 - 10X longer than the time to reach steady state. The characteristic plasma ignition time is given by l/kJ T where k ± is the ionization coefficient and N is the gas density. For an Ar plasma at 5 mTorr this is 1 - 5 μs. Thus the maximum pulsing frequency should be < 20 to 100 kHz so that the plasma achieves steady state during the pulse. A voltage probe installed between the matching network and the powered electrode (target) may be used to check if steady state is being achieved during the pulse. It is optimal to achieve steady state during the pulse so that the deposition conditions are constant during most of the pulse . Pulsed RF NiFe Deposition A similar approach was used for evaluating feasibility of pulsed RF NiFe deposition. Process conditions are shown in Table 4. Two power supplies, the OEM-2000, 2 kW RF power supply and the OEM-12B, 1.2 kW RF power supply were used in two evaluations. The effect of pulse frequency and duty cycle on the film properties are shown in Table 5 (for the OEM2000) and Table 7 (for the OEM-12B) . Table 6 shows the process results for the OEM2000 at 100% duty cycle for comparison purposes. All the films were deposited on 4" Si wafers coated with about 3700 A of Si0 2 . A standard 60 second pre sputter etch at 400 W was used prior to the deposition. The thickness, resistivity, stress and uniformity were measured. Of these, the stress is usually the most sensitive to deposition conditions (power, pressure and bias) . Stress is usually a good measure of film density since it can be correlated to a change in crystal lattice spacing in the absence of appreciable process induced substrate heating and phase change in the deposited film. Film stress tends to become more compressive as the lattice spacing decreases which implies an increase in the film density. Resistivity is also an indirect measure of film density, but for thin film resistivity is governed primarily by grain size and surface scattering effects rather than film density. Ideally, all the film properties should be invariant with duty cycle; only the deposition rate should be affected. This would allow the deposition rate to be reduced without any impact on the other film properties, thereby maintaining film quality. Table 4: Process conditions for PND ΝiFe Table 5: Process results at 250 Hz pulsing frequency for OEM-2000 Table 6: Process results for cw RF deposition for OEM-2000 Comparing the results of Tables 5, 6, and 7 confirms that pulsing the RF power reduces the deposition rate without significantly affecting the other film properties. At 75% duty cycle, the deposition rate (A/min/kW) is approximately the same as that for the cw mode . As the duty cycle is decreased below 50%, the deposition rate decreases substantially. The film stress in the cw mode is tensile and increases with increasing power; the change in stress with average power for the pulsed RF deposited films is lower. The scatter in the uniformity and resistivity is quite random for both the cw and the pulsed RF deposited films. The implication is that the deposition rate for pulsed mode deposition can be varied by altering the duty cycle without appreciably changing other film properties (e.g., stress, resistivity, uniformity, grain size, crystalline structure, etc.) Table 7: Process results at 2500 Hz pulsing frequency for OEM-12B Ta Deposition Using an ENI RPG50 A similar approach was used for evaluating pulsed DC mode Ta deposition. Process conditions are shown in Table 8. The effect of pulsing vs cw on the film properties is shown in Table 9. All the films were deposited on 4" Si wafers coated with about 3700 A of Si0 2 . A standard 60 second pre sputter etch at 600 W was used prior to the deposition. The thickness, resistivity, stress and uniformity were measured. Since the minimum duty cycle in the pulsed mode (i.e. duration of the negative pulse relative to the pulsing period) is 50%, only a 2X reduction in rate is possible using this mode the RPG50 DC power supply. Also, the voltage during the positive pulse cannot be reduced below 80 volts. For such a high positive potential, the electrons will be collected by the target which tends to quench the plasma. Preferably, the positive pulse should be zero, and the duty cycle for the negative pulse should be 10 - 25% so that a 10X - 4X reduction in rate is possible. Since this pulsed mode of operation is not feasible with the present configuration of the RPG50, the sequence mode of operation was used. The sequence of the pulse (i.e. pulsing period and pulse width) can be specified from the front panel of the power supply. However, the shortest pulse period is 25 ms which translates to a 100 ms pulsing period (pulsing frequency of 10 Hz) for a 25% duty cycle. This is lower than desired because the plasma extinguishes between pulses and also because the magnetron rotational frequency (0.5 - 2 Hz) is comparable to the pulsing frequency; this can lead to aliasing (stroboscopic effect) . Surprisingly, the process was stable, repeatable and uniform even under these conditions as described in the following sections. Table 8: Process conditions for physical vapor deposition Ta for the RPG50 Table 9: Process results for cw and pulsed DC Ta The effect of pulsed RF and pulsed DC deposition on deposition rate and film stress is summarized in FIGURES 4A and 4B. Deposition rates as low as 1 A/s can easily be achieved using pulsed RF and pulsed DC deposition without affecting film resistivity. The deposition rate decreases linearly with average power as expected: the deposition rate for cw and pulsed mode deposition is identical for the same average power, indicating that the plasma achieves the same steady state during such pulse as during cw mode. The variation of film stress with average power is much less for the case of pulsed mode deposition compared to cw mode of deposition. Deposition Repeatability The deposition repeatability and film thickness controllability via pulsed mode deposition for Cu are shown in FIGURES 5A and 5B . The wafer sheet resistance variation for spin valve stacks and FeMn/Cu/FeMn stacks implies a repeatability of < 1% (lσ) [FIGURE 5A] and a film thickness control of < 1 A for 20 - 30 A Cu films [FIGURE 5B] . The variation in sheet resistance [R] can be ascribed primarily to thickness variations in the Cu layer, since Cu dominates the conductivity of the stack. In summary, the present invention provides a method and system for lowering the deposition rate for depositing a material on a substrate to build a thin, uniform film using pulsed power mode deposition (both RF and DC deposition) . The pulsed mode deposition of the present invention improves deposition repeatability because of reduction in deposition rate and the averaging effect of the numerous pulses used for depositing thin films of less than 50 A. Deposition rates below 1 A/s can be achieved with the method of the present invention without sacrificing film quality since the target voltage is similar to that for a 100% duty cycle (CW) process operating at the same power. When the present invention is used in conjunction with power supplies with good inherent reproducibility, repeatability of <1% (lσ) can be achieved for 10-30 A films. For stable plasma operation during pulsing, the pulsing frequency is preferably between 0.25-10 kHz for pulsed RF deposition. This ensures that steady state operation is obtained during the pulse and the plasma does not extinguish between pulses. For DC magnetron deposition, a pulsing frequency of approximately 10 Hz (and higher) appears to be adequate. Properties of films deposited using the pulsed power mode of the present invention are similar to those obtained using the conventional continuous wave mode for the same peak power. The present invention has demonstrated the capability to deposit spin valves and stacks of FeMn/3o A Cu/FeMn and determining variability of sheet resistance over a run of 20-40 wafers. Pulsed mode deposition of this invention provides film thickness controllability of <1 A. Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as described by the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A pulsed mode sputtering method for sputtering a material from a target onto a substrate in a deposition process, comprising: generating pulsed power at a pulsing frequency from a power supply; applying the pulsed power to the target comprised of a material ; sputtering the material onto the substrate at a reduced deposition rate; and creating a relatively thin film on the substrate. 2. The method of Claim 1, wherein the pulsing frequency changes over time. 3. The method of Claim 1, wherein the pulsed power further comprises a power on portion and a power off portion wherein the pulsed power during the power off portion is zero. 4. The method of Claim 1, wherein the pulsed power further comprises a power on portion and a power off portion wherein the pulsed power during the power off portion is equal to approximately 5% of the pulsed power during the power on portion. 5. The method of Claim 1, wherein the power supply is a DC power supply that has a duty cycle that varies over time . 6. The method of Claim 5, wherein the pulsing frequency is between 5 Hz and 1000 Hz. 7. The method of Claim 5, wherein in the pulsing frequency is between approximately 10 Hz and approximately 50 Hz. 8. The method of Claim 5, wherein the DC power supply is operated at 10% to 50% duty cycle. 9. The method of Claim 1, wherein the power supply is an RF power supply. 10. The method of Claim 9, wherein the pulsing frequency is between approximately 0.25 kHz and approximately 10 kHz. 11. The method of Claim 9, wherein the RF power supply is operated at 10 to 50% duty cycle. 12. The method of Claim 1, wherein the film thickness is less than 50 angstroms. 13. The method of Claim 1, wherein the film thickness is approximately 5 angstroms. 14. The method of Claim 1, wherein the deposition rate is less than 10 angstroms per second. 15. The method of Claim 1, wherein the deposition rate is less than 1 angstrom per second. 16. The method of Claim 1, wherein generating pulsed power further comprises programming the pulsing frequency within the power supply. 17. The method of Claim 1, wherein generating pulsed power further comprises inputting a wave form to the power supply from an external piece of equipment to define the pulsing frequency. 18. The method of Claim 17, wherein the wave form constitutes a square wave and the piece of equipment is a square wave generator coupled to the power supply. 19. The method of Claim 1, further comprising switching a voltage polarity of the power supply during operation. 20. A pulsed mode sputtering method for sputtering a material from a target onto a substrate in a sputtering deposition process, comprising: generating pulsed power at a pulsing frequency between approximately 10 Hz and approximately 50 Hz from a DC power supply, the pulsed power comprising a power on portion and a power off portion wherein the pulsed power during the power off portion is equal to approximately 5% of the pulsed power during power on portion; applying the pulsed power to the target; depositing the material onto the substrate at a deposition rate less than 10 angstroms per second; and creating a film on the substrate having a film thickness less than 50 angstroms. 21. A pulsed mode system for reduced rate deposition in a sputtering process chamber, comprising: a target comprising a material to be sputtered; a substrate positioned relative to the target to collect the sputtered material; and a power supply coupled to the target within the process chamber, wherein the power supply supplies pulsed power at a pulsing frequency to the target in order to sputter the material onto the substrate to create a relatively thin film on the substrate . 22. The system of Claim 21, wherein the pulsed power further comprises a power on portion and a power off portion, and wherein the pulsed power during the power off portion is equal to approximately 5% of the pulsed power during power on portion. 23. The system of Claim 21, wherein the power supply is a DC power supply, the pulsing frequency is between approximately 10 Hz and approximately 50 Hz, and the DC power supply is operated at 10% to 50% duty cycle. 24. The system of Claim 21, wherein the power supply is an RF power supply, the pulsing frequency is between approximately 0.25 kHz and approximately 10 kHz, and the RF power supply is operated at 10 to 50% duty cycle. 25. The system of Claim 21, wherein the film has a film thickness less than 50 angstroms. 26. The system of Claim 21, wherein the deposition rate is less than 10 angstroms per second. 27. The system of Claim 21, wherein the power supply is operable to define the pulsing frequency internally. 28. The system of Claim 21, further comprising a pulse generator to input a wave form into the power supply to define the pulsing frequency. 29. The system of Claim 21, wherein the power supply voltage polarity is switched during operation. 30. A method of controlling the deposition rate of a material from a target to a substrate in a sputtering chamber when creating a film on the substrate, comprising: generating pulsed power at a pulsing frequency, the pulsed power comprising a power on portion and a power off portion; applying the pulsed power to the target; depositing the material on the substrate at a deposition rate less than 10 angstroms per second; and creating a film on the substrate having a film thickness less than 50 angstroms. 31. The method of Claim 30, wherein the deposition rate is less than 1 angstroms per second. 32. The method of Claim 30, wherein the pulsing frequency changes over time. 33. The method of Claim 30, wherein the pulsed power during the power off portion is approximately 5% of the pulsed power during the power on portion. 34. The method of Claim 30, wherein the power supply is a DC power supply that has a duty cycle that varies over time. 35. The method of Claim 34, wherein the pulsing frequency is between 5 Hz and 1000 Hz. 36. The method of Claim 34, wherein in the pulsing frequency is between approximately 10 Hz and approximately 50 Hz. 37. The method of Claim 34, wherein the DC power supply is operated at 10% to 50% duty cycle. 38. The method of Claim 30, wherein the power supply is an RF power supply. 39. The method of Claim 38, wherein the pulsing frequency is between approximately 0.25 kHz and approximately 10 kHz. 40. The method of Claim 38, wherein the RF power supply is operated at 10 to 50% duty cycle. 41. The method of Claim 30, wherein the film thickness is approximately 5 angstroms . 42. The method of Claim 30, wherein the deposition rate is less than 1 angstrom per second.

Inventors: BUBBER RANDHIR, NAGPAL RAJESH, PARANJPE AJIT, SCHWARTZ PETER, BUBBER, RANDHIR, NAGPAL, RAJESH, PARANJPE, AJIT, SCHWARTZ, PETER
Applicants: CVC INC, CVC, INC.
Application year: 1998
Main classification: C23C14
IPC codes: C23C14