Patent Application
20070227878
This invention relates generally to phase change memories.
Phase change memory devices use phase change materials, i.e., materials that may be electrically switched between a generally amorphous and a generally crystalline state, for electronic memory application. One type of memory element utilizes a phase change material that may be, in one application, electrically switched between a structural state of generally amorphous and generally crystalline local order or between different detectable states of local order across the entire spectrum between completely amorphous and completely crystalline states. The state of the phase change materials is also non-volatile in that, when set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state representing a resistance value, that value is retained until changed by another programming event, as that value represents a phase or physical state of the material (e.g., crystalline or amorphous). The state is unaffected by removing electrical power.
Referring to
Inside the chamber 12 is a grounded shield 14. The grounded shield 14 is coupled to a wafer clamp 18. The wafer clamp 18 clamps a wafer (not shown in
Finally, at the top of the chamber 12 is the target (not shown) which is made of the material to be sputtered on a wafer mounted on the pedestal electrode 16 by the clamps 18.
The vacuum within the chamber 12 may be established by cryopump 20 which communicates through a port (not shown) with the chamber 12. The cryopump 20 maintains a low pressure within the chamber 12. In one embodiment, it may be a two phase pump.
A DC magnetron and radio frequency generator 28 may include a lid cover 27 made of metal, such a aluminum, instead of plastic for better RF shielding to the source. Finally, a metal plate 89 may be located between the target 86 and the generator 28. The plate 89 may be formed of aluminum. The plate 89 may enable better source grounding.
Over the generator 28 may be situated a radio frequency matching circuit 30. The circuit 30 balances out the radio frequency energy from the generator to the chamber load. The RF matching circuit 30 enables the tuning of the RF power supply to the chamber 12. The matching circuit 30 is coupled to a radio frequency power supply 32. In one embodiment, the power supply is a 13.56 MHZ power supply. A radio frequency interference shield G-12 source 29 may be used.
Referring to
The clamp ring 18 may have an edge exclusion, indicated by the distance X, of 6.5 millimeters in some embodiments of the present invention. Such an edge exclusion results in minimal contact with the edge of the wafer W. Also, an increased edge exclusion may protect more surface area to prevent cross contamination in the RF physical vapor deposition environment.
Referring to
The robot buffer chamber 60 also includes a robot. That robot may receive wafers from a load lock chamber 66, and transfer them to different stations surrounding the robot buffer chamber 60 or to the treatment chamber 62 for transfer to the transfer robot chamber 58. For example, the chamber 75 may be a pre-clean chamber and the chamber 56 may provide a barrier chemical vapor deposition chamber. The chambers 70 and 72 may be used for degassing and orientation.
Thus, the robot in the robot buffer chamber 60 grabs a wafer from a load lock chamber 66 and transports the wafer to chambers 70, 72 for degassing and orientation. From there the robot in the chamber 60 transfers the wafer to chamber 56 for chemical vapor deposition barrier layer formation in some embodiments of the present invention. Then, the wafer may be transferred to the pre-clean chamber 75.
Finally, the wafer may be transferred by the robot in the robot buffer chamber 60 to the treatment chamber 62 for transfer to the robot chamber 58. From there, various physical vapor deposition (or other steps) may be completed, including the RF or pulsed DC deposition of highly resistive layers in the chamber 10. Once the processing is done, the robot in the chamber 58 transfers the wafer to the cool down treatment chamber 63. From there, it can be accessed by the robot buffer chamber 60 robot and transferred out of the cluster tool 50 through a load lock chamber 66.
In some embodiments of the present invention, the reactor 10 may RF sputter deposit more highly resistive films, such as chalcogenide films. However, the same chamber may also be utilized for pulsed direct current sputtering as well. Because the RF power source is isolated from the rest of the components in the tool 50, RF interference with other chambers and with computer cluster tool 50 controllers that control the robots and other RF sensitive elements may be reduced.
In particular, better RF shielding for the source may be provided, RF power may be isolated from traveling on communication lines, and better source grounding may be achieved. As a result, in some embodiments of the present invention, RF sputtering may be implemented in a cluster tool despite the sensitivity of other components in the cluster tool to the radio frequency power.
A phase change memory may be formed utilizing the apparatus shown in
One advantage of such a system is that the amount of argon in the deposited layer is reduced. This is particularly important in connection with forming phase change memories with ovonic threshold switch (OTS) access devices. It has been determined that reducing the argon concentration within the chalcogenide used within the ovonic threshold switch improves the performance of the phase change memory.
Conventionally, a phase change memory may be formed with an access device such as an ovonic threshold switch. The ovonic threshold switch may use a chalcogenide material that generally does not change phase in operation. Thus, the ovonic threshold switch is used to access the phase change memory which also includes a chalcogenide layer.
The use of a self-ionization plasma enables lower argon flow to be used during the deposition of the chalcogenide layer used to form the ovonic threshold switch. This results in less contamination with the argon in the deposited layer.
In order to establish a self-ionization plasma, 2.0 MHZ power may be applied at the pedestal and 13.56 MHZ may be applied at the target. In another embodiment, 60 MHZ may be applied at the target and 13.56 MHZ may be applied at the pedestal.
In some embodiments of the present invention, the ovonic threshold switch chalcogenide layer may be deposited using a self-ionization plasma with chamber pressures below 3 milliTorr. In one advantageous embodiment, a chamber pressure of less than 1 milliTorr is used. Thus, the combination of a radio frequency or pulse energy deposition chamber, together with low argon pressures within the chamber, is effective to reduce the contamination by argon of chalcogenide containing layers used to form ovonic threshold switches.
To facilitate the application of the low pressure, an electrostatic chuck 57 may be utilized. Higher pressure may be used to ignite the plasma, but the pressure may be reduced and the electrostatic chuck 57 is effective to leak a relatively small flow of argon into the region of chamber 12 around the wafer.
Conventionally, reducing the argon pressure to such a low pressure to avoid contamination would result in the extinguishing of the plasma. However, a self-ionization plasma may be used at relatively low gas pressures.
Referring to
A pair of insulating layers 114 and 116 may then be formed over the conductor 112. The insulating layer 114 may be thinner than the insulating layer 116 in one embodiment of the present invention. Then, a pore or via hole is formed through the layers 114 and 116. That via hole may then be filled with a lance oxide 130, a lance heater 134, and a phase change memory element 132. Thus, the structure shown in
Overlying the material 132 may be an electrode 118. The electrode 118 may be a common electrode acting as the upper electrode of the ovonic unified memory and the lower electrode of the overlying ovonic threshold switch. In one embodiment, the electrode 118 may be formed of titanium aluminum nitride or titanium and titanium nitride.
A pair of conductive layers 120 and 124 may be formed on either side of a chalcogenide layer 122. It is the layer 122 that is deposited using the equipment described in connection with
Over the upper layer 124 may be formed an upper electrode 126. The upper electrode 126 may be made of the same or different material as the lower electrode 118. Finally, a hard mask 128 may be deposited patterned over the structure.
Referring to
After completing the structure shown in
While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this present invention.
