Patent Application
20080241354
The invention is related to semiconductor processing, in particular, to apparatus and methods for curing a layer of a processable material on a substrate.
Lithographic processes are widely used in the manufacture of semiconductor devices and other patterned structures. In track photolithographic processing used in the fabrication of semiconductor devices, the following sorts of processes may be performed in sequence: resist coating that coats a resist solution on a semiconductor wafer to form a resist film, exposure processing to expose a predetermined pattern on the resist film, heat processing to promote a chemical reaction within the resist film after exposure, developing processing to develop the exposed resist film, etc.
The baking (curing) of organic films is critical to the manufacturing process used for integrated circuits. This process is typically referred to as a “post apply bake” or PAB. Typical films include top coat barrier layers (TC), top coat antireflective layers (TARC), bottom antireflective layers (BARC), imaging layers (PR or photoresist), and sacrificial and barrier layers (hard mask) for etch stopping.
The bake process time and temperature are used to drive out solvents and cure or harden the film and thereby define the characteristics of the film at exposure and post exposure develop where circuit features are defined, prior to etching the features into the substrate. The amount of solvent remaining in this film can influence the lithographic and etch properties. Current technology controls the curing process with a time and temperature relationship, then relies on measuring the film thickness, which is a direct interpretation of the film's optical properties, to verify if the bake process was successful. If the post bake film properties are not identical wafer to wafer, critical dimension may vary as well for the same reasons the film thickness varies: the optical properties of the imaging layer are not consistent.
Current bake systems monitor bake temperature and process start and stop times to insure proper processing. The post bake film characteristics can be somewhat verified with film thickness or other additional testing. However, this testing may no longer be accurate enough to confirm if the desired film characteristics have been achieved as these systems average the film properties through the bulk material. Also the addition of other stops to the manufacturing process is not desirable for throughput and added defect concerns.
What is needed therefore in the art is a real time, in-situ method to ensure the bake process time versus temperature relationship is repeatable and will be more accurate leading to desirable results.
In one embodiment, a heat treatment apparatus is provided for heating a substrate, such as a semiconducting wafer. The heat treatment apparatus comprises an enclosure defining a process space, a substrate support configured to support the substrate in the process space, and a heating element configured to heat the substrate. A residual gas analyzer communicates with the process space. The residual gas analyzer samples an atmosphere inside the process space and generates signals relating to a concentration of at least one gaseous species in the atmosphere. A controller is electrically connected to the residual gas analyzer and is also electrically connected with the heating element. The controller is operable to adjust an amount of time that the heating element transfers heat energy to the substrate in response to the signals communicated from the residual gas analyzer.
In another embodiment, a method is provided for curing a layer of a processable material on a substrate. The method comprises baking the layer of material inside a process chamber to generate a gaseous product evolved from the processable material in the layer and measuring a concentration of the gaseous product inside the process chamber as a function of bake time. The method further comprises adjusting a length of the bake time in response to the measured concentration of the gaseous product.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.
The invention monitors a curing process of a thin film in real time by monitoring a concentration of evolved gases versus time, in-situ. Traditional methods of monitoring film curing in-situ rely on using the parameters of temperature and time, meaning heater zones on a bake plate are monitored for temperature versus process time only. The current state of the art monitors the process inputs or the catalyst for the reaction. The invention described herein will monitor the results or outputs of the reaction in a post apply bake process. This is an improved method to control the chemical composition of post-baked thin films on substrates, such as semiconducting wafers. The method provides a more accurate representation of the film quality after bake than the traditional methods. This invention may be used as part of the processing of a substrate on a coating/developing system and does not require any additional steps to the process or any extra handling of the substrate.
An exemplary coating/developing system 100, as shown in
A cassette support stand 105 is provided at the cassette station 101; the cassette support stand 105 may freely carry a plurality of cassettes C in a row in the X direction (vertically, in
A pattern measuring device 126 may be disposed at the negative X direction side (downward in
A processing station 103 adjacent to the inspection station 102 is provided with a plurality of processing devices disposed in stages, such as five processing device groups G1-G5. The first processing device group G1 and the second processing device group G2 are disposed in sequence from the inspection station 102 side, at the negative X direction side (downward in
Referring now to
Also, as shown in
The fourth processing device group G4 stacks a high precision temperature regulation device 160, pre-baking devices 161-164 for heating the wafer W after resist coating processing, and post-baking devices 165-169, which heat the wafer W after developing, in ten levels in sequence from the bottom.
The fifth processing device group G5 stacks a plurality of heating devices that heat the wafer W, such as high precision temperature regulation devices 170-173, and post-exposure baking devices 174-179 in ten levels in sequence from the bottom.
A plurality of processing devices may be disposed at the positive X direction side of the first transport device 112 as shown in
Provided in the interface unit 104 are a wafer transporter 117 that moves on a transport path 116 extending in the X direction as shown in
The percent concentration of solvent and/or out gassing materials will be monitored during the bake process by a controller, which may be a computer running monitoring software in some embodiments. A trace from a residual gas analyzer output versus the processing time will be created during the bake process. Corrective actions to the wafer in process may be triggered by the trace data being created; meaning immediate adjustments to the length of the bake may be dictated by the data as it is generated.
Embodiments of the invention use a residual gas analyzer (quadrupole mass spectrometer or other suitable detector) to monitor a gas exhausted from at least one of the baking units 161-164. Solvent out gassing may be sufficient, however, other materials such as polymer or other chemical compounds may be added to the gas monitoring system if required for special applications. These systems are commercially available.
The controller determines a suitable baseline trace to compare all subsequent wafer processing by running, measuring, and using statistical analysis to generate a typical trace. A user of the coating/developing system 100 may determine and adjust a length of a sample time and when during the bake process that the trace data will be evaluated for likeness to the baseline trace. This may allow for tuning the system for optimum results. The user may also determine bake time corrections for the system to use, which may be stored in a look-up table available to the controller. Bake times may be adjusted up or down based on the data in this table.
With reference to
The hotplate 16 has a plurality of through-holes 18 and a plurality of lift pins 20 inserted into the through-holes 18. The lift pins 20 are connected to and supported by an arm 22, which is further connected to and supported by a rod 24 of a vertical cylinder 26. When the rod 24 is actuated to protrude from the cylinder 26, the lift pins 20 protrude from the hotplate 16, thereby lifting the wafer W.
The process space 14 is defined by a process chamber or enclosure consisting collectively of a wall 28, a horizontal shielding plate 30, and an exhaust cover 32. Opening 33 may be formed at a front surface side or a rear surface side of the process space 14. The wafer W may be loaded into and unloaded from the process space 14 through the opening 33. In some embodiments, the opening 33 may close to seal the baking unit during the processing of the wafer W. A circular opening 36 is formed at the center of the horizontal shielding plate 30. The hotplate 16 is housed in the opening 36. The hotplate 16 is supported by the horizontal shielding plate 30 with the aid of a supporting plate 38.
In some embodiments, a ring-form shutter 40 is attached to the outer periphery of the hotplate 16. Air holes 46 may be formed along the periphery of the shutter 40 at intervals of central angles of approximately two degrees. The air holes 46 communicate with a cooling gas supply source (not shown).
The shutter 40 is liftably supported by a cylinder 42 via a shutter arm 44. The shutter 40 is positioned at a place lower than the hotplate 16 at non-operation time, whereas, at an operation time, shutter 40 may be lifted up to a position higher than the hotplate 16 and between the hotplate 16 and the exhaust cover 32. When the shutter 40 is lifted up, a cooling gas, such as nitrogen gas or air, may be exhausted from the air holes 46.
With continued reference to
Residual gas analyzers, such as residual gas analyzer 52, are familiar devices used in vacuum technology for the detection of gas species and their concentrations in a processing chamber. The residual gas analyzer 52 may be any type of mass spectrometer and, in one embodiment, is a quadrupole mass spectrometer. Exemplary residual gas analyzers (“RGA”) suitable for use in a processing chamber environment are commercially available from various sources, such as MKS Instruments (Andover, Mass.).
The residual gas analyzer 52 samples the gases flowing in the exhaust pipe 50 and, in particular, analyzes the gases evolved from layer 10 into the atmosphere inside the process space 14 during the baking process by ionizing a fraction of the gas molecules in each sampled volume, separating the ions by mass, and measuring the quantity of ions at each mass. The residual gas analyzer 52 may rely on a mass sampling technique that monitors only one or more user-selected peaks characteristic of the gases evolving from the layer 10. The magnitude of the ion current as measured by the residual gas analyzer 52 is used to determine the partial pressure of the respective gases originating from the heated processable material in the layer 10.
The amounts and/or ratios (e.g., partial pressures) of various residual gases in the process space 14 change as the baking process proceeds and the volume of evolved gas decreases with increasing baking time. Specifically, the amount of the different gas species in the gaseous product 34 evolving from the layer 10 changes as the layer 10 is heat cured. By monitoring the change in the amounts and/or ratios of the evolved gases from layer 10, the residual gas analyzer 52 may be used to improve process control by employing real time, in situ monitoring to regulate the relationship between process temperature and bake process time. The residual gas analyzer 52 may be used to troubleshoot out of control baking processes or to prevent baking processes from reaching an out of control condition.
The gaseous product 34 may be a single solvent or multiple solvents. It may also contain a mixture of any one or more of solvents, polymers, photo acid generators, base inhibitors, or any other by-products that are generated as a result of thermally processing layer 10. The residual gas analyzer 52 may be tuned for a particular solvent or solvents in the gaseous product 34. The residual gas analyzer 52 may be mounted anywhere along the exhaust line, coupled to exhaust pipe 50. For example, it may be mounted proximate to the exhaust port 48 in the exhaust cover 32 as shown in
A compartment 56 defined by the shielding plate 30, two sidewalls 58, 60, and the outer wall 28 is formed below the horizontal shielding plate 30. Hotplate supporting plate 38, shutter arm 44, lift pin arm 22, and liftable cylinders 26, 42 may be arranged in the compartment 56.
With reference to
A controller 64 (
The controller 64 may be taught to recognize an acceptable trace by the process shown in
A feedback system may be created to adjust the bake process time for a representative trace 72 that deviates from the baseline gas trace. The controller 64 is operable to adjust an amount of time that the hotplate 16 transfers heat energy to the wafer W in response to the signals communicated as feedback to the controller 64 from the residual gas analyzer 52. A decision to compensate the bake time or not may be made be based on an average concentration of one or more gas species taken over a sample time 70 between a first time T1 and a second time T2 as best seen on the graph in
An alarm may be included in some embodiments with the ability to alarm and flag wafers W that are not processed identically. A user selectable error value may be inputted to set alarm conditions based on the trace characteristics and processing time. If one trace curve does not fit well when compared to the baseline gas trace, an alarm may be sent to the main user interface for the coating/developing system 100 and the wafer may be identified for special inspection or treatment at the etch step by the controller 64. The controller 64 may issue additional warning alarms for wafers that are within the acceptable range when compared to the baseline gas trace, but may be nearing unacceptable allowable limits.
A process for curing a thin film on a substrate, such as a wafer, that is consistent with the invention can be seen in
The concentrations are sent to a controller where the concentrations are analyzed against a baseline. If the controller determines that the concentrations are within the allowable range (YES branch of decision block 218), the controller then determines if the concentrations are close to unacceptable limits. If the concentrations are not close to the limits (NO branch of decision block 220), the wafer is baked for the standard time and at the standard temperature in block 224. If the controller determines that the concentration is near unacceptable limits (YES branch of decision block 220) as an anomaly, a warning is used to a user in block 222 to notify the user of the anomaly and the wafer is baked for the standard time and at the standard temperature in block 224.
If the concentrations are outside of the acceptable range (NO branch of decision block 218) as an anomaly, the controller determines if the values are too high or too low. If the concentration values are too high (YES branch of decision block 226) as the anomaly, an alarm is issued to a user to notify the user of the anomaly and the baking time for the wafer is increased based on the deviation of the concentration from the baseline in block 228. If the concentration values are too low (NO branch of decision block 226) as the anomaly, an alarm is issued to a user to notify the user of the anomaly and the baking time for the wafer is decreased based on the deviation of the concentration from the baseline in block 230. When an alarm is issued, the user may take additional action as discussed above.
A specific example of traces from two wafers and a baseline may be seen in
An alarm included in the embodiment for this example is configured to alarm and flag wafers W that are not processed identically. User selectable error values are inputted to set alarm conditions based on the trace characteristics and processing time. Trace curves 76, 78 would issue an alarm, which would be sent to the main user interface for the coating/developing system 100. The wafers, being out of compliance with the baseline, would be identified for special inspection or treatment at the etch step by the controller 64.
While the invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant's general inventive concept.
