Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2000-03-15
2003-03-25
Huff, Mark F. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C216S027000, C427S576000, C427S579000, C427S585000
Reexamination Certificate
active
06537707
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to methods and systems for fabricating laser ablation masks and more particularly to approaches to evacuating a vacuum chamber and depositing layers during the fabrication of such masks.
DESCRIPTION OF THE RELATED ART
Laser ablation is one available technique for forming features on the surface of a component or forming through holes in the component. Selected portions of the surface of the component are exposed to high energy laser radiation that causes chemical breakdown of the bonds within the exposed material. Localized expansion occurs as a result of the breaking of the chemical bonds. The material which has expanded can be removed using conventional techniques, such as chemical etching.
A laser ablation mask is typically employed to determine the exposure pattern on the surface of the component. The laser ablation mask utilizes a transparent substrate on which one or more layers can be formed and patterned to provide a coating that defines the exposure pattern. The materials for forming the coating are selected to be resistant to damage as a result of exposure to the laser energy. The substrate and the coating should have a resistance to laser-induced damage during ablation operations in which a laser has a strength greater than 150 mJ/cm
2
. A suitable substrate material is quartz. The coating on the quartz substrate may be a single metal layer, such as a chromium or aluminum layer. Alternatively, the coating may be formed of multiple dielectric layers having alternating high and low refractive indices. U.S. Pat. No. 4,923,772 to Kirch describes a laser ablation mask that is formed of multiple dielectric layers that are patterned to define the exposure pattern.
FIG. 1
is a schematic representation of the use of laser ablation in the process of forming inkjet printheads. The process is described in greater detail in U.S. Pat. No. 5,408,738 to Schantz et al., which is assigned to the assignee of the present invention. A continuous web
10
of polymer material is removed from a roll
12
in a controlled manner. The web material may be the polymer sold by 3M Corporation under the federally registered trademark KAPTON. Sprocket holes
14
along the opposite sides of the web may be used to precisely control movement of the web material relative to a laser source
16
, such as an Excimer laser. While not shown in
FIG. 1
, the laser source is typically located within a laser processing chamber. One or more laser ablation masks
18
can be patterned to define all of the features that are to be formed within the continuous web
10
. The features are repeated at a controlled interval, so that duplicate components for an inkjet printhead may be formed from the web, after the web is diced. In
FIG. 1
, the mask
18
is patterned to define an array of vaporization chambers. In addition to stepping the movement of the continuous web
10
, the laser source
16
may be stepped. The step-and-repeat process is continued until a nozzle member is formed. Optics
20
may be used for focusing the laser energy that propagates through the mask
18
.
The treated portion of the web then advances to a cleaning station, not shown, where any debris is removed from the web. The next station is a bonding station at which heater substrates
22
are secured to the web at positions conforming to the arrays of vaporization chambers. Each heater substrate may be a silicon die on which resistors are formed in an array that matches the array of vaporization chambers, so that there is a one-to-one correspondence between the arrays. The web can then be cut in order to provide individual printheads
24
that are attached to other components to form inkjet cartridges.
Returning to the laser ablation mask
18
that is used in the ablation station, there are a number of equally important mask-fabrication steps. The material for forming the mask substrate should be selected for its optical properties, since the laser energy propagates through the substrate. Quartz is a preferred substrate material. The substrate should be thoroughly cleaned prior to forming the coating on at least one surface of the substrate. The cleaning process removes trace organic layers, such as remnants of the compounds that are used to polish the quartz substrate. Impurities may strongly influence the lifetime of the laser ablation mask. The coating is then applied to the substrate. Conventional Physical Vapor Deposition (PVD) techniques may be utilized. PVD processing requires that the substrate be placed in a vacuum chamber and that the chamber be evacuated. Often, a mechanical pump is controlled by a roughing valve to reduce the pressure within the chamber to a particular setpoint of pressure. A second pump is then used to provide a high vacuum environment within the chamber.
Materials are introduced into the vacuum chamber to vapor deposit layers. As previously noted, the coating on the substrate may be a single layer of metal or composite metal, or may be a dielectric stack. The dielectric stack includes layers having alternating high and low indices of refraction. Absorption of laser energy by the mask coating is a major cause of degradation of the mask. Therefore, the mask coating should be reflective to light having the wavelength of the laser energy. Reflection from the dielectric stack is a result of the constructive and destructive interference at the interfaces of abutting layers. Each layer preferably has a thickness of approximately one quarter-wavelength of the laser energy to which it will be exposed. Each pair of dielectric layers reflects a percentage of the incident light. By depositing a sufficient number of layer pairs, nearly all of the laser energy is reflected.
The coating can then be patterned using conventional techniques. For example, reactive ion etching (RIE) or ion beam etching (IBE) maybe employed. While the resulting mask may operate well for its intended purpose, the operational life of the ablation mask is limited. Laser-induced damage to ablation masks is still critically dependent upon the level of coating defect density. That is, the damage that occurs as a result of exposure to the high energy laser radiation will increase with increases in defect density. With each failed mask, time must be taken to replace the mask. The equipment downtime required to replace masks reduces production throughput in an inkjet printhead manufacturing process.
What is needed is a method and system for fabricating a high energy radiation mask so as to increase the operational life of the mask.
SUMMARY OF THE INVENTION
A method of fabricating a high energy radiation mask includes locating a transparent substrate in a vacuum chamber and then executing at least one of (1) reducing the initial rate of evacuating the chamber relative to conventional evacuation techniques and (2) reducing the deposition rate of silicon oxide layers (e.g., SiO
2
) in a dielectric stack. When the more controlled evacuation procedure is combined with the slower deposition rate of SiO
2
, the resulting coating has a surprisingly low defect density. Consequently, the operational life of the mask is extended.
In the first embodiment of the invention, the controlled evacuation of the vacuum chamber includes a two-stage roughing procedure, followed by a high vacuum evacuation step. A first roughing evacuation connection to the vacuum chamber is activated to reduce the pressure to a level below atmospheric pressure. When the chamber environment is reduced to a first threshold pressure (i.e., a first setpoint), a second roughing evacuation connection is activated. The second roughing connection has a maximum purging rate that exceeds the maximum purging rate of the first connection. This may be accomplished by adding a bypass valve to the conventional roughing valve to a pump. The bypass valve may have an orifice that is smaller than the orifice through the roughing valve, thereby providing the difference in the maximum rates of evacuation. In an alternative implementation, the two connections are to separ
Agilent Technologie,s Inc.
Huff Mark F.
Mohamedulla Saleha R.
LandOfFree
Two-stage roughing and controlled deposition rates for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Two-stage roughing and controlled deposition rates for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two-stage roughing and controlled deposition rates for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3024960