LNF L-Edit Manual

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LNF L-Edit Manual
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  1 LNF L-Edit Manual University of Michigan Victoria Hicks, June 2011: email: victorih@umich.edu Contents University of Michigan................................................................................................................................. 1 1.0 At a Glance ....................................................................................................................................... 2 General Overview of L-Edit for Mask Making ........................................................................................ 2 Dark Field and Clear Fields: ................................................................................................................. 2 Types of Masks Made at the LNF: ....................................................................................................... 2 Pattern Generated (PG) mask: .............................................................................................................. 3 PG reticle mask: ................................................................................................................................... 3 IR mask, (Image Repeat Mask): ........................................................................................................... 3 2.0 L-Edit: Developing a Layout .................................................................................................................. 3 Getting Started  –   Setting Up the Design and Layers ................................................................................ 3 Design-Technology Parameter Set Up: ................................................................................................ 3 Layers: .................................................................................................................................................. 4 Methodology ............................................................................................................................................ 5 Drawing Basics ......................................................................................................................................... 6 Alignment keys ..................................................................................................................................... 7  Navigate:............................................................................................................................................. 10 Return to Alignment Keys: ................................................................................................................. 10 O-Ring Oscillator: .............................................................................................................................. 13 Scribe Lines: ....................................................................................................................................... 14 Assembling the Device: ...................................................................................................................... 14 3.0 FileFracture..................................................................................................................................... 16 GDSII ..................................................................................................................................................... 16 Fracturing ............................................................................................................................................... 18 GDS2PG ................................................................................................................................................. 19 Appendix A ................................................................................................................................................ 22 S TANDARD T OOL -B AR   ....................................................................................................................... 22 E DITING T OOL -B AR   ............................................................................................................................ 22 Hot Keys ................................................................................................................................................. 24 References 26   2 1.0 At a Glance L-edit is a layout editor from Tanner Research and is primarily a VLSI (Very-large-scale integration) design tool. It’s flexibility all ows it to be used for micromachine design, printed circuit board layout and other CAD work. The purpose of this section is to intorduce the uses of L-edit and to explain some of the equipment procedures. General Overview of L-Edit for Mask Making L-edit is used to create a layout for the purpose of generating a photo mask. A photo mask is a physical representation of a CAD design made of a transparent glass with a thin layer (typically < 1micron) of metal (typically chrome) on one side that defines a design. The mask is created using a process called photolithography. In this process the mask is covered, on the metal side, with a layer of light-sensitive organic polymer or epoxy called photo resist. UV Light is exposed to the photo resist in the patterned areas causing in a chemical change. This change results in the pattern transfer of the CAD geometry onto the mask. The mask is then developed removing the exposed resist or the unexposed resist depending on the tone of the resist being positive or negative, respectively. The underlying metal, which is now exposed, is then removed via chrome wet etching. The photo resist is removed in its entirety by use of an organic solvent or aqueous solution (depending on the resist type). The final product is a photo mask with the desired design. Dark Field and Clear Fields:  There are two types of masks: a dark field mask and a clear field mask. The area not taken up by the desired geometry (the masked area) is called the field. A dark field mask allows light to pass through the desired geometry and the field is opaque due to the presence of chrome thin film. In a clear field mask the light passes through the field and the geometry is opaque, See Figure 1. Figure 1 : The mask making machine uses mechanical apatures to form a series of rectangles - which are flashed onto the underlying photoresist - to approximate the dark geometry in the L-edit file. The purpose of a photomask is to transfer a pattern onto a wafer with only a single exposure. A wafer is a silicon substrate used as the base for building a device. Typically the wafer is first coated with a dielectric or metallic thinfilm and then with a layer of photo resist. The pattern on the mask is tranferred onto the photoresist thinfilm for further processing. Types of Masks Made at the LNF:  A device is built one layer at a time and therefore one device may consist of many layers. Each layer requires a mask for tranferring the geometery onto the wafer. Aligning the sucessive L-Edit File L-Edit File Dark Field Mask Clear Field Mask Quartz or Soda lime (Transparent Glass) Chrome Photo Resist Light Rays  3 layer to a previous layer is very important and there are different processes for acomplishing this task. There are three types of masks made at the LNF (Lurie Nanofabrication Facility): a PG mask, PG reticle mask and a IR mask. The type of mask used is a consequence of the device size and the alignment process. Pattern Generated (PG) mask:  The starting phase of any mask making process is a PG mask. A pattern or geometery is transferred to a mask using a lithographic process such as the one mentioned above. If the desired image occupies a large area (> 19.96 x 19.96 mm ) and is not repeated (in an array) then the PG mask will be the final mask. If the image needs to be repeated the PG mask will take on one of the following definitions. PG reticle mask:  A reticle is defined as a master mask that contains a patterned image that needs to be stepped or repeated to expose an array of the pattern over the wafer or mask. Reticles have two major applications: 1)  printing of an image directly onto a wafer in equipment known as a step-and-repeat aligner (a.k.a. the autostep) and 2) printing of an image onto a mask which, in turn, transfers an image onto a wafer. [2] The LNF uses a stepper that reduces the image by 5X and exposes it directly onto the wafer in a single flash. This process can be repeated to form an array of the images over the surface of the wafer. The image is contained in an area called the die which has a maximum size of 19.96 x 19.96 mm. The geometry of the image is drawn in CAD as the size of the finished product and must be within the maximum die size. The image magnification is addressed during the fracturing process, see section 3. IR mask, (Image Repeat Mask):  A mask that ’s  created by using a PG mask to expose a 5X reduced pattern onto another mask via the mask maker in a flood exposure mode. The benefit of this mask type is that you are not limited to a die size and therefore you can processes images that are larger than the maximum die size of the PG reticle mask  , (an inherit limitation imposed by the Autostepper’s lens configuration which cannot be change). 2.0 L-Edit: Developing a Layout L-Edit 2D-CAD software, created by Tanner Research, is used by the LNF for creating layout design of micro machines. The software layers 2D images to build 3D devises. The purpose of this section is to introduce you to the basic methodology and drawing functions of L-Edit. This will be done by working through a tutorial, in which we will build a Ring Oscillator, and an alignment key. Getting Started  –  Setting Up the Design and Layers An icon for L-Edit,, should be on the desktop or in the start-up menu of a designated PC in the LNF CAD lab. Launch the program; will look similar to Figure 2, pg 4. To start new projects select FILE  then new , Table 1, pg 5, item 1. Highlight layout   and < empty  > then select ok  . A blank template will be shown as in Table 1, pg.5, item 2. The next step is to specify the Setup Design-Technology Parameters. Design-Technology Parameter Set Up:  From the standard menu bar, select the S ETUP  pull down menu; then select design . A dialog box will appear called S ETUP D ESIGN ( FILE NAME ) , Table 1, pg 5, item 3. We will cover the basics of these setting, for more details see page 77 of the L-Edit help menu. The technology name   is used to determine whether two design cells are compatible. If you attempt to copy a cell from a file with a technology name different from that of the current cell, L-Edit presents a warning. So give the technology a meaningful name. The display units  , specifies the units that L-Edit uses to display distance and area, as well as the units in which physical distances are specified. Changing the display units will not change the scale of your drawing. The technology units   are the units of the fabrication process. The database resolution   defines the relationship between internal units and the technology (physical) units. Changing the database resolution will change the scale of your drawing. For the purpose of this document we will leave all the settings in this tab as  4 they appear in Table 1, pg 5, item 3; these should be the default settings. The next tab to the left is the grid   tab. In this tab, set the major display grid to 2.5  microns and the minor display grid to 0.250  microns. Other tabs: object snap  , selection  , and drawing  , are user preference tabs; a new user can explore these tabs after becoming familiar with the software. Select ok  . Figure 2 : Major components of the L-Edit interface [1] Table 1 : Screen shots of select L-Edit operation for creating a new project, setting up the design technology and creating new layers. Item 1 : To create a new file highlight Layout, <empty> and select OK. Item 2 : A new file will have a blank layout window and one layer titled, New Layer.
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