set echo cpu log phos poly /gas Trn.0=0.0 bor poly /gas Trn.0=0.0 phos oxide /gas Trn.0=0.0 bor oxide /gas Trn.0=0.0 line x loc=0.0 tag=lft spacing=0.25 line x loc=0.45 spacing=0.03 line x loc=0.75 spacing=0.03 line x loc=1.4 spacing=0.25 line x loc=1.5 tag=rht spacing=0.25 line y loc=0.0 tag=top spacing=0.01 line y loc=0.1 spacing=0.01 line y loc=0.25 spacing=0.05 line y loc=3.0 tag=bot region silicon xlo=lft xhi=rht ylo=top yhi=bot bound exposed xlo=lft xhi=rht ylo=top yhi=top bound backside xlo=lft xhi=rht ylo=bot yhi=bot init boron conc=1.0e16 #deposit the gate oxide deposit oxide thick=0.025 #channel implant implant boron dose=1.0e12 energy=15.0 #deposit the gate poly deposit poly thick=0.500 div=10 phos conc=1.0e19 #anneal diff time=10 temp=1000 #etch the poly away etch poly right p1.x=0.55 p1.y=-0.020 p2.x=0.45 p2.y=-0.55 #anneal this step diffuse time=30.0 temp=950 struct outf=poly.str #do the phosphorus implant implant phos dose=1.0e13 energy=50.0 #deposit the oxide spacer deposit oxide thick=0.400 spac=0.05 #etch the spacer back etch dry oxide thick=0.420 struct outf=imp2.str #after etch anneal method vert fermi grid.ox=0.0 diffuse time=30 temp=950 dry #implant the arsenic implant ars dose=5.0e15 energy=80.0 #deposit a cap oxide deposit oxide thick=0.15 space=0.03 struct outf=imp4.str #do the final anneal diffuse time=20 temp=950 struct outf=ldd.strThe next section begins the definition of the mesh to be used for the simulation. The section
phos poly /gas Trn.0=0.0 bor poly /gas Trn.0=0.0 phos oxide /gas Trn.0=0.0 bor oxide /gas Trn.0=0.0turns off the out diffusion of phosphorus and boron. In this simulation, there are anneals of bare poly. To keep the time step from being limited by the out-diffusion behavior, the gas transport is turned off by setting the transport rate pre-exponential constant to zero.
The next section describes the locations of the x lines in the mesh.
line x loc=0.0 tag=lft spacing=0.25 line x loc=0.45 spacing=0.03 line x loc=0.75 spacing=0.03 line x loc=1.4 spacing=0.25 line x loc=1.5 tag=rht spacing=0.25SUPREM-IV.GS defines x to be the direction across the top of the wafer, and y to be the vertical dimension into the wafer. Similar to Example 4, the location of the mesh lines is chosen to minimize the spatial error and to represent the location of various etch steps.
The next section of input describes the location and spacings of the vertical mesh lines.
line y loc=0.0 tag=top spacing=0.01 line y loc=0.1 spacing=0.01 line y loc=0.25 spacing=0.05 line y loc=3.0 tag=botThe lines are chosen close together near the surface and increasing away from it. Tight spacing is maintained only near the top surface. Since the structure will be passed to PISCES-II, a depth of 3.0 microns is chosen so that the eventual substrate contact will be deep to not unduly influence the simulation.
The next two sections describe the device starting material and the surfaces which are exposed to gas.
region silicon xlo=lft xhi=rht ylo=top yhi=bot bound exposed xlo=lft xhi=rht ylo=top yhi=top bound backside xlo=lft xhi=rht ylo=bot yhi=botThe region statement is used to define the starting materials. In this case the wafer is silicon with no initial masking layers. The bound statement allows the definition of the front and backsides of the wafer. Any gasses on the diffuse, deposit, and etch commands are applied to the surface marked exposed. The backside will not influence the process simulation. However, the backside is the location of a contact when the specfication of the electrodes is made for PISCES-II.
The next line informs SUPREM-IV.GS that the mesh has been defined and should be computed.
init boron conc=1.0e16 #deposit the gate oxide deposit oxide thick=0.025The first line initializes the starting material. The deposited oxide is specified to 0.025 microns thick. This represents the gate oxide that is grown before the uniform boron implant.
The next statement performs the channel implant of the boron.
#channel implant implant boron dose=1.0e12 energy=15.0The implant is modeled with a Pearson-IV distribution. The energy and dose are 1.0E12 cm-2 and 15 KeV respectively. This produces an abrupt boron profile with a shallow junction.
The next commands define the poly deposition and anneal. The poly deposition is done first, then the heat cycle that follows does the temperature cycle that occurs during actual poly deposition.
#deposit the gate poly deposit poly thick=0.500 div=10 phos conc=1.0e19 #anneal diff time=10 temp=1000 #etch the poly away etch poly right p1.x=0.55 p1.y=-0.020 p2.x=0.45 p2.y=-0.55 #anneal this step diffuse time=30.0 temp=950 struct outf=poly.strThe first pair of statements deposit the poly and then provide a temperature step representing the deposition. This temperature step will cause diffusion of the threshold adjust implant. The poly is put down with ten grid layers and doped to concentration of 1.0E19 cm-3 phosphorus. The next statements etch the gate material and perform a poly anneal. The structure is then saved in the file "poly.str".
The phosphorus light implant and spacer definition comes next.
#do the phosphorus implant implant phos dose=1.0e13 energy=50.0 #deposit the oxide spacer deposit oxide thick=0.400 spac=0.05 #etch the spacer back etch dry oxide thick=0.420 struct outf=imp2.strThis implant is the one which will form the lightly doped drain. The next two steps of the full device are to deposit and etch the spacer oxide. The spacer is deposited with 10 divisions, and the curvature is resolved to 0.04 microns. The oxide is etched back a thickness of 0.42 microns. The dry parameter indicates that the oxide surface is to be dropped straight down. Finally, the structure at this stage is saved.
The oxide is regrown and the phosphorus annealed during the next step.
#after etch anneal method vert fermi grid.ox=0.0 diffuse time=30 temp=950 dryThe method command specifies the oxide will grow vertically. No injection of interstitials will be simulated during this oxide growth. The diffuse command specifies that the anneal is to be done for 30 minutes at 950C in dry O2.
The next step implants the heavily doped portion of the drain, and deposits the cap oxide.
#implant the arsenic implant ars dose=5.0e15 energy=80.0 #deposit a cap oxide deposit oxide thick=0.15 space=0.03 struct outf=imp4.strThe arsenic is implanted through the new oxide growth and then a cap oxide is deposited. The structure is saved in the file "imp4.str".
Finally, we want to do the final anneal.
#do the final anneal diffuse time=20 temp=950 struct outf=ldd.strThis anneal will be carried out for 20 minutes at 950C. The structure is saved in the file ldd.str. At this point, any of the structure files can be read back and examined to check the results. Commands and analysis similar to that found in Example 4 may be performed.
To just perform a simple check, the following commands should produce a plot.
plot.2d bound fill y.max=1.0 select z=log10(phos+ars)-log10(bor) contour val=0.0The first command plots the device outline. The second command selects the difference in the logs of the doping. This tends to produce much smoother contours for plotting purposes. The final command plots the junction location, as shown in figure 1.
To prepare a PISCES-II structure file, the following input deck, found in "example/exam5/sup2pis.s4" can be used.
#make the contact hole etch oxide right p1.x=1.4 #put down the aluminum and etch off deposit alum thick=0.1 etch alum left p1.x=1.4 #remove extra grid nodes to save Pisces compute time etch start x=-0.5 y=-0.1 etch cont x=1.6 y=-0.1 etch cont x=1.6 y=-1.0 etch done x=-0.5 y=-1.0 #reflect the structure struct mirror left #save it in Pisces format struct pisc=ldd.meshThe first line etches the oxide to form the drain contact hole. Aluminum is deposited and etched to form contact to the drain. Everything more than 0.1 microns above the surface silicon is removed. This material is uninteresting to PISCES-II since it can not solve for anything more than the silicon substrate. The poly and oxide would just be wasted nodes. This etch uses the polygon specification for illustration. Any number of points forming a polygon can be specified. The material inside this polygon will be removed. The structure is reflected around the left edge. This doubles the number of nodes and forms the complete device with both source and drain contacts.
The structure is saved in PISCES-II format in the file ldd.mesh. This command also reports the location of contacts in the mesh for PISCES-II.
Electrode 1: xmin -0.550 xmax 0.550 ymin -0.100 ymax -0.025 Electrode 2: xmin 1.400 xmax 1.500 ymin -0.100 ymax 0.005 Electrode 3: xmin -1.500 xmax -1.400 ymin -0.100 ymax 0.005 Electrode 4: xmin -1.500 xmax 1.500 ymin 3.000 ymax 3.000From this information, the gate is electrode number 1, the source and drain are 2 and 3, and the backside contact is number 4. The file ldd.mesh can be read by the latest release of PISCES-II and is a "geom" type file.