How to specify writing and/or reading of backup files by means of the graphical user interface (GUI) is described in Chapter 5.2 (see Figure 5.6). In this chapter it is only referred to the actual input files which are read by SESAME during program execution.
In cases where it is necessary to simulate a very large number of electrons to get, for instance, reasonable good statistics, it will be advantageous to periodically write the status of program execution to a file which permits the continuation of the simulation from that status afterwards. This may save significant CPU-time in case of a computer crash during program execution or in case of bad statistics at the end of the simulation.
To write a backup file during execution it is necessary to specify the name of the backup file FETRBK and the number of electrons NETRBK after which a backup file shall be written in the &OUTPUT namelist. NETRBK is no absolute number which means that whenever NETRBK electrons are simulated a backup file will be written. For instance, if NETRN=20000 and NETRBK=10000 (total number of electrons to simulate) then a backup file will be written after the simulation of 10000 electrons and at the end of the simulation. On an OpenVMS platform there will be two backup files (two different version mumbers) whereas on Unix an older version is simply overwritten by a new one, i.e. only the backup file written after 20000 simulated electrons will be availabel if the simulation does not terminate premature. If NETRBK is larger than NETRN then a backup file will be written at the end of the simulation.
The default file name for the backup file is JOB.BCK, JOB being the 'Job Name' which may be specified in the &INIT namelist. The default name for NETRBK is zero and means that no backup file shall be written (see Chapter 9.1).
To continue the simulation by using an existing backup file it is necessary to specify the name of that file by means of the USEBK variable in the &INIT namelist.
The input deck to start the simulation from a specified backup file and the input deck which was used to generate this backup file can only differ in a very restricted set of input variables. These variables which might have modified values are listed in Table 6.7.
Table 6.7: Variables which might be modified in the backup input deck
If, for example, one is interested in some screen output at the very end of a simulation which was started by means of using a bakup file then this output to the screen must have been specified already in the input deck which was responsible for the generation of this backup file. The output to screen during the 'primary' simulation may be supressed by specifying LSCRN=F in the OUTPUT namelist. Specifying LSCRN=T in the input deck reading from the backup file visualizes the specified output.
However, it is recommended to rather write the requested information to files than to visualize it on the screen in case of very large numbers of electrons. Visualization is not very fast and even if LSCRN is set to F does not mean that the calculations needed to get the proper information to the screen are not done. Furthermore, the size of the backup file increases significantly with the number of specified output options.
It is also possible, of course, to start a simulation from a backup file and to write backup files during the same simulation. The following example of an input deck demonstrates how to generate a backup file:
&INIT CUSTXT='THIS IS A FIRST TEST EXAMPLE' JOB='EXA3',TECHQU='SEM' SIGNAL='BE',UNITS='MICRON',&END &ETRNS E0=20.,EF=500.,NETRN=100000,&END &EBEAM ESTD=5,SCAN=T,SPSIZE=0.0035,DIVERG=1,&END &TARGET ATMAT='SI,O2','W' DENS=2.2,19.3 NREG=2,CGFILE='SEM_EXA1.GEO',&END &MODEL MODR(1)='SIN',&END &MSETUP EBTILT=15,EBROT=180 TAKOFF=37.5,37.5,XDEROT=0,180 MAGNI=1000,XESPOT=4,XRANGE=5,&END &OUTPUT LSCRN=F NETRBK=50000 FETRBK='EXA3.BCK' SCREEN(1)='PET' SCREEN(2)='PEB,1' SCREEN(3)='XDD;;SI,KA;1' SCREEN(4)='XCY;;SI,KA;1' SCREEN(5)='XCY;;SI,KA;2' &ENDThe following input deck shows how a simulation may be continued by reading an already existing backup file:
&INIT CUSTXT='THIS IS A FIRST TEST EXAMPLE' JOB='EXA3',TECHQU='SEM' SIGNAL='BE',UNITS='MICRON', USEBK='EXA3.BCK',&END &ETRNS E0=20.,EF=500.,NETRN=120000,&END &EBEAM ESTD=5,SCAN=T,SPSIZE=0.0035,DIVERG=1,&END &TARGET ATMAT='SI,O2','W' DENS=2.2,19.3 NREG=2,CGFILE='SEM_EXA1.GEO',&END &MODEL MODR(1)='SIN',&END &MSETUP EBTILT=15,EBROT=180 TAKOFF=37.5,37.5,XDEROT=0,180 MAGNI=1000,XESPOT=4,XRANGE=5,&END &OUTPUT LSCRN=T NETRBK=120000 FETRBK='EXA4.BCK' SCREEN(1)='PET' SCREEN(2)='PEB,1' SCREEN(3)='XDD;;SI,KA;1' SCREEN(4)='XCY;;SI,KA;1' SCREEN(5)='XCY;;SI,KA;2' &ENDIn this particular case we write two backup files using the first input deck, one after simulating 50000 electrons and the other one at the end of the simulation. The SCREEN output was only specified to have the change to visualize exactly that information during a succeeding simulation using the - then already existing - backup file ( EXA3.BCK). No output will be directed for this input deck since LSCRN is set to false.
We may now take the same input deck and modify it only slightly to be able to continue our simulation. 20000 additional electrons will be simulated in this particular case. Since LSCRN is set to true now the specified output will actually be visualized on your screen. Additionally, a further backup file ( EXA4.BCK) is written at the end of this simulation which allows one to further continue the simulation from that status.
Since the input deck starting the simulation from a backup file can differ only in very few variables from the original input deck one would get exactly the same results as using the previous one with executing the following one:
&INIT USEBK='EXA3.BCK' &END &OUTPUT LSCRN=T NETRBK=120000 FETRBK='EXA4.BCK' &ENDAll three input files may be copied from:
VMS SUBPAC::DEVPROSIM$DISK:[SLED.SESAME.EXAM]SEM_EXA3.INP SUBPAC::DEVPROSIM$DISK:[SLED.SESAME.EXAM]SEM_EXA4.INP SUBPAC::DEVPROSIM$DISK:[SLED.SESAME.EXAM]SEM_EXA5.INP Unix ~tcad/sesame/exam/SEM_EXA3.INP ~tcad/sesame/exam/SEM_EXA4.INP ~tcad/sesame/exam/SEM_EXA5.INP