9

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Self-Heating Effect Analysis

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• Overview
  • Self-Heating Effect Analysis
  • Thermal-Aware DC EM Analysis
  • Hierarchical SHE Analysis
• Data Requirements
• Compatible Software Versions
• Flow Overview
• Performing the Analysis
  • Running Pegasus or PVS LVS
  • Running Quantus Parasitic Extraction
  • Running Post-Layout Simulation using Spectre APS
  • Viewing the Analysis Plots in Voltus-Fi-XL
• Types of Plots
  • Thermal-DeltaT Regions
  • Thermal-DeltaT Tiles
  • RJ_SH - Current Density/Limit - max (SH)
  • JAVG_SH - Current Density/Limit - avg (SH)
  • JACRMS_SH - Current Density/Limit - rms (SH)
• Re-Evaluation of EM Limit Based on dTemp
• EMIR Control File Options
• Batch Mode Support for Running SHE Analysis and Thermal-Aware DC EM Analysis
• Command for Encrypting Data in param.sh File
• Generating Reports

Overview

The following topics are covered in this section:

• Self-Heating Effect Analysis
• Thermal-Aware DC EM Analysis
• Hierarchical SHE Analysis

Self-Heating Effect Analysis

As semiconductor technology scales down to sub-micron dimensions, power density increases, resulting in temperature increases—self-heating effect (SHE)—in devices. Semiconductor components are sensitive to temperature variations.

The main effects of self-heating are as follows:

• Degraded carrier mobility, which leads to a reduced on-current of transistors and, therefore, slower speed
• Higher interconnect metal resistivity, which results in longer delays
• Increased failure rate and reduced reliability of electronic devices, with secondary effects such as interconnect electromigration

In digital circuits, the key consequences are longer delays due to increased interconnect resistance and reliability issues due to electromigration. Analog circuits are more sensitive to temperature variations, which may degrade matching properties. Therefore, thermal simulations and modeling play an important role in the design of integrated circuits today.

The self-heating effect is driven by front-end-of-line (FEOL) self heat and back-end-of-line (BEOL) self heat.

• The FEOL is the first part of IC fabrication where the individual devices such as transistors, capacitors, and resistors are patterned in the semiconductor. FEOL covers everything up to, but not including, the deposition of metal interconnect layers.
• The BEOL is the second part of IC fabrication where the individual devices get interconnected with the wiring on the wafer. Both contribute towards the maximum rise in temperature or deltaT that causes the self-heating effect.

Thermal-Aware DC EM Analysis

The thermal-aware DC EM flow considers the local thermal effect – this includes both joule-heating and self-heating – in DC EM checks.

The thermal-aware DC EM flow is enabled by setting the following variable:

In the Variables form on the EM tab of the IR/EM Results form by specifying the following variable:

coupledSH true

In batch mode by specifying the following command:

set_variable coupledSH true

Voltus-Fi-XL supports the SHE analysis flow and the thermal-aware DC EM flow visualization. You can view the results of the these analyses by plotting them on the Virtuoso layout to show the worst deltaT violations. You can then debug your design to reduce the self-heating effect. In this chapter, the subsequent sections will provide details of the SHE analysis flow that are also relevant to the thermal-aware DC EM flow. Additional parameters and commands for the latter flow will be highlighted within these sections.

Hierarchical SHE Analysis

Voltus-Fi supports the generation of reports that are used by Voltus for Hierarchical SHE analysis. For this, the following option of the emirutil command is specified in the configuration file:

emirutil selfheating_report=[type=mos-region | metal filename=<filename> layer=<layername> tile=<no.of divisions in y-direction, no. of divisions in x-direction>]

For details of the above command, see EMIR Control File Options. The SHE reports that are generated are specified while performing hierarchical SHE analysis, using the Voltus command, analyze_self_heat.

Data Requirements

The table below lists the inputs that are required for, both the SHE analysis and the thermal-aware DC EM analysis in Voltus-Fi-XL:

Table 9-1 Data Required for SHE and Thermal-Aware DC EM Flow

setenv CDS_XVNC_TENBASE '+'

This variable is not required for run the SHE flow and the thermal-aware DC EM flow in the GUI.

This limitation will be removed in a future release of the software.

Compatible Software Versions

The table below lists the compatible software versions that are needed for running the SHE analysis flow and the thermal-aware DC EM flow:

Flow Overview

The diagram below illustrates the Pegasus/PVS LVS – Quantus – Virtuoso® Analog Design Environment L for Netlist and Config file generation – Spectre® APS – Voltus-Fi-XL flow for SHE analysis and thermal-aware DC EM analysis.

Figure 9-1 The High-Level Flow

Performing the Analysis

The following key tasks are performed for the SHE analysis and the thermal-aware DC EM flow:

• Running Pegasus or PVS LVS
• Running Quantus Parasitic Extraction
• Running Post-Layout Simulation using Spectre APS
• Viewing the Analysis Plots in Voltus-Fi-XL

These steps are detailed in subsequent sections.

Running Pegasus or PVS LVS

This is the first step, which involves verifying the layout connectivity and creating an LVS database that is required for the subsequent Quantus parasitic extraction.

Running Quantus Parasitic Extraction

This is the second step, which involves using the Quantus engine to create the xDSPF file for all the device parameters and interconnect parasitics.

Data Requirements for Extraction Setup

While setting up extraction for SHE analysis, ensure the following:

• The Quantus command file should include the following command:
  

  output_setup \
  -keep_temporary_files "true" 

  When set to true, the above command causes Quantus to leave the temporary files in the directory specified by the output_setup -temporary_directory_name command.
  When set to false, Quantus removes the temporary files when extraction has completed. By default this option is set to false.
  For more information about the Quantus command file options, see the “Quantus Command Files” chapter in the Quantus Extraction Users Manual.
• The Quantus version used for performing SHE analysis in Voltus-Fi-XL should be either the same or higher than that being used in the extraction step
• The layout should open within Virtuoso without any pop-up window.
• The OD shapes should be present in the layout for the OD layers specified in the file mentioned through the shParamFile option.

GUI Use Model

In the main menu of the Virtuoso Layout Suite, choose Quantus. Choose the Run Pegasus – Quantus or PVS – Quantus option. The Quantus Parasitic Extraction Run Form opens. Run extraction.

For detailed information about all the settings in the Quantus Parasitic Extraction Run form, see the “Quantus Graphical Interface” chapter in Quantus Extraction Users Manual.

The output includes the following:

• An xDSPF file, which contains all the parasitic information of the design – all the nets, x- and y-coordinates of transistors, parasitic resistors, and nets connected.
• A Quantus output directory, which contains the shape database.

Running Post-Layout Simulation using Spectre APS

Once extraction is done, run post-layout simulation using the EMIR control file (emir.config) file to create the SHE analysis reports. Before performing simulation, ensure the following in the ADEL or the Simulation window:

• Setup transient analysis.
• Choose Setup – Simulation File – Model Files to add the SHE Models. These models are required to create the *.dtemp#.xml file that contains information about the increase in temperature for each device.
• Select Simulation – Reliability – Setup. The Reliability form opens. In this form, specify the following:
  • Select Enable Reliability to enable reliability simulation.
  • Select Enable TMI Flow.
  • In the self-heating/aging(tmiShe) cyclic field, select self-heating only (tmiShe=1). This option enables only the TMI self-heating mode.
    
    This option is available in IC616ISR8 and ICADV12.1ISR10 releases with MMSIM13.1ISR10 or above versions.

Now, you can start the simulation either by using Simulation – Run option or clicking the “run simulation” button provided in the right panel of the ADEL window.

Viewing the Analysis Plots in Voltus-Fi-XL

Once the simulation run is complete, the simulation database saved in the *.emir#_bin file is loaded into Voltus-Fi-XL to view the SHE analysis plots. The SHE analysis and thermal-aware DC EM analysis plots are available on the EM tab of the IR/EM Results form.

The steps for populating the EM tab of the IR/EM Results form are detailed in the Viewing the EM Analysis Results section of the “EM Analysis Results” chapter.

In addition, for the SHE analysis flow, ensure that the following inputs are provided on the EM tab of the IR/EM Results form:

• Enable the QRC Run.
• In the QRC Run Location pop-up window, provide the details of the QRC Run Directory and Run Name.
• Click Variables to open the Variables form. In this form, specify the following variables:
  • shParamFile
  • shXMLFile
    
    For a sample shParamFile, see shParamFile in the “File Formats” chapter.
    To enable the thermal-aware DC EM analysis, in addition to the above variables, the following variable needs to be set to true:
  • coupledSH
• Select rms and avg.

This form is shown below.

Figure 9-2 The IR/EM Results Form

• In the Plot Results group box, the self-heating effect analysis plots are available in the list. These are detailed in the section below.

Types of Plots

The types of self-heating effect analysis and thermal-aware DC EM analysis plots that are available in the list are detailed below.

Figure 9-3 Plot Types

Thermal-DeltaT Regions

Reports the increase in temperature (deltaT) for all OD and metal layers in the entire design on the Virtuoso layout. This plot provides a detailed view of the temperature variations on the design. This is shown in the figure below.

Figure 9-4 The Thermal-DeltaT Regions Plot

Thermal-DeltaT Tiles

Reports the increase in temperature (deltaT) per tile based on the number of tiles, specified in the IR/EM Results form, on the Virtuoso layout. For this plot, specify the dimensions for the tiles in the Tiles text box on the EM tab of the IR/EM Results form. The design in the layout is divided into sections based on the number of tiles that are specified, for example, 15x20.

On the Virtuoso layout, the tiles are colored on the basis of the maximum temperature increase in each tile. This is shown in the figure below.

Figure 9-5 The Thermal-DeltaT Tiles Plot

RJ_SH - Current Density/Limit - max (SH)

Analyzes and reports the J/JMAX violations based on peak current after performing the SHE analysis.

JAVG_SH - Current Density/Limit - avg (SH)

Analyzes and reports the J/JMAX violations based on the average currents after performing the SHE or thermal-aware DC EM analysis.

JACRMS_SH - Current Density/Limit - rms (SH)

Analyzes and reports J/JMAX violations based on the RMS value of the AC currents after performing the SHE analysis. To display the worst deltaT violations, specify the self-heating current limit using the shRmsLimitThreshold variable.

Re-Evaluation of EM Limit Based on dTemp

The EM effect is re-evaluated based on the new temperature. In the SHE flow, this temperature is the sum of the simulation temperature and the changed temperature due to the self-heating effect. In the thermal-aware DC EM flow, this temperature is the sum of the simulation temperature and the changed temperature due to joule heating and the self-heating effect.

The Current_Limit is calculated based on this new temperature and compared with the actual current flowing through the metal resistor to find the EM pass or fail.

The shEMEffect variable is used to re-evaluate the EM limit based on individual metal BEOL_T and tile BEOL_T temperatures. This variable is set using the set_variable command in the Voltus-Fi command file:

To re-evaluate EM on individual metal BEOL_T:

set_variable shEMEffect beolT

To re-evaluate EM limit based on tile BEOL_T temperature:

set_variable shEMEffect tiles_no.of divisions in y-direction X no. of divisions in x-direction

EMIR Control File Options

A complete list of the EMIR control file options that are supported in Voltus-Fi-XL is provided in the table, EMIR Control File Options Supported in Voltus-Fi-XL, in the “Data Preparation” chapter.

In addition, there are some options that are specific to the SHE flow and the thermal-aware DC EM flow. The table below provides a list of options that are specified in the emir.conf file for these analyses.

Table 9-2 Supported EMIR Control File Options for Self-Heating Effect Analysis

emirutil selfheating_report=[type=mos-region filename=mos-region-tiles.txt tiles=15x10]

Heat-Sink Self-Heating Sample Report:

--------------------------------------------------------------------------

VERSION: <version>

HEADER:

OD_Name  llx  lly  urx  ury  od_area  od_dT  od_dT_p  od_dT_p_be  od_dT_p_fe

connecting_wire  layer  totalA_on_region

connecting_via  layer  totalA_on_region

connecting_OD  od_cell  od_dT  od_area  layer

-------------------------------------------------------------------------

Batch Mode Support for Running SHE Analysis and Thermal-Aware DC EM Analysis

You can run the SHE analysis and thermal-aware DC EM analysis in batch mode.

For SHE analysis, set the following variables using the set_variable command:

set_variable shParamFile param_sh.file

set_variable shXMLFile xml_file

set_variable shEMEffect {beolT | tiles_no.of divisions in y-direction X no.of divisions in x-direction}

For thermal-aware DC EM analysis, in addition to the above commands, specify the following:

set_variable coupledSH true

set_variable extendJouleHeating true

set_variable extendSHRegion true

For more information about the above variables, see the “Variables” chapter.

The commands listed below are common for both flows, SHE and Thermal-aware DC EM analysis:

• load_view
  Specifies the layout to be used for SHE analysis. The syntax is provided below.

  load_view \
  -libname lib \
  -cellname cell \
  -viewname layout

• qrc_run_directory
  Specifies the location of the Quantus run directory. The syntax is provided below.

  qrc_run_directory run_directory

• qrc_run_name
  Specifies the Quantus run name. The syntax is provided below.

  qrc_run_name qrc_run_name

• load_em_results
  Loads the results of EM analysis. The syntax is provided below.

  load_em_results \

  -tech_file tech_file_name \

  [-layer_mapfile layer_map_filename] \

  results_file_name

• print_em_report
  Prints the EM analysis reports. The syntax is provided below.

  print_em_report \

  -net -all_nets \

  -type [acrms_sh | avg_sh | peak_sh] \

  -filename output_file_name

• print_thermal_report
  Prints the thermal reports for the hierarchical self-heating EM analysis.

  print_thermal_report \

  -type {mos-region | metal} \

  [-tiles tile_matrix] \

  -filename output_file_name

For details of the above commands, see the “Batch Commands in Voltus-Fi-XL” chapter.

Example

The following set of commands report the results of SHE analysis for cell, cell1 of library, test_lib. The SHE analysis results will be reported in the ./acrms_sh.txt file. The OD regions temperature will be reported in the mos-region.txt file:

load_view
-libname test_lib \
-cellname cell1 \
-viewname layout

qrc_run_directory svdb
qrc_run_name design

load_em_results \
-tech_file qrcTechFile
-layer_mapfile contactmapfile/input.emir0_bin

print_em_report
-net all_nets \
-type acrms_sh \
-filename ./acrms_sh.txt

print_thermal_report \
-type mos-region \
-filename ./mos-region.txt

Command for Encrypting Data in param.sh File

Voltus-Fi supports encrypting the contents of the param.sh file to hide confidential data. Use the below command to encrypt the contents of the file using the vfibatch command:

vfibatch -cmd <cmd-file-name>

The contents of the cmd-file-name file are as follows:

encrypt_file
-input_file_name <filename>
-output_file_name <filename>

Where,

-input_file_name is the name of the file whose contents are to be encrypted

-output_file_name is the encrypted file as viewed by the user. It contains the contents of the input file with confidential data in encrypted form.

In the input file, the text to be encrypted is placed inside below tags:

<Encryption Start>...<Encrypton End>

A sample input file whose contents are to be encrypted is shown below:

line1

line2

line3

line4

<Encryption Start>

Encrypt line1

Encrypt line2

<Encryption End>

line5

line6

The output file for the above input file is shown below:

line1

line2

line3

line4

<Encryption Start>

   u   s   f   i’{BèŸô`¸ïá ×Ù û¢:#zšå„Và´-£¬?~   v   o   l   trcn3 tpeni  ä

Esُvš¬›ˆÐÞArÿù™   v   o   l*ª w±Ä›¯}1–³kB9dP…Ö

<Encryption End>

line5

line6

Generating Reports

The text reports for both SHE and thermal-aware DC EM analysis are only available in batch mode using the sequence of commands detailed in the above section. The types of reports that are generated are detailed below:

• Thermal reports containing temperature rise of OD region and metal resistors.
  The format of the OD region report is as follows:
  Figure 9-6 OD Region Report Format
  
  For thermal-aware DC EM analysis, when the option extendSHRegion is set to true, the OD region report format is as follows:
  Figure 9-7 OD Region Report Format for Thermal-Aware DC EM Flow
  
  The format of the metal resistors report is as follows:
  Figure 9-8 Metal Resistors Report Format
  
• Tiles-thermal reports containing temperature rise of OD region and metal resistors based on the specified tile matrix.
  The format of the metal resistors report (tile-based) is as follows:
  Figure 9-9 Metal Resistors Tile-Based Report Format
  
  The format of the OD region (tile-based) report is as follows:
  Figure 9-10 OD Region Tile-Based Report Format
  
• The SHE EM reports containing dTemp of each parasitic resistor and EM report (including pass/fail, em_limit, and needed width) both with and without the self-heating effect. The following reports are generated:
  • acrms_sh.txt: AC RMS EM report both with and without the self-heating effect
  • avg_sh.txt: Average EM report both with and without the self-heating effect
  • peak_sh.txt: Peak EM report both with and without the self-heating effect
  
  The formats of these report file are provided below.
  Figure 9-11 AC RMS EM Report Format
  
  Figure 9-12 Average EM Report Format
  
  Figure 9-13 Average EM Report Format for Thermal-Aware DC EM Analysis
  
  Figure 9-14 Peak EM Report Format
  
• Thermal resistance report with cell name and thermal resistance (Rth) value. This is only generated in the thermal-aware DC Em flow.
  Figure 9-15 Thermal Resistance Report Format for Thermal-Aware DC EM Analysis