Design Rule Checking 2

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Design Rule Checking 2

• Outline
• Corner-Based Pattern DRC
• Edge-Based Pattern DRC
• Edge-Based DRC
• Hierarchical DRC
• Goal
• Understand DRC algorithms

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Corner-Based Pattern DRC

• Corner patterns
• match at each rectangle corner
• check corresponding rule
• rule compiler to convert from boolean operations
• difficulty with multiple non-coincident edges

Polysilicon Contact Enclosure
Error
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Edge-Based Pattern DRC

• Edge rules - Magic design rule checker
• match at corner and edges
• apply at matching tile edge - corner-stitched
  rectangle database
• more natural than corners
• edge patterns match gt check B along edge
• predicate P matches gt check A at corner
• need rule compiler

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P
2
P
A
C
B
P
Layer Type 1
Layer Type 2
PC
C
2
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Edge DRC

• Scan chip
• sort edges that intersect scan line
• keep edges for max. design rule past scan line
• check rules against each edge
• rule Met-Met spacing gt 3
• check Met edges gt 3 apart
• O(NlogN) time for N edges
• Issues
• have to track which is interior side of edge
• which edges belong to same polygon
• top and bottom edges of object
• object implicitly defined by edges
• can discard edges perpendicular to scan line
• coalesce colinear edges - avoid spurious errors

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Hierarchical DRC

• Designs are specified hierarchically
• to handle complexity
• Designs often have high regularity
• e.g. RAM, datapath
• typically 1-10 of a design is unique
• rest is replicated
• Only check unique geometry
• avoid rechecking replicated instances
• filter to unique geometry
• apply regular DRC algorithm

c
b
b
array - 9 unique symbol neighborhoods a - 1
interior instance b - 4 corner instances c - 4
side instances
a
c
c
b
c
b
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Hierarchical DRC

• Benefits
• 10-100X faster
• less memory
• sensible error messages - no duplicates
• Symbol interaction
• design rule checks between symbol instances
• instances within maximum design rule distance
• overlapping instances

A
B
Check A Check B Check AB interaction
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Hierarchical DRC

• Issues
• interaction analysis might cost more than flat
  DRC with error filtering
• interaction area might be most of chip area
• small symbols vs. interaction distance
• e.g. memory, datapath
• chip might have little regularity
• e.g. routing in standard cells
• most of chip is unique geometry
• automatically-generated flat symbols

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Hierarchical DRC Filter Algorithm

• Check each symbol definition once
• symbol - collection of elements
• Check each unique element pair interaction once
• element - primitive element or symbol instance
• primitive element - geometry, indivisible objects
• pairwise check is suboptimal
• ideally check instance with all neighbors at once
• but pairwise might be faster
• Use symbol bounding boxes to speed comparison
• Write out primitive elements to be checked

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DRC Filter Algorithm
check_symbol(symbol) if checked(symbol)
note symbol bounding-box else if
leaf(symbol) write_out_all_geometry(symbol)
note symbol bounding-box else for each
element if symbol(element) if
!checked(element) check_symbol(element)
note symbol bounding-box else note symbol
bounding-box check_interactions_between_symb
ol_elements(symbol) mark symbol checked
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DRC Filter Algorithm
check_interactions_between_symbol_elements(symbol)
sort elements in x and y for each pair of
elements (a, b) if design_rule_exists(a, b)
if bloated_bounding_box_overlap(a, b)
check_element_interactions(a, b) else
design_rule_check(a, b)
check_element_interactions(e1, e2) if
(symbol(e1) or symbol(e2)) e1 element
which is symbol e2 other element for
each e1 element e if bloated_bounding_box_
overlap(e, e2) check_element_interactions(
e, e2) else design_rule_check(e1, e2)
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DRC Filter Algorithm
design_rule_check(geometry1, geometry2) if
design_rule_exists(geometry1, geometry2)
write out geometry1 write out geometry2
bloated_bounding_box_overlap(e1, e2) bb1
grow(e1.bbox, MAX_DESIGN_RULE/2) bb2
grow(e2.bbox, MAX_DESIGN_RULE/2) if
intersect(bb1, bb2) return(TRUE) else
return(FALSE) main() mark all symbols checked
that are prechecked check_symbol(top-level-symbo
l)
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Example

• Check A
• check C
• check g1-C.1 and g2-C.1 interactions
• DRC check g1-g2
• Check B
• check g4-C.2 interaction
• Check interaction between A and B
• check C.1-g3 interaction
• check C.1-g4 interaction