diff --git a/database/DBtechtype.c b/database/DBtechtype.c
index 5851b5a5..5233d077 100644
--- a/database/DBtechtype.c
+++ b/database/DBtechtype.c
@@ -141,7 +141,7 @@ DBTechInitPlane()
     for (dpp = dbTechDefaultPlanes; dpp->dp_names; dpp++)
     {
 	cp = dbTechNameAdd(dpp->dp_names, (ClientData) dpp->dp_plane,
-			&dbPlaneNameLists);
+			&dbPlaneNameLists, FALSE);
 	if (cp == NULL)
 	{
 	    TxError("DBTechInit: can't add plane names %s\n", dpp->dp_names);
@@ -224,7 +224,7 @@ DBTechInitType()
     for (dtp = dbTechDefaultTypes; dtp->dt_names; dtp++)
     {
 	cp = dbTechNameAdd(dtp->dt_names, (ClientData) dtp->dt_type,
-			&dbTypeNameLists);
+			&dbTypeNameLists, FALSE);
 	if (cp == NULL)
 	{
 	    TxError("DBTechInit: can't add type names %s\n", dtp->dt_names);
@@ -283,7 +283,7 @@ DBTechAddPlane(sectionName, argc, argv)
 	return FALSE;
     }
 
-    cp = dbTechNameAdd(argv[0], (ClientData) DBNumPlanes, &dbPlaneNameLists);
+    cp = dbTechNameAdd(argv[0], (ClientData) DBNumPlanes, &dbPlaneNameLists, FALSE);
     if (cp == NULL)
 	return FALSE;
     DBPlaneLongNameTbl[DBNumPlanes++] = cp;
@@ -315,7 +315,7 @@ DBTechAddNameToType(newname, ttype, canonical)
 {
     char *cp;
 
-    cp = dbTechNameAdd(newname, (ClientData) ttype, &dbTypeNameLists);
+    cp = dbTechNameAdd(newname, (ClientData) ttype, &dbTypeNameLists, TRUE);
     if (canonical)
 	DBTypeLongNameTbl[ttype] = cp;
 }
@@ -455,7 +455,7 @@ DBTechAddType(sectionName, argc, argv)
     }
     else
     {
-	cp = dbTechNameAdd(argv[1], (ClientData) DBNumTypes, &dbTypeNameLists);
+	cp = dbTechNameAdd(argv[1], (ClientData) DBNumTypes, &dbTypeNameLists, FALSE);
 	if (cp == NULL)
 	    return FALSE;
 
@@ -513,7 +513,7 @@ dbTechNewStackedType(type1, type2)
     }
 
     sprintf(buf, "%s+%s", DBTypeShortName(type1), DBTypeShortName(type2));
-    cp = dbTechNameAdd(buf, (ClientData) DBNumTypes, &dbTypeNameLists);
+    cp = dbTechNameAdd(buf, (ClientData) DBNumTypes, &dbTypeNameLists, FALSE);
     if (cp == NULL)
     {
 	TechError("Couldn't generate new stacking type %s\n", buf);
@@ -730,10 +730,11 @@ dbTechNameLookup(str, table)
  */
 
 char *
-dbTechNameAdd(name, cdata, ptable)
+dbTechNameAdd(name, cdata, ptable, alias)
     char *name;	/* Comma-separated list of names to be added */
     ClientData cdata;		/* Value to be stored with each name above */
     NameList *ptable;		/* Table to which we will add names */
+    int alias;			/* 1 if this is an alias (never make primary) */
 {
     char *cp;
     char onename[BUFSIZ];
@@ -769,7 +770,7 @@ dbTechNameAdd(name, cdata, ptable)
 	}
     }
 
-    if (primary)
+    if (primary && (alias == 0))
 	primary->sn_primary = TRUE;
     return (first);
 }
diff --git a/extract/ExtBasic.c b/extract/ExtBasic.c
index bfd25db0..38d76441 100644
--- a/extract/ExtBasic.c
+++ b/extract/ExtBasic.c
@@ -3546,7 +3546,11 @@ extSubsFunc(tile, arg)
     Tile *tile;
     FindRegion *arg;
 {
+    int pNum; 
+    Rect tileArea;
     TileType type;
+    TileTypeBitMask *smask;
+    int extSubsFunc3();
 
     if (IsSplit(tile))
     {
@@ -3554,6 +3558,17 @@ extSubsFunc(tile, arg)
 	if (type == TT_SPACE) return 0;		/* Should not happen */
     }
 
+    /* Run second search in the area of the tile on the substrate plane	*/
+    /* to make sure that no shield types are covering this tile.	*/
+
+    TiToRect(tile, &tileArea);
+    smask = &ExtCurStyle->exts_globSubstrateShieldTypes;
+    for (pNum = PL_TECHDEPBASE; pNum < DBNumPlanes; pNum++)
+	if (TTMaskIntersect(&DBPlaneTypes[pNum], smask))
+	    if (DBSrPaintArea((Tile *) NULL, arg->fra_def->cd_planes[pNum],
+			&tileArea, smask, extSubsFunc3, (ClientData)NULL) != 0)
+		return (1);
+
     /* Mark this tile as pending and push it */
     PUSHTILE(tile, arg->fra_pNum);
 
@@ -3568,11 +3583,22 @@ extSubsFunc2(tile, arg)
 {
     int pNum; 
     Rect tileArea;
+    TileTypeBitMask *smask;
     int extSubsFunc3();
 
     TiToRect(tile, &tileArea);
 
     /* Run second search in the area of the tile on the substrate plane	*/
+    /* to make sure that no shield types are covering this tile.	*/
+
+    smask = &ExtCurStyle->exts_globSubstrateShieldTypes;
+    for (pNum = PL_TECHDEPBASE; pNum < DBNumPlanes; pNum++)
+	if (TTMaskIntersect(&DBPlaneTypes[pNum], smask))
+	    if (DBSrPaintArea((Tile *) NULL, arg->fra_def->cd_planes[pNum],
+			&tileArea, smask, extSubsFunc3, (ClientData)NULL) != 0)
+		return (1);
+
+    /* Run third search in the area of the tile on the substrate plane	*/
     /* to make sure that nothing but space is under these tiles.	*/
 
     pNum = ExtCurStyle->exts_globSubstratePlane;
diff --git a/extract/ExtTech.c b/extract/ExtTech.c
index d778749d..314bed99 100644
--- a/extract/ExtTech.c
+++ b/extract/ExtTech.c
@@ -157,7 +157,7 @@ static keydesc keyTable[] = {
     "style",		STYLE,		2,	4,
 "stylename",
 
-    "substrate",	SUBSTRATE,	3,	3,
+    "substrate",	SUBSTRATE,	3,	4,
 "types plane",
 
     "units",		UNITS,		2,	2,
@@ -675,6 +675,7 @@ extTechStyleInit(style)
 
     style->exts_globSubstratePlane = -1;
     TTMaskZero(&style->exts_globSubstrateTypes);
+    TTMaskZero(&style->exts_globSubstrateShieldTypes);
 }
 
 
@@ -1927,7 +1928,6 @@ ExtTechLine(sectionName, argc, argv)
 	case DEFAULTSIDEWALL:
 	    ExtTechSimpleSidewallCap(argv);
 	    break;
-
 	case DEVICE:
 
 	    /* Parse second argument for device type */
@@ -2587,8 +2587,22 @@ ExtTechLine(sectionName, argc, argv)
 	    ExtCurStyle->exts_stepSize = val;
 	    break;
 	case SUBSTRATE:
+	    /* If the last entry starts with '-', then use it to set	*/
+	    /* the shield types.   Otherwise, the shield types mask is	*/
+	    /* NULL.							*/
+
+	    idTypes = DBZeroTypeBits;
+	    if (*argv[argc - 1] == '-')
+	    {
+		if ((DBTechNameMask(argv[argc - 1] + 1, &idTypes)) == 0)
+		    idTypes = DBZeroTypeBits;
+		argc--;
+	    }
+
 	    TTMaskZero(&ExtCurStyle->exts_globSubstrateTypes);
+	    TTMaskZero(&ExtCurStyle->exts_globSubstrateShieldTypes);
 	    TTMaskSetMask(&ExtCurStyle->exts_globSubstrateTypes, &types1);
+	    ExtCurStyle->exts_globSubstrateShieldTypes = idTypes;
 	    ExtCurStyle->exts_globSubstratePlane = DBTechNoisyNamePlane(argv[2]);
 	    break;
 	case NOPLANEORDER: {
diff --git a/extract/extractInt.h b/extract/extractInt.h
index d5779afa..5e0064e1 100644
--- a/extract/extractInt.h
+++ b/extract/extractInt.h
@@ -872,11 +872,16 @@ typedef struct extstyle
 	 * types that connect to the substrate.  Since for non-SOI
 	 * processes, this generally is used to specify that space on
 	 * the well plane is the substrate, the plane number for the
-	 * well plane is given, too.
+	 * well plane is given, too.  The "shield types" mask is a
+	 * mask of types that prevent any types in exts_globSubstrateTypes
+	 * from contacting the substrate (e.g., deep nwell might be a
+	 * shielding type, or it could be a special marker layer like
+	 * "not_substrate").
 	 */
     char		*exts_globSubstrateName;
     TileTypeBitMask	 exts_globSubstrateTypes;
     int			 exts_globSubstratePlane;
+    TileTypeBitMask	 exts_globSubstrateShieldTypes;
 
     /* Scaling */
 	/*