Because you are using single quotes, escaping doesn't happen and the literal string is used as the path.

perldata:

String literals are usually delimited by either single or double quotes. They work much like quotes in the standard Unix shells: double-quoted string literals are subject to backslash and variable substitution; single-quoted strings are not (except for \' and \\).

Or just test it:

$ perl -wMstrict
my $excelfile = 'd:\\test\\Korea_Checklist.xls';
print "$excelfile\n";
__END__
d:\test\Korea_Checklist.xls
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