Alphabetical index with a compound word which contains another entry

Hello, I want to make an alphabetical index with a concordance file which may search for the terms “Software” and “Free Software” and place the latter as a sub-entry of the first. Unfortunately, as “Free Software” contains the word “Software”, the index does not find the term “Free Software” or it includes the results of the main entry (although I checked the complete word check).

This is my concordance file’s content:

Free Software;;Software;;0;1

Unfortunately I cannot create a secondary entry with the term “Free” only, as it would include many other entries that are not related to software (for example free speech or free beer).

Can anyone tell me how to proceed? Thank you!