Ozone layer is a concentration of ozone molecules up in the Stratosphere (10 to 50 kms)

Ozone is produced only at the ground level and flows to high altitude to form Ozone layer

In Stratosphere Ultraviolet rays break down oxygen molecules into atomic oxygen(O) which then combines with Oxygen molecule(O2) to form Ozone (O3)

Around 90% of the Ozone in our atmosphere is contained in Troposphere only (within 10 kms)