Prior to 1984, these doodles also served a practical purpose. If a competitor produced a similar chip, and examination showed it contained the same doodles, then this was strong evidence that the design was copied (a copyright violation) and not independently derived. A 1984 revision of the US copyright law (the Semiconductor Chip Protection Act of 1984) made all chip masks automatically copyrighted, with exclusive rights to the creator, and similar rules apply in most other countries that manufacture ICs. Since an exact copy is now automatically a copyright violation, the doodles serve no useful purpose.
Integrated Circuits are constructed from multiple layers of material, typically silicon, silicon dioxide (glass), and aluminum. The composition and thickness of these layers give them their distinctive color and appearance. These elements created an irresistible palette for IC design and layout engineers.
The creative process involved in the design of these chips, a strong sense of pride in their work, and an artistic temperament combined compels people to want to mark their work as their own. It is very common to find initials, or groups of sets of initials on chips. This is the design engineer's way of "signing" his or her work.
Often this creative artist's instinct extends to the inclusion of small pictures or icons. These may be images of significance to the designers, comments related to the chip's function, inside jokes, or even satirical references to their corporate masters in the cartoonists tradition (e.g. the mythical never-seen "bill sux" comment on a Pentium chip. The reputed "photo" that shows this is a hoax).
The mass production of these works of art as parasites on the body of a commercial IC goes unnoticed by most observers and is discouraged by semiconductor corporations, primarily from the fear that the presence of the artwork (which is clearly unneeded) will interfere with some necessary function in the chip or design flow.