Clay Aiken -- Alleged Stalker Arrested after Scary Home Encounter

Frightening moment for Clay Aiken ... when an obsessed fan broke on to his property and made it all the way to his front door ... this according to police docs obtained by TMZ.

According to the docs, it all went down on April 3 ... when the fan -- 57-year-old Barbara Saylor -- snuck into Clay's gated community in North Carolina and hopped a fence surrounding the singer's home. Sources connected to the incident tell us the woman was seen trying to peer into a window at the front of the house.

The scary part -- Clay was home at the time.

Someone called 911 -- and cops responded to the scene. Barbara was eventually arrested for misdemeanor stalking and misdemeanor first degree trespassing.

According to the docs, Clay told police it's not the first time the woman -- who lives in the Seattle area -- crashed Clay's N.C. pad. Aiken told cops Barbara had previously "thrown her phone over the fence and reported she had been invited by the victim when actually she had not been."

Sources close to Clay tell TMZ ... the singer was shaken up by the incident ... but he's grateful to local law enforcement for responding so quickly.