How to generate a random number with fixed length only with 0's and 1's and a fixed amount of 1's?

I did some research, but didn't found any solution for my question.

What I want to archive:

Generate a random number out of 0's ($min) and 1's ($max), but with a fixed amount ($many) of 1's in the random number. The random number should have a length of 6 as in my while loop (while($xLoop <= 6)).

Here is my current code:

$min = 0;
$max = 1;

$many = 3;
$xLoop = 1;

while($xLoop <= 6) {
    $nRand = mt_rand($min,$max);

    if($nRand == 1){ //if random number comes out number 1
         $many--; // Prevent number 1 more then $many...

         //Do something...
    }else{ //if random number comes out not number 1
         //Do something and still looping until get 6 times
    }

    echo $nRand.' - '.$many.'</br>'; //For debugin... i want to see how many number 1 comes out.

    $xLoop++;
}

It will loop 6 times, so we have a random number of the length 6, but I want a fixed amount of 1's in my random number, which is $many (here 3). And the rest filled with 0's until we reach the length 6.

How can I fix this code? Or is there a simpler way?