NQueen solution in scala

Question

This is my solution for NQueen problem in scala. I just want to know how to make it more easy to read, modular and areas i need to improve.

object Main {
  def main(args: Array[String]): Unit = {
    val matrix = Array.ofDim[Int](16,16)

    val queen_place = (2,2)

    nQueenSol(matrix,matrix.size)


  }

  def diagonal_rule(x1:Int,y1:Int,x2:Int,y2:Int) = x1 + y1 == x2 + y2 || x1 - y1 == x2 - y2
  def vertical_or_horizontal_rule(x1:Int,y1:Int,x2:Int,y2:Int) = x1 == x2 || y1 == y2

  def queen_places(x:Int,y:Int,chess_board:Array[Array[Int]]):Array[Array[Int]] = {
    for(i <- 0 until chess_board.size;
    j <- 0 until chess_board.size) {
      if(chess_board(i)(j) == 0)
        chess_board(i)(j) = if(diagonal_rule(x,y,i,j)|| vertical_or_horizontal_rule(x,y,i,j))1 else 0

    }
    chess_board
  }
  def printChessBoard(array: Array[Array[Int]]): Unit ={
    array.foreach(y => {
      y.foreach(x => print(x + " "))
      println()
    }
    )
  }

  def queenNotPresentAt(chessBoard:Array[Array[Int]])(x:Int,y:Int) = chessBoard(x - 1)(y) == 0

  def nQueenSol(chessBoard:Array[Array[Int]],nthQueen:Int): Unit ={

    if(nthQueen == 0) {printChessBoard(chessBoard);println}
    else {

      for(i <- 0 until chessBoard.size){
        val touched = chessBoard.map(_.clone())

        if(queenNotPresentAt(touched)(nthQueen, i)) {
          touched(nthQueen - 1)(i) = 2
          val newchessBoard = queen_places(nthQueen - 1,i,touched)

          nQueenSol(newchessBoard,nthQueen - 1)

        }
      }
    }
  }
}