LoadLevelAdditiveAsync

SceneLoader.cs

using UnityEngine;
using System.Collection;

public class Example :  MonoBehaviour
{
    void Start ()
    {
        StartCoroutine (GenerateLoadProcess ("hogehoge"));
    }
    
    private IEnumerator GenerateLoadProcess (string sceneName)
    {
        AsyncOperation asyncOperation = Application.LoadLevelAdditiveAsync (sceneName);
        asyncOperation.allowSceneActivation = false;
        while (asyncOperation.progress < 0.9f && asyncOperation.isDone == false)
            yield return null;
        asyncOperation.allowSceneActivation = true;
    }
}