How to Create an ExcelFile

Here is my code for craeting files,

protected void Button1_Click(object sender, EventArgs e)
    {
        Response.Clear();
        Response.AddHeader("content-disposition",string.Format("attachment;filename={0}.csv","Name"));
        Response.Charset = "";
        Response.ContentType = "application/vnd.xls";
        
        //GET Data From Database                
        SqlConnection cn= new SqlConnection(@"Data Source=WAP-PC\SQLEXPRESS;Initial Catalog=Projects;Integrated Security=True");
        string query = "select * from customer";
        SqlCommand cmd = new SqlCommand(query, cn);
        cmd.CommandTimeout=999999 ;
        cmd.CommandType=CommandType.Text;
        try
       {
        cn.Open();
        SqlDataReader dr = cmd.ExecuteReader();
        StringBuilder sb = new StringBuilder();            
        
        //Add Header          
        for (int count = 0; count < dr.FieldCount; count++)
        {
            if (dr.GetName(count) != null)
                sb.Append(dr.GetName(count));
            if (count < dr.FieldCount - 1)
            {
                sb.Append(",");
            }
        }
        Response.Write(sb.ToString() + "\n");
        Response.Flush();            
        
        //Append Data
        while (dr.Read())
        {
            sb = new StringBuilder();
               
            for (int col = 0; col < dr.FieldCount - 1; col++)
            {
                if (!dr.IsDBNull(col))
                    sb.Append(dr.GetValue(col).ToString().Replace(",", " "));
                    sb.Append(",");
            }
            if (!dr.IsDBNull(dr.FieldCount - 1))
                sb.Append(dr.GetValue(
                dr.FieldCount - 1).ToString().Replace(",", " "));
            Response.Write(sb.ToString() + "\n");
            Response.Flush();
        }
        dr.Dispose();
    }

    catch (Exception ex)
    {
        Response.Write(ex.Message);
    }
    finally
    {
        cmd.Connection.Close();
        cn.Close();
    }
    Response.End();
}

Thanks