Hi amar,
Check this example. Now please take its reference and correct your code.
C#
protected void Page_Load(object sender, EventArgs e)
{
TextBox txtBox = new TextBox();
txtBox.ID = "txtName";
txtBox.Attributes.Add("placeholder", "Enter Name");
form1.Controls.Add(txtBox);
}
VB.Net
Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) Handles Me.Load
Dim txtBox As TextBox = New TextBox()
txtBox.ID = "txtName"
txtBox.Attributes.Add("placeholder", "Enter Name")
form1.Controls.Add(txtBox)
End Sub
Screenshot