How to pause the game in Uniy3D

static float
timeScale;

Description

The scale at which the time is passing. This can be used for slow motion effects.

When timeScale is 1.0 the time is passing as fast as realtime.When
timeScale is 0.5 the time is passing 2x slower than realtime.

When timeScale is set to zero the game is basically paused if all your functions areframe rate independent.

Except for realtimeSinceStartup, timeScale affects all the time and delta time measuring variables of the
Time class.

If you lower timeScale it is recommended to also lower Time.fixedDeltaTime by the same amount.

FixedUpdate functions will not be called when
timeScale is set to zero.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Update() {
        if (Input.GetButtonDown("Fire1")) {
            if (Time.timeScale == 1.0F)
                Time.timeScale = 0.7F;
            else
                Time.timeScale = 1.0F;
            Time.fixedDeltaTime = 0.02F * Time.timeScale;
        }
    }
}