Multi-level photoresist profile method

• US 5,906,910 A
• Filed: 01/16/1998
• Issued: 05/25/1999
• Est. Priority Date: 06/10/1996
• Status: Expired due to Term

• Current Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.), Sharp Microelectronics Technology, Inc.
• Inventors: Nguyen, Tue, Ulrich, Bruce Dale, Evans, David Russell
• Primary Examiner(s): CODD, BERNARD P
• Application Number:
  US09/008,257
• Time in Patent Office: 494 Days
• Field of Search: 430/311, 430/326, 430/5, 216/12
• US Class Current: 430/311
• CPC Class Codes: G03F 1/29 Rim PSM or outrigger PSM; Preparation thereof
• CPC Class Codes: G03F 1/50 Mask blanks not covered by G03F1/20 - G03F1/34; Preparation thereof

Abstract

A method is providing for making a multi-level reticle which transmits a plurality of incident light intensities, which in turn, are used to form a plurality of thicknesses in a photoresist profile. A partially transmitting film, used as one of the layers of the reticle, is able to provide an intermediate intensity light. The intermediate intensity light has an intensity approximately midway between the intensity of the unattenuated light passing through the reticle substrate layer, and the totally attenuated light blocked by an opaque layer of the reticle. The exposed photoresist receives light at two intensities to form a via hole in the resist in response to the higher intensity light, and a connecting line to the via at an intermediate level of the photoresist in response to the intermediate light intensity. A method for forming the multi-level resist profile from the multi-level reticle is provided as well as a multi-level reticle apparatus.

Claims

1. A method for forming a photoresist pattern having a multi-level profile formed from exposure to light transmitted through a reticle having a multi-level profile, wherein the reticle includes one or more films overlying the reticle substrate to partially transmit and shift the phase of incident light, the partially transmitting phase shift film transmitting approximately 30% of incident light and shifting the phase 90 degrees in transmission through the partially transmitting film, and the reticle substrate passing all incident light, and an opaque film overlying the partially transmitting film, the opaque film blocking light so that all incident light is attenuated, the method comprising the steps of:

a) exposing a light sensitive photoresist substrate, having a predetermined thickness, to light transmitted through the reticle for a predetermined amount of time, with light being transmitted through the reticle substrate exposing a first photoresist area to a first dosage, with light being transmitted through the partially transmitting film exposing a second photoresist area to a second, intermediate dosage, and with light being transmitted through the remaining opaque film exposing a third photoresist area to a third dosage; and

b) developing the photoresist substrate exposed in step a) to form a photoresist profile having an opening in the first photoresist area, the photoresist profile having the photoresist predetermined thickness in the third photoresist area, and the photoresist profile having an intermediate thickness, between the predetermined thickness and zero, in the second photoresist area, whereby light introduced to the reticle transmits at least three intensities of light to transform the photoresist substrate into a profile of at least two thicknesses and an opening, generally replicating the multi-level profile of the reticle.

2. A method of patterning a light sensitive photoresist film from a single exposure to a light source, the method comprising the steps of:

a) exposing an area of the photoresist to a first intensity of light, and developing the exposed photoresist area to form an opening through the photoresist film, the first intensity of light being unattenuated in transmission from the light source;

b) exposing an area of the photoresist to a second, intermediate intensity of light, and developing the exposed photoresist area to form a photoresist area having a first, intermediate thickness, the second intensity of light being approximately 30% of light from the light source, shifted in phase approximately 90 degrees in transmission from the light source; and

c) exposing an area of the photoresist to a third intensity of light, and developing the exposed photoresist area to form a photoresist area having a second thickness greater than the first thickness, the third intensity of light being blocked in transmission from the light source.

3. A method of forming a photoresist profile on an integrated circuit substrate using a reticle having a multi-level profile including a transparent substrate, a partially transmitting 90 degree phase shift film overlying predetermined areas of the transparent substrate to transmit approximately 30% of incident light, and an opaque film overlying the predetermined areas of the partially transmitting 90 degree shift film, the method comprising the following steps:

a) depositing a layer of photoresist having a predetermined thickness on the integrated circuit substrate;

b) directing light to the photoresist through the reticle, the reticle transmitting a first intensity through the transparent substrate to create a first exposure pattern, the reticle transmitting a second intensity, less than the first intensity, through the partially transmitting 90 degree phase shift film to create a second exposure pattern, and the reticle transmitting a third intensity, blocking all incident light, through the opaque film to create a third exposure pattern; and

c) developing the photoresist to remove a first thickness of photoresist, approximately equal to the predetermined thickness, in areas of the first exposure pattern, and to remove a second, intermediate thickness of the photoresist, less than the first thickness, in the areas of the second exposure pattern, whereby the profile includes areas of photoresist having a plurality of different thicknesses.