Method of making a silicon nitride film that is transmissive to ultraviolet light

• US 6,924,241 B2
• Filed: 02/24/2003
• Issued: 08/02/2005
• Est. Priority Date: 02/24/2003
• Status: Active Grant

• Current Assignee: ProMOS Technologies, Inc.
• Original Assignee: ProMOS Technologies, Inc.
• Inventors: Lee, Tai-Peng
• Primary Examiner(s): TRINH, MICHAEL MANH
• Application Number:
  US10/373,917
• Publication Number:
  US 20040166696A1
• Time in Patent Office: 890 Days
• Field of Search: 438/636, 438/952, 438/792, 438/791, 438/958, 438/257
• US Class Current: 438/792
• CPC Class Codes: H01L 21/0217 the material being a silicon nitride not containing oxygen, e.g. SixNy or SixByNz H01L21/02126 and H01L21/0214 take precedence
• CPC Class Codes: H01L 21/02211 the compound being a silane, e.g. disilane, methylsilane or chlorosilane
• CPC Class Codes: H01L 21/02274 in the presence of a plasma [PECVD]
• CPC Class Codes: H01L 21/3185 of siliconnitrides
• CPC Class Codes: H01L 29/2003 Nitride compounds
• CPC Class Codes: H01L 29/66825 with a floating gate H01L29/6684 takes precedence
• CPC Class Codes: Y10S 439/952 Jumper for use with specific apparatus

Abstract

A method for producing an ultraviolet light (UV) transmissive silicon nitride layer in a plasma enhanced chemical vapor deposition (PECVD) reactor is presented. The UV transmissive film is produced by reducing, in comparison to a standard silicon nitride process, a flow rate of the silane and ammonia gas precursors to the PECVD reactor, and significantly increasing a flow rate of nitrogen gas to the reactor. The process reduces the concentration of Si—H bonds in the silicon nitride film to provide UV transmissivity. Further, the amount of nitrogen in the film is greater than in a standard PECVD silicon nitride film, and as a percentage constitutes a greater part of the film than silicon. The film has excellent step coverage and a low number of pinhole defects. The film may be used as a passivation layer in a UV erasable memory integrated circuit.

Claims

1. A method for forming a ultra violet (UV) light transmissive silicon nitride film, comprising:

providing a plasma-enhanced chemical vapor deposition (PECVD) reactor with a semiconductor substrate therein;

flowing a gas mixture comprising silane, ammonia, and nitrogen into the PECVD reactor, wherein a flow rate of the silane is between about 130 sccm and about 180 sccm, and a flow rate ratio of the silane to nitrogen is at most 1;

50; and

forming a plasma in the PECVD reactor, whereby the UV light transmissive silicon nitride film is deposited on the semiconductor substrate.

2. The method of claim 1, wherein forming the plasma comprises simultaneously applying both a low frequency RF power and a high frequency RF power to the plasma reactor.

3. The method of claim 1, wherein the UV light transmissive silicon nitride film has a density of Si—

H bonds of about 2e21 bonds/cm³ or less.

4. The method of claim 1, wherein the UV light transmissive silicon nitride film has a greater stoichiometric amount of nitrogen than silicon therein.

5. The method of claim 1, wherein a flow rate ratio of the silane to nitrogen is 1:

100±

10%.

8. The method of claim 2, wherein forming the plasma comprises simultaneously applying both a low frequency RE power and a high frequency RE power to the plasma reactor.

6. A method for forming a ultra violet (UV) light transmissive silicon nitride film, comprising:

providing a plasma-enhanced chemical vapor deposition (PECVD) reactor with a semiconductor substrate therein;

flowing a gas mixture comprising silane and nitrogen into the PECVD reactor, wherein a flow rate of the silane is between about 130 sccm and about 180 sccm, and a flow rate ratio of the silane to nitrogen is at most 1;

50;

forming a plasma in the PECVD reactor, whereby the UV light transmissive silicon nitride film is deposited on the semiconductor substrate, said UV light transmissive silicon nitride film having a stoichiometric composition comprising Si_xN_yH_z, wherein y>

x, and a UV transmissivity of at least 60%.

7. The method of claim 6, wherein the gas mixture further comprises ammonia.

9. The method of claim 6, wherein the UV light transmissive silicon nitride film has a density of Si—

H bonds of about 2e21 bonds cm³ or less.

10. The method of claim 6, wherein a flow rate ratio of the silane to nitrogen is 1:

100±

10%.