Kohji Katoh

Variable Frequency Microwave and Convection Furnace Curing of Polybenzoxazole Buffer Layer for GaAs HBT Technology

Photosensitive polybenzoxazole (PBO) film has been used in GaAs heterojunction bipolar transistor (HBT) technology for stress buffer and mechanical protection layer applications. However, this film needs to be cured at high temperatures for a long period of time in order to obtain its desired excellent material characteristics. High-temperature curing can result in degradation to the electrical characteristics and performance of the underlying GaAs devices due to limited thermal budget. In this paper, we have characterized the effects of curing the PBO film on GaAs HBT wafers using a conventional convection furnace and using a variable frequency microwave (VFM) furnace. The results show that a VFM cure can achieve similar excellent physical, mechanical, thermal, and chemical material characteristics at a lower curing temperature and in a much shorter time, as compared to convection furnace curing, therefore resulting in minimal GaAs device degradation. Based on these results, an optimum curing condition using the VFM method can be obtained that satisfies both stress buffer layer material and device requirements for GaAs HBT technology.

Improvement of post-exposure delay stability of chemically amplified positive resist

We have been developing a novolak-based chemically amplified positive resist for next generation photomask (below 0.18 micrometer) fabrication. This resist prevents footing profile by use of a hydrophilic polyphenol compound. We succeeded in improving PED and PCD stability by addition of an ion- dissociative compound. We obtained vertical resist profiles on a chromium-oxide (CrOx) substrate. With the resist, we could make a well defined 0.25 micrometer line-and-space patterns on a CrOx substrate at a dose of 4.0 uC/cm2. Under the ambient air (amines concentration: 4 ppb, humidity: 45%), the line width change was less than 10 nm when the delay time between EB exposure and post-exposure-baking was from 0 to 8 hours. Under the same condition, the line width change was less than 20 nm even when the post-coating delay (PCD) time was 7 days.

Chemically amplified positive resist for next-generation photomask fabrication

We have been developing novolak-based chemically amplified positive resists for the next generation photomask fabrication. In this paper, we report two different types of EB resists: RE-5150P and RE-5160P. Our resist materials consist of four components: a novolak matrix resin, a polyphenol compound, an acid generator and a dissolution inhibitor. We applied two different types of dissolution inhibitors to our resist materials. RE-5150P and RE-5160P employed respective a high and a low activation energy type of a dissolution inhibitor. RE-5150P has high contrast and RE- 5160P has wide process window. As a result, we confirmed RE- 5150P could achieve 0.24 micrometer line-and-space vertical resist pattern profiles at 8 (mu) C/cm2 using the 50 kV EB- writer HL-800M, and RE-5160P has wide process window: post exposure delay stability is over 24 hrs. and post coating delay stability is over 30 days.

Improvement of the resolution and accuracy of chemical-amplification positive resist for 0.13-μm reticle fabrication

We have developed a novolak-based chemical-amplification resist for 0.13-micrometers or later reticle fabrication. For the 0.13-micrometers or later design-rule reticle-fabrication with OPC patterns, the resist resolution is required under 0.2-micrometers on the mask substrate. To improve the chemical-amplification resist resolution, it is necessary to control the acid- diffusion in the resist film. We have developed the technique of the acid-diffusion control with neutral-salt additives. By use of the resist with this technique, we could fabricate 0.14-micrometers 1/s patterns on a CrOx substrate at a dose of 9.3-(mu) C/cm2. The resist has a good margin of doses.

Chemical-amplification positive-resist design for 0.18-μm reticle fabrication using the 50-kV HL-800M electron-beam system

We have developed a novolak-based chemical-amplification resist for 0.18-micrometers reticle fabrication. This resist prevents resist footing on a chromium-oxide (CrOx) substrate by use of a matrix resin whose molecular-weight distribution is controlled. With the resist, we could fabricate 0.8-micrometers line-and-space patterns on a CrOx substrate at a dose of 6.0 (mu) C/cm2. Under the dry-air condition, the line-width change was less than 10 nm when the delay between e-beam exposure and post-exposure-baking was from 0.5 to 6 hours. When plates of the resist coating were in a chemical filter testing box under the dry-air condition, the resist sensitivity was preserved for 7 days.